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Keywords:

  • FTIR;
  • kinetics;
  • photopolymerization;
  • polysiloxanes;
  • thiol-ene

Abstract

Polysiloxanes are commonly used in a myriad of applications, and the “click” nature of the thiol-ene reaction is well suited for introducing alternative functionalities or for crosslinking these ubiquitous polymers. As such, understanding of the thiol-ene reaction in the presence of silicones is valuable and would lead to enhanced methodologies for modification and crosslinking. Here, the thiol-ene reaction kinetics were investigated in functionalized oligosiloxanes having varying degrees of thiol functionalization (SH), π–π interactions (from diphenyls, DP), and ene types (C[DOUBLE BOND]C). In the ene-functionalized oligomers, π–π interactions were controlled through the use of dioctyl repeats (DO). The polymerization rate and rate-limiting steps were determined for all systems containing an allyl-functionalized oligomer, and rates ranging from 0.10 to 0.54 mol L−1 min−1 were seen. The rate-limiting step varied with the oligomer composition; examples of rate-limited propagation (5:3:2 C[DOUBLE BOND]C:DP:DO/1:1 SH:DP) or chain transfer (5:3:2 C[DOUBLE BOND]C:DP:DO/3:1 SH:DP) were found in addition to cases with similar reaction rate constants (5:2:3 C[DOUBLE BOND]C:DP:DO/1:1 SH:DP). None of the siloxanes were found to exhibit autoacceleration despite their relatively high viscosities. Instead, the allyl-, vinyl-, and acrylate-functionalized siloxanes were all found to undergo unimolecular termination based on their high α scaling values (0.98, 0.95, and 0.82, respectively) in the relation RpRiα. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013