Synthesis and characterization of a novel biodegradable, thermoplastic polyurethane elastomer

A series of biodegradable, thermoplastic polyurethane elastomers poly (epsilon-caprolactone-co-lactide)polyurethane [PCLA-PU] were synthesized from a random copolymer Of L-lactide (LA) and epsilon-caprolactone (CL), hexamethylene diisocyanate, and 1,4-butanediol. The effects of the LA/CL monomer ratio and hard-segment content on the thermal and mechanical properties of PCLA-PUs were investigated. Gel permeation chromatography, IR, C-13 NMR, and X-ray diffraction were used to confirm the formation and structure of PCLA-PUs. Through differential scanning calorimetry, tensile testing, and tensile-recovery testing, their thermal and mechanical properties were characterized. Their glass-transition temperatures were below -8 degrees C, and their soft domains became amorphous as the LA content increased. They displayed excellent mechanical properties, such as a tensile strength as high as 38 MPa, a tensile modulus as low as 10 MPa, and an elongation at break of 1300%. Therefore, they could find applications in biomedical fields, such as soft-tissue engineering and artificial skin.

Synthesis and characterization of new carbazole/fluorene-based derivatives for blue-light-emitting devices

2,7-Bis(9-ethylcarbazol-3-yl)-9,9-di(2-ethylhexyl)fluorene and a segmented copolymer composed of the same chromophores alternated with hexamethylene fragments were synthesized. The obtained materials possess good solubility in common organic solvents, high thermal stability with 1% weight loss temperature of 350-370 degrees C, and suitable glass transition temperatures. Both derivatives show blue fluorescence in dilute solutions as well as in solid state, demonstrating that excimers are not formed in the thin films. The fluorescence spectra of the materials do not show any peaks in the long-wavelength region even after annealing at 200 degrees C in air. An organic LED with the configuration of ITO/copolymer/Al generates blue electroluminescence with the maximum peak at 416 nm, rather low turn-on voltage (4.0 V), and brightness of about 400 cd/m(2). The heterostructure device based on model derivative emitted stable blue light with low operation voltage (100 cd/m(2) at similar to 11 V) and demonstrated luminescence efficiency of 0.8 cd/A.

Direct electrochemical generation of conducting polymer micro-rings

Self-doped polyaniline (PANI) micro-rings have been successfully generated electrochemically. The polymer forming rings were about 100 nm wide, and the ring diameter is tunable from several to dozens of micrometres depending on deferent current densities. The morphology of such nanostructured polyaniline rings was investigated and further confirmed with field-emission scanning electron microscopy (FE-SEM). Furthermore, the film was characterized using UV/visible spectroscopy and cyclic voltammetry. The bubble template formation mechanism of the micro-rings was also proposed. Such nanostructured materials synthesized electrochemically open up a new approach to surface morphology control.

Synthesis of asymmetric H-shaped block copolymer by the combination of atom transfer radical polymerization and living anionic polymerization

A new asymmetric H-shaped block copolymer (PS)(2)-PEO-(PMMA)(2) has been designed and successfully synthesized by the combination of atom transfer radical polymerization and living anionic polymerization. The synthesized 2,2-dichloro acetate-ethylene glycol (DCAG) was used to initiate the polymerization of styrene by ATRP to yield a symmetric homopolymer (Cl-PS)(2)-CHCCCCH2CH2OH with an active hydroxyl group. The chlorine was removed to yield the (PS)(2)-CHCOOCH2CH2OH ((PS)(2)-OH). The hydroxyl group of the (PS)(2)-OH, which is an active species of the living anionic polymerization, was used to initiate ethylene oxide by living anionic polymerization via DPMK to yield (PS)(2)-PEO-OH. The (PS)(2)-PEO-OH was reacted with the 2,2-dichloro acetyl chloride to yield (PS)(2)-PEO-OCCHCl2 ((PS)(2)-PEO-DCA). The asymmetric H-shaped block polymer (PS)(2)-PEO-(PMMA)(2) was prepared via ATRP of MMA at 130 degrees C using (PS)(2)-PEO-DCA as initiator and CuCl/bPy as the catalyst system. The architectures of the asymmetric H-shaped block copolymers, (PS)(2)-PEO-(PMMA)(2), were confirmed by H-1 NMR, GPC and Fr-IR.

The direct synthesis of wholly aromatic poly(p-phenylene)s bearing sulfobenzoyl side groups as proton exchange membranes

Sulfonated poly(p-phenylene)s (SPPs) containing sulfonic acid groups in their side chains had been directly synthesized by Ni(0) catalytic coupling of sodium 3-(2,5-dichlorobenzoyl)benzenesulfonate and 2,5-dichlorobenzophenone. The synthesized copolymers possessed high molecular weights revealed by their high viscosity, and the formation of tough and flexible membranes by casting from DMAc solution. The copolymers exhibited excellent oxidative stability and mechanical properties due to their fully aromatic structure extending through the backbone and pendent groups. Transmission electron microscopic (TEM) analysis revealed that these side-chain type SPP membranes have a microphase-separated structure composed of hydrophilic side-chain domains and hydrophobic polyphenylene main chain domains. The proton conductivities of copolymer membranes increased with the increase of IEC and temperature, reaching values above 3.4 x 10(-1) S/cm at 120 degrees C, which are almost 2-3 times higher than that of Nafion 117 at the same measurement conditions. Consequently, these materials proved to be promising as proton exchange membranes.

Relaxation behavior of polymer blends with complex morphologies: Palierne emulsion model for uncompatibilized and compatibilized PP/PA6 blends

This paper deals with the dynamic rheological behavior of polypropylene/polyamide6 (PP/PA6) uncompatibilized blends and those compatibilized with a maleic anhydride grafted PP (PP/PP-g-MAH/PA6). The terminal relaxation times of the blends predicted by the Palierne emulsion model were compared with those obtained from experimental relaxation time spectra. The Palierne model succeeded well in describing PP/PA6 uncompatibilized blends with relatively low dispersed phase contents (10 wt%) and failed doing so for those of which the dispersed contents were high (30 wt%). It also failed for the compatibilized ones, irrespective of the dispersed phase content (10 or 30 wt%) and whether or not interface relaxation was taken into consideration. In the case of the uncompatibilized blend with high dispersed-phase content, interconnections among inclusions of the dispersed phase were responsible for the failure of the Palierne model. As for the compatiblized blends, in addition to particle interconnections, the existence of emulsion-in-emulsion (EE) structures was another factor responsible for the failure of Palieme model.

Green electroluminescent polyfluorenes containing 1,8-naphthalimide moieties as color tuner

A series of copolymers (CNPFs) containing low-band-gap 1,8-naphthalimide moieties as color tuner was prepared by a Yamamoto coupling reaction of 2,7-dibromo-9,9-dioctylfluorene (DBF) and different amount of 4-(3,6-dibromocarbazol-9-yl)-N-(4'-tert-butyl-phenyl)-1,8-naphthalimide (Br-CN) (0.05-1 mol% feed ratio). The light emitting properties of the resulting copolymers showed a heavy dependence on the feed ratio. In photoluminescence (PL) studies, an efficient color tuning through the Forster energy transfer mechanism was revealed from blue to green as the increase of Br-CN content, while in electroluminescence (EL) studies, the color tuning was found to go through a charge trapping mechanism. It was found that by introduction of a very small amount of Br-CN (0.1-0.5 mol%) into polyfluorene, the emission color can be tuned from blue to pure green with Commission International de l'Echairage (CIE) coordinates being (0.21, 0.42) and (0.21, 0.48). A green emitting EL single-layer device based on CNPF containing 0.1 mol% of Br-CN showed good performances with a low turn-on voltage of 4.2 V, a brightness of 9104 cd/m(2), the maximum luminous efficiency of 2.74 cd/A and the maximum power efficiency of 1.51 lm/W.

A Monte Carlo simulation for the micellization of ABC 3-miktoarm star terpolymers in a selective solvent

We have used Monte Carlo simulation to study the micellization of ABC 3-miktoarm star terpolymers in a selective solvent (good to A segment, bad to B and C segments). The simulation results reveal that the self-assembled morphology is determined by the block length, molecular architecture, terpolymer concentration and insolubility of insoluble block in the solvent. In dilute solution, symmetric terpolymers (N-B = N-C = 30) tend to aggregate into a novel wormlike pearl-necklace structure linked by an alternating arrangement of B and C spheres, whereas the asymmetric terpolymers (NB = 10, NC = 50) are likely to aggregate into spherical or cylindrical micelles (formed by C blocks) connected with some small B spheres, when the concentration of terpolymer is relatively low (chain number is 100). However, when the concentration of terpolymer is relatively high (chain number is 250), the symmetric terpolymers tend to aggregate into a netlike structure linked by an alternation of B and C spheres, whereas the asymmetric terpolymers are likely to aggregate into wormlike micelles (formed by C blocks) connected with some of small spheres (formed by B blocks). Moreover, when the insolubility of insoluble block in the solvent is weak, the insoluble blocks aggregate into some incompact micelles.

Poly(L-lactide)/starch blends compatibilized with poly(L-lactide)-g-starch copolymer

The poly(L-lactide) (PLLA)/starch blends were prepared by the PLLA grafting starch (PLLA-g-St) copolymers as a compatibilizer, and their thermal, mechanical and morphological characterizations were performed to show the better performance of these blends compared to the virgin PLLA/starch blend without the compatibilizer, including PLLA crystallinity, interfacial adhesion between the PLLA matrix and starch dispersive phases, mechanical test, medium resistance, and contact angle. The 50/50 composite of PLLA/starch compatibilized by 10% PLLA-g-St gave a tensile strength of 24.7 MPa and an elongation at break of 8.7%, respectively, vs. 11.3 MPa and 1.5%, respectively, for the simple 50/50 blend of PLLA/starch.

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.

Hydrazide-functionalized hollow porous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) spheres for immobilization of enzyme

Hollow porous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate)(HEMA-co-EDMA) spheres were prepared by emulsifier-free emulsion polymerization, swelling, seed emulsion polymerization and extraction. Then the spheres activated with 2,4,6-trichloro-1,3,5-triazine were functioned with adipohydrazide (AH). After periodate oxidation of its carbohydrate moieties, horseradish peroxidase was immobilized on the hydrazide-functionalized hollow porous poly(HEMA-co-EDMA) spheres. The amount of immobilized enzyme was up to 43.4 mu g of enzyme/g of support. Moreover, the immobilized horseradish peroxidase exhibited high activity and good stability.

Melt rheological properties of polypropylene-polyarnide6 blends compatibilized with maleic anhydride-grafted polypropylene

The melt rheological properties of binary uncompatibilized polypropylene -polyamide6 (PP-PA6) blends and ternary blends compatibilized with maleic anhydride-grafted PP (PP-PP-g-MAH-PA6) were studied using a capillary rheometer. The experimental shear viscosities of blends were compared with those calculated from Utracki's relation. The deviation value delta between these two series of data was obtained. In binary PP-PA6 blends, when the compatibility between PP and PA6 was poor, the deformation recovery of dispersed PA6 particles played the dominant role during the capillary flow, the experimental values were smaller than those calculated, and delta was negative. The higher the dispersed phase content, the more deformed the droplets were and the lower the apparent shear viscosity. Also, the absolute value of delta increased with the dispersed phase composition. In ternary PP-PP-g-MAH-PA6 systems, when the compatibility between PP and PA6 was enhanced by PP-g-MAH, the elongation and break-up of the dispersed particles played the dominant role, and the experimental values were higher than calculated. It was observed that the higher the dispersion of the PA6 phase, the higher the delta values of the ternary blends and the larger the positive deviation.

Nano-reactors for controlling the selectivity of the free radical grafting of maleic anhydride onto polypropylene in the melt

This paper reports on a successful application of the concept of nanoreactors to effectively controlling the selectivity of the free radical grafting of maleic anhydride (MAH) onto polypropylene (PP) in the melt, an industrially relevant process. More specifically, a free radical initiator of type ROOR was first confined into (or encapsulated by) the galleries of an organically modified montmorillonite (o-MMT) whose interdistance was 2.4 nm. Primary free radicals (RO center dot) formed inside the o-MMT galleries had to diffuse out before they could react with the PP backbone. The controlled release of the primary free radicals significantly increased the grafting degree of MAH onto PP and greatly reduced the level of the chain scission of the latter. Those results were better understood by electron spin resonance studies on model systems and by Monte Carlo simulations.

Influence of rubber content in ABS in wide range on the mechanical properties and morphology of PC/ABS blends with different composition

A series of acrylonitrile-butadiene-styrene (ABS) with different rubber content were prepared by diluting ABS grafting copolymer containing 60% rubber with a styrene-acrylonitrile copolymer. ABS prepared were blended with bisphenol-A-polycarbonate (PC) at the ratio of 70/30, 50/50, and 30/70 to prepare PC/ABS blends. Influence of rubber content in ABS on the properties of ABS and PC/ABS blends were investigated. PC/ABS blends with different compositions got good toughness when the rubber in ABS increased to the level that ABS itself got good toughness. The tensile properties and processability of PC/ABS blends decreased with the increase of the total rubber content introduced into the blends. ABS with the rubber content of 30 wt% is most suitable to be used to prepare PC/ABS blends. The rubber content in ABS affected the viscosity of ABS, and subsequently the viscosity ratio of PC to ABS. As a result, the morphology of PC/ABS blends varied. The increase of rubber content in ABS results in finer structure of PC/ABS blends.

Reactive blending of modified polypropylene and polyamide 12: Effects of compatibilizer content on crystallization and blend morphology

The crystallization behavior and morphology of nonreactive and reactive melt-mixed blends of polypropylene (PP) and polyamide (PA12; as the dispersed phase) were investigated. It Was found that the crystallization behavior and the size of the PA12 particles were dependent on the content of the compatibilizer (maleic anhydride-modified polypropylene) because an in situ reaction occurred between the maleic anhydride groups of the compatibilizer and the amide end groups of PA12. When the amount of compatibilizer was more than 4%, the PA12 did not crystallize at temperatures typical for bulk crystallization. These finely dispersed PA12 particles crystallized co-incidently with the 1313 phase. The changes in domain size with compatibilizer content were consistent with Wu's theory. These investigations showed that crystallization of the dispersed phase Could not be explained solely by the size of the dispersion. The interfacial tension between the polymeric components in the blends may yield information on the fractionation of crystallization.