ASSOCIATION OF STEREOREGULAR POLY(METHYL METHACRYLATES) .4. FURTHER STUDY ON THE COMPOSITION OF THE STEREOCOMPLEX

The formation of the stereocomplex of highly isotactic and syndiotactic poly(methyl methacrylate) (it- and st-PMMA) was investigated in dilute solution by viscometry, osmometry, turbidimetry and n.m.r. Crystalline stereocomplexes, isolated from dilute and concentrated mixed solutions or formed by annealing in bulk, were investigated by X-ray diffraction and d.s.c. X-ray diffraction showed that all complexes, in whatever way or from whatever it/st ratio they were made, have the same crystalline structure. Moreover, all stereocomplexes showed a melting point which was independent of the it/st ratio. All this evidence means that only one type of stereocomplex exists. In dilute solutions the maximum deviations of reduced viscosity and osmotic pressure as well as the maximum turbidity were obtained at the composition it st = 1 2. The same ratio could be derived from the maximum crystallinity after prolonged annealing of the mixture in bulk at 140°C, as determined by d.s.c. So contrary to previous statements1 it is now considered that the real stereocomplex from it- and st-PMMA always possesses a composition it st = 1 2. Comparing the X-ray fibre patterns of oriented stereocomplex with the fibre patters of pure it- and st-PMMA showed that the stereocomplex has a structure different from that of the components. © 1979.