Miller & Macosko crosslink density The crosslink density υ of a classical, Bethe-lattice, An+An-1+…+A1+B2 step-growth polymer network can be calculated according to the equation υ = i − 2 2 X i

A chemical clock protocol that enables enhanced temporal control over the onset of two base-catalyzed ‘click’ reactions, the thiol-Michael addition reaction, and the thiol-isocyanate reaction, is described and used in polymerization reactions. Initiating protocols with predictable induction times for both click reactions are developed and characterized using a pair consisting of an electron deficient vinylic species and a nucleophile with an acid. The approach was successfully demonstrated such that the reaction onset is effectively and predictably delayed by up to 20 min, with rapid complete reaction following the controllable induction period. By implementing initiation systems with varying relative concentrations of the electron deficient vinyl, nucleophile, and acid, this approach to formulating a comprehensive initiator system affords a previously unavailable degree of temporal control that is extremely useful for designing and processing cross-linked polymers and other thiol-Michael and thiol-isocyanate polymerizations.

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