STEREOREGULAR OLIGOMERS OF METHYL-METHACRYLATE .6. ISOLATION OF ISOTACTIC AND SYNDIOTACTIC MMA OLIGOMERS FROM 19-MER TO 29-MER BY PREPARATIVE SUPERCRITICAL FLUID CHROMATOGRAPHY AND THEIR THERMAL-ANALYSIS

Isotactic (it-) and syndiotactic (st-) MMA oligomers from 19-mer to 29-mer could be isolated efficiently from it-PMMA (DPBAR = 28.6) and st-PMMA (DPBAR = 26.8) (sample load: 50 mg) by the SFC using a 10 mm i.d. x 250 mm column packed with silica gel. DP of each isolated oligomer was determined by FD mass spectroscopy, and the values agreed well with those calculated from the relative intensity of H-1 NMR signals due to CH3O- and the terminal t-C4H9-groups. Glass transition temperature (Tg) of the it-28-mer measured by DSC was 34.5-degrees-C, which was higher than that of the it-PMMA by 6.5-degrees-C. Tg of both the it- and st-oligomers increased linearly with DP in the range of DP = 20 approximately 29. A 1 : 1 mixture of the it- and st-27-mers annealed at 140-degrees-C showed an endothermic transition at 102.3-degrees-C which was attributable to melting of stereocomplex, whereas an annealed 1 : 1 mixture of the it- and st-PMMAs had a much broader endotherm around 80 approximately 140-degrees-C.