The molecular, thermodynamic, and kinetic factors that govern the formation and concentration of the α and γ polymorphs in metallocene-catalyzed isotactic poly(propylenes) have been studied with a set of polymers that have a wide range in molecular weight and defect contents. With these polymers it was possible to investigate the influence of molecular weight on γ formation at a fixed defect concentration, as well as the role of the defect concentration at constant molecular weight. The major experimental techniques used were wide-angle X-ray scattering and differential scanning calorimetry complemented by microscopy. From these studies the role of chain microstructure, the crystallization temperature, and the thermodynamic and kinetic requirement for the formation of the γ form could be established in more quantitative detail than heretofore. A particular important finding was the fact that at fixed defect concentration the fractional content of the γ polymorph goes through a maximum with crystallization temperature. The results that were obtained establish a quantitative framework within which the underlying bases that lead to formation of the γ form, and its unique crystalline structure, are discussed.

Several poly(perfluorosulfonic acid) membranes (NAFION, EW ) 1100) with the same sulfonic acid content were systematically investigated with SANS under in-situ water vapor sorption and/or with bulk water to quantify the effects of relative humidity (RH), membrane processing (melt-extruded and solution-casting), prehistory (pretreated at 80°C and as-received), and thickness on the nanoscale structure at room temperature. The sorption isotherm (water uptake vs RH) of the membranes showed a strong correlation between the interionic domain distance (L ion ) and RH. The melt-extruded membranes showed evidence of partial alignment of better organized ionic domains than those solution-cast. Pretreating the membranes resulted in a larger L ion and a broader scattering over the entire range of RH. The ionic peak of the melt-extruded membranes (as-received and pretreated) became more symmetric and narrower with sorption time. Diffusion coefficients of water vapor, based on structural evolution and Fick's second law, are in the range of 1 × 10 -7 -3 × 10 -7 cm 2 /s for both extruded (pretreated and as-received) membranes. A thickness-dependent crystalline feature around Q ≈ 0.03 Å -1 was also observed.

The phase behavior of mixtures of polyisobutylene (PIB), polyethylene (PE), and a symmetric polyethylene-block-head-to-head polypropylene copolymer (PE−PP) was studied by transmission electron microscopy (TEM) and small-angle neutron and light scattering. The thermodynamic interactions between PE/PP and PE/PIB are repulsive (Flory−Huggins parameter χ > 0 and decreases with increasing temperature), while those between PP/PIB are attractive (χ < 0 and increases with increasing temperature). When the PE−PP copolymer is added to a 50/50 PE/PIB mixture, the resulting phase diagram in temperature−copolymer composition space exhibits many of the characteristics of “fish-shaped” phase diagrams found in oil/water mixtures stabilized by balanced surfactants. This is due to the interplay between the different χ parameters that characterize the system. Lamellar phases, single droplet microemulsions, and bicontinuous microemulsions were observed. The length scales of these structures and the locations of the phase transition points on the phase diagram determined by TEM and scattering are in reasonable agreement. Phase transitions from a lamellar phase to a single droplet microemulsion phase, and from a bicontinuous microemulsion to a macrophase-separated structure, have been identified.