Extent of intramolecular cyclization in RAFT-synthesized methacrylic branched copolymers using ¹³C NMR spectroscopy

Abstract

Recently, we reported using 1 H NMR spectroscopy to assess the degree of intramolecular cyclization in a series of soluble methacrylic branched copolymers (see J. Rosselgong and S. P. Armes, Macromolecules, 2012, 45, 2731-2737. The key to success in addressing this long-standing problem in polymer science was the selection of a suitable disulfide-based dimethacrylate as the branching comonomer, which was statistically copolymerized with methyl methacrylate using reversible addition-fragmentation chain transfer (RAFT) polymerization. In this earlier work, estimation of the degree of intramolecular cyclization required peak deconvolution of the relevant thiamethylene proton signals. In the present work, we show that quantitative 13 C NMR spectroscopy can also be utilized to determine the intramolecular cyclization for the same series of methacrylic copolymers via peak deconvolution of the oxymethylene carbon signals. Although this technique requires long spectral accumulation times, it offers superior resolution compared to 1 H NMR spectroscopy and hence may ultimately enable this analytical approach to be applied to less esoteric divinyl comonomers.

Exploring the homogeneous controlled radical polymerisation of hydrophobic monomers in anti-solvents for their polymers: RAFT and ATRP of various alkyl methacrylates in anhydrous methanol to high conversion and low dispersity

“…This approach to branched vinyl polymerisation was pioneered by Sherrington and coworkers, [25][26][27][28] initially through the use of conventional free radical polymerisation utilising thiol chain transfer agents, 29,30 and latterly through group transfer polymerisation 31 and various controlled radical approaches. 32,33 As has been reported previously for different branched vinyl polymerisations, the formation of high molecular weights within such reactions are achieved at conversions > 85 %. 34,17 Each polymerisation was, therefore, allowed to reach approximately 99 % conversion, requiring longer reaction times than the equivalent linear p(PEG 113 -block-nBuMA 60 ) syntheses.…”

Expanding the monomer scope of linear and branched vinyl polymerisations via copper-catalysed reversible-deactivation radical polymerisation of hydrophobic methacrylates using anhydrous alcohol solvents

“…59,60 The inclusion of BFM into the polymer structure, whether via intermolecular branching or intramolecular cyclisation, impacts the extent of branching and may also be heavily influenced by the concentration at which polymerisations are conducted. [61][62][63][64] These factors must always be considered when designing new branching copolymerisation reactions using this approach.…”

Polymer Networks From Nanosized Functional Precursors

“…If cross-linker molecules contain ÀS-S-, the cycles can be seen directly by 1H-NMR or 13C-NMR spectrometry. [37,38] Even more versatile is the "isotopic labeling disassembly spectrometry" based on the use of isotopically labeled bifunctional monomers that transfer their labels to multifunctional junctions upon network formation. [39] A telechelic polymer used in network synthesis is provided by two cleavable groups near the labeled and non-labeled end groups.…”

“…Already Minnema and Staverman introduced bis‐unsaturated cross‐linker molecules with hydrolytically cleavable bridge and estimated the fraction of bonds engaged in ring‐closing from the molecular weights of the chains after hydrolysis. If cross‐linker molecules contain −S‐S‐, the cycles can be seen directly by 1H‐NMR or 13C‐NMR spectrometry . Even more versatile is the “isotopic labeling disassembly spectrometry” based on the use of isotopically labeled bifunctional monomers that transfer their labels to multifunctional junctions upon network formation .…”