Preparation of polybenzoxazole fibers via electrospinning and postspun thermal cyclization of polyhydroxyamide

Polybenzoxazole (PBO) fibers with a submicron diameter were successfully prepared by electrospinning its precursor, polyhydroxyamide (PHA), solutions to obtain the PHA fibers first, followed by appropriate thermal treatments for cyclization reaction. BisAPAF‐IC PHA with two different molecular weights (MWs) were synthesized from a low temperature polymerization of 2,2′‐bis(3‐amino‐4‐hydroxyphenyl) hexafluoropropane (BisAPAF) and isophthaloyl chloride (IC). Using dimethylacetamide (DMAc) and tetrahydrofuran (THF), solvent effects on the electrospinnability of PHA solutions were investigated. For balancing the solution properties, it was found that DMAc/THF mixture with a weight ratio of 1/9 was the best cosolvent to prepare smooth PHA fibers; uniform PHA fibers with a diameter of 325–720 nm were obtained by using 20 wt % PHA/(DMAc/THF) solutions. For a fixed PHA concentration, solutions with a lower MW of PHA yielded thinner electrospun fibers under the same electrospinning condition. After obtaining the electrospun BisAPAF‐IC PHA fibers, subsequent thermal cyclization up to 350 °C produced the corresponding thermally stable BisAPAF‐IC PBO fibers with a diameter of 305–645 nm. The structure of the precursor fibers and the fully cyclized fibers were characterized by FTIR. For the cyclized BisAPAF‐IC PBO fibers, thermogravimetric analysis showed a 5% weight loss temperature at 523 °C in nitrogen atmosphere. The interconnected fiber structure in the BisAPAF‐IC PBO fiber mats was irrelevant to the curing process, but resulted from the jet merging during the whipping process as revealed by the high speed camera images. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8159–8169, 2008     

PMDA-BPDA-HAB聚苯并噁唑的合成及耐热性

PMDA-BPDA-HAB聚苯并噁唑的合成及耐热性;均苯四甲酸二酐;联苯四羧酸二酐;二羟基联苯胺;聚酰亚胺;聚苯并噁唑;耐热性     

Hyperbranched polybenzoxazoles incorporated polybenzoxazoles for high‐performance and low‐K materials

This paper reports an effective approach for the fabrication of low‐k polybenzoxazole (PBO) by covalent incorporation of hyperbranched PBO (HBPBO). Soluble o‐aminophenol‐terminated HBPBO was first synthesized by a one‐pot polycondensation, then covalently bonded to poly(hydroxyamide) ended with carbonyl chloride groups, PBO was finally obtained by thermal conversion of the precursor polymers. It was demonstrated that the thermal stability of PBO was not influenced by the incorporation of HBPBO due to their similar chemical compositions, while the glass transition temperature, elastic modulus and hardness were improved because of the linking effects of HBPBO to linear PBO chains. The dielectric constant of PBO was significantly reduced due to the disturbed chain packing of PBO by the globular HBPBO, and the intrinsic cavities in HBPBO, which increased free volume in the materials. Moreover, the material also exhibited reduced coefficient of thermal expansion as compared to neat PBO and low water absorption. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1623–1632     

双(3-氨基-4-羟基苯基)双酚醚类化合物的合成

以双酚化合物及对卤苯酚为起始原料,经用苄基保护、乌尔曼成醚、选择性硝化和还原脱保护4步反应,合成了具有双酚芳香醚结构的4个新型聚苯并噁唑单体：双(3-氨基-4-羟基苯基)双酚醚类化合物的盐酸盐。 确定了乌尔曼成醚反应的最佳工艺条件,证明硝化反应只发生在对卤苯酚苄保护基的邻位,改进了还原脱保护反应的成盐及后处理条件,提高了产物的质量和收率,4步反应总收率可达54.0%。 采用红外光谱、核磁共振H谱和高分辨质谱表征了每步产物的化学结构。     

Chain‐growth condensation polymerization approach to synthesis of well‐defined polybenzoxazole: Importance of higher reactivity of 3‐amino‐4‐hydroxybenzoic acid ester compared to 4‐amino‐3‐hydroxybenzoic acid ester

Application of chain‐growth condensation polymerization (CGCP) to obtain well‐defined polybenzoxazole (PBO) was examined. CGCP of both phenyl 3‐{(2‐methoxyethoxy)methoxy (MEM‐oxy)}‐4‐(octylamino)benzoate ( 1b ) (para‐substituted monomer) and phenyl 4‐MEM‐oxy‐3‐(octylamino)benzoate ( 3b ) (meta‐substituted monomer) was examined in the presence of metal disilazide base and phenyl 4‐nitro‐ or methylbenzoate 2 as an initiator. Polymerization of the latter monomer, but not the former, afforded polymer with controlled molecular weight based on the feed ratio of monomer to initiator and with a narrow molecular weight distribution. Accordingly, monomer 3c , in which the octyl group on the amino nitrogen of 3b was replaced with a 4‐(octyloxy)benzyl (OOB) group, was polymerized in the presence of lithium 1,1,1,3,3,3‐hexamethyldisilazide (LiHMDS), phenyl 4‐methylbenzoate ( 2b ), and LiCl in THF at 0 °C to yield poly 3c with well‐defined molecular weight (M_n = 4520–9080) and low polydispersity (M_w/M_n ≤ 1.11). Treatment of poly 3c with trifluoroacetic acid simultaneously removed the MEM and OOB groups, affording poly(o‐hydroxyamide) (poly 4 ) without scission of the amide linkages. Cyclodehydration of poly 4 proceeded at 350 °C to yield PBO (poly 5 ), which was insoluble in organic solvents and acids. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1730–1736     

Syntheses and properties of hyperbranched polybenzoxazole by thermal cyclodehydration of hyperbranched poly[o‐(t‐butoxycarbonyl)amide] via A2 + B3 approach

The syntheses and properties of hyperbranched poly(o‐hydroxyamide) [poly(HAB‐BCC)‐ABP], poly[o‐(t‐butoxycarbonyl)amide] [poly(HAB‐BCC)‐ABP‐t‐BOC], and polybenzoxazole [poly(HAB‐cycloBCC)] were examined. Poly(HAB‐BCC)‐ABP was obtained from the polycondensation reaction of 3,3‐dihydroxy‐4,4′‐diaminobiphenyl (HAB) as an A₂‐monomer and 1,3,5‐benzenetricarboxylchloride (BCC) as a B₃‐monomer with 2‐amino‐4‐t‐butylphenol (ABP) in NMP in the presence of pyridine for 24 h. The reaction of poly(HAB‐BCC)‐ABP and di‐t‐buthylcarbonate (DiBOC) was performed to obtain the corresponding poly(HAB‐BCC)‐ABP‐t‐BOC with pendant t‐BOC groups. The thermal cyclodehydration of poly(HAB‐BCC)‐ABP‐t‐BOC was carried out in the film sate at 400 °C, affording the poly(HAB‐cyclo‐BCC) in quantitative yield. Furthermore, the solubilities and thermal properties of these polymers were examined. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3640–3649, 2006     

Synthesis of a highly transparent poly(o‐hydroxyamide) in the i‐line region and its application to photosensitive polymers

A novel poly(σ‐hydroxyamide) (PHA) based photosensitive polymer that exhibits high transparency at 365 nm wavelength (i‐line) has been developed. Time‐dependent density functional theory (TD‐DFT) calculations using the B3LYP hybrid functional were performed to predict the transparencies of various hydroxyamides in the i‐line region. Based on the calculations, 4,4′‐sulfonylbis(σ‐aminophenol) (SAP) was prepared and polymerized with 4,4′‐oxybis(benzoyl chloride) (OBBC), and the resulting PHA, which is abbreviated as PHA‐S, showed a high transparency comparable to that of PHA derived from 4,4′‐(hexafluoroisopropylidene)bis(σ‐aminophenol). Positive‐type photosensitive PHA was then formulated based on PHA‐S with a crosslinker 1,3,5‐tris[(2‐vinyloxy)ethoxy]benzene (TVEB) and a photoacid generator (5‐propylsulfonyloxyimino‐5H‐thiophen‐2‐ylidene)‐2‐(methylphenyl)acetonitrile (PTMA) (17:3:1 in weight ratio), and demonstrated photosensitivity and contrast of 14 mJ/cm² and 2.7, respectively, when the resist film was prebaked at 120 °C for 5 min, irradiated by i‐line, post exposure baked at 120 °C for 5 min, developed with an 2.38 wt% TMAH solution for 5 s. A clear positive image featuring 10‐μm line‐and‐space was also printed in a film which was exposed to 50 mJ/cm² of i‐line by contact‐printing. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2527–2535, 2005     

Montmorillonite‐based nanocomposites of polybenzoxazole: Synthesis and characterization (I)

Poly(amic acid) was synthesized by means of low‐temperature‐solution polymerization of 3,3′‐dihydroxybenzidine and pyromellitic dianhydride in N,N‐dimethylacetamide. The precursor polymer was heat‐treated at different temperatures to create a polybenzoxazole (PBO) through a polyimide (PI). PI containing the hydroxyl group was rearranged by decarboxylation with heat treatment, resulting in a fully aromatic PBO. Hexadecylamine was used as an organophilic alkylamine in organo‐clay. We have tried to clarify the intercalation of heterocyclic polymer chains to hexadecylamine–montmorillonite (C₁₆‐MMT) and improve tensile properties. It was found that the addition of only a small amount of organo‐clay was enough to improve the mechanical properties of PBO. Maximum enhancement in the ultimate tensile strength for PBO hybrids was observed for the blends containing 4% C₁₆‐MMT. The initial modulus monotonically increased with further increases in the C₁₆‐MMT content. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 471–476, 2001     

Two‐step thermal conversion from poly(amic acid) to polybenzoxazole via polyimide: Their thermal and mechanical properties

Poly(amic acid) was synthesized with a low‐temperature solution polymerization of 3,3′‐dihydroxybenzidine and pyromellitic dianhydride in N,N‐dimethylacetamide. The cast films were thermally treated at various temperatures. The polyimide containing the hydroxyl group was rearranged by decarboxylation, resulting in a fully aromatic polybenzoxazole at temperatures higher than 430 °C. These stepwise cyclizations were monitored with elemental analysis, Fourier transform infrared, and nuclear magnetic resonance. Microanalysis results confirmed the chemical compositions of poly(amic acid), polyimide, and polybenzoxazole, respectively. A cyclodehydration from poly(amic acid) to polyimide occurred between 150 and 250 °C in differential scanning calorimetry, and a cyclodecarboxylation to polybenzoxazole appeared at 400–500 °C. All the samples were stable up to 625 °C in nitrogen and displayed excellent thermal stability. Polybenzoxazole showed better thermal stability than polyimide, but polyimide exhibited better mechanical properties than polybenzoxazole. However, polyimide showed a crystalline pattern under a wide‐angle X‐ray, whereas polybenzoxazole was amorphous. The precursor poly(amic acid) was readily soluble in a variety of solvents, whereas the polyimide and polybenzoxazole were not soluble at all. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2537–2545, 2000     

Syntheses and properties of new aromatic polybenzoxazoles bearing ether and phenylethylidene or 1‐phenyl‐2,2,2‐trifluoroethylidene linkages

Two new bis(ether acyl chloride)s, 1,1‐bis[4‐(4‐chloroformylphenoxy)phenyl]‐1‐phenylethane and 1,1‐bis[4‐(4‐chloroformylphenoxy)phenyl]‐1‐phenyl‐2,2,2‐trifluoroethane, were prepared from readily available reagents. Aromatic polybenzoxazoles with both ether and phenylethylidene or 1‐phenyl‐2,2,2‐trifluoroethylidene linkages between phenylene units were obtained by a conventional two‐step procedure including the low‐temperature solution polycondensation of the bis(ether acyl chloride)s with three bis(o‐aminophenol)s, yielding poly(o‐hydroxyamide) precursors, and subsequent thermal cyclodehydration. The intermediate poly(o‐hydroxyamide)s exhibited inherent viscosities of 0.39–0.98 dL/g. All of the poly(o‐hydroxyamide)s were amorphous and soluble in polar organic solvents such as N,N‐dimethylacetamide, and most of them could afford flexible and tough films via solvent casting. The poly(o‐hydroxyamide)s exhibited glass‐transition temperatures (T_g's) of 129–194 °C and could be thermally converted into corresponding polybenzoxazoles in the solid state at temperatures higher than 300 °C. All the polybenzoxazoles were amorphous and showed an enhanced T_g but a dramatically decreased solubility with to respect to their poly(o‐hydroxyamide) precursors. They exhibited T_g's of 216–236 °C through differential scanning calorimetry and were stable up to 500 °C in nitrogen or air, with 10% weight‐loss temperatures being recorded between 538 and 562 °C in nitrogen or air. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 914–921, 2003