Patent Application
20100311900
The invention relates to polyimide matrix microparticles or microcapsules having a thermally stable polyimide wall or matrix and functional plastic material additives as core materials which can be incorporated in high melting-point plastic materials by melt compounding. The particle parameters and also the thermal and mechanical stability of the matrix particles or microcapsules can be adjusted specifically via the polyimide structure and/or technological parameters of the particle formation (shearing, reaction conditions for the wall formation). Microparticles made of polyimides and microencapsulated plastic material additives with a simply or complexly constructed particle wall made of polyimides are suitable above all for the production of specially finished polyamides, polyesters and high performance plastic materials, the processing of which requires high temperatures or which are used at high temperatures.
Thermoplastic and duromer polymer materials are adapted in a multiplicity of ways by means of inert fillers and/or functional additives to special requirements of use. The optimizations sought by means of additivation frequently relate both to the mechanical material properties directly (tensile and bending strength, toughness, modulus) and also to further properties of use of the materials, such as light and heat stability, flexibility or burning behaviour. Colourants are also frequently added to plastic materials. In the case of smart materials, more recent developments use plastic materials also as matrices for thermochromic or photochromic or respectively sensory substances and also for absorbing heat storing materials. Plastic material additives must fulfil a series of criteria which crucially jointly determine, in addition to the actual operational effect, the type and limits of use thereof. These are for example agglomerate-free dispersability, compatibility with the polymer matrix, inert behaviour relative to the undamaged polymer matrix, low migration rate etc. In the case of most mass plastic materials, such as polyolefins or vinyl polymers, the predominant number of additives used fulfil these prerequisites. In the case of selected higher priced and many high performance plastic materials, the use of additives is however limited as a result of high compounding and moulding temperatures. Also corrosive conditions of use can influence the stability of additives. By this route, effects on matrix stability via degradation products cannot then be precluded (cf. for example W. Hohenberger, Plastic Materials 92 (2002) H 5, p. 86).
In order to avoid or minimize
The microencapsulation with polymer materials is generally known and described extensively in the scientific and patent literature, such as e.g. in Encyclopaedia of Polymer Science, J. Wiley 86 Sons, 1968, Vol. 8, p. 719; W. Sliwka, App. Chem. Internat. Edit. 14 (1975) 539; Acta Polymerica 40 (1989) 243; 40 (1989) 325; KONA 10 (1992) 65; Drugs Pharm. Sci. 73 (1996) Microencapsulation 1; R. E. Sparks, Microencapsulation in Encyclopaedia of Chemical Processing, p. 162.
In the case of encapsulation technologies, a differentiation should be made in principle between reactive methods with monomers or prepolymers and also non-reactive particle formation processes with native or synthetic polymers. In the case of reactive particle formation, the formation of the wall is effected in parallel with a polymerization, polycondensation or polyaddition process. In the case of non-reactive methods, film-forming polymers are used directly and are brought by a thermodynamic manner to phase separation and to particle formation (cf. for example M. Jobmann, G. Rafter: Pharm. Ind. 60 (1998) 979 and the literature cited there). In addition, an active substance/polymer system is converted into a particulate form from preferably organic solution by dispersing, dropping or spraying processes or via methods which are based on the principle of liquid-liquid phase separation. Dispersing, dropping and spraying methods comprise solvent evaporation; on the other hand, phase separation methods are based on the principle of precipitation of the wall material, e.g. by addition of an incompatible component to the polymer solution.
The range of suitable polymers for non-reactive encapsulation processes, which are soluble in organic or aqueous phases, is wide. Since solubility of the polymer phase is an indispensable prerequisite for the non-reactive particle formation, generally only linear-chain or slightly branched polymers can be used. This has the effect that these microparticles, because of melting or softening, in many cases have only low thermostability. Frequently mentioned raw materials are gelatines, cellulose ether and also polyacrylates and polymethacrylates (cf. R. E. Sparks, I. C. Jacobs, N. S. Mason “Microencapsulation” in Drug Manufacturing Technology, Vol. 3 (1999) 13).
For reactive methods for encapsulation of solid or liquid core materials, melamine formaldehyde resins are very frequently used (DE 199 23 202; UK 2 301 117), but also isocyanate/amine systems are described (AZ 101 56 672). Melamine formaldehyde resins can be used widely and without difficulty for covering hydrophobic core materials and they can be applied for particle formation from the aqueous phase. Reactive methods require core materials which are inert relative to the wall-building monomers or oligomers, i.e. they do not undergo a reaction with other involved components.
In the case of both modes of operation, the application-relevant microparticle parameters, such as particle size and distribution thereof, form and morphology of the particles and the surface thereof, are determined in a complex manner by the chemical structure of the polymer phase of particle wall or matrix and also by the reaction conditions of the particle formation. Control parameters for particle geometry and particle morphology are above all duration and intensity of the dispersion, solution and interface properties of wall- and core material and also structure of the wall- or matrix-forming polymer material. In general, spherical microparticles with diameters between and 150 μm are formed. For low monomer or polymer concentrations using highly shearing dispersion tools, also particles with diameters <1 μm can be produced (EP 0 653 444).
The predominant majority of known thermoplastic and duromer wall materials, because of the meltability thereof or lack of thermal stability, are limited in their applicability for the production of microencapsulated additives for industrial plastic materials with their high processing temperatures of 240 to 280° C. Thermostable and temperature-stable plastic materials, such as polyaramides, polyether ketones, polysulphones or polyphenylene sulphide are, as a result of their chemical structure, frequently not soluble in normal organic solvents, such as are used for particle formation processes. Solvents for these heat resistant and thermostable polymers require complex encapsulation techniques, are difficult to remove from the particles because of high boiling points or limited miscibility with low-boiling extraction means or they dissolve or react with the core materials. Thermostable wall materials made of linear-chain polymers with solubility in solvents which are normal for particle methods are little known. There should be mentioned above all polyacrylnitrile and cellulose ether. In fact these polymers do not melt but their thermal stressability is likewise limited. Thus in DE 10 231 706, an encapsulation process for plastic material additives with polyacrylnitrile is described.
Polyimides have jointly, in addition to polybenzimidazoles and polyoxadiazoles, of all organic polymer materials, the highest thermal and chemical stability. Because of the known solubility problems which these polymer materials present, they have been unable to date to be used for microencapsulation of active substances.
The object underlying the invention is to produce microcapsules or micromatrix particles of high mechanical and thermal stability for the plastic material additivation according to an efficient and reliable in situ process.
The invention is achieved for the matrix microcapsules or matrix microparticles of high mechanical and thermal stability by the features of claim 1 and for the method of production thereof by the features of claim 16. Uses according to the invention of the method are characterized by the features of claim 45. The respective sub-claims contain advantageous developments for the microcapsules or for the method.
According to the invention, the microcapsules or micromatrix particles of high mechanical and thermal stability comprise a polyimide which forms the particle wall in the case of a capsule and the entire microparticle in the case of matrix particles.
If necessary, further functional plastic material additives can be incorporated both in the matrix microparticle and in the -microcapsule. Flame retardants, colour pigments, metal flakes and/or -powder, matting agents and phase change materials are thereby used preferably as additives.
The polyimide particles according to the invention have a monomodal particle distribution, with the avoidance of agglomeration, with an average diameter of 1 and 50 μm, preferably between 2 and 40 μm, particularly between 5 and 30 μm. They display spherical geometry with slight structuring of the particle surface. A characteristic feature of polyimide-based microcapsules and -particles is their high thermal, thermooxidative and chemical stability, based on the chemical structure of the wall or matrix materials. As a function of the chemical structure, a notable mass loss, caused by thermolysis reactions, is observed thermogravimetrically, in a range of 450° C. to 530° C.
The matrix microparticles or -microcapsules based on polyimides have the advantageous property of being stable under inert conditions (nitrogen as inert gas) up to 500° C. and, in air, up to 350° C.
Preferred polyimides for the matrix microparticle formation or -microencapsulation are for example poly(4,4′-diphenyloxide pyromellitimide), poly(4,4′-diphenylmethane pyromellitimide), poly(4,4′-diphenyloxide diphthalimide), poly(m-phenylene isopropylidene diphthalimide), poly(2,2-dimethyl-4,4′-diphenylmethane pyromellitimide), poly(2,2-bis(trifluoromethyl)-4,4′-diphenylmethane oxydiphthalimide and poly(4,4′-diphenyloxide carbonyldiphthalimide).
The polyimide particles can have, from application-relevant aspects, dependent upon the requirement profile for the microencapsulated additives or microparticulate fillers, also a complex shell construction, the second or the third shell being able to be produced both from the same and from different materials. For structurally different shell materials, in addition to the polyimides, above all shells made of linear-chain polymers or from low-molecular organic or inorganic substances, such as waxes, fatty acid derivatives, silicones, siloxanes or silicates are preferred. There are included as polymers which are structurally different from the shell material and which are suitable particularly for the coating of polyimide microparticles, above all polyacrylates, polyethylene glycols and also starch-fatty acid esters and starch carbamates of long-chain isocyanates.
According to the invention, the polyimide particles with a core, shell or matrix structure are formed via a multi-stage method which comprises the steps
The formation of the polyamidocarboxylic acid particles is effected in the following method steps
For synthesis of the polyamidocarboxylic acids, in principle any aliphatic, aromatic and/or aliphatic-aromatic diamine can be made to react with an aliphatic, aromatic and/or aliphatic-aromatic tetracarboxylic acid derivative. There are possible as carboxylic acid derivatives hereby, carboxylic acid anhydrides, free carboxylic acid, carboxylic acid esters and carboxylic acid chlorides. Tetracarboxylic acid anhydrides and diamines which are used preferably for the encapsulation of solid and liquid core materials or the matrix particle formation with polyimides are above all 1,2,4,5-benzene tetracarboxylic acid-(=pyromellitic acid-), 3,3′-4,4′-biphenyltetracarboxylic acid-, 3,3′-4,4′-benzophenone tetracarboxylic acid-(=3,3′-4,4′-benzoylbenzoic tetracarboxylic acid-), 3,3′,-4,4′-isopropylidene diphthalic acid-, 3,3′-4,4′-oxydiphthalic acid- and (hexafluoroisopropylidine)diphthalic acid dianhydride in the case of tetracarboxylic acid dianhydrides and also m-phenylene diamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylether, 4,4′-diaminodiphenylsulphone and 2,2′-bis(4-aminophenyl)propane in the case of diamines.
As an alternative thereto, also even previously synthesized polyamidocarboxylic acids can be dissolved in one of the solvents described below.
In the synthesis, the monomers can be dissolved in solvents which are miscible with water. The solvents known for this synthesis of the amide type, such as dimethylacetamide and N-methylpyrrolidone, are used preferably. The solutions with the formed polyamidocarboxylic acids can be further processed directly into microparticles. Storage at temperatures below room temperature and with moisture exclusion is also possible. Under these conditions, the solutions are stable in storage for several weeks. For the further processing, dilution with the same solvent or even with a different solvent which is miscible with water is possible.
The concentration of the polymer solution is determined by chemical structure and molar mass of the polyamidocarboxylic acid. Both determine the viscosity of the polymer solution which in turn is responsible for the size and morphology of the microcapsules and matrix particles. Better soluble polyamidocarboxylic acids and higher molar masses are used with lower concentrations, not easily soluble ones and those with a lower molar mass require higher concentrations. The concentration of the polymer solution is in a range between 1 and 50% by weight, preferably between 2 and 20% by weight.
All emulsion agents are suitable for the production of the emulsion which have no or only limited miscibility with the solvent, do not react with the polyamidocarboxylic acid and represent a solvent neither for the polymer wall or matrix material nor the plastic material additive. For the mentioned reasons, above all vegetable and mineral oils are suitable for the production of an emulsion with corresponding viscosity, preferably silicone or paraffin oil. The polymer solution or additive suspension in the solution of the polymer is finely distributed in the emulsion agent by intensive mixing. With respect to the dissolved polymer, the emulsion agent is used in excess. It is thereby advantageous if the excess is between a multiple of two to ten, preferably between three to five, of the polymer.
The distribution of the additive-containing or additive-free polymer solution in the emulsion agent is assisted by addition of further organosoluble emulsifiers in a concentration between 0.1 and and 5% by weight, preferably between 0.5 and 2% by weight. At the same time, such emulsifiers also improve the stability of the emulsion and hence they assist also the formation of artefact-free microparticles. Preferred emulsifiers are non-ionogenic or anion-active substances, such as e.g. SPAN®85 or TWEEN®.
The extraction agent is added to the emulsion with agitation. The more slowly this addition is effected, the more intensive the contact for extraction of the polymer solvent and the lower the proportion of agglomerated particles. Single particle distributions facilitate separation, treating and possibly redispersion of the particles. According to the invention, preferably water or aqueous inorganic or organic phases are added as extraction agent. These extraction agents are miscible with the polyamidocarboxylic acid solvent in an unlimited manner and not miscible with the emulsion agent. At the same time, it must be ensured that the extraction agent does not represent a solvent for the polymer and the additive. The ratio between emulsion agent and extraction agent must be adjusted such that the polymer solvent is extracted completely. After formation of the microparticles by curing the particle wall or the particle matrix, these are isolated in a solid-liquid manner by means of normal phase separation methods. There are suitable above all centrifugation and filtration which permit problem-free washing of the particles for separation from the remaining emulsion agent.
For imidation of the polyamidocarboxylic acids, the isolated microcapsules or matrix particles are heated in the air- or inert gas glow or under vacuum for 0.5 to 10 hours, preferably 2 to 5 hours, to a temperature between 100 and 400° C., preferably between 100 and 300° C. The obtained polyimide particles can be used in this form as microfine powders directly for the thermoplastic additivation. For other fields of use, redispersion in aqueous or oil phases and application as a microfine suspension is also possible. Cyclization of the polyamidocarboxylic acid matrix particles, i.e. of microparticles with a relatively small particle size and monomodal particle size distribution by thermal cyclization of the polyamidocarboxylic acid matrix particles or microcapsules, can be effected also in suspension, high boiling-point media requiring to be used, in which the polyamidocarboxylic acids are insoluble. Above all high boiling-point hydrocarbons, fatty acid esters and silicone oils which can then be used directly as suspension or be separated are suitable. Furthermore, it is worthy of mention that this can be effected at a temperature above the boiling point of water but not substantially higher (100-150° C.), in a vacuum or with azeotropic distillation. This is possible above all for flame retardants such as melamine inter alia. The microparticles according to the invention with core-shell or matrix structure are used preferably as particulate fillers for improving the material properties of plastic materials. A further application resides in the introduction of plastic material additives into polymer materials. The microparticles according to the invention can be introduced, analogously to particulate fillers or additives, by means of twin-screw extruders or kneaders, into thermoplastic or duromer polymer materials and the additivated plastic materials are further processed by normal moulding methods, such as injection moulding or extrusion in the case of thermoplasts and by thermopressing in the case of duromers.
The subject according to the invention is intended to be explained in more detail with reference to the subsequent examples without wishing to restrict said subject to the embodiments mentioned here.
0.1 mol 4,4′-diaminodiphenylether (20.02 g) are dissolved in 250 ml N-methylpyrrolidone. 250 ml of a solution of 0.1 mol 3,3′-4,4′-benzophenone tetracarboxylic acid anhydride (32.2 g) are added in drops to the diamine solution within 30 min with agitation at room temperature. For polycondensation of the tetracarboxylic acid anhydride with the diamine, agitation takes place for a further 6 h at room temperature. The solution of the polyamidocarboxylic acid is stored in the closed vessel at 5° C. until further processing in order to avoid uncontrolled secondary or subsequent reactions of the primary acylation reaction. For polymer characterization, a small quantity is removed and the polyamidocarboxylic acid precipitated in ethanol or water.
Analogously to example 1, the monomers compiled in Table 1 are combined and the obtained polyamidocarboxylic acids are used for microencapsulation and matrix particle formation.
6 ml of a 10% solution of poly(4,4′-diphenyloxide carbonyldiphthalic acid amide) (polyamidocarboxylic acid from example 1) in NMP are introduced into 60 ml paraffin oil with intensive agitation at 25° C. 120 ml water is subsequently added to the dispersion within 30 min. After the phase separation, 500 ml n-hexane are added to the upper oily phase, the particle suspension is separated, washed with hexane and ethanol and the separated particles are dried.
The average particle size was determined by means of laser diffraction.
Yield of polyamidocarboxylic acid particles: 0.48 g
Average particle size: d50: 8.3 μm
30 ml of a 10% solution of poly(4,4′-diphenyloxide carbonyldiphthalic acid amide) (polyamidocarboxylic acid from example 1) in NMP are introduced into 300 ml silicone oil with intensive agitation at 25° C. 600 ml water are added subsequently within 30 min to the dispersion. After the phase separation, 1200 ml n-hexane are added to the upper oily phase, the particle suspension is separated, washed with hexane and ethanol and the separated particles are dried.
Yield of polyamidocarboxylic acid particles: 2.81 g
Average particle size: d50: 17.7 μm
Analogously to example 8, respectively 10% NMP solutions of the polyamidocarboxylic acids (Examples 2-7) listed in Table 1 are processed into microparticles and treated. The obtained microparticles are listed in Table 2.
25 g poly(4,4′-diphenyloxide carbonyldiphthalic acid amide) are dissolved in 250 ml DMAc. This polymer solution is introduced with intensive agitation into 300 ml paraffin oil at 25° C. 600 ml water are added subsequently within 30 min to the dispersion. After the phase separation, 1500 ml n-hexane are added to the upper oily phase, the particle suspension is separated, washed with hexane and ethanol and the separated particles are dried.
Yield of polyamidocarboxylic acid particles: 20 g
Average particle size: 13.9 μm
There are added to 40 ml of a 5% solution of poly(4,4′-diphenyloxide pyromellitic acid amide) (polymer example 2) in DMAc, 0.125 g TWEEN® 85 and 1.2 g titanium dioxide (Hüls AG). This titanium dioxide dispersion is added in drops to 60 ml paraffin oil with intensive agitation at 25° C. 120 ml water are added subsequently within 30 min to the dispersion. After the phase separation, 500 ml n-hexane are added to the upper oily phase, the microcapsule suspension is separated, washed with hexane and ethanol and the separated microcapsules are dried.
Yield of microencapsulated titanium dioxide: 2.8 g P Average microcapsule size: 3.8 μm
Analogously to example 17, 1 g AEROSIL R106 is microencapsulated and treated.
Yield of microencapsulated AEROSIL R106: 2.5 g
Average microcapsule size: 10.1 μm
There are added to 40 ml of a 5% solution of poly(4,4′-diphenyloxide pyromellitic acid amide) (polymer example 2) in DMAc, 0.125 g TWEEN®85 and 5 g red phosphorus (Merck AG). This dispersion of red phosphorus in the solution of poly(4,4′-diphenyloxide pyromellitic acid amide) is added in drops to 60 ml paraffin oil with intensive agitation at 25° C. 120 ml of a water/acetone mixture (1:2) are added subsequently within 30 min to the dispersion. After the phase separation, 500 ml n-hexane are added to the upper oily phase, the microcapsule suspension is separated, washed with hexane and ethyl acetate and the separated microcapsules are dried.
Yield of microencapsulated red phosphorus: 6.1 g
Average microcapsule size: 10.2 μm
The polyamidocarboxylic acid microparticles produced according to examples 8-13 are heated in a vacuum cabinet or circulating air drying cabinet for 5 h to 200° C. The polyimide microparticles produced in this way have the usage-relevant material- and particle parameters compiled in Table 3. The beginning of the thermal degradation TT under an inert gas atmosphere was determined thermogravimetrically.
The microencapsulated substances produced according to examples 17-18 are heated analogously to example 20-25 in the vacuum cabinet or circulating air drying cabinet for 5 h to 200° C. The polyimide microcapsules produced in this way have the usage-relevant material- and particle parameters compiled in Table 4.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 016 307.9 | Apr 2006 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2007/002694 | 3/27/2007 | WO | 00 | 3/5/2009 |
