Chuncheng Li

A novel and simple procedure to synthesize chitosan-graft-polycaprolactone in an ionic liquid

An ionic liquid, 1-ethyl-3-methylimidazolium acetate (EMIMAc), was synthesized and employed as a homogeneous and green reaction media to prepare chitosan-graft-polycaprolactone (CS-g-PCL) via ring-opening polymerization, using stannous octoate (Sn(Oct)2) as a catalyst. The structures and compositions of copolymers could be facilely controlled by the reaction conditions and feed ratios. The grafting content of polycaprolactone (PCL) could reach as high as 630%. The chemical structures of the copolymers were systematically characterized by (1)H NMR, Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction (WAXD), while thermal properties were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The thermal stability and glass transition temperature (Tg) of the graft copolymers vary regularly with the change of PCL grafting content.

In situ synthesis of poly(ethylene terephthalate)/graphene composites using a catalyst supported on graphite oxide

An efficient method was developed for the in situ synthesis of poly(ethylene terephthalate)/graphene composites by using a polycondensation catalyst supported on graphite oxide (GO-Cat). The GO-Cat was prepared by loading a catalyst of titanium dioxide/silicon dioxide nanoparticles on organofunctionalized graphene oxide sheets, and was characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. During the in situpolycondensation process, nanoscale dispersion and thermal reduction of graphene oxide were achieved simultaneously. The composites obtained exhibited a rather low electrical percolation threshold due to the homogeneous dispersion of graphene sheets within the matrix and the effective reduction of graphene oxide in the polycondensation process.

Surface decoration of graphene by grafting polymerization using graphene oxide as the initiator

Surface functionalization of graphene oxide (GO) by grafting polymer chains to its surface is achieved by direct use of GO as the initiator for polymerization of N-vinylpyrrolidone (NVP). The functionalized GO can be readily dispersed in a variety of solvents which facilitates graphene processing for a wide range of applications. Fourier-transform infrared, X-ray powder diffraction and transmission electron microscopy investigations show that poly(vinylpyrrolidone) is grafted onto the GO surface, and X-ray photoelectron spectroscopy, elemental analysis and conductivity measurements suggest modest reduction of the functionalized GO during the surface-initialized polymerization. Both electron spin resonance and 13C-NMR spectra indicate that breakage of weak bonds at the defects on the GO surface initialized the radical polymerization of NVP.

Synthesis, Characterization and Degradation of Novel Biodegradable Poly(butylene-co-hexamethylene carbonate) Copolycarbonates

A series of high molecular weight poly(butylene-co-hexamethylene carbonate) (PBHC) copolycarbonates were synthesized by copolymerizations of dimethyl carbonate (DMC), 1,4-butanediol (BD) and 1,6-hexanediol (HD) via a two-step melt polycondensation method. Microstructure analysis determined by high-resolution 13C-NMR showed that butylene carbonate (BC) units and hexamethylene carbonate (HC) units of the synthesized copolymers take a random distribution along the polymer chains. Analyses of the formed byproducts indicated that sublimation of oligomer and thermal degradation of polymer happen during the aliphatic polycarbonate polycondensation. The thermal properties and crystalline structure of the copolymers were studied by DSC, TGA and WAXD. WAXD patterns showed that the copolymers with 11 and 91 mol% HC units form poly(butylene carbonate) (PBC) and poly(hexamethylene carbonate) (PHC) crystals, respectively, while the three other copolymers with intermediate HC unit contents are completely amorphous. The results indicated that the BC and HC units are incompatible in each crystal lattice, and that cocrystallization cannot take place. TGA results indicated that the thermal stability of the obtained PBHC random copolymers is higher than that of PBC and increases with increasing the HC unit content. The enzymatic degradation study revealed that the biodegradation rate of the PBHC copolymers mainly depends not only on the degree of crystallinity and melting temperature but also on the type of crystalline structure, while the composition and microstructure dependences of biodegradability are negligible.

A high-molecular-weight and high-Tg poly(ester carbonate) partially based on isosorbide: synthesis and structure–property relationships

A new family of high-molecular-weight poly(isosorbide carbonate-co-butylene terephthalate)s (PICBTs) partially based on renewable isosorbide (Is) were prepared by incorporating 1,4-butanediol (BD) and dimethyl terephthalate (DMT) into poly(isosorbide carbonate) (PIC), via a two-step bulk condensation polymerization. The incorporation of BD and DMT was developed to compensate for the low reactivity of Is and improve the molecular weight and processability of PIC, while retaining the rigidity and hence high glass transition temperature (Tg) of PIC. The resulting copolymers showed high number-average molecular weights ranging from 30 600 to 52 300 g mol−1 and tunable Tg values from 69 to 146 °C. The molecular structure of the novel poly(ester carbonate)s was confirmed using 1H, 13C, 2D-COSY and 2D-HSQC NMR techniques. 1H NMR analysis revealed the random sequence distributions of the PICBTs. A systematic study on the structure–property relationship revealed that the thermal, dynamic mechanical and mechanical properties of the PICBTs strongly depended on their composition, which would enable molecular design of material properties with the desired balance of material rigidity, ductility, and biobased content.

Modification of chitosan with monomethyl fumaric acid in an ionic liquid solution

Antibacterial and antioxidant monomethyl fumaric acid (MFA) was selected to modify chitosan, using aqueous solution of an ionic liquid as a homogeneous and green reaction media. The chemical structures of resulting polymers were systematically characterized by (1)H NMR, diffusion ordered spectroscopy, solid (13)C NMR and wide-angle X-ray diffraction. The results show that two kinds of MFA modified chitosan materials with totally different chemical structures have been synthesized. One product was a MF-chitosan salt composed of chitosan cation and MFA anion, which was obtained with the mediation of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide. The other one synthesized with the mediation of EDC was a MF-chitosan amide in which MFA and chitosan are covalently attached. Solubility of chitosan has been improved, and MF-chitosan salt can be readily dissolved in water. The antioxidant activity has been enhanced with the introduction of MFA, irrespective of the chemical structure.

Effect of the biobased linear long-chain monomer on crystallization and biodegradation behaviors of poly(butylene carbonate)-based copolycarbonates

To improve the crystallization ability of poly(butylene carbonate) (PBC), a monomer with a linear long chain as a biobased derivative of castor oil was randomly introduced into the PBC main chain. A series of aliphatic copolycarbonates poly(butylene-co-decamethylene carbonate)s (PBDCs), with weight-average molecular weights of 125000 to 202000 g mol−1, were synthesized from dimethyl carbonate, 1,4-butanediol, and 1,10-decanediol via a two-step polycondensation process, using sodium acetylacetonate as the catalyst. The PBDCs, being statistically random copolymers, showed a single Tg over the entire composition range. The DSC results testified that the introduction of a decamethylene carbonate (DC) unit can significantly enhance the crystallization rate of PBC. The PBDC copolycarbonates had a minimum melting point in the plot of melting point versus composition. Wide-angle X-ray diffraction patterns showed that the copolycarbonates with up to 20 mol% DC units formed PBC type crystals, while those with higher DC unit content crystallized in poly(decamethylene carbonate) (PDC) type crystals. This indicates that the PBDC copolycarbonates show isodimorphic cocrystallization. The thermal stability, crystalline morphology, and enzymatic degradation of the PBDC copolycarbonates were also studied.

In situ Synthesis of Poly(methyl methacrylate)/Graphene Oxide Nanocomposites Using Thermal-initiated and Graphene Oxide-initiated Polymerization

A facile and cost-effective method to prepare poly(methyl methacrylate) (PMMA)/graphene oxide (GO) nanocomposites was developed by in situ polymerization. By using thermal-initiated and GO-initiated polymerization of methyl methacrylate (MMA), no extra radical initiator was added during the reaction. Without any pre-functionalization of GO, PMMA chains were covalently bonded to its surface, which was confirmed by Fourier-transform infrared, atomic force microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy investigations. TGA analysis showed that the mass ratio of grafted PMMA and GO was as high as 1.7. Transmission electron microscopy and X-ray powder diffraction investigations demonstrated that the grafting of PMMA chains to GO surfaces resulted in homogeneous dispersion of GO sheets in PMMA matrix, which led to a commendable performance on its mechanical and thermal properties. Dynamic mechanical analysis showed that, at a loading level of just 0.5 wt% for the nanocomposites, the storage modulus of the nanocomposites was improved 14%, and the glass transition temperature was increased 12°C in comparison with that of neat PMMA. Thermogravimetric analysis showed that the onset degradation temperature of the nanocomposites was increased 13°C with a GO content of 0.25 wt%.

A facile and versatile strategy to efficiently synthesize sulfonated poly(butylene succinate), self-assembly behavior and biocompatibility

A series of amphiphilic and anionic copolyesters of sulfonated poly(butylene succinate) (SPBS) with sulfonate groups distributed randomly along the biodegradable backbone were synthesized via addition of sodium hydrogen sulphite to carbon–carbon double bonds on the backbone of poly(butylene succinate-co-butylene fumarate) (PBSF). The content of hydrophilic sulfonate groups can be facilely regulated by changing the initial feed ratio. The structures of PBSF and SPBS were systematically characterized by NMR and GPC. The negatively charged micelles self-assembled from SPBS were prepared by the dialysis method and characterized by NMR, DLS and TEM. In vitro cytotoxicity assay indicates that the SPBS micelles possess excellent biocompatibility. The biocompatibility of SPBS micelles increases with increasing content of sulfonate groups. This work provides a broad new method to facilely synthesize novel anionic copolyesters with high efficiency and controllable anion content. These copolyesters are highly promising as drug delivery carriers for cancer therapy.

A designed synthetic strategy toward poly(isosorbide terephthalate) copolymers: a combination of temporary modification, transesterification, cyclization and polycondensation

A designed synthetic strategy to overcome the low reactivity of isosorbide (Is) and terephthalic acid (TPA) is developed for the preparation of engineering polycondensates. This method contained substitution of unreactive end groups of Is and TPA by reacting with dimethyl carbonate and 1,2-alkanediol or 1,3-alkanediol respectively, followed by transesterification, cyclization of an alkylene carbonate unit, and polycondensation. Is and TPA were temporarily linked by an unstable alkylene carbonate unit and then underwent cyclization with the elimination of five- or six-membered cyclic carbonate at elevated temperature, leading to a family of poly(isosorbide carbonate-co-isosorbide terephthalate)s with high Tg (169–193 °C) and high number-average molecular weights (22 700–28 500 g mol−1). The molecular structure of the copolymer was confirmed using 1H, 13C and 2D NMR techniques. GC-MS, 1H NMR and 13C NMR were used to monitor the molecular structure evolution during the combinatorial polymerization process and a mechanism was proposed. Furthermore, the structure–thermal properties relationship study was also conducted on a range of relevant polyesters.