Research will be carried out along three separate lines: 1. Previous work has shown that the physical state of the amorphous domains of semicrystalline polymers is widely misunderstood. The principal investigator was able to show that these domains have the state of a deformed rubber. It is proposed to further develop these arguments, and to attempt to predict the amorphous domain thickness and the mechanical properties of these systems. 2. The structure factors of certain models of semicrystalline polymer chains can be calculated exactly. The results will be compared with experiment. 3. Techniques will be studied for the computer simulation of the free energy and entropy of dense lattice polymer systems. Such properties cannot be obtained as trivially as those that are defined as ensemble averages of microscopic properties. The technique will then be applied to a number of interesting problems in polymer science, such as blends, amorphous domains, and random copolymers.