均聚物结晶与熔融化转变的稳态和亚稳态统计理论Ⅴ 分子分凝统计结晶动力学—结晶增长速率对结晶生长机制和高聚物起始结构的依赖性

首先对结晶增长速率同浓度、分子量和链柔性依赖性进行总结,然后基于微晶核和粒———高分子键组网络结构模型和高分子分子分凝统计结晶动力学,根据高分子链组是微晶粒同连接链段复合体的结构特征及它们间存在的四个相关性(并存性、简并性、顺反式构象共存性和物料守恒性)的事实,成功地把连接链段缩短增长动力方程同微晶粒体积增大增长动力方程有机结合在一起,从理论上创建出一种微晶粒数增长速率和微晶粒尺寸增长速率表达的一般化计算法,推导出结晶体系的微晶粒数增长速率和微晶粒尺寸增长速率同四种增长机制(近邻折叠,近邻伸直,近邻折叠同近邻伸直并联并存和近邻折叠同近邻伸直串联并存)、结晶温度和高分子起始结构(分子量)间定量表达式.当把分子量的指数同链的构象分数相连后,就又从理论上得到了分子量指数同温度和链柔性间的关系式,并讨论了它们同增长机制间的关系.最后以大量结晶动力学实验数据对上述所得到的关系式进行了验证,结果表明它们均能同实验结果很好符合.     

均聚物结晶与熔融化转变的稳态和亚稳态统计理论Ⅵ. 分子分凝统计结晶动力学-结晶增长速率对结晶生长机制和溶液浓度和的依赖性

首先对结晶增长速率同浓度和链柔性依赖性进行总结,然后基于微晶核和粒———高分子键组网络结构模型和高分子分子分凝统计结晶动力学,根据高分子链组是微晶粒同连接链段复合体的结构特征及它们间存在的四个相关性(并存性、简并性、顺反式构象共存性和物料守恒性)的事实,成功地把连接链段缩短增长动力方程同微晶粒体积增大增长动力方程有机结合在一起,从理论上创建出一种微晶粒数增长速率和微晶粒尺寸增长速率表达式的一般化计算法,推导出结晶体系的微晶粒数增长速率、微晶粒尺寸增长速率同四种增长机制(近邻折叠,近邻伸直,近邻折叠同近邻伸直并联并存和近邻折叠同近邻伸直串联并存)、结晶温度和和结晶浓度间定量表达式.当把浓度指数同链的构象分数相连后,就又从理论上得到了浓度指数同温度和链柔性间的关系式,并讨论了它们同增长机制间的关系.最后以大量结晶动力学实验数据对上述所得到的关系式进行了验证,结果表明它们均能同实验结果很好符合.     

均聚物结晶与熔融化转变的稳态和亚稳态统计理论Ⅲ．分子分凝统计结晶动力学～熔体内结晶增长速率的一般化表征和它们对生长机制的依赖性

首先对微晶粒尺寸增长速率的表征进行总结．从微晶核和粒-高分子链组网络结构特点(高分子链组是微晶核和微晶粒同连接链段的复合体)同增长速率间的三个相关性的特征：①晶核和晶粒加大同连接链段缩短的并存性；②微晶核和粒表面上连接链段的缩短机制存有简并性；③微晶粒内和粒表面上stem的反顺式构象共存性出发．建议了一种评估和计算微晶粒尺寸增长速率的新方法和原则，基于该种计算方法和原则用统计力学和动力学相结合法推导出了高分子熔体内几种不同结晶生长机制(近邻折叠、近邻伸直分凝和近邻折叠同近邻伸直分凝并存等生长方式)下微晶粒-高分子链组中微晶粒数增长速率和微晶粒尺寸增长速率动力学方程．     

均聚物结晶与熔融化转变的稳态和亚稳态统计理论III. 分子分凝统计结晶动力学～熔体内结晶增长速率的一般化表征和它们对生长机制的依赖性

首先对微晶粒尺寸增长速率的表征进行总结.从微晶核和粒—高分子链组网络结构特点(高分子链组是微晶核和微晶粒同连接链段的复合体)同增长速率间的三个相关性的特征: ①晶核和晶粒加大同连接链段缩短的并存性; ②微晶核和粒表面上连接链段的缩短机制存有简并性; ③微晶粒内和粒表面上stem的反顺式构象共存性出发.建议了一种评估和计算微晶粒尺寸增长速率的新方法和原则,基于该种计算方法和原则用统计力学和动力学相结合法推导出了高分子熔体内几种不同结晶生长机制(近邻折叠、近邻伸直分凝和近邻折叠同近邻伸直分凝并存等生长方式)下微晶粒—高分子链组中微晶粒数增长速率和微晶粒尺寸增长速率动力学方程.     

均聚物结晶与熔融化转变的稳态和亚稳态统计理论Ⅳ 分子分凝统计结晶动力学~结晶增长区域的区划和它们对温度和生长机制的依赖性

首先对高分子结晶增长动力学的实验规律进行全面总结,并指出了当前高分子结晶增长动力理论中存在的难题.然后按我们建议的评估微晶粒尺寸增长速率的新方法推导出了四种不同微观生长机制(折叠、伸直、折叠同伸直并联并存和折叠同伸直串联并存等方式)下微晶粒高分子链组的微晶粒尺寸增长速率定量表征式,又导出了四种不同生长机制下微晶粒尺寸增长速率同结晶温度和过冷温度间关系的表达式.根据四种不同微观生长机制同宏观增长方式差别和它们出现的结晶温度同过冷温度之积值高低,可把结晶动力学的结晶增长区域图中三组交叉线区划为三个不同增长区域,最后又根据三个增长区的理论关系式讨论了增长区中晶体形貌同结晶温度和过冷温度间的相关性,其理论预测能同近期实验观测基本符合.     

均聚物结晶与熔融化的稳态和亚稳态转变统计理论

基于多重微晶网络结构模型和分子分凝机制建立了高分子晶体的微晶核 和微晶粒 高分子链组模型 ,推导出了平衡态下高分子预结晶动力学方程 ,计算出了平衡态下不同尺寸微晶核 和微晶粒 高分子链组的几率分布函数 .建立了非稳态下不同尺寸的微晶核 高分子链组的成核演化方程和微晶粒 高分子链组的增长演化方程 ,求解一般状态下的两个演化方程后 ,得到了不同时间和不同尺寸的微晶核 和微晶粒 高分子链组的一般密度分布函数 .最后根据成核自由能和增长自由能对晶核和晶粒的尺寸大小的依赖性 ,提出了微晶核 高分子链组和微晶粒 高分子链组存在稳定性的热力学条件和动力学条件 ,成功地表征为三个特征区 (稳态、亚稳态和非稳态 )     

PCL/SiO2杂化纳米相微结构与晶态成核生长特性

应用扫描电子显微镜、广角X射线衍射和差示扫描量热手段研究了有机高分子/无机组分间以物理次价力(氢键)键合的高分子量PCL/SiO2杂化材料纳米相微结构和PCL高分子链在该微结构环境中的结晶成核生长特性及其影响因素.研究结果表明:杂化体系中高分子/无机组分间的微相分离尺度在纳米数量级,高分子微区的平均相畴尺寸在70nm左右,无机相形态呈现不规则的颗粒状.两相均匀分布程度与体系中组分间的氢键键合强度有关.PCL杂化后结晶度减小,对应的微晶尺寸明显改变,平衡熔点随无机组成含量的增加而下降.高分子链在晶核表面折叠形成结晶结构所需的能量增加.这一结果归因于无机非晶SiO2和键合强度的影响.     

高压结晶PET/PC共混体系中大尺寸聚合物伸直链晶体的形态观察

 大尺寸聚合物伸直链晶体在低维体系物理学的研究中具有不可替代的重要作用。但以往高压合成的聚合物伸直链晶体，尺寸较小且合成时间过长，使其作用至今未能显现。加入10%（质量分数）聚碳酸酯（PC）于聚对苯二甲酸乙二醇酯（PET）中，在研究PET/PC共混体系高压结晶行为的过程中快速合成了大量生长厚度超过100 μm 的聚合物伸直链晶体，并采用扫描电子显微镜对其进行了深入研究。研究表明，高压结晶PET/PC共混体系中存在不同类型的大尺寸伸直链晶体：完善的伸直链晶体、沿平行或垂直于C轴方向发生断裂的伸直链晶体、内聚能密度较大而发生内聚破裂的伸直链晶体、不同断裂方式下呈不同形态的楔形状伸直链晶体以及弯曲的伸直链晶体。同时对不同形态伸直链晶体的形成机理作了阐述。     

冷却速率对温敏聚N-异丙基丙烯酰胺胶体结晶过程的影响

冷却速率对结晶过程具有重要的影响. 本文采用温敏poly-N-isopropylacrylamide (PNIPAM) 胶体晶体体系实时观察了冷却速率对结晶晶粒尺寸的影响. 通过高倍透射明场观察和Bragg衍射观察研究连续冷却下的晶粒形核和生长实时演化过程, 发现随着冷却速率的增加, PNIPAM胶体晶体晶粒尺寸不断减少. 晶粒尺寸与冷却速率符合幂指数关系, 与金属体系具有相似的演化规律.     

Correlation of Cooperatively Localized Rearrangement on the “Fluidized Domain” of Polymers to Their Nonexponentially Viscoelastic Behaviors at Double Aging Processes (I): A Set of Reduced Universal Equations on the Stress Relaxation Modulus and Creep Comp

基于α-和β-微区、微晶、交联和缠结链组网络结构和非线性粘弹性复相涨落模型,提出了双重(物理和力学)老化下不同尺寸和末端向量高分子链组的流动化微区内关联性局部化重排动力学新理论,它能把初级α-微区的降解作用和次级β-微区的再生效应对剪切速率、尺寸大小和温度依赖性有机结合起来．然后用统计力学和动力学结合法计算了三种不同类型高聚物在等温等压双重老化过程中多元链组的总构象改变自由能,证实了它起源于多元链组的尺寸大小、形状和体积的变化．推导出了它们单向拉伸下的本构方程、应力松弛模量和蠕变柔量表征式以及它们相对应的两组对比态普适方程．结果表明该两组对比态下应力松弛模量和蠕变柔量普适方程均具有同K-W-W伸展指数函数完全一致的形式．最终又建立了该两组对比态普适方程中三个分子参数同老化条件、温度和高聚物起始结构之间的相关性．     

Crystallization of an Entangled Ring Polymer: Coexistence of Crystal and Amorphous Regions

We discuss a molecular model of crystallization of a quenched ring polymer of a fixed knot type. Crystallized ring polymers contain not only crystal regions but also amorphous regions consisting of highly entangled chain configurations that could not be obtained simply by folding the polymer chains. In the crystallization process, the growth of a lamella region is accompanied by the reduction of a locally entangled region of the polymer chain. The model should effectively describe the separation and formation processes of amorphous and crystal regions in polymer crystallization. Here, the knot type of an initial configuration of the ring polymer is conserved in time evolution. We find that the average fraction of amorphous regions in the ring chain does not depend on the knot type or the chain length.     

Theoretical analysis of the effect of crystallization temperature on structure formation in flexible-chain polymers

Theoretical analysis of flexible-chain polymer crystallization was carried out over a wide temperature range from glass transition temperature T_g to melting temperature T_m. Temperature dependence of dynamic behavior manifesting in the decrease of crystallizing length with decreasing temperature was taken into account. The dependence of crystallizing length on temperature was obtained using chosen values of it at T_g and T_m. The crystallization with the formation of folded-chain crystals (type I) and uncoiled-chain crystals (type II) was considered. The analysis of thermodynamical favorability of both types of crystals with respect to temperature made it possible to obtain a flexible-chain crystallizing polymer phase diagram. This diagram shows the existence of two ranges where type II crystal formation is more favorable: a narrow range near T_m and the wider one near T_g, separated by the temperature range of crystallization with chain folding. Temperature dependences of type II crystals fraction in the system and their size were calculated. It is shown that the crystallization at considerable supercooling leads to the appearance of a great number of type II small crystals connected by tie chains. The system formed is characterized by a high degree of crystallite interconnection.     

Investigation on the Self-nucleation Behavior of Controlled-rheology Polypropylene

Self-nucleation (SN) behavior is one of the most fascinating behaviors of semicrystalline polymers; it is of great scientific and practical importance. In this study, the crystallization and melting behavior of a series of controlled-rheology polypropylene (CRPP) with different molecular weights were studied by differential scanning calorimetry (DSC) scanning and successive self-nucleation and annealing (SSA) fractionation, and their self-nucleation behavior was studied according to the conventional SN measurement, in order to provide a new understanding on the relationship between the molecular weight and the SN behavior of polymers. The results of DSC scanning and SSA fractionation showed that the decrease of molecular weight led to higher molecular chains mobility, making the crystallization temperature higher and the crystalliation peak narrower; in addition, it significantly restrained the formation of thick lamellae. The results of SN measurements showed that both the upper and lower temperatures of the samples decreased as the molecular weight decreased, which was suggested to be closely related to the reduction of the formation of thick lamellae. The related mechanism is discussed, and it was found that the key parameter determining the occurrence of SN and annealing of CRPP was the ability to form thick lamellae with high melting point, which might be related to the ability for ordered structures to persist at high temperature.     

Morphology,Crystallization, and Melting of Single Crystals and Thin Films of Star‐branched Polyesters with Poly(ϵ‐caprolactone) Arms as Revealed by Atomic Force Microscopy

The morphology and thermal stability of different sectors in solution‐ and melt‐grown crystals of star‐branched polyesters with poly(?‐caprolactone) (PCL) arms, and of a reference linear PCL, have been studied by tapping‐mode atomic‐force microscopy (AFM). Real‐time monitoring of melt‐crystallization in thin films of star‐branched and linear PCL has been performed using hot‐stage AFM. A striated fold surface was observed in both solution‐ and melt‐grown crystals of both star‐branched and linear PCL. The presence of striations in the melt‐grown crystals proved that this structure was genuine and not due to the collapse of tent‐shaped crystals. The crystals of the star‐branched polymers had smoother fold surfaces, which can be explained by the presence of dendritic cores close to the fold surfaces. The single crystals of linear PCL grown from solution showed earlier melting in the {100} sectors than in the {110} sectors, whereas no such sectorial dependence of the melting was found in the solution‐grown crystals of the star‐branched polymers. The proximity of the dendritic cores to the fold surface yields at least one amorphous PCL repeating unit next to the dendritic core and more nonadjacent and less sharp chain folding than in linear PCL single crystals; this evidently erased the difference in thermal stability between the {110} and {100} sectors. Melt‐crystallization in thin polymer films at 53–55°C showed 4 times faster crystal growth along b than along a, and more irregular crystals with niches on the lateral faces in star‐branched PCL than in linear PCL. Crystal growth rate was strictly constant with time. Multilayer crystals with central screw dislocation (growing with or without reorientation of the b–axis) and twisting were observed in both classes of polymers.     

Synergistic Effects of Polyethylene Glycol and Polyhedral Oligomeric Silsesquioxanes on Crystallization Behavior of Poly(L-lactide)

The synergistic effects of poly(ethylene glycol) (PEG) and polyhedral oligomeric silsesquioxanes (POSS) on the crystallization behavior of semicrystalline poly(L-lactide) (PLLA) were systemically investigated using differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Initially, the influences of PEG and POSS, individually, on PLLA crystallization were studied. The results indicated that PEG, as an efficient plasticizer, enhanced the mobility of the PLLA chains, resulting in decreasing of the glass transition temperature. The enhanced crystallization capacity of PLLA was strongly dependent on the molecular weight and content of the PEG, increasing with decreasing of the molecular weight and increasing of the PEG content. The experimental results also indicated that POSS was a heterogeneous nucleating agent, promoting the crystallization of PLLA. The synergistic effects of PEG and POSS on PLLA crystallization were then analyzed. The results showed that in the presence of PEG and POSS the crystallinity of PLLA was further enhanced due to their synergistic effects.     

Thermorheology and Crystallization Behaviors of Polyethylenes: Effect of Molecular Attributes

Correlations between polyethylenes of different compositions and branching architectures and the temperature dependence of their viscoelastic behavior as well as the dependence of the nonisothermal crystallization behaviors on the cooling rate were described. To analyze the thermorheological behavior of the various classical polyethylenes, a method proposed by van Gurp and Palmen was utilized and the classical high-pressure low-density polyethylene (LDPE) was found to be thermorheologically complex, while for high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE), thermorheological simplicity was observed. The Avrami and Mo methods were applied to describe the nonisothermal crystallization kinetics of the different PEs for various cooling rate. The values of the kinetic parameter F(T), kinetic crystallization rate constant (Z_c), and half-time of crystallization (t_1/2) indicated that long-chain branching (LCB) had the role of being a heterogeneous nucleating agent and accelerated the crystallization of polyethylene. Moreover, an HDPE sample of both high molecular weight (M_w) and molecular weight distribution (MWD) had a different crystallization rate dependence from the other samples at various corresponding cooling rates. The crystallization activation energy for nonisothermal crystallization of different PEs was determined using the Kissinger method and showed that the presence of LCB as well as high M_w can increase the crystallization activation energy of polyethylene.