Internal stress of epoxy resin modified with acrylic core-shell particles containing functional groups prepared by seeded emulsion polymerization

In order to reduce the internal stress in a cured epoxy resin, submicrometer-sized poly(butyl acrylate) (PBA)/poly(methyl methacrylate) (PMMA) core-shell particles having cross-links were dispersed in the resin prior to curing. For the introduction of cross-links, monoethylene glycol dimethacrylate or glycidyl methacrylate monomer was copolymerized. Cross-links in the PBA core reduced the shrinkage of the cured epoxy resin, and cross-links at the PMMA shell produced a strong interaction with the epoxy matrix. The internal stress was reduced effectively by the introduction of cross-links.     

Dispersed acrylate rubber-modified epoxy resins for electronic encapsulation

A process was developed to incorporate stable dispersed acrylate rubber particles in an epoxy resin matrix which greatly reduces the stress of cured epoxy resins for electronic encapsulation application. The effect of the alkyl group of the acrylate monomer on the phase separation of resultant elastomers from epoxy resin was investigated. The dispersed acrylate rubbers effectively reduce the stress of cured epoxy resins by reducing the flexural modulus, while the glass transition temperature (T_g) was hardly depressed. Electronic devices encapsulated with the dispersed acrylate rubber-modified epoxy molding compounds have exhibited excellent resistance to the thermal shock cycling test and resulted in an extended device use life.     

Modification of epoxy resins with acrylic rubbers containing a pendant epoxy group

New acrylic rubbers with a pendant epoxy group were prepared by copolymerization of butyl acrylate (BA) with vinylbenzyl glycidyl ether (VBGE). The modification of an epoxy system (bisphenol-A diglycidyl ether/p,p′-diaminodiphenyl sulfone) with the acrylic rubbers was carried out in order to increase the toughness of the cured epoxy resin. The addition of 20 wt.-% of the copolymer containing 74% of BA and 26% of VBGE units resulted in a 30% increase in the fracture toughness (K_IC) of the cured resin at minimal expenses of strength and modulus of the resin. The modified epoxy resin had two-phase morphology in which the rubber particles with average diameter of 2 μm are dispersed in the epoxy matrix. The copolymer without the pendant epoxy group, prepared from BA and vinylbenzyl methoxyethyl ether, was ineffective as a modifier, indicating that the reaction of the pendant epoxide with the epoxy matrix resulted in good interfacial adhesion between the rubber particles and the matrix, and in the increased toughness. The epoxide-containing copolymers with 55 or 86% of BA units were also insufficient modifiers. The addition of the former yielded cured resins with homogeneous structure, whereas that of the latter resulted in macroscopic phase separation between the rubber and the epoxy resin.     

Particle morphology development in hybrid miniemulsion polymerization

Incompatibility between polymer phases resulting from hybrid minienulsion polymerization of acrylic monomers in the presence of alkyd resin leads to interesting particle morphologies. In this paper, morphology was deduced through crosscomparison of results from several forms of microscopy. For the combination of methyl methacrylate and alkyd, a derivative of core/shell morphology was observed through the combination of transmission electron microscopy, scanning electron microscopy, and spin diffusion NMR. A raspherry-like shell was found to form on the hybrid particle surface consisting of a full coverage of small (roughly 25 nm) polymethyl methacrylate spheres anchored to the particle surface through grafting with the alkyd core. Migration of the spheres to tha surface is thought to be induced by phase separation, and the size of the spheres precludes their origin from homoparticles from homogeneous nucleation. Homopolymethyl methacrylate particles were also detected in the particle distribution, resulting from the aqueous-phase initiator and hydrophilicity of methyl methacrylate monomer. For copolymer/alkyd systems (either methyl methacrylate/butyl acrylate/acrylic acid/alkyd or methyl methacrylate/butyl acrylate/alkyd), more traditional core/shell morphologies were observed with a lesser degree of homonucleated particles. A significantly different result was found in the combination of butyl acrylate and alkyd, resulting in a continuous particle-phase of polylbutyl acrylate and small internally dispersed island domains of alkyd. This is likely due to the lesser incompatibility between polybutyl acrylate and alkyd along with their similar hydrophobicity and glass transition temperatures. A higher degree of grafting between the alkyd and polybutyl acrylate also contributed to the compatibility between the two components, when compared to hybrid methyl methyl methacrylate/alkyd systems.     

Acoustic analysis of composite soft materials. I. Characterization of the core and boundary layer from compressibility of core/shell particles dispersed in poly(vinyl chloride)

The sound velocity of butyl acrylate rubber particles modified by poly(methyl methacrylate) in poly(vinyl chloride) was measured as a function of particle concentration. A model for estimating the adiabatic compressibility of the particle and the boundary layer was proposed. From the model, the partial specific adiabatic compressibility of the particles and the rubber core were evaluated. The adiabatic compressibility of the rubber core was estimated as 3.82 × 10⁻¹⁰ Pa⁻¹. The adiabatic compressibility of the poly(methyl methacrylate) shell is discussed based on the modified model. The study indicates that the shell, including the boundary layer between butyl rubber and poly(methyl methacrylate), is perturbed by the butyl acrylate molecules and is so soft as to be comparable to the rubber. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2089–2094, 2001     

Core-shell particles designed for toughening the epoxy resins. II. Core-shell-particle-toughened epoxy resins

The diglycidyl ether of bisphenol A–m-phenylene diamine (DGEBA–MPDA) epoxy resin was toughened with various sizes and amounts of reactive core-shell particles (CSP) with butyl acrylate (BA) as a core and methyl methacrylate (MMA) copolymerized with various concentration of glycidyl methacrylate (GMA) as a shell. Ethylene glycol dimethacrylate (EGDMA) was used to crosslink either core or shell. Among the variables of incorporated CSP indicated above, the optimal design was to obtain the maximum plastic flow of epoxy matrix surrounding the cavitated CSP during the fracture test. It could be achieved by maximizing the content of GMA in a shell-crosslinked CSP, the particle size, and the content of CSP in the epoxy resin without causing the large-scale coagulations. The incorporation of reactive CSP could also accelerate the curing reaction of epoxy resins. Besides, it was able to increase the glass transition temperature of epoxy resins if the particle size ≤0.25 μm and the dispersion was globally uniform. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2313–2322, 1998     

One‐component epoxy resin with imine as water‐initiated latent hardener: Improvement of the mechanical and adhesive properties by the addition of methacrylate copolymer

The effect of addition of methacrylate polymer into a one‐component epoxy resin, containing Epikote 828 and diimine as a water‐initiated hardener, was examined. Although the cured epoxy resin in the presence of methyl methacrylate–butyl acrylate (MMA–BA) copolymer was very brittle, the resin containing MMA–BA–[γ‐(methacryloxy)propyl]trimethoxysilane (TMSMA) copolymer showed good mechanical and adhesive properties. The adhesive strength of the cured epoxy resin containing MMA–BA–TMSMA copolymer was much higher than that without its polymer. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1943–1949, 2005     

粒径可控的聚丙烯酸丁酯/聚甲基丙烯酸甲酯核壳乳液的制备及表征

采用种子乳液聚合法制备了聚丙烯酸丁酯(PBA)乳液,然后通过第二单体甲基丙烯酸甲酯的预溶胀法聚合制备了PBA/聚甲基丙烯酸甲酯(PMMA)乳液,用激光散射粒度仪和透射电子显微镜对乳液粒径和结构进行了表征.结果表明,当乳化剂十二烷基硫酸钠质量分数为丙烯酸丁酯的1.5%时,可制备粒径为53.6 nm且分布窄的PBA种子乳液;通过调整补加乳化剂、单体与种子乳液的用量,可制得粒径为53.6～443.8 nm的一系列单分散PBA乳液;PBA/PMMA乳液具有完善的核壳结构,且在核壳两相间存在着一个过渡层.     

Rubber modification of unsaturated polyester resin with core–shell rubber particles: Effect of shell composition

Poly(butyl acrylate)/poly(vinyl acetate‐co‐methyl methacrylate) PBA/P(VAc‐co‐MMA) core–shell rubber particles with various shell compositions, i.e., VAc/MMA weight ratios, were used to toughen unsaturated polyester. The morphology and surface‐free energy of the rubber particles were determined by transmission electron microscopy (TEM) and contact angle measurements, respectively. The effect of shell structure on the dispersion state of rubber particles inside the unsaturated polyester resin was studied by scanning electron microscopy and TEM. Increasing MMA units in the shell changed the particle dispersion state from small agglomerates or globally well‐dispersed particles to large aggregates in the cured‐resin matrix. For the blends that contain 5 wt% rubber, the highest un‐notched impact toughness, stress‐intensity factor (K_IC), and fracture energy (G_IC) were observed for the blend containing PVAc shell particles. The results showed that by increasing the particle level from 5 to 10 wt%, the highest K_IC and G_IC values were obtained for the blend containing rubber particles with VAc/MMA (80/20 wt/wt) copolymer shell. The crack‐tip damage zone in the neat and rubber‐modified unsaturated polyester resins was observed by means of transmission optical microscopy. In addition, using PVAc shell particles exhibited a minimum reduction in the volume shrinkage and tensile properties of the rubber‐modified resin. POLYM. ENG. SCI., 52:1928–1937, 2012. © 2012 Society of Plastics Engineers     

Templating synthesis of non‐spherical polymer particles and their effect on the fracture toughness of an epoxy‐amine network

Flexible non‐spherical polymer particles were successfully produced via concentrated emulsion polymerization. LUDOX TM‐50 (colloidal silica, 50 wt% suspension in water) was introduced into the continuous phase to strengthen the template and inhibit monomer diffusion between the continuous and dispersed phases. The extent of non‐spherical shape was identified by the roundness value. Transmission electron micrographs showed that the higher the volume fraction of the dispersed phase became, the more non‐spherical were the poly(butyl acrylate) (PBA) particles. As an application, the effect of the non‐spherical particles on the fracture toughness of a modified epoxy‐amine network was studied. Scanning electron micrographs showed that the introduction of the non‐spherical PBA particles improved efficiently the impact strength of the cured epoxy resin. Copyright © 2006 Society of Chemical Industry     

Epoxy networks toughened by core–Shell particles: Influence of the particle structure and size on the rheological and mechanical properties

The core–shell particles considered were poly(butyl acrylate) core/epoxy groups functionalizing the poly(methyl methacrylate) shell. Physical and thermomechanical properties of benzyl dimethylamine (BDMA)‐catalyzed diglycidyl ether of bisphenol A (DGEBA)/dicyandiamine epoxy networks toughened with core–shell particles were studied. The blends were prepared under well‐defined processing conditions. The resulting properties were found to depend on the state of the dispersion of the particles in the prepolymer matrix before crosslinking. These particles were dispersed at different volume fractions in order to vary the interparticle distance. The relationships between the size of the core–shell particles and the level of toughening are reported. Static mechanical tests were performed in tension and compression modes on these core–shell polyepoxy blends. A slight decrease in the Young's modulus and an increase in the ability to plastic deformation were observed. Using linear fracture mechanics (LEFM), an improvement of the fracture properties (K_IC) was measured. By varying the volume fraction of core–shell particles, an optimum toughness improvement was found for an interparticle distance equal to 400 nm (with an average particle size of 600 nm). © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 849–858, 1999     

Synthesis and photopolymerization of acrylic acrylate copolymers

Acrylate‐functionalized copolymers were synthesized by the modification of poly(butyl acrylate‐co‐glycidyl methacrylate) (BA/GMA) and poly(butyl acrylate‐co‐methyl methacrylate‐co‐glycidyl methacrylate). ¹³C‐NMR analyses showed that no glycidyl methacrylate block longer than three monomer units was formed in the BA/GMA copolymer if the glycidyl methacrylate concentration was kept below 20 mol %. We chemically modified the copolymers by reacting the epoxy group with acrylic acid to yield polymers with various glass‐transition temperatures and functionalities. We studied the crosslinking reactions of these copolymers by differential scanning calorimetry to point out the effect of chain functionality on double‐bond reactivity. Films formed from acrylic acrylate copolymer precursors were finally cured under ultraviolet radiation. Network heterogeneities such as pendant chains and highly crosslinked microgel‐like regions greatly influenced the network structure and, therefore, its viscoelastic properties. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 753–763, 2002     

Compatibilizing effect of diglycidyl ether of bisphenol‐A in polymer blend system: Nylon 6 combined with poly(butyl acrylate) core and poly(methyl methacrylate) shell particles

A polymeric blend system of nylon 6 and a core–shell impact modifier was studied. The modifier had a poly(butyl acrylate) core and a poly(methyl methacrylate) (PMMA) shell compatibilized with an epoxy resin, diglycidyl ether of bisphenol‐A (DGEBA). The compatibilization of DGEBA is achieved by the reaction of its glycidyl group with the amine groups of nylon 6, and hydrogen bonds may be generated between the hydroxyl groups and the carbonyl groups on PMMA. The effect of compatibilization was verified by the dramatic increase in impact strength and the finer dispersing of the core–shell particles in the nylon 6 matrix. The effects of compatibilization on other properties of the blend, such as the tensile and rheological properties, were also investigated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 24–29, 2000     

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     

聚丙烯酸酯增韧改性环氧树脂的研究

以丙烯酸正丁酯(BA)、甲基丙烯酸甲酯(MMA)及甲基丙烯酸缩水甘油酯(GMA)为单体通过悬浮聚合反应合成了共聚物P(MMA-BA-GMA)简称(PMBG),采用傅里叶红外光谱仪、核磁共振波谱仪、凝胶渗透色谱仪对PMBG的结构与组成进行了表征。采用合成的PMBG对环氧树脂(DER663)/固化剂(HTP-305)体系进行增韧改性,研究了PMBG含量对体系力学性能和热性能的影响,并通过扫描电镜(SEM)对固化物断面的微观结构进行了分析。结果表明:PMBG改性后的环氧树脂冲击强度及断裂伸长率提高,当PMBG的质量分数为5%时,冲击强度显著提高,增韧改性效果最好,并且对体系的玻璃化转变温度(Tg)影响不大;共聚物在体系固化时发生微相分离,因而提高了环氧树脂的韧性。     

Internal stress of epoxy resin modified with acrylic polymers produced by in situ UV radiation polymerization

A cured epoxy resin is modified with polybutyl acrylate (A) and polyethyl acrylate (B) produced by in situ ultraviolet radiation polymerizations of their corresponding monomers in the epoxy resin, respectively, to reduce the internal stress. In the A system, a heterogeneous structure with submicron domains was formed. In the B system, however, the B mixed well with the epoxy matrix. In both systems, the internal stress was decreased by the modification. The glass transition temperature of the epoxy matrix decreased in the B system more than in the A system. The A-modified resin was superior to the B-modified resin in reducing the internal stress without decreasing the thermal resistance of epoxy resin.     

Synthesis and property behavior of dioctyl phthalate plasticized styrene–acrylate particles by Shirasu porous glass emulsification and subsequent suspension copolymerization

Two‐phase model styrene–acrylate copolymers were synthesized with a soft phase consisting of methyl acrylate, butyl acrylate, and butyl methacrylate. Besides the styrenic copolymers, copolymers containing a hard phase of methyl methacylate and methyl acrylate were also synthesized. Comonomer droplets with a narrow size distribution and fair uniformity were prepared using an SPG (Shirasu porous glass) membrane having pore size of 0.90 μm. After the single‐step SPG emulsion, the emulsion droplets were composed mainly of monomers, hydrophobic additives, and an oil‐soluble initiator, suspended in the aqueous phase containing a stabilizer and inhibitor. These were then transferred to a reactor, and subsequent suspension polymerization was carried out. Uniform copolymer particles with a mean diameter ranging from 3 to 7 μm, depending on the recipe, with a narrow particle size distribution and a coefficient of variation of about 10% were achieved. Based on the glass‐transition temperatures, as measured by differential scanning calorimetry, the resulting copolymer particles containing a soft phase of acrylate were better compatibilized with a hard phase of methyl methacrylate than with styrene with dioctyl phthalate (DOP) addition. Glass‐transition temperatures of poly(MMA‐co‐MA) particles were strongly affected by the composition drift in the copolymer caused by their substantial difference in reactivity ratios. Incorporation of DOP in the copolymer particles does not significantly affect the glass‐transition temperature of MMA‐ or MA‐containing copolymer particles, but it does affect the St‐containing copolymer and particle morphology of the copolymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3037–3050, 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     

Studies of the properties of a thermosetting epoxy modified with block copolymers

Poly[(n‐butyl acrylate)‐block‐poly(methyl methacrylate)‐co‐(glycidyl methacrylate)] (BMG) diblock copolymers incorporating an epoxy‐reactive functionality in one block have been synthesized and used as modifiers for the model epoxy resin E‐51 cured with 4,4′‐diaminodiphenyl methane (DDM). The properties and morphologies of the modified epoxy thermosets were investigated by dynamic mechanical analysis (DMA), impact testing and scanning electron microscopy (SEM). The results reveal that addition of the block copolymers leaves the glass transition temperatures of the blends relatively unchanged, with small decreases in the storage moduli at room temperature. The toughening effect is dependent on the chemical structures of the block copolymers and an increase in the impact strength by a factor of two was obtained by the addition of ‘relatively symmetrical’ block copolymers. Moreover, the impact test results are consistent with the morphologies of the fracture surfaces as evidenced by SEM. Copyright © 2005 Society of Chemical Industry     

环氧改性丙烯酸树脂的合成

以甲基丙烯酸甲酯、苯乙烯、丙烯酸酯等为单体，过氧化苯甲酰为引发剂，环氧树脂为改性剂，经聚合得到热固性环氧改性丙烯酸树脂。介绍了环氧改性丙烯酸树脂的合成及生产工艺过程，讨论了各种影响因素。