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The crystallization behavior of two chemically identical but physically different co-crystallizing poly( l-lactic acid) (PLLA)-based blends is studied. The first set studied involves an all- l unit polymer (PLLA) co-crystallizing with a PDLA-miscible soft polyether-PDLA triblock copoly­mer, where d refers to the d isomer. The second set studied involves homopolymer blends of PLLA/miscible soft polyether/PDLA with compositions identical to the first set. Crystallization is performed under isothermal and non-isothermal crystallization conditions and the crystallization kinetics, crystal perfection, and the blend morphology are investigated. It is clear that the stereocomplex crystallization is significantly slower in the triblock copolymer blends in comparison with the homopolymer blends. Furthermore, based on diffraction, spectroscopic, and thermal data, it is found that the stereocomplex crystals formed in the homopolymer blends achieve higher order and perfection, with a melting temperature 15-20 °C higher than those formed in the triblock blends. [ABSTRACT FROM AUTHOR]

Block copolymers of polystyrene- b-poly(vinyl benzyl trimethylammonium tetrafluoroborate) (PS- b-[PVBTMA][BF4]) were synthesized by sequential monomer addition using atom transfer radical polymerization. Membranes of the block copolymers were prepared by drop casting from dimethylformamide. Initial evaluation of the microphase separation in these PS- b-[PVBTMA][BF4] materials via SAXS revealed the formation of spherical, cylindrical, and lamellar morphologies. Block copolymers of polystyrene- b-poly(vinyl benzyl trimethylammonium hydroxide) (PS- b-[PVBTMA][OH]) were prepared as polymeric alkaline anion exchange membranes materials by ion exchange from PS- b-[PVBTMA][BF4] with hydroxide in order to investigate the relationship between morphology and ionic conductivity. Studies of humidity [relative humidity (RH)]-dependent conductivity at 80 °C showed that the conductivity increases with increasing humidity. Moreover, the investigation of the temperature-dependent conductivity at RH = 50, 70, and 90% showed a significant effect of grain boundaries in the membranes against the formation of continuous conductive channels, which is an important requirement for achieving high ion conductivity. © 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1751-1760, 2013 [ABSTRACT FROM AUTHOR]

The slurry homopolymerization of propylene catalyzed by the isospecific metallocene rac-Et(Ind)2ZrCl2/MAO was investigated using a semi-batch reactor. A full factorial design with three temperatures (50, 65 and 75°C) and four monomer partial pressures (1.5, 2.5, 3.2, and 3.8 atm) was performed. Analysis by ¹H NMR revealed the formation of vinylidene, cis-2-butenyl and 4-butenyl end-groups. A kinetic model based on a coordination-insertion mechanism was developed to predict instantaneous reaction rate, molecular weights and polymer chain ends. The kinetic rate constants were estimated using a systematic optimization strategy. The model predicts that the insertion of the first propylene molecule is rate limiting with respect to propagation. Molecular weight decreases with temperature due to the high activation energy of the main chain transfer reaction (101 kJ/mol) relative to propagation (52 kJ/mol). The percentage of butenyl end-groups with respect to vinylidene decreases with temperature, thus predicting a lower activation energy for the β-hydride elimination after secondary insertion (27 kJ/mol). [ABSTRACT FROM AUTHOR]

A correction to the article "Anion Exchange Membranes: Current Status and Moving Forward" by Michael A. Hickner, Andrew M. Herring and E. Bryan Coughlin that was published in a 2013 issue of the "Journal of Polymer Science Part B: Polymer Physics" is presented.

Understanding the structure-property relationships and the phenomena responsible for ion conduction is one of the keys in the design of novel ionomers with improved properties. In this report, the morphology and the mechanism of ion exchange in a model anion exchange membrane (AEM), poly(vinyl benzyl trimethyl ammonium bromide)-block-poly(methylbutylene) ([PVBTMA][Br]-b-PMB), is investigated with small angle X-ray scattering, high-resolution thermogravimetry, modulated differential scanning calorimetry, dynamic mechanical analysis, and broadband electrical spectroscopy. The hyper-morphology of the material consists of hydrophilic domains characterized by stacked sides of [PVBTMA][Br] which are sandwiched between "spaghetti-like" hydrophobic cylindrical parallel domains of the PMB block. The most important interactions in the hydrophilic domains occur between the dipoles of ammonium bromide ion pairs in the side chains of adjacent chains. A reordering of the ion pair dipoles is responsible for a disorder-order transition (Tδ) at high temperature, observed here for the first time in AEMs, which results in a dramatic decrease of the ionic conductivity. The overall mechanism of long range charge transfer, deduced from a congruent picture of all of the results, involves two distinct ion conduction pathways. In these pathways, hydration and the motion of the ionic side groups are crucial to the conductivity of the AEM. Unlike the typical perfluorinated sulfonated proton-conducting polymer, the segmental motion of the backbone is negligible.