Radical‐initiated curing of unsaturated polyesters with styrene. role of polymer‐bound versus free tertiary amine accelerators

Abstract

AbstractPolyester prepolymers, prepared from maleic anhydride and diethylene glycol were cured with styrene using benzoyl peroxide as the catalyst and tertiary amines as accelerators. The effect of the accelerators on curing rates and efficiencies and resin properties was studied when the accelerators were chemically incorporated into the polyester prepolymer versus when the same accelerators were free. The accelerators employed were diethylaniline (1); N,N‐bis‐(2‐hydroxyethyl)aniline (2); N,N‐bis(2‐hydroxyethyl)propylamine (3); N,N‐bis(2‐hydroxyethyl)‐isopropylamine (4); N,N‐bis(2‐hydroxyethyl)butylamine (5); and dimethylaniline. The efficiency of the free accelerators decreased in the order dimethylaniline > 1 > 2 > 4 > 3 > 5. Each of the accelerators, 2–5, were significantly more efficient when incorporated into the polymer chain than when they were used free according to measured curing times, pot life, and gel times. Furthermore, the initiation energies for polymer‐bound accelerators 3, 4, and 5 are significantly lower than those obtained when these same accelerators are added free. Polymerbound accelerators 2, 3, 4, and 5 gave resins with higher Brinell's hardness, higher tensile strengths, higher softening points, and lower extractable fractions than were obtained for resins prepared with identical amounts of the corresponding free accelerators. Mechanisms to account for these results are suggested.