Thermodynamics and kinetics of phase separation, morphologies and tensile properties of a binary polymer blend: poly(methyl methacrylate)/poly(styrene-co-maleic anhydride)

Abstract

Thermodynamics and kinetics of phase separation, morphologies and tensile properties were investigated in a blend of poly(styrene-co-maleic anhydride) with a commercial sample of poly(methyl methacrylate) containing ethyl acrylate comonomer. Detailed studies through light scattering showed that sample preparation methods affect the miscibility and kinetics of phase separation. The blends exhibit spinodal and cloud point curves at higher temperatures in the case of solution cast than those from melt mixed samples. The relative values of the Cahn-Hilliard growth rate, R(q), depend on temperature, sample preparation methods and the blend concentration. Teh delay time behaviour at the onset of phase separation was observed. It was found that sample preparation method, composition, temperature and scattering wave number have an influence on delay time. Comparisons of the experimental data with recent theoretical developments for entangled polymer blends show a discrepancy, this might be attributed to the omission of some terms in those theories or that the origin of the apparent delay time lies elsewhere. In the late stage of spinodal decomposition, the normalised scaling function profiles of 20/80 and 40/60 SMA/PMMAe blends are in good agreement with the conventional universal scaling function (S~(X)) for off-critical mixture, called the cluster profile. Detailed studies on morphology of the tensile tested specimens manifest that the co-continuous structure were found, indicating that the blends undergo spinodal decomposition. The comparison of droplet size growth rate approximated from light scattering data with the direct measurement from TEM showed a discrepancy. This is suggested to be the result of heat variation due to different sample thickness and heat transfer during measurement. The analysis of the morphological development of two compositions and two phase separation temperatures as a function of reduced time showed a master curve. The Young's modulus appear to be superior for the blends, which were phase separated inside the early stage of spinodal decomposition. This might be the result of the change in composition and molecular re-arrangement, while the change in phase separating domains as observed by TEM did not clearly manifest any effects on Young's modulus.