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.     

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.     

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.     

磁场对聚合物立体构型影响的研究(Ⅰ)——聚甲基丙烯酸甲酯

本文研究了在甲基丙烯酸甲酯聚合过程中,磁场对产物中间同立构含量的影响。间同立构含量的测定是采用红外光谱定量法。实验结果表明: (1)聚甲基丙烯酸甲酯的间同立构百分含量S%值随磁场强度的增加按指数关系增加。 (2)聚甲基丙烯酸甲酯的玻璃化温度随磁场强度的增加而增加。 (3)聚甲基丙烯酸甲酯的平均分子量随磁场强度的增加,也按指数关系增加。 (4)通过公式计算了聚甲基丙烯酸甲酯分子链中能连续出现N个间同立构链节的组成几率F_N值。     

基底表面无规聚甲基丙烯酸甲酯立构复合结构的研究

采用原子力显微镜和反射吸收红外光谱研究了在基底上无规聚甲基丙烯酸甲酯立构复合结构的形成和结构特征,纯等规和间规聚甲基丙烯酸甲酯与等规/间规混合物(有立构复合结构生成)表面聚集形貌比较的结果表明,立构复合结构的生成使聚甲基丙烯酸甲酯在基底上形成树枝状的聚集形貌,因此无规聚甲基丙烯酸甲酯在基底上的树枝状聚集形貌表明了其内部生成了立构复合结构,而且这种结构对聚集形貌产生了重大影响,反射吸收红外光谱的研究表明,在基底表面薄膜中无规聚甲基丙烯酸甲酯主链结构比在本体厚膜中的更加伸展,更有利于立构复合结构的生成.     

PMMA-PEO共混体系的辐射交联

<正> 聚甲基丙烯酸甲酯(PMMA)是典型的辐射裂解型聚合物。经辐照后,PMMA主链发生无规断裂。在聚合物共混体系中,PMMA是否能发生交联,这是辐射化学中一个非常重要的研究课题之一,也是一项探索性工作。 PMMA-PEO共混体系是可以分子水平共溶的体系。本文试图将共混体系的相容性与共混体系中的裂解型聚合物的辐射效应联系起来,讨论PMMA-PEO共混体系的辐射交联。     

异戊二烯-甲基丙烯酸甲酯共聚物的裂解色谱分析

]本文用裂解色谱(PGC)、裂解-色谱质谱(PY-GC/MS)和裂解质谱(PY/MS)等方法对异戊二烯-甲基丙烯酸甲酯共聚物进行了裂解研究,分离鉴定了主要裂解产物,检测出了特征裂解产物——杂二聚体和杂三聚体,以及异戊二烯的三聚体。考察了某些主要裂解产物同无规共聚物的组分含量和裂解温度之间的变化关系。建立了用裂解色谱鉴别不同共聚物和均聚混合物以及分析无规共聚物组分含量的方法。定量方法的精确度为相对标准偏差小于2％。对用均聚混合物作标样的定量可能性进行了探讨。     

共混高聚物的混溶性研究(摘要)

在此介绍马萨诸塞州立大学在共混高聚物方面的研究工作。这些共混高聚物可分为三类:(1)非晶—非晶,如PCL(聚己内酯)(<50％)/PVC(聚氯乙烯);(2)结晶—非晶,如PCL(>50％)/PVC、i-PS(全同立构聚苯乙烯)/PPO(聚苯醚)、i-PS/α-PS(无规聚苯乙烯)、PVF_2(聚偏氟乙烯)/PMMA(聚甲基丙烯酸甲酯);(3)结晶—结晶,如PBT(聚对苯二甲酸丁二酯)/PET(聚对苯二甲酸乙二酯)。为研究第一类非晶共混物的混溶性,以 PCL/PVC     

聚(1,4-环己二烯碳酸酯)立体低聚物的合成及微结构分析

聚合物微结构控制是配位催化聚合领域最重要的目标之一.而合成各种立构规整性低聚物及其核磁碳谱研究是聚合物微结构定性和定量分析的关键.本文以手性环己-4-烯-1,2-二醇为原料,采用N,N'-羰基二咪唑和三光气作为羰化试剂,设计合成了CO_2/1,2-环氧-4-环己烯交替共聚物(聚(1,4-环己二烯碳酸酯),PCEC)全同立构和间同立构的二聚体、四聚体、六聚体、八聚体和十二聚体模型化合物.通过分析全同立构和间同立构模型化合物的核磁碳谱,完成了PCEC微结构的碳谱信息归属.发现聚合物全同立构序列的羰基、次甲基和亚甲基区域的出峰位置分别在δ=154.04、73.83和29.91;间同立构序列的羰基、次甲基和亚甲基区域的出峰位置分别在δ=153.72、72.97和28.98.     

聚合温度对聚甲基丙烯酸三丁基锡酯等规度的影响(Ⅰ)

本文测定了0—130℃温度范围内,由~(60)Co-γ射线和两种活性不同的引发剂引发聚合的聚甲基丙烯酸三丁基锡酯的等规度。利用~(13)C-NMR测定聚合物分子链的等规度,如预料的那样,以间同立构为主,并随着聚合温度的升高间同立构等规度降低。作者认为影响聚合物等规度的因素主要是取代基的极性效应。计算出的控制等规度的活化能参数与聚甲基丙烯酸甲酯和聚甲基丙烯酸三甲基锡酯的属同一数量级,可相互比较。     

Luminescence studies in polymers—IV. Effect of orientation,tacticity and crystallinity on polystyrene and polyvinylcarbazole fluorescence

The fluorescence spectra of amorphous atactic, amorphous isotactic and crystallized isotactic polystyrene films have been compared. The effect of chain orientation has also been analysed on amorphous atactic samples. The results show that the fluorescence yield increases with crystallinity at room temperature and 77°K. The contribution of excimer fluorescence at 77°K increases according to the sequence: atactic < atactic oriented < isotactic amorphous < isotactic crystallized. An increase of the fluorescence yield with crystallinity was also observed for polyvinylcarbazole samples although the contribution of excimer fluorescence at 77°K is independent of crystallinity for this polymer. The results are interpreted in terms of energy migration.     

Photodegradation behavior of tert-butyl vinyl ketone polymers and copolymers with styrene and α-methylstyrene

Photodegradation behavior of atactic and isotactic polymers of tert-butyl vinyl ketone (t-BVK) and its copolymers with styrene and α-methylstyrene was studied in dioxane as a solvent at room temperature. The quantum yield of main-chain scission of atactic poly(t-BVK) was found to be larger than that of isotactic poly(t-BVK) and atactic poly(methyl vinyl ketone). From the Stern-Volmer plots on the quenching study of atactic poly(t-BVK) with naphthalene and 2,5-dimethyl-2,4-hexadiene, it was found that 60–70% of its photochemical reaction underwent main-chain scission from the triplet state. It was also found that the increase in t-BVK contents of both copolymers accelerated the photodegradation, and the copolymer with styrene was more photodegradable than that with α-methylstyrene. These results seemed to suggest that the main-chain scission of these vinyl ketone polymers and copolymers proceeded through a Norrish type II photoelimination mechanism.     

Thermally stimulated currents depolarization study of gamma ray irradiated PMMA

We will investigate the effect of γ-irradiation on the polymethyl methacrylate (PMMA) properties. The Fourier transform infrared spectroscopy technique in attenuated total reflexion mode (FTIR-ATR) results allowed us to show that the irradiated PMMA undergoes a scission in its lateral chain combined to an oxidation phenomenon. In fact, a decrease in the carbonyl index, versus the radiation dose, is observed. The differential scanning calorimetry and the thermostimulated depolarization currents revealed that the scission in the lateral chain provides a better flexibility to the PMMA chain and an increase in the free volume of the material. The consequences of these phenomena appear in the decrease of the activation energy of PMMA and the appearance of a local order in the material at a temperature T_c which decreases versus the radiation dose.     

Characterization of Interdiffusion between PVDF and Stereoregular PMMA by Using ATR-FTIR Spectroscopy

In this study we investigated the interdiffusion between PVDF and PMMA below the melting temperature of PVDF by ATR-FTIR spectroscopy. The influence of the stereoregularity of different PMMA samples was studied. The PMMA tacticity showed a significant influence on the kinetics of the diffusion. Syndiotactic PMMA diffuses faster than isotactic and atactic PMMA which can be explained from the difference of chains stiffness between the two stereoisomers.     

Effect of Tacticity of Poly(Methyl Methacrylate) on Conductivity of Poly(Ethylene Oxide)-Poly(Methyl Methacrylate) Blend-Based Polymeric Electrolytest

Abstract

Polymer electrolytes based on blends of poly(ethylene oxide) (PEO) with various stereoisomers of poly(methyl methacrylate) (PMMA) were studied by means of impedance spectroscopy and DSC. It was found that isotactic poly(methyl methacrylate) (1PMMA)-based electrolytes exhibit ambient temperature conductivities at least one order of magnitude higher than the electrolytes containing other stereoisomers of PMMA. The highest value of room temperature conductivity equal to 9 × 10^?5 S/cm was measured for a sample containing 30 wt% IPMMA. The effect observed results from the presence of a flexible amorphous phase in PEO-IPMMA blends which is favorable for fast ionic transport. A small increase of ionic conductivity with decreasing molecular weight of the added atactic poly(methyl methacrylate) was also observed.     

Lewis‐Acid‐Mediated Stereospecific Radical Polymerization of Acrylimides Bearing Chiral Oxazolidinones

Lewis acid (MgBr₂)‐catalyzed radical polymerization of acrylimides bearing chiral oxazolidinones gave highly isotactic polyacrylimides with up to >99 % meso tetrad (mmm) selectivity. Polymerization in the absence of Lewis acid gave atactic polymers with 80 % racemo diad (r) selectivity; the selectivity was deliberately tuned from 80 % r to >99 % mmm by varying the polymerization conditions. The polyacrylimide was quantitatively converted to corresponding polyacrylates while preserving the stereoregularity, thus providing a general method for the synthesis of atactic to isotactic polyacrylates.