Jc. Lucas et al., CURE OF UNSATURATED POLYESTER RESINS .1. HEAT OF COPOLYMERIZATION ANDGLASS-TRANSITION TEMPERATURE, Polymer, 34(15), 1993, pp. 3216-3219
An unsaturated polyester (UP) resin based on maleic anhydride, isophth
alic acid, propylene glycol and dipropylene glycol was cured with vari
able amounts of styrene, using benzoyl peroxide as initiator. Differen
tial scanning calorimetry was used to determine heats of copolymerizat
ion, thermal mechanical analysis was employed to measure glass transit
ion temperatures and Fourier-transform infra-red spectroscopy was used
to follow the individual conversions of styrene (S) and UP double bon
ds (E). A heat of copolymerization equal to 66 kJ mol-1 was obtained,
independently of the initial S/E ratio. Taking the overall conversion
into account, the theoretical value for complete conversion of double
bonds was estimated as 69 kJ mol-1. These values are in good agreement
with literature values for the copolymerization of diethyl fumarate a
nd styrene (65-70 kJ mol-1) and styrene homopolymerization (68.5-73 kJ
mol-1). The maximum glass transition temperature (T(g)) was obtained
for formulations with S/E between 2 and 3, undergoing a near-azeotropi
c copolymerization. A single relationship between T(g) and overall con
version was obtained for different cure temperatures.