Influence of the tacticity of poly(methyl methacrylate) on the miscibility with poly(vinyl chloride)

It can be concluded from the work of Schurer et al.¹⁰ that poly(vinyl chloride) (PVC) is more miscible with syndiotactic than with isotactic poly(methyl methacrylate) (PMMA). By choosing different molar masses for the various tactic forms of PMMA it is possible to obtain blends with PVC with similar phase behaviour, i.e. in all cases a cloud-point curve with a minimum in the vicinity of 190°C. In this way a more quantitative statement about the influence of the tacticity of PMMA on its miscibility with PVC can be made. One of the principal differences between syndiotactic or atactic PMMA and isotactic PMMA is the higher flexibility of the latter. Using Flory's equation of state theory it will be shown that the effect of this difference is large enough to explain the difference in phase behaviour observed. Heats of mixing of low molar mass analogues were also measured and found to be negative.