Nafeesa Mushtaq

Synthesis and crosslinking study of isomeric poly(thioether ether imide)s containing pendant nitrile and terminal phthalonitrile groups

Two novel series of highly organosoluble and curable polyimides containing pendant nitrile groups PI (a–d) and phthalonitrile-terminated polyimides PN-PI (a–d) were prepared by solution polycondensation of isomeric bis(chlorophthalimides)s and 2,6-dichlorobenzonitrile with 4,4′-thiobisbenzenethiol. The inherent viscosities of these copolymers were in the range of 0.37–0.59 dL g−1 in N-methyl-2-pyrrolidone (NMP) at 30 °C. The phthalonitrile and pendant nitrile groups in isomeric poly(thioether-ether-imide)s were thermally crosslinked without a catalyst through thermal curing up to 280–360 °C, which led to the transformation from thermoplastic polymers to thermosetting polymers. All PIs before and after crosslinking were characterised by gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) spectroscopy. PN-PI (a–d) and PI (a–d) were found to be highly soluble in some solvents, such as chloroform, dimethylacetamide, m-cresol, dimethlyformamide and N-methyl-2-pyrrolidone, while the crosslinked polymers were insoluble in all tested solvents. The crosslinking results of pendant nitrile and terminal phthalonitrile groups are also compared. Both series of PIs showed high thermal stability based on 5% weight loss temperature (T5%) in the range of 471–509 °C and increased up to 35 °C after thermal curing. Polyimides showed high glass transition temperatures (Tgs) ranging from 191–213 °C as determined by DSC, but no detectable Tg was observed after thermal heating, indicating the crosslinked structure of PIs. The mechanical properties also enhanced after the crosslinking of the copolymers. The tensile modulus and strength of the cured PI films were in the range of 3.3–4.7 GPa and 68–122 MPa, respectively, which were up to 62% and 35% higher than the uncured films.

Organosoluble and high Tg polyimides from asymmetric diamines containing N-amino and N-aminophenyl naphthalimide moieties

To investigate the asymmetric effect of the naphthalimide moiety on the thermal, mechanical, optical properties and water uptake of polyimides (PIs), two novel asymmetric diamines, 4-(4-aminophenoxy)-N-amino-1,8-naphthalimide 3 and 4-(4-aminophenoxy)-N-(4-aminophenyl)-1,8-naphthalimide 4 were synthesized. Two series of PIs 5b–e and 6a–e were prepared from diamines 3 and 4 by solution polymerization method, respectively. The resulting polyimides demonstrated good solubility, high glass transition temperature (Tg) of 311–421 °C and good thermal stability based on the 5% weight loss temperature (T5%) of 435–563 °C in nitrogen. These PIs also exhibited good mechanical properties with tensile strengths of 107.3–172.2 MPa, tensile moduli of 2.8–4.9 GPa, and elongations at break of 2.9–9.1%. The water uptake of PIs was in the range of 0.33–1.96%. The polyimides displayed UV-vis absorption maxima and an intense fluorescent intensity in the range of 361–371 and 480–700 nm, respectively.

Synthesis of organosoluble and transparent phenolphthalein-based cardo poly(ether sulfone imide)s via aromatic nucleophilic substitution polymerization

A series of cardo poly(ether sulfone imide)s (PESI-C) containing bulky phthalide groups were prepared via aromatic nucleophilic substitution reaction of phenolphthalein with 4,4′-difluorodiphenyl sulfone and 4,4′-bis(4-fluorophthalimido)diphenyl ether (BFPI). The glass transition temperatures and 5% weight loss temperatures in nitrogen of the resulting PESI-C increased from 258°C to 278°C and from 468°C to 495°C with increasing the content of imide moiety in the polymer chain, respectively. These PESI-C films were transparent and essentially colorless and exhibited good mechanical properties with tensile strengths of 91–124 MPa, elongations at break of 6.9–12.8%, and tensile moduli of 2.2–2.8 GPa, respectively. It is noted that the tensile strengths, elongations at break, and tensile moduli of PESI-C also increased with increasing the content of BFPI in the copolymerization, indicating that the properties could be adjusted by controlling the ratio of BFPI and 4,4′-difluorodiphenyl sulfone.

Processable poly(benzoxazole imide)s derived from asymmetric benzoxazole diamines containing 4-phenoxy aniline: synthesis, properties and the isomeric effect

Two asymmetric diamine monomers, incorporating both aryl ether and non-linear benzoxazole groups, namely 5-amino-2-(4-(4-aminophenoxy)phenyl)benzoxazole (p-BOODA) and 5-amino-2-(3-(4-aminophenoxy)phenyl)benzoxazole (m-BOODA), were designed and synthesized. Two novel series of poly(benzoxazole imide)s (PBOIs), PI-3(a–e) and PI-4(a–e), were prepared via thermal imidization of commercial tetracarboxylic dianhydrides with diamines p-BOODA and m-BOODA, respectively. The effects of chain isomerism on molecular packing and the physical properties of PBOIs are investigated. These PBOIs showed excellent mechanical properties with tensile strengths of 106–168 MPa, tensile moduli of 2.7–5.5 GPa and elongations at break of 4.4–9.3%; in addition, they exhibited good thermal stability (T5% = 488–570 °C) and high glass transition temperatures (Tgs) up to 333 °C. Moreover, BTDA (3,3′,4,4′-benzophenone tetracarboxylic dianhydride) derived PBOIs, PI-3b and PI-4b, showed crystalline transition in spite of bent groups and the asymmetric chain structure. The incorporation of the asymmetric benzoxazole structure with flexible ether connecting groups improved the solubility of the PBOI system. Furthermore, the controlled molecular weight (Mw) polymer PI-4e-PA derived from m-BOODA demonstrated excellent solution and melt processability with the lowest complex viscosity of 44 Pa s at 380 °C.

Synthesis of high Tg and organosoluble poly(N-arylene benzimidazole ether imide) copolymers by C–N/C–O coupling reaction

A series of poly(N-arylene benzimidazole ether imide) copolymers PEIBIs were prepared from 1H,3′H-5,5′-bis-benzimidazole, bisphenol-A and 4,4′-bis(4-fluorophthalimido)diphenyl ether by nucleophilic displacement polymerization. The resulting copolymers PEIBI(10–90) demonstrated moderate to good solubility in polar aprotic solvents and high glass transition temperatures (Tgs) of 228–336°C, good thermal stability with 10% weight loss temperatures in the range of 503–548°C. All copolymer films showed good mechanical properties with tensile strengths of 101–130 MPa, tensile moduli of 3.3–4.0 GPa, elongations at break of 5–7%, and also presented low water uptake (0.15–0.34%). The wide-angle X-ray diffraction results revealed the amorphous nature of copolymers. The copolymer PEIBI-80 showed good balance in solubility, thermal and mechanical properties.