STEREOREGULAR OLIGOMERS OF METHYL-METHACRYLATE .7. ISOTACTIC AND SYNDIOTACTIC PENTACONTAMERS (50MERS) OF METHYL-METHACRYLATE OBTAINED BY FRACTIONATION WITH PREPARATIVE SFC - THE GPC ANALYSIS OF THE 50 MERS AND THEIR STEREOCOMPLEX

Highly isotactic (it-) and highly syndiotactic (st-) 25mers and 50mers 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 25mers and 50mers 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-50mer eluted faster than the st-50mer in the GPC using THF as eluent. When a solution of a 1:1 mixture of the it- and st-50mers in THF was subjected to the GPC measurement at 3-degrees-C, the chromatogram showed two peaks at the elution volumes corresponding to the 50 and 100mers. The elution peak for the 100mer suggests that the it- and st-50mers form stereocomplex in a 1:1 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 ii- and st-50mers was allowed to stand. Stereocomplex formation was not observed for a mixture of the it- and st-25mers by similar GPC experiments.