Xiaoye Ma

Properties, Morphology and Structure of BPDA/PPD/TFMB Polyimide Fibers

Abstract A family of random co-poly(amic acid)s containing 4,4′-oxydianiline (ODA) moiety were synthesised in N,N′-dimethylacetamide. The co-poly(amic acid) solutions were used as spinning dope for dry jet wet spinning process into as spun poly(amic acid) (PAA) fibres. The polyimide (PI) fibres were obtained from PAA fibres after being imidised and drawn in furnace. The processability and mechanical properties of the fibres were notably improved by incorporating ODA into 3,3′,4,4′-biphenyltetracarboxylic dianhydride/p-phenylenediamine (BPDA/PPD) backbone. The best strength and modulus of BPDA/PPD/ODA PI fibre (diamine mole ratio of PPD/ODA = 85∶15) attained 2·25 and 96·5 GPa respectively, which were approximately three times the tenacity of the BPDA/PPD PI fibre. The SEM image showed that the cross-section of each stage fibres was round and void free. In addition, ‘skin–core’ and microfibrillar structure were not observed. The thermal properties of PI fibres were also investigated. The results showed that the PI fibres have excellent thermal stability; moreover, the dimensional stability and structural homogeneity of the fibres were significantly improved by heat drawn stage. Tg was found to be ∼290°C by thermomechanical and dynamic mechanical analyses. The X-ray (wide angle X-ray diffraction and small angle X-ray scattering) experiments indicated that the ordering degree of longitudinal and lateral stacks, as well as the molecular orientation of PI fibre, was improved in the preparation process of fibres. Furthermore, the mechanical properties of fibres are profoundly affected by the heat drawn conditions.

An Optically Active Polymer for Broad-Spectrum Enantiomeric Recognition of Chiral Acids

Recognition of enantiomers of chiral acids by anion-π or lone pair-π interactions has not yet been investigated but is a significant and attractive challenge. This study reports an optically active polymer-based supramolecular system with capabilities of discriminating enantiomers of various chiral acids. The polymer featuring alternate π-acidic naphthalenediimides (NDIs) and methyl l-phenylalaninates in the backbone exhibits an unprecedented slow self-assembly process that is susceptible to perturbation by various chiral acids. Thus, the combination of anion-π or lone pair-π interactions and sensitivity of the polymeric self-assembly process to external chiral species endows the system with recognition capabilities. This is the first time that anion-π or lone pair-π interactions have been applied in the recognition of enantiomers of various chiral acids with a single system. The results shed light on new strategies for material design by integrating π-acidic aromatic systems and chiral building blocks to afford relevant advanced functions.

Ni-Catalyzed cross coupling of aryl grignard reagents with aryl halides in a nonpolar solvent and an efficient synthesis of biaryls under neat conditions

This study details Ni-catalyzed cross coupling of aryl Grignard reagents with aryl halides in toluene, a nonpolar solvent with a high boiling point. The reaction was applied for the synthesis of various biaryls in good yields without the introduction of a large steric ligand. The Kumada-Tamao-Corriu(KTC) reaction in toluene was then successfully modified to proceed under neat conditions for the efficient syntheses of symmetrical biaryls, particularly in large-scale preparations. Unactivated aryl chlorides show higher reactivity than aryl bromides, particularly under neat conditions. Mechanistic investigations suggest a radical procedure for the catalytic cycle, and the origin of the radical intermediates being aryl halides.

Synthesis and properties of fluorescence poly(benzoxazole–imide)s containing naphthalene

Novel aromatic poly(benzoxazole–imide)s containing naphthalene were prepared from synthesized 1,4-di(5-aminobenzoxazol-2-yl)naphthalene and commercial dianhydrides by conventional two-step polymerization. The polymers showed high levels of tensile strength of up to 294 MPa and modulus of up to 6.5 GPa. The glass transition temperatures of the polymers were observed between 267°C and 345°C. The 5% weight loss temperatures of the polymers were tested in the range of 517–562°C in nitrogen atmosphere. The excellent properties of polymers were attributed to their rigid-rod-like molecular structure. The polymers emitted different fluorescence with maximum emission wavelengths in the range of 470–560 nm. Increasing the dianhydride electron affinity, the emission spectra peak value of polyimides (PIs) except PI6 increased gradually, but the fluorescent intensity of the PIs decreased. The 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride-derived PI film exhibit highly fluorescent characteristics; however, the PI film from pyromellitic dianhydride was nonfluorescent.

Preparation and Properties of Imidazole-containing Polyimide/Silica Hybrid Films

Imidazole-containing polyimide/silica(PI/SiO2) hybrid films were prepared from 3,3′,4,4′-biphenyltetra-carboxylic dianhydride(BPDA) and 2,2′-di(p-aminophenyl)-5,5′-bibenzimidazole in N,N-dimethylacetamide(DMAc) by sol-gel method and thermal imidization. The hybrid film with high silica mass fraction up to 40% was transparent. Scanning electron microscope(SEM) and transmission electron microscope(TEM) results of the film indicate a homogeneous dispersion of silica nanoparticles in the polyimide matrix. One hybrid film PI/SiO2 with 15% SiO2 exhibits better mechanical properties with a tensile strength of 222 MPa, an elongation at break of 12%, and a tensile modulus of 5.66 GPa. The reinforced mechanism on mechanical properties was also studied.

The properties, morphology and structure of BPDA/ PPD/ BOA polyimide fibers

Abstract A family of random copoly(amic acid)s (coPAAs) containing the 2-(4- aminophenyl)-5-aminobenzoxazole (BOA) moiety were synthesized in DMAc, followed by dry-jet wet spinning process into as-spun PAA fibers. The modified polyimide (PI) fibers were obtained from PAA fibers after imidized and drawn in a furnace. The mechanical properties of fibers were improved by incorporating BOA into BPDA/PPD backbone. SEM photo showed that the cross-section of each stage fibers was round and voids free. Besides, the “skin-core” and microfibrillar structure were not observed. The thermal properties of PI fibers were also investigated. The results showed that the PI fibers owned excellent thermal stability, moreover, the dimensional stability and the microphase separation of fibers were improved by heat-drawn stage. The Tg were found to be around 290°C by TMA and DMA. The X-ray (WAXD and SAXS) experiments indicated that the longitudinal stacks, the molecular orientation and the structural homogeneity of PI fiber were improved in the preparation process of fibers.

Sequence‐Dependent Self‐Assembly of Chiral Polyimides

Sequence-defined chiral polyimides comprising identical asymmetric diamine monomers arranged in different directions along the main chain were designed and prepared. These new sequence-defined polymers exhibit sequence-dependent self-assembly behaviors and responses to ibuprofen enantiomers, as revealed by their chiroptical spectra and gelation properties. For the first time, the self-assembly of polymers and their interactions with guest molecules have been successfully controlled by means of the directional arrangement of the monomers in their polymer backbones.

Supramolecular self-assembly of chiral polyimides driven by repeat units and end groups

Pyromellitic diimides (PMDIs) are effective building blocks for the construction of supramolecular systems but are infrequently used in comparison with other electron-deficient aromatic systems. We report PMDI-based chiral polyimides that form polymeric supramolecular systems with unique self-assembly features that show time-dependent spectroscopic behaviour. Extensive investigations revealed the driving forces for the self-assembly of the polyimides. One is the complementary aromatic π–π stacking between electron-accepting PMDI and electron-donating phenyl ring in the polymer backbones, and another is the hydrogen bonding interactions of the end groups. The self-assembly is readily disrupted by guest molecules with strong associations with the PMDI and the end groups. The introduction of flexible arylether diimides into the PMDI-based copolymer backbones and the sequence of PMDIs and arylether diimides in the copolymer backbones significantly influence the self-assembly of the polyimides. The results elucidate the mechanisms of polymeric self-assembly of chiral polyimides, providing important information for the development of materials based on polymeric supramolecular systems with properties and functions regulated by composition, sequence and end groups.