RAFT polymerization of styrene mediated by naphthyl-functionalized trithiocarbonate RAFT agents

Abstract

New oxazolyl benzhydryl and oxazolyl benzyl-functionalized trithiocarbonate RAFT agents, 1-(butylsulfanylthiocarbonylsulfanyl)-1-[4-(4,5-dihydro-4,4-dimethyl-2-oxazolyl)phenyl]-1-phenylmethane and 2-[4-((butylsulfanylthiocarbonylsulfanyl)methyl)phenyl]-4,5-dihydro-4,4-dimethyloxazole, were prepared and employed as chain transfer agents in RAFT polymerization reactions. The RAFT polymerization of styrene, mediated by the appropriate oxazolyl-functionalized trithiocarbonate RAFT agent with AIBN as initiator at 70 °C, proceeded via controlled/living polymerization processes to produce the corresponding α-oxazolyl-functionalized polystyrene derivative, with the oxazolyl group introduced at the α-terminus of the polymer chain and the absence of any unfunctionalized polystyrene. Post-RAFT polymerization chain end modification of α-oxazolyl-functionalized polystyrene by acid-catalyzed hydrolysis reactions with dilute hydrochloric acid afforded the corresponding α-carboxyl-functionalized polystyrene derivative, with the retention of the butylsulfanylthiocarbonylsulfanyl moiety at the ω-terminus of the polymer chain. Polymer kinetic measurements show that each RAFT polymerization reaction follows first-order rate kinetics with respect to the percentage monomer consumption. The oxazolyl-functionalized benzhydryl fragmentation radical provides better control of the re-initiation of the polymerization of styrene than the oxazolyl-functionalized benzyl fragmentation radical. After consumption of the RAFT agent, the number average molecular weights of the functionalized polymers increases linearly with the percentage monomer conversion to produce α-oxazolyl-functionalized polystyrene derivatives with narrow molecular weight distributions. New oxazolyl benzhydryl and oxazolyl benzyl-functionalized trithiocarbonate RAFT agents, 1-(butylsulfanylthiocarbonylsulfanyl)-1-[4-(4,5-dihydro-4,4-dimethyl-2-oxazolyl)phenyl]-1-phenylmethane and 2-[4-((butylsulfanylthiocarbonylsulfanyl)methyl)phenyl]-4,5-dihydro-4,4-dimethyloxazole, were prepared and employed as chain transfer agents in RAFT polymerization reactions. The RAFT polymerization of styrene, mediated by 1-(butylsulfanylthiocarbonylsulfanyl)-1-[4-(4,5-dihydro-4,4-dimethyl-2-oxazolyl)phenyl]-1-phenylmethane or 2-[4-((butylsulfanylthiocarbonylsulfanyl)methyl)phenyl]-4,5-dihydro-4,4-dimethyloxazole as chain transfer agents with AIBN as the initiator at 70 °C, proceeds via a controlled/living polymerization process to produce the corresponding α-oxazolyl-functionalized polystyrene derivative, with the oxazolyl group introduced at the α-terminus of the polymer chain.