ABSTRACT:Highly isotactic (it-) and highly syndiotactic 2Smers and SOmers of MMA have been isolated from it-and st-PMMAs, respectively, by means of the preparative supercritical fluid chromatography (SFC) using carbon dioxide/ethanol as mobile phase and silica gel as stationary phase. The 2Smers and SOmers with definite molecular weight (2561 and 5064) were useful as the standard materials in GPC for the calibration of molecular weight and the direct evaluation of instrumental spreading. The it-SOmer eluted faster than the st-SOmer in the GPC using THF as eluent. When a solution of a I: I mixture of the it-and st-SOmers in THF was subjected to the GPC measurement at 3°C, the chromatogram showed two peaks at the elution volumes corresponding to the 50 and lOOmers. The elution peak for the lOOmer suggests that the it-and st-SOmers form stereocomplex in a I : I ratio. The peak area for the stereocomplex varied from 0 to 9.0% of the whole chromatographic peaks, depending on the conditions (time and temperature) under which the mixed solution of the it-and st-SOmers was allowed to stand. Stereocomplex formation was not observed for a mixture of the it-and st-25mers by similar GPC experiments.
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