Synthesis and characterization of acetylene‐terminated polybenzoxazines based on polyaralkyl‐phenolic prepolymer

Xylok polybenzoxazine with acetylene group terminals (XPBZAs) were synthesized by the Mannich‐like condensation of Xylok prepolymer, formaldehyde, aminophenylacetylene, and aniline, and their structures were characterized by Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (¹H NMR). The curing behavior of XPBZAs was determined by differential scanning calorimetry and FTIR. Thermal behavior and dynamic mechanical properties of the cured XPBZAs were investigated using thermogravimetric analysis and dynamic mechanical analysis. The results showed glass transition temperature (T_g), the thermal stability, and anaerobic char residue of cured XPBZAs increased as the content of acetylene groups increased. POLYM. ENG. SCI., 50:1751–1757, 2010. © 2010 Society of Plastics Engineers     

Curing kinetics,thermal, and adhesive properties of acetylene‐terminated benzoxazine

The acetylene‐terminated benzoxazine monomer (BB‐apa) has been synthesized using 2,2‐bis(4‐hydroxyphenyl)butane, 3‐aminophenylacetylene, and paraformaldehyde. The structure of the monomer was characterized by FTIR spectroscopy and ¹H NMR spectra, which indicated that the reactive oxazine ring and acetenyl groups existed in molecular structure of BB‐apa. The polymerization behavior was monitored by FTIR and non‐isothermal differential scanning calorimetry (DSC), which showed that the BB‐apa had completely cured with multiple polymerization mechanisms according to oxazine ring‐opening and ethynyl addition polymerization. The curing kinetics results revealed that the introduction of ethynyl groups can accelerate the ring‐opening polymerization of benzoxazine, leading to a lower curing temperature and apparent activation energy. Moreover, the thermoset derived from the BB‐apa exhibits higher thermal stability and lap shear strength (at 350 °C) with the glass transition temperature of 353 °C compared with the traditional benzoxazine polymer without ethynyl groups (BB‐a). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44547.     

Novel acetylene‐terminated polyimide oligomers with excellent processability and high toughness of films

A series of acetylene‐terminated imide oligomers based on 2,3,3′,4′‐Diphenyl ether tetracarboxylic acid dianhydride (a‐ODPA), 3,4′‐Oxydianiline (3,4′‐ODA), and 3‐Ethynylaniline (3‐EA) with different molecular weights were synthesized by using acetic anhydride and triethylamine as dehydrating agent. Their main structure was confirmed by Fourier transform infrared spectroscopy (FT‐IR). Thermal curing processing was characterized by FT‐IR and differential scanning calorimetry (DSC). All the uncured imide oligomers showed excellent solubility (more than 30 wt %) in organic solvent such as N,N‐dimethylacetamide (DMAc) and N‐methyl‐2‐pyrrolidone (NMP). These imide oligomers also possessed a very low viscosity, thus provided better processing window. These oligomers were formulated into thermosetting films by thermal crosslinking of the ethynyl groups. The properties of cured films were evaluated by dynamic mechanical thermal analysis (DMA), thermogravimetric analysis (TGA), and tensile measurement. The glass transition temperature (T_g) and elongation at break of the cured films were found to be almost >260°C and >9.2%, respectively. The cured films in air resulted in higher thermal stability than those under N₂ atmosphere. Experimental results suggested that the introduction of asymmetric and flexible ether‐hinge with 3‐EA in polyimide oligomers can improve the processability of the imide oligomers and the toughness for a cured sample without sacrificing their thermal‐oxidative stability. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42537.     

Synthesis,characterization, and properties of thermosets based on the cocuring of an acetylene‐terminated liquid‐crystal and silicon‐containing arylacetylene oligomer

A thermotropic acetylene‐terminated liquid‐crystal monomer, 2‐methyl‐1,4‐phenylene bis(4‐ethynylbenzoate) (MPBE), was prepared and used as a modification composition to react and cocure with a silicon‐containing arylacetylene (PSA) oligomer for improving PSA resin. The curing behavior of the PSA–MPBE resins were characterized by differential scanning calorimetry and Fourier transform infrared spectroscopy. The microstructure and morphology of the PSA–MPBE resins were investigated by scanning electron microscopy (SEM) and transmission electron microscopy. Their dynamic mechanical properties and thermostability were measured by dynamic mechanical analysis (DMA) and thermogravimetric analysis. The results indicate that the thermotropic acetylene‐terminated liquid‐crystal monomer melted into a schlieren texture. MPBE and PSA could copolymerize to fix the mesogenic domain in the crosslinked network and form a homogeneous‐phase sea‐island structure, which improved the rigidity and toughness of the materials. DMA showed that the storage modulus of the PSA–MPBE resins increased by about 400 MPa compared to the those of the pure components. The SEM experiments showed a noticeable change in the morphology, from a typical brittle fracture for the pure PSA to microplastic deformation behavior for the PSA–MPBE resins. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45141.     

Synthesis and characterization of a novel acetylene‐ and maleimide‐terminated benzoxazine and its high‐performance thermosets

A novel acetylene‐ and maleimide‐terminated benzoxazine, 3‐(3‐ethynylphenyl)‐3,4‐dihydro‐2H‐6‐(N‐maleimido)‐1,3‐benzoxazine (MBZ‐apa), was successfully synthesized with N‐(4‐hydroxyphenyl)maleimide, paraformaldehyde, and 3‐aminophenylacetylene. The structure of the benzoxazine is confirmed by FTIR and ¹H‐NMR spectroscopies. MBZ‐apa is easily dissolved in common organic solvents. Differential scanning calorimetry (DSC) was used to study thermal cross‐linking behavior of MBZ‐apa. The DSC curve shows only a single exothermic peak due to the oxazine ring‐opening polymerization and the polymerization of the acetylene and maleimide groups occurring simultaneously in the same temperature range. Dynamic mechanical analyses (DMA) reveals that the novel polybenzoxazine exhibits high glass‐transition temperature (T_g) (ca. 348°C). The storage modulus arrives at 4.5 GPa in the range of room temperature to 330°C. The polybenzoxazine exhibits good thermal stability as evidenced by thermogravimetric analysis (TGA). Pyrolysis‐gas chromatography/mass spectrometry (Pyrolysis‐GC/MS) was employed to characterize the polybenzoxazine. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Gas permeation and separation properties of sulfonated polyimide membranes

Permeability and selectivity of pure gas H₂, CO₂, O₂, N₂ and CH₄ as well as a mixture of CO₂/N₂ for sulfonated homopolyimides prepared from 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA) and 2,2-bis[4-(4-aminophenoxy)phenyl] hexafluoro propane disulfonic acid (BAPHFDS) were measured and compared to those of the non-sulfonated homopolyimide having the same polymer backbone. The polyimide in a proton form (NTDA-BAPHFDS(H)) displayed higher selectivity of H₂ over CH₄ without loss of H₂ permeability. Strong intermolecular interaction induced by sulfonic acid groups decreased diffusivity of the larger molecules. The CO₂/N₂ (19/81) mixed gas permeation was investigated as a function of humidity. With increasing relative humidity from 0% RH to 90% RH, the CO₂ permeability for NTDA-BAPHFDS(H) polyimide increased by more than one order of magnitude, and the selectivity of CO₂/N₂ also increased twice or more. On the other hand, the gas permeability for the non-sulfonated polyimide slightly decreased with increasing humidity. NTDA-BAPHFDS(H) polyimide displayed a CO₂ permeability of 290×10⁻¹⁰ cm³ (STP) cm/(cm² s cmHg) and a separation factor of CO₂/N₂ of 51 at 96% RH, 50 °C and total pressure of 1 atm.     

Novel acetylene‐terminated polyisoimides with excellent processability and properties comparison with corresponding polyimides

Two novel acetylene‐terminated isoimide oligomers and their corresponding imide oligomers have been synthesized by using trifluoroacetic anhydride or acetic anhydride as dehydrating agent, respectively. Their main structure was confirmed by Fourier transform infrared spectroscopy (FTIR). The isoimide oligomers were amorphous and showed excellent solublility in many common solvents, such as acetone and tetrahydeofuran, whereas the imide oligomers cannot dissolve in them. Differential scanning calorimetry and rheometer were used to study crosslinking behavior and processability of these oligomers. The isoimide oligomers exhibited considerably wider processing window and lower viscosity compared with imide ones. As expected, the isoimide form could be converted to imide form through thermal treatment, which could be demonstrated by FTIR. After the oligomers were cured, the polyisoimides showed similar properties compared with corresponding polyimides. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Characterization and gas permeation properties of UV‐cured fluorine‐containing telechelic polyimide membranes with a crosslinker

The characterization and gas permeation properties of ultraviolet (UV)‐cured fluorine‐containing telechelic polyimide membranes and end‐capped with a crosslinker with acryloyl groups were investigated. Membrane formation property was improved by the addition of crosslinker by using UV irradiation. The densities of UV‐cured membranes were almost similar to each other, and high gel fraction was shown on the UV‐cured membranes. This result suggests that the crosslinker promotes crosslink reaction at the polymer chain ends and does not induce appreciable membrane densification. Furthermore, the gas permeability of the UV‐cured membranes was higher than that of the membrane without the crosslinker. The higher gas permeability is due to the new crosslink structure formed at the polymer chain ends, which was promoted by the crosslinker after UV irradiation, but did not induce appreciable membrane densification. The use of a BEI crosslinker in the telechelic polyimide membranes promoted the crosslink reaction and increased the H₂ selectivity because H₂ permeability was not sensibly affected by the crosslink reaction. POLYM. ENG. SCI., 54:1089–1099, 2014. © 2013 Society of Plastics Engineers     

Gas permeation and separation properties of polyimide/ZSM‐5 zeolite composite membranes containing liquid sulfolane

The preparation, characterization, and gas permeation properties of novel composite membranes containing polyimide (PI), liquid sulfolane (SF), and zeolite (ZSM‐5) were investigated to address the interface defects between the PI and the zeolite. The free‐standing composite membranes were prepared by the solvent casting method. The gas permeability of the PI+ZSM‐5 membrane was higher than that of PI, whereas its gas selectivity was significantly reduced, suggesting that these results are attributed to the interface defects. The CO₂ selectivity of PI+ZSM‐5+SF was higher than those of the PI+ZSM‐5 membranes because of the introduction of liquid SF into the interface defects. Furthermore, liquid SF enhanced the CO₂/H₂ selectivity near the recent upper bound. Therefore, the use of liquid SF could be an effective approach to preventing interface defects and increasing the CO₂ selectivity, particularly for CO₂/H₂. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and characterization of fluorinated polyimide oligomers terminated with a phenylethynyl group

Novel all-aromatic phenylethynyl-terminated imide oligomers were prepared by the reaction of 4,4-oxydiphthalic anhydride (ODPA) or 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with 1,4-(4-amino-2-trifluoromethyl-phenoxy)-2-(3′-trifluoro-methylphenyl) benzene and 4-(1-phenylethynyl)1,8-naphthalic anhydride (PENA). The resulting polymers were thermally crosslinked at 370 °C. The cured polymers exhibited good solvent resistance and high thermal stability up to 540 °C under nitrogen. They also exhibited small light absorption at 1.31 and 1.55 μm. The refractive index of the polymers was in the range of 1.5515–1.5976 at 1550 nm. The surface relief depth of the phenylethyl terminated imide (PETI) oligomer films before and after curing was less than 1 nm over a range of 1 μm × 1 μm.     

Synthesis and characterization of hydroxypropyl terminated polydimethylsiloxane‐polyurethane copolymers

Polyurethane (PU) block copolymers were synthesized using prepared hydroxypropyl terminated polydimethylsiloxane (HTPDMS MW 990) and polyether diols (N‐210) as soft segment with 4,4′‐diphenylmethane diisocyanate (MDI) and 1,4‐butanediol. This low molecular weight polydimethylsiloxanes (PDMS) containing hydroxypropyl end‐groups displayed better compatibility with PU than common PDMS. In this article, we illustrate its synthesis routes and confirmed the proposed molecular structures using NMR and infrared radiation (IR). We varied the contents of HTPDMS and N‐210 in soft segments (HTPDMS—N‐210: 0 : 100, 20 : 80, 40 : 60, 60 : 40, 80 : 20, and 100 : 0) to synthesize a series of PDMS‐PU copolymer. IR spectroscopy showed the assignment characteristic groups of each peak in copolymers and confirmed that the desired HTPDMS‐PU copolymers have been prepared. The different thermal, dynamic mechanical and surface properties of the copolymers were compared by thermogravimetry, DMA, contact angle and solvent resistance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis,characterization, and permeation properties of polyether-based polyurethanes

A system of synthesis of polyether-based urethanes was developed which had sufficient flexibility in composition so that transport properties could be optimized. Mixtures of poly(oxyethylene) glycol (PEG) and poly(oxypropylene) glycol (PPG) of a variety of molecular weights were tied together by varying amounts of kinds of “hard segments.” Thus, the water swell, the mechanical properties, and the size of the soft blocks and hard blocks could be varied. With a fixed content of hard segments, the water absorption decreased with decrease in the PEG/PPG ratio, demonstrating the feasibility of producing controlled changes in hydrophilicity of the polymer without significant change in the mechanical strength. Some polyurethanes based on PEG 600 and PPG 425 had a very good high value of P_w/P_s but a somewhat low value of P_w. The polyurethanes prepared by using phenylenediamines as chain extenders had markedly enhanced modulus and an extended rubbery plateau region, as anticipated.     

Synthesis and characterization of ethoxy‐terminated ladder‐like polymethylsilsesquioxane oligomer

A fully ethoxy‐terminated ladder‐like polymethylsilsesquioxane oligomer (EtO‐Me‐T) has been synthesized and characterized for the first time using an effective transient catalyst (tetramethylammonium hydroxide, TMAH) via the dehydration alcoholysis reaction of hydroxy‐terminated ladder‐like polymethylsilsesquioxane (HO‐Me‐T) prepared by a modified stepwise coupling polymerization approach. Compared with the common acidic or basic catalysts, use of the transient catalyst TMAH can not only make the HO‐Me‐T molecules fully ethoxy‐terminated but also enables the catalyst to be readily and thoroughly removed after completion of the alcoholysis reaction. It is noteworthy that the common acidic or basic catalysts widely used in the dehydration alcoholysis reaction are clearly unsuitable for the preparation of EtO‐Me‐T oligomer because the latter would be hydrolyzed unavoidably back to the parent HO‐Me‐T during the washing process. In addition, preliminary exploration indicates that, when compared with the tetraethyl orthosilicate (Si(OEt)₄) generally used as a crosslinking agent for the room‐temperature vulcanization of silicone rubber (RTV‐SR), the oligomer EtO‐Me‐T is a promising replacement which can greatly improve the mechanical properties of RTV‐SR Copyright © 2003 Society of Chemical Industry     

Preparation and permeation characterization of β‐zeolite‐incorporated composite membranes

In this work, several β‐zeolite‐incorporated polymer composite membranes were fabricated with the solution‐casting method. The zeolite loadings were 10, 20, and 30 wt %, respectively. Scanning electron microscopy characterization showed that the zeolite particles could be uniformly distributed in the whole polymer matrix. Gas permeation results demonstrated that after the incorporation of the same β‐zeolite, the polyimide exhibited a significant increase in gas permeability but a decrease in permselectivity, and both were quite pronounced at high zeolite loadings; this resulted from the loose structure that formed. The poly(ether sulfone) composite membranes showed obvious increases in both permeability and selectivity, and the permeability increase was considerably greater at higher zeolite loadings. The permselectivity increase could possibly be attributed to the pore sieving and preferential adsorption of β‐zeolite entities for the test gases as the heat treatment may have resulted in the formation of a defect‐free microstructure. However, breakthrough of the upper‐bound line was not achieved for these composite membranes, as reflected by Robeson plots. Our results suggest that changes in membrane performance not only are attributable to the properties and content of β‐zeolite particles but also depend on the heterogeneous microstructure created by zeolite entities. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and properties of fluorene‐based polyimide adhesives

Five kinds of fluorene‐based polyimides (PIs) based on 4,4′‐oxydiphthalicanhydride (ODPA), 9,9′‐bis(4‐aminophenyl)fluorene (BAFL), and 3,4′‐diaminodiphenyl ether (3,4′‐ODA) were synthesized through two‐step method. The partially or fully imidized PI films were cast from poly(amic acid) (PAA) solution and were imidized by far‐infrared radiation at various temperatures. The degree of imidization was characterized by FT‐IR and TGA. The fully imidized PI films were characterized by DMTA, TGA, and tensile tests. The partially imidized PI films were adhered to stainless steel plates for preparing the single lap joints. Lap shear strength (LSS) at room temperature was measured to compare the adhesive strength of single lap joint. Fractured surfaces were analyzed using scanning electron microscopy (SEM). The effects of fluorene content on thermal, tensile, and adhesion properties of PIs were elaborately studied. The results showed that PI films exhibited high glass transition temperature (T_g), good thermalplasticity, and thermal stability. The LSS of PIs increased abruptly with the incorporation of fluorene groups. The LSS of PI‐50/50 was the highest, which was 22.3 MPa. The LSS of PI‐50/50 was also measured at high temperature to investigate the thermal resistance of fluorene‐based PI adhesive. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers.     

Processing robustness for a phenylethynyl‐terminated polyimide composite

The processability of a phenylethynyl‐terminated imide resin matrix (PETI‐5) composite was investigated. Unidirectional prepregs were made through the coating of an N‐methylpyrrolidone solution of an amide acid oligomer (PETAA‐5/NMP) onto unsized IM7 fibers. Two batches of prepregs were used: one was made by the National Aeronautics and Space Administration in house, and the other was from an industrial source. The composite processing robustness was investigated with respect to the prepreg shelf life, the effect of B‐staging conditions, and the optimal processing window. The prepreg rheology and open hole compression (OHC) strengths were not to affected by prolonged ambient storage (i.e., up to 60 days). Rheological measurements indicated that the PETAA‐5/NMP processability was only slightly affected over a wide range of B‐stage temperatures (from 250 to 300°C). The OHC strength values were statistically indistinguishable among laminates consolidated under various B‐staging conditions. An optimal processing window was established with response surface methodology. The IM7/PETAA‐5/NMP prepreg was more sensitive to the consolidation temperature than to the pressure. A good consolidation was achievable at 371°C (700°F)/100 psi, which yielded a room‐temperature OHC strength of 62 ksi. However, the processability declined dramatically at temperatures below 350°C (662°F), as evidenced by the OHC strength values. The processability of the IM7/PETI‐5 prepreg was robust. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3212–3221, 2006     

Synthesis,characterization, and properties of a novel positive photoresist polyimide

An aqueous base-soluble polyimide (BAPAF/6FDA) was obtained from the polycondensation of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (BAPAF) and 4,4′-(hexafluoroisopropylidene)–bis(phthalic anhydride (6FDA). It exhibits high thermal stability and high transparency at 365 nm. A novel positive photoresist was prepared by protecting BAPAF/6FDA with a trimethylsilyl group while using diazonaphthoquinone as the photosensitizer. In addition, the silylated polyimide was converted to aqueouse base-soluble polyimide in the presence of an acid and a slight amount of water. This photoresist yields a sensitivity of 110 mJ/cm² and a contrast of 3.24. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 67:1313–1318, 1998     

Synthesis and properties of fluorinated bis‐benzocyclobutene‐terminated arylene ether monomers

Four novel bis‐benzocyclobutene‐endcapped arylene ether monomers, 1,1′‐bis[4‐(4′‐benzocyclobutenyloxy)phenyl]‐1‐phenyl‐2,2,2‐trifluoroethane (BOPP3FE), 1,1′‐bis[4‐(4′‐benzocyclobutenyloxy)phenyl]‐1‐(3′,5′‐ditrifluoromethyl)phenyl‐2,2,2‐trifluoroethane(BOPP9FE), 2,2′‐bis[4‐(4′‐benzocyclobutenyloxy)phenyl]‐1,1,1,3,3,3‐hexfluoropropane (BOP6FP), and 2,2′‐bis[4‐(4′‐benzocyclobutenyloxy)phenyl]‐propane (BOPP) were prepared and characterized. All the four monomers showed similar curing behaviors under N₂ (Differential scanning calorimetry: extrapolated onset and peak temperatures at 225–229°C and 261–263°C) and demonstrated low and steady melt viscosities between 110 and 200°C, indicating their good processability. After cure, the resulting BCB resins exhibited high T_g (232–282°C) and excellent thermal stability (T_5% > 433°C). The resins also showed good mechanical properties with the flexural strengths of 68–88 MPa and the flexural modulus of 2.52–3.15 GPa. Moreover, the resins also exhibited low dielectric constants (2.58–2.88), low dissipation factors (2.7 to 8.4 × 10?4) and low water absorptions in boiling water for 24 h (0.29–0.59%). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Novel phenylethynyl‐endcapped polyimide oligomers: Synthesis and characterization

A series of novel phenylethynyl‐endcapped polyimide oligomers were prepared by polycondensation of an aromatic diamine mixture of 1,3‐bis(4‐aminophenoxy) benzene (1,3,4‐APB) and 3,4′‐oxydianiline (3,4′‐ODA) with different aromatic dianhydrides including 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), 4,4′‐(hexafluoro isopropylidene)diphthalic anhydride (6FDA), 4,4′‐oxydiphthalic anhydride (ODPA), and 4,4′‐[2,2,2‐trifluoro‐1‐(3′,5′‐bis‐(trifluoro‐methyl)phenyl)ethylidene]diphthalic anhydride (9FDA) in the presence of 4‐phenyl‐ethynylaniline (PEA) as endcapping agent in aprotic solvent at elevated temperature. The chemical structures, thermal behavior, and melt rheological properties of the synthesized polyimide oligomers were investigated. Experimental results indicated that the fluorinated polyimide oligomers derived from 6FDA (PI‐2) and 9FDA (PI‐4) are amorphous solid resins and exhibited lower melt viscosities than those prepared from the unfluorinated aromatic dianhydrides such as BPDA and ODPA. The BPDA‐based polyimide oligomers with a molar ratio of 1,3,4‐APB/3,4′‐ODA = 50:50 (PI‐5) showed lower melt viscosity than those derived from a mixture of 1,3,4‐APB and 3,4′‐ODA with molar ratios of 75:25 and 100:0, respectively. In addition, the melt viscosity of the polyimide oligomers increased obviously with increasing of the polymer calculated molecular weights. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers