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 ANDTHEIR STEREOCOMPLEX

Highly isotactic (it-) and highly syndiotactic (st-) 25mers and 50mers of MMA have been isolated from it- and st-PMMAs, respectively, by mea ns of the preparative supercritical fluid chromatography (SFC) using c arbon dioxide/ethanol as mobile phase and silica gel as stationary pha se. The 25mers and 50mers with definite molecular weight (2561 and 506 4) 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 T HF was subjected to the GPC measurement at 3-degrees-C, the chromatogr am 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 stere ocomplex varied from 0 to 9.0% of the whole chromatographic peaks, dep ending 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 s imilar GPC experiments.