Kinetic analysis of epoxy resins: Competing intermolecular and intramolecular polymerization reactions
The modeling of complex, non-linear, network forming, chemical reactions is fundamental to developing an understanding of thermoset resins. The literature reveals that rate expressions descriptive of intramolecular reactions are practically non-existent. Analysis of thermosets will provide insight to this development.
This work used kinetic reaction theory to model several examples. The first case is a step-growth, thermoset polymerization of a monomer of functionality f. Next an anhydride cured epoxy resin is considered. Finally amine cured epoxy resins are modeled.
Analytical solutions are obtained for the polymerization of the f functional monomer with competing intermolecular and intramolecular reactions. Weighted differential equations for the population density distribution are converted to moments of the distribution. Equations descriptive of population density distribution, number, weight and crosslink average molecular weights are derived.
Anhydride cured epoxy resins are modeled with competing intermolecular and intramolecular reactions. Moments of the population density distribution are derived. Relationships expressing the constituent molecules as a function of degree of polymerization, extent of branching and reacted functional groups are derived. Experimental procedures for verification of the theoretical results are discussed.
Amine cured epoxy resins are modeled for an unequal reactivity of primary and secondary amines, considering second order or third order autocatalytic, intermolecular, reaction kinetics. Theoretical relationships derived describe constituent molecules in terms of their number of amine and epoxy monomer units and the number of primary amines as a function of time. Derivations can be used to simulate the formation of polyimides, polyamides, etc. Experimental procedures for the evaluation of theoretical results are presented. Inclusion of intramolecular reactions yield complex rate equations. The moments are numerically generated.
Simulations yield moments that are consistent with experimental measurements prior to gelation. Future experimental research should address basic intramolecular reactions in thermosets. Current kinetic rate expressions were selected basically to demonstrate equation formulation and solution based on classic kinetic reaction models.