Synthesis and performance of flexible epoxy resin with long alkyl side chains via click reaction

Epoxy resin is a thermosetting polymer with excellent performance and wide application. However, it suffers from low toughness and high brittleness because of its high crosslink density. To overcome these disadvantages, this study synthesizes a toughened, flexible, and hydrophobic epoxy resin (DGEBDBP) by introducing a flexible segment into the polymer network via a thiol-ene click reaction. The cured flexible epoxy resin is obtained by mixing E44, DGEBDBP, and polyamide curing agents of varying contents. The long alkyl side chains significantly improve the mechanical properties and hydrophobicity of the cured epoxy resin. The sample containing 75% DGEBDBP and 25% E44 achieve the highest breaking elongation that was nine times that of pure E44, the highest compressive strength of 112.8 MPa, and the highest contact angle of 101.4°. The introduction of side chains through the thiol-ene click reaction can provide a simple and effective method for designing and preparing multifunctional epoxy resins.     

Transparent and toughening epoxy thermosets modified by linear telechelic polymer containing rigid spiroacetal moieties: Uncovering the relationship between the heterogeneous crosslinked network and thermoset performances

Spiroacetal moieties containing linear telechelic polymers (LTPs) with two terminal epoxy groups were facilely synthesized via the successive thiol-ene and thiol-epoxy click additions. The LTPs were incorporated into epoxy matrix to fabricate the transparent and toughening thermosets. In term of the miscibility of epoxy with the adduct of ethanedithiol and 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]undecane (BTU), it is proposed that the size of the formed nanostructures was small enough to allow light penetrate. Therefore, the modified thermosets were transparent, which was further confirmed by small-angle X-ray scattering (SAXS) measurements. The LTPs with an alternating structure of rigid spiroacetal moiety and soft thioether could formed heterogeneous crosslinked networks (HCNs) and obviously toughen epoxy thermosets. Flexural strength increased from 1.06 GPa for neat epoxy to 2.09 GPa for toughening thermosets modified with 15 wt% LTPs. The stress field intensity (K_IC) value reached up to 3.93 by more than 125% compared with that of the control sample (1.75). This work uncovered the role of HCNs on performance and paved a way for technological advances toward transparent and toughening materials in epoxy thermosets.     

The synergistic effects of β-nucleating agent and ethylene–octene copolymer on toughening isotactic polypropylene

The mechanical properties of isotactic polypropylene (iPP) and ethylene–octene copolymer (POE) blends with or without β-nucleating agent (β-NA) were systematically studied. Results demonstrated that, after β-NA and POE were separately added, the impact strength of injection molded iPP samples increased. β-NA and POE were also found to have a synergistic toughening effect on iPP matrix, and the effect was significant. When the contents were 0.05 wt% β-NA and 10 wt% POE, the impact strength reached the maximum, i.e., almost 15 times that of neat iPP. SEM further revealed that POE in skin and core layers existed as long and narrow strips along the flow direction and throughout crystals. The tensile strength did not deteriorate because of the special phase morphology and tight interfacial interaction between POE phase and matrix. WAXD and DSC revealed that POE addition had negligible influence on crystal form, and a considerable number of β crystals was generated by adding β-NA. SEM results also confirmed a critical β-NA content. When β-NA content was lower than the critical value, perfect β sphaerocrystals were generated. When β-NA was higher, “bundle-like” crystal structures formed. Perfect β sphaerocrystals were more efficient for dissipating energy because of the looser stacking pattern, thus showing better toughness.     

Properties of Poly(butylene terephthalate)/Bisphenol A Polycarbonate Blends Toughening with Epoxy-Functionalized Acrylonitrile–Butadiene–Styrene Particles

Glycidyl methacylate functionalized acrylonitrile–butadiene–styrene particles (ABS-g-GMA) prepared via an emulsion polymerization method were used to toughen poly(butylene terephthalate) (PBT)/bisphenol A polycarbonate (PC) blends. DMA results showed PBT was partially miscible with PC and the addition of ABS-g-GMA improved the miscibility between PBT and PC. DSC tests further testified that the introduction of ABS-g-GMA improved the miscibility of PBT and PC according to the T_m depression criterion. SEM displayed a very good dispersion of ABS-g-GMA particles in the PBT/PC blends and the dispersed phase size of PC decreased due to the compatibilization effect of ABS-g-GMA. The mechanical properties showed that the addition of 10 wt% ABS-g-GMA was sufficient to induce a super-tough fracture behavior to the PBT/PC blends and a notched impact strength of more than 1000J/m was achieved. The Vu-Khanh test showed that stable crack propagation took place for PBT/PC blends with the addition of ABS-g-GMA and led to ductile failure.     

Synergistic effect of SEBS-g-MA and epoxy on toughening of polyamide 6/glass fiber composites

Maleated styrene-ethylene-butylene-styrene block copolymer (SEBS-g-MA) and epoxy monomer, individually or in combination, are used to toughen polyamide 6/glass fiber composites. The epoxy monomer enhanced interaction between polyamide 6 and glass fiber. SEBS-g-MA rubber is uniformly dispersed in polyamide 6 matrix caused by the preferred compatibilizing reaction between the anhydride group of rubber and the amine terminal group of polyamide 6. The addition of epoxy does not affect the fine dispersion of SEBS-g-MA. Polyamide 6/glass fiber binary composites are brittle. The addition of epoxy monomer alone does not change their brittle features. Similarly, in the absence of epoxy monomer, adding 20 wt % of SEBS-g-MA to polyamide 6/glass fiber composites does not greatly increase the tensile ductility. Only when both SEBS-g-MA and epoxy monomer are present in some combination, do the polyamide 6/glass fiber composites show prominent ductile characteristics, such as stress-whitening and necking. This synergistic effect of epoxy monomer and SEBS-g-MA also imparts higher notched impact strengths to the ternary composites. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1448–1458, 2007     

Cavitation of rubber particles in high-impact polystyrene: Effects of crosslinking by γ-irradiation

Tensile tests on high-impact polystyrene (HIPS) show that a 60 Mrad dose of γ-radiation raises the yield stress from 11.5 to 19.8 MPa, and the flow stress from 10.0 to 19.6 MPa, while reducing the elongation at break from 50 to 4%. Similar reductions in fracture resistance are observed in irradiated Charpy impact specimens. The T_g of the rubber phase shifts from −70 to −57 °C, and its estimated shear modulus increases from 0.1 to 0.5 MPa. It is concluded that the observed changes in mechanical properties are due almost entirely to crosslinking of the polybutadiene. This not only inhibits cavitation and fibrillation in the rubbery membranes of the “salami” particles, thereby delaying yield, but also makes the fibrillated membranes more resistant to further dilatation, so that rates of craze thickening in the polystyrene matrix are reduced. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2168–2180, 2004     

相变增韧陶瓷Ⅱ型裂纹增韧分析

本文采用压力敏感和权函数法，对相变增韧陶瓷Ⅱ型裂纹的增韧效应进行了理论预测。分别给出了静止裂纹和定常扩展裂纹相变性屏蔽的理论表达式，结果表明；相变对静止裂纹无增韧效应，纹尖端屏蔽来自于裂纹扩展尾区的贡献。     

聚对苯二甲酸丙二醇酯的无卤阻燃化改性

聚对苯二甲酸丙二醇酯作为新型聚酯材料,具有非常优良的性能,但其易燃性很大的限制了它的应用范围。为了提高对苯二甲酸乙二醇酯的阻燃性能,本文以无卤膨胀型EPFR-300A为阻燃改性剂,马来酸酐接枝聚烯烃(POE-g-MAH)弹性体为增韧剂,对聚对苯二甲酸丙二醇酯树脂(PTT)进行阻燃改性。通过热重分析仪(TGA)、示差扫描量热仪(DSC)、扫描电子显微镜(SEM)、力学性能等技术手段研究了阻燃剂和增韧剂对PTT树脂力学、热学和阻燃性能的影响。结果表明,增韧剂POE和POE-g-MAH的添加提高了PTT树脂的综合力学性能。当质量分数相同时,POE-g-MAH对PTT树脂的增韧效果要优于POE,且当POE-g-MAH质量分数为7%时,综合力学性能最佳。当添加相同质量分数增韧剂,EPFR-300A质量分数达到20%时,阻燃PTT材料阻燃性能最佳,极限氧指数(LOI)达到28.0%,垂直燃烧阻燃等级达到UL94 V-0级。EPFR-300A阻燃剂与PTT树脂间相容性良好,可以有效地促进PTT树脂成炭并提高材料的阻燃性能。     

Synergistic Effect of Polycarbonate on Reactive Core-Shell Particles Toughened Poly(Butylene Terephthalate)

Glycidyl methacrylate functionalized methyl methacrylate-butadiene-styrene copolymer (MBS-g-GMA) core-shell particles were prepared via an emulsion polymerization process. MBS-g-GMA was used to toughen poly(butylene terephthalate) (PBT) and the synergistic toughening effect of polycarbonate (PC) on PBT/MBS-g-GMA blends were investigated. Notched impact tests showed the percolation threshold became lower with the increase of PC content. Transmission electron microscopy displayed a very good dispersion of MBS-g-GMA particles in the PBT matrix with the different PC contents. The synergistic toughening effect was due to the encapsulation structure of PC which could facilitate the whole PBT matrix to yield. The more perfect the encapsulation structure formed, the more obvious the synergistic toughening the PC achieved. Sufficient strength of the phase interface was important to ensure the stress transfer effectively and facilitate the whole PBT matrix to yield. The interface strength between PC and MBS-g-GMA could be ensured by the good miscibility between Poly(methyl methacrylate) (PMMA) (grafted onto the polybutadiene-based rubber core) and PC. For the PBT/PC, the transesterification between PBT and PC improved the interface strength of the PBT and PC phases, as demonstrated by Fourier transform infrared spectroscopy (FTIR) scans. Scanning electron microscopy results showed shear yielding of the matrix and cavitation of the rubber particles were the major toughening mechanisms.     

Toughening of nylon 6 with a maleated core-shell impact modifier

Super-tough nylon 6 was prepared by using maleic anhydride grafted polyethylene-octene rubber/semicrystalline polyolefin blend (TPEg) as an impact modifier. The morphology, dynamic mechanical behavior, mechanical properties, and toughening mechanism were studied. Results indicate that TPEg with a semicrystalline polyolefin core and a polyethylene-octane rubber shell, possesses not only a better processability of extruding and pelletizing with a lower cost, but also an improved toughening effect in comparison with the maleated pure polyethylene-octene rubber. The shear yielding is the main mechanism of the impact energy dissipation. In addition, the influence of melt viscosity of nylon 6 on toughening effectiveness was also investigated. High melt viscosity of matrix is advantageous to the improvement of notched Izod impact strength. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1987–1994, 1998