Complexation of stereoregular poly(methyl methacrylates). XI: A mechanistic model for stereocomplexation in the bulk

The process of stereocomplexation between isotactic and syndiotactic PMMA in the bulk was studied by means of differential scanning calorimetry and wide-angle X-ray scattering as a function of annealing time and temperature. It appeared that in all cases the material obtained was partly crystalline. For low annealing temperatures the samples showed multiple endotherms with different characteristics. A mechanistic model, in which subsequent crystallization of the complexed chain sections plays an important role, is presented which accounts for the observed phenomena. At low annealing temperatures complexation proceeds much faster than subsequent crystallization resulting in a fringed-micellar kind of growth, while at higher annealing temperatures lamellar crystallization occurs directly. The endotherms are interpreted respectively as the decomplexation of complexed sections partly organized into fringed-micellar clusters of complexes (T sub m exp 1 ) and the simultaneous decomplexation and melting of lamellarly crystallized complexes (T sub m exp 3 ). Apart from these main endotherms also a small endotherm was found (T sub m exp 2 ), which was assigned to the decomplexation of complexed sections, formed during scanning. The critical sequence length necessary for complexation and the mobility of the chains, and consequently the annealing temperature and molar mass of the polymers employed, are the most important parameters in the mechanistic scheme presented. 34 ref.--AA