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Towards high molecular weight poly(bisphenol a carbonate) with excellent thermal stability and mechanical properties by solid-state polymerization
Abstract
Poly(bisphenol A carbonate) (BPA-PC) was post-polymerized by solid-state polymerization (SSP) after supercritical CO2-induced crystallization in low molecular weight particles prepolymerized via melt transesterification reaction. The effects of the crystallization conditions on melting behavior and SSP of BPA-PC were investigated with differential scanning calorimetry (DSC), Ubbelohde viscosity method and gel permeation chromatography (GPC). The reaction kinetics of the SSP of crystallized prepolymers was studied as a function of reaction temperatures for various reaction periods. As a result, the viscosity average molecular weight of BPA-PC particles (2 mm) increased from 1.9 × 104 g/mol to 2.8 × 104 g/mol after SSP. More importantly, the significantly enhanced thermal stability and mechanical properties of solid-state polymerized BPA-PC, compared with those of melt transesterification polymerized BPA-PC with the same molecular weight, can be ascribed to the substantial avoidance of undergoing high temperature during polymerization. Our work provides a useful method to obtain practical product of BPA-PC with high quality and high molecular weight.
The thermal degradation mechanism and stabilization strategies of isosorbide (ISB)-co-1,4-cyclohexanedimethanol (CHDM) polycarbonate (IcC-PC) and IcC-PC/bisphenol-A polycarbonate (BPA-PC) blends were systematically investigated. IcC-PC is more prone to molecular weight decrease and yellowing than BPA-PC during high-temperature processing. MALDI-TOF-MS and ¹H-NMR analysis results show that ISB-PC and CHDM-PC underwent hydrolysis, β-elimination, and ISB-unit oxidation reactions, in which the former two reactions reduced molecular weight, and the latter induced yellowing. The addition of phosphite antioxidants, which have a strong peroxide removal ability, and free radical scavengers with low steric hindrance can inhibit the hydrolysis and ISB-unit oxidation. Accordingly, the thermal stability of IcC-PC is significantly improved. By reducing the reaction time (even if the catalysts loading is increased) and adding antioxidants, the thermal stability of reactive blends can be further improved, and the IcC-PC/BPA-PC transparent alloys close to the PC raw materials were prepared.
Organ-on-chips (OOCs) are microfluidic devices used for creating physiological organ biomimetic systems. OOC technology brings numerous advantages in the current landscape of preclinical models, capable of recapitulating the multicellular assemblage, tissue–tissue interaction, and replicating numerous human pathologies. Moreover, in cancer research, OOCs emulate the 3D hierarchical complexity of in vivo tumors and mimic the tumor microenvironment, being a practical cost-efficient solution for tumor-growth investigation and anticancer drug screening. OOCs are compact and easy-to-use microphysiological functional units that recapitulate the native function and the mechanical strain that the cells experience in the human bodies, allowing the development of a wide range of applications such as disease modeling or even the development of diagnostic devices. In this context, the current work aims to review the scientific literature in the field of microfluidic devices designed for urology applications in terms of OOC fabrication (principles of manufacture and materials used), development of kidney-on-chip models for drug-toxicity screening and kidney tumors modeling, bladder-on-chip models for urinary tract infections and bladder cancer modeling and prostate-on-chip models for prostate cancer modeling.
Melt post‐polycondensation (MPP) process is one of manufactures industrially that can efficiently increase the molecular weight of polycarbonate (PC). Herein, the MPP experiments of several PC materials using quaternary ammonium hydroxides and alkali metal compounds as the catalyst in the film state are studied. The reaction products are characterized by Ubbelohde viscometer, DSC, ¹H‐NMR, ultraviolet spectrophotometry, advanced polymer chromatography and rotational rheometer. It is found that MPP can effectively improve the intrinsic viscosity of PC. After a certain reaction time at a specific temperature, the number average molecular weight (Mn) of PC is raised from 19,000 to 54,600 g/mol. Furthermore, the ¹H‐NMR results reveal that Fries rearrangement products are produced during the MPP process. Based on the functional group model, a reaction kinetic model, combining the effects of the main melt polycondensation reaction and the Fries rearrangement reaction, is established for the first time. The reaction rate constants at different temperatures and the reaction activation energies of the two PC materials are obtained. This work provides a new reaction kinetics model to guide the MPP process of PC, which contains Fries rearrangement reaction.
The principal aim of the present study is to develop a method for the production of cellulose nanofibers, from the banana peel (BP) and bract (BB). It is also the aim of this study to produce cellulose-based biopolymers through acetyl and lauroyl modifications. The microwave digestion method and ball milling assisted ultra-sonication method was optimized for sustainable extraction of micro and nano cellulose fibers, respectively. The microwave digestion method was found to be effective in the removal of hemicellulose and lignin. Micro and nano cellulose fibers of BP and BB were found to contain type I cellulose structure. Thermal stability and crystallinity index of cellulose nanofibers were examined to be higher than it's native micro cellulose. Nano cellulose fibers were examined to be a potential source for production of acetyl and lauroyl cellulose, with a high degree of substitution and thermal stability. Hence, microwave digestion and ball milling assisted ultra-sonication method was proven to be effective in the extraction of nano cellulose fiber for development of cellulose-based polymers.
Despite the good biodegradable and mechanical properties, poly(lactic acid) still suffers from a highly inherent flammability, which restricts its applications in the electric and automobile fields. In order to improve the flame retardancy of PLA, in this work, melamine polyphosphate (MPP) and zinc bisdiethylphosphinate (ZnPi) were firstly incorporated into PLA, and the synergistic effect of them on flame retardance of PLA was investigated using limiting oxygen index (LOI), UL-94 vertical measurement, scanning electron microscopy (SEM) and cone calorimeter tests etc. The results showed that PLA composite with 15 wt% of MPP/ZnPi (3:2) had the best flame-retardant efficiency with LOI value of 30.1 and V0 rating in UL-94 tests, which was far better than using MPP or ZnPi alone. What is more, although a wide range of flame retardants have been developed to reduce the flammability, so far, they normally compromise the mechanical properties of PLA. On the premise of maintaining good flame-retardant performance, we improved the toughness of flame-retardant PLA composite, and the impact strength of flame-retardant PLA composite was more than tripled (8.08 kJ/m²) by adding thermoplastic urethanes (TPU). This work offers an innovative method for the design of the unique integration of extraordinary flame retardancy and toughening reinforcement for PLA materials.
In this article, hybrid fillers with different dimensions, namely, 2-dimensional (2-D) expanded graphite (EG) and 1-dimensional (1-D) multi-walled carbon nanotubes (CNTs), were added to aromatic nylon MXD6 matrix via melt-blending, to enhance its thermal and electrical conductivity as well as electromagnetic interference shielding effectiveness (EMI SE). For ternary composites of MXD6/EG/CNTs, the electrical conductivity reaches up nine orders of magnitude higher compared to that of the neat MXD6 sample, which turned the polymer-based composites from an insulator to a conductor, and the thermal conductivity has been enhanced by 477% compared with that of neat MXD6 sample. Meanwhile, the EMI SE of ternary composite reaches ~50 dB at the overall filler loading of only 18 wt%. This work can provide guidance for the preparation of polymer composites with excellent thermal and electrical conductivity via using hybrid filler.
Adding conductive filler is an effective way to enhance the dielectric constant while usually also increases the dielectric loss of polymer. In this study, we demonstrated that polymer composites with much improved dielectric constant while maintaining ultra-low dielectric loss could be achieved via using hybrid filler and controlling the dispersion of conductive filler in polymer matrix. To do this, the graphene oxide was designed to be immobilized on the surface of large-sized insulating hexagonal boron nitride (h-BN) via electrostatic self-assembly, and afterwards introducing this hybrid filler into epoxy accompanied with chemical reduction. In this case, since the reduced graphene oxide (rGO) sheets were fixed on the surface of h-BN, rGO sheets were well separated from each other even at high loading. Hence not only significantly enhanced dielectric constant was observed, but also a very low dielectric loss comparable to that of neat epoxy was achieved. This low dielectric loss was believed to be ascribed to both embedded insulating network of h-BN to inhibit the mobility of charge carrier and well-separated rGO sheets via immobilization. In addition to obviously improved dielectric properties, the nanocomposites also exhibited good thermal conductivity. We believe that this special structure will provide a new thought for fabricating dielectric materials with much enhanced dielectric constant as well as well-suppressed dielectric loss.
Cellulose films with excellent mechanical strength are of interest to many researchers, but unfortunately they often lack the ductility and water resistance. This work demonstrates an efficient and easily industrialized method for hydrophobic cellulose films made of modified microfibrillated cellulose (MFC). Prior to film fabrication, the simultaneous exfoliation and acylation of MFC was achieved through the synergetic effect of mechanical and chemical actions generated from ball milling in the presence of hexanoyl chloride. Largely enhanced tensile strength and elongation at break have been achieved (4.98 MPa, 4.37% for original MFC films, 140 MPa, 21.3% for modified ones). Due to hydrophobicity and compact structure, modified films show excellent water resistance and decreased water vapor permeability. Moreover, optical performance of modified films is also improved compared with the original MFC films. Our work can largely expand the application of this biodegradable resource and ultimately reduce the need for petroleum-based plastics.
Several measurements of the heat of fusion and of specific volume were carried out on bisphenol A-polycarbonate of varying degrees of crystallinity. A linear correlation was established between these two physical variables and from this an enthalpy of fusion for the polycarbonate crystal of 26 Kcal. was deduced.
Research on the kinetics of crystallization of polycarbonates based on bisphenol A at 190°C. has been carried out on six polydisperse samples. It was found that the process of crystallization, after a long period of induction, follows a course which can be described by the classical equation of Avrami. The final amounts of crystallization are small, ranging from 18 to 28%. Crystallization kinetics of polycarbonates depends on molecular weight and on the previous treatment of the polymer.
Amorphous poly(ethylene terephthalate) has been isothermally annealed in a wide range of temperatures from Tg to Tm. The effects of temperature and time of thermal treatment on density, melting curve and WAXS have been systematically explored. The results showed that densification and crystal perfection take place through a step mechanism involving partial melting and diffusion. The evaluation of the activation energies suggests that diffusion is the rate determining step in the low temperature range.
A high-pressure differential scanning calorimetric technique is described for studying polymer plasticization by compressed gases at pressures to 100 atm. The in situ measurements avoid problems due to gas desorption encountered with conventional DSCs thus providing an accurate way to determine the change in glass transition temperature, Tg, with pressure, p. The entire Tg-p curve can be established in less than 2 days. The glass transition was observed as a sharp step in the case of 100-200-μm thin samples, whereas thicker samples gave a broad transition; highly reproducible results were obtained for the thin samples. For PS-CO2, the measured Tgs under various pressures were found to be in good agreement with literature values. Results for the systems PS-HFC134a, PVC-CO2, and PC-CO2 are also reported.
Experimental results are reported for the crystallization and sorption kinetics of poly(ethylene terephthalate) in the presence of CO2 at 35 °C and pressures of 40, 50, and 60 atm. The results show that the time scale for crystallization is significantly greater than the time scale for CO2 sorption at these conditions. Crystallization occurs uniformly throughout the polymer film in this kinetic regime, and the sorption isotherm is characterized by a maximum in CO2 solubility as a function of time.The effect of increasing CO2 pressure over the pressure range studied is to enhance both the sorption and crystallization kinetics, although larger rate enhancements are obtained for crystallization. These results suggest that crystallization may occur on a time scale less than that for sorption at even higher CO2 pressures. Crystallization would not occur uniformly throughout the polymer in this kinetic regime, but would move as a front through the polymer film. The morphology of thin polymer films which undergo crystallization at higher pressure may therefore be substantially different from the morphology obtained by crystallization at the CO2 pressures studied here.This work has general significance for dense gas or supercritical fluid extractions of low molecular weight components from polymeric materials. Our results show that the effect of pressure on the extraction can involve more than the solvent properties of the dense gas or supercritical fluid; the effect of pressure on the relative rates of crystallization and sorption, and on polymer morphology must also be considered. The results of this study also suggest that CO2 pressure may be used to control the kinetics of crystallization and sorption in thin films of poly(ethylene terephthalate) and thereby provides the means to manipulate the morphology of this semi-crystalline polymer.
Several attempts1–5 have been made to control the rate of crystallization and the morphology by the addition of very finely-divided substances which promote abundant nucleation. However, these studies have mostly been carried out on an empirical basis and, except in a few cases (self-seeding6, epitaxy2–5), the mechanism of action of these nucleating agents is poorly understood despite several attempts at modelling1,2. This is particularly so in the case of most technical nucleating agents such as mica, talc and organic salts. We report here that the mechanism of action of organic nucleating agents such as sodium benzoate and its derived salts completely differs from the generally accepted model, at least in the case of polyesters. The nucleating agent reacts as a true chemical reagent with the molten macromolecules and produces ionic end groups which constitute the true nucleating species.
Poly(bisphenol A carbonate) was synthesized by solid-state polymerization (SSP) using supercritical CO2 to induce crystallinity in low molecular weight polycarbonate beads. The CO2-induced crystallization was studied as a function of time, temperature, molecular weight, and pressure. There was an optimum temperature for crystallization which depended on the molecular weight of the polymer. The molecular weight and percent crystallinity of the polymer produced by SSP were determined as a function of time and radial position in the bead. The molecular weight and percent crystallinity were strong functions of the particle radius, probably because of the slow diffusion of phenol out of the polymer particles. Nitrogen and supercritical CO2 were used as sweep fluids for the SSP process. The polymerization rate was always higher in supercritical CO2 at otherwise comparable conditions. We hypothesize that supercritical CO2 plasticizes the amorphous regions of the polymer, thereby increasing chain mobility and the rate of phenol diffusion out of the polymer. This permits the reaction temperature to be reduced, thereby suppressing side reactions that lead to color body formation. These advantages result in higher molecular weight product with good optical clarity when supercritical CO2 is the sweep fluid.
The likely mechanism which allows the required migration of functional groups for solid-state polymerization (SSP) of polyamides and polyesters is shown to be interchange reactions. This “chemical diffusion” of functionality has exactly the same mathematical form as that of classical diffusion of small molecules. The consequent model for kinetics of SSP in fine geometries is seen to fit experimental data well. It yields an estimate of the critical distance over which the functionality jumps with each interchange reaction. The critical reaction distance thus obtained, 5 Å, is similar to those determined from diffusion-controlled reactions of small molecules. The profound changes that interchange reactions can produce during SSP in the topology of chain segments in the intercrystalline regions of flexible and semirigid polymers, especially in oriented structures, are revealed.
The solid-state polymerization (SSP) of small particles (20 μm) of poly(bisphenol A carbonate) resulted in high molecular weight material (Mw of 36 000 g/mol). Molecular weight distribution broadening was not observed in polycarbonate in the form of small granulated powders but did occur in large polycarbonate beads (3.6 mm diameter). We hypothesize that this broadening is due to slow diffusion of phenol inside the larger polymer particles. A systematic investigation of the role of CO2 pressure and temperature was performed. It was found that the increase in molecular weight was a strong function of CO2 pressure and temperature. Additionally, the chain extension reactions occurred faster at higher supercritical CO2 flow rates. The SSP of polycarbonate in the presence of supercritical CO2 can be accomplished at temperatures as low as 90 °C, which is 60 °C lower than the Tg of polycarbonate at normal conditions. This should suppress the side reactions that lead to color body formation, thereby resulting in a product with good optical clarity and color.
The kinetics of solid-state polymerization (SSP) of poly(bisphenol A carbonate) was investigated with N2 as the sweep gas. The N2 flow rate and prepolymer particle size were chosen to eliminate the influence of both external and internal phenol diffusion, and to ensure that the kinetics was controlled by the rate of the forward transesterification reaction. The forward reaction rate constants were evaluated at different temperatures between 120 and 165 °C, and the activation energy for SSP of poly(bisphenol A carbonate) with N2 as the sweep gas was determined to be 99.6 kJ/mol. At each temperature, the polymer molecular weight increased with time, eventually reaching an asymptotic value. The asymptotic molecular weight increased with temperature. The glass transition temperature (Tg) of the polymer increased as the molecular weight increased. At lower reaction temperatures, Tg approaches the reaction temperature as the polymerization proceeds, and the achievable molecular weight appears to be limited by decreased end group mobility. At the highest reaction temperature, which was well above the final Tg of the polymer, the stoichiometric ratio of the two end groups appears to determine the achievable molecular weight.
The melting behavior of semicrystalline poly(ether ether ketone) (PEEK) has been studied by differential scanning calorimetry (DSC). When PEEK is annealed or cold-crystallized from the amorphous glassy state at high supercooling or melt-crystallized at low supercooling, it usually shows two melting peaks. The low-temperature endotherm has been found to represent only a portion of the melting endotherm of original crystals. The high-temperature endotherm is the melting of crystals reorganized during a heating scan. This double-melting behavior can be explained by the sum of four contributions: melting of most original crystals, their recrystallization, remelting of recrystallized PEEK, and melting of residual crystalline regions. A Hoffman-Weeks plot using the high-temperature melting peak and the crystallization temperature (Tc) for the melt-crystallized PEEK (Tc > 310°C) indicates that an equilibrium melting temperature is 389 ± 4°C. As a result of isothermal crystallization and reorganization during a heating scan, the lamellae are found to be thickened by a factor of 1.7.
The reactive pyrolysis−gas chromatography technique was applied to verify the branching and/or cross-linking structures in an industrially available PC sample and its thermally treated ones through identification of specific pyrolysis products directly reflecting the related abnormal structures. On the pyrograms of the thermally treated samples, the peaks reflecting the abnormal structures such as branching and/or cross-linking were observed together with those reflecting main chain and end groups. Although the formations of these branching and/or cross-linking structures during the thermal treatment of PC had been suggested early, the identification of these pyrolysis compounds by reactive pyrolysis verified the existence of these structures. Furthermore, the fact that some of those characteristic peaks were also observed on the pyrogram of the industrially available PC sample prepared by the melt method indicated that the branching and/or cross-linking reactions would occur to some extent in the industrial polymerization reactor to synthesize the PC by the melt method.
We report that, under carefully controlled conditions, poly(aryl carbonate)s can undergo chain extension in the solid state to substantially high molecular weight polymers, until this time considered inaccessible through melt polycondensation reactions. The prepolymer of poly(aryl carbonate) used in our study was prepared from bisphenol A and diphenyl carbonate using a melt phase carbonate interchange reaction.
A mathematical model is presented to analyze the kinetics of solid-state polymerization of bisphenol A polycarbonate. The reaction kinetic model incorporated in the solid-state polymerization model is a hybrid of a molecular species model and a functional group model derived from the original model developed by Flory. The solid-state polymerization model allows for the calculation of time evolution of complete polymer chain length distributions in a polymer particle at different radial positions under various reaction conditions. The model simulations show that large polymer particles exhibit strong intraparticle diffusion resistance to phenol, and as a result, the chain length distribution varies significantly from position to position in the polymer particle. Also, some polymer chains have very large chain lengths, several times larger than the average chain length, and some polymer chains have less than 10 repeating units even with a very large average molecular weight. The model simulations also show that one of the most important kinetic parameters that affect the performance of solid-state polymerization is the end group mole ratio in the prepolymer used for solid-state polymerization. The more the end group mole ratio deviates from its stoichiometric ratio in a prepolymer, the longer the reaction time needed to obtain high molecular weight polymer in the solid state. Also, the stoichiometric imbalance in the prepolymer severely limits the maximum obtainable molecular weight. The model simulation shows that an increasing polymer crystallinity during the solid-state polymerization has an effect of increasing the concentrations of catalyst and reactive end groups and hence the polymerization rate.
By studying the molecular weights of various solutions of cis ‐1,4‐polyisoprene the authors arrived at the formula \documentclass{article}\pagestyle{empty}\begin{document}$$\left[ \eta \right] = \sqrt {2/c} \sqrt {\eta _{sp} - {\rm l}n\eta } _{rel} $$\end{document} which allowed the calculation of the intrinsic viscosity of the polymer solutions by a single viscosity determination. The formula was verified for different systems of polymer–solvent and the values are in accord with those obtained by extrapolation. An operating concentration of about 0.2% is recommended.
A comprehensive model has been developed to handle the reactions in polymers undergoing polycondensation reactions in the solid state. The polymer crystalline fraction is modeled as containing only repeat units, thus concentrating end groups and condensate in the amorphous fraction. In addition, by using a general framework for the equations, many previously neglected effects are included; for example, variable crystallinity and gas phase mass transfer effects. This model is compared to PET and nylon reaction data with good results. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1233–1250, 1998
Static pressure usually increases the transition temperatures of polymers by decreasing their free volume. If the pressurizing medium is soluble in the polymer matrix, the opposing effect of increasing the free volume is possible. Those shifts of transition temperatures were monitored with a medium-pressure Differential Scanning Calorimetry (DSC) device. The influences of sorbed and surrounding gas molecules are demonstrated by changes occurring in the transition temperature regions. The results show the severe plasticizing effect of CO2 on poly(p-phenylene sulphide) (PPS). The glass transition temperature TG and the temperature of crystallization TC are influenced by sorbed gas molecules. They decrease due to sorbed CO2 molecules. Glass transition is lowered, but is difficult to interpret, as relaxation phenomena which diminish with increasing pressure occur during DSC runs. In crystallites no gas solution is usually possible, so that the melting point of PPS is mainly affected by influences other than plasticization.
The crystallization and melting behavior of bisphenol A polycarbonate treated with supercritical carbon dioxide (CO2) has been investigated with differential scanning calorimetry. Supercritical CO2 depresses the crystallization temperature (Tc) of polycarbonate (PC). The lower melting point of PC crystals increase nonlinearly with increasing treatment temperature. This indicates that the depression of Tc is not a constant at the same pressure. Tc decreases faster at a higher treatment temperature than at a lower temperature. The leveling off of the depression in Tc at higher pressures is due to the antiplasticization effect of the hydrostatic pressure of CO2. The melting curves of PC show two melting endotherms. The lower melting peak moves to a higher temperature with increasing treatment temperature, pressure, and time. The higher temperature peak moves toward a higher temperature as the treatment temperature is increased, whereas this peak is independent of the treatment pressure, time, and heating rate. The double melting peaks observed for PC can be attributed to the melting of crystals with different stability mechanisms. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 280–285, 2004
The mechanism of solid state polycondensation has been subjected to a fundamental analysis. Equations were formulated for combined diffusion and chemical reaction for two separate situations. One was for solid state polycondensation in polymer flakes or chips. The other dealt with polymer powders. The resultant solutions related molecular weight changes to rate functions. A technique for deriving the rate functions from experimental data is described.
Solid state polycondensations were then studied for nylon 66, nylon 6-10, and polyethylene terephthalate. These data which ranged from 120 to 200°C. were tested with various mechanisms. The most appropriate one was found to be that developed in the present work. Chemical reaction was found to be the rate controlling step in solid state polycondensation in nylon 66, polyethylene terephthalate, powders of nylon 6-10 and larger particles of nylon 6-10 at and above 160°C. Diffusion of byproduct through the solid was the rate controlling step for larger particles of nylon 6-10 at temperatures below 160°C. Thermograms of nylon 6-10 indicated morphological changes which possibly influenced the behavior of the larger nylon 6-10 particles. The Arrhenius relation was fitted to the situations where chemical reaction controlled.
A mathematical model for simulation of industrial process of solid state polycondensation of poly(ethylene terephthalate) (PET) has been developed. The model eliminates errors evident in the earlier models by proper formulation. The model results have been validated by experimental data in the literature. It enables prediction of the influence of particle shape, size, temperature, etc. on the polycondensation process correctly in all different regimes of operation, apart from bringing out the importance of gas-side resistance, influence of carrier gas, etc. for the first time.
Supercritical carbon dioxide readily induces crystallization in bisphenol A polycarbonate. Crystallization begins within one h of exposure to the CO2 at temperatures and pressures as low as 75°C and 100 atm. The degree of crystallinity increases sharply as the CO2 pressure is raised from 100 to 300 atm but levels off thereafter. This behavior is likely due to a minimum in the Tg of the polycarbonate/CO2 mixture owing to the opposite effects of the pressure on the Tg of the polymer and on the equilibrium weight fraction of CO2 absorbed. Percent crystallinities of over 20%, comparable to that achieved using acetone or other organic liquids, have been obtained after 2 h exposure to supercritical CO2. Since polycarbonate degasses quickly and quantitatively at ambient temperature and pressure, the high Tg of bisphenol A polycarbonate can be regained in the crystallized material without further vacuum treatment.
The effect of prepolymer molecular weight on the solid-state polymerization (SSP) of poly(bisphenol A carbonate) was investigated using nitrogen (N2) as a sweep fluid. Prepolymers with different number–average molecular weights, 3800 and 2400 g/mol, were synthesized using melt transesterification. SSP of the two prepolymers then was carried out at reaction temperatures in the range 120–190 °C, with a prepolymer particle size in the range 20–45 μm and a N2 flow rate of 1600 mL/min. The glass transition temperature (Tg), number–average molecular weight (Mn), and percent crystallinity were measured at various times during each SSP. The phenyl-to-phenolic end-group ratio of the prepolymers and the solid-state synthesized polymers was determined using 125.76 MHz 13C and 500.13 MHz 1H nuclear magnetic resonance (NMR) spectroscopy. At each reaction temperature, SSP of the higher-molecular-weight prepolymer (Mn = 3800 g/mol) always resulted in higher-molecular-weight polymers, compared with the polymers synthesized using the lower molecular weight prepolymer (Mn = 2400 g/mol). Both the crystallinity and the lamellar thickness of the polymers synthesized from the lower-molecular-weight prepolymer were significantly higher than for those synthesized from the higher-molecular-weight prepolymer. Higher crystallinity and lamellar thickness may lower the reaction rate by reducing chain-end mobility, effectively reducing the rate constant for the reaction of end groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4959–4969, 2008
A numerical method to seek a solution for the solid-state polycondensation (SSP) proces has been proposed to analyze the mechanism of SSP. Results expound that, for the industrial SSP process of PET, the overall reaction rate in a single pellet is appropriately simulated by the diffusion and reaction rate jointly controlling the model. From the core to the surface the SSP rate increase monotonically due to a gradual reduction of the concentration of such by-products as ethylene glycol and water. However, the SSP rate at any location within the pellet is constrained between two purely reaction rate controlling cases. © 1995 John Wiley & Sons, Inc.
The presence of organic acid salts in bisphenol-A polycarbonate (PC) completely modifies the crystallization mechanism, the melting behavior, and the morphology of the polymer. Organic salts are not ordinary nucleating agents for PC since they react with the polymer, producing metal phenoxide chain ends. On reaction, abundant instaneous nucleation is induced. The seeds are likely to be polymer crystalline fragments preexisting in the melt. The phenoxide chain ends significantly increase the growth rate of the crystalline phase. Melting points and enthalpies of fusion are unusually high, suggesting a high degree of crystalline perfection. Thick multilamellar crystals, which are likely to contain chains in extended configuration, are observed by electron microscopy. No trace of spherulitic morphology is found. The chemical instability of PC containing ionic chain ends is also shown to seriously affect the crystallization rate, the maximum degree of crystallinity, and the melting point.
The crystallization of amorphous poly(ethylene terephthalate) has been investigated using differential scanning calorimetry (dsc) and x-ray techniques. In particular, the occurrence of double melting peaks in the dsc thermograms has been examined. It is shown that the high temperature peak is due to a recrystallization and melting process taking place while the material is being scanned. Hence the dsc peaks are not a direct reflection of the state of the material at room temperature prior to the scan. As a result, some proposals in the literature for the structural changes accompanying the crystallization of poly(ethylene terephthalate) must be re-examined. Some interesting differences between the effect of temperature and time on the crystallization of poly(ethylene terephthalate) are also reported.
Conventional production of aromatic polycarbonates (PCs) involves interfacial polycondensation between phosgene (COCl2) and bisphenol A (BPA). This COCl2 process has several drawbacks such as environmental and safety problems involved in using the highly toxic COCl2 as the reagent, which resulted in the formation of chlorine salts of a stoichiometric amount, and in using copious amounts of methylene chloride as the solvent. For these reasons, environmentally friendly processes for PC production without COCl2 have been developed such as melt transesterification of BPA and diphenyl carbonate (DPC). However, COCl2-free production of DPC is not easy yet because of its severe equilibrium constraint, and therefore obtaining DPC efficiently is the most important step to develop a successful COCl2-free PC process. DPC can be obtained via two methods without using COCl2: two-step synthesis of DPC from dimethyl carbonate (DMC) and phenol and direct oxidative carbonylation of phenol. The DPC reacts with BPA to form PC precursors, which are amenable to the subsequent polycondensation step to obtain high molecular weight PC. Alternatively, BPA can be directly carbonylated with DMC or CO. In this work, we review and discuss different reaction routes and the involved catalytic chemistry of possible COCl2-free PC syntheses based on literature as well as our own experimental results. We compare reaction characteristics and the nature of PC precursors produced from different synthetic routes and provide a perspective on an improved COCl2-free PC process.
The kinetics of solid-state polymerization (SSP) of poly(bisphenol A carbonate) was investigated with supercritical CO2 (scCO(2)) as the sweep fluid. The CO2 flow rate and polymer particle size were chosen to ensure that the kinetics was controlled by the rate of the forward transesterification reaction, i.e., so that both external and internal phenol diffusion limitations were negligible. The forward reaction rate constants were determined between 90 and 135 degreesC, at CO2 pressures of 138, 207, and 345 bar. At a given temperature, the reaction rate was higher with scCO(2) as the sweep fluid than with N-2, especially at lower temperatures. The rate constant for the forward transesterification reaction increased with increasing CO2 pressure up to about 207 bar, at which point the rate constant was no longer sensitive to CO2 pressure. The activation energy decreased from 23.9 kcal/mol in N-2 to 15.5, 11.6, and 11.4 kcal/ mol at CO2 pressures of 138, 207, and 345 bar, respectively. The effect of scCO(2) on the rate of polymerization can be understood in terms of the solubility of CO2 in the polymer.
Diffusion in poly-(ethylene-terephthalate) (PET), during treatment in a supercritical CO2-atmosphere, was investigated in order to achieve a better understanding of the mass transfer mechanism in the amorphous regions of polymers. Recently, some promising applications have been developed where mass transfer in the polymer phase by means of a supercritical fluid is of major importance. Examples are the dyeing of PET with supercritical CO2, membrane separations of gas–fluid mixtures and the treatment of polymers with supercritical fluids to change their properties (generation of foams, extraction of impurities, etc.). A new experimental method to determine diffusion coefficients has been developed. It is based on the gravimetric measurements of mass transport with a simultaneous investigation of the swelling behavior of PET in supercritical CO2, on a single polymer sample. The swelling of PET was compared with the swelling behavior of another glassy polymer (bisphenol-A polycarbonate) in supercritical CO2. Experimental data of the sorption of CO2 and different kinds of disperse dyes in the polymeric matrix have been measured in order to calculate diffusion coefficients for the different substances. The diffusion coefficients have been calculated by a classical diffusion model for cylindrical solids. It could be shown that diffusion of disperse dyes in PET strongly depends on the dye itself, which is key information for the process development.
Handbook of polycarbonate science and technology”, Marcel Dekker
- D G Legrand
- J T Bendler
- DG LeGrand
Chemistry and physics of polycarbonates
- H Schnell
Polycarbonate resins
- KL Ring
Polycarbonate resins
- K L Ring
- H Janshekar
- G Toki
- KL Ring
- Z Y Zhang
- Y P Handa
- Z Y Zhang
- Y P Handa
- ZY Zhang