Effect of crosslinking density on the viscoelastic properties of unsaturated polyesters

Abstract

Viscoelastic properties of unsaturated polyesters were investigated in the glass‐rubber transition region in relation to the temperature dependence of specific volume. Polyesters which are homologous with respect to crosslinking density were prepared by using mixtures of succinic and fumaric acid as the dibasic acid component. The temperature dependence of the specific volume was determined by refractive index measurement, the specific refractivity being assumed to be independent of temperature. The temperature dispersion of dynamic viscoelasticity was measured at a constant frequency. Results are summarized as follows. Specific volume and glass temperature are linearly related to the logarithm of crosslinking density. The thermal expansion coefficient and steepness of viscoelastic dispersion decrease with increasing crosslinking density. Fractional free volume and expansion coefficient of free volume, both of which were calculated by WLF equation, are in good agreement with the temperature dependence of specific volume. The results indicate that the effect of crosslinking is largely attributable to the change in amount and distribution of free volume in polymer networks.

Thermal, viscoelastic, and mechanical properties of DCPD-containing polymers

“…Finally, the obtained DCPD-modified unsaturated polyesters were chemically modified in order to prepare novel DCPD- The DMA results and the results obtained based on mechanical studies of cured DCPD-containing polymers are depicted in Table 2. The results show that the tgd max , transition breadth and the temperature of the tgd max of each polymer is determined by the cross-linking density, as is the rubbery modulus [19][20][21]. An increase in the cross-linking density (m e ) is connected with the decrease in molecular mobility of the polymer chains and thus with the increase of the glass transition temperature (described as maximum of the temperature of tgd max ), the storage modulus (E 0 20 C ), flexural modulus at bending (E mod ), hardness and decrease of deflection at maximum force (e-F max ).…”

Silicon‐Containing Cycloaliphatic Epoxy Resins with Systematically Varied Functionalities: Synthesis and Structure/Property Relationships

“…For thermosetting resins, the crosslinking density is correlated with glass transition temperature (T g ) according to [23] …”

Modified unsaturated polyester resins synthesized from poly(ethylene terephthalate) waste, 1. Synthesis and curing characteristics

“…So, the net result of this variation is an increase of the number of curable double bonds along the unsaturated polyester chains. It is well known [25][26][27][28][29][30] that the curing reaction gets faster and more exothermic with increasing double bond intensity per each unsaturated polyester chain. Horie et al [27] studied the effect of the chemical structure of unsaturated polyester resins on their curing behavior and reported that the final degree of curing under isothermal conditions increases remarkably with increasing amount of fumarate/maleate unsaturations per polyester chain.…”