Reaction kinetics of liquid crystalline epoxy cured with aromatic diamine: Its synthesis and mechanical and electrical characteristics

The effect of the molar ratio of diglycidyl ether of 4,4′-biphenyl (DGEBP) to p-phenylene diamine (PDA) on the cure reaction rate was studied by the Kissinger and isoconversional equations. The cure mechanism was studied by FTIR analysis and the liquid crystalline phase structure was analyzed by wide angle X-ray diffraction (WAXD). With an increasing molar ratio of DGEBP/PDA, the preexponential factor was increased by the increasing collision probability between epoxide groups and primary or secondary amine groups in noncataltyic or catalytic modes. The activation energy also increased because of the increasing content of rigid rodlike mesogen and the high crosslink density, which hindered the diffusion of functional groups. The activation energies obtained from the Kissinger equation were in good agreement with average values obtained from the isoconversional equation. The WAXD pattern showed a smectic layer structure with a layer thickness of 15.3 Å and an intermolecular distance of 4.3 Å. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2372–2380, 2001     

Relationship between anisotropic orientation and curing of liquid crystalline epoxy resin

The effect of macroscopic orientation of liquid crystalline epoxy (LCE) resin, 4,4′‐di(2,3‐epoxypropenyloxy)phenyl benzoate, on the curing and liquid crystalline phase of LCE/diaminodiphenylester (DDE) mixture was investigated. Birefringence and curing rate of uniaxially aligned LCE/DDE on rubbed PI surface was compared with those of unaligned LCE/DDE. Anisotropic orientation accelerated the curing of LCE and facilitated the formation of liquid crystalline phase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1712–1716, 2006     

Synthesis and curing of liquid crystalline epoxy resin based on asymmetric mesogen

A novel liquid crystalline epoxy resin (LCER) derived from asymmetric mesogen unit was synthesized. Its structure and liquid crystalline behavior were characterized by hydrogen nuclear magnetic resonance (H‐NMR), differential scanning calorimetry (DSC), polarized optical microscopy (POM). The results indicated that the LCER converted to a nematic phase at 85°C during heating and finally became isotropic at 145°C. The curing behavior and phase behavior of the LCER with 4,4′‐diaminodiphenyl methane and methyl hexahydrophthalic anhydride were also studied by DSC and POM, respectively. Their apparent activation energy (E_a) was evaluated according to the Ozawa's isoconversional method. The results suggested that autocatalytic reaction had occurred in these two systems. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

DSC法研究聚异氰酸酯／环氧树脂胶粘剂的固化反应动力学及固化工艺

采用差示扫描量热法(DSC)研究了聚异氰酸酯／环氧树脂的固化过程,研究了不同配比对固化反应的影晌,固化度与固化温度的关系,计算了固化反应表观活化能和反应级数,确定了聚异瓤酸酯／环氧树脂胶粘剂的固化工艺。结果表明:胶粘剂中固化剂的含量对环氧树脂的固化反应过程有显著的影响,随着聚异氰酸酯的增加,固化放热量增加。当聚异氰酸酯的含量达到1．2份时,固化反应放热量达到最大值;不同升温速率下,体系固化温度有很大差异,随着升温速率的提高,固化温度增加。通过动力学计算得到体系最佳固化温度为108℃,固化时间为6-8h,固化体系的活化能为43．31kJ／mol,反应级数为1．17。     

Modification of an o‐cresol formaldehyde epoxy resin by the thermotropic liquid crystalline polymer

Two novel liquid crystalline polymers, polydiethyleneglycol bis(4‐hydroxybenzoate) terephthaloyl and block copolymer (PDBH), were synthesized by condensation reaction. The blends of the two liquid crystalline polymers and o‐cresol formaldehyde epoxy resin were prepared by linear phenol‐formaldehyde resin as curing reagent. Both mechanical and thermal properties of the blends containing liquid crystalline polymer were improved to a certain extent. By adding 5 wt % PDBH, the impact strength, bending strength, and the glass transition temperature were enhanced by 128%, 23.84%, and 28°C, respectively, compared with the unmodified version. The results of curing kinetics showed that the curing reaction active energy of the modified system by PDBH decreased from 79.70 to 70.26 kJ/mol. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1626–1631, 2005     

一种低熔点芳香酯型液晶环氧树脂的合成与固化

本文合成了一种低熔点的芳香酯型液晶环氧树脂双4-环氧丙氧基乙氧基邻甲基对苯二酚酯(MPEPEB),并用IR、EA、1H-NMR、DSC和POM对其结构和性能进行了表征,结果表明MPEPEB在78.7℃～133.9℃之间为向列型液晶,并在降至-50℃后仍能保持液晶态。DSC研究表明,比较升温固化与等温固化的数据表明固化速率,不仅是反应温度和反应程度的函数,同时还与反应历程有关。固化后的体系具有较低的玻璃化温度,并且室温下保留的液晶结构在升温至86℃～88℃时消失。     

新型环氧树脂胶粘剂的固化动力学研究

在不同升温速率下采用非等温差示扫描量热（DSC）技术对一种新型改性环氧树脂胶粘剂的固化反应过程进行了跟踪,并利用Kissinger、crane方程以及Arrhenius方程对该固化反应进行了动力学分析。结果表明,该固化反应的活化能为59.18kJ／mol,反应级数为0．89;结合Dsc谱图确定其固化工艺为130℃／1h＋150℃／2h＋175℃／3h。     

Synthesis and characterization of the two novel liquid crystalline epoxy resins based on bisphenol‐s mesogen

Two novel liquid crystalline epoxy resins (LCER) based on bisphenol‐S mesogen, 4,4′‐Bis‐(2,3‐epoxypropyloxy)‐sulfonyl bis(1,4‐phenylene) (p‐BEPSBP) and sulfonyl bis(4,1‐phenylene) bis[4‐(2,3‐epoxypropyloxy)benzoate] (p‐SBPEPB), were synthesized. Their liquid crystalline behavior and structure were characterized by Fourier transmittance infrared ray (FTIR), differential scanning calorimetry (DSC), ¹HNMR, polarized optical microscopy (POM) and X‐ray diffraction (XRD). The results show that p‐BEPSBP is a kind of thermotropic liquid crystal and has a smectic mesophase with a melting point (T_m) at 165°C; the p‐SBPEPB is a kind of nematic mesophase with the temperature range of 155–302°C from the T_m to the clearing point T_i. The curing behaviors and texture of the liquid crystalline epoxy resins with 4,4′‐diaminodiphenyl ether (DDE) were also studied by DSC and some kinetic parameters were evaluated according to the Ozawa's method. The dynamic mechanical properties of curing products were also investigated by torsional braid analysis (TBA), and the results suggest that the dynamic mechanical loss peak temperature (T_p) of p‐BEPSBP/DDE and p‐SBPEPB/DDE is 120 and 130°C, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Curing behavior and thermal and mechanical properties enhancement of tetraglycidyl‐4,4′‐diaminodiphenylmethane/4,4′‐diaminodiphenylsulfone using a liquid crystalline epoxy

A thermosetting resin system, based on tetraglycidyl‐4,4′‐diaminodiphenylmethane, has been developed via copolymerization with 4,4′‐diaminodiphenylsulfone in the presence of a newly synthesized liquid crystalline epoxy (LCE). The curing behavior of LCE‐containing resin system was evaluated using curing kinetics method and Fourier transform infrared spectroscopy. The effect of LCE on the thermal and mechanical properties of modified epoxy systems was studied. Thermogravimetric analysis indicated that the modified resin systems displayed a high T_0.05 and char yield at lower concentrations of LCE (≤5 wt%), suggesting an improved thermal stability. As determined using dynamic mechanical analysis and differential scanning calorimetry, the glass transition value increased by 9.7% compared to that of the neat resin when the LCE content was 5 wt%. Meanwhile, the addition of 5 wt% of LCE maximized the toughness with a 175% increase in impact strength. The analysis of fracture surfaces revealed a possible effect of LCE as a toughener and showed no phase separation in the modified resin system, which was also confirmed by dynamic mechanical analysis. © 2016 Society of Chemical Industry     

Synthesis and thermal properties of combined liquid crystalline epoxy resins

Liquid crystalline epoxy resins were prepared by the curing reaction of epoxy and amine compounds with a mesogenic group in the mesomorphic temperature range. Some epoxy resins exhibited a typical liquid crystalline phase. Curing reaction of a mesogenic epoxy compound with an aliphatic amine compound containing cyano biphenyl group was faster than that of another epoxy resins confirmed by thermally controlled Fourier transform infrared measurements. The glass transition temperature of the liquid crystalline epoxy resin containing cyano biphenyl group increased with increasing curing reaction time. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1979–1990, 1998     

联苯酚醛环氧树脂固化动力学及热性能研究

以4,4'-二氨基二苯砜(DDS)为固化剂,采用非等温示差扫描量热法(DSC)研究了联苯酚醛环氧树脂(BPNE)的固化动力学。通过外推法确定了体系的固化工艺。采用Kissinger、Ozawa法计算出固化体系的表观活化能,根据Crane理论计算得到该体系的固化反应级数。采用DSC,热重分析(TGA)研究了固化物的耐热性。结果表明:BPNE的固化工艺为160℃/2h+200℃/2h+230℃/2h;固化反应的活化能约为61.86kJ/mol,指前因子为5.27×105min-1,反应级数为1.1;玻璃化转变温度(Tg)为167℃,其10%热失重温度为398.1℃,800℃残炭率为29.37%,与双酚A环氧树脂/DDS固化物相比,分别提高了22℃,11.71%。     

非等温DSC法研究环氧树脂固化反应动力学过程

采用非等温DSC(差示扫描量热)法研究了环氧树脂(EP)体系的固化过程,并采用Kissinger方程、Crane方程和T-β(温度-升温速率)外推法计算出该EP体系固化反应的动力学参数和固化温度。研究结果表明:当m(EP)∶m(填料)∶m(固化剂)∶m(促进剂)=100∶30∶90∶0.4时,EP体系固化反应的表观活化能为78.90 kJ/mol、指前因子为2.58×109min-1和反应级数为0.914,其最佳固化条件为"从室温升温至92℃(开始凝胶)→继续升温至140℃(恒温固化)→最后升温至169℃(进行后固化处理)"。     

Dielectric relaxation and mechanical properties of liquid crystalline epoxy thermosets

This article describes the dielectric relaxation behavior and mechanical properties of novel liquid crystalline (LC) epoxy thermosets. Thermal simulated current experiments show that there is an additional relaxation caused by the local orientation of mesogens. From the mechanical test, it is found that the LC thermoset exhibits higher tensile strength and even little more deformation. It shows that the cured networks can be strengthened by LC domain orientation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1568–1573, 2000     

环氧粉末涂料的固化动力学和固化工艺的研究

采用非等温示差扫描量热法(DSC)研究了E-12/双氰胺(固化剂)和E-12/双氰胺/2-甲基咪唑(促进剂)体系的固化反应动力学。采用Kissinger法和Crane公式对DSC数据进行处理,获得了固化反应动力学参数,应用热重分析(TGA)研究了固化产物的热稳定性。结果表明:双氰胺、2-甲基咪唑的最佳用量分别为环氧树脂质量的4%和0.4%,最佳固化条件为160℃/15min。E-12/双氰胺体系和E-12/双氰胺/2-甲基咪唑体系的表观活化能分别为105.12kJ/mol和70.62kJ/mol,固化反应级数n=0.92。起始分解温度约为410℃,促进剂2-甲基咪唑的加入对体系热稳定性没有影响。     

丁香酚环氧有机硅树脂的制备及其固化动力学研究

利用丁香酚环氧和环四硅氧烷硅氢加成得到新型生物基环氧树脂D4EUEP,通过核磁共振氢谱和飞行时间质谱表征其准确结构。使用非等温DSC对D4EUEP/33DDS固化体系进行分析,采用双参数自催化模型和Málek判据建立了该体系固化动力学模型。模型计算结果与实验结果相关系数大于99%,证明该模型可以较好地描述D4EUEP/33DDS体系的固化过程。通过AICM方法研究了体系的有效活化能与转化率之间的关系,揭示了微观反应机理的变化,并通过Vyazovkin法对D4EUEP/33DDS体系进行了等温固化预测。     

吡啶型聚醚离子液体的合成及其与环氧树脂固化体系的力学性能

以三氟化硼乙醚络合物(Et2O·BF3)为催化剂,对环氧氯丙烷(ECH)进行阳离子开环聚合,合成了端羟基聚环氧氯丙烷(PECH)。再将其与吡啶反应,制备了吡啶型聚醚离子液体(PPIL),用FTIR光谱和1H-NMR表征了其化学结构。然后将该离子液体与环氧树脂进行共混,用FTIR和DSC光谱对共混物进行了表征。最后以乙二胺为固化剂对共混物进行固化,研究了吡啶型聚醚离子液体对固化体系力学性能的影响。结果表明,当离子液体与环氧树脂质量比为20:80、40:60、60:40时,固化体系的冲击强度较纯环氧树脂分别提高了58%、160%、340%,其中离子液体与环氧树脂质量比为60:40时,尽管样条厚度达6mm,却可以随意弯曲,呈现出明显的橡胶弹性。PPIL:EP为20:80时固化体系的韧性得到很大提高,且强度变化不大。     

改性双氰胺衍生物固化环氧树脂的研究

针对双氰胺固化环氧树脂时固化温度过高的缺点,从自行设计并合成的一系列改性双氰胺中筛选出一种,将其与环氧树脂复配制成单组分潜伏性环氧树脂胶粘剂,利用差示扫描量热法(DSC)和红外光谱法(FT-IR) 对单组分环氧树脂固化体系的固化反应进行了分析和研究。结果表明,改性双氰胺与双氰胺相比,具有较高的活性,显著降低了固化反应的反应温度;所配制的单组分环氧树脂胶粘剂具有较长的贮存期和良好的固化性能。     

环氧树脂/苯乙烯-马来酸酐共聚物体系固化动力学研究

用示差扫描量热仪(DSC)对环氧树脂/苯乙烯-马来酸酐共聚物/甲基咪唑体系的固化反应过程进行了分析,并用Kissinger和Ozawa方法分别求得固化反应的表观活化能ΔE为58.27 kJ/mol和64.93 kJ/mol;根据Crane理论计算得到该体系的固化反应级数n=0.85,为该环氧树脂体系的固化工艺确定提供理论依据。     

Morphology,thermal and mechanical performance of epoxy/polysulfone composites improved by curing with two different aromatic diamines

Epoxy/polysufone (PSF) composites cured with 4,4'-diaminodiphenyl sulfone (DDS) and 4,4'-diaminodiphenyl methane (DDM) were fabricated, and the effect of dual curing reaction of diamines with epoxy on morphology, mechanical, and thermal performance was investigated. DSC results indicated that DDM was more reactive than DDS and the activation energy decreased with the rising of DDM content. Structures with small domain size at the early stage of phase separation were fixed by the fast epoxy-DDM reaction. When the DDM content was elevated to a high level, large dual structures were changed to fine bicontinuous structures, which was favorable to improve the mechanical property. The mechanical performance of epoxy composites was enhanced and the maximum values were achieved when the DDM/DDS ratio was located at 75/25 (PSF/DDS0.25-DDM0.75). The flexural and tensile strength relative to epoxy/DDM system were enhanced more than those relative to epoxy/DDS, while the increase in toughness was the opposite. TGA measurement showed that thermal stability of epoxy/PSF composites was improved because of the restricting effect of continuous PSF domains on thermal motion of epoxy. DMA analysis exhibited two relaxation peaks for PSF/DDS0.25-DDM0.75, which could be attributed to the formation of phase separated morphology and epoxy network with different cross-link density.