Samples of bacterial poly(d-hydroxybutyrate-co-fl-hydroxyvalerate) (P(HB-co-HV)) were analyzed by 250-MHz 1H nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. The compositions of 40 copolyester samples, as determined by NMR, ranged from 0 to 47 mol % ß-hydroxyvalerate (HV). The shapes and intensities of numerous IR bands, particularly those at 1279,1228, and 1185 cm"1, were found to be sensitive to the degree of crystallinity. FTIR bands sensitive to composition include the C-H bands around 2900 cm'1 and the C-C band at 977 cm"1. By use of the 2900-cm"1 bands, methods were developed for composition analysis of as-received samples of equal degree of crystallinity in the solid state and in solution. Relative areas, in which the C-H area was normalized to the compositioninsensitive C=0 area, were calibrated to the copolymer compositions determined by 250-MHz 1H NMR. The experimental uncertainties of composition analysis of P(HB-co-HV) by NMR and FTIR were estimated to be ±1 and ±2-3 mol % HV, respectively. FTIR and wide-angle X-ray diffraction (WAXS) studies on solution-cast and melt-quenched samples showed a dramatic trend in that the rate of crystallization of these copolyesters decreases with increasing HV content. A two-stage crystallization process was identified for P(HB-co-HV) cast from solution and was attributed to changes in both nucleation rate and rate of crystal growth, whereas crystallization from the melt is largely nucleation rate limited. The crystallinity index (Cl) determined by FTIR for as-received samples of P(HB-co-HV) was nearly independent of HV content, indicating that the copolyesters are as highly crystalline as PHB homopolymer. The degree of crystallinity (Xc) derived from X-ray diffraction was used to follow crystallization from the melt. The final value of Xc ranged from 62 to 69% for equilibrated copolyesters quenched from the melt. Crystallization of these copolyesters from the melt is faster than for solution-cast samples. However, both processes are slow when compared to the rate of crystallization of solution-precipitated samples.
The chnal ansa-metallocenes 1,2-ethylenebis(q6-l-indenyl)-and 1,2-ethylenebis(q5-l-tetrahydroindeny1)zirconium dichloride (1 and 2, respectively) can be supported on partially dehydroxylated SiOz and A l 2 0 3 , and these supported systems can be used to polymerize propylene in the presence of methylaluminoxane. The most active supported systems were derived from partially dehydroxylated Si02 or Alz03 that had been pretreated with excess trimethylaluminum. The properties of the polypropylene produced are essentially indistinguishable from that produced under homogeneous conditions using these same catalysts. IntroductionThe discovery of homogeneous Ziegler-Natta catalysts, derived from metallocene compounds and methylaluminoxane cocatalyst, that combine high activity with excellent stereoregularity in the isotactic polymerization of a-olefins has led to a resurgence of interest in this field.2 Metallocene catalysts that provide access to isotactic,2gpi-k isotactic-stereoblock,2' syndiotactic,2h and isotactic-atactic block2d polymers of propylene have been developed. A significant impediment to the commercialization of such catalytic systems is the cost reflected in the requirement that a verylarge excess of methylaluminoxane (MAO) must be employed to obtain high catalytic activity and catalyst stability., One approach to overcome this problem that has met with some success, at least for ethylene polymerization, involves the preparation of cationic, do, 14 e-, metallocene compounds which do not require a cocatalyst for p~lymerization.~ Another approach, the results of which have been mainly disclosed in the patent literature,, has involved adsorbing an appropriate metallocene compound, with or without an aluminum alkyl, on silica, alumina, or other high surface area support5 and using such systems for ethylene polymerization. In several cases, it is claimed that additional MA0 is not required during polymerization if it is initially deposited or prepared on the surface.As far as we are aware, these studies have been concerned with ethylene polymerization; there appear to have been few reports on propylene polymerization using supported versions of the well-studied ethylenebis(s5-indenyl)-and ethylenebis(~5-tetrahydroindenyl)zirconiwn dichloride catalysts (1 and 2, respectively).6 In this paper, we describe the preparation of supported versions of these catalysts and their use in the polymerization of propylene.
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