镧配合物对等规聚丙烯等温结晶性能的影响

利用Avrami方程和Lauritzen-Hoffman结晶动力学理论研究了一种镧配合物LaC对等规聚丙烯(iPP) 等温结晶行为的影响. 差示扫描量热法(DSC)和X射线衍射技术(XRD)研究表明, LaC的加入并未改变iPP的结晶形态, 但LaC的存在能提高体系的结晶度并显著加速iPP的结晶过程. 在130 ℃进行等温结晶时, 含0.5%LaC(质量分数)的iPP与纯iPP相比, Avrami指数n值无显著差异, 但前者总的结晶速率常数k值比后者提高约4倍,而半结晶时间t1/2值减少到后者的62%, Avrami方程分析结果表明LaC的存在主要起到增加晶核的作用. 利用Lauritzen-Hoffman结晶动力学理论, 通过对iPP在121 ℃、124 ℃、127 ℃和130 ℃下等温结晶的数据进行分析可知, 加入0.5%的LaC后, 体系的成核常数kg从纯PP的3.3×105 K2增加到PP/LaC的3.8×105 K2, 而结晶生长时大分子在垂直于分子链方向折叠的界面自由能σe从纯PP的0.223 J·m-2降低到PP/LaC的0.154 J·m-2, 表明LaC在iPP结晶过程中不仅起到增加晶核的作用, 同时使大分子链更易排入晶格, 即起到促进结晶成长的作用.     

苯乙烯-丙烯嵌段共聚物等温结晶动力学的研究

用DSC法研究苯乙烯-丙烯嵌段共聚物(iPS-b-iPP)的等温结晶动力学。结果表明,在所选择的结晶温度(127～132℃)范围内,共聚物很好地符合Avrami动力学方程;共聚物结晶温度、结晶速率、结晶成核和生长方式都与共聚物结构和组成比有关,随着嵌段共聚物中iPS段含量的增加,结晶速率和Avranu指数(n)明显降低。     

Kinetics of Nonisothermal and Isothermal Crystallization of Metallocene Polyethylene

Thedevelopmentofmetallocenecatalystsundoubtedlyrepresentsarevolutioninthepolyolefinbusiness.MetallocenePE(MPE)coverspolyethyleneswhichareproducedbymetallocenecatalysttechnology.EXXONChemicalCo.developedanewmeta-llocenepolyethylene-EXCEED'PEin1991.Nowmoreandmoreeffortsarespentonthisinterestingproject.Uniformmolecularstructureandnarrowmoleculardistribution,makeMPEbetterphysicalpropertiesthanthoseofconventionalPE,andalsomakeitlowmeltstrengthandbadprocessability.Sotherelationshipbetween…     

等规聚丙烯自成核的等温结晶动力学

近年来 ,有关等规聚丙烯 (i PP)的自成核研究已引起了人们的关注 [1 ] ,但有关其结晶动力学的报道并不多见 .Carfagna等 [2 ]用膨胀计法研究了 i PP在未完全熔融重结晶情况下的等温结晶动力学 ,得到的 Avrami指数远远小于 3 .张新远等[3 ] 研究了 i PP未完全熔融情况下的非等温结晶动力学 .到目前为止 ,i PP自成核的熔体降温等温结晶动力学尚未见报道 .本文在 i PP自成核研究的基础上 [4] ,用 DSC方法研究了 i PP自成核在较高温度下的等温结晶动力学 ,讨论了结晶机理 .结果表明 ,在本实验的自成核条件下 ,i PP依然是三维球晶生长 ,…     

固相缩聚PET等温结晶动力学

高聚物等温结晶动力学方面的研究者甚多,由熔融缩聚制备的不同分子量PET的等温结晶动力学及几种不同缩聚催化体系固相缩聚PET的等温结晶动力学已有报道.本文采用一个修正的Avrami方程对固相缩聚PET样品进行系统的等温结晶动力学研究.     

聚醚醚酮酮等温结晶动力学的研究

聚醚醚酮酮等温结晶动力学的研究陈艳，王军佐，曹俊奎，那辉，吴忠文（吉林大学化学系，长春，１３００２３）关键词聚醚醚酮酮，等温结晶动力学，差示扫描量热法聚醚醚酮酮（ＰＥＥＫＫ）是在聚醚醚酮（ＰＥＥＫ）基础上开发成功的一种耐热高分子材料。它保持了ＰＥＥＫ...     

等规聚丙烯在混合稀释剂中结晶行为

利用偏光显微镜和扫描电子显微镜研究了等规聚丙烯(iPP)在混合稀释剂中的非等温结晶行为和由热致相分离(TIPS)法制备的iPP微孔材料的结构。iPP的质量分数固定为30%,采用不同配比的邻苯二甲酸二丁酯(DBP)/大豆油组成混合稀释剂。结果表明,混合稀释剂的配比影响体系的粘度和稀释剂与iPP的相容性,进而影响iPP球晶的生长和TIPS法制备的iPP微孔材料结构。在2K/min的降温速率的条件下,iPP球晶半径和球晶的生长速率均随时间的延长呈指数增长,iPP球晶生长速率随混合稀释剂中DBP含量的增加而降低,当iPP球晶生长时间达2min时,混合稀释剂中DBP的质量分数从0增加到60%,iPP球晶生长速率从41.9μm/min降至10.3μm/min,所制得的微孔材料断面均呈蜂窝状结构,且孔径随混合稀释剂中DBP含量的增加有明显增大的趋势。     

热塑性聚酰亚胺与聚醚醚酮共混物的等温结晶动力学

采用熔融共混方法制备了热塑性聚酰亚胺(TPI)与聚醚醚酮(PEEK)的共混物; 用示差扫描量热分析(DSC)研究了共混物的等温结晶动力学. 分别采用Avrami方程和Hoffman-Lauritzen方程分析共混物的等温结晶动力学、端表面自由能(σe)和分子链折叠功(q). 结果表明, 加入TPI后PEEK的结晶速率降低, 结晶活化能、σe和q均增加. 但这些数值的变化与TPI含量不呈线性关系, 并从共混物的相容性和表面形貌给出了可能的解释.     

聚丁二酸丁二醇酯的自成核结晶行为

利用差示扫描量热仪(DSC)研究了自成核对聚丁二酸丁二醇酯(PBS)的结晶行为的影响. 研究结果表明, PBS的有效自成核温度处理区间为118～120 ℃. PBS经自成核处理后结晶温度提高, 可以在100~118 ℃温度区间内迅速结晶. 同时, 研究了自成核处理后样品在100～104 ℃范围内的等温结晶行为、动力学过程及熔融行为. 结果表明, 随着等温结晶温度的升高, 结晶速率变慢, 熔融曲线出现多重熔融峰. Hoffman-Weeks方程分析结果表明, 自成核处理对PBS的平衡熔点没有影响. Avrami等温结晶动力学方程适合分析自成核处理样品的等温结晶动力学过程, 获得其动力学参数K与n, 其中n值偏大的原因在于自成核的样品结晶生长点增多. 根据Arrhenius方程, 计算获得PBS自成核处理后等温结晶活化能为-286 kJ/mol.     

稀土高顺式聚丁二烯等温结晶动力学及结晶形态的研究

通过稀土催化丁二烯配位聚合制备了一系列不同分子量、分子量分布及顺-1,4结构含量的稀土高顺式聚丁二烯(cis-PB),采用扫描示差量热仪法(DSC)研究了cis-PB在-18~-27℃范围内等温结晶过程,采用配有在线冷热台的偏光显微镜(POM)观测结晶形态.结果表明,在cis-PB等温结晶过程中,Avrami指数(n)在2.0~3.0之间,呈现三维球晶的生长方式,与微观结构参数及结晶温度无关,但其球晶尺寸与微观结构有关,并随着顺-1,4结构含量升高而增大;当顺-1,4结构含量小于98.4%时,半结晶期(t1/2)随其含量增加而缩短,结晶速率加快,但若其含量继续增加至99.0%左右时,结晶速率反而有所降低;若同时提高聚合物分子量及顺-1,4结构含量或者在分子量及顺-1,4结构含量相近的前提下使分子量分布变窄,均有利于提高结晶速率;随顺-1,4结构含量增加,过冷度(ΔT)增加,结晶驱动力增大;结晶活化能(ΔE)为负值,降低结晶温度有利于提高结晶速率,当顺-1,4结构含量大于98.2%时,ΔE值接近(~-137 k J/mol),结晶速率对温度的依赖程度相近.     

Isothermal Crystallization Kinetics and Crystalline Morphologies of Poly(butylene adipate-co-butylene 1,4-cyclohexanedicarboxylate) Copolymers

In this study, the isothermal crystallization kinetics and crystalline morphology of poly(butylene adipate-co-butylene 1,4-cyclohexanedicarboxylate)(PBAC), which refers to a copolyester containing a non-planar ring structure, were investigated by differential scanning calorimetry and polarized optical microscopy, and compared with those of neat poly(butylene 1,4-cyclohexanedicarboxylate)(PBC). The results indicate that the introduction of butylene adipate(BA) unit into PBAC did not change the intrinsical crystallization mechanism. But, the crystallization rate and ability, and equilibrium melting temperature of PBAC copolymers were reduced. All PBC and PBAC copolymers could only form high density of nucleation from melt at given supercooling, while no Maltese cross or ring-banded spherulites could be observed. PBAC copolymers with a high amount of BA unit became amorphous after quenching with liquid nitrogen from melt, while PBC and PBAC copolymers with a low amount of BA unit could still form a large amount of nuclei under the same treatment.     

Kinetics of Isothermal Crystallization of the Thermotropic Polyester Poly(ethylethylene-4,4-diphenoxyterephthalate)

Differential scanning calorimetry was used to study the isothermal kinetics of three-dimensional ordering formation from the mesophase of the thermotropic polyester poly(ethylethylene-4,4-diphenoxyterephthalate). An Avrami exponent of 4 was found and the measured rates of transformation were related with the efficiency of packing. A nucleation and growth process was assumed in the determination of the temperature coefficient, and the interfacial free energies are discussed in terms of the chain flexibility. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Crystallization Kinetics on Microstructure and Charge Transport of Polythiophenes

We have examined the effects of crystallization kinetics of poly(3‐hexylthiophene) and poly[2,5‐bis(3‐hexadecylthiophen‐2‐yl)thieno(3,2‐b)thiophene] on microstructure and charge transport. Rapid crystallization increases the density of tie molecules in polythiophenes. As a consequence, ordered regions are better connected resulting in higher charge carrier mobilities. Our results suggest that controlling the crystallization kinetics might be an important factor for maximizing the charge mobility in semicrystalline polythiophene thin films.     

A Monte Carlo Simulation of Homogeneous Crystallization in Confined Spaces: Effect of Crystallization Kinetics on the Avrami Exponent

Homogeneous nucleation in polymers and subsequent crystallization in spaces confined relative to spherulitic dimensions in one direction has been simulated for a wide range of nucleation and growth rates. An empirical equation based on simulation results relating an Avrami exponent of crystallization to growth and nucleation rates along with the characteristic dimension of crystallizing volume has been proposed. It was found that for ideal homogeneous crystallization, the Avrami exponent can be significantly lower than the anticipated values for free unconstrained growth; therefore, all crystallization conditions and parameters must be taken into account in order to make a conclusion on the character of the observed crystallization.

     

Isothermal and Non-Isothermal Crystallization Kinetics and Morphology of Poly(trimethylene terephthalate)/Multiwalled Carbon Nanotube Composites

Summary: Multiwalled carbon nanotubes (MWCNTs) synthesized using chemical vapor deposition method were dispersed in poly(trimethylene terephthalate) (PTT, Mv = 88,000) by melt compounding technique using DMS microcompounder. The nanocomposites consisting of varying amounts of MWCNTs were characterized by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effect of carbon nanotubes on the crystallization behavior (under isothermal and non isothermal crystallization conditions) of PTT was studied using DSC. The presence of carbon nanotubes didn't show any significant effect on crystallization temperature of PTT matrix under non-isothermal conditions. Crystallization studies under isothermal conditions were carried out at different temperatures i.e 185, 190, 195 and 200 °C. Complete crystallization was observed within 60 sec at 185 °C whereas at 200 °C, longer time was required for complete crystallization. Crystal growth was also investigated using hot stage polarizing microscope (PLM). The effect of annealing time at 200 °C was investigated in the presence as well as in the absence of varying amounts of MWCNTs. Spherulitic growth was seen and the spherulite size in all the samples increased with annealing time. Morphological characterization using SEM and TEM showed a uniform dispersion of MWCNTs and poor compatibility with PTT matrix.     

晶化温度对SAPO-34结构稳定性的影响

用二乙胺结构导向剂, 分别在473和573 K水热晶化得到两种SAPO-34分子筛材料. SEM和XRD结果表明, 晶化温度升高, SAPO-34晶粒增大, 结晶度提高, 比表面积和孔径增大. 升高晶化温度, 提高了样品的最高焙烧和水蒸汽热处理承受温度.     

Temperature Effect on the Lithium Electrode Kinetics

The effect of temperature on the kinetics of processes occurring on metallic lithium covered by an ion-conducting passive film, in contact with a LiClO₄ solution in propylene carbonate, is studied by the pulsed voltammetry method. Symmetrical anodic and cathodic polarization curves for a lithium electrode in the temperature range –35 to 80°C include a portion of ohmic current j _ohm caused by intrinsic ionic conductivity of the passive layer. Following an increase in overvoltage E, the j _ohm portion is replaced by a portion of injection current j _inj with a characteristic exponential dependence j _inj E ⁿ, where n 2 and varies with temperature. The reason for this is presumed to be some structural imperfectness (structural disordering) of the passive-layer material, which leads to the emergence of dispersions in the hop distances and heights of energy barriers for charge carriers. When calculating a current–voltage curve, stochastic charge carrier transport in a disordered solid, which is characterized by a wide dispersion of times of interpoint hops, leads to the exponential function j _inj E ⁿ with n depending on temperature as follows: T: n = 1 + (a – b/T)^–2. Experimental data nicely fit this model. Comparing experimental j vs.E curves with theoretical equations permits the determination of a set of microscopic transport parameters, which include the average hop distance and effective localization radius of the charge, the frequency of attempts at hopping, and the average energy-barrier height.     

聚氯乙烯等温燃烧反应动力学

聚氯乙烯等温燃烧反应动力学;PVC;燃烧反应;化学动力学     

聚合物结晶动力学

本文介绍了聚合物等温及非等温结晶动力学过程的理论和实验方法，对影响动力学过程的一些因素进行了讨论。