POLYMER BLENDS, COPOLYMERS AND NETWORKS - SCATTERING PROPERTIES AND PHASE-BEHAVIOR

The phase behavior and scattering properties of polymer blends, copoly mers and networks in solution and in bulk art: examined. The theoretic al framework used here is based upon the extension of the random phase approximation to polymers proposed by de Gennes and its application t o chains with various architectures. The case of blends containing sti ff chains is considered and the effect of nematic interaction on the p hase behavior and scattering properties is discussed. The compressibil ity problem is reviewed in connection with the free volume theory mode ls. The coupling between density and composition fluctuations is exami ned together with the effects of pressure on the structural and thermo dynamic properties of blends. The dynamics of copolymers are also exam ined in the light of the new developments both from the theoretical an d experimental fronts. The extent to which the chain architecture affe cts phase behavior, static scattering and dynamic behavior is discusse d. A particular emphasis is put on the case of cyclic homopolymers and copolymers. Free chains in a network and crosslinked blends are also a subject of particular interest in this paper. The interplay between macrophase and microphase transitions due to the crosslinks and the el ectrostatic forces for charged polymers is also considered. De Gennes' analogy betwen the elastic restoring forces in the network and the Co ulomb forces in the dielectric medium is generalized by including the screening phenomenon. This generalization is required in order to acco unt for the experimental observations in the low momentum transfer ran ge. Following Briber et at, it is argued that die new screening length can be related to the initial fluctuations at the temperature of cros slinking.