PET-季戊四醇共聚酯的固相聚合及其结晶性能

采用固相聚合的方法合成了一系列PET-季戊四醇共聚酯,测试了共聚酯的特性黏度随固相缩聚时间的变化,并且用差示扫描量热法研究了该体系的非等温结晶过程,采用偏光显微镜观察了其结晶形态。结果表明:季戊四醇的含量越高,PET-共聚酯的特性黏度出现先下降后上升趋势、形成支化结构的时间越早。在固相聚合反应初期,共聚酯的结晶温度上升,半结晶时间减少;但随着固相聚合时间的延长,共聚酯的结晶温度下降,形成的晶粒变小;而且,共聚酯具有二次结晶现象。     

Effect of synthesis parameters on the electrical conductivity of polypyrrole‐coated poly(ethylene terephthalate) fabrics

The effects of pyrrole, anthraquinone‐2‐sulphonic acid (AQSA) and iron(III) chloride (FeCl₃) concentrations, reaction time and temperature on the electrical conductivity of polypyrrole (PPy)—coated poly(ethylene terephthalate) (PET) fabrics were investigated. With an increase in both the AQSA and FeCl₃ concentrations, resistivity decreased to a point beyond which higher concentrations led to increased surface resistivity. Erosion of the polymer coating, in dynamic synthesis from continual abrasion, manifested as an exponential increase in the resistance of the coated textile substrate. This was not encountered in static synthesis conditions. Temperature affected the degree of surface and bulk polymerisation. The effect of polymerisation temperature on conductivity was negligible. Conductive polymer coating on textiles through chemical polymerisation enabled a smooth coherent film to encase individual fibres, which did not affect the tactile properties of the host substrate. The optimum FeCl₃/pyrrole and AQSA FeCl₃/pyrrole molar ratios were found to be 2.22 and 0.40 respectively. Copyright © 2003 Society of Chemical Industry     

Molar mass of poly (ethylene terephthalate) (PET) during ultimate uniaxial drawing

The changes of the average molar mass M_w, M_n, M_z, and molar mass distributions during multistep uniaxial drawing of poly(ethylene terephthalate) (PET) to achieve ultimate mechanical properties have been studied in detail by means of size exclusion chromatography (SEC) with triple detection: concentration, viscosimetry, and light scattering, using HFIP as solvent. An increase in molar mass of PET due to post‐polycondensation and/or transesterfication during drawing at a high temperature of 160 to 230°C was found. Moreover, drawing leads to crystallization and large orientation in the amorphous phase, which results in lower molecular mobility and prevents a further growth in chain length. Crazing under extreme drawing conditions occurs and affects a decrease in molar mass.     

Crystallisation kinetics of novel branched poly(ethylene terephthalate): a small‐angle X‐ray scattering study

Three types of poly(ethylene terephthalate) (PET) were investigated: linear (unprocessed) bottle‐grade PET (intrinsic viscosity, IV ～ 0.82 dL g^?1); a branched PET produced from linear PET by reactive extrusion with 0.4% w/w pyromellitic dianhydride and pentaerythritol in 5:1 molar ratio (IV ～ 0.97 dL g^?1); and a control sample produced from the same linear PET by extrusion under the same conditions without the reactive agents (IV ～ 0.71 dL g^?1). A key finding is that the reactive extrusion process, presumably as a consequence of branching and branch distribution, significantly modifies the crystallisation kinetics and changes the final morphology. Using small‐angle X‐ray scattering (SAXS) and differential scanning calorimetry (DSC), the crystallisation kinetics of PET was monitored from the melt (270 °C) to a crystallisation temperature of either 205 or 210 °C. The IV of the branched PET was ～ 21% greater than that of the unprocessed PET, and the rate of melt crystallisation (from DSC measurements) was 510 s for the branched, 528 s for the control, and 640 s for the unprocessed PET. The lamellae spacings measured from the equilibrium SAXS patterns were ～160 ± 10 Å for the branched PET and ～180 ± 10 Å for the unprocessed PET. Such properties offer the potential for new applications requiring high‐melt‐strength PET. Copyright © 2006 Society of Chemical Industry     

Rubber toughened semicrystalline PET: influence of the matrix properties and test temperature

This article is concerned with the effect of the inherent matrix properties (matrix molar mass and crystallinity) as well as the temperature on the impact behaviour of rubber toughened semicrystalline polyethylene terephthalate (PET). The dispersed phase consists of a blend of an ethylene-co-propylene rubber (EPR) and a copolymer of ethylene and 8 wt% glycidyl methacrylate (E-GMA8) acting as a compatibilising agent, leading to PET/(EPR/E-GMA8) blends. The influence of the matrix molar mass on the impact behaviour of rubber toughened PET is found to primarily originate from its effect on the blend phase morphology, rather than from an inherent effect of the molar mass itself. The dispersed phase particle size is seen to decrease with increasing PET molar mass. A direct correlation between the impact strength and the interparticle distance could be established. A critical interparticle distance (ID_c) of 0.1 μm could be determined, independent of the PET molar mass. The brittle-ductile transition temperature (T_bd) of the blends with a varying matrix molar mass also displayed a strong correlation with the interparticle distance, independent of the matrix molar mass. However, this correlation appears to depend on the crystalline characteristics of the PET matrix material since an incompletely crystallised PET matrix leads to an increase of the T_bd.     

The complicated influence of branching on crystallization behavior of poly(ethylene terephthalate)

The randomly branched poly(ethylene terephthalate) (BPET) was prepared by bulk polycondensation from dimethyl terephthalate (DMT) and ethylene glycol (EG), with 0.4–5.0 mol % (with respect to DMT) of glycerol (GL) as a branching agent. The glass transition and crystallization behavior was studied by differential scanning calorimetry (DSC). It was found that the glass transition temperature of BPET reduced with the increasing content of GL until 1.2 mol %, and then increases a little at high degrees of branching. When compared with a linear PET, the crystallization temperature of BPET from the melt shifted to higher temperature as GL content was smaller than 1.2 mol %, and then became lower while GL load was added. Nonisothermal crystallization kinetics was studied through the modified Avrami analysis. It was revealed that the overall crystallization rate parameter of BPET became larger when the GL content was less than 1.2 mol %, then turned to lower at higher branching degree. This indicated that low degree of branching could enhance the overall crystallization of poly(ethylene terephthalate) (PET), whereas high degree of branching in the range of 3.5–5.0 mol % would block the development of crystallization. On the basis of Hoffman's secondary crystallization theory, the product σσ_e of the free energy of formation per unit area of the lateral and folding surface was calculated. According to the change of the product σσ_e with the degree of branching, a possible explanation was presented to illuminate this diverse effect of different degrees of branching on crystallization. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Melt polymerization of copoly(ethylene terephthalate–imide)s and thermal properties

Copoly(ethylene terephthalate–imide)s (PETI) were prepared by melt polycondensation of bis(2-hydroxyethyl)terephthalate (BHET) and imide containing oligomer, i.e., 4,4′-bis[(4-carbo-2-hydroxyethoxy)phthalimido]diphenylmethane(BHEI). The apparent rate of poly-condensation reaction was faster than that of homo poly(ethylene terephthalate) (PET) due to the presence of imide units. The PETI copolymers with up to 10 mol % of BHEI unit in the copolymer showed about the same molecular weight and carboxyl end group content as homo PET prepared under similar reaction conditions. The increase in T_g of copolymer was more dependent on molar substitution of BHEI than on substitution of BHEN, reaching 91°C with 8 mol % BHEI units in the copolymer from T_g = 78.9°C of homo PET. In the case of PETN copolymer, 32 mol % of bis(2-Hydroxyethyl)naphthalate (BHEN) units gave T_g of 90°C. The maximum decomposition temperature of PETI copolymer was about the same as that of homo PET by TGA analysis. The char yield at 800°C was higher than that of homo PET. © 1996 John Wiley & Sons, Inc.     

Dynamic rheology of branched poly(ethylene terephthalate)

Branched poly(ethylene terephthalate)s (BPET) of varying molar mass have been synthesized with glycerol and pentaerythritol as branching comonomers, and their rheological behaviour has been measured. In this study, we describe the use of dynamic and steady shear measurements to examine the influence of the proportion and type of branching comonomers on the melt viscosity of BPET. Steady shear rheology has been used to measure the shear rate dependence on the apparent viscosity. Dynamic (oscillatory) measurements have been used to obtain the complex viscosity η* (ω) and the storage modulus G′ (ω) as a function of frequency. G′ (ω) represents the elastic component of the viscoelastic melt; this variable was measured as a function of frequency at various temperatures in the linear viscoelastic domain. Linear poly(ethylene terephthalate) (LPET) exhibited nearly Newtonian behaviour, while BPET became shear thinning at relatively low shear rates. The viscosity and elasticity increased with increase in molar mass and specific branching composition. This was attributed to increasing chain entanglements at higher molar mass and to increasing branching of the BPET. At higher shear rates or frequencies, the BPET show much greater shear thinning character than LPET and this is more pronounced with higher branching proportions. © 2000 Society of Chemical Industry     

Ionic liquid‐catalyzed aminolysis of poly(ethylene terephthalate) waste

Aminolytic depolymerization of poly(ethylene terephthalate) (PET) bottle waste with ethanolamine and hydrazine hydrate under atmospheric conditions was investigated in the presence of room temperature ionic liquids. 1‐Hexyl‐3‐methylimidazolium trifluoromethanesulfonate (Hmim.TfO) and 1‐butyl‐3‐methylimidazolium hydrogen sulfate (Bmim.HSO₄). (Hmim.TfO) was found to be the most efficient catalyst to obtain high yields of the aminolysis products bis(2‐hydroxy ethylene) terephthalamide and terephthalic dihydrazide using ethanolamine and hydrazine hydrate, respectively. These products were characterized by IR spectroscopy, ¹H NMR, ¹³C NMR, mass spectroscopy, and differential scanning calorimetry. The influence of experimental parameters, such as the amount of catalyst, reaction time, molar ratio of ethanolamine, and hydrazine hydrate with respect to PET was investigated. This protocol proves to be efficient and environmentally benign in terms of high yields (>84%) and low reaction times (up to 30 min). © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Molecular structure and rheological properties of a poly(ethylene terephthalate) modified by two different chain extenders

This paper compares the molecular structure and rheological properties of a commercial poly(ethylene terephthalate) (PET) after reactive processing with different concentrations of either pyromellitic dianhydride (PMDA) or a multifunctional epoxide (Joncryl®ADR-4368) as a chain extender. By size exclusion chromatography with triple detection, an increase of molar mass, a broadening of molar mass distribution, and the generation of long-chain branched molecules were found for both chain extenders. While gel-free materials were obtained with PMDA, the processing with Joncryl leads to the formation of gels. The effect of branching, indicated by the Mark–Houwink exponent, is more pronounced for materials with Joncryl compared to PMDA and points to a more compact branching structure of the PET/Joncryl molecules. Rheological measurements in shear and elongation support the analysis from SEC and reveal a complex tree-like branching structure for both chain extenders. In addition, the role of the two modifiers with respect to processing was assessed.     

Solid-state polycondensation of poly(ethylene terephthalate) modified with isophthalic acid: kinetics and simulation

The kinetics for the solid-state polycondensation (SSP) of poly(ethylene terephthalate) modified with isophthalic acid at the protection of nitrogen gas was studied in the paper. A kinetic model controlled by the reversible chemical reactions and the three dimension diffusions of small molecule by-products has been established. The kinetic parameters of the SSP of PET at different temperatures, including the forward rate constants of transesterification reaction (k₁) and esterification reaction (k₂), the diffusion coefficients of EG (D₁) and water (D₂), the concentrations of EG (g_s) and water (w_s) on the surface of PET chips in SSP, and the activation energies of these kinetic parameters were obtained by experiments and solution of the model. Using the model and the kinetic parameters, the SSP of poly(ethylene terephthalate) modified with isophthalic acid can be simulated with good accuracy. In addition, the influences of nitrogen gas flow rate, the chip dimension and the carboxyl end-group concentration of the PET prepolymer on the molecular weight of PET after SSP, and the change of the EG concentration of PET chips with reaction time were also studied by simulation.     

Solid-state polycondensation of poly(ethylene terephthalate) recycled from postconsumer soft-drink bottles. II

Poly(ethylene terephthalate) (PET) taken from postconsumer soft-drink bottles was subjected to solid-state polycondensation after cutting into small pieces or after dissolution in trifluoracetic acid, trifluoracetic acid/dichloromethane mixture (50/50%, v/v), or nitrobenzene, and coagulation in methanol. The effect of various reaction parameters such as time and temperature of reaction (180, 200, 220, and 230°C) on intrinsic viscosity [η] and carboxyl and hydroxyl end-group content have been investigated. The highest number average molecular weight, M?_n = 61,400 was obtained from PET (M?_n = 20,300) dissolved in nitrobenzene and solid-state polycondensated by heating under vacuum at 230°C for 8 h. The thermal behavior of solid-state samples was studied by differential scanning calorimetry (DSC); all samples showed a characteristic double endothermal melting peak and no glass-transition temperature. The PET samples taken from the bottles without dissolution were also studied by thermomechanical analysis. The heat distorsion temperatures obtained by this analysis were in very good agreement with the two endothermal melting peaks taken by DSC. This finding indicates that in these samples the crystallites form a coherent matrix and the amorphous phase is dispersed in the voids. © 1995 John Wiley & Sons, Inc.     

Modified unsaturated polyester resins synthesized from poly(ethylene terephthalate) waste, 1. Synthesis and curing characteristics

The depolymerization of poly(ethylene terephthalate) (PET) by alcoholysis reaction is an easy operation and gives prospects for the valorization of wastes. PET waste was first depolymerized by glycolysis reaction at different molar ratios of diethylene glycol (DEG), in the presence of Mn acetate as a transesterification catalyst. The glycolyzed products obtained were reacted with p‐hydroxybenzoic acid (PHBA) and maleic anhydride (MA) to prepare modified unsaturated polyesters. The molar ratio of added PHBA was varied in order to investigate its effect on the curing characteristics of these modified unsaturated polyesters. The data obtained revealed that an increasing molar ratio of PHBA, within the studied range of concentrations, leads to a reduction in the peak exothermic temperature (T_max) accompanied with the required delay in the curing time. The curing characteristics of these modified polyesters are not so fast anymore, which is not manageable and considered as disadvantageous from the practical point of view, showing instead a moderate speed.     

Morphological consequences of interchange reactions during solid state copolymerization in poly(ethylene terephthalate) and polycarbonate oligomers

Poly(ethylene terephthalate) (PET) (IV:0.15 dL/g) oligomer was obtained by depolymerisation of high molecular weight PET. Polycarbonate (PC) oligomer (IV: 0.15 dL/g) was synthesized by standard melt polymerization procedure using bisphenol A and diphenyl carbonate in the presence of a basic catalyst. Blends of varying compositions were prepared by melt blending the chemically distinct PET and PC oligomers. The copolymer, poly(ethylene terephthalate-co-bisphenol A carbonate) was synthesized by simultaneous solid state polymerization and ester-carbonate interchange reaction between the oligomers of PET and PC. The reaction was carried out under reduced pressure at temperatures below the melting temperature of the blend samples. DSC and WAXS techniques characterized the structure and morphology of the blends, while ¹NMR spectroscopy was used to monitor the progress of interchange reactions between the oligomers. The studies have indicated the amorphisation of the PET and PC crystalline phases in solid state with the progress of solid-state polymerization and interchange reaction.     

Efficient method for recycling poly(ethylene terephthalate) to poly(butylene terephthalate) using transesterification reaction

A method of recycling postconsumer poly(ethylene terephthalate (PET) using transesterification was studied. Shredded flakes of postconsumer PET waste were transesterified with higher diols, such as 1,4‐butanediol, 1,4‐cyclohexane dimethanol, and 1,6‐hexanediol, to yield copolyesters in the presence of Ti(iPrO)₄ and Sb₂O₃ as catalysts. The extent of the formation of undesirable tetrahydrofuran side products was dependent on the molar ratio of PET to1,4‐butanediol and the time of reflux during transesterification. Quantitative insertion of the butylene moiety into PET could be achieved under appropriate reaction conditions. The mechanical properties of PBT obtained by a transesterification reaction of PET with 1,4‐butanediol were comparable to those of virgin PBT (obtained by direct reaction of dimethyl terephathalate with 1,4‐butanediol). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3720–3729, 2004     

Effect of alkali on filaments of poly(ethylene terephthalate) and its copolyesters. II. Presence of quaternary ammonium salt in the alkali-bath

Influence of alkyl (C₁₂–C₁₄)-dimethyl-benzyl ammonium chloride in the solution of sodium hydroxide on the hydrolysis of poly(ethylene terephthalate) (PET), anionically modified poly(ethylene terephthalate) copolyster (CDP), and block polymer of poly(ethylene terephthalate)-poly(ethylene glycol) (EDP), has been studied under a variety of proportions, concentrations, time and temperature of reaction, M : L ratio, etc. Mechanical properties of treated polymeric materials are evaluated. Hydrolysis of two polymers in the same bath is compared with that in separate baths.     

支化聚酯的合成及热性能研究

通过直接酯化-缩聚工艺,在聚对苯二甲酸乙二醇酯(PET)聚合的缩聚过程中分别引入第三组分——3-羟甲基丙烷(TMP)、季戊四醇(PER)或双季戊四醇(DPT)合成了一系列不同的支化PET,并采用氢核磁共振波谱仪(1H-NMR)、差示扫描量热仪(DSC)和热重分析(TG)表征了产物的结构和性能。结果表明:与纯PET相比,经TMP、PER或DPT改性后的支化PET的玻璃化转变温度(Tg)均下降,含摩尔分数0.3%DPT改性的支化PET的Tg最低;除TMP1-PET外,各支化PET的冷结晶温度(Tc)都增大;各支化PET的熔点(Tm)也都呈现下降趋势;除PER3-PET外,各支化PET的结晶焓ΔHc都有所下降,而各支化PET的熔融焓ΔHm却变化不大;所得到的各支化PET具有较好的热稳定性能。     

废聚对苯二甲酸乙二醇酯的醇解研究

研究了醇解条件对废聚对苯二甲酸乙二醇酯(PET)醇解过程的影响,并通过凝胶渗透色谱、差示扫描量热、红外光谱、紫外分光光度仪、黏度计等多种测试手段对醇解产物进行了表征。研究表明:随着反应时间的增加,固相的数均相对分子质量、结晶度先增加后下降;醇解液的特性黏度[η]增加,紫外光透过率下降。固相完全消失后继续延长反应时间,醇解液的[η]变化不大。在实验条件下,多元醇醇解废PET的反应活性大小顺序为乙二醇>丙二醇>甘油。     

固相缩聚反应温度与时间对PET结晶的影响

研究了聚对苯二甲酸乙二醇酯(PET)切片在固相缩聚反应中特性粘数和结晶度随反应条件的变化及其热行为。结果表明:固相缩聚PET特性粘数随反应温度和反应时间不断增大,反应温度为215～ 225℃时较佳,随反应的进行新结晶产生,一定时间后结晶度增加缓慢并趋于平衡;DSC分析表明固相缩聚反应后的PET存在一个特征熔融峰(253℃左右)和固相缩聚峰,随着反应温度和反应时间的增加,固相缩聚峰不断向特征熔融峰靠拢,一定反应温度和反应时间后融合为单峰,之后低温峰跨过特征熔融峰向高温移动。     

Glycolysis of poly(ethylene terephthalate) wastes in xylene

To reclaim the monomers or prepare intermediates suitable for other polymers zinc acetate catalayzed glycolysis of waste poly(ethylene terephthalate) (PET) was carried out with ethylene or propylene glycol, with PET/glycol molar ratios of1 : 0.5–1 : 3, in xylene at 170–245°C. During the multiphase reaction, depolymerization products transferred to the xylene medium from the dispersed PET/glycol droplets, shifting the equilibrium to glycolysis. Best results were obtained from the ethylene glycol (EG) reaction at 220°C, which yielded 80 mol % bis-2-hydroxyethyl terephthalate monomer and 20 mol % dimer fractions in quite pure crystalline form. Other advantages of employment of xylene in glycolysis of PET were improvement of mixing at high PET/EG ratios and recycling possibility of excess glycol, which separates from the xylene phase at low temperatures. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2311–2319, 1998