Kinetic, structural, and relaxational aspects of polymerizations of multifunctional monomers
Abstract
The formation of highly crosslinked polymers is typically accomplished by polymerization of multifunctional monomers. Reactions of this type are typically accompanied by heterogeneity of the polymer structure, autoacceleration and autodeceleration of reaction kinetics, and formation of a glassy polymer. Theoretical models were developed to understand the polymer structure and the reaction kinetics of ethylene glycol dimethacrylate polymerization reactions. Kinetic gelation simulations were used to predict the polymer structure, particularly the heterogeneity during the polymerization. These simulations involved modification of previous kinetic gelation simulations by addition of monomer size, molecular mobility, and realistic initiation mechanisms. The simulations correctly predicted that heterogeneity during the polymerization would result in varying reactivity of pendant double bonds. At low conversions to the pendant double bond is highly reactive because of its high local concentration, but at high conversions shielding of the pendant bond lowers its reactivity. In order to predict the coupled reaction kinetics and volume relaxation a free volume based model for the kinetic constants and relaxation time was developed. The model was able to predict the behavior observed in these systems including the attainment of a maximum conversion, the dependence of the maximum conversion on reaction rate, and the relationship between the volume relaxation and the reaction kinetics. Photopolymerizations of ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, and ethylene glycol 600 dimethacrylate initiated by 0.1, 1.0, and 4.0 wt.% 2,2-dimethoxy-2-phenylacetophenone and ultraviolet light of 0.015, 0.2, and 2.0 mW/cm$\sp2$ intensity were performed. Differential scanning calorimetry was used to follow the rate of reaction while an interferometric technique was used to determine the volume shrinkage. Polymerization results are in qualitative agreement with the predictions of the model coupling reaction kinetics and volume relaxation. Increasing monomer molecular weight (the separation of the methacrylate groups) was found to cause an increase in the rate of reaction and the maximum conversion. The maximum shrinkage increased from ethylene glycol dimethacrylate to diethylene glycol dimethacrylate and then decreased through ethylene glycol 600 dimethacrylate.
Degree
Ph.D.
Advisors
Peppas, Purdue University.
Subject Area
Chemical engineering
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