Aliphatic-aromatic copolyesters containing phosphorous cyclic bulky groups

A series of phosphorus-containing copolyesters was prepared by polycondensation of 2-(6-oxido-6H-dibenz<c,e><1,2>oxaphosphorin-6-yl)-1,4-naphthalene diol, 1, or of an equimolecular amount of 1 and different aliphatic diols 2, such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol and 1,12-dodecanediol, with an aromatic diacid chloride containing two preformed ester groups 3, namely terephthaloyl-bis-(4-oxybenzoyl-chloride). The copolyesters exhibited good thermal stability having the decomposition temperature above 375 °C. The glass transition temperature was in the range of 96-146 °C. The polymers exhibited thermotropic liquid crystalline behavior, as was observed with polarized optical microscopy. DSC and X-ray experiments were also found in concordance with mesophase formation.     

共聚酯的结晶性能研究

通过添加二元酸或二元醇来制备共聚酯,采用DSC对共聚酯的结晶性能展开研究,分析了二元酸或二元醇对共聚酯结晶性能的影响。     

CHDM改性PBT共聚酯的非等温结晶动力学研究

采用直接酯化熔融缩聚工艺路线,以1,4-环己烷二甲醇(CHDM)为第三单体,制备了CHDM改性聚对苯二甲酸丁二醇酯(PBT)共聚酯(PBTG),利用差示扫描量热仪测定了PBT及PBTG在不同降温速率下的降温曲线,并采用Jeziorny方法分析了PBTG的非等温结晶动力学。结果表明:随着降温速率的增加,PBT及PBTG的结晶温度降低,结晶曲线变宽;在相同降温速率下,相比PBT,加入第三单体CHDM后的PBTG的非等温结晶动力学速率常数降低,证明PBTG的非等温结晶能力降低,结晶速率变慢; CHDM的加入不利于PBT结晶。     

Synthesis and crystallization behavior of segmented copolyesters/silica composites

Silica were introduced to segmented copolyester system (poly(butylene terephthalate)‐poly(ethylene terephthalate‐co‐isophthalate‐co‐sebacate) (PBT‐PETIS)) by in situ polymerization. Investigations on melting behavior and crystalline structure were undertaken, and the dispersion situation of silica in segmented copolyester composites was detected. A diverse crystallization characteristic has been found when the modified Avrami analytical method was applied to investigate nonisothermal crystallization behavior of the composites. Crystallization rate was restricted rather than be promoted by increasing loading of silica. The values of Avrami exponent ranged from 2.25 to 2.45, presenting a mechanism of three‐dimensional spherulitic growth with heterogeneous nucleation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1052–1058, 2006     

低熔点PBT共聚酯的制备及其熔融结晶行为分析

以间苯二甲酸(IPA)作为第三单体,采用直接酯化熔融缩聚的方法制备了低熔点聚对苯二甲酸丁二醇酯(PBT)共聚酯(PIBT)。采用乌氏黏度计、差示扫描量热仪和偏光显微镜分别对PIBT的黏均相对分子质量(Mη)、熔融和结晶行为进行了表征和研究。结果表明:制备的PIBT的Mη均达到聚合物水平;随着IPA含量的增加,PIBT的熔点逐渐降低,当IPA摩尔分数为15%时,PIBT的熔点为201.68℃,与PBT的熔点相比下降了24.21℃;在相同降温速率下,随着IPA含量的增加,PIBT的结晶温度及结晶速率常数逐渐降低,结晶速率逐渐变慢,PIBT等温结晶所得球晶直径逐渐变小。     

Effect of linear comonomers on the rate of crystallization of copolyesters

Small amounts of dimethyl‐4,4′‐biphenyldicarboxylate, 2,7‐dimethyl‐4,5,9,10‐tetrahydropyrenedicarboxylate, and dimethyl‐2,7‐pyrenedicarboxylate have been copolymerized into poly(ethylene) terephthalate (PET). The thermal transitions of the copolymers have been characterized, and the crystallization rates have been measured isothermally. Avrami analysis indicates that all the copolymers crystallized at a slower rate than that of the PET homopolymer. Addition of perylene to the copolymers containing pyrene enhanced the rate of crystallization, which could be the consequence of stacked arene assemblies serving as templates for crystal formation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2696–2704, 2001     

A simple one-step synthesis of unsaturated copolyesters

Copolyesters containing pendent vinylidine groups were prepared in a one-step synthesis by reacting either chloro- or bromoacetic acid with 2-(bromomethyl)acrylic acid and triethylamine in diethyl ether. Polymers were characterized by IR, ¹H- and ¹³C-NMR, DSC, and TGA. Copolymer formation supports a mechanism involving a triethylammonium carboxylate salt acting as an active nucleophilic species in a manner analogous to that seen in phase transfer catalysis involving carboxylate anions. Comparison of ¹³C-NMR spectra intensities indicates that 2-(bromomethyl)acrylic acid is much more reactive than the haloacetic acids leading to higher copolymer incorporation than in the monomer feed. Unsaturation in the copolymers provides a site for crosslinking during radical polymerization with an added vinyl monomer, similar to the way unsaturated polyesters function in commercial fiberglass formulations. This was confirmed by polymerization of both styrene and methyl methacrylate in the presence of an unsaturated copolymer giving insoluble semi-interpenetrating networks. These unsaturated copolymers are the first examples of soluble biodegradable glycolic acid polyesters containing such reactive functionality.     

Fast crystallization of liquid crystalline copolyesters based on poly(ethylene terephthalate)

Crystallization of a series of liquid crystalline copolyesters prepared from p‐hydroxybenzoic acid (HBA), hydroquinone (HQ), terephthalic acid (TA), and poly(ethylene terephthalate) (PET) was investigated by using differential scanning calorimetry (DSC). It was found that these copolyesters are more crystalline than copolyesters prepared from PET and HBA. Insertion of HQ–TA disrupts longer rigid‐rod sequences formed by HBA and thus enhances molecular motion and increases the crystallization rate. The effects of additives on the crystallization of the copolyesters were also studied. Sodium benzoate (SB) and sodium acetate (SA) increase the crystallization rate of the copolyesters at low temperature, but not at high temperature. It is most likely that liquid crystalline copolyesters do not need nucleating agents, and small aggregates of local‐oriented rodlike segments in nematic phase could act as primary nuclei. Chain scission of the copolyesters caused by the reaction with the nucleating agents was proved by the determination of intrinsic viscosity and by the IR spectra. Diphenylketone (DPK) was shown to effectively promote molecular motion of chains, leading to an increase in the crystallization rate at low temperature, but it decreased the crystallization rate at high temperature. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 497–503, 2001     

Aromatic-aliphatic copolyesters: structure and properties

Aromatic-aliphatic copolyesters synthesized by interfacial polycondensation were characterized by differential scanning calorimetry. X-ray diffraction and density measurements. A decrease in the T_g and melting temperature was observed on increasing the glycol content of the copolyesters. The wholly aromatic polyesters showed changes both in the Bragg angle position and intensity of the reflections, whereas in the aromatic-aliphatic copolyesters no sharp change was observed.     

Sequence distribution, crystallization and melting behavior of poly(ethylene terephthalate-co-trimethylene terephthalate) copolyesters

The compositions of a series of copolyesters of ethylene- and trimethylene- terephthalate were determined by NMR. The values of randomness parameter revealed these copolyesters were random copolymers with average-number sequence lengths varied from 1 to 10. These copolyesters were investigated using temperature-modulated differential scanning calorimeter (TMDSC) and wide angle X-ray diffractometer (WAXD). The crystallization behavior was evidenced from the non-isothermal DSC thermograms and WAXD patterns. The crystallization rate and the intensity of diffraction peaks decrease with increasing the minor co-monomer content. The copolyester with equal amounts of monomers is still crystallizable even though the average sequence length is only 2.0, and its WAXD pattern is quite different from those of homopolymers. In the melting study, three distinct peaks of reversing melting were observed. Two peaks in the high temperature side are due to remelting of the recrystallized crystals formed during the heating scan, whereas the highest temperature peak is attributed to the melting of the crystals that are formed in relatively high temperature. The results of WAXD and TMDSC support the mechanism of melting-recrystallization-remelting for the multiple melting behaviors.     

Nuclear magnetic resonance studies of selectively deuterated aromatic liquid crystalline copolyesters

Deuterium n.m.r. has been used to follow the molecular dynamics of three polyester materials over a temperature range of −150°C to 150°C. Two of the materials are liquid crystalline copolymers, one of perdeuterated hydroxybenzoic acid and hydroxynaphthoic acid and the other of hydroxybenzoic acid, isophthalic acid and perdeuterated hydroquinone. The third sample is crystalline poly(ethylene terephthalate) (PET) in which the benzene rings are deuterated. At the lowest temperatures examined all three materials give n.m.r. lineshapes characteristic of little molecular motion. On heating the liquid crystalline materials, the onset of motion is observed, first in the form of 180^o flips and then unrestricted rotation about the polymer axes. The PET spectra show a small degree of 180^o ring flipping to be taking place above 100°C, but most of the motion is in the form of near random motion that comes to dominate at 150°C. The results confirm the relatively stiff rod-like nature of the liquid crystalline polymers in comparison to the more flexible PET.     

In situ FTIR microscope study on crystallization of crystalline/crystalline polymer blends of bacterial copolyesters

This study describes in situ observation of crystallization in a spherulite of blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [PHBV] and poly(3-hydroxybutyrate-co-3-hydroxypropionate) [PHBP] by FTIR microscopy. In order to trace the crystallization processes of blend components separately, PHBV was deuterated. The C-D and CO stretching bands in the IR spectra, respectively, show the crystallization behavior of PHBV and the whole blend. D-PHBV containing 6 and 8% HV [D-PHBV6 and D-PHBV8] are blended with PHBP containing 11% HP [PHBP11]. The crystallization rates of D-PHBV6, D-PHBV8 and PHBP11 decrease in this order. In case of the blend of D-PHBV8 and PHBP11 the crystalline peaks of C-D and CO bands grows simultaneously during crystallization, and the growth rates are rather close to that of D-PHBV8. The results indicate that D-PHBV8, which is the component that shows higher crystallization rate in the pure state, leads the cocrystallization of the blend. For D-PHBV6/PHBP11, on the other hand, the crystalline peak of C-D band grows faster than that of CO band, indicating that the crystallization of D-PHBV6 proceeds before the crystallization of PHBP11. During the crystallization of D-PHBV6, PHBP11 molecules get away from the growing front of the spherulite, i.e. the phase segregation precedes the crystallization. These results demonstrate that FTIR microscopy is a powerful tool to trace the formation of different crystalline phases, such as cocrystallization and phase segregation.     

Morphological studies of bisphenol series thermotropic liquid crystalline wholly aromatic copolyesters

A family of aromatic thermotropic liquid crystal (TLC) copolyesters are prepared based on terephthalic acid (TPA), isophthalic acid (IPA), p-hydroxybenzoic acid (HBA), and a family of bisphenols. The morphological behaviors of the copolyesters are studied by using polarized optical microscopy, small-angle light scattering (SALS), and depolarized light intensity (DLI) analysis. The copolyester melts exhibit nematic mesophase textures within wide temperature ranges without showing transitions to isotropic phases. The textures under different temperatures and deformation conditions are investigated. Scattering patterns of the mesophases change greatly during shear deformation and relaxation. The early formation of the mesophases is a one-dimension heterogeneous nucleation based on isothermal condition. © 1994 John Wiley & Sons, Inc.     

Expressions of supersaturation in crystallization studies

The driving force for crystallization in a binary system is considered from the thermodynamic viewpoint. Exact relationships, derived for particular cases, are compared with commonly used expressions of supersaturation calculated from solution concentrations. Errors incurred when activity coefficient ratios are ignored are evaluated. The need to incorporate the number of ions, into which a molecule dissociates, in the expressions of supersaturation for electrolyte solutions is emphasized. Examples are given for the crystallization of several inorganic salts from aqueous solution.     

Sequence distribution,thermal properties,and crystallization studies of poly(trimethylene terephthalate‐co‐1,4‐cyclohexylene dimethylene terephthalate) copolyesters

A series of novel poly(trimethylene terephthalate‐co‐1,4‐cyclohexylene dimethylene terephthalate) (PTCT) with various compositions were synthesized by melt polycondensation of 1,3‐propanediol, 1,4‐cyclohexanedimethanol and dimethyl terephthalate. The resulting copolyesters were characterized using ¹³C and ¹H nuclear magnetic resonance. The average length of both trimethylene terephthalate (TT) and cyclohexylene dimethylene terephthalate (CT) sequences varies from 1 to 10, and the chain structure is statistically random. The crystallization was investigated using wide angle X‐ray diffractometer (WAXD) and differential scanning calorimeter. The WAXD patterns can be divided in two groups according to the composition: copolyesters with less than 35 mol % CT content exhibit PTT‐type lattice, and those with CT unit content higher than 42 mol % crystallize with the PCT‐type lattice. The crystallizability of CT sequence is higher than that of TT sequence. Thermodynamic analysis shows that the comonomer is excluded from the PTT‐type or PCT‐type crystal of the copolyesters. The thermal decomposition temperature of copolyesters increases with increasing CT content, and their thermal stability is improved as compared to that of PTT. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Computer-aided design and scale-up of crystallization processes: Integrating approaches and case studies

Scaling up a crystallization process often results in significant changes to crystal size distribution (CSD), purity and morphology, which are key determinants of product quality and has implications for downstream operations such as filtration. This unwelcome observation results from the interplay between hydrodynamics and crystallization kinetics that scale in different ways. Computer-aided tools, such as process system engineering (PSE) software and computational fluid dynamics (CFD) simulations, offer a means to understand these interactions within system constraints and to use the insight thus gained to guide scale-up strategies. This article outlines approaches to scaling up crystallizers and how to develop new processes, showing how numerical simulations and other software tools can be used to address typical issues arising in each case.     

晶化温度与晶化时间对4A分子筛合成的影响

以硅酸钠试剂为硅源,铝酸钠试剂为铝源,反应体系各组分的物质的量之比为n(SiO2)∶n(Al2O3)∶n(Na2O)∶n(H2O)=2∶1∶1∶1∶50,采用水热合成法制备了4A分子筛,考察了晶化温度与晶化时间对该型分子筛结构和形貌的影响,并利用X射线衍射(XRD)、电镜扫描(SEM)及红外(IR)测试等手段对其进行了表征。结果表明,4A分子筛在晶化温度为100℃,晶化时间为14h的条件下具有良好的微孔结构及形貌。     

Bio-inspired synthesis: understanding and exploitation of the crystallization process from amorphous precursors

Many biominerals, such as mollusk nacre, sea urchin, bone and teeth, are found to form by an amorphous precursor pathway, and these biominerals have remarkable properties, which are better than their artificial material counterparts that are formed at high temperatures and high pressures. More than ever, synthesizing technologically relevant materials following nature's way with a specific size, shape, orientation, organization, and complex form has been a focus of ongoing interest due to the increasing need for low cost and environmentally friendly approaches to processing advanced materials. Herein, we present recent developments in the crystallization process from amorphous precursors by primarily drawing on results from our own laboratory, and discuss some unique characteristics from the transformation process that can be exploited for the design and synthesis of artificial functional materials.     

Isomorphic crystallization of aliphatic copolyesters derived from 1,6-hexanediol: Effect of the chemical structure of comonomer units on the extent of cocrystallization

The crystallization behavior has been investigated for poly(hexamethylene sebacate-co-hexamethylene suberate)s [P(HSe-co-HSu)] and poly(hexamethylene suberate-co-hexamethylene adipate)s [P(HSu-co-HA)] copolyesters by differential scanning calorimeter (DSC), wide angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR) spectrometer. Cocrystallization of comonomer units was found in the crystalline phase of both P(HSe-co-HSu) and P(HSu-co-HA) copolymers. Moreover, both P(HSe-co-HSu) and P(HSu-co-HA) copolymers exhibit isodimorphism. The PHSe and the PHSu type crystals were respectively developed in P(HSe-co-HSu)s, while the PHSu and the PHA type crystals were developed in P(HSu-co-HA)s respectively. The inclusion of the comonomer units in the PHSu type crystalline lattice is more favored than that in the PHSe type crystal of the P(HSe-co-HSu)s. Meanwhile, it is easier for the comonomer units to be incorporated into the PHA type crystalline lattice than into the PHSu type crystal of P(HSu-co-HA)s. Moreover, comparison between the isomorphic crystallization of P(HSe-co-HSu), P(HSe-co-HA) and P(HSu-co-HA) series copolyesters indicates that minimization of the difference in chemical structure helps in increasing the extent of cocrystallization of comonomer units.