Synthesis and Stabilization of Novel Aliphatic Polycarbonate from Renewable Resource

A novel aliphatic polycarbonate from renewable resource was prepared by copolymerization of furfuryl glycidyl ether and CO2 using rare earth ternary catalyst; its number-average molecular weight (M-n) reached 13.3 x 10(4) g/mol. The furfuryl glycidyl ether and CO2 copolymer (PFGEC) was easy to become yellowish at ambient atmosphere due to post polymerization cross-linking reaction oil the furan ring; the gel content was 17.2 wt % after 24 h exposure to air at room temperature. PFGEC could be stabilized by addition of antioxidant 1010 (tetrakis[methylene (3.5-di(tert-butyl)-4-hydroxhydrocinnamate)]methane) in 0.5-3 wt % after copolymerization. The Diels-Alder (DA) reaction between N-phenylmaleimide and the pendant furan ring was also effective for the stabilization of PFGEC by reducing the amount of furan ring and introducing bulky groups into PFGEC. The cyclization degree could reach 72.1% when the molar ratio of N-phenylmaleimide to furan ring was 3: 1, and no gel was observed after 24 h exposure to air. The glass transition temperature (T-g) of PFGEC was 6.8 degrees C, and it increased to 40.3 degrees C after DA reaction (molar ratio of N-phenylmaleimide to furan ring was 3: 1).

SYNTHESIS AND CHARACTERIZATION OF HYPERBRANCHED VINYL POLYMERS FROM RAFT POLYMERIZATION OF AN ASYMMETRIC DIVINYL MONOMER

Hyperbranched vinyl polymers were prepared by reversible addition-fragmentation chain transfer ( RAFT) polymerization of a styrenic asymmetric divinyl monomer. This was achieved by using cumyl dithiobenzoate or S-dodecyl-S'-(alpha,alpha'-dimethyl-alpha ''-acetic acid) trithiocarbonate as the chain transfer agent, 1,1'-azobis(cyclohexanecarbonitrile) or thermal initiation as a source of radicals. Cross-linking was inhibited by a rapid RAFT-based equilibrium between active propagation chains and dormant species, and thus a hyperbranched polymer with a monomer conversion as high as 80% was obtained. The hyperbranched structure and properties of the resultant polymers were characterized by a combination of H-1-NMR spectroscopy and a triple detection size exclusion chromatography (TRI-SEC). The hyperbranched vinyl polymer has a broad molecular weight distributions and a low Mark-Houwink exponent alpha value compared with the linear counterpart.

A Novel Strategy to Branched Polyacrylonitrile Via One-Pot RAFT Copolymerization of Acrylonitrile and an Asymmetrical Divinyl Monomer

Branched polyacrylonitriles were prepared via the one-pot radical copolymerization of acrylonitirle and an asymmetric divinyl monomer (allyl methacrylate) that possesses both a higher reactive methacrylate and a lower reactive allyl. RAFT technique was used to keep a low-propagation chain concentration via a fast reversible chain transfer euilibration and thus the cross-linking was prevented until a high level of monomer conversions. This novel strategy was demonstrated to engenerate a branched architecture with abundant pendant functional vinyl and nitrile groups, and controlled molecular weight as a behavior of controlled/living radical polymerization characteristics. The effect of the various experimental parameters, including temperature, brancher to monomer molar ratio, and chain transfer agent to initiator molar ratio, on the control Of moleculer dimension (molecular weight and polydispersity indices) and the degree of branching were investigated in detail. Moreover, H-1 NMR and gel permeation chromatography confirm the branched architecture of the resultant polymer. The intrinsic viscosity of the copolymer is also lower than the linear counterpart.

Suppression of phase separation in PC/PMMA blend film by thermoset oligomer

Phase separation of bisphenol A polycarbonate (PC) and poly(methyl methacrylate) (PMMA) thin blend film is suppressed by addition of solid epoxy oligomer. Epoxy has strong intermolecular interactions with both PC and PMMA, while PC and PMMA are quite incompatible with each other. Consequently, phase separation in the PC/PMMA blend film pushes epoxy to the interface; at the same time, PC and epoxy react readily at the interface to form a cross-linking structure, binding PMMA chains together. Therefore, the interface between PC and PMMA is effectively reinforced, and the PC/PMMA thin blend film is stabilized against phase separation. On the other hand, only an optimal content of epoxy (i.e., 10 wt %) can serve as an efficient interfacial agent. In contrast to the traditional reactive compatibilization, here we observed that the cross-linking structure along the interface is much more stable than block or graft copolymers. Atomic force microscopy (AFM) is used to characterize the morphological changes of the blend films as a function of annealing time. Two-dimensional fast Fourier transform (2D-FFT) of AFM data allows quantitative investigation of the scaling behavior of phase separation kinetics.

Electron-beam irradiation on poly(propylene carbonate) in the presence of polyfunctional monomers

Poly(propylene carbonate) (PPC) showed predominantly degradation under electron-beam irradiation, accompanied by deterioration of its mechanical performance due to sharp decrease of the molecular weight. Crosslinked PPC was prepared by addition of polyfunctional monomer (PFM) to enhance the mechanical performance of PPC. When 8 wt% of PFM like triallyl isocyanurate (TAIL) was added, crosslinked PPC with a gel fraction of 60.7% was prepared at 50 kGy irradiation dose, which showed a tensile strength at 20 degrees C of 45.5 MPa, whereas it was only 38.5 MPa for pure PPC. The onset degradation temperature (T-i) and glass transition temperature (T-g) of this crosslinked PPC was 246 degrees C and 45 degrees C, respectively, a significant increase related to pure PPC of 211 degrees C and 36 C. Therefore, thermal and mechanical performances of PPC could be improved via electron-beam irradiation in the presence of suitable PFM.

A stable PEO-tethered PDMS surface having controllable wetting property by a swelling-deswelling process

A PEO-tethered layer on a PDMS (polydimethylsiloxane) cross-linked network has been prepared by a swelling-deswelling process. During swelling, the PDMS block of a PDMS-b-PEO diblock copolymer penetrates into the PDMS substrate and interacts with PDMS chains because of the van der Waals force and hydrophobic interaction between them. Upon deswelling, the PDMS block is trapped in the PDMS matrix while the PEO, as a hydrophilic block, is tethered to the surface. The PEO-tethered layer showed stability when treated in water for 16 h. The surface fraction of PEO and the wetting property of the PEO-tethered PDMS surface can be controlled by the cross linking density of the PDMS matrix. A patterned PEO-tethered layer on a PDMS network was also created by microcontact printing and water condensation figures (CFs) were used to study the patterned surface with different wetting properties.

Design of silicone rubber according to requirements based on the multi-objective optimization of chemical reactions

The explicit expression between composition and mechanical properties of silicone rubber was derived from the physics of polymer elasticity, the implicit expression among material composition, reaction conditions and reaction efficiency was obtained from chemical thermodynamics and kinetics, and then an implicit multi-objective optimization model was constructed. Genetic algorithm was applied to optimize material composition and reaction conditions, and the finite element method of cross-linking reaction processes was used to solve multi-objective functions, on the basis of which a new optimization methodology of crosslinking reaction processes was established. Using this methodology, rubber materials can be designed according to pre-specified requirements.

Grafting of maleic anhydride onto linear polyethylene: A Monte Carlo study

Monte Carlo simulation was used to study the graft of maleic anhydride (MAH) onto linear polyethylene (PE-g-MAH) initiated by dicumyl peroxide (DCP). Simulation results revealed that major MAH monomers attached onto PE chains as branched graft at higher MAH content. However, at extremely low MAH content, the fraction of bridged graft was very close to that of branched graft. This conclusion was somewhat different from the conventional viewpoint, namely, the fraction of bridged graft was always much lower than that of branched graft under any condition. Moreover, the results indicated that the grafting degree increased almost linearly to MAH and DCP concentrations. On the other hand, it was found that the amount of grafted MAH dropped sharply with increasing the length of grafted MAH, indicating that MAH monomers were mainly attached onto the PE chain as single MAH groups or very short oligomers. With respect to the crosslink of PE, the results showed that the fraction of PE-(MAH)(n)-PE crosslink structure increased continuously, and hence the fraction of PE-PE crosslink decreased with increasing MAH concentration.

Polyhedral oligomeric silsesquioxane nanocomposite thin films via layer-by-layer electrostatic self-assembly

Fabrication of ultrathin polymer composite films with low dielectric constants has been demonstrated. Octa( aminophenyl) silsesquioxane (OAPS) was synthesized and assembled with poly( acrylic acid) (PAA) and poly( styrene sulfonate) (PSS) via a layer-by-layer electrostatic self-assembly technique to yield nanoporous ultrathin films. The OAPS was soluble in water at pH 3 or lower, and suitable pH conditions for the OAPS/PAA and OAPS/PSS assemblies were determined. The multilayer formation process was studied by contact angle analysis, X-ray photoelectron spectroscopy, atomic force microscopy, quartz crystal microgravimetry, UV-vis spectroscopy, and ellipsometry. The multilayer growth was found to be steady and uniform, and the analysis of the film surface revealed a rough topography due to OAPS aggregates. The incorporation of porous OAPS molecules into the thin films significantly lowered their dielectric constants. The OAPS/PAA multilayer thin film thus prepared exhibited a dielectric constant of 2.06 compared to 2.58 for pure PAA film. The OAPS/PAA multilayer film was heated to effect cross-linking between the OAPS and the PAA layers, and the transformation was verified by reflection-absorption Fourier transform infrared spectroscopy.

Facile preparation of amperometric laccase biosensor with multifunction based on the matrix of carbon nanotubes-chitosan composite

The carbon nanotubes-chitosan (CNTs-CS) composite provides a suitable biosensing matrix due to its good conductivity, high stability, and good biocompatibility. Enzymes can be firmly incorporated into the matrix without the aid of other cross-linking reagents. The composite is easy to form insoluble film in solution above pH 6.3. Based on this, a facilely fabricated amperometric biosensor by entrapping laccase into the CNTs-CS composite film has been developed. At pH 6.0, the fungi laccase incorporated into the composite film remains better catalytic activity than that dissolved in solution. The system is in favor of the accessibility of substrate to the active site of laccase, thus the affinity to substrates is improved greatly, such as 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS), catechol, and 0, with K. values of 19.86 mu M, 9.43 mu M, and 3.22 mM, respectively. The major advantages of the as-prepared biosensor are: detecting different substrates (ABTS, catechol, and 02), possessing high affinity and sensitivity, durable long-term stability, and facile preparation procedure. On the other hand, the system can be applied in fabrication of biofuel cells as the cathodic catalysts based on its good electrocatalysis for oxygen reduction.

Composite film of carbon nanotubes and chitosan for preparation of amperometric hydrogen peroxide biosensor

A new amperometric biosensor for hydrogen peroxide was developed based on cross-linking horseradish peroxidase (HRP) by glutaraldehyde with multiwall carbon nanotubes/chitosan (MWNTs/chitosan) composite film coated on a glassy carbon electrode. MWNTs were firstly dissolved in a chitosan solution. Then the morphology of MWNTs/chitosan composite film was characterized by field-emission scanning electron microscopy. The results showed that MWNTs were well soluble in chitosan and robust films could be formed on the surface. HRP was cross-linked by glutaraldehyde with MWNTs/chitosan film to prepare a hydrogen peroxide biosensor. The enzyme electrode exhibited excellent electrocatalytic activity and rapid response for H2O2 in the absence of a mediator. The linear range of detection towards H2O2 (applied potential: -0.2 V) was from 1.67 x 10(-5) to 7.40 x 10(-4) M with correction coefficient of 0.998. The biosensor had good repeatability and stability for the determination of H2O2. There were no interferences from ascorbic acid, glucose, citrate acid and lactic acid.

Neodymium oxide co-catalyzed melt free radical grafting of maleic anhydride onto co-polypropylene by reactive extrusion

Rare earth oxide, neodymium oxide (Nd2O3), CO-catalyzed melt grafting of maleic anhydride (MAH) onto co-polypropylene (co-PP) in the presence of dicumyl peroxide (DCP) was carried out by reactive extrusion. The experimental results reveal that the addition of Nd2O3 as a coagent leads to an enhancement in both MFR and the grafting degree of MAH, along with a simultaneous decrease in the gel content. When the Nd2O3 concentration is 6.0 mmol%, the increment of the grafting degree of MAH maximally is up to about 20% compared with the related system without adding Nd2O3, and the gel content decreases simultaneously to a very low level of about 3%. Attenuated total reflection FTIR (ATR-FTIR) indicates that the gel in the graft copolymers mainly arise from the cross-linking reaction between ethylene units of co-PP. A reasonable reaction mechanism has been put forward on the basis of our experimental results and other mechanisms reported in the literature. We also tentatively explain above results by means of synergistic effect between DCP and Nd2O3, which causes a higher concentration of the macroradical, in particular the tertiary macroradical.

Studies on Mechanical Properties of Full-Biodegradable Starch-PVA-Polyester Films

A kind of full-biodegradable film material is discussed in this article. The film material is composed of starch, PVA, degradable polyesters(PHB, PHB-V, PCL) with built plasticizer, a cross-linking reinforcing agent and a wet strengthening agent. It contains a high percentage of starch, costs cheap and is excellent in weather fastness, temperature resistance and waterproof and it could be completely biodegraded. The present paper deals mainly with a new technical route using a new type of electromagnetic dynamic blow molding extruder and some effects on mechanical properties of the system.

Monte Carlo simulation of the grafting of maleic anhydride onto polypropylene at higher temperature

The graft of maleic anhydride (MAH) onto isotactic polypropylene (iPP) initiated by dicumyl peroxide (DCP) at 190 degreesC was studied by means of the Monte Carlo method. The ceiling temperature theory, i.e., no possibility for the homopolymerization of MA-H to occur at higher temperatures, was used in this study. The simulation results show that most MAH monomers were grafted onto the radical chain ends arising from beta scission at a lower MAH concentration, whereas the amount of MAH monomers attached to the tertiary carbons was much larger than that grafted onto the radical chain ends at a higher MAH concentration for various DCP concentrations. This conclusion gives a good interpretation for the disagreement on the grafting sites along a PP chain. Moreover, it was found that the grafting degree increased considerably up to a peak value; thereafter, it decreased continuously with increasing MA-H concentration. The peak shifted in the lower MAH concentration direction and became lower and lower with increasing DCP concentration. When the DCP concentration was below 0.1 wt %, the peak was hardly observed. Those results are in good agreement with the experiments.