Synthesis and Properties of Poly(Styrene-b-Trimethylvinylsilane)

The diblock copolymer poly(styrene-b-trimethylvinylsilane) was made anionically by sequential addition of the monomers. The copolymer is amphipathic and will stabilize foams consisting of nitrogen and polymer hydrocarbon solutions. The foam stabilization properties of poly(sty-rene-b-trimethylvinylsilane) are dependent upon molecular weight, composition, and concentration. The optimum diblock copolymer has M n in the range of 9 000-30 000, contains about 0.10 mole fraction trimethylvinylsilane, and is used at about 0.3 wt% concentration for foams consisting of nitrogen dispersed in a solution of polystyrene in styrene monomer. The diblock copolymer poly(styrene-b-trimethylvinylsilane) is readily made by sequentially and anionically polymerizing styrene and trimethylvinylsilane. Kinetics place limitations upon the length of the poly(trimethylvinylsilane) segment and conversion of trimethylvinylsilane monomer due to a termination reaction. Two transitions are observed in DSC thermograms indicating that the poly(styrene) and poly(trimethylvinylsilane) segments reside in separate domains. The amphipathic nature of the diblock copolymer is revealed from molecular weight and GPC data, which show that the polystyrene) segment is more lyophilic in tetrahydrofuran than the poly(trimethylvinylsilane) segment. The foaming properties of the diblock copolymer were found to depend upon composition, molecular weight, and concentration. Typically, concentrations of 0.3 wt% of a diblock copolymer having M n in the range 9 000-30 000 and 0.10 mole fraction styrene stabilized fine-celled foams of nitrogen and polystyrene-styrene solutions. Both the foaming properties and inertness to carbanions make poly(styrene-b-trimethylvinylsilane) a good candidate as a foaming agent in an anionic poly(styrene) RIM process.