Synthesis of polystyrene by dispersion polymerization in 1,1,1,2-tetrafluoroethane (R134a) using inexpensive hydrocarbon macromonomer stabilizers

We describe here the use of inexpensive poly(vinyl acetate) (PVAc) macromonomer stabilizers for the free radical dispersion polymerization of styrene in 1,1,1,2-tetrafluoroethane (R134a). PVAc was identified from a wide range of polymers as being highly soluble in R134a at low pressures (<10 bar). The phase behavior of PVAc (M-w = 12 000-500 000 g/mol) in R134a was studied over a range of temperatures and pressures. It was found that PVAc exhibits LCST phase behavior in R134a. Based on the results of these solubility studies, PVAc macromonomer stabilizers were synthesized for use in dispersion polymerization. The dispersion polymerization of styrene in R134a gave rise to polystyrene microspheres (4-5 mum diameter) in good yields (up to 95%) with number-average molecular weights as high as 42 000 g/mol. The polystyrene microspheres could be redispersed in neat R134a after isolation and purification.