Monitoring Atom Transfer Radical Polymerisation using 14C-radiolabelled initiators

Radio thin layer chromatography (R-TLC) and liquid scintillation counting, of fractions collected from conventional gel permeation chromatography (GPC), have been used to study the fate of 14C-labelled initiators in the ambient methanolic ATRP of 2-hydroxypropyl methacrylate at different targeted number average degrees of polymerisation. Benzyl 2-bromoisobutyrate was synthesised in unlabelled form and with 14C-labels at different locations to establish no adverse effects of the radiolabel. Target chain lengths of 10, 25 and 50 monomer units were synthesised and comparison of GPC and R-TLC showed a significant under-utilisation of the initiator with approximately 16% clearly observable at high monomer conversion (>97%). New chains appeared to be initiated at monomer conversions >90% and as late as 300 minutes after polymerisation had commenced. Purification by repeated precipitation was shown to be superior to flash chromatography for the ability to remove residual unreacted or terminated initiator although increased fractionation could be seen with each repeat.