Synthesis and characterization of divinyl monomers for styrene-based reaction injection molding
The motivation for this project was to develop a suitable replacement crosslinker for technical divinylbenzene (DVB) for use in a styrene-based Reaction Injection Molding (RIM) system. This thesis describes the synthesis of a,w-bis(4-vinylphenyl)alkane (BVPA) compounds, the determination of their anionic homopolymerization and copolymerization kinetic parameters, and the evaluation of the physical and thermal properties of crosslinked polymers made with these compounds. A general lithium coupling synthesis was developed to produce BVPA monomers with alkyl linkages of six or more carbons. 1,8-bis(4- Vinylphenyl)octane (BVPO) was synthesized in a 30% yield for use in physical testing. 1,2-bis(4-Vinylphenyl)ethane (BVPE) was produced in sufficient quantities for both kinetic and physical testing using a Grignard coupling synthesis. The kinetics of the sec-butyllithium initiated homopolymerization of styrene, p-methylstyrene, p-t-butylstyrene (TBS), and BVPE were determined in aromatic solvents. The kinetics of the anionic copolymerization of styrene with TBS, and BVPE with TBS were also investigated. A new anionic copolymerization rate model was derived that gives an excellent fit to experimental data. The reactivity ratios of the two copolymerizations were found to be nearly ideal with rStyrene-TBS = 1.78 and rBVPE-TBS = 1.67. A simulation using experimental data predicts BVPE crosslinked TBS to have a significantly more homogenous network structure than TBS crosslinked with DVB. The use of BVPA compounds was shown to impart improved physical and thermal properties to crosslinked TBS polymers relative to divinylbenzene by virtue of their lower reactivity and flexible alkyl linkage. In particular, BVPO produced a thermoset that satisfies the material property objectives for Tg and flexural strength while favorably affecting cure shrinkage.