Thermally stable and solvent-resistant conductive polymer composites

Abstract

A thermally stable and solvent resistant conductive polymer composite and its manufacturing friendly preparation method are disclosed. The disclosed composite presents great electrical conductivity with thermal stability and solvent resistance. A method of mixing a host thiophene conjugated polymer and a crosslinkable silane precursor simultaneously introduces both dopant and rigid cross-linked siloxane network into polymer system. The thin film made by the disclosed thermally stable and solvent resistant conductive polymer composite can be applied to fabricate various devices.

Description

TECHNICAL FIELD

The present disclosure is generally related to thermally stable and solvent-resistant conductive polymer composite and methods for preparing the same.

BACKGROUND

Conjugated polymers (CPs) have been widely used in all kinds of electronic devices. To improve CPs' robust electrical conductivity under elevating temperatures and/or various solvent environments, doping is demonstrated to be a powerful means. However, organic doping is typically sensitive to external stimuli such as heat, moisture and chemicals which lead to a de-doping process. For instance, thermal stress often induces and accelerates conformational changes of polymer chains, and further results in microscale or morphological disorder in conjugated polymer thin films. In doped thin films, this process is often accompanied with the expelling of dopant molecules, and causes a decrease of conductivity and degradation of device performance. Molecular dopants such as ferric chloride or F₄TCNQ enable stable doping of poly(3-hexylthiophene) under ambient conditions, but exhibit a large tendency to diffuse out at high temperatures because of their relatively small sizes, thus suffer from the thermal instability.

Since designing novel dopants or developing new doping methods to achieve CPs' robust electrical conductivity with the conventional doping approaches requires huge synthesis or processing efforts, simple and efficient designs and manufacturing friendly preparation methods for thermally stable and solvent-resistant doped systems are highly desired.

SUMMARY

Described herein are a thermally stable and solvent-resistant conductive polymer composite and methods for preparing the same.

In one aspect, the disclosure describes a thermally stable and solvent-resistant conductive polymer composite comprising a doped host electron-rich thiophene conjugated polymer (CP) and a crosslinked siloxane network.

In some embodiments, the crosslinked siloxane network is produced from a crosslinkable silane precursor with a formula of

wherein n is an integer greater than 0; X is a monomer unit and is selected from one or more of a group including: oxygen, urea group (N₂H₂CO—), C₁-C₃₀ alkyl, C₂-C₃₀ alkenyl, C₂-C₃₀ alkynyl, C₂-C₃₀ alkylcarbonyl, C₁-C₃₀ alkoxy, C₃-C₃₀ alkoxyalkyl, C₂-C₃₀ alkoxycarbonyl, C₄-C₃₀ alkoxycarbonylalkyl, C₁-C₃₀ aminylcarbonyl, C₄-C₃₀ aminylalkyl, C₁-C₃₀ alkylaminyl, C₁-C₃₀alkylsulfonyl, C₃-C₃₀ alkylsulfonylalkyl, C₆-C₁₈ aryl, C₃-C₁₅ cycloalkyl, C₃-C₃₀ cycloalkylaminyl, C₅-C₃₀ cycloalkylalkylaminyl, C₅-C₃₀cycloalkylalkyl, C₅-C₃₀ cycloalkylalkyloxy, C₁-C₁₂ heterocyclyl, C₁-C₁₂heterocyclyloxy, C₃-C₃₀ heterocyclylalkyloxy, C₁-C₃₀heterocyclylalkyloxy, C₁-C₃₀ heterocyclylaminyl, C₅-C₃₀heterocyclylalkylaminyl, C₂-C₁₂ heterocyclylcarbonyl, C₃-C₃₀heterocyclylalkyl, C₁-C₁₃ heteroaryl, or C₃-C₃₀ heteroarylalkyl, or any combination, among others; each of R₁, R₂, R₃, R₄, R₅, and R₆ is independently selected from a group including: hydrogen, halide groups, hydroxyl group, carboxylic groups, C₁-C₃₀ alkyl, C₂-C₃₀ alkenyl, C₂-C₃₀ alkynyl, C₂-C₃₀ alkylcarbonyl, C₁-C₃₀ alkoxy, C₃-C₃₀ alkoxyalkyl, C₂-C₃₀ alkoxycarbonyl, C₄-C₃₀ alkoxycarbonylalkyl, C₁-C₃₀ aminylcarbonyl, C₄-C₃₀ aminylalkyl, C₁-C₃₀ alkylaminyl, C₁-C₃₀alkylsulfonyl, C₃-C₃₀ alkylsulfonylalkyl, C₆-C₁₈ aryl, C₃-C₁₅ cycloalkyl, C₃-C₃₀ cycloalkylaminyl, C₅-C₃₀ cycloalkylalkylaminyl, C₅-C₃₀cycloalkylalkyl, C₅-C₃₀ cycloalkylalkyloxy, C₁-C₁₂ heterocyclyl, C₁-C₁₂heterocyclyloxy, C₃-C₃₀ heterocyclylalkyloxy, C₁-C₃₀heterocyclylalkyloxy, C₁-C₃₀ heterocyclylaminyl, C₅-C₃₀heterocyclylalkylaminyl, C₂-C₁₂ heterocyclylcarbonyl, C₃-C₃₀heterocyclylalkyl, C₁-C₁₃ heteroaryl, or C₃-C₃₀ heteroarylalkyl, among others; at least three out of R₁, R₂, R₃, R₄, R₅, and R₆ are selected from a group including a chloride group, a bromine group, a hydroxyl group or an alkyloxyl groups which can form condensation reactions; and at least one out of R₁, R₂, R₃, R₄, R₅, and R₆ comprise a doping agent.

In some embodiments, the crosslinked siloxane network is produced from a crosslinkable silane precursor with a formula of

wherein each of R₇, R₈, R₉, and R₁₀ is independently selected from a group including: hydrogen, halide groups, hydroxyl group; carboxylic groups, C₁-C₃₀ alkyl, C₂-C₃₀ alkenyl, C₂-C₃₀ alkynyl, C₂-C₃₀ alkylcarbonyl, C₁-C₃₀ alkoxy, C₃-C₃₀ alkoxyalkyl, C₂-C₃₀ alkoxycarbonyl, C₄-C₃₀ alkoxycarbonylalkyl, C₁-C₃₀ aminylcarbonyl, C₄-C₃₀ aminylalkyl, C₁-C₃₀ alkylaminyl, C₁-C₃₀alkylsulfonyl, C₃-C₃₀ alkylsulfonylalkyl, C₆-C₁₈ aryl, C₃-C₁₅ cycloalkyl, C₃-C₃₀ cycloalkylaminyl, C₅-C₃₀ cycloalkylalkylaminyl, C₅-C₃₀cycloalkylalkyl, C₅-C₃₀ cycloalkylalkyloxy, C₁-C₁₂ heterocyclyl, C₁-C₁₂heterocyclyloxy, C₃-C₃₀ heterocyclylalkyloxy, C₁-C₃₀heterocyclylalkyloxy, C₁-C₃₀ heterocyclylaminyl, C₅-C₃₀heterocyclylalkylaminyl, C₂-C₁₂ heterocyclylcarbonyl, C₃-C₃₀heterocyclylalkyl, C₁-C₁₃ heteroaryl, or C₃-C₃₀ heteroarylalkyl, among others; at least three of the R₇, R₈, R₉, and R₁₀ group are selected from a group including chloride group, bromine group, hydroxyl group or alkyloxyl groups which can form condensation reaction; and at least one out of R₇, R₈, R₉, and R₁₀ comprise a doping agent.

In some embodiments, the siloxane network is produced from a combination of silane precursors which include at least one of two crosslinkable silane precursors immediately listed above. Besides any of the crosslinkable silane precursors immediately listed above, non-crosslinkable silane precursors which cannot form crosslinked siloxane network may be included in the system.

In some embodiments, the siloxane network is produced from a crosslinkable chlorosilane precursor with a formula of

wherein n is an integer greater than 0, and equal to or less than 13.

In some embodiments, the siloxane network is produced from a crosslinkable chlorosilane precursor with a formula of

wherein R₁₁ is selected from a group including: hydrogen, halide groups, hydroxyl group; carboxylic groups, C₁-C₃₀ alkyl, C₂-C₃₀ alkenyl, C₂-C₃₀ alkynyl, C₂-C₃₀ alkylcarbonyl, C₁-C₃₀ alkoxy, C₃-C₃₀ alkoxyalkyl, C₂-C₃₀ alkoxycarbonyl, C₄-C₃₀ alkoxycarbonylalkyl, C₁-C₃₀ aminylcarbonyl, C₄-C₃₀ aminylalkyl, C₁-C₃₀ alkylaminyl, C₁-C₃₀alkylsulfonyl, C₃-C₃₀ alkylsulfonylalkyl, C₆-C₁₈ aryl, C₃-C₁₅ cycloalkyl, C₃-C₃₀ cycloalkylaminyl, C₅-C₃₀ cycloalkylalkylaminyl, C₅-C₃₀cycloalkylalkyl, C₅-C₃₀ cycloalkylalkyloxy, C₁-C₁₂ heterocyclyl, C₁-C₁₂heterocyclyloxy, C₃-C₃₀ heterocyclylalkyloxy, C₁-C₃₀heterocyclylalkyloxy, C₁-C₃₀ heterocyclylaminyl, C₅-C₃₀heterocyclylalkylaminyl, C₂-C₁₂ heterocyclylcarbonyl, C₃-C₃₀heterocyclylalkyl, C₁-C₁₃ heteroaryl, or C₃-C₃₀ heteroarylalkyl, among others.

In some embodiments, the siloxane network is produced from some crosslinkable chlorosilanes with the formula of:

The disclosed thermally stable and solvent-resistant electrochromic conjugated polymer composite comprises a host electron-rich thiophene conjugated polymer (CP) which comprises a p-type thiophene conjugated polymers with an oxidation potential lower than 0.4 V vs. Ag/AgCl.

Various embodiments described here are involved in the different host thiophene CPs forming the disclosed thermally stable and solvent-resistant conductive polymer composite. In some embodiments, the host thiophene CP comprises a copolymer with a formula of

wherein a and b are integers equal to or greater than 0; values of a and b indicate ratios of two monomer units, but not necessarily an exact monomer sequence in the polymer; n is an integer greater than 0; each of R₁₂-R₁₅ is independently selected from a group including, but not limited to, hydrogen, C₁-C₃₀ alkyl, C₂-C₃₀ alkenyl, C₂-C₃₀ alkynyl, C₂-C₃₀ alkylcarbonyl, C₁-C₃₀ alkoxy, C₃-C₃₀ alkoxyalkyl, C₂-C₃₀ alkoxycarbonyl, C₄-C₃₀ alkoxycarbonylalkyl, C₁-C₃₀ aminylcarbonyl, C₄-C₃₀ aminylalkyl, C₁-C₃₀ alkylaminyl, C₁-C₃₀ alkylsulfonyl, C₃-C₃₀ alkylsulfonylalkyl, C₆-C₁₈ aryl, C₃-C₁₅ cycloalkyl, C₃-C₃₀ cycloalkylaminyl, C₅-C₃₀ cycloalkylalkylaminyl, C₅-C₃₀ cycloalkylalkyl, C₅-C₃₀ cycloalkylalkyloxy, C₁-C₁₂ heterocyclyl, C₁-C₁₂ heterocyclyloxy, C₃-C₃₀ heterocyclylalkyloxy, C₁-C₃₀ heterocyclylalkyloxy, C₁-C₃₀ heterocyclylaminyl, C₅-C₃₀ heterocyclylalkylaminyl, C₂-C₁₂ heterocyclylcarbonyl, C₃-C₃₀ heterocyclylalkyl, C₁-C₁₃ heteroaryl, or C₃-C₃₀ heteroarylalkyl; and at least one of R₁₂-R₁₅ is electron rich that has excess electrons to be donated.

In some embodiments, the host thiophene CP comprises a dioxythiophene copolymer with a formula of

wherein a and b are integers equal to or greater than 0; values of a and b indicate ratios of two monomer units, but not necessarily an exact monomer sequence in the polymer; n is an integer greater than 0; each of R₁₆-R₁₉ is independently selected from a group including, but not limited to, hydrogen, C₁-C₃₀ alkyl, C₂-C₃₀ alkenyl, C₂-C₃₀ alkynyl, C₂-C₃₀ alkylcarbonyl, C₁-C₃₀ alkoxy, C₃-C₃₀ alkoxyalkyl, C₂-C₃₀ alkoxycarbonyl, C₄-C₃₀ alkoxycarbonylalkyl, C₁-C₃₀ aminylcarbonyl, C₄-C₃₀ aminylalkyl, C₁-C₃₀ alkylaminyl, C₁-C₃₀ alkylsulfonyl, C₃-C₃₀ alkylsulfonylalkyl, C₆-C₁₈ aryl, C₃-C₁₅ cycloalkyl, C₃-C₃₀ cycloalkylaminyl, C₅-C₃₀ cycloalkylalkylaminyl, C₅-C₃₀ cycloalkylalkyl, C₅-C₃₀ cycloalkylalkyloxy, C₁-C₁₂ heterocyclyl, C₁-C₁₂ heterocyclyloxy, C₃-C₃₀ heterocyclylalkyloxy, C₁-C₃₀ heterocyclylalkyloxy, C₁-C₃₀ heterocyclylaminyl, C₅-C₃₀ heterocyclylalkylaminyl, C₂-C₁₂ heterocyclylcarbonyl, C₃-C₃₀ heterocyclylalkyl, C₁-C₁₃ heteroaryl, or C₃-C₃₀ heteroarylalkyl.

In some embodiments, the host thiophene CP comprises a dioxythiophene copolymer with a formula of

wherein a and b are integers equal to or greater than 0; values of a and b indicate ratios of two monomer units, but not necessarily an exact monomer sequence in the polymer; n is an integer greater than 0; each of R₁₆-R₁₉ is independently selected from a group including, but not limited to, hydrogen, C₁-C₃₀ alkyl, C₂-C₃₀ alkenyl, C₂-C₃₀ alkynyl, C₂-C₃₀ alkylcarbonyl, C₁-C₃₀ alkoxy, C₃-C₃₀ alkoxyalkyl, C₂-C₃₀ alkoxycarbonyl, C₄-C₃₀ alkoxycarbonylalkyl, C₁-C₃₀ aminylcarbonyl, C₄-C₃₀ aminylalkyl, C₁-C₃₀ alkylaminyl, C₁-C₃₀ alkylsulfonyl, C₃-C₃₀ alkylsulfonylalkyl, C₆-C₁₈ aryl, C₃-C₁₅ cycloalkyl, C₃-C₃₀ cycloalkylaminyl, C₅-C₃₀ cycloalkylalkylaminyl, C₅-C₃₀ cycloalkylalkyl, C₅-C₃₀ cycloalkylalkyloxy, C₁-C₁₂ heterocyclyl, C₁-C₁₂ heterocyclyloxy, C₃-C₃₀ heterocyclylalkyloxy, C₁-C₃₀ heterocyclylalkyloxy, C₁-C₃₀ heterocyclylaminyl, C₅-C₃₀ heterocyclylalkylaminyl, C₂-C₁₂ heterocyclylcarbonyl, C₃-C₃₀ heterocyclylalkyl, C₁-C₁₃ heteroaryl, or C₃-C₃₀ heteroarylalkyl.

In some embodiments, the host thiophene CP comprises a dioxythiophene copolymer which contains solubilizing 3,4-propylenedioxythiophene (ProDOT) units and electron rich 3,4-ethylenedioxythiophene (EDOT) units with a formula of

wherein x is an integer greater than 0; y is an integer equal to or greater than 0; and n is an integer greater than 0. The values of x, y may indicate ratios of two monomer units, but not necessarily the real monomer sequence in the polymer. This means the reaction might be ordered polymerization or random polymerization. The host CP comprises ProDOT_x-EDOT_y (P_xE_y) with the average ratio of y:x ranging from 0 to 10. An example P_xE_y polymer is PE₃, which sequence can be, for example, PE-PEEEE-PEE-PEEEEE-PEEE . . . with average ratio of y:x is 3 for random polymerization and PEEE-PEEE-PEEE-PEEE-PEEE . . . for ordered polymerization.

In some embodiments, the host CPs comprises dioxythiophene copolymers P_xE_y with x=1, and y=1, 2 or 3.

In another aspect, the disclosure describes a method for preparation of the thermally stable and solvent-resistant conductive polymer composite. The method comprises: providing a solution of crosslinkable silane precursors in a solvent; providing a solution of electron-rich thiophene conjugated polymers in a solvent; producing a composite solution by mixing the solution of crosslinkable silane precursors with the solution of host thiophene conjugated polymers with a weight ratio of the crosslinkable silane precursors in a range of 0.1 to 90 wt % for a reaction time up to 168 hours; an optional step of breaking the hydrogen bond with a hydrogen bond interrupting solvent and promoting the solution consistency if needed. Conventional coating techniques can be used to coating the composite solution onto a substrate to form the thermally stable and solvent-resistant conductive polymer composite thin film.

In some embodiments, the solvent for preparing the solution of crosslinkable silane precursors and the solution of host conjugated polymer is selected from one or more of aprotic solvents, such as chloroform, dichloromethane, nitromethane, or toluene.

In some embodiments, the hydrogen bond interrupting solvent is a solvent which can be used to break hydrogen bond. Example hydrogen bond interrupting solvents may include alcohol and acetone.

In some illustrative embodiments, the present invention relates to a device or a machine incorporated the composite thin film as disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain features of various embodiments of the present technology are set forth with particularity in the appended claims. A better understanding of the features and advantages of the technology will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings below.

FIG. 1 (A)-(D) are schemes of components for the disclosed conductive polymer composite. FIG. 1 (A) shows a scheme of crosslinked siloxane network formed by crosslinkable silane precursors; FIG. 1 (B) is a simplified diagram of the crosslinked siloxane network; FIG. 1 (C) shows a scheme of host thiophene conjugated polymers (CPs); FIG. 1 (D) is a scheme of conductive polymer composite comprised of host CPs and crosslinked siloxane network.

FIG. 2 (A)-(B) contain AFM phase images of pure PE₃ host CP (FIG. 2 (A)) and C₆—Si/PE₃ (FIG. 2 (B)).

FIGS. 3(A)-(B) contain AFM phase images of L₆-Si/PE₃ (FIG. 3 (A)) and F—Si/PE₃ (FIG. 3 (B)).

FIG. 4 shows IR spectra of C₆—Si/PE₃, L₆-Si/PE₃ and pure PE₃ thin films.

FIG. 5 shows IR spectra of C₆—Si/PE₃ composites thin film as spun, after annealing at 373K for 30 minutes, and after annealing at 373 K for 60 minutes.

FIG. 6 is a diagram illustrating conductivity comparison of three silane/PE₃ composites (C₆—Si/PE₃, L₆-Si/PE₃ and F—Si/PE₃) at different silane precursor concentrations.

FIGS. 7(A)-(D) are AFM phase images of C₆—Si/PE₃ composites with different concentrations of C₆—Si, about 72% wt (FIG. 7 (A)), about 56% wt (FIG. 7 (B)), about 39% wt (FIG. 7 (C)) and about 24% wt (FIG. 7 (D)).

FIG. 8 is a diagram illustrating normalized UV-vis absorption spectra of composite thin films of pure PE₃, C₆—Si/PE₃, L₆-Si/PE₃, and F—Si/PE₃.

FIG. 9 is a diagram illustrating conductivity comparison of different silane/PE₃ composites before (left) and after (right) annealing at 393K.

FIGS. 10(A)-(C) are diagrams illustrating normalized in-situ UV-Vis absorption spectra of different silane/PE₃ composites with temperatures increased from 293 K to 453 K. FIG. 10 (A) is for C₆—Si/PE₃, FIG. 10 (B) is for L₆-Si/PE₃, and FIG. 10 (C) is for F—Si/PE₃.

FIG. 11 is a diagram illustrating optical density ratio (OD at 550 nm/OD at 1600 nm) comparison for different silane/PE₃ composites at elevating temperatures.

FIG. 12 is a diagram illustrating normalized conductivity of different silane/PE₃ composites at 353K for 6 hours.

FIGS. 13(A)-(C) are diagrams illustrating IR spectra of C₆—Si/PE₃ composites (FIG. 13(A)), C₁₀—Si/PE₃ composites (FIG. 13(B)) and C_M—Si/PE₃ composites (FIG. 13(C)) before annealing (as spun), after annealing at 373 K for 30 minutes, and after annealing at 373 K for 60 minutes.

FIG. 14 is a diagram illustrating conductivity comparison of different polymers P_xE_y host CPs (PE₁, PE₂, and PE₃) and their conductive polymer composites C_M—Si/P_xE_y.

FIG. 15 is a diagram illustrating normalized conductivity comparison of C_M—Si/P_xE_y composites with different P_xE_y host CPs (PE₁, PE₂, and PE₃) at 353K for 24 hours.

FIGS. 16(A)-(C) are diagrams illustrating normalized UV-Vis absorption spectra of C_M—Si/P_xE_y composites with different P_xE_y host polymers with temperatures increasing from 293 K to 453 K. FIG. 16(A) is for C_M—Si/PE₃ composites, FIG. 16(B) is for C_M—Si/PE₂ composites, and FIG. 16(C) is for C_M—Si/PE₁ composites.

FIG. 17 shows I-V curves of C_M—Si/PE₃ thin film before and after being immersed in water for 1 hour.

FIG. 18 is a diagram illustrating normalized UV-Vis absorption spectra of a C_M—Si/PE₃/PE₃ composite thin film before and after water treatment or chloroform treatment.

FIGS. 19(A)-(C) contains the following images: FIG. 19(C) a glass substrate, FIG. 19(B) a pure polymer PE₃ film on a glass substrate, FIG. 19(A) a C_M—Si/PE₃ composite thin film on a glass substrate after the corresponding bottom half parts dipped in a chloroform bath.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the invention. However, one skilled in the art will understand that the invention may be practiced without these details. Moreover, while various embodiments of the invention are disclosed herein, many adaptations and modifications may be made within the scope of the invention in accordance with the common general knowledge of those skilled in this art. Such modifications include the substitution of known equivalents for any aspect of the invention in order to achieve the same result in substantially the same way.

Unless the context requires otherwise, throughout the present specification and claims, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including, but not limited to.” Recitation of numeric ranges of values throughout the specification is intended to serve as a shorthand notation of referring individually to each separate value falling within the range inclusive of the values defining the range, and each separate value is incorporated in the specification as it were individually recited herein. In the present disclosure the term “about” can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range. Additionally, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may be in some instances. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

The disclosure describes a thermally stable and solvent-resistant conductive polymer composite comprising a doped host thiophene conjugated polymer (CP) and a crosslinked siloxane network.

Reference throughout this specification to the testing results of “conductive polymer composites” or “composites” are referring to the testing results of the processed thin films deposited on glass substrate.

Various embodiments described herein are directed to different forms of crosslinkable silane precursors as well as different host electron-rich thiophene conjugated polymers (CPs) to form the thermally stable and solvent-resistant conductive polymer composite thin films. The low oxidation potentials of the host thiophene conjugated polymers allow them to be readily doped. The crosslinkable silane precursors need at least three functional groups to form a crosslinked siloxane network by condensation reactions and also have at least one doping agent for the doping reaction. When mixing the solutions of the silane precursors and the thiophene conjugated polymers, the crosslinkable silane precursors form a crosslinked siloxane network inside the host thiophene CPs while the doping reaction between the silane precursors and the thiophene conjugated polymers simultaneously occurs (as illustrated in FIG. 1 (A)-(C)). The siloxane network is formed by mixing host thiophene conjugated polymers with crosslinkable silane precursors. During mixing, the functional groups which can have condensation reactions are substituted with hydroxides from the marginal amount of moisture in the chloroform, producing silanol groups in the solution. Two neighboring silanol groups in adjacent precursors go through the condensation reactions in the solution to form the crosslinked siloxane network as shown in FIG. 1 (A). In addition, the low oxidation potentials of the host thiophene conjugated polymers illustrated in FIG. 1 (B) allow them to be readily doped. The doping agents from silane precursor can perform doping reactions with the host CPs while forming the crosslinked network within the host CPs to form the conductive polymer composites as shown in FIG. 1 (C). The crosslinked siloxane network prevents rearrangement of doped polymer chain and dopant diffusion by confining the doped polymer chains, as well as benefits the doping stability since de-doping is also a process associated with conformational and morphological changes. Thus, the introduction of the crosslinked siloxane network not only can greatly enhance the electrical conductivity of CPs, but also can improve the thermal stability and solvent resistance of the CPs.

In some embodiments, the crosslinked siloxane network is produced from a crosslinkable silane precursor with a formula of

wherein:

• • n is an integer greater than 0;
  • X is a monomer unit and is selected from one or more of a group including: oxygen, urea group (N₂H₂CO—), C₁-C₃₀ alkyl, C₂-C₃₀ alkenyl, C₂-C₃₀ alkynyl, C₂-C₃₀ alkylcarbonyl, C₁-C₃₀ alkoxy, C₃-C₃₀ alkoxyalkyl, C₂-C₃₀ alkoxycarbonyl, C₄-C₃₀ alkoxycarbonylalkyl, C₁-C₃₀ aminylcarbonyl, C₁-C₃₀ aminylalkyl, C₁-C₃₀ alkylaminyl, C₁-C₃₀alkylsulfonyl, C₃-C₃₀ alkylsulfonylalkyl, C₆-C₁₈ aryl, C₃-C₁₅ cycloalkyl, C₃-C₃₀ cycloalkylaminyl, C₅-C₃₀ cycloalkylalkylaminyl, C₅-C₃₀cycloalkylalkyl, C₅-C₃₀ cycloalkylalkyloxy, C₁-C₁₂ heterocyclyl, C₁-C₁₂heterocyclyloxy, C₃-C₃₀ heterocyclylalkyloxy, C₁-C₃₀heterocyclylalkyloxy, C₁-C₃₀ heterocyclylaminyl, C₅-C₃₀heterocyclylalkylaminyl, C₂-C₁₂ heterocyclylcarbonyl, C₃-C₃₀heterocyclylalkyl, C₁-C₁₃ heteroaryl, or C₃-C₃₀ heteroarylalkyl, or any combination, among others;
  • each of R₁, R₂, R₃, R₄, R₅, and R₆ is independently selected from: hydrogen, halide groups, hydroxyl group; carboxylic groups, C₁-C₃₀ alkyl, C₂-C₃₀ alkenyl, C₂-C₃₀ alkynyl, C₂-C₃₀ alkylcarbonyl, C₁-C₃₀ alkoxy, C₃-C₃₀ alkoxyalkyl, C₂-C₃₀ alkoxycarbonyl, C₄-C₃₀ alkoxycarbonylalkyl, C₁-C₃₀ aminylcarbonyl, C₄-C₃₀ aminylalkyl, C₁-C₃₀ alkylaminyl, C₁-C₃₀alkylsulfonyl, C₃-C₃₀ alkylsulfonylalkyl, C₆-C₁₈ aryl, C₃-C₁₅ cycloalkyl, C₃-C₃₀ cycloalkylaminyl, C₅-C₃₀ cycloalkylalkylaminyl, C₅-C₃₀cycloalkylalkyl, C₅-C₃₀ cycloalkylalkyloxy, C₁-C₁₂ heterocyclyl, C₁-C₁₂heterocyclyloxy, C₃-C₃₀ heterocyclylalkyloxy, C₁-C₃₀heterocyclylalkyloxy, C₁-C₃₀ heterocyclylaminyl, C₅-C₃₀heterocyclylalkylaminyl, C₂-C₁₂ heterocyclylcarbonyl, C₃-C₃₀heterocyclylalkyl, C₁-C₁₃ heteroaryl, or C₃-C₃₀ heteroarylalkyl, among others;
  • at least three out of R₁, R₂, R₃, R₄, R₅, and R₆ are selected from a group including a chloride group, a bromine group, a hydroxyl group or an alkyloxyl group which can form condensation reaction, and at least one out of R₁, R₂, R₃, R₄, R₅, and R₆ comprise a doping agent.

Although silane precursors have at least three functional groups which can form condensation reactions to form the crosslinked siloxane network, silane precursors with two functional groups which can form condensation reactions can form linear siloxane bridges which can wind and twist within the host thiophene conjugated polymer and form a siloxane matrix. Although such siloxane matrix is not crosslinked, it helps confine the polymer chains to some degree, thus can also greatly enhance electrical conductivity (4-5 orders compared with 6 orders for systems formed by at least three functional groups for some embodiments) of CPs, but its thermal stability is not as good as the silane precursor with at least three functional groups.

In some embodiments, the crosslinked siloxane network is produced from a crosslinkable silane precursor with the formula of

• • wherein each of R₇, R₈, R₉, and R₁₀ is independently selected from: hydrogen, halide groups, hydroxyl group; carboxylic groups, C₁-C₃₀ alkyl, C₂-C₃₀ alkenyl, C₂-C₃₀ alkynyl, C₂-C₃₀ alkylcarbonyl, C₁-C₃₀ alkoxy, C₃-C₃₀ alkoxyalkyl, C₂-C₃₀ alkoxycarbonyl, C₄-C₃₀ alkoxycarbonylalkyl, C₁-C₃₀ aminylcarbonyl, C₄-C₃₀ aminylalkyl, C₁-C₃₀ alkylaminyl, C₁-C₃₀alkylsulfonyl, C₃-C₃₀ alkyl sulfonylalkyl, C₆-C₁₈ aryl, C₃-C₁₅ cycloalkyl, C₃-C₃₀ cycloalkylaminyl, C₅-C₃₀ cycloalkylalkylaminyl, C₅-C₃₀cycloalkylalkyl, C₅-C₃₀ cycloalkylalkyloxy, C₁-C₁₂ heterocyclyl, C₁-C₁₂heterocyclyloxy, C₃-C₃₀ heterocyclylalkyloxy, C₁-C₃₀heterocyclylalkyloxy, C₁-C₃₀ heterocyclylaminyl, C₅-C₃₀heterocyclylalkylaminyl, C₂-C₁₂ heterocyclylcarbonyl, C₃-C₃₀heterocyclylalkyl, C₁-C₁₃ heteroaryl, or C₃-C₃₀ heteroarylalkyl, among others;
  • at least three of the R₇, R₈, R₉, and R₁₀ group are selected from a group including a chloride group, a bromine group, a hydroxyl group or an alkyloxyl group which can form condensation reaction, and at least one of the R₇, R₈, R₉, and R₁₀ group comprises a doping agent.

Although silane precursors require at least three functional groups which can form condensation reactions to form the crosslinked siloxane network, silane precursors with two functional groups which can form condensation reactions can form linear siloxane bridges which can wind and twist within the host thiophene conjugated polymer and form a siloxane matrix. Although such siloxane matrix is not crosslinked, it helps confine the polymer chains to some degree, thus can also greatly enhance electrical conductivity (4-5 orders compared with 6 orders for systems formed by at least three functional groups for some embodiments) of CPs, but the thermal stability is not as good as the silane precursor with at least three functional groups.

In some embodiments, the siloxane network is produced from a combination of silane precursors which include at least one of two crosslinkable silane precursors of the above formulas (1) and (2). Besides any of the crosslinkable silane precursors in formulas (1) and (2), non-crosslinkable silane precursors which cannot form crosslinked siloxane network (for example, silane precursors with only one or two functional groups) may be included in the system.

In some embodiments, the crosslinked siloxane network is produced from a crosslinkable chlorosilane with a formula of

wherein:

• • n is the number of spacer carbon;
  • n is an integer greater than 0 and ranges from 1-13.

Here chlorine groups function not only for condensation reaction, but also act as doping agents and form doping reaction with the host CPs.

In some embodiments, the crosslinked siloxane network is produced from a crosslinkable chlorosilane precursor with a formula of

• • wherein R₁₁ is selected from a group including: hydrogen, halide groups, hydroxyl group; carboxylic groups, C₁-C₃₀ alkyl, C₂-C₃₀ alkenyl, C₂-C₃₀ alkynyl, C₂-C₃₀ alkylcarbonyl, C₁-C₃₀ alkoxy, C₃-C₃₀ alkoxyalkyl, C₂-C₃₀ alkoxycarbonyl, C₄-C₃₀ alkoxycarbonylalkyl, C₁-C₃₀ aminylcarbonyl, C₁-C₃₀ aminyl alkyl, C₁-C₃₀ alkyl aminyl, C₁-C₃₀alkylsulfonyl, C₃-C₃₀ alkylsulfonylalkyl, C₆-C₁₈ aryl, C₃-C₁₅ cycloalkyl, C₃-C₃₀ cycloalkylaminyl, C₅-C₃₀ cycloalkylalkylaminyl, C₅-C₃₀cycloalkylalkyl, C₅-C₃₀ cycloalkylalkyloxy, C₁-C₁₂ heterocyclyl, C₁-C₁₂heterocyclyloxy, C₃-C₃₀ heterocyclylalkyloxy, C₁-C₃₀heterocyclylalkyloxy, C₁-C₃₀ heterocyclylaminyl, C₅-C₃₀heterocyclylalkylaminyl, C₂-C₁₂ heterocyclylcarbonyl, C₃-C₃₀heterocyclylalkyl, C₁-C₁₃ heteroaryl, or C₃-C₃₀ heteroarylalkyl, among others;

In some embodiments, the crosslinkable chlorosilane precursor is mono-trichlorosilyl (C_M—Si), or 1,6-bis(trichlorosilyl)hexane (C₆—Si), or 1,10-bis(tricholorosilyl)decane with 10 spacers (C₁₀—Si), with the formulas of:

These crosslinkable chlorosilane precursors are all referred as C—Si in the following paragraphs.

The disclosed thermally stable and solvent resistant conductive polymer composite comprises a host thiophene conjugated polymer (CP) which comprises a p-type thiophene conjugated polymer with an oxidation potential lower than 0.4 V vs. Ag/AgCl.

Various embodiments described here are involved with the different host electron-rich thiophene CPs which can form the disclosed thermally stable and solvent-resistant electrochromic thiophene conjugated polymer composites with crosslinked siloxane networks. The host CPs comprises a polymer with a formula of

• • wherein a and b are integers equal to or greater than 0; values of a and b indicate ratios of two monomer units, but not necessarily an exact monomer sequence in the polymer; n is an integer greater than 0; each of R₁₂-R₁₅ is independently selected from a group including, but not limited to, hydrogen, C₁-C₃₀ alkyl, C₂-C₃₀ alkenyl, C₂-C₃₀ alkynyl, C₂-C₃₀ alkylcarbonyl, C₁-C₃₀ alkoxy, C₃-C₃₀ alkoxyalkyl, C₂-C₃₀ alkoxycarbonyl, C₄-C₃₀ alkoxycarbonylalkyl, C₁-C₃₀ aminylcarbonyl, C₄-C₃₀ aminylalkyl, C₁-C₃₀ alkylaminyl, C₁-C₃₀ alkylsulfonyl, C₃-C₃₀ alkylsulfonylalkyl, C₆-C₁₈ aryl, C₃-C₁₅ cycloalkyl, C₃-C₃₀ cycloalkylaminyl, C₅-C₃₀ cycloalkylalkylaminyl, C₅-C₃₀ cycloalkylalkyl, C₅-C₃₀ cycloalkylalkyloxy, C₁-C₁₂ heterocyclyl, C₁-C₁₂ heterocyclyloxy, C₃-C₃₀ heterocyclylalkyloxy, C₁-C₃₀heterocyclylalkyloxy, C₁-C₃₀ heterocyclylaminyl, C₅-C₃₀ heterocyclylalkylaminyl, C₂-C₁₂ heterocyclylcarbonyl, C₃-C₃₀ heterocyclylalkyl, C₁-C₁₃ heteroaryl, or C₃-C₃₀ heteroarylalkyl; and at least one of R₁₂-R₁₅ is electron rich that has excess electrons to be donated. An example polymer might include

In some embodiments, the host thiophene CPs comprises a polymer with a formula of

wherein a and b are integers equal to or greater than 0; values of a and b indicate ratios of two monomer units, but not necessarily an exact monomer sequence in the polymer; n is an integer greater than 0; each of R₁₆-R₁₉ is independently selected from a group including, but not limited to, hydrogen, C₁-C₃₀ alkyl, C₂-C₃₀ alkenyl, C₂-C₃₀ alkynyl, C₂-C₃₀ alkylcarbonyl, C₁-C₃₀ alkoxy, C₃-C₃₀ alkoxyalkyl, C₂-C₃₀ alkoxycarbonyl, C₄-C₃₀ alkoxycarbonylalkyl, C₁-C₃₀ aminylcarbonyl, C₄-C₃₀ aminylalkyl, C₁-C₃₀ alkylaminyl, C₁-C₃₀ alkylsulfonyl, C₃-C₃₉ alkylsulfonylalkyl, C₆-C₁₈ aryl, C₃-C₁₅ cycloalkyl, C₃-C₃₀ cycloalkylaminyl, C₅-C₃₀ cycloalkyl alkyl aminyl, C₅-C₃₀ cycloalkylalkyl, C₅-C₃₀ cycloalkylalkyloxy, C₁-C₁₂ heterocyclyl, C₁-C₁₂ heterocyclyloxy, C₃-C₃₀ heterocyclylalkyloxy, C₁-C₃₀heterocyclylalkyloxy, C₁-C₃₀ heterocyclylaminyl, C₅-C₃₀ heterocyclylalkylaminyl, C₂-C₁₂ heterocyclylcarbonyl, C₃-C₃₀ heterocyclylalkyl, C₁-C₁₃ heteroaryl, or C₃-C₃₀ heteroarylalkyl. An example polymer might include

In some embodiments, the host thiophene CPs comprises a polymer with a formula of

• • wherein a and b are integers equal to or greater than 0; values of a and b indicate ratios of two monomer units, but not necessarily an exact monomer sequence in the polymer; n is an integer greater than 0; each of R₁₆-R₁₉ is independently selected from a group including, but not limited to, hydrogen, C₁-C₃₀ alkyl, C₂-C₃₀ alkenyl, C₂-C₃₀ alkynyl, C₂-C₃₀ alkylcarbonyl, C₁-C₃₀ alkoxy, C₃-C₃₀ alkoxyalkyl, C₂-C₃₀ alkoxycarbonyl, C₄-C₃₀ alkoxycarbonylalkyl, C₁-C₃₀ aminylcarbonyl, C₄-C₃₀ aminylalkyl, C₁-C₃₀ alkylaminyl, C₁-C₃₀ alkylsulfonyl, C₃-C₃₀ alkylsulfonylalkyl, C₆-C₁₈ aryl, C₃-C₁₅ cycloalkyl, C₃-C₃₀ cycloalkylaminyl, C₅-C₃₀ cycloalkylalkylaminyl, C₅-C₃₀ cycloalkylalkyl, C₅-C₃₀ cycloalkylalkyloxy, C₁-C₁₂ heterocyclyl, C₁-C₁₂ heterocyclyloxy, C₃-C₃₀ heterocyclylalkyloxy, C₁-C₃₀ heterocyclylalkyloxy, C₁-C₃₀ heterocyclylaminyl, C₅-C₃₀ heterocyclylalkylaminyl, C₂-C₁₂ heterocyclylcarbonyl, C₃-C₃₀ heterocyclylalkyl, C₁-C₁₃ heteroaryl, or C₃-C₃₀ heteroarylalkyl.

In some embodiments, the host thiophene CPs comprises dioxythiophene copolymers which contained solubilizing 3,4-propylenedioxythiophene (ProDOT) units and electron rich 3,4-ethylenedioxythiophene (EDOT) units with a formula of

wherein x is an integer greater than 0; y is an integer equal to or greater than 0; n is an integer greater than 0; The values of x, y indicate ratios of two monomer units, but not necessarily the real monomer sequence in the polymer. This means the reaction might be ordered polymerization or random polymerization. The host CP comprises ProDOT_x-EDOT_y (P_xE_y) with the average ratio of y:x ranging from 0 to 10. An example P_xE_y polymer is PE₃, which sequence can be, for example, PE-PEEEE-PEE-PEEEEE-PEEE . . . with average ratio of y:x is 3 for random polymerization and PEEE-PEEE-PEEE-PEEE-PEEE . . . for ordered polymerization. In some embodiments, the host CPs comprises a dioxythiophene copolymers P_xE_y with x=1, and y=1, 2 or 3, corresponding to PE₁, PE₂ and PE₃, respectively. An example polymer might also include

EXAMPLES

1. Ability to Form Crosslinked Siloxane Network

Various following embodiments are involved with the crosslinkable 1,6-bis(trichlorosilyl)hexane (referred as C₆—Si in the following paragraphs) as an example crosslinkable silane precursor with at least three chlorine groups, and the host CPs comprises dioxythiophene random copolymers which contain one solubilizing 3,4-propylenedioxythiophene (ProDOT) unit and three electron rich 3,4-ethylenedioxythiophene (EDOT) units with a formula of ProDOT₁-EDOT₃ (PE₃) as an example host CP. For comparison, two noncrosslinkable silane precursors with one or two chlorine groups which cannot form crosslinked siloxane network are also evaluated. The silane precursor with two or one chlorine groups is separately referred to linear silane precursor (L₆-Si) or flowable silane precursor (F—Si). The formulas of L₆-Si and F—Si are shown as follow:

Atomic force microscopy (AFM) phase images of the pure thiophene conjugated polymer PE₃ and the conductive polymer composites thin film formed with different silane precursors C₆—Si, L₆-Si, and F—Si are shown in FIG. 2 (A)-(B) and FIG. 3 (A)-(B). As shown in FIG. 2 (B), the conductive polymer composite formed from PE₃ and C₆—Si displays obvious phase separation between the thiophene conjugated polymers while pure PE₃ do not. On the other hand, FIG. 3 (A)-(B) show that both composite thin films from L₆-Si/PE₃ and F—Si/PE₃ do not show obvious phase separation. This indicates that although L₆-Si can form a linear matrix which might twist and wind within the host and F—Si can form a flowable matrix during film processing, they cannot form crosslinked network by condensation reactions inside the entire composites. The formation of cross-linked siloxane network in the C₆—Si/PE₃ composites is further confirmed by monitoring the presence of the IR bands at about 1050 cm⁻¹ and 1150 cm⁻¹, which represent characteristics of Si—O—Si stretching vibrations shown by the arrows in FIG. 4. Due to the lack of trichlorosilyl groups that form crosslinked network during condensation reactions, L₆-Si and F—Si composites form a linear matrix and a flowable matrix, thus less Si—O—Si stretching vibrations bands in the IR spectra. When the host CP solution is mixed with the silane precursor solution, the conductive polymer composite is already spontaneously formed in the solution. After being coating into a thin film, annealing treatment at 393K is applied to the thin film. Intriguingly, the temperature dependent in-situ IR spectrum of C₆—Si/PE₃ composites overlapped well before and after thermal annealing at 393 K as shown in FIG. 5, indicating a cross-linked siloxane network formed simultaneously at room temperature.

2. Effect of Silane Precursor Concentration on the Electrical Performance

Concentrations of silane precursor have great effect on the electrical performance of conductive polymer composites. However, conductive polymer composites with different silane precursors and thiophene conjugated polymer may have different optimal concentrations. Here, efforts are made as a model to investigate the influence of specific silane precursor (C₆—Si, L₆-Si, and F—Si) concentration on the electrical performance of the conductive polymer composites with specific conjugated polymer (PE₃). The conductivities of three different conductive polymer composites C₆—Si/PE₃, L₆-Si/PE₃ and F—Si/PE₃ with different concentrations of silane precursors are shown in FIG. 6. For better presentation of the difference among different concentration, the conductivities are displayed in log scale. Among various contents of silane precursors, all three conductive polymer composites show the highest conductivity with about 56% wt silane precursors. The conductivity of PE₃ is only 10'S/cm, while those of all three conductive polymer composites are mostly above 0.1 S/cm. This greatly improved conductivities are attributed to the presence of chlorine (a p-type dopant) and silanol (a well-known electron trap). This is further confirmed by the most abundant phase separation observed for C₆—Si/PE₃ with about 56% wt of silane precursor as shown in the phase AFM images in FIG. 7 (B). Excess silane precursors lead to a scarcity of conductive domains in the composites, so the conductivities drop for all three composites with about 72% wt silane precursors in FIG. 6, which may due to the insufficient and isolated conducting domains in the composites, as shown in FIG. 7(A). In addition, among three different silane precursors (crosslinkable C₆—Si, noncrosslinkable L₆-Si and noncrosslinkable F—Si), the highest conductivity increase (up to 6 orders) is achieved for about 56% wt C₆—Si/PE₃ while lower conductivity increase is achieved for both L₆-Si/P and F—Si/PE₃. With the same 56% wt of silane precursors, the C₆—Si/PE₃ composite with crosslinked network introduces the most abundant chlorine species among three different composites, therefore displays the highest conductivity. Since about 56% wt silane precursor demonstrates to generate the best electrical performance of conductive polymer composites, about 56% wt silane precursor is used for all the following experiments as long as no other concentration is particularly specified.

3. Doping Process

UV-vis absorption spectrum of pure PE₃ and three conductive polymer composites C₆—Si/PE₃, L₆-Si/PE₃ and F—Si/PE₃ with about 56% wt silane precursors is used to monitor the doping process, as shown in FIG. 8. Each spectrum is normalized to the absorbance at 400 nm respectively. When mixing the host CP and silane precursors, doping process simultaneously happens between the doping agents from silane precursors and the host CP while crosslinked siloxane network forms. Here, the chlorine group functions as the doping agent. There are three critical peaks (neutral absorption band at 550 nm, polarons peak at 850 nm, bipolarons peak at ˜λ_max), as shown in the shaded wavelength range in FIG. 8. The neutral absorption band at ˜550 nm is usually related to the band gap energy needed to excite an electron from the valence band to the conduction band. The decrease of the neutral peaks indicates the elevation of polymer conductivity caused by the doping process. The polarons peak (˜850 nm) and the bipolarons peak (˜λ_max) are often used to denote the generation of different charge carriers along the polymer backbone upon doping. The neutral absorption peaks at 550 nm decreases for all three silane/PE₃ composites when compared with PE₃ polymer, which indicates the doping process happens to all three composites. The increases of both polaron peaks and bi-polaron peaks further demonstrate the formation of doping process for all three composites. FIG. 8 also shows both polaron peak and bi-polaron peak for C₆—Si/PE₃ composite increase most and then L₆-Si/PE₃ and then F—Si/PE₃, which increase order is corresponding to the abundance order of the chlorine groups from silane precursors. The more chlorine group, the more doping effect and the more increase of both polaron peak and bi-polaron peak.

4. Thermal Stability Introduced by Crosslinked Siloxane Network and Abundant Doping

As stated above, three different techniques (AFM, IR and UV-vis absorption) all demonstrate both crosslinked siloxane network and more doping process happen to the conductive polymer composite (C₆—Si/PE₃) with crosslinkable silane precursor when compared with other composites (L₆-Si/PE₃ and F—Si/PE₃) formed from non-crosslinkable silane precursor and less chlorine doping agents. Correspondingly, the thermal stability of these three composites are examined to investigate the thermal stability impact from the crosslinked siloxane network and abundant doping process. Cl⁻ anions can easily diffuse out from the non-thermal stable system after being annealing at 373 K, leading to decreased conductivity. If the composite has good thermal stability, its conductivity will not change much after heating. Thus, the conductivity changes before and after being thermal annealing at 373 K for 1 hour are examined for C₆—Si/PE₃, L₆-Si/PE₃ and F—Si/PE₃ with about 56% wt silane precursors. As shown in FIG. 9, after one hour of annealing at 373 K, only C₆—Si/PE₃ composites remain high stable conductivity as it still maintains more than 90% of the original electrical conductivity, while the other composites with linear and flowable matrices barely exhibited conductive behavior. This result demonstrates the great thermal stability introduced by crosslinked siloxane network along with the doping process, which is barely achieved by linear or flowable silane matrices. Since the doping agents come from the silane precursors, the doping process happens simultaneously together with the crosslinking process. In this specification, the process for both the doping and the crosslinked siloxane network formation may be simplified as the process for the crosslinked network formation.

The electrical thermal stability is further investigated by monitoring the de-doping process in the composites at elevating temperatures by the in-situ temperature dependent UV-vis absorption spectra of three composites (C₆—Si/PE₃, L₆-Si/PE₃, F—Si/PE₃) at various temperatures from 293 K to 453 K as shown in FIG. 10 (A)-(C). For each conductive polymer composite thin film, absorbance values at different temperatures are all normalized to the absorbance of 400 nm at 293K. As shown in FIG. 10 (A), at room temperature, C₆—Si/PE₃ composite shows a broad signal at λ_max (˜1600 nm) which is attributed to the bipolaron absorption. As the temperature increases, the bipolaron absorption peak at λ_max (˜1600 nm) keeps decreasing, and the polaron peak at λ=˜850 nm emerges higher and higher from 373K, 393K to 413K and then slightly decreases (but remains higher than that at 373K) after temperature further increases to 433K and 453K. Meanwhile, the neutral peaks at 550 nm keeps increasing when the temperature increases. The increasing of polaron peak before 413K may be due to the generation of polaron from bipolaron is greater the degeneration of polaron. When temperature increases to 433K, the degeneration of polaron dominate the de-doping process, which lead to the slight decrease of polaron peak. The neutral peaks at 550 nm normally dominate when the conjugated polymer is not doped. The reducing bipolaron peak at ˜1600 nm along with the increasing neutral peak at 550 nm indicates the effect of de-doping process. When comparing FIG. 10 (A)-(C), much higher bipolaron and polaron peaks, as well as much lower neutral peak are observed for C₆—Si/PE₃ than those from L₆-Si/PE₃ and F—Si/PE₃ composites at all testing temperatures, indicating greater conductivities of C₆—Si/PE₃ at the testing temperatures. Meanwhile, smaller decreases of polaron and bipolaron peaks as well as smaller increase of neutral peak happen to C₆—Si/PE₃ than those from L₆-Si/PE₃ and F—Si/PE₃ composites. The insignificant changes of the polaron, bipolaron, and neutral peak intensity demonstrate the thermal stability of C₆—Si/PE₃ composites.

Since the intensities of bipolaron peaks and neutral peaks more directly reflect the conductivities of the composites, an optical density ratio between the neutral peak (˜550 nm) and bi-polaron peak (˜1600 nm) is used to indicate the conductivity and thermal stability of the composites. The smaller the optical density ratio of the composites, the higher conductivity of the composites. With the increasing temperatures, the smaller the optical density ratio change of the composites, the higher thermal stability of the composites. The optical density ratio changes for three silane/PE₃ composites (C₆—Si/PE₃, L₆-Si/PE₃, F—Si/PE₃) at various elevating temperatures are further evaluated. As shown in FIG. 11, C₆—Si/PE₃ composite displays the smallest ratios as well as the smallest ratio changes with increased temperatures, which indicates that C₆—Si/PE₃ composite has the most thermal stability among three composites. As stated above, only C₆—Si/PE₃ composite forms the crosslinked siloxane network. The crosslinked siloxane network in the composites effectively confines the doped polymer and limits the mobility of doped polymer chains, thus, it greatly reduces the morphology change and the diffusion of dopants at high temperatures, thus endows the resulting conductive polymer composite great thermal stability.

5. Impact of the Spacer Carbon Numbers in Crosslinkable Silane Precursors on the Thermal Stability of the Composites

The increased rigidity of the crosslinked networks can be controlled by the spacer carbon numbers in the crosslinkable silane precursors, leading to further improved thermal stability of the composite. To investigate the impact of different spacer carbon numbers in crosslinkable silane precursors on the thermal stability of the composites, two other crosslinkable chlorosilanes, hexyltrichlorosilane with mono-trichlorosilyl (C_M—Si) and 1,10-Bis(tricholorosilyl)decane with 10 spacers (C₁₀—Si) are compared with C₆—Si. The conductivities of three types of composites are examined in situ at 353K for 6 hours, as show in FIG. 12. All data are normalized to the corresponding conductivity at time zero. For better presentation, the normalized conductivities are displayed in log scale. As a control, non-crosslinkable silane precursor L₆-Si is also compared. As shown in FIG. 12, the conductivity of L₆-Si/PE₃ drops dramatically in the first hour for almost 2 orders, and remains about 5% of the as-spun conductivities in the pro-longed thermal stress. On the other hand, all the three C—Si/PE₃ composites show insignificant conductivity changes. The C₆—Si/PE₃ and C₁₀/PE₃ composites with flexible spacers in the siloxane network drop to about 60% of their as-spun conductivities, whereas C_M—Si/PE₃ composites maintain their as-spun conductivity. The superior thermal stability of C_M—Si composite is attributed to its most rigid crosslinked network without flexible spacers in the silane precursors. The great drop of conductivity for L₆-Si/PE₃ composites indicates the bad thermal stability due to the lack of crosslinked siloxane network.

The effects of the number of spacer carbon on the thermal stability of the disclosed conductive polymer composite thin film are further evaluated by the presence of the IR bands at about 1050 cm⁻¹ and 1150 cm⁻¹, which correspond to the Si—O—Si stretching vibrations. IR spectra for three conductive polymer composite, C₆—Si/PE₃, C₁₀—Si/PE₃, and C_M—Si/PE₃ are compared before and after thermal annealing at 393 K for 30 mins and 60 mins, as shown in FIG. 13 (A)-(C). Although all three composites exhibit clear IR bands about 1050 cm⁻¹ and 1150 cm⁻¹, shown by the arrows. C_M—Si/PE₃ composites show the broadest Si—O—Si bands between 1050-1150 cm⁻¹, which indicates the most abundant siloxane network. Furthermore, the IR spectra of C_M—Si/PE₃ composites before and after 393K thermal stress overlap with each other, indicating the greatest thermal stability C_M—Si silane precursor introduces to the resulting composite. Overall, due to the greatest thermal stability C_M—Si silane precursor introduces to the resulting composite, C_M—Si silane precursor is used for the following experiments.

6. Effect of Different Host CPs on Electrical Performance and Thermal Stability

The electrical performance of C—Si/P_xE_y composites also depends on the oxidation potential of CPs. To investigate the effect of different host CPs on the electrical performance of the disclosed conductive polymer composite thin films, composites formed with three different host CPs are compared. Those three CPs are similar dioxythiophene copolymers which contain solubilizing 3,4-propylenedioxythiophene (ProDOT) units and electron rich 3,4-ethylenedioxythiophene (EDOT) units with the formula of ProDOT_xEDOT_y, P_xE_y (x=1; y=1, 2, 3 separately for three host CPs). Conductivities of composites formed from C_M—Si silane precursor and different CPs (PE₁, PE₂, PE₃) are compared with the pure polymers' conductivity, as shown in FIG. 14. The conductivities of all three CPs greatly increase after doping with chlorosilane precursors. For better presentation, the conductivity is displayed in log scale. For the pure host CPs, PE₁, PE₂ and PE₃ have conductivity values about 10⁻⁷, 10⁻⁶ and 10⁻⁶ S/cm, respectively. Upon doping with C_M—Si by blending polymer solutions with chlorosilane precursors, the conductivities of PE₁, PE₂ and PE₃ increased to 10⁻⁶, 10⁻¹ and 6 S/cm, respectively. The increasing magnitudes of conductivity for PE₁, PE₂ and PE₃ are 10³, 10⁵, 10⁶, respectively. The highest conductivity and the greatest conductivity increase upon doping are found for PE₃, which indicates that PE₃ is most likely to be doped among three PCs. This may be because the increasing EDOT content in the repeat unit of P_xE_y copolymers may lower the onset oxidation potential and the electron gap (Eg) of the polymer.

The thermal stability of the three C_M—Si/P_xE_y composites with the same different CPs are compared by their conductivity changes under thermal stress in FIG. 15 and in-situ temperature dependent UV-vis absorption spectra in FIGS. 16(A)-(C). FIG. 15 shows the in-situ measured normalized conductivity changes at 353K for 24 hours. All data are normalized to the conductivity of C_M—Si/PE₃ at time zero. For better presentation, the normalized conductivities are displayed in log scale. The conductivities of C_M—Si/PE₂ and C_M—Si/PE₃ remain almost the same over the 24 hour baking at 353K (over 80% of their original conductivity) while the conductivity of C_M—Si/PE₁ slightly increases in the first few hours and dramatically decreases after long time baking (˜19 hours) with more than 90% of its original conductivity lost. Thus, FIG. 15 indicates the C_M—Si/PE₂ and C_M—Si/PE₃ show higher thermal stability than C_M—Si/PE₁. FIG. 16 (A)-(C) show the in-situ temperature dependent UV-vis absorption spectra of the three C_M—Si/P_xE_y composites at various temperatures from 293 K to 453. For each conductive polymer composite thin film, spectra at different temperatures are normalized to the absorbance at 400 nm at 293K. At 293K, very high bipolaron absorption and very low natural absorption are observed for C_M—Si/PE₃ composites, which indicates C_M—Si/PE₃ has very good conductivity. Polaron absorption peak first increases from 293K to 393K, then decreases a little bit from 413K to 453K. However, the final polaron absorption at 453K still show clear peak and higher intensity than that at the initial 293K, which indicates the great thermal stability of C_M—Si/PE₃. C_M—Si/PE₂ in FIG. 16(B) shows similar trend on absorption peak changes with increasing temperature as C_M—Si/PE₃ with lower bipolaron and polaron peaks. C_M—Si/PE₁ in FIG. 16(C) shows even lower bipolaron and polaron band absorptions, and more drop of polaron band absorptions, indicating lower conductivity and less thermal stability. Overall, C_M—Si/PE₃ shows the best thermal stability.

7. Solvent Resistance of the Disclosed Composite Thin Film

The disclosed conductive polymer composites not only exhibit great thermal stability, but also exhibit great water and organic solvent resistance due to the entanglement of polymers within the cross-linked siloxane network. The solvent resistance of the disclosed C—Si/PE₃ composites is evaluated with C_M—Si/PE₃ composite by monitoring the change of the electrical conductivity and UV-vis absorption spectra before and after being dipped into water or organic solvents which are commonly used in conductive polymer composites processing. As shown in FIG. 17, after being immersed in water for 1 hour, the I-V curve of C_M—Si/PE₃ composites (grey line) only show slightly offset from the original one before immersing in water (black line). FIG. 18 shows the UV-vis absorption spectra of C_M—Si/PE₃ composites before and after 1 hour water treatment as well as after 1 minute chloroform treatment. For each treatment, the entire spectrum is normalized to the absorbance at 400 nm. The spectra after 1 hour water treatment show less than 10% drop when compare with the original one before water treatment. In addition, C_M—Si/PE₃ composites also display great organic solvent robustness. After being dipped in chloroform, the intensities of absorption peak only slightly decreases, indicating the excellent solvent robustness of C_M—Si/PE₃ composite.

The excellent organic solvent resistance of C_M—Si/PE₃ composite thin film can also be visualized as shown in FIGS. 19(A)-(C). The bottom half portions of glass substrate, pure PE₃ thin film and C_M—Si/PE₃ composite thin film are dipped into a bath of chloroform for 1 minute. Clear color change between the top half and the bottom half is observed for the pure PE₃ thin film with naked eyes, while no notable color change between two half portions is seen for both C_M—Si/PE₃ composite thin film and glass substrate under the same treatments, indicating great organic solvent resistance of the C_M—Si/PE₃ composite thin film. Similar results are also observed for another commonly used organic solvent, acetone. This again confirms the excellent solvent resistance of C_M—Si/PE₃ composite thin film.

In another aspect, the disclosure describes a method for preparation of the thermally stable and solvent-resistant conductive polymer composite.

To achieve robust electrical conductivity under elevating temperatures and/or various solvent environments of conjugated polymers, doping appears to be a promising approach. However, how to design and synthesize a simple and efficient doping method to achieve thermally stable and solvent resistant system remains quite challenging. The preparation method for the disclosed thermally stable and solvent-resistant conductive polymer composite thin film is only involved with simple mixing of conjugated polymers and crosslinkable silane precursors in ambient air under room temperature. While mixing, crosslinking and doping are simultaneously occurs, resulting the disclosed thermally stable and solvent-resistant conductive polymer composite sol-gel solution. Conventional film coating techniques can be used to easily produce the disclosed conductive polymer composite thin film.

The method comprises: providing a crosslinkable silane precursor solution in a solvent; providing a host thiophene conjugated polymer solution in a solvent; producing a composite sol-gel solution by mixing the crosslinkable silane precursor solution with the host conjugated polymer solution with a ratio of the silane precursor in a range of 0.1 to 90% wt for a reaction time up to 168 hours; an optional step of breaking the hydrogen bond with a hydrogen bond interrupting solvent and promoting the solution consistency if needed. Conventional film coating techniques can be used to coat the composite solution onto a substrate to form the disclosed thermally stable and solvent-resistant conductive polymer composite thin film. The preparation method described here can be used to make a conductive polymer composite from a doped electron-rich thiophene conjugated polymer and a crosslinked siloxane network describe in the first aspect.

In some embodiments, the solvent for the crosslinkable silane precursor and the solvent for the thiophene conjugated polymer are selected from one or more of aprotic solvent, such as chloroform, dichloromethane, nitromethane, toluene.

In some embodiments, the hydrogen bond interrupting solvent is a solvent which can be used to break hydrogen bond. Example hydrogen bond interrupting solvents may include alcohol and acetone.

In some embodiments, the thin-films can be processed by spin-coating. slot-die coating, spray coating, bar coating, among others known in the art.

In some embodiments, the annealing method used for the coating process includes thermal annealing, IR irradiation annealing.

In one embodiment, a method for forming a C₆—Si/PE₃ composite thin film is provided. PE₃ solution is prepared in dichloromethane with the concentration of 25 mg/mL C₆—Si solutions is prepared in dichloromethane, and the concentration is 80 mg/mL. The two solutions are blended with about 56% wt C₆—Si. After blending for more than 48 hrs, the blend changes to a sol-gel solution. For the purpose of film processing, 5-20 μl (preferably 10 μl) ethanol is added to the gel to break the hydrogen bonding and the mixture returned to solution state. Silane/PE₃ composites are deposited on the glass substrate by spin-coating at a speed of 1500 rpm for 60 seconds. After spin coating, the thin film is dried in the oven for 10 min at 353K.

In another embodiment, a method of forming a C_M—Si/PE₁ composite thin film is provided. PE₁ solution is prepared in chloroform with the concentration of 25 mg/mL, C_M—Si solutions is prepared in chloroform, and the concentration preferably 80 mg/mL. The two solutions are blended with 56% wt C_M—Si. After blending for 24 hrs, the blend changes to a sol-gel solution. The solution-gel mixture is deposited on the glass substrate by spin-coating at a speed of 1500 rpm for 60 seconds. After spin coating, the thin film is dried in the oven for 10 min at 353K.

In another embodiment, a method of forming a C₆—Si/PE₂ composite thin film is provided. PE₃ solution is prepared in chloroform with the concentration of 25 mg/mL, C₆—Si solutions is prepared in chloroform, and the concentration preferably 80 mg/mL. The two solutions are blended with 24% wt C₆—Si. After blending for 24 hrs, the blend changes to a sol-gel solution. The solution-gel mixture is deposited on the glass substrate by spin-coating at a speed of 1500 rpm for 60 seconds. After spin coating, the thin film is dried in the oven for 10 min at 353K.

In another embodiment, a method of forming a C₆—Si/ProDOT composite thin film is provided. ProDOT solution is prepared in chloroform with the concentration of 25 mg/mL Heptyltrichlorosilane (C₆—Si) solution is prepared in chloroform with the concentrations of 80 mg/mL. The two solutions are blended with 56% wt C₆—Si. After blending for 90 hrs, the blend changes to a sol-gel solution. For the purpose of film processing, 5-20 μl (preferably 10 μl) ethanol is added to the gel to break the hydrogen bonding and the mixture returned to solution state. C₆—Si/ProDOT composite is deposited on the glass substrate by spin-coating at a speed of 1500 rpm for 60 seconds. After spin coating, the composite thin film is dried in the oven for 10 min at 353K. Overall, the present disclosure discloses a thermally stable and solvent resistant conductive polymer composite comprising a host thiophene conjugated polymer and a crosslinked siloxane network. The disclosure also presents a manufacturing friendly preparation method to make the disclosed composite. The approach by simply mixing a host thiophene conjugated polymer and a crosslinkable silane precursor to simultaneously introduce both dopant and rigid cross-linked siloxane network into polymer system is disclosed to improve stability of doped system. The thin film made by the disclosed thermally stable and solvent resistant conductive polymer composite can be applied to fabricate various devices, such as OLED, OECD.

Claims

1. A conductive polymer composite, comprising a doped host thiophene conjugated polymer and a crosslinked siloxane network, wherein the doped host thiophene conjugated polymer comprises a copolymer with a formula of

2. The conductive polymer composite of claim 1, wherein the crosslinked siloxane network is produced from a crosslinkable silane precursor with a formula of

3. The conductive polymer composite of claim 2, wherein the crosslinkable silane precursor comprises a crosslinkable chlorosilane precursor with a formula of

4. The conductive polymer composite of claim 3, wherein the crosslinkable chlorosilane precursor comprises 6 or 10 spacer carbons with the formulas of

5. The conductive polymer composite of claim 1, wherein the crosslinked siloxane network is produced from a crosslinkable silane precursor with a formula of

6. The conductive polymer composite of claim 5, wherein the crosslinkable silane precursor comprises a crosslinkable chlorosilane precursor with a formula of

7. The conductive polymer composite of claim 6, wherein the crosslinkable chlorosilane precursor comprises a mono-trichlorosilyl with the formula of

8. The conductive polymer composite of claim 1, wherein the doped host thiophene conjugated polymer comprises a p-type thiophene conjugated polymer with an oxidation potential lower than 0.4 V vs. Ag/AgCl.

9. A device incorporating a thin film made of the conductive polymer composite of claim 1.

10. A conductive polymer composite, comprising a doped host thiophene conjugated polymer and a crosslinked siloxane network, wherein the doped host thiophene conjugated polymer comprises a copolymer with a formula of

11. The conductive polymer composite of claim 10, wherein the crosslinked siloxane network is produced from a crosslinkable silane precursor with a formula of

12. The conductive polymer composite of claim 10, wherein the crosslinked siloxane network is produced from a crosslinkable silane precursor with a formula of

13. A conductive polymer composite, comprising a doped host thiophene conjugated polymer and a crosslinked siloxane network, wherein the doped host thiophene conjugated polymer comprises a copolymer with a formula of

14. The conductive polymer composite of claim 13, wherein the doped host thiophene conjugated polymer comprises a copolymer with a formula of

15. The conductive polymer composite of claim 12, wherein x is equal to 1, and y is equal to 1, 2 or 3.

16. The conductive polymer composite of claim 13, wherein the crosslinked siloxane network is produced from a crosslinkable silane precursor with a formula of

17. The conductive polymer composite of claim 13, wherein the crosslinked siloxane network is produced from a crosslinkable silane precursor with a formula of

18. A method of making a conductive polymer composite, the method comprising: providing a solution of crosslinkable silane precursors in a solvent;providing a solution of host electron rich thiophene conjugated polymers in a solvent;producing a solution comprising the conductive polymer composite by mixing the solution of crosslinkable silane precursors with the solution of host thiophene conjugated polymers with a ratio of the crosslinkable silane precursors in a range of 0.1 to 90 wt % for a reaction time up to 168 hours; andadding a hydrogen bond interrupting solvent to break the hydrogen bond and improve solution consistency after producing the solution comprising the conductive polymer composite.

19. The method of claim 18, wherein the solvents for preparing the solution of crosslinkable silane precursors and the solution of host thiophene conjugated polymers are selected from one or more of aprotic solvents.

20. The method of claim 14, wherein the hydrogen bond interrupting solvent includes at least one of alcohol or acetone.