Nano-phase structures and mechanical properties of epoxy/acryl triblock copolymer alloys

Phase structures and mechanical properties of epoxy/acryl triblock copolymer alloys using several curing agents were studied. PMMA-b-PnBA-b-PMMA triblock copolymers synthesized by living anionic polymerization were applied as the toughening modifiers for the epoxy resins. An aromatic amine, an acid anhydride and an anionic polymerization catalyst as curing agents resulted in macro-phase separation in the epoxy/triblock copolymer blends during the cure process. However, a phenol novolac as the curing agent created nano-phase structures in the epoxy blends. The size of the spherical phases or cylindrical phases was about 40 nm in diameter, and the main component in the nano-phases was the PnBA of the triblock copolymer. The fracture toughness of the epoxy/triblock copolymer alloys with the nano-cylindrical phases reached 2530 J/m². The fracture toughness was more than twenty fold relative to the unmodified epoxy resin, and was equivalent to the toughness of polycarbonates.     

Effect of the structure of curing agents modified by epoxidized oleic esters on the toughness of cured epoxy resins

The aim of this study was to determine the effect of the ester carbon chain length of curing agents modified by epoxidized oleic esters on the toughness of cured epoxy resins. An amine‐terminated prepolymer (i.e., curing agent G) was synthesized from a bisphenol A type liquid epoxy resin and triethylene tetramine. The toughening curing agents (G1 and G2) were prepared by reactions of epoxidized oleic methyl ester and epoxidized oleic capryl ester, respectively, with curing agent G. Fourier transform infrared spectrometry was used to characterize the chemical structure of the curing agents. The effects of the carbon chain length of the oleic ester group in the curing agents on the toughness and other performances of the curing epoxy resins were investigated by analysis of the Izod impact strength, tensile strength, elongation at break, thermal properties, and morphology of the fracture surfaces of the samples. The results denote that the toughness of the cured epoxy resins increased with the introduction of oleic esters into the curing agents without a loss of mechanical properties and that the toughness and thermal stability of the materials increased with increasing ester carbon chain length. The toughness enhancement was attributed to the flexibility of the end carbon chains and ester carbon chains of the oleic esters in the toughening curing agents. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of diphenylsilanediol modified epoxy resin and curing agent

A series of diphenylsilanediol modified epoxy resins and novel curing agents were synthesized. The modified epoxy resins were cured with regular curing agent diethylenetriamine (DETA); the curing agents were applied to cure unmodified diglycidyl ether of bisphenol A epoxy resin (DGEBA). The heat resistance, mechanical property, and toughness of all the curing products were investigated. The results showed that the application of modified resin and newly synthesized curing agents leads to curing products with lower thermal decomposition rate and only slightly decreased glass transition temperature (T_g), as well as improved tensile modulus and tensile strength. In particular, products cured with newly synthesized curing agents showed higher corresponding temperature to the maximum thermal decomposition rate, comparing with products of DGEBA cured by DETA. Scanning electron microscopy micro images proved that a ductile fracture happened on the cross sections of curing products obtained from modified epoxy resins and newly synthesized curing agents, indicating an effective toughening effect of silicon–oxygen bond.     

Photosynthesis and application of polyfunctional poly(n-butyl acrylate) elastomers for use in epoxy resin toughening

Medium molecular weight, novel polyfunctional elastomers, namely epoxy groups on poly(n-butylacrylate) (ETPnBA) and carboxyl groups on poly(n-butylacrylate) (CTPnBA) were photosynthesized for evaluation as the toughening agents in epoxy resins. The effect of the functionality and kind of functional group of the elastomers upon the toughening of epoxy resins modified with these rubbery copolymers as a second phase was investigated by tensile tests, impact test, and electron microscopy. It was found that there exists an optimum functionality of elastomers for maximum impact resistance in epoxy groups (ETPnBA) and carboxyl groups (CTPnBA) copolymer-modified systems. Studies on morphology of the modified epoxy resin system indicated that the better toughening effects of multiple distribution of particle sizes. The aggregation of rubber particles occurring in carboxyl group CTPnBA modified epoxy resin caused a loss of toughness.     

环氧树脂增韧改性研究进展

介绍了几种增韧改性环氧树脂的方法,包括互穿网络增韧、液晶聚合物增韧、核壳结构增韧、嵌段共聚物增韧及柔性固化剂增韧,分析了其机理,综述了上述改性方法的国内外研究进展。     

Novel amphiphilic block copolymer modifiers based on chain‐extended polyester for improved toughness of epoxy resins

Novel amphiphilic block copolymer modifiers based on chain‐extended polyester for improved toughness of epoxy resins were synthesized by attaching polyols having different structures and compatibilities with a dianhydride chain‐extender. Used polyols in this research were polytetrahydrofuran as miscible and hydroxyl‐terminated polybutadiene as immiscible segment. Generated carboxyl groups will be prepolymerized with an excess of epoxy resin to exclusively form epoxy groups between the polyol spacer. Resulting morphologies in the prepared diglycidyl ether of bisphenol‐A‐based epoxy thermosets cured with dicyandiamide and urea were strongly dependent on the initial parameters of the block copolymerization process. Changing the dianhydride concentration as well as relation between miscible and immiscible polyol spacer showed various particle sizes including unimodal and bimodal distributions. The best mechanical performance in terms of fracture toughness (K_1C) could be achieved with bimodal particle size distributions indicating synergistic effects between the different particle sizes in the range of 0.1–7 μm. POLYM. ENG. SCI., 59:E216–E223, 2019. © 2018 Society of Plastics Engineers     

Studies on isotactic poly(phenyl glycidyl ether)‐modified epoxy resins. II. Toughening of epoxy resins

A semicrystalline polymer, isotactic poly(phenyl glycidyl ether) (i‐PPGE) was used as a modifier for epoxy resin; 1,8‐Diamino‐p‐methane (MNDA) and 4,4′‐Diamino diphenyl sulfone (DDS) were used as curing agents. In the MNDA‐cured resins, the dispersed phase were spherical particles with diameters in the range of 0.5–1.0 μm when the resin was blended with 5 phr i‐PPGE. In the DDS‐cured resins, the particle size distribution of the dispersed phase was much wider. The difference was traced back to the reactivity of the curing agent and the different regimes used for curing. Through dynamic mechanical analysis, it was found that in the MNDA‐cured systems, i‐PPGE had a lower crystallinity than in the DDS‐cured system. In spite of the remarkable difference in the morphology and microstructure of the modified resins cured with these two curing agents, the toughening effects of i‐PPGE were similar for these resins. The critical stress intensity factor (K_IC) was increased by 54% and 53%, respectively, for the resins cured by DDS and by MNDA, blending with 5 phr of the toughner. i‐PPGE was comparable with the classical toughners carboxyl‐terminated butadiene‐acrylonitrile copolymers in effectiveness of toughening the epoxy resin. An advantage of i‐PPGE was that the modulus and the glass‐transition temperature of the resin were less affected. However, this modifier caused the flexural strength to decrease somewhat. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1223–1232, 2002; DOI 10.1002/app.10445     

先进复合材料基体树脂的增韧研究

通过4种聚醚酰亚胺(PEI)PID、PIM、PIP和PIB改性3种热固性树脂(环氧、氰酸酯以及双马来酰亚胺树脂)的研究,讨论了PEI结构、用量、分子质量以及固化剂用量等因素对改性体系的相结构以及力学性能的影响,结果表明控制相结构是增韧基体树脂的关键因素,对基体树脂增韧的研究有指导意义。对不同的热固性树脂体系需采用不同的结构、配方和固化工艺。PIP改性环氧体系呈现的双连续相结构,PEI改性双马来酰亚胺体系,PEI质量分数为5%时呈现了PIM分散粒子相结构,PEI质量分数为10%时呈现了双连续相结构而PEI质量分数大于15%时呈现了相反转结构,PIP分子质量为18 000或20 000时呈现了双连续相结构,而对于PIP改性氰酸酯体系高PIP分子质量较低的呈现双连续相结构,该体系在120℃固化6 h呈现相反转结构,而150℃或180℃固化形成双连续相结构,双连续相结构增韧效果明显。     

Enhancement of antifillet cracking performance for no‐flow underfill by toughening method

Fillet cracking of no‐flow underfill in a flip‐chip device during a reliability test such as thermal shock or thermal cycling has been a serious reliability problem. The effect of toughening agents and modification of epoxy on fillet cracking of no‐flow underfill was investigated. The best epoxy formulation and the appropriate loading level of toughening agent regarding the antifillet cracking performance were found. In the case where the epoxy was modified with polysiloxanes, the second‐phase particle with a submicron particle size was formed and the size of the particle depended on the kind of toughening agent. The morphology was observed by a scanning electron microscopy and confirmed by a dynamic mechanical analyzer measurement. The physical properties such as the fracture toughness, flexual modulus, coefficient of thermal expansion, and adhesion were measured, and the liquid–liquid thermal shock (LLTS) test under ?55 to 125°C was performed with different formulations. One of the formulations toughened by amine/epoxy‐terminated polysiloxane, which has higher die shear strength, lower modulus, and higher toughness, passed 1000 cycles of the LLTS test. In order to obtain a high reliable no‐flow underfill, the physical properties of the no‐flow underfill should be well controlled and balanced. Finally, a correlation between physical properties of the no‐flow underfill and the fillet cracking capability for those approaches was discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2439–2449, 2003     

Effect of crosslink density on fracture behavior of model epoxies containing block copolymer nanoparticles

Model diglycidyl ether of bisphenol-A based epoxy resins containing well-dispersed 15 nm block copolymer (BCP) nanoparticles were prepared to study the effect of matrix crosslink density on their fracture behavior. The crosslink density of the model epoxies was varied via the controlled epoxy thermoset technology and estimated experimentally. As expected, it was found that the fracture toughness of the BCP-toughened epoxy is strongly influenced by the crosslink density of the epoxy matrix, with higher toughenability for lower crosslink density epoxies. Key operative toughening mechanisms of the above model BCP-toughened epoxies were found to be nanoparticle cavitation-induced matrix shear banding for the low crosslink density epoxies. The toughening effect from BCP nanoparticles was also compared with core-shell rubber-toughened epoxies having different levels of crosslink density. The usefulness of the present findings for designing toughened thermosetting materials with desirable properties is discussed.     

Non-reactive and reactive block copolymers for toughening of UV-cured epoxy coating

Reactive and non-reactive diblock copolymers based on polyethylene oxide (PEO) and a poly(glycidyl methacrylate) (PGMA, reactive) or polystyrene (non-reactive) block, respectively, are prepared via ATRP and those are incorporated into a cycloaliphatic epoxy matrix. Crosslinking of the matrix is then performed by cationic UV curing, producing modified thermosets. ¹H NMR and SEC measurements are carried out and used to analyze the composition, the molar mass and dispersity of the prepared block copolymers. The viscoelastic properties and morphology of the modified epoxy are determined using DMTA and FESEM, respectively. The addition of 4 and 8 wt% of the reactive PEO-b-PGMA block copolymer into epoxy resin has only minor effects on the glass transition temperature, T_g. The reactive homopolymer PGMA significantly increases and the non-reactive block copolymer PEO-b-PS slightly decreases the glass transition temperature of the epoxy matrix. The non-reactive block copolymer PEO-b-PS causes a little decrease in T_g values. The measurement of the critical stress factor, K_IC, shows that the fracture toughness of the composite materials is enhanced by inclusion of the non-reactive block copolymer. In contrary, the reactive block copolymer has negative effect on the fracture toughness especially in case of short PEO block. FESEM micrographs studies on the fracture surfaces sustain the microphase separation and the increase in surface roughness in the toughened samples, indicating more energy was dissipated.     

中温固化环氧复合材料的颗粒增韧技术

介绍了几种复合材料的颗粒增韧方法,通过分析比较选择了热塑性树脂颗粒层间增韧和基体增韧的方法对中温固化环氧树脂进行改进,着重研究了增韧剂用量对增韧效果的影响。     

环氧树脂的改性研究进展

介绍了环氧树脂的特性和环氧树脂改性的主要趋势-提高环氧树脂的韧性,分别论述了橡胶类弹性体增韧环氧树脂、热塑性塑料增韧环氧树脂、热致液晶聚合物增韧环氧树脂、柔性链段固化剂增韧环氧树脂、无机纳米材料改性环氧树脂以及互穿网络(IPN)结构的环氧树脂体系等环氧树脂增韧改性的方法.同时,对聚氨酯的特性、用聚氨酯改性环氧树脂的六种方法以及互穿聚合物网络技术,进行了较为详细的介绍,并分析了改性环氧树脂目前存在的技术问题.     

Toughening by nanostructure

Block copolymer modified epoxy resins have generated significant interest since it was demonstrated that the combination could lead to nanostructured thermosets through self-assembly. Over moderate to high polymer concentration the system behaves as expected for a block copolymer in a solvent selective for one block. Two types of copolymers have been studied: non-reactive and reactive modifiers. Morphologies such as copolymer vesicle and spherical/wormlike micelles can be formed under the appropriate conditions. The enhancement of the modified thermosets' mechanical properties depends on the morphology adopted by the polymers. Besides improving mechanical properties, the morphology was found to also have an effect on the glass transition in the studied systems. In this review we collect the available data on the block copolymers used to fabricate nanostructured epoxy resins and critically appraise the properties reported.     

改性环氧树脂的固化与稀释增韧研究

研究了改性环氧树脂的固化、稀释增韧效果。探讨了不同种类的固化剂及活性稀释剂对改性环氧树脂的冲击强度、拉伸强度及维卡软化点等性能的影响。研究结果表明,在固化剂9032和活性稀释剂的共同作用下,能制得室温固化型增韧环氧树脂,且其具有较高的强度和耐热性。     

环氧树脂增韧增强改性研究进展

综述了国内环氧树脂增韧增强改性的最新研究进展,详细介绍了纳米粒子、液体橡胶、热塑性树脂、原位聚合物、液晶聚合物、核壳聚合物、大分子固化剂和膨胀型单体增韧增强环氧树脂的一些重要研究现状。对它们的增韧增强环氧树脂的优缺点和机理进行了探讨。     

聚硫橡胶对环氧树脂固化动力学及力学强度的影响

用红外光谱分析了在环氧树脂中加入聚硫橡胶的固化及增韧过程,通过差示扫描量热法研究了增韧体系的反应动力学,探讨了聚硫橡胶用量对固化产物力学强度的影响,并对试样断口形貌进行了扫描电镜观察。结果表明,聚硫橡胶的加入降低了环氧树脂的表观活化能而没有改变反应级数,使得固化反应的总放热量减少、放热过程更加平均。聚硫橡胶对环氧树脂的增韧效果明显,二者通过化学键结合,韧性撕裂的冲击断面形貌验证了这种活性增韧。当聚硫橡胶用量为30份(质量)时,环氧树脂固化物的冲击强度可达到未增韧者的896%。     

Synthesis and properties of copolymer epoxy resins prepared from copolymerization of bisphenol A,epichlorohydrin, and liquefied Dendrocalamus latiflorus

Dendrocalamus latiflorus Munro (ma bamboo) was liquefied in phenol and polyhydric alcohol (polyethylene glycol/glycerol cosolvent) with H₂SO₄ as catalyst. Liquefied bamboos reacted with bisphenol A and epichlorohydrin were then employed to prepare copolymer epoxy resins. The curing property and thermal property of copolymer epoxy resins were investigated. The results showed that copolymer epoxy resins could cure at room temperature after the hardener was added, and its curing process was an exothermic reaction. Comparison showed that copolymer epoxy resins prepared with phenol‐liquefied bamboo as raw material had higher heat released than those prepared with polyhydric alcohol‐liquefied bamboo during curing. The DSC analysis showed that heat treatment could enhance the crosslinking of copolymer epoxy resins cured at room temperature. However, resins prepared with polyhydric alcohol‐liquefied bamboo had a lower glass transition temperature. The TGA analysis showed that resins prepared with phenol‐liquefied bamboo had better thermal stability. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The effect of urea bond on structure and properties of toughened epoxy resins

In this article, modified poly(oxypropylene) diamines were synthesized and used as a new flexible curing agent for epoxy resins. The purpose of modification is to introduce urea group into epoxy resins. The reaction rate, mechanical properties, glass transition temperature (T_g), and fracture surface morphology of these toughened epoxy resins were investigated. Because of urea groups, the reactivity between poly(oxypropylene) diamines and epoxy resins was significantly enhanced. At the same time, the urea groups resulted in strong intersegmental hydrogen bonding between modified poly(oxypropylene) chain, which reduced the compatibility of poly(oxypropylene) with epoxy resins and resulted in higher T_g of toughened epoxy. The modified sample had tensile strength of 15.8 MPa and ultimate elongation of 118% at room temperature, whereas the unmodified sample only had 6.2 MPa and 70%. The scanning electron microscope analysis showed that the modified system displayed tough fracture feature, whereas the unmodified system showed typical brittle fracture. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

One-component epoxy adhesive for repair of cell phone board

The development of a one-component epoxy adhesive for cell phone board repair was described. The most important goal of this study is to obtain long storage stability in conjunction with the curing reaction process at a relatively low temperature of 95 °C. Bisphenol-A type, bisphenol-F type, and NBR-based epoxy resins were used as the basic resins. Dicyandiamide (DICY) was used as a curing agent, and 2-methylimidazole (2MI) was used as an accelerator. 2MI was encapsulated using a copolymer of methacrylic acid and dodecyl methacrylate to achieve latent curing performance. After mixing the epoxy resin with DICY and encapsulated 2MI, this curing system showed excellent storage stability with almost no viscosity increase for 2 months at 20 °C, and full curing was achieved at 95 °C for 50 min. We determined the optimum formulation of the epoxy adhesive for adhesion of a cell phone board after the measurement of physical properties.