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

Abstract

An alkylborane initiated reversible addition-fragmentation chain transfer (AI-RAFT) process was developed for the synthesis of star-polymers using a onepot approach at room-temperature in the presence of oxygen. Linear poly(tertbutyl 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 starpolymer 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, lowtemperatures, and metal-free conditions. K E Y W O R D S star polymers, reversible addition fragmentation chain transfer, alkylborane initiation, oxygen tolerant, room temperature, controlled radical polymerization

Oxygen‐Demanding Photocontrolled RAFT Polymerization Under Ambient Conditions

“…1b). In addition, the characteristic peak with a chemical shift at 66.13 ppm in the 19 F NMR spectrum was attributed to the fluorine atom in the benzenesulfonyl fluoride fragment (Figure S2, Supporting Information). Furthermore, the characteristic infrared peaks at 1722 and 1658 cm -1 were assigned to the carbonyl bond in the ester and benzophenone groups, respectively (Figure S3, Supporting Information).…”

“…The chemical structure of the synthesized PHEA was also analyzed by 1 [31] and the characteristic chemical shift at 64.46 ppm in the 19 F NMR spectrum was assigned to the fluorine atom in the benzenesulfonyl fluoride group (Figure S6, Supporting Information). These data indicated that the benzophenone and benzenesulfonyl fluoride fragments inherited from the RAFT agent BP-FSBC were preserved at opposite ends of the PHEA chain.…”

“…Furthermore, the complex can release reactive BR 3 by the addition of a reactive decomplexation agent referred to as a deblocker, which cannot only overcome the limitation that BR 3 is unstable in air, but also conveniently initiate polymerization. [ 18–20 ] For instance, Wilson [ 20,21 ] et al. used an air‐stable alkylborane–amine complex instead of BR 3 , which was chemically deblocked with carboxylic acid or isocyanate functionalities to liberate reactive alkylboranes to perform RAFT polymerization of vinyl monomers under air conditions, and prepared nanocomposites based on thiol‐ene reactions.…”

“…used an air‐stable alkylborane–amine complex instead of BR 3 , which was chemically deblocked with carboxylic acid or isocyanate functionalities to liberate reactive alkylboranes to perform RAFT polymerization of vinyl monomers under air conditions, and prepared nanocomposites based on thiol‐ene reactions. Timmins [ 19 ] et al. developed a RAFT process initiated by an alkylborane–amine complex under the reaction of a deblocker, which was employed to synthesize star polymers under ambient temperature and atmosphere (ambient conditions).…”

New method for controlled synthesis of polylactide block copolymers: organoborane/p‐quinone system and reversible‐deactivation radical polymerization

“…There has been an increased interest in polymer synthesis using boron-containing compounds. [22][23][24][25][26][27][28][29][30][31][32][33][34] One of the benefits of polymerization in the presence of organoboranes is a high rate of initiation at ambient temperature even in the presence of atmospheric oxygen. Chung et al discovered that polymerization of some monomers in the presence of a trialkylborane/atmospheric oxygen system proceeds in a controlled manner due to the dissociation-recombination of active terminal borane fragments.…”