Modeling the Kinetics and Microstructure of a Thermally Initiated Thiol-Ene Polymerization

A mathematical model of a thermally initiated thiol-ene polymerization is developed and assessed with experimental data gathered in the polymerization of 2,2'-(ethylenedioxy)diethanol (EDDT) as dithiol and diallyl adipate (DAA) as diene. The model considers the main mechanisms of addition (propagation) and chain transfer reactions by which the thiol-ene polymerization proceeds, but also reaction mechanisms that yield to side products formed by reaction of initiator radicals with ene functional groups and by combination termination reactions. The model predicts in addition to kinetics and molar masses, the molar fractions of all the polymer species produced. Conversions of the ene functional groups are determined by in situ H-1-NMR, absolute molar masses are determined by size exclusion chromatography with a multiangle light scattering detector (SEC/MALS) and molar fractions of copolymer species are measured by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF). The experimental data are used for estimating some of the rate coefficients of the kinetic scheme. The model predicts reasonably well the effects of the initiator concentration on the kinetics and underestimates the molar masses. On the other hand, the model predicts three of the five species experimentally detected by MALDI-TOF.