Preparative fractionation and characterization of polycarbonate/eugenol-siloxane copolymers

Bisphenol-A polycarbonate/eugenol-siloxane copolymers were fractionated at the preparative scale by the continuous polymer fractionation (CPF) technique. It is the first example of copolymer fractionation by CPF. The distribution of siloxane species across the fractions was assessed for copolymers differing in initial siloxane concentration and block length. On- and off-line combinations of size exclusion chromatography and infrared spectroscopy were used to analyze chemical composition (CC) of the unfractionated samples across the molecular weight distribution enabling comparison with the fractions. A polycarbonate-siloxane copolymer containing 10 wt% of very short siloxane blocks (dp=2) was fractionated solely according to molecular weight (MW). By contrast, a copolymer containing 5 wt% siloxane blocks with a larger degree of polymerization (dp=23) was fractionated according to MW, as well as to CC. This ‘chemical drift’ effect for the larger siloxane block length can be ascribed to large solubility differences of low MW chains, which drastically vary in composition according to the (small) number of siloxane blocks they contain.     

Enhanced crystallization of bisphenol-A polycarbonate by nano-scale clays in the presence of supercritical carbon dioxide

The crystallization behavior of bisphenol-A polycarbonate (PC) and PC/clay nanocomposites were studied in the presence of supercritical carbon dioxide (SCCO₂) using DSC, WAXD and AFM. In the absence of SCCO₂, nano-scale clay itself does not change the crystallization behavior of PC under our experimental conditions. In the presence of SCCO₂, clay appears to be an efficient nucleating agent and enhances the crystallization of PC. The addition of clay reduces the induction time of crystallization and increases the crystallization rate. The increase in crystallinity with clay depends on the crystallization time. When the crystallization time is sufficient, PC and PC/clay composites tend to have similar crystallinity in the range of 26%. Two melting temperatures are observed during the DSC heating scan, and are mainly associated with the melting of both secondary and primary crystals. Results show that the clay influences the primary crystallization process more than the secondary crystallization process.     

Diluent effects on carbonate mobility in bisphenol-A polycarbonate in the solid state

The effect of miscible low molecular weight additives on the mobility of the carbonate group in bisphenol-A polycarbonate (BPAPC) has been studied using n.m.r. and dielectric relaxation experiments in the solid state. Proton-enhanced dipolar-decoupled carbon-13 n.m.r. spectra of BPAPC, isotopically enriched at the carbonate position, are obtained without magic-angle sample spinning. The resolved chemical shift anisotropy allows study of nuclear spin relaxation for the carbonate groups in the polymer that have different orientations relative to the static magnetic field in the laboratory frame. The spin-lattice relaxation time in the rotating frame (T_1?) is measured at a motional-probe frequency of 50 kHz for the undiluted polymer and for BPAPC-diluent blends containing either dibutylphthalate or dinitrobiphenyl. The T_1? exhibits some dependence on orientation in all systems studied. In the blend containing dibutylphthalate (DBP), T_1? is decreased by a factor of two for all orientations of the carbonate group. This implies that DBP substantially increases the spectral density of 50 kHz motions in the carbonate region of the polymer at ambient temperature. In contrast, dinitrobiphenyl does not significantly alter the Fourier component of thermal fluctuations at 50 kHz. Dielectric relaxation measurements at 10 kHz reveal that the primary (T_g) and secondary (β) motional processes in BPAPC are affected by low molecular weight additives. An intermediate relaxation process appears in the temperature interval between the glass transition temperature (T_g) and the sub-T_g β-relaxation (T_β) in the polymer-diluent blends. The n.m.r. spin-lattice relaxation rate in the rotating frame, T^?1_1?, correlates well with the relative magnitude of the dielectric dissipation factor (tan δ_ε) between T_g and T_β.     

聚碳酸酯非光气法合成工艺研究进展

综述了近年来聚碳酸酯的酯交换法合成工艺的研究进展,着重阐述了其预聚反应动力学,介绍了该工艺中传热传质等因素对聚合过程的影响以及国内外相关研究现状和研究前景。     

Crystallization of polycarbonate induced by spinodal decomposition in polymer blends

We found that amorphous polycarbonate (PC) can be crystallized in several minutes by blending poly(ethylene oxide) (PEO). When the blends were annealed in the two-phase region below the upper critical solution temperature, highly interconnected two-phase structure characteristic of the spinodal decomposition was developed and then the crystallization occurred in the PC-rich phase during the spinodal decomposition. As the molecular weight of PEO decreased, the crystallization rate decreased and the crystallizable temperature became narrower in spite of the acceleration of the polymeric segmental motion. These results suggest that the crystallization of the PC is not induced by the acceleration of the polymeric segmental motion, but by the up-hill diffusion of the liquid-liquid phase separation via spinodal decomposition. Owing to the competitive progress of the crystallization and the spinodal decomposition, the melting peak of the PC crystallites shifted to lower temperature with increasing annealing temperature.     

Solubility and diffusion coefficient of supercritical-CO2 in polycarbonate and CO2 induced crystallization of polycarbonate

The solubility and diffusion coefficient of supercritical CO₂ in polycarbonate (PC) were measured using a magnetic suspension balance at sorption temperatures that ranged from 75 to 175 °C and at sorption pressures as high as 20 MPa. Above certain threshold pressures, the solubility of CO₂ decreased with time after showing a maximum value at a constant sorption temperature and pressure. This phenomenon indicated the crystallization of PC due to the plasticization effect of dissolved CO₂. A thorough investigation into the dependence of sorption temperature and pressure on the crystallinity of PC showed that the crystallization of PC occurred when the difference between the sorption temperature and the depressed glass transition temperature exceeded 40 °C (T − T_g ≥ 40 °C). Furthermore, the crystallization rate of PC was determined according to Avrami's equation. The crystallization rate increased with the sorption pressure and was at its maximum at a certain temperature under a constant pressure.     

双酚A专利技术评述

简要介绍了波兰重有机合成研究院、日本千代田公司、美国道化学公司生产双酚A的工艺流程,并对这三种生产方法的优缺点进行了评述。     

Flow induced orientation of multiwalled carbon nanotubes in polycarbonate nanocomposites: Rheology, conductivity and mechanical properties

We investigated the effect of flow field and deformation rate on the nanotube alignment and on the properties of PC/multiwalled carbon nanotube nanocomposites. Samples of various MWCNT loadings were prepared by diluting a commercial masterbatch containing 15 wt% nanotubes using optimized melt mixing conditions. Different processing conditions were then used to systematically change the degree of nanotube alignment, from random orientation to highly aligned. Morphological studies and Raman spectroscopy analysis revealed that the nanotubes are preferentially aligned in the flow direction, particularly at large injection or compression rates. Rheological measurements corresponding to high shear rate conditions showed drastic changes in the viscoelastic behavior. The complex viscosity significantly decreased and percolation threshold notably rose. High degrees of nanotube alignment also resulted in a significant increase in the electrical percolation threshold. The mechanical properties of the nanocomposites for different nanotube loadings were also shown to depend on the processing conditions, and somehow improved when the material was processed at higher rates. Finally, we used a power-law type equation to correlate the percolation behavior and the nanotube alignment. The estimated percolation threshold and the power index, q, significantly increase with the degree of nanotube alignment as determined by Raman analysis.     

我国聚碳酸酯合成技术发展前景

重点介绍了PC合成技术的发展历程和发展方向,对主要PC合成技术特点进行了比较,提出了我国PC合成技术开发存在问题,并预测了将来的发展前景.     

Thermally induced phase separation in liquid crystalline polymer/polycarbonate blends

Thermally induced phase separation in liquid crystalline polymer (LCP)/polycarbonate (PC) blends was investigated in this study. The LCP used is a main‐chain type copolyester comprised of p‐hydroxybenoic acid and 6‐hydroxy‐2‐naphthoic acid. Specimens for microscopic observation were prepared by melt blending. The specimens were heated to a preselected temperature, at which they were held for isothermal phase separation. The preselected temperatures used in this study were 265, 290, and 300°C. The LCP contents used were 10, 20, and 50 wt %. These parameters corresponded to different positions on the phase diagram of the blends. The development of the phase‐separated morphology in the blends was monitored in real time and space. It was observed that an initial rapid phase separation was followed by the coarsening of the dispersed domains. The blends developed into various types of phase‐separated morphology, depending on the concentration and temperature at which phase separation occurred. The following coarsening mechanisms of the phase‐separated domains were observed in the late stages of the phase separation in these blends: (i) diffusion and coalescence of the LCP‐rich droplets; (ii) vanishing of the PC‐rich domains following the evaporation‐condensation mechanism; and (iii) breakage and shrinkage of the LCP‐rich domains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Variation of flow induced phase morphology of fluoroelastomer and polycarbonate blends and their mechanical properties

The variations of the flow induced phase morphology of fluoroelastomer/polycarbonate (FL/PC) extruded blends and their mechanical properties were investigated in this paper. The phase morphology and mechanical property of extruded blends under the capillary die were examined by scanning electron microscope (SEM) and tensile machine, respectively. From SEM observation, the dispersed phases in the longitudinal direction for these extruded blends were categorized as sphere, ellipsoid, rod, and fiber. Furthermore, the processing window for the deformation of phase morphology in the longitudinal direction for FL/PC 10/90 w/w and 25/75 w/w extruded blends at 235 and 260 °C was studied. As shear stress was smaller than 7.0 × 10⁴ Pa, the spherical phase almost did not deform. The transformation from the sphere to the fiber form occurred in the range of shear stress 7.0 × 10⁴ Pa and 15.8 × 104 Pa. In particular, as shear stress was larger than 15.8 × 10⁴ Pa, the fiber broke up into a series of small droplets. Finally, it was concluded that the morphology with the mixture of fiber-like and spherical structures in the longitudinal direction could enhance the FL/PC blends with longer break elongation and higher Young’s modulus.     

Transport of helium in polycarbonate membranes

The transport of helium in membranes of poly(bisphenol A carbonate-co-4,4′-(3,3,5-trimethylcyclohexylidene)diphenyl carbonate) (PBCDC) is reported. The experimental values of the diffusion and permeability coefficients, under the upstream pressure of 176 cmHg, are (10.9±0.7)×10⁻⁶ cm² s⁻¹ and 61.4±0.5 barrers, respectively, at 30°C. Both coefficients obey Arrhenius behavior with activation energies of 1.9 and 3.0 kcal mol⁻¹, respectively. The dynamics of helium in the membranes was simulated using the transition state approach (TSA). Very good agreement between the theoretical and experimental values of the diffusion coefficient was found. However, the simulated solubility coefficient is nearly one order of magnitude higher than the experimental value.     

Synthesis and flame retardancy of phosphorus containing polycarbonate

Novel P-containing copolycarbonate was prepared via melt polycondensation of diphenyl carbonate (DPC), bisphenol-A (BPA) and 2-(6-oxid-6H-dibenz〈;c,e〉〈1,2〉oxa-phosphorin-6-yl)-1,4-benzenediol (ODOPB). The copolycarbonates were characterized by infra-red spectra, reduced viscosity, and differential scanning calorimetry. The copolycarbonates with reduced viscosities of 0.21∼0.25 dL/g were obtained in quantitative yields. These phosphorus containing copolycarbonates have excellent thermal and flame retardant properties. Owing to the incorporation of the rigid structure of ODOPB and the pendant P group, the resulting phosphorus containing copolycarbonates exhibited better flame retardancy, higher char yield, higher degradation temperature and thermal stability than homopolymers of polycarbonate (PC). High LOI value and UL 94-VO rating could be achieved with a phosphorus content of as low as 0.75% for PC, and no fumes or toxic gas emissions were observed.     

Siloxane modification of polycarbonate for superior flow and impact toughness

Reactive modification of polycarbonate (PC) with a small amount of ultra-high molecular weight polydimethylsiloxane (PDMS) provides an effective route to a novel blend polymer with superior flow and excellent impact toughness. Low temperature impact toughness for such a blend was found to be comparable to polycarbonate copolymers made by interfacial copolymerization of bisphenol A and specialty silicones with phosgene. Interestingly, the blend also showed strong shear thinning behavior and a viscosity that is almost an order of magnitude lower than the starting PC resin. Analysis of the blend composition and blend morphology revealed the presence of both PC-PDMS copolymer and un-grafted siloxane as a dispersed phase in the polycarbonate matrix. The PC-PDMS copolymer provides a compatibilization effect for the stable sub-micron blend morphology in an otherwise immiscible PC-PDMS blend system. Improvement of low temperature ductility (e.g., at −40 °C) by PDMS was thus made possible. The lubricating effect from siloxane and the possibility of fibrillation flow at high shear stress are suspected to be the main reasons for high flow characteristics of these blends.     

聚碳酸酯合成技术进展

综述了聚碳酸酯的国内外合成技术进展情况。介绍了目前工业生产中采用的界面光气法、溶液光气法、普通熔融酯交换法及非光气熔融法生产工艺 ,讨论了苯酚氧化羰基化法与双酚A氧化羰基化法合成聚碳酸酯的最新研究动态。对我国聚碳酸酯工业的发展提出了建议     

双酚A聚碳酸酯合成新方法的研究进展

介绍了双酚A聚碳酸酯不同于工业生产中常用的光气法和熔融酯交换法的3种新的合成方法,即固相缩聚法、开环聚合法、完全非光气法的实施方法、主要特点及其新进展,探讨了各种方法存在的主要问题以及对生成的聚合物结构和性能的影响。固相缩聚是由预聚物结晶后在固相缩聚,可以获得结晶型双酚A聚碳酸酯并提高聚合物质量;开环聚合法首先合成环状碳酸酯低聚物再开环聚合得到聚合物,可以获得很高分子质量聚合物;完全非光气法在合成过程中完全避免了光气的使用,环境友好,聚合物质量高,很有发展前景。     

Experimental and simulation studies of gas sorption processes in polycarbonate films

This work reports the experimental isotherms describing the concentration of oxygen and nitrogen in poly(bisphenol A carbonate-co-4,4′-(3,3,5-trimethylcyclohexylidene) diphenol carbonate) vs pressure, at 30 °C. The solubility coefficients are interpreted in terms of the Flory-Huggins theory, obtaining reasonable values for the enthalpic polymer-gas parameter. A new method is outlined to simulate the probabilities of inserting/removing a gas molecule in a host matrix already containing n molecules of gas. The simulated isotherms representing the pressure dependence of the concentration exhibit the same pattern as those experimentally obtained.