Effect of styrene on properties of vinyl ester resins,I

The paper describes the effect of styrene on the properties of bis(methacryloxy) derivatives of epoxy resins (vinyl ester resins). The styrene concentration in the resin was systematically varied between 20–60 wt.-%. The curing characteristics of vinyl ester resins changed only marginally on dilution with styrene. Dilution with styrene resulted in a decrease in tensile modulus and increase in elongation of neat resin castings and glass fibre reinforced laminates. The glass transition temperature of laminates was determined by dynamic mechanical analysis and was found to decrease with increasing styrene content.     

Vinyl ester resins, 3. Effect of ethyl methacrylate on thermal and mechanical properties

This paper describes the effect of ethyl methacrylate (EMA) on the thermal and mechanical properties of glass fibre-reinforced laminates of vinyl ester resins derived from diglycidyl ether of bisphenol-A and methacrylic acid. The thermal stability and the curing characteristic of the resins were investigated by thermogravimetric analysis and differential scanning calorimetry. The glass transition temperature of the laminates decreased with increase in EMA content. Dilution of vinyl ester resin with EMA resulted in a decrease in flexural strength and flexural modulus of the laminates.     

Effect of α-methyl styrene on curing behaviour and interfacial properties of glass fibre-reinforced vinyl ester resins

The curing behaviour of bismethacryloyl derivative of diglycidyl ether of bisphenol A (vinyl ester VE resin) containing styrene and α-methyl styrene (MS) as reactive diluents was studied. Delayed curing was observed in samples containing increasing proportions of MS. Interfacial shear stress of untreated as well as γ-methacryloyloxy-propyl trimethoxy silane (MTS) treated, glass fibre-reinforced VE resin composites were measured by single fibre technique. In comparison to untreated glass fibres, a 30 – 50% increase in interfacial shear stress was observed in composites based on MTS treated glass fibres. Addition of up to 5 wt.-% MS to VE resin did not affect the interfacial shear strength (ILSS). This behaviour was observed by using ILSS measurement of both glass fabric-reinforced composites as well as single fibre specimens. Further increase in MS to 15 wt.-% resulted in an increase in ILSS and bending stiffness as well as flexural strength.     

Curing kinetics of divinyl ester resins with styrene

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. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1044–1053, 1999     

Vinyl ester resin modified with silicone‐based additives: II. Flammability properties

Silicone‐based additives have been used as fire retardants for thermoplastics, presenting the advantages of improving processing and impact resistance of the polymers. In this work we used three different silicone‐based additives as modifiers of a thermoset based on a vinyl ester resin. The additives are fine powders made up of about 50 wt % ultra high molecular weight polydimethylsiloxane and 50 wt % silica. The differences between them are the functional groups inserted on the additives and the size and size distribution of the particles. The additives were dispersed in resin containing 35 wt % of styrene. For curing the mixture a conventional catalyst and initiator were used and the reaction was carried out in two ways, differing in the curing temperature, the post curing temperature, and the time, and in the addition of dimethylaniline (DMA) as a promoter of the polyaddition reaction. The samples were characterized by thermogravimetric analyses and swelling experiments. The fire retardances of the samples were evaluated by the determination of the flash‐ignition, self‐ignition, and pyrolysis temperatures (ASTM D1919–91a), and of the oxygen index (ASTM D‐2863–91). The results obtained showed that the silicone‐based additives and the methods used in the preparation of the modified resin influence the flash‐ignition, self‐ignition, and pyrolysis temperatures, but not the oxygen index. Samples cured by different methods present different network characteristics, which influence their thermal decomposition. The volatile species produced by thermal decomposition may be a combination of inert and active species. The network structure may influence only the inert fraction of the volatiles, not the combustibles. These volatile inert species (smoke‐black, water vapor, carbon dioxide, etc.) probably dilute the combustibles in the solid and in the gaseous phase, increasing the flash‐ignition temperature of the samples. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 644–649, 2006     

MMA对乙烯基酯树脂及其复合材料性能的影响

通过粘度分析和力学性能、阻燃性能测试,研究了以甲基丙烯酸甲酯(MMA)作活性稀释剂的乙烯基酯树脂的流变性能及其对复合材料性能的影响。结果表明:常温下MMA能有效降低乙烯基酯树脂的粘度,20~40℃下,添加量>30%时,树脂体系的粘度在450 mPa.s以内,可应用于RTM工艺;固化后该复合材料的拉伸、弯曲强度、抗冲击性能、层间剪切强度和阻燃性能优异,可应用于高性能阻燃型复合材料构件的制备。     

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.     

Vinyl resins with retention properties for heavy metal ions

Summary Resins with carboxylic pendant groups were synthesized. The resins were characterized by elemental analyses and FT-IR spectroscopy, and the ability to bind copper (II) and uranium (VI) by batch method at different pH was studied. Uranium(VI) is adsorbed at pH 3 and pH 4 above 88%. The maximum capacity of load for uranium(VI) is higher than IRA-400, a commercial resin. Elution assays for Cu(II) and U(VI) from the loaded resins with sulfuric acid and sodium carbonate were also carried out.     

Resacetophenone-formaldehyde resins,II. Chelation ion-exchange properties

The resacetophenone-formaldehyde (RAP-F) resin showed to be a selective chelating ion-exchange resin for certain metal ions. A batch equilibration method was used in the study of the selectivity of metal ion uptake. The method involved the measurement of distribution of a given metal ion between an aqueous solution and the resin. The study was carried out over a wide pH range and in media of various ionic strengths.     

Curing kinetics and thermal properties of vinyl ester resins

The curing kinetics of dimethacrylate-based vinyl ester resins were studied by scanning and isothermal DSC, gel time studies, and by DMTA. The rate of polymerization was raised by increased methyl ethyl ketone peroxide (MEKP) concentration but the cocatalyst, cobalt octoate, retarded the reaction rate, except at very low concentrations. By contrast, the gel time was reduced for all increases in either peroxide or cobalt concentration. This contradictory behavior was explained by a kinetic scheme in which the cobalt species play a dual role of catalyzing the formation of radicals from MEKP and of destroying the primary and polymeric radicals. The scanning DSC curves exhibited multiple peaks as observed by other workers, but in the present work, these peaks were attributed to the individual influence of temperature on each of fundamental reaction steps in the free radical polymerization. Physical aging appeared to occur during the isothermal polymerization of samples cured below the “fully cured” glass transition temperature (T_g). For these undercured materials, the difference between the DSC T_g and the isothermal curing temperature was approximately 11°C. Dynamic mechanical analysis of a partially cured sample exhibited anomalous behavior caused by the reinitiation of cure of the sample during the DMTA experiment. For partially cured resins, the DSC T_g increased monotonically with the degree of cure, and this dependence was fitted to an equation related to the Couchman and DiBenedetto equations. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 769–781, 1997     

Effect of percolation on electrical and dielectric properties of acrylonitrile butadiene styrene/graphite composite

Prelocalized Acrylonitrile Butadiene Styrene/graphite composites were prepared by hot compression molding technique. The increased conductivity with increase of graphite content exhibits percolation phenomenon. The current–voltage characteristics are found to change from nonlinear to linear above the percolation threshold. A positive temperature coefficient of resistance is observed in these composites, and this effect is more pronounced in samples having graphite concentration near percolation threshold. The dielectric constant was found to increase slowly up to the percolation concentration and beyond it a sudden increase in its value is observed. The dissipation factor exhibits maxima in the vicinity of percolation threshold. The dielectric properties are discussed in terms of the interfacial Maxwell‐Wagner effects. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Control of volume shrinkage and residual styrene of unsaturated polyester resins cured at low temperatures. II. Effect of comonomer

The effect of a comonomer, methyl methacrylate (MMA), on volume shrinkage and residual styrene content of an unsaturated polyester (UP) resin with low profile additives (LPAs) cured at low temperature was investigated by an integrated reaction kinetics-morphology-property analysis. MMA affects the volume shrinkage and residual styrene content differently depending on MMA to styrene (St) CC bond molar ratio. At low MMA/St ratio, residual styrene decreases and the volume shrinkage of the resin system remains unchanged. At high MMA/St ratio, residual styrene can be substantially reduced, but the resin system suffers poor volume shrinkage control. Reactivity of the comonomer MMA and its compatibility to other components in the resin system can explain the observed results. A series of Seemann composites resin infusion molding process (SCRIMP) were conducted to study the relationship among materials, processing, and properties of molded composites in low temperature curing processes.     

Vinyl ester and unsaturated polyester resins in contact with different chemicals: Dynamic mechanical behavior

A prior study has shown for a vinyl ester resin that the adequate choice of the curing conditions becomes completely necessary to reach the maximum glass transition temperature. In the same study, the variations produced in the dynamic mechanical properties because of exposure to different solvents were related to the chemical structure of both the resin and solvent. This investigation was undertaken in an attempt to analyze the effects of solvent exposure on the viscoelastic properties of resins currently used for applications in which the resin is kept in contact with the solvents. Several vinyl ester resins as well as various unsaturated polyester resins immersed in different liquids were investigated. The influence of exposure time to the solvent as well as that for the temperature were characterized using dynamic mechanical analysis. The chemical structure of the resin was found to be determinant in the changes produced after solvent exposure. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 21–28, 1999     

Vinyl ester resin modified with silicone‐based additives. I. Mechanical properties

Silicone‐based additives have been used as fire retardants for thermoplastics and present the advantages of improving the processing and impact resistance of the polymers. In this study, we used three different silicone‐based additives as modifiers of a vinyl ester resin. The additives were fine powders made up of about 50 wt % polydimethylsiloxane and 50 wt % silica. The differences among them were the functional groups inserted in the polymer chains and the size and size distribution of the particles. The additives were dispersed in resin containing 35 wt % styrene. To cure the mixture, a conventional catalyst and initiator were used, and the reaction was carried out in three ways, which differed in the curing temperature, postcuring temperature, time, and addition of dimethylaniline (DMA) as a promoter of the polyaddition reaction. Dynamic mechanical analysis showed that the phase behavior of the resulting composites depended strongly on the curing conditions. The flexural modulus of composites containing 5 wt % additive was lower than that for the cured resin. The impact resistance of the composites also depended on the curing conditions but not on the composition or size of the particle of the additive. The fracture morphologies of specimens subjected to impact resistance tests were different for samples cured in the presence or in the absence of DMA, which suggested that it influenced the mechanism of network formation. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Effect of diffusional limitations on the gelation of cyanate ester resins

The effect of diffusion control-induced unequal reactivities of functional groups on the gelation of cyanate ester resins was analyzed. By introducing differentiation into the recursive approach, a gelation model was developed to calculate the gel points of systems under diffusional limitations. Modeling results for a Zn-catalyzed cyanate resin show that the unequal reactivities have a significant effect on the gel point and the gelation is delayed to a higher conversion. However, other factors, which may include localized reactions and cycle formation, also contribute to the delay of gelation. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 115–125, 1997     

聚三唑酯树脂的合成及其性能

通过酯化反应合成丁二酸二炔丙醇酯(DPS)、间苯二甲酸二炔丙醇酯(DPIP)、对苯二甲酸二炔丙醇酯(DPP),与三官能团叠氮化合物(TAMTMB)反应,制备了3种热固性聚三唑酯(PTAE)树脂,研究了树脂的加工特性、固化行为、树脂固化物的力学性能,制备和表征了T700单向碳纤维增强PTAE树脂复合材料。结果表明,PTAE树脂具有良好的加工性能,可在较低温度(80℃)下固化;固化后的PTAE树脂的玻璃化转变温度(Tg)受主链结构影响,3种树脂的Tg均高于140℃,浇铸体弯曲强度高于170 MPa,T700单向纤维增强PTAE树脂复合材料的常温弯曲强度高于1500 MPa。     

Thermal aging of plasticized PVC. II. Effect of plasticizer loss on electrical and mechanical properties

The change of mechanical properties was followed during thermal aging at 85, 95, 105, and 120°C of the 10 PVC–didecylphthalate extrudates studied in the first part of this paper, but also of four new samples differing only by the plasticizer concentration. For these latter samples, the change of dielectric properties was also studied. It appears that the dielectric properties are essentially the function of the plasticizer concentration whatever is the initial concentration or aging conditions. In contrast, the mechanical properties vary in a more complex way and cannot be predicted by a simple physical model. It is suggested that, among other factors, the depth distribution of plasticizer can play an important role.     

Effect of structure on mechanical properties of vinyl ester resins and their glass fiber‐reinforced composites

The article describes the effect of structure of vinyl ester resins (VE) on the mechanical properties of neat sheets as well as glass fabric‐reinforced composites. Different samples of VE were prepared by reacting ester of hexahydrophthalic anhydride (ER) and methacrylic acid (MAA) (1 : 1 molar ratio) followed by reaction of monomethacrylate terminated epoxy resin with glutaric (E) or adipic (F) or sebacic acid (G) (2 : 1 molar ratio). The neat VE were diluted with styrene and sheets were fabricated by using a glass mold. A significant reduction in the mechanical properties was observed by increasing the methylene content of resin backbone (i.e., sample E to G). Glass fabric‐reinforced composites were fabricated by vacuum assisted resin transfer molding (VARTM) technique. Resin content in the laminates was 50 ± 5 wt %. Increase in the number of methylene groups in the vinyl ester resin (i.e., increasing the bridge length) did not show any significant effect on limiting oxygen index (LOI) value (21 ± 1) of the laminates but tensile strength, tensile modulus, flexural strength, and flexural modulus all increased though these values are significantly lower than observed in laminates based on resin B. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Use of allyl‐functional benzoxazine monomers as replacement for styrene in vinyl ester resins

New vinyl ester systems are prepared using allyl‐functional benzoxazine monomers, 3‐allyl‐6‐methyl‐3,4‐dihydro‐2H‐benzo[e][1,3]oxazine (pC‐ala) or bis(3‐allyl‐3,4‐dihydro‐2H‐benzo[e][1,3]oxazin‐6‐yl)methane (BF‐ala), as reactive diluents for vinyl ester resins derived from an epoxy resin, diglycidyl ether of bisphenol A, instead of using styrene. Different initiators are used to investigate the copolymerization of allyl function from pC‐ala with vinyl function from vinyl ester resin prepolymer. The temperature dependence of viscosity is studied to demonstrate the retention of processability of the new vinyl ester resins. Dynamic mechanical and thermogravimetric analyses are used to investigate the dynamic mechanical properties and thermal stability of the new resins. Copyright © 2012 Society of Chemical Industry     

Preparation and properties of novel resins based on cyanate ester and hyperbranched polysiloxane

A novel kind of high performance cyanate ester (CE) resins was developed by copolymerizing 2, 2′-bis(4-cyanatophenyl) iso-propylidene with hyperbranched polysiloxane (HBPSi). HBPSi was synthesized through the hydrolysis of 3-(trimethoxysilyl)propyl methacrylate. The effect of the stoichiometry between CE and HBPSi on the structure and property of modified CE resins was investigated systematically. Results show that the incorporation of HBPSi can not only effectively promote the curing reaction of CE, but also increase the apparent free volume fraction of the cured network, and thus brings significant influence on the performances of the resultant resin. The impact strength of modified CE resin with 15 wt% of HBPSi is 19.6 KJ/m², which is more than 2 times of that of pure CE resin. In addition, the toughened CE resin also exhibits better thermal stability, dielectric property and moisture resistance than original CE resin. The novel modified CE system successfully overcomes the key shortcomings of original CE resin, importantly, this work demonstrates that the new method proposed in this work for modifying CE resin by hyperbranched polymers maybe a right road to be used for developing high performance thermosetting resins.