Cure behaviors of vinyl ester resins with low profile thermoplastic additives and thermoplastic elastomers

Abstract

Vinyl ester was prepared from diglycidyl ether of bisphenol A based epoxy resin and methacrylic acid and then dissolved in styeren monomer at the mole ratio of vinyl ester/styrene=1/2. The cure reaction, a free radical growth crosslinking copolymerization, was performed in the presence of various kind of additives. The additives were poly(methyl methacrylate) [PMMA], poly(vinyl acetate) [PVAC] having function of low profile additive and vinyl terminated butadiene-acrylonitrile cololymer [VTBN] having function of toughening agent and poly (styrene-ethylenebytylene-styrene) block copolymer[S-EB-S], poly(styrene-isoprene-styrene) block copolymerp[S-I-S] having function of thermoplastic elastomer. Those additives were characterized by compatibility and reactivity with vinyl ester resin. A series of experiments were performed to charcterize the cure kinetics and cure behaviors of vinyl ester resing with various kind of additives. Differential scanning calorimeter(DSC) was used to investigate the rate of cure, the degree of cure and the vitrification time. It was also used to determine kinetic parameters and physical property such as glass transition temperature. The rate of cure passed through a maximum and then decreased as the degree of cure increased. The maximum value became smaller and its position shifted toward a longer cure time when the cure temperature became lower. Such behavior is similar to the autocatalytic reactions which often appeared in the condensation reaction. The reaction mixture was not completely cuued under isothermal condition. And the final degree of cure increased along with cure temperatrue. It was due to the vitrification which occurs when the glass transition temperature approaches the cure temperature. Also the viscosity change with the cure time showed gelation point through which a liquid state transforms to rubbery state. Hence, the kinetic model was developed on the base of the phenomena of autocatalytic behavior, vitrification, a...