Jianqun Gan

Biodegradable, thermoresponsive PNIPAM-based hydrogel scaffolds for the sustained release of levofloxacin

A series of novel thermoresponsive biodegradable hydrogels (TBHs) was prepared from N-isopropyl acrylamide (NIPAM) and two biodegradable crosslinkers, poly(e-caprolactone) dimethacrylate (PCLDMA) and bisacryloylcystamine (BACy). The morphology, thermal behavior, swelling/deswelling kinetics, compression properties, in vitro drug delivery and biodegradation were investigated. The results indicated that the properties of the TBHs strongly depended on temperature and the feeding molar ratio of the PCLDMA to BACy components. Levofloxacin (LVF)-loaded hydrogels were prepared to explore their stimuli-responsive release process. The cumulative release profile of LVF-loaded TBHs exhibited a thermo-induced slow sustained drug release and a reduction-induced fast release. At a physiological pH, TBHs could be biodegraded slowly in glutathione (GSH) at 37 °C. Due to their homogeneous pore diameter, highly interconnected architecture, degradable chemistry and thermoresponsive properties, the TBHs developed herein are highly attractive with respect to tissue engineering scaffold applications.

Pseudo-graft polymer based on adamantyl-terminated poly(oligo(ethylene glycol) methacrylate) and homopolymer with cyclodextrin as pendant: its thermoresponsivity through polymeric self-assembly and host–guest inclusion complexation

A series of well-defined adamantyl-terminated thermally responsive copolymers (Ad-POEGMAs) were synthesized by atom transfer radical polymerization (ATRP), in which 2-(2-methoxyethoxy) ethyl methacrylate (MEO2MA) and oligo(ethylene glycol) methacrylate (OEGMA) served as the thermosensitive building blocks. Moreover, cyclodextrins (CDs) as bulky pendant grafted polymers (PGCD) were synthesized by homopolymerization of aminoethyl methacrylate β-cyclodextrin (GCD). The thermal-responsive behaviors were investigated by a combination of 1H NMR, UV-vis spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM). In comparison to other thermal-responsive copolymers based on POEGMAs, Ad-POEGMAs exhibited unusual thermally induced aggregation processes. The Ad group assembled and POEGMA chains associated to produce stable water-soluble nano-aggregates, followed by a rearrangement process at the second thermal transition. Moreover, it was found that a noncovalently connected supramolecular pseudo-graft polymer was formed via inclusion complexation in aqueous solution. This pseudo-graft polymer underwent a reversible temperature-induced transition from solution to micelle under suitable conditions. The cyclodextrin (CD) moiety attached to the main chain played two roles. As supramolecular host moieties, CDs formed inclusion complexes with guest-ended polymers, leading to graft-like polymers. As bulky hydrophilic moieties, CDs stabilized the micelles induced by the coil-to-globule transition of POEGMA segments.

Relationship between crosslinking structure and low dielectric constant of hydrophobic epoxies based on substituted biphenyl mesogenic units

In this work, a series of low dielectric constant hydrophobic epoxies based on substituted biphenyl mesogenic were prepared and characterized. The liquid crystalline phase structure and the crosslink density of substituted biphenyl epoxies were determined by polarized optical microscopy, wide angle X-ray diffraction measurements and dynamic storage moduli data. Relationship between crosslinking structure and dielectric and water resistance properties was discussed in our paper. The samples showed lower dielectric constants down to 2.24, owing to the oriented structure and increased crosslink network density caused by the orientation of biphenyl mesogenic, indicating a new idea to prepare low dielectric constant epoxies by introducing the mesogenic units into epoxy resins. And the comprehensive contributions of oriented structure and increased crosslink network in epoxies cured by aromatic amines, less hydroxyl groups existing in epoxies cured with anhydride and the hydrophobic methyl substituents or larger tert-butyl substituents, could afford good water resistance properties with water absorptions during 48 h at 25 °C ranging from 0.31–0.36%, which indicated that the water resistance was apparently better than that of conventional epoxy systems.

High thermo-responsive shape memory epoxies based on substituted biphenyl mesogenic with good water resistance

In this work, a novel epoxy monomer denoted as 3,5′-di-t-butyl-5,3′-dimethyl biphenyl diglycidyl ether (t-BuMBPDGE) was synthesized and applied into in situ composites with 3,3′,5,5′-tetramethyl-4,4′-biphenyl diglycidyl ether (TMBPDGE), accompanied with curing agent aromatic amines. The liquid crystalline phase structure and the crosslink density of substituted biphenyl epoxies were determined by polarized optical microscopy, wide angle X-ray diffraction measurements and dynamic storage moduli data. The samples showed good mechanical properties and could recover quickly from a second state to their initial states with a shape fixity ratio higher than 98% and shape recovery ratio higher than 99%, owing to the oriented structure and increased crosslink network density caused by the orientation of biphenyl mesogenic. The high glass transition temperatures ranging from 160 to 178 °C and good water resistance could contribute to a stable fixed shape. The water resistance is analyzed by contact angles test. The samples exhibited contact angles of 92–98 degrees, which indicated that the water resistance was apparently better than that of conventional epoxy systems.

Synthesis and encapsulation of an amphiphilic thermoresponsive star polymer with β-cyclodextrin and hyperbranched poly(oligo(ethylene glycol)methacrylate) as building blocks

Novel macromolecular star polymers with triazole and cyclodextrin (CD) segments as branch points and poly(oligo(ethylene glycol)methacrylate) (POEGMAs) as dense hydrophilic branches were synthesized via a combination of azide–alkyne click chemistry and atom transfer radical polymerization (ATRP). Firstly, a tetrafunctional linking agent (PETP) was prepared by the reaction of pentaerythritol (PE) and propargyl bromide, and then a four arm β-CD terminated star polymer (PE-CD) was obtained through the click chemistry reaction. Finally, thermally-responsive star polymers (PE-CD–POEGMAs) with PE as the central core, triazole and CD segments as branch points, and POEGMAs as side branches were synthesized by the ATRP of MEO2MA and OEGMA using PE-CD terminated with bromines as macroinitiators. A study on the thermoresponsivity and morphology of PE-CD–POEGMAs indicated that polymeric nano-aggregates existed as multimolecular micelles and behaved with tunable thermosensitivity, which were driven by the strong hydrophobic–hydrophilic interactions in the inner core and outer shell. The encapsulation capacities towards multi-guest molecules were investigated and the results indicated that water soluble guests could be encapsulated by PE-CD–POEGMAs, and the guest encapsulation capacities were derived from the special star molecular structure properties of PE-CD–POEGMAs and the synergistic encapsulation phenomenon of different guest molecules. This unique amphiphilic star polymer illustrated the potential applications in supramolecular science, drug delivery and other nanotechnology applications.

Synthesis and characterization of novel bisphthalonitrile resins linked by different molecular weight main-chain polybenzoxazines

ABSTRACT A series of novel type bisphthalonitriles with different molecular weight main-chain polybenzoxazines as linkages have been successfully synthesized using 4, 4′-diaminodiphenyl methane, paraformaldehyde, bisphenol A and 4-nitrophthalonitrile as initial materials. The structures were characterized by Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance (1H-NMR). The formation of benzoxazine and the existence of nitrile groups were confirmed by the absorbance at 950cm−1 of benzene attached with oxazine ring and 2231 cm−1 of nitrile groups. The characteristic resonance peaks observed at about 4.52 (C-CH2-N) and 5.28 ppm (N-CH2-O) also determined the structure of benzoxazine ring. The curing behaviors were monitored by differential scanning calorimetry (DSC) and FT-IR. Two-stage polymerization mechanisms were observed according to the ring-opening of benzoxazine and the polymerization of nitrile groups catalyzed by phenolic hydroxyl groups, which generated during the curing reaction of benzoxazine. The polymerization of these bisphthalonitriles exhibited self-promoted curing behaviors. The completion of polymerization was proved by the disappearance of the band located at 950 cm−1 in FT-IR. Thermogravimetric analysis (TGA) was used to investigate the thermal stability, and the results showed that the cured polymers achieved extremely high char yield from 61.1% up to 74.2% at 800°C under nitrogen and exhibited increasing decomposition temperature as the contents of phthalonitrile groups increased, which indicated that the polymerization of phthalonitriles could improve the thermal stability.

UV-cured hyperbranched polyester polythiol(H20-SH)-epoxy acrylate networks: Preparation, thermal and mechanical properties

ABSTRACT A hyperbranched polyester polythiol(H20-SH) was synthesized and characterized by FTIR spectral analysis, 1H-NMR spectral analysis and GPC analysis. H20-SH was added into the formulation of UV-curable epoxy acrylate networks based on thiol-acrylate chemistry. The effects of H20-SH on polymerization kinetics, thermal and mechanical properties of thiol-epoxy acrylate networks were investigated by Real-time infrared spectroscopy, dynamic mechanical analysis (DMA), thermogravimetric (TGA), tensile test and water absorption characterization. Results show that epoxy acrylate resin with the addition of H20-SH massively reduces oxygen inhibition, improves the uniformity of cured films and enhances the tensile strength of the films. However, the thermal stability and glass transition temperature (Tg) decreases with the increasing amount of H20-SH.

Synthesis and Characterization of a Lateral Phthalonitrile Functionalized Main-Chain Polybenzoxazine Precursor

A lateral phthalonitrile functionalized main-chain polybenzoxazine precursor has been successfully synthesized. The structure was characterized by proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FTIR). The formation of benzoxazine rings were confirmed by the characteristic resonances observed at about 4.55 (C-CH2-N) and 5.30 ppm (N-CH2-O) and the absorbance at 950 cm-1 of benzene attached with an oxazine ring. The curing behavior was monitored by differential scanning calorimetry (DSC) and in situ FTIR. The completion of polymerization was proved by the disappearance of the band located at 950 cm-1 in FTIR. Thermogravimetric analysis (TGA) was used to investigate the thermal stability, and the results indicated that the thermal stability of the cured polymer gained significant improvement than that without phthalonitrile functionalization.