Pushing Monomer Conversions High in Bulk ATRP: The Effects of ICAR Agent Concentrations on the System Livingness and Polymer Molecular Weight Control

Abstract

Controlled radical polymerization often loses control over polymer molecular weight at high monomer conversions due to diffusion-controlled reactions. This is particularly true for bulk polymerization systems. In this work, bulk atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was carried out by employing an initiator for continuous activator regeneration (ICAR) method. Binary systems of ICAR agents, that is, low temperature azobisisobutyronitrile (AIBN) and high temperature tert-butyl peroxybenzoate (TBPB) or tert-butyl peroxide (TBP) were used. The polymerization was run at 70 C at the beginning and completed at an elevated temperature. The objective was to investigate the effects of ICAR agent concentration on the system livingness and control at high conversions. It was found that both ICAR agents significantly affected the rate of catalyst regeneration and consequently the rate and control of polymerization. By optimizing the concentrations of the ICAR agents and employing step temperature profile, MMA was polymerized with 50 ppm CuBr 2 up to 98% conversion in less than 5 hours. The final products had dispersity (Đ) about 1.3.

Kinetics of Atom Transfer Radical Polymerization

“…thermal decomposition of conventional radical initiator leads to the formation of radicals which can reduce Cu II /L, but can also initiate polymerization, resulting in decreased α-chain end functionality which can be introduced by substituted alkyl halides. The effect of the amount thermal radical initiators on the MW and livingness of the system was investigated in detail by Zhu, et al[288] Alternatively, external stimuli such as light or electric current can be utilized as a -cleaner‖ solution. However, photoATRP still requires the use of an excess of ligand, or other free aliphatic amine, e.g.…”