结晶对等规立构聚甲基丙烯酸甲酯辐射消旋和辐射裂解的影响

本文通过核磁氢谱、DSC和分子量测定,研究了结晶对等规立构聚甲基丙烯酸甲酯辐射消旋和辐射裂解的影响.分子量测定的结果表明,等规立构聚甲基丙烯酸甲酯结晶后,其辐射裂解反应减弱,裂解G值减小将近一半.核磁氢谱测定辐照试样的空间立构变化结果为:随着辐照剂量的增加,等规立构逐渐变为无规立构和间规立构,其变化规律相似于非晶试样.结果还表明,晶区的消旋反应比裂解反应更为显著.DSC测得的试样熔点,随着辐照剂量的增加而急剧下降,由Flory结晶熔化理论计算得晶区的辐射破坏G值为8.8.该值远大于聚乙烯晶区的破坏G值.     

聚甲基丙烯酸甲酯辐射裂解和消旋的空间立构效应

本文研究了三种不同空间立构聚甲基丙烯酸甲酯的辐射效应,提出裂解过程是一种裂解与重合的动态平衡过程。分子量降低和消旋作用对温度的依赖性,是由于分子运动和笼罩效应以及重合的空间位阻效应所致。辐照温度愈高,裂解产额愈大。相同条件下辐照,全同立构比无规立构试样的裂解产额更大。 全同立构聚甲基丙烯酸甲酯辐照后,不仅分子链断裂,而且空间立构也发生很大变化。随着辐照剂量的增加,全同立构含量逐渐减少,而无规立构含量和间同立构含量却逐渐增加。     

分子活动性对iso-PMMA辐射裂解和消旋的影响

以全同立构聚甲基丙烯酸甲酯(iso-PMMA)为对象, 用核磁共振谱和分子量测定等手段, 研究了不同物理状态, 即无定型固态, 结晶态和稀溶液状态下的辐射裂解和辐射消旋反应. 结果表明, 在稀溶液状态下辐照, 其裂解反应最强, 而消旋反应最弱; 结晶状态下辐照, 则裂解反应最弱而消旋反应最强. 这充分说明了分子的活动性对反应的影响, 进一步验证了前已提出的高分子链断裂-重合-消旋的平衡反应机理.     

茂金属间规立构聚丙烯结晶动力学研究

用ＤＳＣ和密度法对茂金属间规立构聚丙烯（ｓＰＰ）样品进行了等温和非等温结晶动力学研究．测得平衡熔点Ｔ０ｍ为１５８℃,平衡熔融热焓ΔＨ０ｍ为３７ｋＪ／ｍｏｌ,侧表面自由能σ＝５２ｅｒｇ／ｃｍ２,折叠链表面自由能σｅ＝６９ｅｒｇ／ｃｍ２,链堆砌功ｑ＝３３７５ｋＪ／ｍｏｌ．对非等温结晶过程研究表明,由熔体结晶的ｓＰＰ具有非均相成核,三维球状生长机理．成核与生长活化能ΔＥ＝７３１ＫＪ／ｍｏｌ     

聚左旋乳酸/聚消旋乳酸共混物的结晶行为

非晶态聚消旋乳酸(PDLLA)对PLLA的结晶行为有较大的影响。本文利用差示扫描量热仪(DSC)和偏光显微镜(POM)对不同分子量PLLA、PDLLA按不同比例制得的共混物结晶进行了系统研究。结果表明随PDLLA含量的增大PLLA冷结晶温度升高,且越接近熔融温度。PDLLA分子量较小时PLLA球晶特征被明显破坏,PDLLA分子量较大时PLLA更易形保持球晶特征且易形成环带球晶形貌,这与结晶速率与非晶组分的扩散速率匹配程度有关。低分子量的PDLLA使PLLA的最大生长速率对应的温度出现在较低温度。     

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.     

微波辐射下L-氨基酸的快速消旋方法

微波辐射作用下的L-氨基酸消旋反应是一种新的氨基酸消旋方法，具有对环境友好的优点。本文报道了在微波辐射下，以1．Omol／L氢氧化钠水溶液替代有机酸作为反应溶剂，水杨醛为催化剂，水杨醛与L-氨基酸的摩尔比为0．1，L-氨基酸可以快速消旋；消旋反应随微波辐射功率的提高而加快，在600W时已接近最大反应速率。同时也讨论了微波作用下L-氨基酸的消旋反应机理。     

聚酰胺—1010的辐射裂解与后裂解机理的ESR研究

用电子顺磁共振技术（ＥＳＲ）研究了ｒ－辐射聚酰胺－１０１０中俘获自由基的结构、升温中的转化与行为，及它们与其结构和转变多得性的联系，讨论了聚酰胺－１０１０辐射解和后裂解的反应机理及反应区域等问题。     

高分子立构复合结晶的研究进展

立构复合结晶是高分子结晶中的一种普遍现象,也是不同高分子之间共结晶的特殊形式.互为立体异构高分子在共混物和立体嵌段共聚物中可形成立构复合结晶.由于这种独特的链凝聚结构,立构复合结晶材料与相应的同质结晶材料的性能显著不同,立构复合结晶通常可提高高分子材料的熔点、耐热性、结晶能力、结晶度、机械力学性能、耐溶剂性能等.通过立构复合结晶,可使一些非晶或难结晶的高分子转变为可结晶或高结晶度的状态,从而实现材料性能的转变.因此,互为立体异构高分子之间的立构复合结晶为聚合物材料的性能优化和调控提供了有效的途径.文献已报道了多类可立构复合结晶的聚合物体系,包括脂肪族聚酯、脂肪族聚碳酸酯、聚甲基丙烯酸酯、聚酰胺和聚酮等.本文根据聚合物化学结构的不同,针对文献已报道的可立构复合结晶的高分子体系,综述了其立构复合结晶的形成条件、结构特征与物理性质.     

AN ATOMIC FORCE MICROSCOPY STUDY ON THE AGGREGATION OF ISOTACTIC POLY（METHYL METHACRYLATE）

Aggregation process of isotactic poly(methyl methacrylate) (i-PMMA) has been studied extensively for many years, and considerable progress has been made in both experimental and theoretical studies. They are, however, seldom sustained by real-space observations of the underlying morphology. In this paper, the aggregation process of i-PMMA in concentrated acetone solutions and the fractal structure of the resulting three-dimensional clusters were characterized on the basis of real-space AFM observations of their two-dimensional projection. It was found that spherical multiple-chain particles formed upon collapse and aggregation of the involving chains as a whole during quenching the solution to room temperature. By keeping the solution at room temperature, the initially formed particles stick together upon contact to form larger particles through reassembling very slowly. The succeeding collision of the enlarged spherical particles leads to the formation of small clusters. These newly formed small clusters grow when they meet with other clusters or single Brownian particles. This leads to the formation of large clusters with fractal dimension of 1.95$±0.05, which suggest a reaction-limited cluster aggregation of i-PMMA in a concentrated acetone solution. This is in accordance with the conclusion obtained by light scattering measurements.     

NEW DEVELOPMENTS IN THE DEGRADATION,STABILIZATION, AND SENSITIZATION OF POLY(METHYL METHACRYLATE)

Abstract

Physical and chemical processes, combined under the general term aging, begin immediately after formation of a polymer. Oxygen and other components of the environment -ozone, water, etc.-are involved. Aging is accelerated by a rise in temperature, light, strong ionizing radiations, and mechanical stresses, which are especially rapid under processing conditions for thermoplastic polymers. Poly(methy1 methacrylate) (PMMA) is of particular interest, since at least at temperatures where thermal degradation is important, photolysis occurs by end-group initiation and is accompanied by extensive depolymerization. This polymer has also been photodegraded in air at room temperature by radiation from a low-pressure mercury lamp, and a quantum yield for random chain scission has been determined. Owing to the importance of these points, it is believed that a review of studies of degradation, stabilization, and sensitization of PMMA up to the present date will supply information on the most general problems of behavior of polymeric items during their service lives.     

COMPATIBILITY IN POLYMER BLENDS OF POLY (VINYL ACETATE) AND POLY (METHYL METHACRYLATE)STUDIED BY NMR

Compatibility of poly (vinyl acetate) (PVAc) with poly (methyl methacrylate) (PMMA) mixtures has been studied by using nuclear magnetic relaxation, differential scanning calorimeter and small-angle X-ray scattering techniques. The nuclear magnetic relaxation time T_1's were measured as a function of composition in blends of PMMA and PVAc prepared from chloroform solution. The results show that the system is miscible for casting from chloroform solution.     

VISCOMETRIC STUDY OF POLY(METHYL METHACRYLATE) AND POLYSTYRENE BLENDS IN DIFFERENT SOLVENTS

The intermolecular interaction between poly(methyl methacrylate) (PMMA) and polystyrene (PS) intetrahydrofuran (THF) and N,N'-dimethyl formamide (DMF) solvents was studied at 28℃ using a dilute solution viscometrymethod. Solvent is believed to play a key role in characterizing the viscosity behavior of the polymer solution. The intrinsicviscosity and viscosity interaction parameter were experimentally measured for the binary (solvent/polymer) and for theternary systems in two solvents. The compatibility of the polymer mixture was discussed in terms of the sign of △b_m. Theresults show that the compatibility of PMMA/PS blend in DMF is larger than that in THF.     

STUDIES OF THE CRYSTALLIZATION BEHAVIOR IN THE CRYSTALLINE/AMORPHOUS POLYMER BLENDS: POLY(ETHYLENE OXIDE)/POLY(METHYL METHACRYLATE) AND POLY(ETHYLENE OXIDE)/POLY(VINYL ACETATE)

The crystallization process of poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA)and PEO/poly(vinyl acetate) (PVAc) blends has been characterized by Fourier Transform Infrared(FTIR) spectra in conjunction with Differential Scanning Calorimeter (DSC) measurements. Thecrystallinity of PEO varies consistently with PEO content in PEO/PVAc blends and the PEO/PMMAblends containing 50 wt% or less PMMA. For the PEO/PMMA blends containing 60 wt% ormore PMMA, the crystallinity of PEO decreases more than PEO content but develops with crystal-lization time. These results can be explained in terms of difference between the crystallization tem-perature (T_c) and glass transition temperature (T_g) of the blends as a function of content of amorphouscomponent.     

含三价铕荧光络合物与聚甲基丙烯酸甲酯的发光材料

用荧光性能优异的Eu(TTA) 3 ·2TPPO络合物与聚甲基丙烯酸甲酯 (PMMA)制备了一系列发出红色荧光的光致发光材料 .荧光测定结果表明 :PMMA膜的荧光强度随膜中络合物含量的增加而增大 .红外光谱研究表明络合物与PMMA之间存在相互作用 .透射电镜观测结果表明络合物在复合膜中是以亚微米颗粒分散的 .     

SYNTHESIS OF POLY(METHYL METHACRYLATE)-SILICA NANO-COMPOSITES. II. POLY[METHYL METHACRYLATE-block-(METHYL METHACRYLATE-co-2-HYDROXYETHYL METHACRYLATE)]

ABSTRACT

One kind of poly(methyl methacrylate [MMA]-block-2-hydroxyethyl methacrylate [HEMA]) block copolymer and two kinds of poly[MMA1-block-(MMA-co-HEMA)] block-random copolymers were synthesized by atom transfer radical polymerization. Then, poly(methyl methacrylate) [PMMA]-silica nano composites were synthesized by blending perhydropolysilazane (PHPS: NN-110) and block or block-random copolymers in 1,4-dioxane and casting the blend solutions. All composite films were transparent. Silica and organic domains were microphase separated in the composites. The effects of PHEMA content and blend ratio of PHPS to hydroxyl group on the microphase separation were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The thermal properties of the composites were investigated by differential scanning calorimetry (DSC) and thermal gravitic analysis (TGA).     

SYNTHESIS OF POLY(METHYL METHACRYLATE)-SILICA NANO-COMPOSITE

ABSTRACT

Transparent organic/pre-ceramic composite films of poly(methyl methacrylate) [PMMA] and perhydropolysilazane [PHPS] were synthesized by blending poly(methyl methacrylate-co-2-hydroxyethyl methacrylate) [P(MMA-co-HEMA)] random copolymers and PHPS. In the blend films, P(MMA-graft-PHPS) graft copolymers were formed, PMMA and PHPS were microscopically phase-separated in the solid state. Morphology of the microphase separation was investigated by transmission electron microscopy by changing HEMA content of the random copolymers and blend ratio of PHPS to HEMA. To convert PHPS to silica glass, the blend films were calcinated at 100°C. The morphology of the microphase separation of the films was not changed by the calcinations; the calcinated films were transparent. When the molar content of HEMA of P(MMA-co-HEMA) and the molar content of PHPS to HEMA in feed were 14.5% and 150%, respectively, the morphology was well ordered lamellae of PMMA and silica.