Uniaxial drawing of poly(ethyleneoxide)/poly(methyl methacrylate) blends by solid-state extrusion

Ultradrawn ribbons of solution-cast blends of poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) have been prepared by a solid-state coextrusion in a capillary rheometer. An increase of noncrystallizable PMMA in the blends drastically decreased the drawability from a draw ratio of 36 for pure PEO to 5 for a mixture of PEO/PMMA 40/60% by weight. A low crystallinity and depression of melting temperature for PEO were observed with increasing draw. The Flory-Huggins theory for melting temperature depression has been used to derive the binary interaction parameter for these blends.     

Absorption of toluene in poly(aryl-ether-ether-ketone)

The absorption and swelling of poly(aryl-ether-ether-ketone) (PEEK) in toluene as a function of resin morphology and temperature in the range 35–95°C was investigated. In all cases the weight gain curves exhibit three characteristics: (1) an induction period, which is a strong function of both temperature and initial crystallinity, (2) a main absorption region, which is linear with square-root time, and (3) a final equilibrium value, namely, solubility. The solubility of amorphous PEEK decreases with temperature and the heat of solution is ?0.93 kcal/mol. The induction period varies with the fourth power of the crystallinity and decreases with temperature with an apparent activation energy of 50 kcal/mol. The strength of the interaction between the crystalline regions is markedly reduced at temperatures greater than 80°C. Swelling accompanying the absorption of the toluene is highly anisotropic with most of the dimensional changes occurring in the thickness direction. The deswelling process, however, is essentially isotropic. The concentration of toluene in solution has a strong effect on the transport process; the equilibrium solubility of toluene in amorphous PEEK immersed in a toluene/iso-octane mixture is a linear function of toluene concentration; but the pseudo-diffusion coefficient for the absorption of toluene varies approximately with the fourth power of its concentration.     

Transport of methylene chloride in poly(aryl-ether-ether-ketone) (PEEK)

The sorption of methylene chloride in neat PEEK was investigated as a function of temperature, sample thickness, surface treatment, and thermal history. The solubility of H₂CCl₂ in neat PEEK is 23 wt.% and is independent of thickness. Both surface treatment and thermal annealing strongly affect the rate of penetration; the as-Received material sorbs H₂CCl₂ more rapidly than abraded or annealed samples; however, the bulk solubility is independent of surface treatment. The sorption and desorption processes are considerably different, and the diffusion process is not simple Fickian Case I. The penetrant advances as a sharp front, suggesting a two-step, relaxation-controlled diffusion mechanism.     

The solubility and diffusion of water in poly(aryl-ether-ether-ketone) (PEEK)

The transport properties of water in neat poly(aryl-ether-ether-ketone) (PEEK) coupons (2 to 6 mm thick) were investigated by gravimetric and mass spectrometric methods. The solubility of water increases from 0.44 wt.% at 35°C to 0.55 wt.% at 95°C; the temperature coefficient is 8 kJ/mol (1.9 kcal/mol). The diffusion processes for sorption, desorption, and resorption at 35°, 50°, 65°, 80°, and 95°C are, within experimental error, the same. The activation energy for diffusion is 42.7 kJ/mol (10.2 kcal/mol). The diffusion process is classical Case I Fickian in the temperature region investigated.     

聚癸二酸丙三醇酯对聚乳酸的改性

以丙三醇和癸二酸为单体通过熔融缩聚制得了聚癸二酸丙三醇酯(PGS),并用其预聚物(p-PGS)对聚L-丙交酯(PLLA)进行共混改性.利用傅立叶变换红外光谱(FT-IR)、核磁共振氢谱(1H-NMR)及凝胶渗透色谱(GPC)法对P-PGS的结构进行表征,并研究了改性后材料的力学性能、两相相容性、亲水性能和细胞相容性.结果表明:P-PGS具有支化分子结构,分散系数约为2.7;共混改性后的材料弹性模量和拉伸强度均有所下降,而断裂伸长率从7 %显著提高到150%左右;PLLA/PGS属于海岛式共混结构,PGS以小于10μm的尺寸均匀分布在PLLA基体中;共混后材料的亲水性也有一定的提高,且几乎保持了PLLA原有的细胞相容性.     

Solvent-induced crystallinity in poly(aryl-ether-ether-ketone) [PEEK]

The amount and structure of the crystals formed by the solvent-induced crystallization (SIC) following a sorption-desorption cycle of five fluids (benzene, toluene, chloroform, methylene chloride, and carbon disulfide) in amorphous PEEK was determined by wideangle x-ray scattering (WAXS). The SIC crystal structure was compared with that produced by thermal methods, both those formed at low temperature by heating the amorphous material 10–20°C above T_g or by cooling from the melt. Although smaller in size, the SIC crystals are tighter and more organized than those produced thermally. The WAXS data indicates that all five fluids produce approximately 35% crystallinity in PEEK. Gravimetric data suggest that a low-density region, consisting of either microvoids or highly disordered amorphous region, surrounds the crystals.     

Uniaxial drawing of polytetrafluoroethylene virgin powder by extrusion plus cold tensile draw

Polytetrafluoroethylene (PTFE) virgin powder was ultradrawn uniaxially by a two-stage draw. A film, compression molded from powder below the melting temperature (T_m), was initially solid-state coextruded to an extrudate draw ratio (EDR) of 6–20 at an established optimum extrusion temperature of 325°C, near the T_m of 335°C. These extrudates from first draw were found to exhibit the highest ductility at 45–100°C for the second-stage tensile draw, depending on the initial EDR and draw rate. The maximum achievable total draw ratio (DR_{t, max}) was 36–48. Such high ductility of PTFE, far below the T_g (125°C) and T_m, is in sharp contrast to other crystalline polymers that generally exhibit the highest ductility above their T_g and near T_m. The unusual draw characteristics of PTFE was ascribed to the existence of the reversible crystal/crystal transitions around room temperature and the low intermolecular force of this polymer, which leads to a rapid decrease in tensile strength with temperature. The structure and tensile properties of drawn products were sensitive to the initial EDR, although this had no significant influence on DR_t,max. The most efficient and highest draw was achieved by the second-stage tensile draw of an extrudate with the highest EDR 20 at 100°C, as evaluated by the morphological and tensile properties as a function of DR_t. The efficiency of draw for the cold tensile draw at 100°C was a little lower than that for solid-state coextrusion near the T_m. However, significantly higher tensile modulus and strength along the fiber axis at 24°C of 60 ± 2 GPa and 380 ± 20 MPa, respectively, were achieved by the two-stage draw, because the DR_t,max was remarkably higher for this technique than for solid-state coextrusion (DR_t,max = 48 vs. 25). The increase in the crystallite size along the fiber axis (D₀₀₁₅), determined by X-ray diffraction, is found to be a useful measure for the development of the morphological continuity along the fiber axis of drawn products.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2551–2562, 1998     

高分子量聚对二氧环己酮改进聚DL-乳酸柔韧性的研究

为了提高DL-聚乳酸(PDLLA)的柔韧性,将10～20wt%不同比例的由本课题组自主合成的高分子量聚对二氧环己酮(PPDO)加入到PDLLA基体中,对共混物的微观两相形态、力学性能、热学性能和表面性质、降解性能等物化性质进行了研究.实验结果表明,PPDO加入后,在PDLLA/PPDO共混物的柔韧性得到显著提高的同时,共混物表面亲水性相应提高,降解速率也随之加快.     

Molecular analysis of the crystallization behavior of poly(aryl-ether-ether-ketone)

The crystallization behavior, via annealing, of PEEK was investigated using FTIR spectroscopy. It was found that predominantly amorphous PEEK (e.g., quenched polymer) follows two distinct mechanisms when it is annealed. One is a lower energy relaxation process that involves the partial rotation of the ether linkages, allowing the molecular chains in the disordered phase to become better packed, and occurs from 50 to 140°C (slightly below T_g). This relaxation process is also observed by dynamic mechanical analyses. The other process is a crystallization that takes place above the glass transition, with its onset characterized by the rotation of the benzophenone linkages near T_g. Isothermal crystallization kinetics data on PEEK can be described by an Avrami equation with an Avrami constant n of about 1.     

The absorption of organic liquids in poly(aryl-ether-ether-ketone) [PEEK]

The absorption and subsequent desorption of benzene, toluene, carbon disulfide, and chloroform in amorphous and 27% crystalline poly (aryl-ether-ether-ketone) (PEEK) were determined. At 35°C, the equilibrium weight gain (solubility) of benzene, toluene, chloroform, and CS₂ are 23.5, 19.8, 51.2, and 21.2 wt%, respectively. The initial weight gain is linear with root-time and pseudodiffusion constants for absorption into amorphous PEEK ranging from 0.35 to 9.85 x 10^-12m²/s were calculated. The desorption processes are two-step and are controlled by the T_g of the penetrant-resin mixture. The rate of diffussion into the crystalline material is extremely slow; crystalline PEEK reaches saturation (12.5 wt%) after immersion in CS₂ (35°C) for several hundred hours but, even after 1300 h immersion, the other fluids do not reach saturation.     

Poly(Urethane)-Crosslinked Poly(HEMA) Hydrogels

Abstract

Hydrogels have been prepared from 2-hydroxyethyl methacrylate polymerized in the presence of isocyanate-terminated poly(ethylene glycol) (PEG) crosslinking agents. PEGS of molecular weights 200, 400, and 1000 were investigated. The crosslinked nature of the hydrogels was demonstrated by their insolubility in solvents which normally dissolve poly(HEMA). Hexamethylene diisocyanate (HDI) was mainly used as the isocyanate. The molecular weight of the PEG and the crosslinker content significantly influenced the equilibrium water sorption and mechanical properties of the saturated networks. It was observed that as the molecular weight of the PEG increased, the water sorption increased and the nominal modulus decreased. However, for higher levels of cross-linker, water sorption decreased and modulus increased at low molecular weight PEG; for PEG 1000, water absorption increased as crosslinker content increased. These results are explained by the competing effects of flexibility, crosslink density, and hydrophobicity contributed by the various constituents of the hydrogels.     

Modification of Poly(Ethylene Terephthalate) Track Membranes by Sorption of Poly(Ethylene Glycol)

Sorption of poly(ethylene glycol) on poly(ethylene terephthalate) track membranes was studied at different pH. The hydrophilic-hydrophobic properties of the intact membranes and those modified with poly(ethylene glycol) are compared. The membrane-aqueous human serum albumin and membrane-aqueous insulin adhesive tensions were determined for modified membranes. The competitive sorption of human serum albumin and poly(ethylene glycol) from aqueous solution on the track membranes is analyzed.     

聚对苯二甲酸乙二醇酯和聚对苯二甲酸丁二醇酯化学扩链反应

综述了用于聚对苯二甲酸乙二醇酯（ＰＥＴ）、聚对苯二甲酸丁二醇酯（ＰＢＴ）化学扩链反应的羧基加成型和羟基加成型扩链剂，以及缩合型扩链反应、羧基加成型扩链反应和羟基加成型扩链反应、羧羟基同时加成型扩链反应。讨论了扩链反应、反应特性和扩链产物的性能，并简要介绍了国内研究概况。参考文献２０篇。     

The effect of morphology on the transport of dichloromethane in poly(aryl-ether-ether-ketone)

A study of the transport of the dichloromethane in neat poly(aryl-ether-ether-ketone) (PEEK) samples with thicknesses from 0.08 to 3.0 mm with different morphologies was conducted at 35°C. Both sorption and desorption of the solvent were studied. Thermal annealing was used to vary the sample morphology, and density measurements were used to determine the crystallinity of the samples. The equilibrium concentration of solvent and rate of solvent sorption were found to vary with sample morphology. The density of the dichloromethane when in the PEEK resin was found to be 1.65 g/cm³. Solvent desorption was independent of sample morphology or any previous sample treatment and depended only upon desorption temperature. Solvent sorption appears to alter the morphology of amorphous samples by increasing the crystallinity to about 20% after one sorption/desorption cycle. Small amounts of the solvent, less than 0.5 wt.%, remain trapped in fully desorbed samples. The micromorphology of solvent-induced crystallization appears to be different from that induced by thermal treatment.     

Uniaxial alignment of poly(3-hexylthiophene) nanofibers by zone-casting approach

The preparation of large area coverage of films with uniaxially aligned poly(3-hexylthiophene)(P3HT) nanofibers by using zone-casting approach is reported.The length and the orientation of the nanofibers are defined by the solubility of the solvent,the P3HT molecular weight and the substrate temperature.The length of the oriented nanofibers could be increased from 1 μm to more than 10 μm by adding poor solvent into the P3HT solution.It is found that for P3HT of relatively low molecular weight,a solvent with relatively low solubility has to be chosen to get the oriented film.While for the high molecular weight P3HT,the solvent with a relatively high solubility has to be used.The well-aligned film could be obtained because of the solute concentration gradient in the region where the critical concentration is reached during the zone-casting process.Particularly,the solvent evaporation rate and crystallization rate must be chosen properly to satisfy the stationary conditions above,which were controlled by an appropriate choice of solvent and substrate temperature.The film prepared by zone-casting approach had microcrystalline P3HT domains with more inter-chain order than spin-coating film.Meanwhile,the P3HT π-π stacking direction was parallel to the alignment direction of the nanofibers.     

Poly(L-lactide) Nano- and Microfibers by Electrospinning: Influence of Poly(L-lactide) Molecular Weight

Summary: The electrospinning technique based on single and multi-jet systems was applied for poly(L -lactide) (PLA) nano- and microfibers as well as fibrous mats manufacture; the latter with dimensions suitable for the tensile tests. The PLA's employed were prepared by the controlled ring-opening polymerization of the L,L -lactide (LA) monomer. The resulting fibers thickness was correlated with molecular weights of PLA's and viscosities of spinning solutions. The scanning electron microscopic, thermal, and tensile characteristics of the polymeric materials and fibrous mats were also examined.     

联苯二胺类与噻吩共聚物的金属配合物催化法合成

联苯二胺,3,3′-二甲基联苯二胺在二价镍配合物存在下,直接与2,5-二溴噻吩的格氏(Grignard)试剂共聚,用红外光谱、核磁共振等对共聚物进行了表征。该合成方法所得联苯二胺与噻吩共聚物、3,3′-二甲基联苯二胺与噻吩共聚物的收率分别为63．4％和70.8％。在25℃测得的特性粘度分别为O．75dL／g和O.67dL／g。聚合物的循环伏安测定表明该类聚合物具有一定的电化学活性,每种聚合物均在O～O．8V之问出现两对氧化一还原峰。紫外一可见吸收光谱测试结果表明共聚物分别在415nm和450nm处有最大吸收峰。     

Functionalization of Conductive Poly(thiophenes) and Poly(pyrroles)

New methods for functionalization of conductive poly(thiophenes) and poly(pyrroles) using fused aromatics or crown ethers are discussed.