Investigation of the nanocellular foaming of polystyrene in supercritical CO2 by adding a CO2‐philic perfluorinated block copolymer

Nanocellular foaming of polystyrene (PS) and a polystyrene copolymer (PS‐b‐PFDA) with fluorinated block (1,1,2,2‐tetrahydroperfluorodecyl acrylate block, PFDA) was studied in supercritical CO₂ (scCO₂) via a one‐step foaming batch process. Atom Transfer Radical Polymerization (ATRP) was used to synthesize all the polymers. Neat PS and PS‐b‐PFDA copolymer samples were produced by extrusion and solid thick plaques were shaped in a hot‐press, and then subsequently foamed in a single‐step foaming process using scCO₂ to analyze the effect of the addition of the fluorinated block copolymer in the foaming behaviour of neat PS. Samples were saturated under high pressures of CO₂ (30 MPa) at low temperatures (e.g., 0°C) followed by a depressurization at a rate of 5 MPa/min. Foamed materials of neat PS and PS‐b‐PFDA copolymer were produced in the same conditions showing that the presence of high CO₂‐philic perfluoro blocks, in the form of submicrometric separated domains in the PS matrix, acts as nucleating agents during the foaming process. The preponderance of the fluorinated blocks in the foaming behavior is evidenced, leading to PS‐b‐PFDA nanocellular foams with cell sizes in the order of 100 nm, and bulk densities about 0.7 g/cm³. The use of fluorinated blocks improve drastically the foam morphology, leading to ultramicro cellular and possibly nanocellular foams with a great homogeneity of the porous structure directly related to the dispersion of highly CO₂‐philic fluorinated blocks in the PS matrix. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Gas sorption and transport in syndiotactic polystyrene with nanoporous crystalline phase

In this contribution we analyse sorption and transport of several gases in semicrystalline syndiotactic polystyrene with nanoporous crystalline δ form. Investigation was performed on amorphous samples and on samples characterized by different degrees of crystallinity. Sorption isotherms of carbon dioxide, nitrogen and oxygen in the crystalline phase have been determined starting from experimental results obtained for semicrystalline and amorphous samples. Corresponding isosteric heats of sorption were evaluated for the crystalline and amorphous phase. Permeation tests were also performed to gather information on mass transport properties of semicrystalline samples, evaluating average diffusivities of carbon dioxide and oxygen, in the limit of small concentrations as function of degree of crystallinity.     

CO2‐assisted polymer processing: A new alternative for intractable polymers

CO₂‐assisted polymer processing is proposed as an alternative route for intractable and high molecular weight polymers based on the plasticization effects of CO₂ and its direct effect on the melting behavior of semicrystalline polymers. A modified processing system was used to process a variety of polymers in the presence of high‐pressure CO₂. The system includes an extruder that was modified to allow for high pressures created by the injection of CO₂. The new design includes a modified feed section that allows a given mass of polymer to interact with CO₂ before and during the extrusion process. The inherent shear mixing and the presence of CO₂ allow for a specific control over the extrudate morphology. Results suggest that this alternative design provides a new and easy route to melt process high melt viscosity polymers of commercial importance, such as polytetrafluoroethylene (PTFE), fluorinated ethylene propylene copolymer (FEP), and syndiotactic polystyrene (s‐PS). The increased processability of these systems in CO₂ is related to the plasticization effect of CO₂ that was quantified through a depression in the glass‐transition temperature according to the Chow model. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1501–1511, 2004     

Pressure effects on polymerization of syndiotactic polystyrene

Polymerization pressure has a direct effect on the synthesis of syndiotactic polystyrene (s-PS) with metallocene as a catalyst. The polymerization rate, yield rate, and average molecular weight show a linear relationship with pressure, that is, they all increase with increased polymerization pressure. However, under 1000 psi, the yield of s-PS increases with polymerization duration while the yield rate decreases. As a whole, this syndiotactic polymerization proceeds relatively fast in comparison with ordinary vinyl polymerization. Optimal conditions (pressure, temperature, and duration) for the synthesis of s-PS have been explored. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1747–1752, 1998     

Preparation of polystyrene/montmorillonite nanocomposites in supercritical carbon dioxide

The preparation of polystyrene (PS)/montmorillonite (MMT) composites in supercritical carbon dioxide (SC? CO₂) was studied. Lipophilic organically modified MMT can be produced through an ion‐exchange reaction between native hydrophilic MMT and an intercalating agent (alkyl ammonium). PS/clay composites were prepared by free‐radical precipitation polymerization of styrene containing dispersed clay. X‐ray diffraction and transmission electron microscopy indicated that intercalation of MMT was achieved. PS/clay composites have a higher thermal decomposition temperature and lower glass‐transition temperature than pure PS. The IR spectrum analysis showed that the solvent of SC? CO₂ did not change the structures of the PS molecules, but there were some chemical interactions between the PS and the clay in the composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 22–28, 2005     

Synthesis and characterization of acetylated syndiotactic polystyrene

Acetylation of highly stereoregular syndiotactic polystyrene has been accomplished in a heterogeneous process by using carbon disulfide as the dispersing medium, and acetyl chloride and anhydrous aluminium chloride as acetylating agent and catalyst, respectively. The acetylation reaction can be well controlled and carried out to a high degree of acetylation. The resultant polymer was characterized by FTIR and NMR spectroscopy. The incorporation of acetyl groups into syndiotactic polystyrene was found to have an effect on the thermal properties of these new materials. The degree of crystallinity was decreased by the presence of acetyl groups, while the glass transition temperature increased. Copyright © 2004 Society of Chemical Industry     

Effects of maleated syndiotactic polystyrene on the morphology,mechanical properties,and crystallization behavior of syndiotactic polystyrene/polyamide 6 blends

The compatibilization of syndiotactic polystyrene (sPS)/polyamide 6 (PA‐6) blends with maleic anhydride grafted syndiotactic polystyrene (sPS‐g‐MA) as a reactive compatibilizer was investigated. The sPS/PA‐6 blends were in situ compatibilized by a reaction between the maleic anhydride (MA) of sPS‐g‐MA and the amine end group of PA‐6. The occurrence of the chemical reaction was substantiated by the disappearance of a characteristic MA peak from the Fourier transform infrared spectrum. Morphology observations showed that the size of the dispersed PA‐6 domains was significantly reduced and that the interfacial adhesion was much improved by the addition of sPS‐g‐MA. As a result of reactive compatibilization, the impact strengths of the sPS/PA‐6 blends increased with an increase in the sPS‐g‐MA content. The crystallization behaviors of the blends were affected by the compatibilization effect of sPS‐g‐MA. A single melting peak of sPS in the noncompatibilized blend was gradually split into two peaks as the amount of the compatibilizer increased. A single crystallization peak of PA‐6 in the noncompatibilized blend became two peaks with the addition of 3 wt % sPS‐g‐MA. The new peak was a result of the fractionation crystallization. As the amount of sPS‐g‐MA increased, the intensity of the new peak increased, and the original peak nearly disappeared. Finally, the crystallization peak of PA‐6 disappeared with 20 wt % sPS‐g‐MA in the blend. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2502–2506, 2003     

超临界CO2萃取含油污泥研究现状与进展

含油污泥是一种含有大量有机物、絮状体的复杂多相稳定乳化胶体体系,主要来源于油气开采和集输过程。污泥中的含油量一般为10%~30%（体积分数）,利用超临界二氧化碳（supercritical CO₂,scCO₂）提取和回收其中的油基成分可实现污泥的无害化处理,并产生可观的经济效益。本文综述了scCO₂萃取原理及工业化应用情况,分析了萃取条件及携带剂对萃取率的影响,重点论述了scCO₂萃取含油污泥的相平衡热力学及动力学机制研究进展。指出应坚持实验与理论相结合的手段,着重开展以下三方面的研究：①针对含油污泥组成复杂、极性组分含量高的特点,结合scCO₂与含油污泥多组分复杂体系相平衡实验,建立scCO₂萃取含油污泥的相平衡模型,阐明scCO₂萃取含油污泥的相平衡特征及影响因素;②考虑不同分子间的键结合能与非键结合能,从scCO₂萃取油基的微观效应出发,探究油基与污泥基质间的吸附、解吸及扩散规律,定性描述、定量揭示scCO₂萃取油的动力学特征与作用机制;③考虑萃取工艺的经济性,以萃取率最高为目标函数,建立萃取条件优化模型,为scCO₂萃取含油污泥工艺的设计、优化及工业化应用提供理论与技术支撑。     

Synthesis and physical properties of sulfonated syndiotactic polystyrene ionomers

Sulfonation of highly stereoregular syndiotactic polystyrene has been accomplished in 1,1,2‐trichloroethane and chloroform (60/40 v/v) mixed solvent. FTIR spectroscopy was used to confirm that the sulfonated syndiotactic polystyrene was the product of the sulfonation reactions. Sodium, potassium, zinc (II), manganese (II) and cobalt (II) salts of the sulfonated polymers exhibited behaviour indicative of strong interactions. FTIR spectroscopy and DSC data showed that the roles of the cation–anionic site interactions in alkali form and transition metal form ionomers are somewhat different. The DSC data also showed that the alkali metal cations had more pronounced effect on T_g than did the transition metal cations. In addition, the crystallization behaviour of the ionomers with a low degree of sulfonation also exhibited considerable differences in comparison with the neat syndiotactic polystyrene. The melting points (T_m) and the degree of crystallization (X_c) were significantly lowered by the presence of the sulfonic acid groups or the sulfonate metal groups. Moreover, the ionomers were more thermally stable and more hygroscopic than the unmodified polymer. © 2001 Society of Chemical Industry     

Study of multiple melting behaviour of syndiotactic polystyrene in β‐crystalline form

A series of syndiotactic polystyrene (SPS) samples in β‐crystalline form were prepared by cooling from the melt at various rates. The effects of cooling rate from the melt, DSC heating rate and annealing on the multiple melting behaviours of β crystals were investigated by differential scanning calorimetry (DSC) and temperature modulated differential scanning calorimetry (TMDSC), from which the nature of the multiple melting behaviour was determined. The two melting endotherms of β‐form crystals were considered to arise from the occurrence of simultaneous melting, recrystallization and remelting processes in the melting region. It is suggested that the lower melting endotherm is due to the melting of imperfect β crystals originally present in the sample, whereas the higher melting endotherm comes from the melting of recrystallized SPS crystals, ie more perfect β crystals that formed during the DSC scanning process. © 2000 Society of Chemical Industry     

Failure and deformation studies of syndiotactic polystyrene

Syndiotactic polystyrene (sPS) is a chemically resistant, high-heat, semi-crystalline polymer which is currently under development by The Dow Chemical Co. The research reported herein was undertaken to determine the critical fracture strength, i.e., the critical stress intensity factor, K_1C, and the fracture energy, G_1C, of sPS. The studies were aimed at developing a basic understanding of the failure mechanism and toughness of sPS. This work included investigations of the effect of molecular weight, as well as flow-induced anisotropy. Scanning electron microscopy (SEM) was used to aid in the determination of the failure mechanism. During failure testing, it was observed that sPS fails with a slow, controlled crack growth and ruptures with an almost nondetectable amount of yielding, as based on a tensile dilatometry investigation and a plane strain, biaxial yield experiment. The proposed failure mechanism, based on the scanning electron micrographs, is one of constrained crazing, followed by void coalescence with the spherulite nucleators acting as stress concentrators in the system. The damage appears to be greatly confined, with little initial cold-drawing of the spherulites. Addition of a nucleator reduces the K_1C values somewhat, as added nucleation sites proliferate the sites for stress concentration across the sample. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 673–681, 1997     

合成间同立构PS用单中心催化剂的研究进展

综述了茂金属催化剂和非茂钛催化剂合成间同立构聚苯乙烯的研究进展,其中,茂金属催化剂主要包括茂钛催化剂、单茂钛催化剂、茚钛催化剂、双核金属催化剂及负载型催化剂等。今后的研究重点是负载型茂金属催化剂和非茂钛催化剂,单中心催化剂将对合成间同立构聚苯乙烯的工业化发展发挥重要的作用。     

Viscoelastic behavior of thermosetting epoxy mixtures modified with syndiotactic polystyrene during network formation

The rheological behavior of thermosetting epoxy mixtures modified with thermoplastic syndiotactic polystyrene (sPS) was monitored during the curing of the epoxy resin. The selected thermosetting system was diglycidyl ether of bisphenol A cured with 4,4′‐methylene bis(3‐chloro‐2,6‐diethylaniline) in the presence of various compositions of sPS (from 2.5 to 12.5 wt %). The storage and loss shear moduli of the systems were monitored during network formation. The validity of the Winter–Chambon criterion for the accurate determination at the gelation point from rheological data was demonstrated. The influence of the sPS concentration on the dynamic rheological properties of the samples was investigated. The experimental data showed that at sPS concentrations lower than 7.5 wt %, phase separation induced a quick increase in the viscosity, which was related to a crystallization‐induced phase separation of sPS. For sPS concentrations higher than 7.5 wt %, near the phase‐inversion composition, the rheological behavior of the mixtures was characteristic of a cocontinuous structure. After the viscosity jumped at the onset of phase separation, a decrease in the viscosity was found, and later on, the viscosity increased again because of gelation. Additionally, the influence of the cure temperature on the rheological properties was studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2348–2355, 2006     

Melting and chemical behaviors of isothermally crystallized gamma-irradiated syndiotactic polystyrene

Melting and chemical behaviors of isothermally crystallized gamma-irradiated sPS have been investigated using differential scanning calorimetry, FTIR, and X-ray diffraction techniques. Amorphous sPS samples were subjected to gamma radiation in vacuum and in oxygen at different doses from 200 to 1000 kGy. Irradiated samples were heated to 310 °C, cooled to 220-260 °C range, held for 10 min, and re-melted. Three melting endothermic peaks observed for irradiated and non-irradiated samples isothermally crystallized at 220 °C were decomposed into individual Gaussian distributions, and enthalpies of the total melting endotherm and individual peaks were determined. Both α and β crystalline forms coexist in the crystallized irradiated sPS, regardless of the radiation treatment environment. Dose and irradiation environment have a great effect on the melting behaviors and chemical structures of the isothermally crystallized gamma-irradiated sPS. Crystallinity increases with increasing dose of irradiation in both vacuum and oxygen, with level of increase is greater in oxygen. The three melting peak temperatures decrease with increasing dose regardless of irradiation environments. Ketone and aldehyde oxidized products are formed in the isothermally crystallized gamma-irradiated sPS in oxygen through a combination of hydrogen abstraction or chain scission process and hydroxyl free radicals formation.     

茂金属催化苯乙烯间规聚合物的颗粒形态

以均相单茂钛化合物［Cp*Ti(OPh)₃ 和Cp*Ti(OPhOMe)₃］为主催化剂,配以烷基铝氧烷（MAO）和三异丁基铝(TIBA),进行了苯乙烯的本体间规聚合.研究发现,聚合过程中生成聚合物的快速结晶对于避免反应体系的凝胶化,制得颗粒状产物十分重要.但正因为这种结晶成核机理,使所得颗粒的形貌极不规整,调控也十分困难.聚合过程中sPS种子的加入没有明显改善生成聚合物的颗粒形态.但当聚合体系中引入少量其他聚合物后,得到了较为规整的sPS颗粒,尤其当加入的聚合物与无定形sPS热力学不相容时（如mEPDM）,得到了十分规则的球状颗粒.     

Solid‐state structure of thermally crystallized syndiotactic polystyrene

The solid‐state structure of syndiotactic polystyrene (s‐PS) after crystallization from the melt and the glassy state was examined by differential scanning calorimetry (DSC), density, and X‐ray diffraction analysis. It was possible to prepare semicrystalline s‐PS containing either the pure α‐ or the pure β‐crystalline form by melt crystallizing s‐PS from 280 or 330°C. The measurements confirmed the low density of both crystalline forms, which in the case of α‐crystalline form was smaller and in the case of β‐crystalline form was only slightly larger than the density of the glassy amorphous s‐PS. An endeavor to introduce the crystalline phase in s‐PS through cold crystallization at constant temperature above the glass transition resulted in a complex ordered phase. This ordered phase, depending on the crystallization temperature, contained the planar chain mesomorphic phase and the α‐crystalline phase with a low degree of perfection (cold crystallization in the range 120–175°C) or a mixture of the α‐ and β‐crystalline forms with a high degree of perfection (cold crystallization in the range 210–260°C). The combination of DSC and X‐ray measurements enabled us to resolve the complex ordered structure in semicrystalline s‐PS after cold crystallization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2705–2715, 2002     

新型超临界水中煤气化制氢产物的CO2分离过程

目前CO₂的分离方式主要局限在常压条件下,在高压条件下分离CO₂的研究鲜有报道。本文为了解决这一问题,针对煤在超临界水中气化过程压力高的特点,构建了高压水吸收法分离CO₂系统,建立了高压多组分气液相平衡的能量分析模型和 分析模型;并对CO₂的分离过程进行分析,获得了高压吸收器中压力对各种气体产物摩尔分数和液相中气体吸收率的影响规律;针对高压水吸收法分离CO₂的流程,建立了CO₂分离过程中的能量分析模型和 分析模型,得到了高压吸收器中压力发生变化时,CO₂分离过程的能量效率、 效率以及CO₂分离能耗的变化规律,为超临界水中煤气化制氢新技术中分离器的设计提供了依据。     

溶液聚合间规聚苯乙烯非等温结晶动力学

介绍了有关物质结晶行为的Ozawa方程和Liu方法的理论背景。用DSC方法研究了间规聚苯乙烯（s-PS）的非等温结晶动力学。结果表明,降温速率越大,s-PS的结晶峰越小,结晶度也越小。s-PS非等温结晶行为服从Ozawa方程和Liu方法。Ozawa指数为3,是以异相成核的三维生长或均相成核的二维生长方式结晶的;相对结晶度为0.20～0.80时,降温速率的对数与结晶时间的对数具有较好的线性关系。     

Molding of syndiotactic polystyrene under its melting temperature

Syndiotactic polystyrene (SPS), a thermoplastic polymer that exhibits a high T_m in some crystalline forms, can be conveniently processed by a cold‐compaction technique. Processing temperatures in the range of 150–210°C, well below the T_m, gives rise to physicomechanical properties comparable and even better than those obtained by thermal compression or injection molding. The optimum treatment temperature seems to fall around 175°C. X‐ray diffraction analysis, thermal analysis, and density measurements suggest that such behavior is connected to phase transitions of SPS and favored by the presence of styrene included in the crystalline fraction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 377–383, 2001