SynopsisExperimental data, which includes catalyst lifetimes, thermal analyses, fractionation by urea complexation, x-ray diffraction, and 13C-NMR spectroscopy, are presented to confirm the successful synthesis of ABA propylene-ethylene block copolymers. A dry catalyst system of DEAC-TiC13(AA) and a gas-phase polymerization technique was used to prepare the copolymers. PRP-and ERE-type copolymers (P-isotactic polypropylene, E-polyethylene, and R-random propylene-ethylene copolymer block) were prepared. Some preliminary physical property data are given which indicate that PRP-type copolymers can behave as elastomeric fibers. The stress-strain behavior also indicates block copolymer formation.
EXPERIMENTALThe preparation of the active dry catalyst from Et2AlCl and TiC13(AA) and the technique for sequential addition of propylene and ethylene has already been d e~c r i b e d .~?~ Experimental conditions for the various copolymers are summarized in Table 1. The random B blocks were synthesized by admitting both monomers simultaneously, in various ratios, to the reaction vessel. The end A
After flowing in a dilatometer bulb for a small fraction of the duration of the transformation, a relaxed melt of poly(ethylene oxide) (M̄n = (5.9 ± 0.1) × 103) showed marked increases in isothermal crystallization rate. The extent of increase was greater when flow was imposed at modestly later stages rather than at the earliest stage of a crystallization. Kinetic parameters for the flow‐induced crystallizations were obtained via modification of the conventional mathematical treatment of the kinetics of phase change, thereby allowing the analytical resolution of the overall process into flowinduced and quiescent components. Determination of the flow‐induced crystallization parameters required independent determination of the kinetic parameters for quiescent crystallizations at that temperature. The Avrami exponents nf which characterized the flow‐induced portions of the crystallizations were larger for those instances in which flow was imposed at the more advanced stages of the crystallizations, thus indicating a transition in crystallization mechanism. It is suggested that prior crystallinity present at the time of flow contributed to the crystallization by serving as a source of nucleation sites. However, in light of the experimental procedure employed, values of nf approximating 4 that were obtained are not susceptible to mechanistic interpretations now extant.
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