Detection and quantification of branching in polyacrylates by size-exclusion chromatography (SEC) and melt-state 13C NMR spectroscopy

Abstract

Chain branching has been investigated in a homologous series of poly( n-alkyl acrylates) (methyl, ethyl, n-butyl, n-hexyl) obtained by radical polymerization. The total amount of chain branching was quantified using melt-state 13C nuclear magnetic resonance (NMR) spectroscopy. It gave access to low degrees of branching in both soluble and insoluble polyacrylates, homopolymers and copolymers. The lowest degree of branching was found for the ethyl member of the series with quantification by conventional solution-state NMR found to take a prohibitively long time. The method proposed here is compared to the ones published previously, and previous literature results are critically reviewed. The presence of long-chain branching (LCB) was selectively detected using multiple-detection size-exclusion chromatography (SEC), with LCB being found for all soluble homopolymers but the poly( n-butyl acrylate). This finding was confirmed by close examination of the Mark–Houwink parameters for the various polyacrylates studied in this work or those previously published.