Effects of reactive low‐profile additives on the properties of cured unsaturated polyester resins. I. Volume shrinkage and internal pigmentability

The effects of reactive poly(methyl methacrylate) (PMMA) and poly(vinyl acetate)‐block‐PMMA as low‐profile additives (LPAs) on the volume shrinkage characteristics and internal pigmentability for low‐shrink unsaturated polyester (UP) resins during curing at 110°C were investigated. These reactive LPAs, which contained peroxide linkages in their backbones, were synthesized by suspension polymerization with polymeric peroxides as initiators. Depending on the LPA composition and molecular weight, the reactive LPAs led to a considerable volume reduction or even to a volume expansion after the curing of styrene (ST)/UP/LPA ternary systems; this was attributed mainly to the expansion effects of the LPAs on the ST‐crosslinked polyester microgel structures caused by the reduction in the cyclization reaction of the UP resin during curing as well as to the repulsive forces between the chain segments of UP and LPAs within the microgel structures. The experimental results were explained by an integrated approach of measurements for the static phase characteristics of the ST/UP/LPA system, reaction kinetics, cured sample morphology, and microvoid formation with differential scanning calorimetry, scanning electron microscopy, optical microscopy, and image analysis. With the aid of the Takayanagi mechanical model, the factors leading to both a good volume shrinkage control and acceptable internal pigmentability for the molded parts were also explored. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 264–275, 2005     

Effects of poly(methyl methacrylate)‐based low‐profile additives on the properties of cured unsaturated polyester resins. II. Volume shrinkage characteristics and internal pigmentability

The effects of three series of self‐synthesized poly(methyl methacrylate) (PMMA)‐based low‐profile additives (LPAs), including PMMA, poly(methyl methacrylate‐co‐butyl acrylate), and poly(methyl methacrylate‐co‐butyl acrylate‐co‐maleic anhydride) with different chemical structures and MWs on the volume shrinkage characteristics and internal pigmentability for low‐shrink unsaturated polyester (UP) resins during curing were investigated by an integrated approach of static phase characteristics of the ternary styrene (ST)/UP/LPA system, reaction kinetics, cured‐sample morphology, microvoid formation, and property measurements. The relative volume fraction of microvoids generated during the cure was controlled by the stiffness of the UP resin used, the compatibility of the uncured ST/UP/LPA systems, and the glass‐transition temperature of the LPAs used. On the basis of the Takayanagi mechanical model, the LPA mechanism on volume shrinkage control, which accounted for phase separation and microvoid formation, and factors leading to both a good volume shrinkage control and acceptable internal pigmentability for the molded parts are discussed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3388–3397, 2004     

Effects of reactive low‐profile additives on the volume shrinkage and internal pigmentability for low‐temperature cure of unsaturated polyester

The effects of reactive poly(vinyl acetate)‐block‐poly(methyl methacrylate) (PVAc‐b‐PMMA) and poly(vinyl acetate)‐block‐polystyrene (PVAc‐b‐PS) as low‐profile additives (LPA) on the volume shrinkage characteristics and internal pigmentability for low‐shrink unsaturated polyester resins (UP) during the cure at 30°C were investigated. These reactive LPAs, which contained peroxide linkages in their backbones, were synthesized by suspension polymerizations, using polymeric peroxides (PPO) as initiators. Depending on the LPA composition and molecular weight, the reactive LPA could lead to a reduction of cyclization reaction for UP resin during the cure, and would be favorable for the decrease of intrinsic polymerization shrinkage after the cure. The experimental results have been explained by an integrated approach of measurements for the static phase characteristics of the styrene (ST)/UP/LPA system, reaction kinetics, cured sample morphology, and microvoid formation by using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), optical microscopy (OM), and image analysis. Based on the Takayanagi mechanical model, factors leading to both a good volume shrinkage control and acceptable internal pigmentability for the molded parts have been explored. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 967–979, 2006     

Effects of poly(vinyl acetate) and poly(vinyl chloride‐ co‐vinyl acetate) low‐profile additives on properties of cured unsaturated polyester resins. I. Volume shrinkage characteristics and internal pigmentability

Three series of self‐synthesized poly(vinyl acetate)‐based low‐profile additives (LPAs) with different chemical structures and molecular weights, including poly(vinyl acetate), poly(vinyl chloride‐co‐vinyl acetate), and poly(vinyl chloride‐co‐vinyl acetate‐co‐maleic anhydride), were studied. Their effects on the volume shrinkage characteristics and internal pigmentability for low‐shrink unsaturated polyester (UP) resins during cure were investigated. The experimental results were examined with an integrated approach involving measurements of the static phase characteristics of the ternary styrene/UP/LPA system, the reaction kinetics, the cured sample morphology, and microvoid formation by using differential scanning calorimetry, scanning electron microscopy, optical microscopy, and image analysis. Based on the Takayanagi mechanical model, factors leading to both good volume shrinkage control and acceptable internal pigmentability for the molded parts were explored. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3336–3346, 2003     

Effects of poly(methyl methacrylate)‐based low‐profile additives on the properties of cured unsaturated polyester resins. I. Miscibility,curing behavior,and glass‐transition temperatures

The effects of three series of self‐synthesized poly(methyl methacrylate) (PMMA)‐based low‐profile additives (LPAs), including PMMA, poly(methyl methacrylate‐co‐butyl acrylate), and poly(methyl methacrylate‐co‐butyl acrylate‐co‐maleic anhydride), with different chemical structures and MWs on the miscibility, cured‐sample morphology, curing kinetics, and glass‐transition temperatures for styrene (ST)/unsaturated polyester (UP) resin/LPA ternary systems were investigated by group contribution methods, scanning electron microscopy, differential scanning calorimetry (DSC), and dynamic mechanical analysis, respectively. Before curing at room temperature, the degree of phase separation for the ST/UP/LPA systems was generally explainable by the calculated polarity difference per unit volume between the UP resin and LPA. During curing at 110°C, the compatibility of the ST/UP/LPA systems, as revealed by cured‐sample morphology, was judged from the relative magnitude of the DSC peak reaction rate and the broadness of the peak. On the basis of Takayanagi's mechanical models, the effects of LPA on the final cure conversion and the glass‐transition temperature in the major continuous phase of ST‐crosslinked polyester for the ST/UP/LPA systems was also examined. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3369–3387, 2004     

低收缩不饱和聚酯及其染色性研究

以甲基丙烯酸甲酯(MMA)和苯乙烯(St)为共聚单体,改变MMA和St的单体配比,用悬浮聚合方法合成了一系列共聚物,并以此作为低收缩添加剂(LPA),溶解于St中,加入到不饱和聚酯(UP)中进行固化反应。在此基础上,改变固化反应温度,LPA用量和种类,研究了LPA/UP体系固化后的体积收缩率、染色性能和力学性能。结果表明:MMA-St共聚物作为LPA,可以有效地降低UP固化后的体积收缩,并且保证了固化产物力学性能不降低和着色的均一性。     

Effect of co-promoter and secondary monomer on shrinkage control of unsaturated polyester (UP)/styrene (St)/low-profile additive (LPA) systems cured at low temperatures

The shrinkage of unsaturated polyester (UP)/styrene (St) resins cured at low temperatures can be reduced by the presence of low-profile additives (LPAs). It is believed that the reaction-induced phase separation and the polymerization shrinkage in both the LPA-rich and UP-rich phases result in the formation of microvoids, which partially compensates the resin shrinkage. The relative reaction rate in the two phases plays an important role in shrinkage control. In this study, secondary monomers [such as divinylbenzene (DVB) and trimethylopropane trimethacrylate (TMPTMA)] and a co-promoter, 2,4-pentandione (2,4-P), were added into the UP/St/LPA resin systems to investigate their effect on the shrinkage control of resins cured at low temperatures. Dilatometery results showed that the addition of both TMPTMA and 2,4-P resulted in an earlier volume expansion during curing and better shrinkage control. The phase separation, reaction kinetics, and viscosity changes in the LPA-rich and UP-rich phases during curing were also investigated. The results confirmed that the increased reaction rate in the LPA-rich phase led to an earlier formation of microvoids and, consequently, less volume shrinkage of the cured resin. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 738–749, 2001     

碱式硫酸镁晶须填充不饱和聚酯树脂体系的研究

利用碱式硫酸镁晶须填充不饱和聚酯（UP）树脂,对浇铸体的收缩率、冲击强度及阻燃性能进行了研究。结果表明,利用碱式硫酸镁晶须填充后,UP树脂的上述性能均有不同程度的改进。当晶须质量分数从0增至20％时,浇铸体的固化收缩率由0．8％降至0．32％;随着晶须含量的增加,冲击强度呈现先增加后降低的趋势,当晶须质量分数为15％时,冲击强度达最大值18．95kJ／m^2,比纯UP树脂提高了50．64％;另外,晶须可提高材料的阻燃性能,当加入质量分数30％的晶须后,氧指数提高到27．6％。     

Effects of chemical structure of polyurethane‐based low‐profile additives on the miscibility,curing behavior,volume shrinkage,glass transition temperatures,and mechanical properties for styrene/unsaturated polyester/low‐profile additive ternary systems. I: Miscibility,curing behavior,and volume shrinkage

The effects of chemical structure and molecular weight of three series of thermoplastic polyurethane‐based (PU) low‐profile additives (LPA) on the miscibility of styrene (ST)/unsaturated polyester (UP) resin/LPA ternary systems prior to reaction were investigated by using the Flory‐Huggins theory and group contribution methods. The reaction kinetics during the cure at 110°C and the cured sample morphology were also studied by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), respectively. The phase‐separation characteristics of ST/UP/LPA systems during the cure, as revealed by the cured‐sample morphology, and the DSC reaction‐rate profile, could be generally predicted by the calculated upper critical solution temperature for the uncured ST/UP/LPA systems. Finally, based on the measurements for volume change and microvoid formation, volume shrinkage characteristics for the cured ST/UP/LPA systems have been explored. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 543–557, 2000     

Toughened interpenetrating polymer network materials based on unsaturated polyester and epoxy

Simultaneous interpenetrating polymer networks (IPNs) based on epoxy (diglycidyl ether of bisphenol A) and unsaturated polyester (UP) were prepared by using m‐xylenediamine and benzoyl peroxide as curing agents. A single glass transition temperature for each IPN was observed with differential scanning calorimetry, which suggests good compatibility of epoxy and UP. This compatibility was further confirmed by the single damping peak of the rheometric dynamic spectroscopy. Curing behaviors were studied with dynamic differential scanning calorimetry, and the curing rates were measured with a Brookfield RTV viscometer. It was noted that an interlock between the two growing networks did exist and led to a retarded viscosity increase. However, the hydroxyl end groups in UP catalyzed the curing reaction of epoxy; in some IPNs where the hydroxyl concentration was high enough, such catalytic effect predominated the network interlock effect, leading to fast viscosity increases. In addition, the entanglement of the two interlocked networks played an important role in cracking energy absorption and reflected in a toughness improvement. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 585–592, 1999     

Effect of nanoclay on shrinkage control of low profile unsaturated polyester (UP) resin cured at room temperature

The addition of a small amount of nanoclay (1-3 wt%) can provide excellent volume shrinkage control of unsaturated polyester (UP)/styrene (St)/poly(vinyl acetate) (PVAc) systems cured at room temperature. PVAc serves as the low profile additive (LPA). In this study, both temperature-induced phase separation of the uncured resin mixture and transmission electron microscopy (TEM) of the cured sample revealed that nanoclay resided in the LPA-rich phase, leading to a higher reaction rate and earlier onset of micro-cracking in the LPA-rich phase or at the interface of the LPA-rich and UP-rich phases. Consequently, an earlier volume expansion during curing was observed in reactive dilatometry, resulting in better shrinkage control. On-line measurement of the composite thickness change during vacuum-infusion liquid composite molding [e.g. the Seemann Composite Resin Infusion Molding Process (SCRIMP)] further proved excellent volume shrinkage control of nanoclay filled systems, leading to a smoother composite surface.     

Relation between volumetric changes of unsaturated polyester resin and surface finish quality of fiberglass/unsaturated polyester composite panels

Resin dimensional changes, including cure shrinkage and thermal expansion, highly influence the surface finish quality of composite parts. Low profile additives (LPA) are commonly incorporated in unsaturated polyester (UP) resins to compensate for resin shrinkage and obtain a high quality surface finish. In this study, the dimensional change of an UP resin with different LPA contents was characterized. Both resin cure shrinkage and resin thermal expansion were measured. A simple methodology was then developed to estimate the surface finish quality of panels, manufactured by resin transfer molding (RTM), based on the prediction of part thickness variation during the process. Results show good agreement with the experimental investigations. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

The effect of molecular weight distribution on polyethylene film properties

Polymer molecular weight heterogeneity affects the rheological properties of polymer melts such as melt viscosity, fracture and die swell. These rheological properties affect the conversion of the polymer from the bulk resin state to its final usable form. In this particular study, the effect of molecular weight distribution on polyethylene blown film characteristics was studied. The effect of the molecular weight heterogeneity on the rheological characteristics of the polymer in the molten state and its effect on the film properties is presented. The properties studied included film gloss, haze, tear resistance and film impact strength. This study shows that broadening the molecular weight distribution increases haze and reduces film gloss. Further, it was shown that a linear relationship exists between film gloss and external haze. Both values are measures of surface irregularities in the film which are affected by the drawing characteristics of the polymer. A broader molecular weight distribution results in increased impact strength as measured by the Dart Drop Impact Test. This is, it is believed, a result of the increase in long chain branching of the higher molecular weight fractions of the polymer which cause a higher degree of molecular weight entanglement at the branch sites. In contrast the tear strength is reduced as the molecular weight distribution broadens because of the low molecular weight fraction in the broad spectrum material which tend to decrease resistance to tear.     

环氧改性不饱和聚酯及其固砂性能研究

针对普通不饱和聚酯(UP)作为油田固砂剂存在的固化后收缩率大、抗压强度偏低等缺点,研究了使用不同型号环氧(EP)树脂复配改性UP树脂的工艺.通过选择合适的固化体系固化后,树脂的抗压强度达到12 MPa以上,相比使用纯UP树脂时提高了70％以上.固结砂的抗压强度随EP树脂比例的增加而线性增加,但渗透率下降幅度在30％以内...     

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.     

Low‐profile mechanisms in a PVAc/polyester blend

The different steps associated with the curing of a PVAc/polyester blend are identified and correlated to the mechanism of shrinkage control in the presence of a low‐profile additive (LPA). Poly(vinyl acetate) (PVAc) is used as a LPA and is shown to induce a phase separation upon curing that leads to an interconnected globule morphology. This morphology strongly modifies the rheokinetics of the blend compared to that of the neat polyester resin. In particular, the presence of PVAc delays the cure kinetics and the gel time. A comparison between these delays, called shift times, demonstrates an increase in the gel conversion of polyester in the presence of PVAc. This, coupled to the thermal expansion of PVAc at the early stages of curing, contributes to the low‐profile effect. Microvoids in the LPA‐rich phase, which are believed to play a key role in the mechanism of shrinkage control, are efficient at the later stages of curing and during cooling and complete the low‐profile effect. However, it is also shown that the formation of microvoids may indirectly induce macroscopic voids that could be at the origin of pinholes at the surface of the parts molded with this material. POLYM. ENG. SCI. 46:303–313, 2006. © 2006 Society of Plastics Engineers     

Polycarbonate/acrylonitrile–styrene–acrylic elastomer terpolymer blends with enhanced interfacial adhesion and surface gloss

A blend of bisphenol A polycarbonate (PC) and an acrylonitrile–styrene–acrylic elastomer (ASA) terpolymer with high surface gloss and excellent interfacial properties was developed for automobile applications. Because PC and the styrene‐co‐acrylonitrile (SAN) copolymer that formed the matrix in the PC/ASA blend were not miscible, two different types of compatibilizers were examined to improve the compatibility of the blend. A diblock copolymer composed of tetramethyl polycarbonate and poly(methyl methacrylate) (PMMA) was more effective than PMMA in increasing interfacial adhesion between PC and SAN. The surface gloss of the PC/ASA blend was always lower than that of the pure ASA included in the blend because of PC existing at the surface of the injection‐molding specimen. The PC/ASA blend with optimum surface gloss and enhanced interfacial adhesion was developed through the control of the molecular weight of PC and the compatibilizer. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2097–2104, 2005     

Control of shrinkage and residual styrene of unsaturated polyester resins cured at low temperatures: I. Effect of curing agents

In low temperature molding processes, control of resin shrinkage and residual monomer is an important concern. The presence of low profile additives (LPAs) can reduce the shrinkage of unsaturated polyester (UP)/styrene (St) resins under proper processing conditions but may increase the residual styrene content. A systematic study was carried out to investigate the effect of the initiator system and reaction temperature on sample morphology, final resin conversion, and resin shrinkage of UP resins with LPA. It was found that the final conversion of the resin system could be improved by using dual initiators. The effect is more obvious at low temperatures. Volume shrinkage measurements of the resin system initiated with dual initiators revealed that good LPA performance was achieved at low (e.g. 35 °C) and high (e.g. 100 °C) temperatures but not at intermediate ones. This can be explained by how temperature affects phase separation, reaction kinetics in the LPA-rich and UP-rich phases, micro-void formation, and thermal expansion.     

活性端基聚氨酯橡胶改性不饱和聚酯树脂的研究(Ⅱ)

通过在不饱和聚酯树脂中加入活性端基聚氨酯橡胶来降低树脂的体积收缩.树脂固化前,橡胶与不饱和聚酯树脂相溶性好;树脂固化时橡胶中的不饱和双键反应可参与反应,并呈一定粒径的胶粒析出.本文研究了几种活性端基聚氨酯橡胶对不饱和聚酯树脂收缩控制的影响.     

低温固化PVAc／UP体系低收缩控制研究进展

本文介绍了国外关于不饱和聚酯树脂在低温固化时,ＬＰＡ对收缩控制影响的研究。