Copolyester studies. IV. Dyeing behavior of drawn and undrawn fibers derived from tetramethylene terephthalate–tetramethylene sebacate copolymers

Drawn and undrawn fibers of tetramethylene terephthalate–tetramethylene sebacate copolymers, containing up to 20 mol % of the latter, have been dyed in an infinite dyebath with a disperse dye. The dyeing process has been interpreted in terms of the equilibrium dye absorption, the half-time of dyeing, and the diffusion coefficient. Increasing sebacate content has been found to have a marked effect on the rate and level of dye uptake. Deviations from Fickian behavior have been observed for the drawn fiber and related to presence of voids.     

Copolyester studies. III. Melt-spinning,drawing, and mechanical properties of tetramethylene terephthalate–tetramethylene sebacate copolymer fibers

Fibers have been prepared from tetramethylene terephthalate–tetramethylene sebacate copolymers, containing up to 20 mol % of the latter, using a conventional melt-spinning technique. The mechanical properties of these undrawn fibers and of highly oriented fibers prepared from them have been evaluated. The changes in mechanical properties brought about by the introduction of sebacate groups in poly(tetramethylene terephthalate) have been related to the glass-transition temperatures of the copolymers and to the flexible nature of the sebacate unit. The formation of voids during a continuous drawing process and during mechanical testing is discussed.     

Copolyester studies. I. Preparation and characterization of tetramethylene terephthalate–tetramethylene sebacate copolymers

Tetramethylene terephthalate–tetramethylene sebacate copolymers containing up to 20 mol % sebacate have been prepared and characterized. Molecular weights and distributions have been evaluated using viscometry and gel-permeation chromatography. Compositions have been established by NMR spectroscopy. Thermal properties have been studied by differential scanning calorimetry and dynamic mechanical methods. Melting and glass-transition temperatures and moduli are discussed in terms of the structural differences, particularly the effect of composition on chain flexibility. Density and thermal methods of crystallinity determination are critically discussed for these systems.     

Synthesis and properties of poly(tetramethylene terephthalate-co-ethylene terephthalate)–poly(tetramethylene ether) segmented copolymers

A series of polyether–copolyester segmented copolymers ((PBT–PET)PTMG) based on hard segments of tetramethylene terephthalate–ethylene terephthalate copolyester (PBT–PET) and soft segments of poly(tetramethylene ether)(PTMG) was synthesized. The hard : soft segment weight ratio was 30 : 70 and the mole ratio of PBT : PET was 1 : 10; 1 : 6; 1 : 1; 3 : 1, respectively. Their mechanical properties, morphology, crystallization behavior and optical transparency were investigated and compared with poly(tetramethylene terephthalate)–poly(tetramethylene ether)(PBT–PTMG), as well as with poly(ethylene terephthalate)–poly(tetramethylene ether)(PET–PTMG), consisting of the equivalent composition ratio of hard and soft segments. It was found that the transparency could be improved by introducing a small amount of PBT into PET–PTMG through copolymerization. However, a decrease was observed in the transparency if more PBT was added. This is due to the fact that the copolymerization makes both crystallinity and crystallization rate decrease.     

Crystallization of 2‐methyl‐1,3‐propanediol substituted poly(ethylene terephthalate). I. Thermal behavior and isothermal crystallization

Differential scanning calorimetry (DSC) was used to evaluate the thermal behavior and isothermal crystallization kinetics of poly(ethylene terephthalate) (PET) copolymers containing 2‐methyl‐1,3‐propanediol as a comonomer unit. The addition of comonomer reduces the melting temperature and decreases the range between the glass transition and melting point. The rate of crystallization is also decreased with the addition of this comonomer. In this case it appears that the more flexible glycol group does not significantly increase crystallization rates by promoting chain folding during crystallization, as has been suggested for some other glycol‐modified PET copolyesters. The melting behavior following isothermal crystallization was examined using a Hoffman–Weeks approach, showing very good linearity for all copolymers tested, and predicted an equilibrium melting temperature (T_m⁰) of 280.0°C for PET homopolymer, in agreement with literature values. The remaining copolymers showed a marked decrease in T_m⁰ with increasing copolymer composition. The results of this study support the claim that these comonomers are excluded from the polymer crystal during growth. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2592–2603, 2006     

Copolyester studies. V. Preparation and characterization of tetramethylene terephthalate–poly(tetramethylene oxide) random block copolymers

Random block copolymers of tetramethylene terephthalate and polytetrahydrofuran (PTHF) were prepared by melt polycondensation. Five different molecular weights of PTHF were used in the polymerizations with up to 30% by weight incorporation. The copolymers so obtained were characterized in terms of their molecular weight by means of endgroup analysis and solution viscometry. Compositions were established by nuclear magnetic resonance spectroscopy. Thermal properties were studied by differential scanning calorimetry and dynamic mechanical methods. Melting and glass transition temperatures are discussed in terms of the structural differences, particularly the effect of polyether composition and block size on chain flexibility.     

热致液晶聚合物 Ⅱ.结晶及熔融行为

采用差示扫描量热法(ＤＳＣ)在等温结晶过程中,研究了热致液晶聚合物的结晶及熔融行为。结果发现,在非等温结晶过程中没有明显的冷热结晶峰;随着时间的延长,熔触焓逐渐增大,并趋于定值;在２８０℃下,结晶度最高,结晶速率也最快;通过外推,估算了平衡熔点。     

PET-PTMG聚醚酯熔融与结晶行为的研究

采用熔融缩聚法合成了一系列聚对苯二甲酸乙二醇酯(PET)-四氢呋喃聚醚(PTMG)聚醚酯，用DSC、偏光显微镜表征了材料的熔融与结晶性能，讨论了组成对聚醚酯的熔点、结晶温度、结晶度、结晶形态的影响。结果表明，PET—PTMG聚醚酯的熔点与组成的关系符合Baur公式；其结晶度随着聚醚含量的增加呈现先升高后下降的趋势；并为明显的结晶与非结晶的两相结构形态。     

Inter-lamellar crystallization in poly(tetramethylene oxide)

High molecular weight poly(tetramethylene oxide) crystallizes isothermally from the bulk to a final crystallinity level of approximately 50%. Further crystallization can be induced in this material by cooling. This effect has been studied by differential scanning calorimetry (d.s.c.) and small angle X-ray scattering (SAXS). The additional crystalline material has a lower melting point than the original and its presence causes a pronounced decrease in the small angle spacing (correlation function maximum). The propensity to crystallize further at low temperatures decreases with increasing secondary crystallization under the original isothermal conditions. Additional crystallinity can also be induced, without temperature change, by cleaving chains by prolonged exposure to an X-ray source. These facts are explained in terms of the additional crystallinity occurring by growth of new thin lamellae between the original isothermally grown lamellae. The new lamellae grow preferentially in the thicker amorphous regions, which are reduced in size and number by secondary crystallization. The radiation damage effects indicate that amorphous chain constraint as well as available space is an important factor inhibiting crystallization between preformed lamellae.     

Extreme thermal behaviors of polytetrafluoroethylene and random tetrafluoroethylene fluorinated copolymers

By differential scanning calorimetry (DSC), the thermal behavior of polytetrafluoroethylene (PTFE) and random fluorinated copolymers of tetrafluoroethylene-containing hexafluoropropylene (FEP copolymers) or perfluoroalkylvinylether (PFA copolymers) as comonomers was investigated. Rapid-melt crystallization was employed to provide new data about the problem of inclusion/exclusion of co-units from the homopolymer crystal lattice. Equilibrium melting points were determined and tested in light of random copolymer predictions. Both nonequilibrium and equilibrium behaviors seem to point to the inclusion of  CF₃ side groups and the exclusion of larger ones. Finally, a new value of the equilibrium melting point of PTFE is given, in good agreement with those present in the literature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 919–925, 1999     

Crystallization behaviour of random block copolymers of poly(butylene terephthalate) and poly(tetramethylene ether glycol)

The morphology and crystallization behaviour of random block copolymers of poly(butylene terephthalate) and poly(tetramethylene ether glycol) have been investigated. Single crystals have been grown in thin films crystallized from the melt. Well defined lamellae, exhibiting (hkO) single crystal electron diffraction patterns have been observed in copolymers containing down to 49 wt% (0.83 mole fraction) poly(butylene terephthalate). WAXS and electron diffraction support a model of a relatively pure poly(butylene terephthalate) crystal core with the poly(tetramethylene ether glycol) (soft segment) sequences and short hard segments being rejected to the lamellar surface and the soft segment rich matrix. The lateral dimensions of the lamellae are determined by the number of hard segment sequences long enough to traverse the stable crystal size at the crystallization temperature. This leads to an initial population of crystals formed at T_c and a second set of smaller crystals that grow from the short hard segment sequences upon cooling to room temperature. The result is fractionation by sequence length due to a coupling of the sequence distribution with the stable crystal size at the crystallization temperature.     

聚酰胺酯结晶行为研究

利用差式扫描量热法对聚酰胺酯进行结晶行为分析。结果表明:与常规PET相比,聚酰胺酯玻璃化温度、冷结晶温度、熔点、熔融结晶温度均较低,同时其熔融结晶速率也较慢;且随着共聚酯中聚酰胺成分的增加,玻璃化温度、熔点、熔融结晶温度逐渐降低并呈现一定的变化关系;在相同结晶温度下,聚酰胺成分增加,共聚酯半结晶周期t_(1/2)增加,结晶随之变慢。     

Thermorheological and mechanical behavior of polylactide and its enantiomeric diblock copolymers and blends

In this study, different compositions of nearly monodispersed diblock copolymers of dl-lactide or d-lactide and l-lactide were synthesized by living ring-opening polymerization with a dinuclear indium catalyst. The effects of molecular weight and block length ratio on the rheological behavior of dl and l-lactide diblock copolymers in the disordered state were investigated. For comparison, blends of PDLLA and PLLA homopolymers of equivalent molecular weights to the diblock copolymers were prepared. We found that the time–temperature (t–T) superposition principle is applicable to the diblock copolymers PLLA-b-PDLLA and blends in the disordered state. However, the t–T superposition failed at low temperatures close to the temperature of crystallization. In contrast, diblock copolymers PLLA-b-PDLA formed stereocomplex crystallites of high melting point (slightly above 200 °C) that causes a viscosity enhancement. The failure of t–T superposition was found due to existing of micro homo or stereocomplex crystallites. The non-isothermal crystallization behavior was investigated using differential scanning calorimetry (DSC). The DSC thermograms of blends exhibited a single glass transition at 50–60 °C followed by melting point of PLLA at 177 °C. With decreasing of the PLLA content in the blends, the intensity of the melting peak decreased. In addition, different crystallization behavior was observed for diblock copolymers compared to their equivalent blends. Specifically, low temperatures and enthalpies of melting peaks were observed for diblock copolymers. These also show improvement in elongation at break and tensile strength as compared to their counterpart homopolymer blends.     

Copolyester studies. VI. Melt spinning and mechanical properties of tetramethylene terephthalate–poly(tetramethylene oxide) random block copolymers

Fibers were prepared from tetramethylene terephthalate–polytetrahydrofuran (PTHF) random block copolymers, containing the latter in the range of molecular weights 1000–5000 with up to 30% by weight incorporation, using a conventional melt spinning technique. The spinnability of the copolymer and the mechanical properties of these undrawn fibers were evaluated. The changes in mechanical properties brought about by the incorporation of PTHF groups in 4GT units were related to the PTHF block size and content in the copolymer. X-ray diffraction data are also discussed briefly in terms of the structural differences.     

On the melting behavior of isothermally crystallized 1‐octene linear low‐density polyethylene copolymers

The melting behavior of two 1‐octene linear low‐density polyethylene (LLDPE) copolymers is investigated. One made using Dow′s INSITE constrained geometry catalyst technology (LLDPE‐A) and the other using titanium‐based Ziegler–Natta catalysts (LLDPE‐B). Both have similar comonomer content as well as melt flow index. Differential scanning calorimetry (DSC) was used throughout the work. Isothermal crystallizations in the DSC for several times were carried out at various temperatures between 90 and 100°C for LLDPE‐A and between 105 and 112.5°C for LLDPE‐B. As a result of the isothermal crystallizations for both copolymers, multiple melting peaks are found in the DSC traces on subsequent heating. The melting behavior was also examined as a function of heating rate (1, 2.5, 5, 10, and 20°C/min). The multiple melting behavior indicates that they are inhomogeneous. In addition, a melting–recrystallization process was shown to be responsible for the appearance of one of the melting peaks in LLDPE‐B. A lowering in heating rate from the crystallization temperature favors the occurrence of melting–recrystallization during the dynamic experiment. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2022–2028, 2001     

Crystallization kinetics of poly(1,4‐butylene‐co‐ethylene terephthalate)

The crystallization kinetics of poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), and their copolymers poly(1,4‐butylene‐co‐ethylene terephthalate) (PBET) containing 70/30, 65/35 and 60/40 molar ratios of 1,4‐butanediol/ethylene glycol were investigated using differential scanning calorimetry (DSC) at crystallization temperatures (T_c) which were 35–90 °C below equilibrium melting temperature . Although these copolymers contain both monomers in high proportion, DSC data revealed for copolymer crystallization behaviour. The reason for such copolymers being able to crystallize could be due to the similar chemical structures of 1,4‐butanediol and ethylene glycol. DSC results for isothermal crystallization revealed that random copolymers had a lower degree of crystallinity and lower crystallite growth rate than those of homopolymers. DSC heating scans, after completion of isothermal crystallization, showed triple melting endotherms for all these polyesters, similar to those of other polymers as reported in the literature. The crystallization isotherms followed the Avrami equation with an exponent n of 2–2.5 for PET and 2.5–3.0 for PBT and PBETs. Analyses of the Lauritzen–Hoffman equation for DSC isothermal crystallization data revealed that PBT and PET had higher growth rate constant G_o, and nucleation constant K_g than those of PBET copolymers. © 2001 Society of Chemical Industry     

sPS/PBA-aPS共混物的结晶与熔融行为

通过熔融共混法制备了间规立构聚苯乙烯/聚丙烯酸丁酯无规立构聚苯乙烯核壳乳胶粒子（sPS/PBA-aPS）共混物,采用差示扫描量热仪、X射线衍射仪和偏光显微镜研究了PBA-aPS对sPS结晶性能、结晶形态的影响,以及共混物在不同降温速率下、等温结晶条件下所得试样的熔融行为。结果表明, PBA-aPS的引入对sPS的结晶起阻碍作用,sPS及其共混物存在明显熔融重结晶再熔融现象,sPS平衡熔点为293.2 ℃,共混物的平衡熔点随PBA-aPS含量增加而降低,sPS形成β型大球晶完善性变差,sPS/PBA-aPS共混物的冲击强度明显提高,sPS/PBA-aPS质量比为80:20时,冲击强度提高了117 %。     

The anomalous melting behavior of water in aqueous PVME solutions

The Wertheim lattice thermodynamic perturbation theory is used to predict the liquid-liquid and solid-liquid coexistence data for a model polymer solution. The theory predicts bimodal LCST phase behavior and an unusual step with composition in the solid-liquid equilibrium of the solvent.The theoretical solid-liquid equilibrium calculations are used to interpret experimental data obtained for aqueous solutions of poly(vinyl methyl ether) (PVME), which is known to show bimodal LCST phase behavior. An experimental method is proposed, employing Fourier transform infrared (FTIR) spectroscopy to determine the equilibrium melting line of water in the presence of PVME. In addition, the complete melting line of water is obtained by partial integration of the melting endotherm observed using modulated temperature differential scanning calorimetry (MTDSC). Both, the FTIR and MTDSC methods are in good agreement, experimentally confirming the predicted step with composition in the solid-liquid equilibrium. This peculiar concentration dependence of the melting curve of ice provides a new explanation for the inhibited crystallization of water in aqueous PVME solutions, since the actual supercooling (at high polymer concentration) is smaller than it could be anticipated for a conventional course of the melting curve. Hence, the vicinity of the glass transition region in these highly concentrated polymer mixtures leads to a dramatic slowing down of the nucleation rate and thus the subsequent crystallization. Moreover, the atypical shape of the equilibrium melting line also provides a new explanation for the double melting endotherm observed in (MT)DSC experiments, which is conventionally attributed to the melting at different temperatures of bound and free water.     

Effects of processing on the microstructure,melting behavior,and equilibrium melting temperature of polypropylene

Polypropylene (PP) was extruded and injection-molded several times to mimic the effect of recycling procedures on PP. Differential scanning calorimetry (DSC) was used to follow crystallization rates under isothermal conditions in a temperature range of 120–150°C. Melting behavior and equilibrium melting temperatures were studied using the Hoffman-Weeks method of extrapolation. Optical microscopy combined with a hot stage was also used to follow the spherulite microstructure and crystal phase upon recycling of PP. Wide-angle X-ray spectroscopy identified the crystal phase at different isothermal crystallization temperatures. Twin melting peaks obtained for PP melting following isothermal crystallization were associated with crystal rearrangement during fusion. PP spherulite size and equilibrium melting temperatures were seen to increase with processing events, whereas reprocessing decreased nuclei density. © 1996 John Wiley & Sons, Inc.     

PA6T/1010共聚物热性能研究

以对苯二甲酸、己二胺和癸二酸、癸二胺为原料合成了新型半芳香PA6T/1010共聚物,通过差示扫描量热仪(DSC)、熔点测定仪和热重分析仪(TG)对不同组成PA6T/1010的熔融行为、结晶行为和热稳定性进行了表征。结果表明:当PA6T含量大于40%时,PA6T/1010共聚物的结晶性能明显下降,熔融峰和结晶峰均消失;当PA6T含量为40%时,共聚物共熔点降至165℃;PA6T/1010共聚物的热降解过程为一步降解,热降解温度超过400℃。