双向拉伸聚丙烯薄膜shish-kebab结构的辐照劣化模型研究

高能射线辐照会导致电容器储能介质发生交联和降解等化学变化,进而影响到电容器的宏观电气性能和应用性能。该文以双向拉伸聚丙烯(biaxially oriented polypropylene,BOPP)薄膜典型的串晶结构(shish-kebab)为对象,研究了γ辐照积累剂量D对分子链结构和结晶特性的影响,建立了辐照劣化模型。研究结果表明,当D<10 kGy时,辐照交联和降解反应同时发生且程度相当,结晶度和大分子含量均无明显变化;当D≥10 kGy时,辐照降解反应占主导,shish晶逐渐被破坏,结晶度和大分子含量逐渐下降;当D=1000 kGy时,shish-kebab结构几乎完全破坏,薄膜内主要为片晶和无定形结构。该模型描述了γ辐照下shish-kebab结构的劣化过程,为聚合物晶体结构的辐照老化机理研究提供参考。

SYNTHESIS AND PROPERITIES OF SHISH-KEBAB-TYPE LIQUID CRYSTALLINE POLY(p-PHENYLENE)S

Abstract The novel shish-kebab-type liquid crystalline poly（p-phenylene）s were synthesized through Suzuki coupling reaction from 2,5-bis[（4-n-alkoxyl）benzoyloxy]1,4-dibromobenzene （monomer 1） and 1,4-benzenediboronic acid bistrimethylene cyclic ester （monomer 2）. Their structure and properties were characterized by GPC, DSC, X-ray diffraction and polarizing optical microscope （POM）. It was found that the polymers turned to liquid crystalline phase above their melting point. The melting point （Tm） of the polymers decreases when the length of the alkoxy tails of the mesogenic units increases. The mesophase was identified by X-ray diffraction method. The polymers could dissolve in common organic solvents and show strong blue fluorescence. The maximum absorption bands of polymers prepared from annealed films have large red-shift due to the spontaneous orientation of the liquid crystalline side chains. The same phenomena were also observed in the fluorescence spectra.

PREPARATION AND CHARACTERIZATION OF SHISH-KEBAB TYPE LIQUID CRYSTALLINE POLY(p-PHENYLENEVINYLENE)

Novel shish-kebab type liquid crystalline poly（p-phenylenevinylene） derivatives were synthesized by Stille coupling reaction from 2,5-bis[（4-n-alkoxyl）benzoyloxy]1,4-dibromobenzene （monomer l） and 1,2-bis（tributylstannyl） ethylene （monomer 2）. The polymers with alkoxy groups are soluble in common organic solvents and exhibit blue fluorescence. Both the cast film and the annealed film have large red-shifts in fluorescence spectra and show yellow fluorescence. The polymers with CN and NO2 groups show poor solubility and green fluorescence. All the polymers possess liquid crystalline smectic phases. The melting point （Tm） of the polymers decreases when the length of the alkoxy tails of the mesogenic units increases. The polymers are easily aligned under a magnetic field of 10 Tesla. It is found that the conjugated backbone and LC side chain are aligned perpendicular and parallel to the magnetic field, respectively. The polymers show optical dichroism in fluorescence spectra, suggesting that they are available for advance materials with linear optical polarization.

SYNTHESIS AND CHARACTERIZATION OF NOVEL CHIRAL SMECTIC C(Sc~*) PHASE SHISH-KEBAB TYPE LIQUID CRYSTALLINE BLOCK COPOLYMERS

A new series of chiral shish-kebab type liquid crystal block copolymers that form the smectic C(Sc*) phase was synthesized by solution polycondensation. The copolymers were characterized by GPC, DSC, TG, POM, X-ray diffraction and polarimeter. The copolymers 7 entered into liquid crystal phase whin they were heated to their melting temperatures (T-m) and the copolymers 8 were in liquid crystal phase at room temperature with low viscosities. The smectic sanded texture or focal-conic texture were observed on POM. All the chiral block copolymers showed high optical activity. No racemization has happened. Temperature-variable X-ray diffraction study together with POM and polarimetric analysis realized that they are chiral smectic C(Sc*) phase. Thus we offer in this report the first example of shish-kebab type liquid crystal block copolymers that form a chiral smectic C(Sc*) phase. The variation of melting and isotropization temperatures with molecular structure was also discussed.

High-yield Synthesis of Nanohybrid Shish-kebab Polyethylene-carbon Nanotube Structure

We report a novel method to prepare nanohybnd shish-kebab （NHSK） structure of polyethylene （PE）and carbon nanotube （CNT）. Pristine CNTs without surface modification with high concentration was effectively dispersed in xylene solution by a simple shearing method, which induces the quick crystallization of PE in xylene to form a novel NHSK structure with more dense and smaller PE kebab on CNT axis. The flocculated NHSK productwas transferred quickly from the xylene solution to the ethanol solution, in order to shorten the preparation time. The freeze-drying method was used in vacuum instead of high-temperature drying to avoid the aggregation of NHSK product. These improvements allow the formation of NHSK with an absolute yield of 200 mg.h-1, which is 2000 folds of that reported previously. It is favorable to apply this structured material in high performance nano- composite, by improving the compatibility of CNTs in p polymer and the interfacial force between CNTs and polymer.

Porous Shish-Kebab Structure Prepared from Oriented UHMWPE Films by Processing in Supercritical CO_(2)

For the first time, a highly crystalline porous shish-kebab structure with a high degree of crystallinity was obtained by using a combination of two methods for the formation of porous polymeric materials. A treatment procedure using supercritical carbon dioxide(sc CO_(2))was carried out for oriented ultrahigh molecular weight polyethylene(UHMWPE) films, which provided special conditions for the crystallization of dissolved UHMWPE macromolecules on the surface of oriented UHMWPE crystals. The prepared porous materials were investigated by scanning electron microscopy(SEM) and differential scanning calorimetry(DSC). The particularity of the obtained porous shish-kebab is the absence of the amorphous phase between lamellar crystals(kebabs). The obtained pores had an oval shape, and they were oriented in the orientation direction of the UHMWPE macromolecules. The pore size ranged from 0.05 μm to 4 μm. Controlling the conditions for the crystallization of the UHMWPE macromolecules using supercritical CO_(2) gives the possibility to control the size of both lamellar disks and pores formed.

Fabrication of shish-kebab-structured carbon nanotube/poly(ε-caprolactone) composite nanofibers for potential tissue engineering applications

The electrospinning process was applied to fabricate the nanofibers of biodegradable poly(ε-caprolactone)(PCL) in which different contents of multiwalled carbon nanotubes(MWCNTs) were embedded. Afterward,the electrospun nanofibers were successfully decorated with shish-kebab structure via a self-induced crystallization technique. The topographical features and the mechanical properties of the composite scaffolds were characterized,and the biocompatibility of the material was assessed by using human osteogenic sarcoma osteoblasts(MG-63 cells). The carbon nanotube(CNT) concentration is found to affect the fiber diameter and mechanical properties of electrospun nanofibers and the periodic distance of the shish-kebab architecture. Cellular attachment and proliferation assays reveal that 0.5 wt% CNT-embedded PCL scaffold shows enhanced biocompatibility with MG-63 cells than their counterparts made of neat PCL, and the collagen-like nanotopology provided by the shish-kebab structure further facilitates the cell adhesion and proliferation. The superior interactions between cells and scaffolds demonstrate that the shish-kebab-structured CNTs/PCL nanofibers may be promising candidate for tissue engineering scaffold application.

The Influence of Ethyl Branch on Formation of Shish-Kebab Crystals in Bimodal Polyethylene under Shear at Low Temperature

Formation of shish-kebab crystals using a bimodal polyethylene system containing high molecular weight(HMW)component with different ethyl branch contents was investigated.In situ small-angle X-ray scattering(SAXS)and wide-angle X-ray diffraction(WAXD)techniques were used to monitor the formation and evolution of shish-kebab structure sheared at low temperature in simple shear mode and low rate.Only the bimodal PE with no branch formed shish-kebab crystals at the shear temperature of 129℃,and the shish length increased with the crystallization time,while bimodal PE with branch has no observable shish under the same conditions.The degree of crystallization for bimodal PE with no branch increased with time up to above 7%,while those with ethyl branch increased continually up to above 23%.Furthermore,bimodal PE's Hermans orientation factor with no branch increased to 0.60,while those with ethyl branch only increased to a value below 0.15.This study indicated that the shish-kebab crystal formed at the low temperature of 129℃is due to the stretch of entangled chains under shear for the bimodal PE with no branch.Only partly oriented lamellar crystals were formed for the bimodal PE with ethyl branch.All the results at the shear temperatures higher,closed to,and lower than the melting point,the modulation of shish crystals formation owing to different mechanisms of the coil-stretch transition and the stretched network by changing shear temperature was achieved in the bimodal PE samples.

Structure and Morphology of Poly(ε-caprolactone)Heterogeneous Shish-Kebab Structure Induced by Poly(lactic acid)Nanofibers

In recent years,the hybrid shish-kebab structure with excellent physical properties and functionalities has attracted much attention because it provides a way of blending nanofibers with different properties into polymer matrix in a regular arrangement.It is often not easy to induce the formation of the hierarchically ordered structure for the semi-crystalline polymer in heterogeneous shish-kebab structure.A poly(lactic acid)(PLA)/poly(ε-caprolactone)(PCL)heterogeneous shish-kebab structure,i.e.,the PCL crystals periodically crystallized onto PLA nanofibers,was successfully created and the interfacial crystal morphology of the PLA/PCL heterogeneous shish-kebab structure was observed using scanning electron microscopy and atomic force microscopy.NaOH aqueous solution was applied to modify the surface of the PLA nanofibers to produce adsorption sites and carboxyl groups.The total reflectance Fourier transform infrared spectroscopy(ATR-FTIR)and X-ray diffraction(XRD)results demonstrated that the formation of the heterogeneous shish-kebab structure was mainly due to the hydrogen bonding interaction between the kebab and shish interface,and the growth process of the kebab crystals also promoted the crystallization of the shish fibers.This heterogeneous nanostructure of biodegradable polymers will have great applications in tissue engineering and regenerative medicine.

LINEARLY POLARIZED WHITE FLUORESCENCE FROM SHISH-KEBAB TYPE LIQUID CRYSTALLINE POLY(P-PHENYLENEVINVLENE)S WITH(P-PHENYLENE)S AS KEBAB

Liquid crystalline （LC） polymers with a shish-kebab-type moiety on their cross-conjugated （p-phenylene）s-poly（p- phenylenevinylene）s main chains were synthesized through Gilch polymerization in order to develop a kind of polymers available for linearly polarized white-light-emitting from single chain. In this system, the 2,5-bis（4＇-alkoxyphenyl）benzene as the ＂kebabs＂ connects with poly（p-phenylenevinylene） （PPV） main chain backbone using its molecular gravity center and the PPV as the ＂shish＂ or ＂skewer＂ （the ＂shish-kebab＂）. The polymers possess desirable properties such as excellent solubility and liquid crystalline properties. To drop the ＂kebabs＂ of the 2,5-bis（4＇-alkoxyphenyl）benzene into the orientation microgroove of aligned polyimide film, not only the ＂shish＂ of polymer main chain can be aligned by the virtue of orientation of ＂kebabs＂ but also the uniform cross-conjugated structure between the ＂kebabs＂ and ＂shish＂ can be broken. Then, the alignment of the polymer main chain showed yellow light emission and was also accompanied by orientation of the LC side chains showing blue light emission, this gave rise to a notable linearly polarized white fluorescence.

聚丙烯在单向拉伸力场中形成双向自增强片材及其结构与性能的研究

采用普通挤出设备 ,在机头内 ,于单向拉伸应力场中实现了聚丙烯片材的双向自增强 ,纵向拉伸强度提高了 6.33倍 ,横向拉伸强度提高了近 1倍。同时纵横向拉伸强度表现出同步增长的趋势 ,其值随机头收敛角的不同而变化。运用 SEM、DSC等测试手段对微观结构进行表征 ,揭示出试样内形成了串晶啮合结构 。

高耐压HDPE自增强管挤出系统及试样的结构与性能

本文针对管件在输送压力流体时的特殊应力状态，提出了管材周向自增强的构想，据此设计出了自增强挤出系统．该系统利用芯棒旋转，使大分子链沿管周向取向并在适当的压力、温度条件下生成串晶结构，从而大大提高了管材的周向强度及模量．利用ＤＳＣ、ＷＡＸＤ和ＳＥＭ等检测手段对试件的凝聚态结构进行分析。

在低频振动场中注射成型HDPE试样的力学性能及其形态控制

利用自行研制的低频振动注射实验装置探讨HDPE振动注射试样力学性能和微观形态之间的关系 .实验中对常规注射和振动注射成型的试样力学性能和微观形态进行了对比实验 .SEM实验结果显示 ,振动注射制件芯层的形态由常规注射的球晶转变为垂直于振动波传递方向排列的片晶结构 ,在剪切层中同时存在串晶或柱状堆砌的片晶结构 .频率的改变 (0 <f <2 33Hz)使晶粒细化 ,片晶有一定程度的取向 ,剪切层中的结晶度由常规注射时的 5 9 77%增加到振动注射时的 6 7 6 7% ,芯层的结晶度更是得到 13 6 5 %的提高 ,有利于充分挖掘材料的综合力学性能 ;振动压力幅度 (0 <PA <5 9 4MPa)的增加则能明显地使片晶取向 ,片晶厚度增加 ,剪切层和芯层中的结晶度都有 2 %左右的增加 ,材料的拉伸强度提高 ,伸长率变小 .

单向拉伸流场中挤出双向自增强透明HDPE管材

采用普通的工业用挤出设备,通过对加工参数的特殊控制,在单向拉伸流场中制得透明双向自增强高密度聚乙烯管材,其轴向拉伸强度比普通高密度聚乙烯管材提高了3.2倍,周向拉伸强度提高了1.4倍。利用SEM、DSC等测试手段对管材的微观结构进行了表征,揭示了管材双向自增强的原因是形成了串晶互锁结构,管材透明的原因是晶粒尺寸比可见光的波长小。

超薄微注塑等规聚丙烯制品形态结构及注射速度的影响分析

针对100μm和200μm厚的2种超薄微制品,采用单因素实验,对等规聚丙烯微注塑制品的形态结构进行研究,并分析注射速度对超薄微注塑制品形态结构的影响。研究结果表明,超薄微注塑制品中呈现出2种典型的形态结构,200μm微制品厚度方向呈现出纯剪切层的无芯结构,剪切层内为明显的Shish-Kebab结构;100μm厚微制品内部形态为含大比例柱晶结构的皮芯结构;广角X射线衍射结果显示无芯结构内形态沿流动方向呈现高度取向,且β晶含量微弱。含柱晶层皮芯结构的取向也较明显,且结构中有明显β晶存在。注射速度对超薄微注塑制品的形态结构、结晶度和取向度都有重要的影响,存在临界注射速度,当注射速度小于该临界速度时,制品内部结晶度、取向度随着注射速度的提高而提高。

聚合物气体辅助注射成型制品的形态结构

作为一种由常规注射成型发展起来的聚合物加工技术,气体辅助注射成型具有节约原材料、缩短成型周期以及提高制品性能等优点,已得到广泛的应用。由于气辅成型过程是一个在刚、柔双重约束界面条件下进行的多相复杂体系的多次流动过程,因而其形态结构的形成、发展和演化要远比常规注塑成型复杂。然而在气辅成型的形态结构方面,国内外的研究一直以来开展得较少。近年来,作者在聚合物及其共混物、复合材料气辅成型制品的形态结构方面已开展了广泛的研究工作,本文对这些工作和一些重要结果作了总结,并简要分析了成型过程中剪切场对形态演化的影响,最后对该研究方向的发展趋势作了展望。

气体辅助注射成型聚丙烯的多层次结构

用扫描电镜(SEM)观察了气体辅助注射成型(GAIM)和常规注射成型(CIM)等规聚丙烯(iPP)在不同部位的结晶形态。发现CIM试样的"皮-芯"结构不明显,而GAIM试样在不同部位则形成了包括球晶、串晶和取向片晶,进而表现出明显的多层次结构。在结晶形态分析的基础上,初步探讨了GAIM制品多层次结构的形成机理。

含手性碳的串型液晶共聚物的合成与表征

以对苯二甲酰氯 ,2 ,5 -二 [4- ((S) - 3-甲基戊氧基 )苯甲酰氧基 ]对苯二酚和 1,10 -癸二醇为单体 ,采用溶液共缩聚的方法 ,合成了一系列新的含手性碳的串型液晶共聚物。共聚物通过 GPC、DSC、TG、WAXD、偏光显微镜和旋光仪等方法表征。发现所有的共聚物加热至各自的熔点以上都能形成液晶态 ,在液晶态可以观察到破碎焦锥织构或沙地织构。通过变温 X射线衍射证明它们为手性近晶 C(S*c )相。所有共聚物的熔点 (Tm)和液晶态清亮点 (Ti)随共聚物分子中 1,10 -癸二醇用量的改变呈规律性变化。共聚物有很高的旋光性 。

注塑双向自增强聚丙烯的力学性能与形态

采用动态保压注塑技术，在单方向剪切应力场中制得了双方向自增强的聚丙烯试样。研究了其沿流动方向和垂直于流动方向的拉伸强度和冲击强度，结果显示，双向自增强试样增强效果明显，在流动方向的拉伸强度提高了６６％，冲击强度提高４．７倍；在垂直于流动方向，拉伸强度提高４１％，冲击强度提高２８％。通过扫描电镜观察试样内部形态，发现在双向自增强试样的外剪切层形成了串晶横向互相啮合的拉链式凝聚态结构，在芯层形成了细化的球晶。

串晶结构对自增强HDPE短期力学性能和耐慢速裂纹扩展性能的影响

采用自行设计制造的动态保压(DPIM)装置和慢速裂纹增长监测装置,对通用级纯料HDPE5000S进行自增强和串晶对慢速裂纹增长影响研究。结果表明:动态保压试样有大量的串晶结构生成;动态保压试样的拉伸强度高达98.7 MPa,是静态试样24.2 MPa的4.08倍,提高了307.9%,实现了聚乙烯的自增强,动态试样拉伸强度的提高主要是由于有大量的互锁串晶结构形成和结晶度的提高共同所致。动态试样在拉应力是静态试样1.83倍的情况下,因慢速裂纹扩展而发生断裂的时间是静态试样的6.17倍。聚合物耐慢速裂纹增长的能力与聚合物的晶体结构有关,动态试样的串晶结构对慢速裂纹增长的阻止作用非常明显。串晶结构阻止慢速裂纹扩展的主要原因有:高强度的脊纤维晶断裂需克服很大的能量;串晶中片晶间互相紧密接触或重叠给慢速裂纹扩展带来较大的阻力;结晶度的提高。