Benzoxazine-bismaleimide blends: Curing and thermal properties

A blend of bisphenol A based benzoxazine (Bz-A) and a bismaleimide (2,2-bis[4(4-maleimidophenoxy) phenyl] propane (BMI), was thermally polymerised in varying proportions and their cure and thermal characteristics were investigated. The differential scanning calorimetric analysis, supplemented by rheology confirmed a lowering of the cure temperature of BMI in the blend implying catalysis of the maleimide polymerisation by benzoxazine. FTIR studies provided evidences for the H-bonding between carbonyl group of BMI and -OH group of polybenzoxazine in the cured matrix. The cured matrix manifested a dual phase behaviour in SEM and DMTA with the minor phase constituted by polybenzoxazine dispersed in an interpenetrating polymer network (IPN) of polybenzoxazine and cured BMI. The IPN possessed improved thermal stability over the constituent polybenzoxazine. A benzoxazine monomer possessing allyl functional groups, 2,2′-bis(8-allyl-3-phenyl-3,4-dihydro-2H-1,3-benzoxazinyl) propane (Bz-allyl) was reactively blended with the same bismaleimide in varying stoichiometric ratios (Bz-allyl/BMI), where the curing involved mainly Alder-ene reaction between allyl- and maleimides groups and ring-opening polymerisation of benzoxazine. The rheological analysis showed the absence of catalytic polymerisation of BMI in this case. The overall processing temperature was lowered in the blend owing to the co-reaction of the two systems to form a single-phase matrix. The cured resins of both Bz-A/BMI and Bz-allyl/BMI blends exhibited better thermal stability than the respective polybenzoxazines. The T_g of the IPN was significantly improved over that of polybenzoxazine (Bz-A). However, the co-reaction resulted in a marginal decrease in the T_g of the system in comparison to the polybenzoxazine (Bz-allyl).     

苯并噁嗪中间体/蛭石插层纳米复合物热固化行为的研究

通过对双酚A型苯并嗪中间体 (BOZ A) 蛭石插层纳米复合物固化过程的分析表明长链烷基铵阳离子对BOZ A的热开环聚合反应没有表现出催化作用 ,也不影响纳米复合物的结构形态 .不同蛭石含量的插层纳米复合物 ,在形成不同纳米分散状态的纳米复合物的过程中 ,蛭石晶片对BOZ A的热开环聚合具有明显不同的阻碍作用 ,蛭石含量为 3%的插层纳米复合物 16 0℃的凝胶化时间较纯树脂延长约 7min ,活化能升高约8kJ mol,固化反应热焓降低约 14J g ,使得固化物的固化程度较纯树脂降低约 7%～ 10 % ,阻碍作用最大 ,其它含量的次之     

Microphase separation in polybenzoxazine thermosets containing benzoxazine-terminated poly(ethylene oxide) telechelics

Benzoxazine-terminated poly(ethylene oxide) telechelics (Ba-terminated PEO) was synthesized and incorporated into polybenzoxazine to obtain the nanostructured thermosets. The morphology of the thermosets was investigated by means of atomic force microscopy (AFM), small angle X-ray scattering (SAXS) and dynamic mechanical analysis (DMA). The formation of the nanophase structures in the thermosetting composites was addressed on the basis of the mechanism of reaction-induced microphase separation (RIMPS), which was in marked contrast to the case of the binary thermosetting blends of polybenzoxazine with hydroxyl-terminated poly(ethylene oxide). The occurrence of RIMPS resulted from the copolymerization reaction of the end groups of Ba-terminated PEO telechelics with the precursor of thermosetting matrix (i.e., benzoxazine), which suppressed the occurrence of the macroscopic phase separation. It was found that the formation of the nanostructures has a significant effect on the melting behavior of PEO in the thermosets, thermal transition properties of the PBZ thermosets.     

Cyclotriphosphazene Fibre Reinforced Poly(benzoxazine-co-ε-caprolactam) Nanocomposites for Flame Retardant Applications

Cyclophosphazene nanotube(PZT) incorporated poly(benzoxazine-co-ε-caprolactam)(P(BZ-co-CPL)) nanocomposites were developed for improving flame retardant properties. The effects of PZT on the flammability properties of P(BZ-co-CPL) matrix were evaluated through UL-94 flammability test and limiting oxygen index(LOI). The UL-94 results of P(BZ-co-CPL)/PZT hybrid nanocomposites showed V-1 rating, whereas neat P(BZ-co-CPL) showed burning rating. The LOI values are increased from 25.4 to 31.4 for 1.5 wt% PZT incorporated P(BZ-co-CPL) nanocomposite systems. SEM was used to study the char morphology of P(BZ-co-CPL)/PZT after being exposed to UL-94 flammability test. Data from thermal studies indicate that the PZT incorporated P(BZ-co-CPL) systems possess better Tg and thermal degradation behavior when compared to the neat P(BZ-co-CPL). The values of dielectric constant are decreased with increasing temperature. From the values, it is ascertained that the P(BZ-co-CPL)/PZT systems exhibit stable dielectric behavior with regard to variation in temperature. The TEM images ascertain the uniform dispersion of PZT in the P(BZ-co-CPL) matrix.     

苯并噁嗪/蒙脱土插层体系和苯并噁嗪体系的动态固化行为比较

比较了苯并噁嗪单体(BZ)和插层于蒙脱土层间的苯并噁嗪单体(BZ/MMT)两种体系的动态固化特性.实验发现,经有机化处理的蒙脱土在BZ/MMT体系的固化行为中起着重要的作用,使该体系存在催化聚合和热聚合两类固化单元反应.结果造成两种体系在特征固化温度、固化速率、反应热、反应级数以及表观活化能上存在明显的差别.     

Thermal degradation behaviors of polybenzoxazine and silicon-containing polyimide blends

Thermal behaviors of polymer blends between common-type polybenzoxazine (PBA-a) and polysiloxane-block-polyimide (SPI) were studied using Dynamic Mechanical Analysis (DMA) and Thermogravimetric Analysis (TGA). The polymer blends showed only one glass-transition temperature (T_g) that increased as the content of SPI increased. Synergistic behavior in the char formation of the alloys was clearly observed. The DTG curves showed three stages and two stages of decomposition reaction in neat PBA-a and SPI, respectively. For the blending systems with 25 wt%, 50 wt%, and 75 wt% of SPI, the DTG thermograms of the blends exhibited four stages of thermal decomposition reaction. The apparent activation energies (E_a) of each step were determined using Kissinger method, Flynn-Wall-Ozawa method and Coats-Redfern method. The type of solid state mechanism was determined by Criado method. From the calculation, the solid state thermal degradation mechanism is proposed to be F1 (random nucleation with one nucleus on the individual particle) type for PBA-a, SPI, and their blends.     

Synthesis, characterization and properties of naphthoxazine-functional poly(propyleneoxide)s

Thermally curable naphthoxazine-functionalized polymers were synthesized by the reaction of linear (diamines) and branched (triamines) poly(propyleneoxide)s (Jeffamine series) having various molecular weights, with p-formaldehyde, and 2-naphthol. The structures of the resulting polymers were characterized by using FT-IR and ¹H-NMR. In addition, curing behavior of these polymers was studied using differential scanning calorimeter (DSC). Hydrophilicity of these polymers, both in cured and non-cured states, was investigated by water contact angle measurements. The surface topographies of the polymers were also examined by atomic force microscope (AFM).     

Synthesis and characterization of polybenzoxazine containing phosphorus

The novel benzoxazine monomer containing phosphorus has been synthesized based on multifunctional amine route from bis(4-aminophenyl)phenylphosphate,p-cresol and formaldehyde.Subsequently,the benzoxazine monomer was thermo-cured into polybenzoxazine containing phosphorus.The chemical structures were identified by nuclear magnetic resonance(NMR),Fourier transform infrared spectroscopy(FT-IR).The curing reaction was monitored by differential scanning calorimetry(DSC) and FT-IR.The thermal and flame-retardant properties of obtained polybenzoxazine were evaluated by dynamic mechanical thermal analysis(DMA),thermal gravimetric analysis(TGA) and oxygen index meter, respectively.The results show that the novel polybenzoxazine has high limiting oxygen index(38.1) and glass transition temperature(232℃).     

Polymerisation and degradation of an aromatic amine-based naphthoxazine

Pyrolysis mass spectrometry (MS) analysis of aromatic amine-based naphthoxazine monomer (15-Na) and Poly15-Na has been carried out. Evaporation and degradation of the monomer are detected during the curing process while the polymerisation proceeded. The polymerisation and degradation mechanisms are proposed for 15-Na and Poly15-Na, respectively. The proposed polymerisation mechanism for naphthoxazine monomer was through the aniline units either by coupling of the radicals generated by cleavage of the side rings or by substitution to the benzene ring of aniline. It has been determined that polymerisation followed opposing paths yielding some thermally less stable linkages through which thermally crosslinked polynaphthoxazine (Poly15-Na) suffers from low thermal stability. It has been shown that pyrolysis MS is a very useful technique to investigate the polymerisation and degradation mechanisms and degradation products of these materials.