The influence of polydispersity on the transitions occurring in the weak segregation regime and on the scattering functions of the disordered phase in diblock copolymers is studied for one-component and multicomponent systems including mixtures with homopolymers. Application of the fluctuation corrections given by Fredrickson and Helfand9 leads to the determination of the transition windows as a function of degree of polymerization N, polydispersity U, and composition /. The applicability of the fluctuation corrections appears to be extended to lower N and f with increasing U. The prediction of transitions is facilitated by the concept of a reduced phase diagram.Recently, Fredrickson and Helfand9 have extended Leibler's theory to include the effect of composition fluctuations using a method established by Brazovskii.10 They find that Leibler's theory is only valid in the limit N -* <=°a nd that direct transitions from the homogeneous melt

In-situ structural evolution during uniaxial extension and subsequent retraction of a thermoplastic elastomer (TPE) based on propylene-dominant ethylene-propylene (EP) copolymer was studied. Combined measurements of time-resolved wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) as well as stress-strain curves revealed molecular mechanism responsible for the elastic behavior. During the first cycle of deformation, a fraction of the crystals was destroyed, while the rest was reoriented. At strains larger than 1.0, strain-induced R-crystals in the lamellar form took place, resulting in the creation of a network with well-oriented lamellae having their normals parallel to the stretching direction. With the increase of strain, more crystals were induced, forming an enhanced network with strain-hardening behavior. During retraction and even after complete relaxation to zero stress, the majority of the strain-induced crystalline network remains in tact as being "permanent set", where lamellar stacks act as the network points. This strain-induced crystalline network structure is thermally stable at room temperature and is responsible for the elastic behavior during subsequent cyclic deformation, similar to a vulcanized rubber.

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