聚对苯二甲酸乙二醇酯-双酚A型聚碳酸酯共混体系中聚合物伸直链晶体的形态分析

利用扫描电子显微镜(SEM)和原子力显微镜(AFM)等表征手段,研究了聚对苯二甲酸乙二醇酯-双酚A型聚碳酸酯(PET-PC)共混物的高压结晶样品。研究发现共混体系中存在具备不同形态特征的伸直链晶体,其中包括楔形晶体、弯曲晶体以及楔形弯曲晶体。通过对这些晶体的形态观察,揭示出体系中大尺寸聚酯伸直链单晶体的增厚生长首先要经历形成折叠链晶核的成核阶段,然后才是在酯交换反应和链滑移扩散两种机制共同作用下的等温增厚的链伸展过程。有助于深入理解PET-PC共混物中伸直链单晶体生长过程的本质因素,以便在类似聚合物体系中合成大尺寸的同类晶体。     

高密度聚乙烯（HDPE）在静高压下的结晶研究

 高密度聚乙烯（HDPE）在1~2 GPa的静高压下发生熔体结晶。实验中HDPE从熔融态以5 ℃/min的速率冷却。对经过高压处理后的样品在大气压下进行了DSC，SEM和WAXD测量。测量结果表明，高压后的HDPE的结晶度由原来的68.2%提到89.9%。<100>方向的伸直链晶体的存在，静高压和温度的控制是形成PE伸直链晶体的关键。     

高压下尼龙1010-单壁碳纳米管复合材料的结晶行为

 采用XKY-6×1200MN型六面顶压机,在不同温度、压力条件下处理30 min后制备了尼龙1010(PA1010)-单壁碳纳米管（SWCNT）复合材料的高压结晶样品,通过X射线衍射（XRD）、差热分析仪（DSC）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）,研究了高压处理样品的结晶行为、结构变化及形貌特征。结果表明：在1.0~2.5 GPa压力下,属于高压熔体结晶;在3.0和4.5 GPa压力下属于高压退火处理;高压结晶或高压退火均有助于聚合物片层晶体的增厚,并且高压熔体结晶的增厚效果优于高压退火处理。XRD结果表明,PA1010的三斜晶型在高压处理后保持不变,高压熔体结晶或高压退火都可以使(100)晶面和(010)晶面间距减小,即高压处理致使聚合物分子链紧密堆积。DSC结果表明：在高压熔体结晶过程中,升高压力和温度可以得到片层厚度较大的PA1010晶体;在2.0 GPa、350 ℃下获得的高压结晶样品的熔点和结晶度最高,分别达到208.5 ℃和64.6%。SEM和TEM结果表明：与常压结晶样品相比,高压结晶样品内部出现c轴厚度超过150 μm的大尺寸晶体;SWCNT与PA1010基体之间形成相互穿插的网络结构,刚性的SWCNT作为高压成核剂促进PA1010晶体生长和增厚。     

高压下聚酰胺-6结晶行为的研究

 用自制高压装置，对聚酰胺-6（PA6）在常压至1.2 GPa压力下熔体的结晶行为进行了研究。通过差示扫描量热（DSC）、宽角x射线衍射（WAXD）以及扫描电子显微镜（SEM）分析发现，在特定高压条件下，生成了含伸直链晶体、结构规整的PA6材料。     

高密度聚乙烯（HDPE）在静高压下的强度研究

 高密度聚乙烯（HDPE）在1~2 GPa的静高压下发生熔体结晶。用压缩的方法对经过高压处理后的样品进行了杨氏模量的测量。测量结果表明：样品的杨氏模量随压力和结晶度的增加而增大，最大值达到1.46 GPa。伸直链晶体的形成是杨氏模量增加的重要因素。     

高压对溶液中聚左旋乳酸单晶生长的影响

采用高压技术实现了500 MPa下聚左旋乳酸(PLLA)在稀薄二甲苯溶液中的单晶生长,采用透射电子显微镜、拉曼光谱和红外光谱对样品的结晶形态和结构进行了表征,考察了高压对聚左旋乳酸单晶生长行为的影响。结果表明,在相同的结晶温度和时间下,高压结晶PLLA的单晶仍为α-型晶体,但单晶尺寸明显大于常压样品;高压环境下PLLA分子链在晶核两端的生长扩散速率不同,容易形成非对称的菱晶形态;高压影响PLLA晶体中分子链的构象分布;在单晶生长期,高压诱导有利于PLLA晶体成核,但不利于单晶生长。     

半晶态聚合物的分子动力学模拟

采用粗粒化聚乙烯醇模型,应用分子动力学方法模拟熔融态聚合物经过缓慢冷却、局部结晶形成半晶态聚合物的过程.静态结构因子的演变显示出在结晶初期小角散射强度的增大先于布拉格峰的出现,这与小角/大角X射线散射实验现象相一致.模拟得到的半晶态聚合物呈现为折叠链构成的晶区与非晶区交杂在一起的结构形态,与缨状微束结构模型相一致.研究发现在不同的冷却阶段具有不同的有序结构形成机制.从结晶温度到玻璃化温度的凝固过程中,存在分子链的伸展和伸直分子链之间平行排列两种形式的结构转变;而在玻璃化温度之后,材料的活性只允许调整伸直分子链之间的相对排列位置.     

伽马射线辐射原位强化增韧含三羟甲基丙烷三丙烯酸酯的PET/弹性体合金

在少量的交联剂三羟甲基丙烷三丙烯酸酯存在下,研究了高能伽马射线辐射对PET/弹性体（ST2000）合金的原位强化增韧效应.在PET合金熔融共混的高温下,TMPTA可与PET和ST2000的分子链发生反应,使PET和ST2000发生分子内和分子间的交联,增强界面相互作用,使得PET合金的冲击性能提高,但拉伸强度有所下降.PET合金经过高吸收剂量的伽马射线辐照后,可以原位增加体系内部弹性相和界面相的化学交联程度,进一步提升PET合金的综合力学性能.当吸收剂量为100 kGy时,样条在冲击测试条件下未发生断裂,同时拉伸强度几乎保持不变.     

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.     

Size-Frustrated Thickening Growth of Extended-Chain Crystals in a Poly (Ethylene Terephthalate)/Bisphenol A Polycarbonate Blend Under High Pressure

High-pressure crystallized blend samples of poly (ethylene terephthalate)/bisphenol A polycarbonate (PET/BAPC) were investigated with scanning electron microscopy (SEM), confocal laser micro-Raman spectroscopy, and a standard general area detector diffraction system (GADDS) X-ray micro-diffraction system. The results showed that long time annealing at high pressure could result in extended-chain polymer single crystals with thicker lamellae. However, the large size of such crystals was also found to frustrate their thickening growth along the c-axis thickness, as demonstrated by the observation of a novel wrinkled crystal. The winkled crystals with different morphologies were thought to be formed as the compromise between the kinetic pathway and the thermodynamic driving force during the size-frustrated thickening growth of the large polymer crystals. Further observations revealed that environmental confinement was the main factor responsible for the creation of the wrinkled structures in polymer extended-chain crystals. The present study may promote understanding of the fundamental nature of the crystal thickening in these binary polyester blends.     

Crystallization and dissolution of flow-induced precursors

We make use of a specially synthesized linear high density polyethylene with a bimodal molecular weight distribution (MWD) to demonstrate that it is possible to produce a suspension of extended-chain (shish) crystals only. Such a suspension can be generated at high temperatures, above but close to the equilibrium melting temperature of the unconstrained extended-chain crystals (T(m)(0)=141.2 degrees C) and requires stretch of the longest chains of the MWD. After the application of a shear flow of 120 s(-1) for 1 s at 142 degrees C, x-ray scattering suggests the presence of a large number of metastable needlelike precursors with limited or no crystallinity. Precursors that are too small dissolve on a timescale that correlates perfectly with the reptation time of the longest polymer molecules. Whereas, precursors that exceed a critical size crystallize forming extended-chain shishes.     

THE HIGH-PRESSURE CRYSTALLIZATION AND ANNEALING BEHAVIORS OF POLYETHYLENE TEREPHTHALATE OLIGOMER

Polyethylene terephthalate (PET) oligomer samples crystallized and annealed at high pressure were investigated with differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The results showed that better crystals were obtained through high-pressure crystallization from the melt than annealing under the same conditions. The difference of the effects of crystallization and annealing on the morphology of crystals reduced with the increase of crystallization time. The melting temperature was determined by the lamellar thickness when it was shorter than the length of the molecular chains, while the main factor governing the melting temperature changed from lamellar thickness to density of chain-end defects when the lamellar thickness was much longer than the molecular length. PET oligomer extended-chain crystals with thickness up 100 μm were obtained.     

Stacked-Lamellar Structure in High-Speed Spun PET Fibers as Revealed by TEM

Morphological study of high-speed spun poly(ethylene terephthalate) (HSS-PET) fibers spun at 6 km/min was performed by a combination of alkaline etching, surface replica method, and transmission electron microscopy. In the two-stage replica of the alkaline-etched fiber, the stacked-lamella-like structure was observed, in which lamella-like striations were stacked in a direction leaning at about 40° away from the fiber axis. The spacing between the adjacent striations, namely the lamellar periodicity, was measured to be 10–30 nm. We have proposed that the stacked-lamellar structure, which is mainly composed of mosaic lamellar crystals and has the extended-chain crystals connecting the adjacently stacked lamellae, is an appropriate model for the fiber structure of HSS-PET fibers.     

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.     

Isolation of extended-chain crystals from high-pressure crystallized polyethylene by selective dissolution

In recent years the formation of extended-chain crystals has received increasing attention, and a number of mechanisms for it have been proposed [1–5]. These mechanisms are classified into two groups, one being the thickening of folded-chain crystals [1, 2] and the other being the direct formation of extended-chain crystals from the melt [3–5]. In order to clarify the mechanism, it is necessary to study the microstructure of the isolated extended-chain crystals in detail. In this paper the isolation of the extended-chain crystals from high-pressure crystallized polyethylene by selective dissolution of folded-chain crystals is described.     

The role of the amorphous fraction for the equilibrium shape of polymer single crystals

The equilibrium state of polymer single crystals is considered by explicitly taking into account the amorphous fraction formed by loops and tails of the chains using a statistical model introduced by Muthukumar (Philos. Trans. R. Soc. London, Ser. A 361, 539 (2003)). We show that under realistic conditions below the equilibrium melting temperature, tight loops and close re-entries are favored, and that the amorphous fraction can be mapped into an excess surface free energy. The model is extended to many-chain crystals where it is shown that the lamellar thickness increases with the number of chains in the crystal and extended-chain conformations are thermodynamically favored if the number of chains in the crystal is sufficiently large. The number of chains necessary to form an extended-chain crystal in thermodynamic equilibrium scales with the square of the degree of polymerization of the chains. We discuss the temperature behavior of the equilibrium crystal thickness in the under-cooled state.     

Study on hydrophilicity of polymer surfaces improved by plasma treatment

Surface properties of polycarbonate (PC), polypropylene (PP), polyethylene terephthalate (PET) samples treated by microwave-induced argon plasma have been studied with contact angle measurement, X-ray photoelectron spectroscopy (XPS) and scanned electron microscopy (SEM). It is found that plasma treatment modified the surfaces both in composition and roughness. Modification of composition makes polymer surfaces tend to be highly hydrophilic, which mainly depended on the increase of ratio of oxygen-containing group as same as other papers reported. And this experiment further revealed that CO bond is the key factor to the improvement of the hydrophilicity of polymer surfaces. Our SEM observation on PET shown that the roughness of the surface has also been improved in micron scale and it has influence on the surface hydrophilicity.     

双层深度编码探测器的晶体表面优化

设计了双层LSO晶体和位置灵敏型光电倍增管耦合构成的用于小动物PET成像的 深度编码探测器. 众所周知, 晶体的不同的表面处理影响着光输出量, 进而影响着它们构建的PET探测器的性能. 为了优化设计的深度编码探测器的性能, 测试了两种不同表面处理的LSO闪烁晶体阵列探测器的晶体分辨能力及其能量、时间和空间分辨率, 结果表明, 光滑表面LSO晶体构建的深度编码探测器显示出良好的空间、能量及时间分辨特性.