Antisolvent crystallization and solid‐state polymerization of bisphenol‐A polycarbonate

Bisphenol‐A polycarbonate (BAPC) was synthesized by solid‐state polymerization (SSP) using a semicrystalline prepolymer crystallized by antisolvent method. The antisolvent crystallization was investigated as a function of antisolvent types using X‐ray diffraction (XRD), different scanning calorimetry (DSC), and scanning electron microscopes (SEM). The results showed antisolvent types had a significant effect on the crystallization of BAPC. Prepolymer induced by acetone as an antisolvent gained a higher crystallinity of 37.0%, more uniform particle size, and mature crystal structure compared with the samples crystallized by methanol and ethanol. Then crystallization of BAPC by acetone was carried out at crystallization temperature in the range of 40–80 °C for 1–5 h. A high crystallinity of 42.0% was acquired with the crystallization conducted at 70 °C for 2 h. Prepolymer with appropriate crystallinity of 37.8% resulted in high‐molecular‐weight polymer of 57,411 via SSP due to the effect of crystallinity and plasticization of residual solvent. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43636.     

Solid state polymerization of bisphenol A polycarbonate: Effect of the crystallization method and polymerization conditions

A study on the effect of the crystallization method on the solid state polymerization (SSP) process of bisphenol A polycarbonate has been performed. Prepolymer samples were crystallized via four different techniques (solvent induced, shear induced, organic salt induced, and thermal crystallization) and SSP progress was checked by measuring the molecular weight increase. The fastest polymerization rate was obtained with prepolymers crystallized with acetone. The reaction rates were correlated with the crystallinity and plasticization of solvents, which both affected the chain mobility. The experiments conducted using different sweep gas flow rates and different particle sizes showed that, for the acetone‐crystallized prepolymers, the reaction rate was limited by the by‐product diffusion inside the polymer particles and from the surface of the particles into the sweep gas. ¹H‐nuclear magnetic resonance analysis proved that polymers prepared through a solid state process had a consistently lower content of Fries rearrangement by‐products with respect to commercial samples obtained by standard melt polycondensation methods. POLYM. ENG. SCI., 55:1024–1029, 2015. © 2014 Society of Plastics Engineers     

Preparation of Micron‐Sized Spherulitic Bisphenol A Polycarbonate Particles in Thin Films

A facile technique is presented to prepare discrete µm‐sized spherulitic particles of BAPC in thin polymer films. Unlike in bulk precipitation or spray crystallization, the present technique offers a method to prepare three‐dimensional semicrystalline particles of narrow particle size distribution that can be readily isolated and collected from the glass substrate as discrete particles. We report the effects of polymer molecular weight, polymer type, and the precursor polymer film thickness on the formation of spherulitic particles and their morphologies. The three‐dimensional spherulitic particles prepared in this study have large specific surface areas, higher crystallinity and melting temperature than the bulk precipitated and crystallized polycarbonate particles.

     

Low temperature solid‐state extrusion of recycled poly(ethylene terephthalate) bottle scraps

The processing of poly(ethylene terephthalate) (PET) involves thermal and hydrolytic degradation of the polymer chain, which reduces not only the intrinsic viscosity and molecular weight, but also the mechanical properties of recycled materials. A novel PET/bisphenol A polycarbonate/styrene–ethylene–butylene–styrene alloy based on recycled PET scraps is prepared by low temperature solid‐state extrusion. Hydrolysis and thermal degradation of PET can be greatly reduced by low temperature solid‐state extrusion because the extrusion temperature is between the glass‐transition temperature and cold‐crystallization temperature of PET. Modification of recycled PET by low temperature solid‐state extrusion is an interesting method; it not only provides an easy method to recycle PET scraps by blend processing, but it can also form novel structures such as orientation, crystallization, and networks in the alloy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2692–2699, 2006     

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。     

Monodisperse‐porous poly(styrene‐co‐divinylbenzene) beads providing high column efficiency in reversed phase HPLC

A multistage polymerization protocol, the so‐called “modified seeded polymerization,” was developed for the production of monodisperse‐porous poly(styrene‐co‐divinylbenzene) providing high column efficiency as a packing material in reversed phase high performance liquid chromatography (RPLC). In the first stage of the multistage production, uniform polystyrene seed particles, produced by dispersion polymerization, were swollen by an organic agent (i.e., the diluent) and then by a monomer mixture containing styrene and divinylbenzene. The final porous particles were obtained in the monodisperse form by the polymerization of monomer mixture in the seed particles. By the use of a small size seed latex with low molecular weight and by the selection of the appropriate diluent, relatively small monodisperse‐porous particles with suitable pore structure could be achieved. In the reversed phase separation of alkylbenzenes, under isocratic conditions, theoretical plate numbers up to 40,000 plates/m were achieved by using 5.2 μm porous particles, obtained by a toluene‐dibutyl phthalate mixture as the diluent. No significant decrease in the resolution power was observed by the fourfold increase in the mobile phase flow rate. The column efficiency and the resolution observed with 5.2 μm monodisperse‐porous particles were significantly higher with respect to the currently available polymer based packing materials used in the reversed phase HPLC. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1430–1438, 2005     

Temperature modulated DSC studies of melting and recrystallization in poly (oxy‐1,4‐phenyleneoxy‐1,4‐phenylenecarbonyl‐1,4‐phenylene) (PEEK)

The thermal and crystal morphological properties of amorphous and melt crystallized poly(oxy‐1,4‐phenyleneoxy‐1,4‐phenylenecarbonyl‐1,4‐phenylene) (PEEK) were investigated. Two different molecular weights were studied by Temperature Modulated DSC (TMDSC) over a broad range of annealing times and temperatures. The lower molecular weight PEEK under all crystallization conditions was found to exhibit secondary crystal melting in the low endotherm region, followed by melting of primary crystals melting in the low endotherm region, followed by melting of primary crystals superimposed with a large recrystallization contribution. Primary crystal melting broadly overlapped with melting of the recrystallized species and contributed to the broad highest endotherm. Recrystallization contributions and the interpretation of TMDSC were partially confirmed by independent rapid heating rate melting point determinations and variable heating rate DSC. The higher molecular weight PEEK showed many similarities but generally had smaller levels of reorganization above the annealing temperature under most higher temperature crystallization conditions. TMDSC provides excellent resolution of recrystallization and related events compared to standard DSC. The broad and substantial exothermic recrystallization in amorphous samples was also examined, showing that recrystallization continues through the final melting region.     

Structure and properties of ultra‐high molecular weight bisphenol a polycarbonate synthesized by solid‐state polymerization in amorphous microlayers

The structure and properties of ultrahigh molecular weight polycarbonate synthesized by solid‐state polymerization in micro‐layers (SSP_m) are reported. A low molecular weight prepolymer derived from the melt transesterification of bisphenol A and diphenyl carbonate as a starting material was polymerized to highly amorphous and transparent polycarbonate of molecular weight larger than 300,000 g mol^?1 in the micro‐layers of thickness from 50 nm to 20 µm. It was observed that when the polymerization time in micro‐layers was extended beyond conventional reaction time, insoluble polymer fraction increased up to 95%. Through the analysis of both soluble and insoluble polymer fractions of the high molecular weight polycarbonate by ¹H NMR spectroscopy and pyrolysis‐gas chromatography mass spectrometry (Py‐GC/MS), branches and partially crosslinked structures have been identified. The thermal, mechanical and rheological properties of the ultra‐high molecular weight nonlinear polycarbonates synthesized in this study have been measured by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and rheometry. The nonlinear chain structures of the polymer have been found to affect the polymer's thermal stability, mechanical strength, shear thinning effect, and elastic properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41609.     

Application of a solid‐state postpolycondensation method for synthesis of high molecular weight polycarbonates

Studies on the possibility of the application of the solid‐state postpolycondensation (SSP) process to increase the average molecular weight of bisphenol A‐based polycarbonate (PBC) were carried out. The thermally stable PBC with a very high molecular weight reaching about 50,000 g/mol was obtained by the applied SSP technique. Some factors influencing the effectiveness of the SSP process were initially examined: the mode of preparation (crystallization) of the PBC prepolymer, condensation temperature and time, and the vacuum applied in the reaction vessel. It was found that the superior yield of the high molecular weight PBC was obtained by the employing as high as possible values of the parameters taken into consideration. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2165–2171, 2000     

Unique pressure‐crystallized structures in ternary bisphenol‐a polycarbonate/dioctyl phthalate/fullerene C60 composites

We report pressure‐controlled fast growth of unique crystalline structures of bisphenol‐A polycarbonate (PC) was achieved by the introduction of both dioctyl phthalate (DOP) and fullerene C60. PC/DOP/C60 ternary composites with an overall good C60 dispersion were prepared by an easy physical and mechanical route, and then crystallized in a piston‐cylinder high‐pressure apparatus by varying temperature, pressure, crystallization time and composite composition. The crystallization of PC was greatly hastened by the blending with DOP and C60, and its melting point was increased to 288.25 degrees centigrade by the subsequent high‐pressure treatment, which was around 40° centigrade higher than that of the samples crystallized at normal pressure. Three‐dimensional spiky crystalline spheres were formed with the increase of crystallization temperature, which began with zero‐dimensional nanogranules, and then developed by merging process through the stages of one‐dimensional lamellar crystallites and two‐dimensional dendrites. With pressure increased, the granules merged first into plate crystals, and then into micro‐spheres with rugged surfaces or porous structures. Also, sometimes the granules organized into rugged crystalline nanoballs, and peony‐like stereo‐open structures were observed by changing composite composition. The as‐prepared three‐dimensional crystalline structures, with their large specific areas, may diversify niche functional applications as surface active materials. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Isothermal crystallization kinetics and melting behaviors of nanocomposites of poly(trimethylene terephthalate) filled with nano‐CaCO3

The isothermal crystallization and subsequent melting behavior of poly(trimethylene terephthalate) (PTT) composites filled with nano‐CaCO₃ were investigated at designated temperatures with differential scanning calorimetry. The Avrami equation was used to fit the isothermal crystallization. The Avrami exponents were determined to be 2–3 for the neat PTT and PTT/CaCO₃ composites. The particles of nano‐CaCO₃, acting as nucleating agents in the composites, accelerated the crystallization rate, with the half‐time of crystallization decreasing or the growth rate constant (involving both nucleation and growth rate parameters) increasing. The crystallization activation energy calculated from the Arrhenius formula was reduced as the nano‐CaCO₃ content increased from 0 to 2%, and this suggested that nano‐CaCO₃ made the molecular chains of PTT easier to crystallize during the isothermal crystallization process. Subsequent melting scans of the isothermally crystallized composites exhibited triple or double melting endotherms: the greater the content was of nano‐CaCO₃, the lower the temperature was of the melting peak. The degree of crystallization deduced from the melt enthalpy of composites with the proper concentration of nano‐CaCO₃ was higher than that of pure PTT, but it was lower when the nano‐CaCO₃ concentration was more than 2%. The transmission electron microscopy pictures suggested that the dispersion state of nano‐CaCO₃ particles in the polymer matrix was even when its concentration was no more than 2%, whereas some agglomeration occurred when its concentration was 4%. Polarized microscopy pictures showed that much smaller or less perfect crystals formed in the composites because of the interaction between the molecular chains and nano‐CaCO₃ particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Vapor‐induced crystallization behavior of bisphenol‐A polycarbonate

The effects of exposure time and vapor pressure on the crystallization behaviors of bisphenol‐A polycarbonate (BAPC) films were investigated at 25°C by using differential scanning calorimetry (DSC). Double melting peaks were observed for various BAPC samples after vapor‐induced crystallization. The low temperature melting peak shifted to higher temperature and became sharper with increasing exposure time, and could be assigned to defective crystals with smaller crystal size. Crystallinity and average crystal dimension normal to (020) were calculated from wide‐angle X‐ray diffraction spectra. A good agreement was obtained between crystallinity values obtained from WAXD and those from DSC. The morphology of crystallized samples after various exposure time periods was examined by means of polarized optical microscopy. Nucleation occurred at the initial stage of vapor‐induced crystallization. Poor crystals become perfect through segment reorganization with increasing exposure time, and spherulites' growth was observed. The average diameter of spherulites increased from 2 μm for 1 h, to 7 and 16 μm after 3 and 56 h, respectively. POLYM. ENG. SCI., 46:729–734, 2006. © 2006 Society of Plastics Engineers     

Synthesis of PLLA‐PEOMA comb‐block‐comb type molecular brushes based on AGET ATRP and ring‐opening polymerization

BACKGROUND: Molecular brushes are types of macromolecules with densely grafted side chains on a linear backbone. The synthesis of macromolecular brushes has stimulated much interest due to their great potential in applications in various fields. Poly(L ‐lactide)–poly(ethylene glycol) methyl ether methacrylate (PLLA‐PEOMA) comb‐block‐comb molecular brushes with controlled molecular weights and narrow molecular weight distributions were successfully synthesized based on a combination of activator generated by electron transfer (AGET) atom transfer radical polymerization (ATRP) and ring‐opening polymerization. The synthetic route is a combination of the ‘grafting through’ method for AGET ATRP of the PEOMA comb block and the ‘grafting from’ method for the synthesis of the PLLA comb block. Poly(2‐hydroxyethyl methacrylate) (PHEMA) was synthesized by ATRP, and PLLA side chains and PEOMA side chains were grown from the backbones and the terminal sites of PHEMA, respectively. RESULTS: The number‐average degrees of polymerization of PLLA chains and poly[poly(ethylene glycol) methyl ether methacrylate] (PPEOMA) comb blocks were determined using ¹H NMR spectroscopy, and the apparent molecular weights and molecular weight distributions of the brush molecules were measured using gel permeation chromatography. The crystallization of the components in the comb‐block‐comb copolymers was also investigated. The crystallization of PLLA side chains is influenced by PLLA chain length and the content of PPEOMA in the molecular brushes. The comb‐block‐comb copolymer composed of hydrophobic PLLA and hydrophilic PEOMA can self‐assemble into a micellar structure in aqueous solution. CONCLUSION: A combination of AGET ATRP and ring‐opening polymerization is an efficient method to prepare well‐defined comb‐block‐comb molecular brushes. The physical properties of the molecular brushes are closely related to their structures. Copyright © 2009 Society of Chemical Industry     

Carbon‐13 NMR,GPC, and DSC study on a propylene‐1‐butene copolymer fractionated by temperature rising elution fractionation

A random copolymer of propylene with small amounts of 1‐butene comonomer, synthesized with a Ziegler–Natta catalyst, was fractionated by temperature rising elution fractionation (TREF) to systemically investigate the fraction samples' molecular microstructure, as well as their relationship to the melting and crystallization behavior. First, TREF was employed to fractionate the sample, and then crystallization analysis fractionation (Crystaf) was used to check the effect of the TREF experiment. In the characterization of the molecular microstructure, carbon‐13 NMR spectroscopy (¹³C NMR) and gel permeation chromatography (GPC) experiments gave the following results: the fraction samples have relatively uniform molecular microstructure; with an increase in elution temperature, the 1‐butene content in the fraction samples decreases, but the molecular weight (M_n) and number average sequence length of propylene (n?_P) increase. In the study on melting and crystallization behavior, differential scanning calorimetry (DSC) experimental results show that the melting temperature increasingly decreases with an increase in 1‐butene content; however, dependence of the melting temperature on molecular weight becomes weaker and weaker with an increase in the number average molecular weight in the range of number average molecular weight below 1.82 × 10⁵ g/mol. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 845–851, 2006     

Miscibility and morphology of poly(vinylidene fluoride)/poly[(vinylidene fluoride)‐ran‐trifluorethylene] blends

This study presents an investigation of the effect of the different crystalline phases of each blend component on miscibility when blending poly(vinylidene fluoride) (PVDF) and its copolymer poly[(vinylidene fluoride)‐ran‐trifluorethylene] [P(VDF–TrFE)] containing 72 mol % of VDF. It was found that, when both components crystallized in their ferroelectric phase, the PVDF showed a strong effect on the crystallinity and phase‐transition temperature of the copolymer, indicating partial miscibility in the crystalline state. On the other hand, immiscibility was observed when both components, after melting, were crystallized in their paraelectric phase. In this case, however, a decrease in crystallization temperatures suggested a strong interaction between monomers in the liquid state. Blend morphologies indicated that, in spite of the lack of miscibility in the crystalline state, there is at least miscibility between PVDF and P(VDF–TrFE) in the liquid state, and that a very intimate mixture of the two phases on the lamellar level can be maintained upon crystallization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1362–1369, 2002     

Solid‐state compaction and drawing of nascent reactor powders of ultra‐high‐molecular‐weight polyethylene

The continuous production of ultra‐high‐molecular‐weight polyethylene (UHMWPE) filaments was studied by the direct roll forming of nascent reactor powders followed by subsequent multistage orientation drawing below their melting points. The UHMWPE reactor powders used in this study were prepared by the polymerization of ethylene in the presence of soluble magnesium complexes, and they exhibited high yield even at low reaction temperatures. The unique, microporous powder morphology contributed to the successful compaction of the UHMWPE powders into coherent tapes below their melting temperatures. The small‐angle X‐ray scattering study of the compacted tapes revealed that folded‐chain crystals with a relatively long‐range order were formed during the compaction and were transformed into extended‐chain crystals as the draw ratio increased. Our results also reveal that the drawability and tensile and thermal properties of the filaments depended sensitively on both the polymerization and solid‐state processing conditions. The fiber drawn to a total draw ratio of 90 in the study had a tensile strength of 2.5 GPa and a tensile modulus of 130 GPa. Finally, the solid‐state drawn UHMWPE filaments were treated with O₂ plasma, and the enhancement of the interfacial shear strength by the surface treatment is presented. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 718–730, 2005     

Solid‐state polymerization and bulk crystallization behavior of poly(ethylene terephthalate) (PET)

The main variables involved in solid‐state polymerization of PET homopolymers, originally with molecular weight within the commercial range, were sequentially studied to determine their influence in polymerized products. These variables were precursor crystallinity, catalyst, and time and reaction temperature. An increasing molecular weight sequence was then used to study the bulk crystallization behavior with Avrami analyses. It was determined that thermal conditions at dissolution affect the prereaction morphology. This was important in the polymerization process because it was found that high crystallinity levels in precursors result in higher molecular weights. In agreement with other reports, typical catalysts used in melt polymerizations enhance postpolycondensation processes in the solid state. High reaction times and temperatures were also required to obtain high molecular weights. As the molecular weight increased, there was a decrease in nucleation density and Avrami analyses, applied to the isothermal bulk crystallization, indicating that the nucleation process changed from instantaneous to spontaneous with the increase in molecular weight. The consequences and relative importance of the observed results is discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 78–86, 2000     

Solvent‐ and thermal‐induced crystallization of poly‐L‐lactic acid in supercritical CO2 medium

The effect of different annealing treatments with supercritical carbon dioxide (SCCO₂) on the structural and mechanical properties of semicrystalline poly‐L ‐lactic acid (L ‐PLA) was investigated. 2000, 27,000, 100,000, and 350,000 g mol^?1 molecular weight L ‐PLA polymers were used in the study. The solid‐state processing of L ‐PLA at temperatures lower than the effective melting point led to solvent‐ and thermal‐induced crystallization. Solvent‐induced and isothermal crystallization mechanisms could be considered similar regarding the increase of polymer chain mobility and mass‐transfer in the amorphous region; however, quite different microstructures were obtained. SCCO₂ solvent‐induced crystallization led to polymers with high crystallinity and melting point. On the contrary, SCCO₂ thermal‐induced crystallization led to polymers with high crystallinity and low melting point. For these polymers, the hardness increased and the elasticity decreased. Finally, the effect of dissolving SCCO₂ in the molten polymer (cooling from the melt) was analyzed. Cooling from the melt led to polymers with high crystallinity, low melting point, low hardness, and low elasticity. Distinctive crystal growth and nucleation episodes were identified. This work also addressed the interaction of SCCO₂‐drug (triflusal) solution with semicrystalline L ‐PLA. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis of star‐shaped poly(ε‐caprolactone)‐b‐poly(L‐lactide) copolymers: From star architectures to crystalline morphologies

Hexa‐armed star‐shaped poly(ε‐caprolactone)‐block‐poly(L ‐lactide) (6sPCL‐b‐PLLA) with dipentaerythritol core were synthesized by a two‐step ring‐opening polymerization. GPC and ¹H NMR data demonstrate that the polymerization courses are under control. The molecular weight of 6sPCLs and 6sPCL‐b‐PLLAs increases with increasing molar ratio of monomer to initiator, and the molecular weight distribution is in the range of 1.03–1.10. The investigation of the melting and crystallization demonstrated that the values of crystallization temperature (T_c), melting temperature (T_m), and the degree of crystallinity (X_c) of PLLA blocks are increased with the chain length increase of PLLA in the 6sPCL‐b‐PLLA copolymers. On the contrary, the crystallization of PCL blocks dominates when the chain length of PLLA is too short. According to the results of polarized optical micrographs, both the spherulitic growth rate (G) and the spherulitic morphology are affected by the macromolecular architecture and the length of the block chains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Morphological changes of poly(ethylene terephthalate‐co‐isophthalate) during solid state polymerization

Poly(ethylene terephthalate‐co‐isophthalate) (PETI) prepolymer was submitted to solid state polymerization (SSP) at 184–230°C in a fixed bed reactor, to study the evolution of morphological changes during the process. Short reaction times were selected to investigate crystallization phenomena during nonisothermal (heating) and isothermal SSP phases. More specifically, multiple PETI melting behavior was observed and attributed to secondary crystallization, the rate of which increased significantly with SSP temperature. Reaction time was also found to exert a positive effect on solid‐phase perfection of secondary crystals, leading at each temperature to melting points close to the value of bottle‐grade poly(ethylene terephthalate). Finally, the mass fraction crystallinity of the SSP grades was found to comply with the crystal morphology encountered. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011