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Arm‐first star‐polymer synthesis in one‐pot via alkylborane‐initiated RAFT
Journal article   Peer reviewed

Arm‐first star‐polymer synthesis in one‐pot via alkylborane‐initiated RAFT

Renee L. Timmins, Olivia R. Wilson and Andrew J. D. Magenau
Journal of polymer science (2020), v 58(10), pp 1463-1471
15 May 2020
DOI: https://doi.org/10.1002/pol.20200089

Abstract

alkylborane initiation controlled radical polymerization oxygen tolerant reversible addition fragmentation chain transfer room temperature star polymers
An alkylborane initiated reversible addition‐fragmentation chain transfer (AI‐RAFT) process was developed for the synthesis of star‐polymers using a one‐pot approach at room‐temperature in the presence of oxygen. Linear poly(tert‐butyl acrylate) arms were first polymerized using a latent trialkylborane‐amine initiator, which generated trialkylborane, in situ, and subsequently radicals after reaction with oxygen. Polymerizations were optimized to maximize monomer conversion (~70–80%) and minimize arm‐dispersity (~1.10) through the oxygen concentration, initiator concentration, and polymerization time. The oxygen concentration was a critical AI‐RAFT parameter, providing maximum conversion at a ~0.5:1 molar ratio of oxygen‐to‐initiator. After arm‐polymerization, multifunctional acrylates were injected into the reactor to commence crosslinking without intermediate purification. The impact of the crosslinking time and the crosslinker's functionality, concentration, and injection time were investigated to enhance arm incorporation and diminish star‐polymer dispersity, quantified by deconvolution of size‐exclusion chromatography data. Crosslinker concentration had the largest influence on arm conversion with optimal concentrations at a 20‐25‐fold excess to chain transfer agent. Under optimal conditions, arm conversions were maximized to ~75–85% and star‐dispersity minimized to ~1.35–1.50. Herein an initial effort is made toward the synthesis of star‐polymers with well‐defined structures and high‐arm conversions, while also striving for oxygen tolerance, minimal purification, low‐temperatures, and metal‐free conditions. An oxygen tolerant alkylborane‐initiated reversible addition‐fragmentation chain transfer (AI‐RAFT) polymerization is reported for the synthesis of well‐defined star polymers at room temperature using a one‐pot, arm‐first approach. Alkylborane initiation uniquely consumes oxygen to generate radicals, which drives RAFT without an external stimulus as in thermal, photochemical, or electrical processes. Critical parameters were studied and optimized for the arm and crosslinking steps to maximize arm conversion to ~75–85% and to minimize star‐dispersity values to ~1.35–1.50 without intermediate purification.

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