SYNTHESIS AND THERMAL PROPERTIES OF POLYBENZOXAZOLE FROM SOLUBLE PRECURSOR WITH HYDROXY-SUBSTITUTED POLYENAMINONITRILE

Aromatic polybenzoxazole (PBO) precursor, hydroxy-substituted polyenaminonitrile, was prepared by direct polycondensation of 1,4-bis(l-chloro-2,2-dicyanovinyl)benzene (CCB) and 4,6-diaminoresorcinol dihydrochloride (DAR) using pyridine and N,N-dimethylacetamide as condensing agent and solvent. The precursor has good solubility in polar aprotic solvent which is due to the strong dipolar nature of the main chain. The soluble precursor was subjected to thermal cyclization in an inert atmosphere to convert it into the corresponding PBO, which has its 5% weight loss temperature at 540℃ The fully cyclized PBO were characterized by FT-IR and TGA. The introduction of 10% mol 1,3,5-benzenetricarboxylic chloride (BTC) into the main chain not only has little effect on the solubility of PBO precursor but also raises its 5% weight loss temperature to 552℃ and char yield at 700℃ for the cyclized PBO with BTC.     

Preparation and properties of polybenzoxazole-silica nanocomposites via sol-gel process

A novel organic/inorganic hybrid material has been prepared through the sol-gel process. A high temperature polymer, polybenzoxazole (PBO), was chosen as the organic phase due to its inherent low dielectric constant and low water absorption. The inorganic phase was generated via sol-gel reaction from a silica precursor, phenyltriethoxysilane (PTEOS). Due to the hydroxyl groups in the PBO precursor backbone and the water release during the cyclization of the precursor, the sol-gel reaction proceeded without the addition of water and any catalyst. After curing at 350 °C, we obtained the PBO/silica nanocomposites. From TEM and SEM photographs, the silica particles dispersed in the PBO matrix were nano-sized. With an addition of 100 wt% of PTEOS, the T_g of PBO was increased 35 °C. The dielectric constant of the hybrid materials increased with the increasing amount of PTEOS.     

Thermal conversion of hydroxy-containing polyimides to polybenzoxazoles. Does this reaction really occur?

Hydroxy-containing polyimides with a low level of structural defects have been produced by the reaction of aromatic tetra-carboxylic acids with hydroxy containing aromatic diamines in water, as this method avoids the normal ester impurities formed by the standard polyimide synthesis techniques using tetra-carboxylic dianhydrides in dry polar solvents. Detailed FTIR studies focused on the controlled thermolysis of these purified alpha-hydroxypolyimides and their model compounds has revealed that the hydroxy groups are lost at significantly lower temperatures and times than the imide groups. This observation does not support previous literature reports which suggested that benzoxazole formation occurs and has implications for the style of materials ultimately produced. We propose a new mechanism and provide evidence to indicate that the polymers initially produced by the thermolysis reaction of alpha-hydroxypolyimides are actually crosslinked, imide containing biphenylene derivatives.     

Synthesis and characterization of new cardo poly(bisbenzoxazole)s containing fluorenylidene unit

A series of poly(bisbenzoxazole)s (PBOs V) containing fluorenylidene unit are prepared from 9,9-bis(3-amino-4-hydroxyphenyl)fluorene (BAHPF) and various aromatic or alkene diacids by direct polycondensation. These polymers exhibit improved solubility and good thermal stability. The decomposition temperatures at 10% weight loss of them are above 500 °C. X-ray diffractograms of PBOs V_1–5 show that all of them are amorphous. The maximum absorption wavelengths of PBOs V_1–5 are blue or red shifted relative to poly(p-phenylene-2,6-benzobisoxazole) (PBO). The bandgaps of PBOs V_1–5 are in the range of 2.48–2.98 eV, which widen the tunable range of the optical bandgap. The results of photoluminescence (PL) emission spectra indicate the energy transportation has happened between the fluorenylidene and benzoxazole ring. The emission wavelengths of PBOs V_1–5 are blue shifted in contrast to PBO and the emission wavelengths of them are in the region of blue or green light, respectively. The PL quantum yields of them are improved due to the introduction of fluorenylidene group. The results of EPR studies show the intrinsic paramagnetic defects in this class of polymers.     

Free-Radical-Initiated Copolymerization of A-Methylstyrene with Maleimide

Alternating copolymers of α-methylstyrene (α-MeSt) and maleimide (MI) were prepared by free-radical initiated polymerization at different monomer-to-monomer concentrations in the feed in CHCl₃, as solvent. The equilibrium constant of -MeSt and MI was determined by the transformed Benesi-Hildebrand NMR method in CDCl₃, and has a value of 0.03 L/mol. From the equation R_p = R_p(f) + R_p(CT) proposed by Shirota and coworkers, R_pf) and R_pCT) were calculated, and it was found that the copolymerization of -MeSt with MI proceeds predominantly through participation of the CT complex. Alternating copolymers have a glass transition temperature of 567 K (DSC method). Alternating copolymer decomposes via a one-step reaction at 350°C.     

一种新的4,6-二氨基间苯二酚盐酸盐的制备方法及与对苯二甲酸的缩合聚合

以间苯二酚为原料,通过乙酰化、肟化、Beckmann重排、水解反应制备4,6-二胺基间苯二酚盐酸盐(DAR·2HCl),并用FTIR,MS,元素分析,¹HNMR和¹³CNMR等对DAR·2HCl及中间体进行了表征.同时,将DAR·2HCl和对苯二酸(TPA)成盐,然后进行缩聚得到具有较高分子量的PBO.通过FTIR和固体¹³CNMR表征了PBO的结构,并研究了PBO的热性能.