Controlled One‐Pot Synthesis of Polystyrene‐block‐Polycaprolactone Copolymers by Simultaneous RAFT and ROP

Abstract

A convenient one-pot method for the controlled synthesis of polystyrene-block -polycaprolactone (PS-b -PCL) copolymers by simultaneous reversible addition-fragmentation chain transfer (RAFT) and ring-opening polymerization (ROP) processes is reported. The strategy involves the use of 2-(benzylsulfanylthiocarbonylsulfanyl)ethanol (1) for the dual roles of chain transfer agent (CTA) in the RAFT polymerization of styrene and co-initiator in the ROP of ε -caprolactone. One-pot poly merizations using the electrochemically stable ROP catalyst diphenyl phosphate (DPP) yield well-defi ned PS-b -PCL in a relatively short reaction time (≈4 h; M n = 9600−43 600 g mol −1 ; M w / M n = 1.21−1.57). Because the hydroxyl group is strategically located on the Z substituent of the CTA, segments of these diblock copolymers are connected through a trithiocarbonate group, thus offering an easy way for subsequent growth of a third segment between PS and PCL. In contrast, an oxidatively unstable Sn(Oct) 2 ROP catalyst reacts with (1) leading to multimodal distributions of polymer chains with variable composition.

Synthesis of Grafted Block Copolymers Based on ε‐Caprolactone: Influence of Branches on Their Thermal Behavior

“…Therefore, we reported macromolecular dimensions corresponding to the theoretical molar mass, M n , which was calculated from conversion data obtained from 1 H NMR analysis of aliquots taken from the reaction and diluted with CDCl 3 assuming quantitative reaction of the CTA, and purified polymer samples (after precipitation). The high efficiency (near quantitative reaction) of the CTA in initiating the ROP process and in mediating the RAFT polymerization has been previously verified by our group …”

“…Nonisothermal crystallization kinetics was further analyzed using the Ozawa's model equation, which is an extension from the Avrami's equation originally applied in the isothermal crystallization . Thus, it is assumed that sample is cooled at a constant cooling rate . In this case, Equation is applied where K ( T ) is the Ozawa's crystallization cooling function and m is the Ozawa's exponent, which depends on the dimension of crystal growth.…”

“…2‐Hydroxyethylmethacrylate (HEMA, Aldrich, 97%), ε‐CL (Aldrich, 99%), diphenyl phosphate (DPP, 99%), 1,1′‐azobis(cyclohexanecarbonitrile) (VAZO catalyst 88, Aldrich, 98%), toluene (Aldrich), methanol (Química Industrial), dimethylformamide (DMF, 99.8%), chloroform (Aldrich, 99.5%), deuterated chloroform (CDCl 3 ), and petroleum ether were used as solvents without any further purification. (Benzylsulfanylthiocarbonylsulfanyl) ethanol (BSTSE) chain transfer agent was prepared following a one‐pot procedure previously described elsewhere . The resulting BSTSE was further purified by column chromatography on silica using petroleum ether as eluent and recrystallized under cold conditions.…”

Thermal Characterization of “Comb‐Like” Block Copolymers Based on PCL Obtained by Combining ROP and RAFT Polymerizations

“…In the last years, ROP have been combined with other polymerization processes in order to obtain polymers with specific properties. For example, RAFT and ROP have been employed in a one‐step route to synthesize well‐defined copolymers . The reaction is mediated by a bifunctional compound (i.e.…”

“…The reaction is mediated by a bifunctional compound (i.e. the CTA agent of the RAFT process) with an alcohol function able to initiate simultaneously the ROP process …”