Unsaturated polyester resins kinetics

Whereas McGee [188] did not verify any effect of particulate fillers (i.e., glass, calcium carbonate, and aluminum) on the reaction kinetics, Lem and Han [185], working with calcium carbonate and clay in an unsaturated polyester resin, concluded that the reaction rate increases by increasing the filler content. 

Several researchers have modeled the cure kinetics of thermosetting resins in the past, including an unsaturated polyester resin [8], epoxies [9-11], and bismaleimide [5], As an example, a graphite/BMI material, IM6/3100, was modeled in [5] using... 

Differential scanning calorimetry (DSC) was used in investigating the curing kinetics of the unsaturated polyester resin. For the study, we used a DuPont 1090 Thermal Analyzer, equipped with a 910 DSC Module. Indium was used for temperature and calorimetric calibrations, following the procedure described in the operating meinual of the instrximent. The experimental procedure employed is very similar to that described in the literature (8-13) cind we have discussed it elsewhere (14). 

It is interesting to note that Eq. (28) is sufficiently general and describes well the kinetics of curing of fundamentally different systems with phase segregation like, for example, unsaturated polyester resin. This is shown in Fig. 32 where there are compared experimental data of Ref. [129] and curves calculated by Eq. (28). 

Similar plots can be obtained from kinetic data of unsaturated polyester resins (24, 25). This behavior is independent of the identity of the nitrogen substituents of the amine or the monomer. Previous publications from this laboratory have pointed out that the a+ value of the amine ring substituent yielding maximum reactivity, i.e., minimum polymerization (or cure) time, occurs at approximately -0.2 in the cases examined (26-29). The optimum value is anticipated to be fairly insensitive to the type of monomer and experimental conditions. 

For a free radical polymerisation system, an unsaturated polyester resin, an auto-acceleration was observed close to the onset of vitrification. To model the curing kinetics for these systems, including the mobility-controlled regions, a specific diffusion control model will need to be incorporated in a mechanistic reaction model. The heat capacity and the mobility factor can still give information about how vitrification is occurring, and how it is related to the auto-acceleration effect. 

Table 10.1 Cure kinetic parameters for an epoxy resin (epon862/w curing agent) and for an unsaturated polyester resin with 2 wt% MEKP...

Vilas JL, Laza JM, Garay MT, Rodriguez M, Leon LM. Unsaturated polyester resins cure Kinetic, rheologic, and mechanical-dynamical analysis. I. Cure kinetics by DSC and TSR. Journal of Applied Polymer Science, 2001 79(3) 447 57. DOI http //dx.doi.org/10.1002/1097-4628(20010118)79 3<447 AID-APP70>3.0.CO 2-M. 

An internal-reflection prism cell has been used for reaction-kinetics measurement of styrene-unsaturated polyester resins at elevated curing temperatures and pressures [133]. Other researchers have estimated the cross-linking efficiency in methyl methacrylate-ethylene glycol dimethacrylate copolymer networks by laser Raman spectroscopy [134], while recently... 

Kicko-Walczak, E., Kinetics of thermal decomposition of unsaturated polyester resins with reduced flammability, J. Appl. Polym. Set, 88 (13), pp2851-2857 (2003). 

The curing reaction of unsaturated polyester resin involves the copolymerization of unsaturated polyester and styrene in the presence of an organic initiator. Like any other free-radical polymerization (e.g., bulk polymerization of methyl methacrylate), the organic initiator first decomposes to form an initiator radical [/ ], which will then react with unsaturated polyester to form a polyester radical [ ] and with styrene monomer to form a styrene radical [S ]. Therefore, the curing reaction can be treated by a free-radical polymerization approach. Below, we describe briefly the mechanistic kinetic model for unsaturated polyester (Han and Lee 1987a, 1987b Stevenson 1986). 

Since anhydrides are much more reactive than carboxylic acids, reaction kinetics is controlled by the second step. The scope and apphcations of this reaction are the same as direct polyesterification but are practically limited to the synthesis of unsaturated polyesters and alkyd resins from phtliahc and maleic anhydrides (see Sections 2.4.2.1 and 2.4.23). 

Because of all these minor components (e.g., catalysts and inhibitors, added to major ones) the cure of vinyl ester resins is very complex, involving many competitive reactions. There are some new variables to account for, such as the inhibitor and initiator concentrations and induction time. Several papers [81,96,200,201] use the mechanistic approach, claiming that the phenomenological models do not explicitly include these facts, resulting in a new parameter characterization after each change in resin formulation [96]. Despite these arguments, the phenomenological approach is the most widely used and is based on an autocatalytic model which has been successfully applied to epoxy resins. Many authors [30,34,74,199,202,203] proposed the Equation 2.30 to describe the cure kinetic of unsaturated polyesters ... 

The model that best represents the curing kinetics of thermosetting resins such as epoxy and unsaturated polyester, and as reflected in a TTT-diagram, is a diffusion modified Kamal-Sourour reaction model [9, 14, 13]. To model autocatalytic cure kinetics, the model can be applied as... 

Curing Kinetics of Unsaturated Polyester and Vinyl Ester Resins... 

Because of the high degree of unsaturation present in the polyester resin, the fully cured system was highly crosslinked. Assuming typical polymerization kinetics apply to these systems, elementary kinetics analysis indicates that the reaction order... 

The synthesis of unsaturated polyesters has been studied by several workers. Such materials have been used in the formation of cross-linked resins, particularly where reinforced polymers are to be used. The kinetics of the thermo-setting process has been investigated by differential scanning calorimetry. Photocrosslinkable unsaturated polyesters containing pendant chalconyl and cinnamylidenemalomyl moieties have also been produced. Such polymers were found not to exhibit any pronounced photofastness. Several other studies have described the synthesis and characterization both of the prepolymer, and the unsaturated resin. ... 

Several applications of hyperbranched polymers as precursors for synthesis of crosslinked materials have been reported [91-97] but systematic studies of crosslinking kinetics, gelation, network formation and network properties are still missing. These studies include application of hyperbranched aliphatic polyesters as hydroxy group containing precursors in alkyd resins by which the hardness of alkyd films was improved [94], Several studies involved the modification of hyperbranched polyesters to introduce polymerizable unsaturated C=C double bonds (maleate or acrylic groups). A crosslinked network was formed by free-radical homopolymerization or copolymerization. 

The cure reaction in polyester gel coat systems makes them particularly useful model coatings materials since the cure kinetics can be studied by several analytical techniques. The initiation of cure in polyester gel coat resins begins with the decomposition of hydroperoxide (MEKP is predominately hydroperoxide) and the subsequent copolymerization of styrene with the unsaturated groups, either fumarate or maleate, incorporated into the resin backbone. ... 

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