Effects of low-profile additives on the curing reaction of unsaturated polyester resins

The effect of low-profile additives (LPA), i.e., poly(vinyl acetate) (PVAC) and poly(methyl methacrylate) (PMMA), on the curing reaction of unsaturated polyester (UPE) resins was studied by gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The curing reaction profiles were determined by DSC, while GPC was used to investigate the variation of the sizes of microgel particles during the early stage of curing reaction in UPE–styrene resins. The DSC experimental results indicated that the curing reaction rate decreased as the concentration of LPA increased. At a fixed LPA concentration, the curing reaction rate was slower for resins mixed with LPA possessing worse compatibility with UPE resins. During the early stage of curing reaction, the size and structure of the UPE microgels formation strongly depended on the concentration of LPA and also on the compatibility of the components in the curing system. The experimental results of this study revealed that the concentration of LPA and the compatibility of LPA with UPE resins had a strong influence on the polyester microgel formation and the curing behavior. © 1995 John Wiley & Sons, Inc.     

Monitoring the cure of unsaturated polyester resins by pressure DSC and FTIR-PLC

A high pressure differential scanning calorimeter (DSC) and a Fourier transform infrared (FTIR) spectrometer with a prism liquid cell (PLC) were used to monitor the reaction kinetics of styrene-unsaturated polyester resins at elevated curing temperatures and pressures. The thermal method is easy to perform but provides only an overall reaction exotherm. The spectroscopic method can detect the detailed reaction mechanism of copolymerizations. It is, however, less quantitative and the calculation is much more time-consuming compared to the thermal analysis. Reactions of two unsaturated polyester resins with different molecular structure were measured by these two methods. Results showed that applying cure pressure on unsaturated polyester resins reduced the reaction rate but increased the final conversion. The styrene reaction was enhanced more than the polyester reaction at high curing temperatures.     

Waterborne unsaturated polyester resins

The transformation of solvent soluble unsaturated polyester resins into resins able to form stable water dispersion is presented in this paper. The methods of modification are discussed, consisting of the introduction of polar hydrophilic groups such as carboxylic and sulfonic ones (sodium 5‐sulfonatoisophthalic acid) into the resin molecule, which ensure good tolerance with water. Instead of styrene, glycerol monoethers of allyl alcohol and unsaturated fatty alcohols were used as reactive built‐in crosslinking monomers for resin modification. The influence of the resin composition and method of synthesis on the dispersion stability and properties of photocurable lacquer coatings obtained from the waterborne resins were investigated.     

不饱和聚酯树脂微乳液的研究(Ⅰ)不饱和聚酯树脂的微乳化

合成了不同磺酸盐含量的三种不饱和聚酯，通过拟三元相图分析磺酸盐含量、苯乙烯、不同正构醇和水组成的体系对微乳区域的影响。研究结果表明，磺酸盐不饱和聚酯同苯乙烯互溶的前提下，磺酸盐含量越大，其微乳液增溶的水量越大；磺酸盐含量一定时，苯乙烯含量越小，其微乳液增溶的水量越大；正构醇质量分数为在2％～10％范围内，其微乳液增溶的水量最多；三种醇相比较，正丁醇体系的微乳区是W／O型向O／W型过渡的连续区域，正丙醇体系的O／W型微乳液区明显不同于正丁醇体系，正戊醇体系不能形成水包油型的微乳区。     

The effect of free radical initiators and fillers on the cure of unsaturated polyester resins

The heats of polymerization for two unsaturated polyester resins are presented using two free radical initiator systems. The first was 1% methyl ethyl ketone peroxide/0.2% cobalt octoate (12%) and the second was 2% benzoyl peroxide/0.2% dimethylanyline. The heats of reaction were measured using a differential scanning calorimeter under dynamic and isothermal modes. Infrared spectroscopy and exotherm peak temperature test were employed to further establish the differences between the initiators and to determine the influence of three fillers (sand, clay, and fly-ash) on the cure reaction.     

Control of gel time and exotherm behaviour during cure of unsaturated polyester resins

The curing behaviour of an unsaturated polyester resin has been studied by gel time and pseudo‐adiabatic exotherm measurements. The gel time corresponded closely with the initial rise in exotherm temperature. Incorporation of tert‐butyl catechol inhibitor increased the gel time in a linear fashion and the exotherm was similarly delayed. An increase in the concentrations of initiator (either methyl ethyl ketone peroxide or acetyl acetone peroxide) or cobalt octoate accelerator decreased the gel time in a reciprocal fashion and increased the rate of polymerization. These results are fitted to a theoretical model for inhibition and initiation. © 2001 Society of Chemical Industry     

Effects of resin chemistry on redox polymerization of unsaturated polyester resins

Unsaturated polyester resins are the most widely used thermoset resins in the composite industry. In this study, three well‐defined unsaturated polyester resins were used. These resins have similar number‐average molecular weights, and they have different numbers of C?C bonds per molecule. The reaction kinetics of unsaturated polyester resins was studied using a differential scanning calorimeter (DSC) and a Fourier transform infrared (FTIR) spectrometer. The glass transition temperature of the isothermally cured resin was also measured. Trapped radicals were observed in the cured polyester resin from electron spin resonance (ESR) spectroscopy. Considering the diffusion‐limitation effect, a simple kinetic model was developed to simulate the reaction rate and conversion profiles of polyester vinylene and styrene vinyl groups, as well as the total reaction rate and conversion. Experimental results from DSC and FTIR measurements compare favorably with the model prediction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 211–227, 2002; DOI 10.1002/app.10317     

不饱和聚酯树脂的粗化工艺

介绍了不饱和聚酯树脂的粗化工艺流程及各工艺规范通过正交试验确定了最佳粗化工艺条件：粗化液的体积分数为400ml／L温度为80～85℃,粗化时间为20min。讨论了粗化液用量、粗化温度和时间对粗化效果和镀层质量的影响经检测表明,该金属镀层与基体结合力良好目前该工艺已应用于生产中。     

Effects of post-curing of unsaturated polyester resins in various media

Experimental studies were performed on the effects of postcuring of' styrenated, unsaturated polyesters in nitrogen gas, water or its vapor, hexane vapor, dimethyl sulfoxide (DMSO), and dirnethyl formamide (DMF) all at 100°C It was found that, nitrogen gas and water are inactive, hexane acts as a chain transfer agent, and DMF and DMSO behave as solvents which extract residual styrene monomer and anhydrides from the resins. Post-treatment in inert media can result in further reaction leading to more complete cure as free radicals and residual monomer continue to react. The post-curing reaction is a radical copolymerization. Further condepgation polymerisation does not occur. Post-curing in, hexane vapor1eads to a transfer of the active sites from the radicals to the hexane and to no further radical polymerization.     

Viscoelastic investigation on the cure of unsaturated polyester coatings

The change of the viscoelastic behavior of an unsaturated polyester resin during curing was followed by a vibrometric technique, while the portion converted to gel in applied films was also determined by means of extraction with a solvent. Some relationship between the viscoelastic properties and the amount gelling has been found to exist. The dependency of the curing rate of polyesters on the concentration of initiator as well as accelerator seemed not to be unity. A marked delay in cure has been observed in the region of low concentrations of initiator and accelerator.     

Rheology of unsaturated polyester resins. II. Thickening behavior of unsaturated polyester and vinyl ester resins

The rheological properties of mixtures of unsaturated polyester resin and viscosity thickener were determined as thickening progressed. Two commercially available resins were used: (1) general purpose unsaturated polyester resin (Ashland Chemical, Aropol 7030), and (2) vinyl ester resin (Dow Chemical, XD-7608.05). As thickening agent, a magnesium oxide (MgO) paste dispersed in styrene monomer was used. No fillers, pigments, or other additives were used. During thickening, the following measurements were also made: (1) acid number by titration and (2) molecular weights by gel permeation chromatography (GPC). For the Ashland Chemical polyester resin, it was found that, over a period of 300 h, the titration method indicated that the number-average molecular weight (M _n) increased by a factor of 2 and the weight-average molecular weight (M _w) increased by a factor of 3. The GPC measurements, however, showed that M _n increased very little whereas M _w increased by a factor of about 2. Over the same period, the viscosity of the Ashland Chemical polyester resin increased from 0.9 N·s/m² (9 P) to 10⁴ N·s/m² (10⁵ P), and the viscosity of the Dow Chemical vinyl ester resin increased from 0.7 N·s/m² (7 P) to 2 × 10³ N·s/m² (2 × 10⁴ P). Such a large increase in viscosity cannot be explained by the existing molecular theory, in view of the fact that the molecular weights increased relatively little. We speculate that the exceedingly large increase in viscosity during thickening is attributable primarily to ionic associations between the carboxylic anions and the magnesium ions, rather than to the formation of chain branching suggested in the literature. It was found further that mixtures of polyester resins and viscosity thickener exhibit normal stress effects, increasing with thickening time and following the behavior of a second-order fluid when the first normal stress difference was plotted against shear rate. Interestingly enough, however, plots of first normal stress difference vs. shear stress yield a correlation which becomes independent of thickening time. An explanation is offered to the correlation obtained.     

Process cure monitoring of unsaturated polyester resins,vinyl ester resins,and gel coats by Raman spectroscopy

The curing process of unsaturated polyester resins, vinyl ester resins, and gel coats was studied by using a process Raman spectrometer, equipped with a remote fiber‐optic probe. The resins were cured and Raman spectra were recorded during the curing reaction. The spectral changes were identified and, from the intensities, the cure process could be monitored. Gel times given by the resin suppliers correlated well with the Raman results. It could also be seen that the curing process continues for a long time, up to several weeks. Postcuring will finally complete the curing process. White and lightly colored gel coats could easily be monitored by Raman spectroscopy, but fluorescent problems were encountered with heavily colored pigments. The curing of laminates containing 50–70 wt % glass fiber mat could also be followed by Raman spectroscopy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1285–1292, 2004     

不饱和聚酯增韧技术进展及机理探讨

简单介绍不饱和聚酯树脂增韧的研究进展及基本理论,并分别探讨不饱和聚酯树脂的液体橡胶增韧、互穿网络增韧和刚性粒子增韧的增韧机理。     

Effects of poly(vinyl acetate) and poly(methyl methacrylate) low-profile additives on the curing of unsaturated polyester resins. II. Morphological changes during cure

The effects of two low-profile additives (LPA), poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA), on the morphological changes during the cure of unsaturated polyester (UP) resins at 110°C were investigated by an approach of integrated reaction kinetics-morphology-phase separation measurements by using a differential scanning calorimeter (DSC), scanning electron microscopy (SEM), optical microscopy (OM), and a low-angle laser light-scattering appartus (LALLS). For the UP resins cured at 110°C, adding LPA could facilitate the phase separation between LPA and crosslinked UP phases early in the reaction, and discrete microgel particles were thus allowed to be identified throughout the reaction. Microvoids and microcracks responsible for the volume shrinkage control could also be observed evidently at the later stage of reaction under SEM. Depending on the types of LPA and the initial molar ratios of styrene to polyester C?C bonds, the morphological changes during the cure varied considerably. The progress of microstructure formation during reaction has been presented. Static ternary phase characteristics for the styrene–UP–LPA system at 25°C have also been employed to elucidate the resulting morphology during the cure in both the continuous and the dispersed phases. © 1995 John Wiley & Sons, Inc.     

Infrared study of the cure of unsaturated polyester

The infrared spectra of unsaturated polyesters in process of cure have been taken of samples free from unreacted protion. Styrene and polyester fractions in the curing polyester films were assessed from comparison of the band intensities at 695 and 740 cm.^?1. The styrene fraction in curing films was found to increase as cure proceeded, and the delayed curing was seen to be accompanied by a build-up of films of lower styrene content. The differences between samples observed in the mechanical behavior were considered attributable for the most part to the difference in styrene content.     

Improving glass transition temperature of unsaturated polyester thermosets: Conventional unsaturated polyester resins

Highly crosslinkable unsaturated polyester resins (UPR) have attracted many interests in the application as reinforced matrix materials. Here, we present a systematical study of the influence of different curing conditions and styrene concentrations on resin viscosity and dynamic-mechanical properties of the thermoset. The pure maleic Palapreg® P18-03 was selected as model UPR because of its broad industrial use. By applying newly developed thermal curing profiles (without thermal initiators) and by raising the styrene content, the T_g of the network could be increased up to 206/215°C (1/10 Hz). For the first time, a fast curable UPR based on propylene glycol and neopentyl glycol with a T_g of up to 215°C is described. A partial substitution of problematic styrene with methylmethacrylate, tert-butylacrylate, and maleic anhydride (MA) was studied as well. MA leads to significantly improved resin reactivity. A resin containing 42 wt% styrene and 8 wt% MA yields thermosets with remarkably improved mechanical properties and with a narrower glass transition range compared to the original P18-03.     

Rheology of unsaturated polyester resins. III. Effects of filler and low-profile additive on the thickening behavior of unsaturated polyester resin

An investigation was made of the rheological behavior of unsaturated polyester resin during thickening in the presence of filler or low-profile additive alone and, also, in the presence of both filler and low-profile additive. For the study, two different types of filler (CaCO₃ and clay) and two different types of low-profile additive (PMMA and PVAc) were evaluated. Compared to the resin/thickener system, the resin/filler/thickener system exhibits shear-thinning behavior as thickening progresses, and gives rise to smaller normal stress effects. On the other hand, the resin/low-profile additive/thickener system exhibits two distinct Newtonian regimes in the viscosity-shear stress curves and gives rise to larger normal stress effects. The viscosity behavior of the resin/filler/low-profile additive/thickener system was found to be very similar to that of the resin/low-profile additive/thickener system. In all cases, when the first normal stress difference was plotted against the shear stress, a correlation was obtained which was independent of thickening period. This behavior was exactly the same as for thickening polyester resin alone, as discussed in Part II of this series.     

Rheology of unsaturated polyester resins. I. Effects of filler and low-profile additive on the rheological behavior of unsaturated polyester resin

Measurements were taken of the bulk rheological properties of concentrated suspensions of particulates in unsaturated polyester resins, using a cone-and-plate rheometer. The particulates used were clay, calcium carbonate, and milled glass fiber. With clay and milled glass fibers, shear-thinning behavior of suspensions was observed at low shear rates or low shear stresses as the concentration of particulates was increased, whereas concentrated suspensions of calcium carbonate exhibited Newtonian behavior over the range of shear stresses or shear rates investigated. The cone-and-plate rheometer was also used for measurements of the bulk rheological properties of various mixtures of polyester resin and low-profile additives. For low-profile additives, solutions, in styrene, of poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA) were used. It was found that the bulk viscosities of all mixtures of polyester resin and PVAc solution lie between those of the individual components, whereas the bulk viscosities of some mixtures of polyester resin and PMMA solution go through a minimum and a maximum, depending on the composition of the mixture. While all mixtures of polyester resin and PVAc solution exhibited negligible normal stress, some mixtures of polyester resin and PMMA solution exhibited noticeable normal stresses. It should be mentioned that polyester resin follows Newtonian behavior. It turned out that all mixtures of polyester resin and PVAc solution exhibited clear, homogeneous solutions, whereas mixtures of polyester resin and PMMA solution exhibited optical heterogeneity, i.e., turbidity. When polyethylene powders were used as low-profile additives, suspensions of polyester resin and polyethylene powders exhibited negative values of normal stress as the concentrations of suspension reached a critical value. When both filler and low-profile additive were put together in polyester resin, the rheological behavior became quite complex, indicating that some interactions exist between the filler and the low-profile additive.     

Curing reaction of saturated aliphatic polyester modified unsaturated polyester resins

Two series of unsaturated polyesters (UPE from isophthalic acid, fumaric acid, and propylene glycol) were prepared. In series-A resins, UPEs wee thickened with isocyanate-terminated saturated aliphatic polyestes, i.e., an isocyanate-terminated polycaprolactone diol (PE-di-OL), through reaction of the isocyanate group with the hydroxyl group of the UPE. In series-B resins, the UPEs were mixed with saturated aliphatic polyesters i.e., PE-di-OL. The curing reaction of these two series of UPEs with styrene was studied by using differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). The DSC data show that for a fixed PE-di-OL molecular weight, the curing reaction rate of series-A UPE is faster than that of series-B UPE. The variation of microgel size during curing ws studied by GPC. These results revealed that microgel formation has a great effect on the kinetics of cure for the unsaturated polyester-styrene system. The curing of these two series of UPEs is found to strongly depend on the compatibility of the components in the curing system.     

Prediction of gel-time in the cure of unsaturated polyester resins: Phenomenological modeling vs. statistical analysis

A series of kinetic and rheological measurements were carried out using a differential scanning calorimeter (DSC) and a Rheometrics Dynamic Analyzer (RDA). The effects of temperature, inhibitor level, initiator level, and initiator type on the curing of unsaturated polyester resins were investigated. Two models based on the free radical polymerization mechanism were developed for predicting the time to reach liquid-solid transition. These models adapted a concept that gelation occurred at a critical radical concentration. The applicability of these models was compared to that of a statistical analysis.