Isomeric compositions in amide acids and poly(amic acid)s derived from 1-(trifluoromethyl)-2,3,5,6-benzenetetracarboxylic dianhydride

Two different poly(amic acid)s were synthesized by the polycondensations of 1-(trifluoromethyl)-2,3,5,6-benzenetetracarboxylic dianhydride (CF3DAN) with p-phenylene diamine and benzidine. In addition, an amide acid model compound was prepared from CF3DAN and aniline. Isomeric units in the poly(amic acid)s as well as the amide acid were investigated by ¹H and ¹³C-nuclear magnetic resonance (NMR) spectroscopies. Spectroscopic results indicate that the major isomeric component was a CF3-meta-isomeric unit centered on the aromatic carbon substituted with the trifluoromethyl group. In particular, the amide acid compound was determined to be composed of 80 mol % CF3-meta-isomer and 20 mol % H-meta-isomer. Therefore, for the poly(amic acid)s, the minor isomeric component is speculated to be a H-meta-isomeric unit rather than a para-isomeric unit. The result might result mainly from the strong electron-withdrawable and bulky trifluoromethyl substituent in the CF3DAN monomer. The strong electron withdrawability might significantly enhance the reactivities of the adjacent carbons in the monomer to the nucleophilic attack of the amino nitrogen in the aniline and diamines, and consequently overcome the role of the bulkyness, ultimately leading to the amide acid and poly(amic acid)s rich with the CF3-meta-isomeric unit. In addition, a portion of the imide form was detected in the dried AN-CF3DAM-AN amide acid. Thus, the formation of imide linkage might be involved in a small portion for the dried poly(amic acid)s. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1755–1765, 1998     

Polyimide containing internal acetylene units linked para to the aromatic ring

4,4′-Diaminodiphenylacetylene (p-intA) was reacted with 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA) in N-methyl-2-pyrrolidone (NMP) to give poly(amic acid) solution of moderate to high viscosity. Thermal imidization gave polyimide having acetylene units that are linked para to the aromatic connecting unit. Polyimide having acetylene units that are linked meta to the aromatic connecting unit also was prepared utilizing 3,3′-diaminodiphenylacetylene (m-intA) for comparison. The crosslinking behavior of the acetylene units was observed with DSC. Exotherm due to the crosslinking of the para-linked acetylene units appeared at ca. 340 to 380°C depending on the structure of polyimide, whereas meta-linked acetylene units appeared at lower temperature as 340–350°C. After thermal treatment at high temperature such as 350 or 400°C, the amount of the exotherm became smaller and finally disappeared on DSC, confirming the progress of crosslinking. Dynamic mechanical properties of the polyimide films show that glass transition temperature increased with higher heat treatment, also confirming the progress of crosslinking. Tensile properties of the polyimide films showed that rigid polyimide films consisting of p-intA with BPDA or PMDA have considerably higher modulus than those consisting of m-intA. Cold-drawing of the poly(amic acid) followed by imidization gave much higher modulus in the case of rigid polyimide. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2395–2402, 1997     

Synthesis and properties of polyimides derived from 1,6-bis(4-aminophenoxy)naphthalene and aromatic tetracarboxylic dianhydrides

1,6-Bis(4-aminophenoxy)naphthalene ( I ) was used as a monomer with various aromatic tetracarboxylic dianhydrides to synthesize polyimides via a conventional two-stage procedure that included ring-opening polyaddition in a polar solvent such as N,N-dimethylacetamide (DMAc) to give poly(amic acid)s, followed by thermal cyclodehydration to polyimides. The diamine ( I ) was prepared through the nucleophilic displacement of 1,6-dihydroxynaphthal-ene with p-chloronitrobenzene in the presence of K₂CO₃, followed by catalytic reduction. Depending on the dianhydrides used, the poly(amic acid)s obtained had inherent viscosities of 0.73–2.31 dL/g. All the poly(amic acid)s could be solution cast and thermally converted into transparent, flexible, and tough polyimide films. The polyimide films had a tensile modulus range of 1.53–1.84 GPa, a tensile strength range of 95–126 MPa, and an elongation range at break of 9–16%. The polyimide derived from 4,4′-sulfonyldiphthalic anhydride (SDPA) had a better solubility than the other polyimides. These polyimides had glass transition temperatures between 248–286°C (DSC). Thermogravimetric analyses established that these polymers were fairly stable up to 500°C, and the 10% weight loss temperatures were recorded in the range of 549–595°C in nitrogen and 539–590°C in air atmosphere. © 1995 John Wiley & Sons, Inc.     

Synthesis and properties of novel aromatic poly(ester-imide)s bearing 1,5-bis(benzoyloxy)naphthalene units

Two series of new aromatic poly(ester-imide)s were prepared from 1,5-bis(4-aminobenzoyloxy)naphthalene (p-1) and 1,5-bis(3-aminobenzoyloxy)naphthalene (m-1), respectively, with six commercially available aromatic tetracarboxylic dianhydrides via a conventional two-stage synthesis that included ring-opening polyaddition to give poly(amic acid)s followed by chemical imidization to polyimides. The intermediate poly(amic acid)s obtained in the first stage had inherent viscosities of 0.41-0.84 and 0.66-1.37 dl/g, respectively. All the para-series and most of the meta-series poly(ester-imide)s were semicrystalline and showed less solubility. Two of the meta-series poly(ester-imide)s derived from less rigid dianhydrides were amorphous and readily soluble in polar aprotic solvents, and they could be solution-cast into transparent and tough films with good mechanical properties. The meta-series polymers derived from rigid dianhydrides were generally semicrystalline and showed less solubility. Except for one example, the meta-series poly(ester-imide)s displayed discernible T_gs in the range 239-273 °C by DSC. All of these two series poly(ester-imide)s did not show significant decomposition below 450 °C in nitrogen or in air.     

Synthesis and thermal behaviour of silicon containing poly(ester imide)s

A series of silicon containing poly(ester imide)s [PEIs] were synthesized using novel vinyl silane diester anhydride (VSEA) and various aromatic and aliphatic dimines by two-step process includes ring-opening polyaddition reaction to form poly(amic acid) and thermal cyclo-dehydration process to obtain poly(ester imide)s. VSEA was synthesized by using dichloro methylvinylsilane and trimellitic anhydride in the presence of K₂CO₃ by nucleophilic substitution reaction. The PEIs were characterized by FTIR spectroscopy. The thermal properties of PEIs were investigated by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) methods. The prepared PEIs showed glass transition temperatures in the range of 320–350°C and their 5% mass loss was recorded in the temperature range of 500–520°C in nitrogen atmosphere. These had char yield in the range of 45–55% at 800°C.     

Synthesis and properties of polyimides derived from 1,7-bis(4-aminophenoxy)naphthalene and aromatic tetracarboxylic dianhydrides

The novel diamine, 1,7-bis(4-aminophenoxy)naphthalene (1,7-BAPON), was synthesized and used to prepared polyimides. 1,7-BAPON was synthesized through the nucleophilic displacement of 1,7-dihydroxynaphthalene with p-fluoronitrobenzene in the presence of K₂CO₃ followed by catalytic-reduction. Polyimides were prepared from 1,7-BAPON and various aromatic tetracarboxylic dianhydrides by the usual two-step procedure that included ring-opening polyaddition to give poly(amic acid)s, followed by cyclodehydration to polyimides. The poly(amic acid)s had inherent viscosities of 0.74-2.48 dL/g. Most of the polyimides formed tough, creasible films. These polyimides had glass transition temperatures between 247–278°C and their 10% weight loss temperatures were recorded in the range of 515–575°C in nitrogen atmosphere. © 1995 John Wiley & Sons, Inc.     

Synthesis and properties of new adamantane‐based poly(ether imide)s

A new adamantane‐based bis(ether anhydride), 2,2‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]adamantane dianhydride, was prepared in three steps starting from nitrodisplacement of 4‐nitrophthalonitrile with the potassium phenolate of 2,2‐bis(4‐hydroxyphenyl)adamantane. A series of adamantane‐containing poly(ether imide)s were prepared from the adamantane‐based bis(ether anhydride) and aromatic diamines by a conventional two‐stage synthesis in which the poly(ether amic acid)s obtained in the first stage were heated stage‐by‐stage at 150–270°C to give the poly(ether imide)s. The intermediate poly(ether amic acid)s had inherent viscosities between 0.56 and 1.92 dL/g. Except for those from p‐phenylenediamine, m‐phenylenediamine, and benzidine, all the poly(ether amic acid) films could be thermally converted into transparent, flexible, and tough poly(ether imide) films. All the poly(ether imide)s showed limited solubility in organic solvents, although they were amorphous in nature as evidenced by X‐ray diffractograms. Glass transition temperatures of these poly(ether imide)s were recorded in the range of 242–317°C by differential scanning calorimetry and of 270–322°C by dynamic mechanical analysis. They exhibited high resistance to thermal degrdation, with 10% weight loss temperatures being recorded between 514–538°C in nitrogen and 511–527°C in air. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1619–1628, 1999     

Molecular weight dependence of mechanical properties of poly(p,p′-oxydiphenylene pyromellitimide) films

The mechanical properties, i.e., Young's modulus, elongation, and tensile stress, were determined as functions of the molecular weight for films of poly(oxydi-p-phenylene pyromellitimide) prepared by thermal cyclization of the precursor poly(amic acid). The molecular weights of the samples were controlled by the monomer stoichiometry employed for the solution condensation of pyromellitic dianhydride and p,p′-oxydianiline. Weight-average molecular weights were determined by light scattering of the precursor poly(amic acid) as well as the fully cyclized polyimide. The elongation-at-break is most sensitive to the molecular weight, undergoing a rapid increase at M _w ? 8000 and reaching a limiting value of about 60% for M _w > 20,000.     

Synthesis and characterization of new fluorene‐based poly(ether imide)s

A novel bis(ether anhydride) monomer, 9,9‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]fluorene dianhydride (4), was synthesized from the nitrodisplacement of 4‐nitrophthalonitrile by the bisphenoxide ion of 9,9‐bis(4‐hydroxyphenyl)fluorene (1), followed by alkaline hydrolysis of the intermediate tetranitrile and dehydration of the resulting tetracarboxylic acid. A series of poly(ether imide)s bearing the fluorenylidene group were prepared from the bis(ether anhydride) 4 with various aromatic diamines 5a–i via a conventional two‐stage process that included ring‐opening polyaddition to form the poly(amic acid)s 6a–i followed by thermal cyclodehydration to the polyimides 7a–i. The intermediate poly(amic acid)s had inherent viscosities in the range of 0.39–1.57 dL/g and afforded flexible and tough films by solution‐casting. Except for those derived from p‐phenylenediamine, m‐phenylenediamine, and benzidine, all other poly(amic acid) films could be thermally transformed into flexible and tough polyimide films. The glass transition temperatures (T_g) of these poly(ether imide)s were recorded between 238–306°C with the help of differential scanning calorimetry (DSC), and the softening temperatures (T_s) determined by thermomechanical analysis (TMA) stayed in the range of 231–301°C. Decomposition temperatures for 10% weight loss all occurred above 540°C in an air or a nitrogen atmosphere. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1403–1412, 1999     

Synthesis and evaluation of novel polyimides derived from spirobichroman diether anhydride

A spirobichroman structure-containing diether anhydride (SBCDA), 6,6′-bis(3,4-dicarboxyphenoxy)-4,4,4′,4′,7,7′-hexamethyl-2,2′-spirobichroman dianhydride, was prepared by the nucleophilic nitrodisplacement of 4-nitrophthalonitrile with the phenolate ion of 6,6′-dihydroxy-4,4,4′,4′,7,7′-hexamethyl-2,2′-spirobichroman, followed by alkaline hydrolysis of the intermediate tetranitrile and dehydration of the resulting tetraacid. A series of high molecular weight poly(ether imide)s with inherent viscosities between 0.45 and 1.28 dL/g were synthesized from SBCDA and various aromatic diamines via a conventional two-stage procedure that included ring-opening polyaddition in N,N-dimethylacetamide (DMAc) to give poly(amic acid)s, followed by thermal cyclization to poly(ether imide)s. The intermediate poly(amic acid)s had inherent viscosities of 0.70–1.50 dL/g. Except for the poly(ether imide) obtained from p-phenylenediamine, the other poly(ether imide)s were soluble in various organic solvents and could be solution-cast into transparent, flexible, and tough films. These poly(ether imide)s had glass transition temperatures in the range 175–262°C and showed no significant decomposition below 420°C, with 10% weight loss being recorded above 446°C in nitrogen or air. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2801–2809, 1997     

Synthesis and properties of new polyimides derived from 1,5-bis(4-aminophenoxy)naphthalene and aromatic tetracarboxylic dianhydrides

Novel aromatic polyimides containing bis(phenoxy)naphthalene units were synthesized from 1,5-bis(4-aminophenoxy)naphthalene (APN) and various aromatic tetracarboxylic dianhydrides by the usual two-step procedure that included ring-opening polyaddition in a polar solvent such as N,N-dimethylacetamide (DMAc) to give poly(amic acid)s, followed by cyclodehydration to polyimides. The poly(amic acid)s had inherent viscosities between 0.72 and 1.94 dL/g, depending on the tetracarboxylic dianhydrides used. Excepting the polyimide IVb obtained from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), all other polyimides formed brown, flexible, and tough films by casting from the poly(amic acid) solutions. The polyimide synthesized from BPDA was characterized as semicrystalline, whereas the other polyimides showed amorphous patterns as shown by the x-ray diffraction studies. Tensile strength, initial moduli, and elongation at break of the APN-based polyimide films ranged from 105–135 MPa, 1.92–2.50 GPa, and 6–7%, respectively. These polyimides had glass transition temperatures between 228 and 317°C. Thermal analyses indicated that these polymers were fairly stable, and the 10% weight loss temperatures by TGA were recorded in the range of 543–574°C in nitrogen and 540–566°C in air atmosphere, respectively. © 1993 John Wiley & Sons, Inc.     

Thianthrene-containing polyimides with monomer formation via nucleophilic aromatic substitution

Thianthrene-2,3,7,8-tetracarboxylic dianhydride was synthesized via nucleophilic aromatic substitution of N-phenyle-4,5-dichlorophthalimide with thiobenzamide, thioacetamide, and sodium sulfide. This monomer was then polymerized with aromatic diamines by the con-ventional low temperature technique in N,N-dimethylacetamide (DMAc) to yield soluble poly(amic acid)s. Polyimides were obtained by thermal cyclization of the poly(amic acid) films. Polymers obtained formed creasable thin films and had excellent thermal stability in air and nitrogen. The bent thianthrene structure limited crystallization and chain packing, as indicated by x-ray analysis. The amorphous thianthrene-containing polyimides were only soluble in H₂SO₄. © 1995 John Wiley & Sons, Inc.     

Synthesis and characterization of some Schiff-base-containing polyimides

The diamine, 4-aminophenyloxy-N-4-[(4-amiophenyloxy)benzylidene]aniline, was prepared via the nucleophilic substitution reaction and was polymerized with different dianhydrides either by one-step solution polymerization reaction or two-step procedure. The latter includes ring-opening polyaddition to give poly(amic acid), followed by cyclodehydration to polyimides. The inherent viscosity ranges from 0.61–0.79 dl/g. Some of the polymers were soluble in most of the organic solvents such as DMSO, DMF, DMAc, NMP, and m-cresol even at room temperature. The degradation temperature of the resultant polymers falls in the ranges from 240–500 °C in nitrogen with only 10% weight loss. Specific heat capacity at 200 °C ranges from 1.0929–2.6275 J g⁻¹ k⁻¹. The temperature at which the maximum degradation of the polymer occurs ranges from 600–630 °C. The glass transition temperature (Tg) values of the polyimides ranged from 185 to 272 °C. The activation energy and enthalpy of the polyimides ranged from 47.5–55.0 kJ/mole and 45.7–53.0 kJ/mole and the moisture absorption in the range of 0.23–0.72%.     

Synthesis and properties of polyimides derived from 1,4-bis(4-aminophenoxy)2,5-di-tert-butylbenzene

Novel aromatic polyimides containing symmetric, bulky di-tert-butyl substituents unit were synthesized from 1,4-bis(4-aminophenoxy)2,5-di-tert-butylbenzene (BADTB) and various aromatic tetracarboxylic dianhydrides by the conventional two-stage procedure that included ring-opening polyaddition in a polar solvent such as N,N-dimethylacetamide to give poly(amic acid)s, followed by cyclodehydration to polyimides. The diamine was prepared through the nucleophilic displacement of 2,5-di-tert-butylhydroquinone with p-chloronitrobenzene in the presence of K₂CO₃, followed by catalytic reduction. Depending on the dianhydrides used, the poly(amic acid)s obtained had inherent viscosities of 0.83–1.88 dL g⁻¹. Most of the polyimides formed transparent, flexible, and tough films. Tensile strength and elongation at break of the BADTB-based polyimide films ranged from 68–93 MPa and 7–11%, respectively. The polyimide derived from 4,4′-hexafluoro-isopropylidenebisphathalic anhydride had better solubility than the other polyimides. These polyimides had glass transition temperatures between 242–298°C and 10% mass loss temperatures were recorded in the range of 481–520°C in nitrogen. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1527–1534, 1997     

Synthesis and characterization of new cardo polyimides prepared from 5,5-Bis[4-(4-aminophenoxy)phenyl]-4,7-methanohexahydroindane

A new cardo diamine monomer, 5,5-bis[4-(4-aminophenoxy)phenyl]-4,7-methanohexahydroindane (II), was prepared in two steps with high yield. The monomer was reacted with six different aromatic tetracarboxylic dianhydrides in N,N-dimethylacetamide (DMAc) to obtain the corresponding cardo polyimides via the poly(amic acid) precursors and thermal or chemical imidization. All the poly(amic acid)s could be cast from their DMAc solutions and thermally converted into transparent, flexible, and tough polyimide films which were further characterized by x-ray and mechanical analysis. All of the polymers were amorphous and the polyimide films had a tensile strength range of 89–123 MPa, an elongation at break range of 6–10%, and a tensile modulus range of 1.9–2.5 GPa. Polymers V_c, V_e, and V_f exhibited good solubility in a variety of solvents such as N-methyl-2-pyrrolidinone (NMP), DMAc, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), pyridine, γ-butyrolactone, and even in tetrahydrofuran and chloroform. These polyimides showed glass-transition temperatures between 274 and 299°C and decomposition temperatures at 10% mass loss temperatures ranging from 490 to 521°C and 499 to 532°C in nitrogen and air atmospheres, respectively. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2815–2821, 1999     

Synthesis and characterization of photo‐crosslinkable poly(amic acid ester)s with 2‐hydroxy‐4‐oxo‐hept‐5‐enyl side chain

Photosensitive poly(amic acid ester)s (PAEs) with 2‐hydroxy‐4‐oxo‐hept‐5‐enyl side group were simply synthesized from a non‐photosensitive polyamic acid (PAA), which was prepared from cyclobutane‐1,2,3,4‐tetracarboxylic dianhydride (CBDA) and 4,4′‐diaminodiphenyl ether (DDE) in N‐methyl‐2‐pyrrolidinone (NMP). 1‐oxiranyl‐pent‐3‐en‐2‐one was added to the poly(amic acid) solution to give the photosensitive PAEs by a ring opening esterification of the poly(amic acid). The esterification reaction was conducted with changing a reaction time and amounts of 1‐oxiranyl‐pent‐3‐en‐2‐one. The degree of esterification (DOE) increased with increasing esterification reaction time and amounts of 1‐oxiranyl‐pent‐3‐en‐2‐one. A photo‐lithography evaluation for the PAE‐D4 with the highest DOE was conducted in the presence of 1‐[4‐(phenylthio)phenyl]‐2‐(O‐benzoyloxime)‐1,2‐octanedione (PPBO) as a photoinitiator at a wavelength of 365 nm using a high‐pressure mercury lamp. The normalized film thicknesses for PAE‐D3 were measured with various post‐exposure baking (PEB) temperatures, which showed that the optimum PEB temperature was 120°C. The resolution of the resulting polyimide film cured at 250°C for 60 min was 25 µm. The initial decomposition temperature of the polyimide film was around 354°C and there was no weight loss at the temperature of 250–350°C. Copyright © 2009 John Wiley & Sons, Ltd.     

Syntheses and properties of aromatic polyamides and polyimides derived from 9,9-bis[4-(p-aminophenoxy)phenyl]fluorene

9,9-Bis[4-(p-aminophenoxy)phenyl]fluorene ( II ) was used as a monomer with various aromatic dicarboxylic acids and tetracarboxylic dianhydrides to synthesize polyamides and polyimides, respectively. The diamine II was derived by a nucleophilic substitution of 9,9-bis(4-hydroxyphenyl)fluorene with p-chloronitrobenzene in the presence of K₂CO₃ and then hydro-reduced. Polyamides IV _a-g having inherent viscosities of 0.73–1.39 dL/g were prepared by the direct polycondensation of the diamine II with various aromatic diacids using triphenyl phosphite and pyridine as condensing agents. All the aromatic polyamides were amorphous and readily soluble in various polar solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, dimethylsulfoxide, and N-methyl-2-pyrrolidone. Transparent and flexible films of these polymers could be cast from the DMAc solutions. These aromatic polyamides had glass transition temperatures in the range of 283–309°C and 10% weight loss occurred up to 460°C. The polyimides were synthesized from diamine II and various aromatic dianhydrides via the two-stage procedure that included ring-opening poly-addition in DMAc to give poly(amic acid)s, followed by thermal or chemical conversion to polyimides. The poly(amic acid)s had inherent viscosities of 0.62–1.78 dL/g, depending on the dianhydrides. Most of the aromatic polyimides obtained by chemical cyclization were found to be soluble in NMP. These polyimides showed almost no weight loss up to 500°C in air or nitrogen atmosphere. © 1993 John Wiley & Sons, Inc.     

Investigation on the gelation behavior of biodegradable poly(butylene succinate) during isothermal crystallization process

The early stage of polymer crystallization may be viewed as physical gelation process,i.e.,the phase transition of polymer from liquid to solid.Determination of the gel point is of significance in polymer processing.In this work,the gelation behavior of poly(butylene succinate)(PBS) at different temperatures has been investigated by rheological method.It was found that during the isothermal crystallization process of PBS,both the storage modulus(G′) and the loss modulus(G″) increase with time,and the rheological response of the system varies from viscous-dominated(G′G″),meaning the phase transition from liquid to solid.The physical gel point was determined by the intersection point of loss tangent curves measured under different frequencies.The gel time(t_c) for PBS was found to increase with increasing crystallization temperature.The relative crystallinity of PBS at the gel point is very low(2.5%-8.5%) and increases with increasing the crystallization temperature.The low crystallinity of PBS at the gel point suggests that only a few junctions are necessary to form a spanning network,indicating that the network is"loosely"connected,in another word,the critical gel is soft.Due to the elevated crystallinity at gel point under higher crystallization temperature,the gel strength S_g increases, while the relaxation exponent n decreases with increasing the crystallization temperature.These experimental results suggest that rheological method is an effective tool for verifying the gel point of biodegradable semi-crystalline polymers.     

Correlations between the morphology and the thermo-mechanical properties in poly(vinyl acetate)/epoxy thermosets

The mechanical properties of poly(vinyl acetate) (PVAc)/epoxy thermosets as a function of the PVAc content were investigated through dynamic mechanical thermal analysis from −100 to 220 °C and through tensile tests at room temperature. The morphology of the thermosets was examined by scanning electron microscopy. Cured PVAc/epoxy blends are phase separated, arising two phases that correspond to a PVAc-rich phase and to the epoxy rich-phase. The morphology evolves from nodular to inverted as the PVAc content increases. Intermediate compositions present combined morphologies, in which nodular and inverted regions are detected. The tensile properties at room temperature reveal that combined morphologies present the most ductile behaviour. The glass transition temperatures (T _g) of PVAc and of epoxy phases in the blends are different from those of the neat polymers. The profile of the loss modulus (E″)–temperature curves are correlated with the change in morphology that appears increasing the PVAc content. The storage modulus (E′)–temperature curves are highly dependent on the morphology of the samples. The E′-composition dependence is predicted using several models for two-phase composites. The low-temperature β-relaxation of the epoxy is slightly modified by the presence of PVAc. The activation energies of the α and β-relaxations are not dependent on the blend morphology.     

Synthesis and characterization of novel aromatic poly(imide–benzoxazole) copolymers

New poly(imide–benzoxazole) copolymers were prepared directly from a dianhydride, a diacid chloride, and a bis(o‐diaminophenol) monomer in a two‐step method. In the first step, poly(amic acid–hydroxyamide) precursors were synthesized by low‐temperature solution polymerization in an organic solvent. Subsequently, the thermal cyclodehydration of the poly(amic acid–hydroxyamide) precursors at 350 °C produced the corresponding poly(imide–benzoxazole) copolymers. The inherent viscosities of the precursor polymers were around 0.19–0.33 dL/g. The cyclized poly(imide–benzoxazole) copolymers had glass‐transition temperatures in the range of 331–377 °C. The 5% weight loss temperatures ranged from 524 to 535 °C in nitrogen and from 500 to 514 °C in air. The poly(imide–benzoxazole) copolymers were amorphous, as evidenced by the wide‐angle X‐ray diffraction measurements. The structures of the precursor copolymers and the fully cyclized copolymers were characterized by Fourier transform infrared, ¹H NMR, and elemental analysis. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6020–6027, 2005