End-Group Control in the Radical Polymerization of Methyl Methacrylate with tert-Butyl Peroxypivalate Initiator in the Presence of Thiol Chain Transfer Agents

Abstract

The radical polymerization of methyl methacrylate (MMA) by the thermal initiator tert-butyl peroxypivalate (tBPPiv) and in the presence of various thiol-containing chain transfer agents (CTAs) has been studied to quantitatively determine the chemical selectivity and fate of initiator radicals. Deuterated MMA-d 5 was used to follow polymerization reactions by 1D and 2D NMR spectroscopy and to determine the identity and quantity of small molecule byproducts, together with the distribution of polymer end-groups. These data have resulted in a detailed understanding of initiator decay pathways, radical selectivity, and of key importance to the design of well-defined polymers for commercial applications, the efficiency of so-called end-group functionalization. In the presence of a thiol-containing small molecule, chain transfer to CTA leads predominantly to initiation by the resulting thiyl radical; however, direct initiation by initiator radicals and a variety of other reactions reduce the total number of CTA-functionalized chain-ends. The approach reported here gives fundamental insights into the fates of radicals in the polymerization of a model methacrylate, increased control over end-groups, and can be extended to a range of commercially relevant polymer compositions. Moreover, these results provide a quantitative framework that can potentially open the door to the design of end-functional polymers by industrially relevant methods, avoiding the need for more timeconsuming and complex reversible-deactivation radical polymerization (RDRP) techniques.

Photocurable Thiol–yne Alginate Hydrogels for Regenerative Medicine Purposes

“…Apart from the radical-scavenging effect of thiols in water environments, thiols are also known to act as chain transfer agents in free-radical polymerization [ 64 , 65 , 66 ]. Especially in aqueous solutions [ 67 ], a higher thiol concentration could lead to incremental radical chain transfer phenomena and a subsequent decrease in crosslinking, explaining the poorer mechanical properties at higher molar ratios.…”

Accessing new and scalable high molecular weight branched copolymer structures using transfer-dominated branching radical telomerisation (TBRT)

“…2B, to determine DP n . The data generated was used to determine the chain transfer coefficients from the gradient of the subsequent Mayo plots, 20,50 Fig. 2C (Table S1, Fig.…”

“…1. 18,19 The approach utilised alkyl thiol telogens (also known as chain transfer agents, CTAs, when used at low concentration relative to mono-vinyl monomers), 20 multi-vinyl taxogens (MVTs; monomers that contain more than one vinyl double bond) and sources of free radicals that are generated by thermal decomposition (azo initiators). By establishing free radical telomerisation conditions, [21][22][23] propagation of the MVT is restricted on average to a DP n < 2 vinyl groups and gelation is avoided.…”

Polymers via Reversible Addition–Fragmentation Chain Transfer Polymerization with High Thiol End-Group Fidelity for Effective Grafting-To Gold Nanoparticles

“…End-group functional polymers are of importance for materials and medical applications, such as block copolymers, , surface modification for nanoparticles, − biopolymer conjugates, − etc. To date, various types of end-group functional polymers have been successfully synthesized through controlled living polymerization methods, such as anionic polymerization, cationic polymerization, atom-transfer radical polymerization (ATRP), and reversible addition–fragmentation chain transfer (RAFT) polymerization . Among them, the RAFT polymerization method is more favorable owing to its broad monomer scope, metal-free and facile reaction conditions, and overall ease of use .…”

“…To date, various types of end-group functional polymers have been successfully synthesized through controlled living polymerization methods, such as anionic polymerization, 12 cationic polymerization, 13 atom-transfer radical polymerization (ATRP), 14 and reversible addition−fragmentation chain transfer (RAFT) polymerization. 15 Among them, the RAFT polymerization method is more favorable owing to its broad monomer scope, metal-free and facile reaction conditions, and overall ease of use. 16 Polymers prepared by RAFT polymerization have molecular weights that can be well-controlled by adjusting the ratio of monomer to chain-transfer agent (CTA), normally a thiocarbonylthio-containing compound.…”