Syntheses of benzhydryl 2-propanoyl-functionalized trithiocarbonates and its use as chain transfer agents in the RAFT polymerization of styrene

Abstract

Abstract The preparation of three new benzhydryl 2-propanoyl-functionalized trithiocarbonate RAFT agents, benzhydryl 2-(ethylsulfanylthiocarbonylsulfanyl)propanoate, benzhydryl 2-(butylsulfanylthiocarbonylsulfanyl)propanoate, benzhydryl 2-(dodecylsulfanylthiocarbonylsulfanyl)propanoate is described. The RAFT polymerization of styrene, mediated by the appropriate benzhydryl 2-(alkylsulfanylthiocarbonylsulfanyl)propanoate as the chain transfer agent, with AIBN as initiator at 70 0C, proceeds via reversible-deactivation radical polymerization processes to produce the corresponding α-benzhydryl 2-propanoyl polystyrene derivative, with the benzhydryl ester group introduced at the α-terminus of the polymer chain. Polymerization kinetics measurements show that each RAFT polymerization reaction follows first order rate kinetics with respect to percentage monomer consumption and the number average molecular weights of the functionalized polymers increase linearly with the percentage monomer conversion to produce functionalized polymers with narrow molecular weight distributions. The percentage monomer conversion with time for each polymerization reaction was monitored by 1H NMR spectroscopy by evaluating the consumption of styrene with respect to polymerization time. Post-RAFT polymerization chain end modification of α-benzhydryl 2-propanoyl-functionalized polystyrene by the acid catalyzed ester hydrolysis reactions with concentrated sulfuric acid afforded the corresponding α-carboxyl functionalized polystyrene derivative, with the retention of the thiocarbonylthio moiety at the ω-terminus of the polymer chain. The benzhydryl 2-propanoyl-functionalized trithiocarbonate chain transfer agents and the different functionalized polystyrene derivatives were characterized by 1H NMR, 13C NMR and FTIR spectroscopy, size exclusion chromatography, thin layer chromatography and mass spectrometry measurements.