Controlled radical polymerization of a styrenic sulfonium monomer and post-polymerization modifications

Abstract

The controlled radical polymerization (CRP) of a sulfonium salt-type monomer, 4-vinylbenzyltetrahydrothiophenium tetrafluoroborate (4VBThtBF4), was investigated under initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) and reversible addition–fragmentation chain-transfer (RAFT) polymerization conditions. A progressive loss of control over the polymerization was observed under ICAR ATRP conditions when an alkyl bromide initiator was used, due to the reaction of the bromine-capped dormant chain ends with tetrahydrothiophene which is formed in the reaction mixture by slow decomposition of the monomer. The use of a chloride initiator (less sensitive towards nucleophiles) leads only to a limited improvement because of the comparatively low initiation efficiency. 4VBThtBF4 can be polymerized in a controlled fashion under RAFT conditions using a tertiary trithiocarbonate chain transfer agent (CTA). The polymerizations proceeded quickly to high monomer conversion (>85% within 5 hours) and afforded materials with narrow molecular weight distribution dispersities (around 1.15). The obtained polymeric sulfonium salt (poly4VBThtBF4) was used successfully as a building block in the synthesis of block copolymers with polystyrene segments. The reaction of poly4VBThtBF4 with sodium benzylthiolate and sodium azide was investigated in detail, and optimized to afford the corresponding polymeric thioethers (poly4VBSBn) and azides (poly4VBN3). Finally, the pendant benzylic methylene groups in poly4VBThtBF4 were deprotonated and the formed polymers with multiple attached ylide functionalities (not isolated) were reacted with benzaldehyde to yield polymers with pendant epoxide groups.