Curing kinetics of divinyl ester resins with styrene

Abstract

ABSTRACT:The curing reaction of a divinyl ester resin with different proportions of styrene-4, 20, and 40% by weight-was investigated by differential scanning calorimetry (DSC) using isothermal and dynamic modes. The different constraints on the reaction rate was globally considered, taken the reaction as divided in two regimens: below the vitrification regimen and during the vitrification regimen. Below the vitrification regimen, the autocatalytic model developed by Kamal was used to perform the analysis of the curing kinetics of divinyl ester resin with styrene. Experimental data from dynamic and isothermic runs, at a fixed composition, were simultaneously considered, while the actual temperature records (measured during the DSC runs) were also taken into account. The adjusted kinetic parameters took into account the gel effect on the radicals' termination rate and the structure constraints on the reactivity of pendant vinyls groups, present during this stage. During the vitrification stage, the diffusion control due to the low mobility of the reactive groups and molecules was incorporated into the overall rate constant according to the Rabinowitch model, which considers the two regimen contributions to the overall reaction rate kinetic. The Vogel-Fulcher relationship was adopted to express the temperature dependence of the rate constant during the vitrification stage. The method presented here has been satisfactorily applied to dynamic and isothermal curing reactions, allowing a simple and general kinetic expression useful in the design, optimization, and control of the processing of composites based on these thermoset polymers to be obtained.

Radiation and postirradiation crosslinking and structure of two unsaturated polyester resins

“…The difference in the type of saturated aromatic diacid seems to be the only cause for the shift of beginning of radiation crosslinking to higher doses and lower extents of both radiation and postirradiation reactions in resin A compared to resin I. Although compounds containing phenyl rings are usually included into polyester to increase its compatibility with styrene and reactivity of the resin [12], from our results, it is obvious that the outcome greatly depends on the type of the phthalate used. Large carboxylic groups tend to position themselves apart as far as possible, and so the best conformation of two orthophthalic carboxylic groups is the one in which carboxylic groups are on the opposite sides of phenyl ring.…”

“…This is one of the reasons why full conversion is impossible in isothermal conditions [11]. Although it is most often used, unpolar styrene is not a thermodynamically good solvent for relatively polar polyester [10,12,13], and so various saturated diacids or higher dialcohols are added in the preparation of polyesters to improve compatibility. Orthophthalic and isophthalic acids are the most often used diacids, because it is expected that their aromatic rings will increase compatibility with styrene, and the reactivity of the resin can be modified in that manner too, because polyester becomes less flexible and less reactive [14].…”

Properties of a Vinyl Ester Resin Modified with a Liquid Polymer

“…The cessation of reaction at values lower than full conversion is due to diffusion limitations and has been widely observed [20][21][22][23][24]. The fact that the mobility of small styrene molecules is less affected by the increase of crosslinking density has also been shown for a similar system, unsaturated polyester (UP), in a previous study [25].…”

Curing characteristics and mechanical properties of carbon fiber‐interlayered fabric composites based on a polyurethane matrix

“…18−20 Differential scanning calorimetry (DSC) has been widely used to follow the chemical conversion of reactants during curing due to the associated heat evolution resulting from the exothermic nature of the polymerization reactions. 21 Infrared spectroscopy has also used to follow directly the kinetics of reactions by monitoring the disappearance of the isocyanate groups and the formation of side-products. 22,23 Reaction injection molding (RIM) is a relatively new manufacturing technology for the production of polyurethane matrix composite.…”