Anqiang Zhang

The synthesis and characterization of supramolecular elastomers based on linear carboxyl-terminated polydimethylsiloxane oligomers

Supramolecular elastomers obtained through a two-step reaction of linear carboxyl-terminated polydimethylsiloxane oligomers (PDMS–COOH2) with diethylenetriamine (DETA) and urea show reasonable hysteresis and acceptable self-healing properties. The results of temperature-dependent infrared analysis suggest the existence of hydrogen bonding interactions with good thermal reversibility in the matrix. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses demonstrate that the supramolecular network structure is totally amorphous at room temperature. The rheological, mechanical and self-healing properties are closely related to the PDMS chain length, whereas the stability seems to be independent of the PDMS chain length. The viscoelastic properties of these materials are believed to be the result of entangled chains in the amorphous matrix. Only the hydrogen bonds formed by 1,1-dialkylurea groups and imidazolidone derivatives serve as effective crosslinks for contributing to the stability of the supramolecular network.

The synthesis and characterization of carboxybetaine functionalized polysiloxanes for the preparation of anti-fouling surfaces

Nonspecific protein adsorption and bacterial adhesion have caused serious problems in biomedical devices, marine engineering, membrane separation and many other areas. In order to develop a water-soluble bio-adhesion resistant material, a series of novel zwitterionic polymers, carboxybetaine functionalized polysiloxanes (PDMS-g-CB), were synthesized via a three-step procedure. FT-IR and NMR were used to characterize the chemical structures of PDMS, and the solution properties (i.e. CMC) and biological characteristics were investigated. The high biocompatibility of PDMS-g-CB was demonstrated by hemolysis assay, skin irritation evaluation and acute oral toxicity testing. To evaluate the anti-fouling and hydrophilic properties of PDMS-g-CB, it was blended with PDMS elastomer to form films (b-PDMS). Water contact angle and ATR-FTIR measurements revealed that the hydrophobic PDMS surfaces were converted to hydrophilic surfaces after the introduction of PDMS-g-CB. The anti-fouling properties of b-PDMS were evaluated by protein adsorption and bacterial adhesion tests. Results showed that the amount of adsorbed protein and bacteria adhesion were significantly reduced compared with the untreated PDMS. These findings suggest that PDMS-g-CB is a biocompatible and promising material for the construction of anti-fouling surfaces.

Preparation of anti-fouling silicone elastomers by covalent immobilization of carboxybetaine

Polydimethylsiloxane (PDMS) is a widely used material for biomedical applications. In this work, a convenient method for the covalent modification of PDMS with carboxybetaine was developed and used to construct a biocompatible and anti-fouling coating. Following the preparation of a Si–H functionalized PDMS film by adjusting the molar ratio of the two components used in Sylgard 184 silicone elastomer networks, the allyl carboxybetaine (ACB) was grafted to the PDMS surface via a hydrosilylation reaction in the presence of a Karstedts catalyst. ATR-FTIR and water contact angle measurements revealed that carboxybetaine was introduced to the PDMS surface successfully. The biocompatibilities of PDMS and carboxybetaine-modified PDMS (PDMS-CB) films were evaluated by cytotoxicity, hemocompatibility, and dynamic clotting time. The anti-fouling properties of PDMS-CB were evaluated by protein adsorption and bacterial adhesion measurements. The results showed that the carboxybetaine layer could enhance the biocompatibility of PDMS and reduce the adsorption of protein and adhesion of bacteria efficiently.

Synthesis and Characterization of Carboxyl Terminated Polydimethylsiloxanes

A series of hydrogen terminated polydimethylsiloxanes (PDMS-H) had been controlled synthesized via ring-opening polymerization. Then, methylmethacrylate (MMA) and tert-butyl methacrylate (tBMA) were grafted to PDMS-H via hydrosilylation reactions in the presence of Speiers catalyst, the hydrosilylation addition patterns of MMA and tBMA showed a strong preference toward β-1,2 addition, no α-1,2 addition product or 1,4-addition product was observed. Carboxyl terminated polydimethylsiloxanes were prepared by subsequent hydrolysis reaction in an aqueous NaOH/ethanol solution and under acid condition, respectively. Both methods could obtain carboxyl terminated polydimethylsiloxanes successfully. However, a significant decrease of the molecular weight of products was observed in the alkaline hydrolysis process, while the acid hydrolysis of tertiary butyl ester group terminated polydimethylsiloxanes could be conducted in a highly controlled manner. Besides, the synthesis of carboxyl terminated polydimethylsiloxanes via acid hydrolysis reaction can be conducted well only when the terminal group of polydimethylsiloxanes is tertiary butyl, this can be explained by the specificity of tertiary butyl.

Properties of Natural Rubber Vulcanizates/Nanosilica Composites Prepared Based on the Method of In-situ Generation and Coagulation

Using the characteristics of silica sol dispersing well in water and easy formation of silica gel when the silica sol is heated, by mixing a system of concentrated natural rubber latex and silica sol, the silica sol can in-situ generate SiO2 particles when heated. After coagulation of the mixed system, natural rubber/nanosilica composites C(NR/nSiO2) were obtained. The composites C(NR/nSiO2) and their vulcanizates were studied using a rubber processing analyzer (RPA), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The influence of silica contents on the C(NR/nSiO2) vulcanizates mechanical properties, cross-linking degree, Payne effect, dissipation factor (tanδ), and the particle size and dispersion of SiO2 in NR were investigated. The results obtained were compared with the NR/SiO2 composites based on traditional dry mixing of bale natural rubber and precipitated silica (white carbon black). The results showed that when using a sulfur curing system with a silica coupling agent ...

Supramolecular elastomer based on polydimethylsiloxanes (SESi) film: synthesis, characterization, biocompatibility, and its application in the context of wound dressing.

Supramolecular elastomer based on polydimethylsiloxanes (SESi) is a kind of novel elastomer cross-linked by the multihydrogen bonds supplied by the functional groups linked to the end of the PDMS chains, such as amide, imidazolidone, pending urea (1,1-dialkyl urea), and bridging urea (1,3-dialkyl urea). SESi showed lower glass transition temperature (T g) at about −113 °C because of the softer chain of PDMS, and could show real rubber-like elastic behaviors and acceptable water vapor transmission rate under room temperature. The high biocompatibility of SESi in the form of films was demonstrated by the cytotoxicity evaluation (MTT cytotoxicity assay and direct contact assay), hemolysis assay, and skin irritation evaluation. Based on detailed comparisons between commercial Tegaderm™ film and SESi film using a full-thickness rat skin model experiment, it was found that SESi film showed similar wound contraction rate as that of Tegaderm™ film on day seven, 10, and 14; only on day five, SESi film showed a significant (p < 0.05) lower wound contraction rate. And, the wounds covered with SESi film were filled with new epithelium without any significant adverse reactions, similar with that of Tegaderm™ film.

Novel supramolecular elastomer films based on linear carboxyl-terminated polydimethylsiloxane oligomers: preparation, characterization, biocompatibility, and application in wound dressings

A novel supramolecular elastomer (SESi) based on multiple hydrogen bond associations between low-molecular-weight polydimethylsiloxane chains was obtained through a two-step reaction of linear carboxyl-terminated polydimethylsiloxane oligomers with diethylenetriamine and urea, and the reaction mechanism was characterized. The results of differential scanning calorimetry and X-ray diffraction analyses indicated that the supramolecular network structure is completely amorphous, endowing SESi with rubber-like elastic behavior at room temperature. The transparent SESi film prepared by hot pressing displayed nice viscoelasticity, benign water absorption, water vapor transition rates, and ideal biocompatibility; and did not show cytotoxicity or skin irritation. These properties allow the elastomer to function as an occlusive wound dressing. To demonstrate its potential in wound dressings, a detailed comparison of commercial 3M Tegaderm™ film and the SESi film was conducted. The SESi film exhibited similar effects in wound healing, and the wound bed was covered by the SESi film without the occurrence of significant adverse reactions.

Carbon Black Filled Powdered Natural Rubber

Carbon black (CB) filled powdered natural rubber [P(NR/N234)] was prepared using a patented method of latex/CB coagulation technology. The influence of curing recipes and CB contents on the curing, mechanical, and dynamic properties were studied in depth, and the results were compared with that of NR/N234 compounds based on traditional dry mixing of bale NR and CB. The results showed that, compared with NR/N234, P(NR/N234) showed higher tensile strength, tear strength, rebound elasticity and flexibilities, and the antiabrasion properties were similar, while the dynamic temperature-build-up and dynamic compression permanent set were about 50% of that of NR/N234. The analysis based on scanning electron micrographs (SEM) and the Payne effect showed that the fine dispersion of CB in the rubber and the enhanced interaction between CB and rubber contributed to the excellent properties of P(NR/N234), sufficient that they make P(NR/N234) a potential material for the tread compounds of heavy-duty all-steel cord radial tires.

Toughening Effect of Poly(ethene-co-1-butene)-graft-methyl Methacrylate and Acrylonitrile on Styrene-acrylonitrile Copolymer (SAN)

Poly(ethene-co-1-butene)-graft-methyl methacrylate-acrylonitrile (PEB-g-MAN), synthesized by suspension grafting copolymerization of methyl methacrylate and acrylonitrile onto PEB, was blended with styrene-acrylonitrile copolymer (SAN). The mechanical properties, phase structure, toughening mechanism, miscibility, and thermal stability of the SAN/PEB-g-MAN blends were studied using a pendulum impact tester, tension tester, scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TG). The results showed that PEB-g-MAN has an excellent toughening effect on SAN resin. The notched impact strength of the blends (containing 25 wt% PEB) was 63.3 kJ/m2, which was nearly 60 times that of SAN resin. The brittle-ductile transition of SAN/PEB-g-MAN blends occurred when the weight percentage of PEB was between 17.5 and ∼20 wt%. SAN and PEB-g-MAN were partially miscible. The toughening mechanism of the blends changed with the PEB content. When the PEB content was low, the toughening mechanism of the blends was branching and termination of cracks with slight cavitation. As the content of PEB increased, the toughing mechanism gradually changed from branching and termination of crack with slight cavitation to both branching and termination of crack and cavitation, to extensive cavitation, and finally to shear yielding accompanied by cavitation. The phase structure of the blends changed from a “sea-island’’ structure to a cocontinuous structure as the PEB content increased. ATG analysis showed that the thermal properties of the SAN resin in the blends were enhanced by adding the PEB-g-MAN.

Synthesis of EPDM-g-MAN by suspension graft copolymerization and its toughening effect on SAN resin

Suspension graft copolymerization of methyl methacrylate and acrylonitrile onto ethylene–propylene–diene terpolymer (EPDM) was carried out under different reaction conditions. A series of graft products of EPDM-graft-methyl methacrylate and acrylonitrile (EPDM-g-MAN), characterized by Fourier-transform infrared spectroscopy, was blended separately with styrene–acrylonitrile (SAN) resin to investigate their toughening effect on SAN matrix. The relationship between the polarity of EPDM-g-MAN and toughness of EPDM-g-MAN/SAN resin blends (AEMS) was evaluated. The compatibility and morphologies of AEMS were probed by dynamic mechanical analysis, transmission electron microscopy, and scanning electron microscopy to determine the toughing mechanism of the blends. Thermogravimetry results showed that the thermal stability of AEMS was enhanced with the incorporation of EPDM-g-MAN graft copolymer.