Synthesis of "meso"-and "racemic"-like diastereomers of Me2Si(3-MeInd)(Ind)ZrCl2 (5 and 6, respectively) was achieved through either metathetical reactions between the dianion of Me2(3-MeIndH)-(IndH) (4) with ZrCl4 or via amine elimination reactions, followed by fractional crystallization. Propylene polymerizations using meso-5 in the presence of methyl aluminoxane under a variety of conditions leads to the formation of low molecular weight, semicrystalline, low tacticity, poly(propylene) (PP). The dominant chain transfer mechanism in this case is shown to involve -H transfer to monomer. In contrast, rac-6 provides higher molecular weight, semicrystalline, elastomeric poly(propylene) (elPP) under a variety of conditions; chain transfer in this case involves, predominantly, -H transfer to Zr. The properties of elPP produced using catalyst 6 show a gradual change from a lightly, cross-linked elastomer to a poorly crystalline thermoplastic, depending on both polymer molecular weight and crystallinity as revealed by differential scanning calorimetry and tensile testing. In particular, more crystalline material exhibits a higher initial modulus, yielding behavior and lower strain to break than less crystalline material of equivalent molecular weight. These findings further define polymer properties for the synthesis of flexible elastomers using this class of catalysts.
SYNOPSISConversion of analytical TREF data to accurate branching distributions of polyethylene requires a calibration of branching frequency as a function of elution temperature. It has been found that the elution temperature of a semicrystalline polymer such as polyethylene depends on molecular weight, branch content, branch length, and branch clustering. It stands to reason that every polymer will have its own unique relation of branch frequency and elution temperature. Ideally, the polymer would be fractionated by a preparative TREF technique and the fractions analyzed by NMR or IR to determine branch frequency with respect to elution temperature. This method is tedious and time-consuming. An alternative method is described here to determine the relation between branch frequency and TREF elution temperature and to generate a calibration from analytical TREF data only. A twodetector system is used to simultaneously measure both concentration and branching frequency as a function of elution temperature. Each polymer is analyzed using analytical TREF data alone, eliminating the need for preparative TREF fractionation and NMR analysis of the fractions.
SYNOPSISIn a multidetector SEC system it is necessary to match the outputs of the detectors that sense eluant concentration with those that are molecular weight dependent. There are several methods to accomplish this. The most common is to determine the interdetector volume or time difference between detectors. The difficulty with this technique is that with detector systems where the column eluent is split, the interdetector time difference varies with solution viscosity. Two new techniques were implemented on a high temperature SEC/DRI/LALLS/VISC system which take into account changes in solution viscosity due to high molecular weight polymers. Both techniques use calibration curves of hydrodynamic volume versus elution volume for the different detectors to determine the "instantaneous" time difference between the detectors as it varies with solution viscosity. Either method provides the correct interdetector time lag information. We note also that in multidetector systems the configuration of the detectors should be such as to maximize solvent flow rates through each detector and hence to minimize band broadening effects. 0 1995
SYNOPSISAnalysis of analytical temperature rising elution fractionation ( TREF) data involves conversion of elution temperature information to branching information via a calibration curve relating the two. The curve is generated by analysis of polymer fractions recovered using preparative TREF techniques. In preparative TREF a stepwise temperature ramp is used to recover these fractions so that samples with sharp branching distributions are obtained. A continuous temperature ramp, as in analytical TREF, produces samples that differ in branching properties from the stepwise ramp at the same temperatures. The analytical TREF data can be corrected for these differences by an iterative computer program so that a calibration curve generated by preparative techniques can be used to convert the analytical
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