星形聚苯乙烯的玻璃化转变温度和液1-液2松弛

用扭辫仪(TBA)和线膨胀仪测定了一组规则的星形聚苯乙烯的玻璃化转变温度T_g和T_ll松弛。两种实验方法的结果表明:支链分子量相同的星形结构聚合物的T_g随着支化度增加而升高,但也发现星形聚苯乙烯的T_g却低于具有相同分子量的线形聚苯乙烯的T_g·液₁-液₂松弛温度T_ll和损耗峰的强度也依赖其支化度。与以二乙烯基苯为凝胶核的星形结构相比较,证实了后者的双T_g转变。     

短链支化对低分子量聚乙烯结晶及熔融行为的影响

研究了金属茂催化的低分子量支化聚乙烯和线性聚乙烯的结晶及熔融行为 ,发现支化聚乙烯的结构与线性聚乙烯相同为正交结构 ,但晶格略有膨胀 .支链的存在对熔融行为影响不大 ,两种聚乙烯的熔点均随结晶温度的升高而非线性增加 ,表现出低分子量样品的共同特征 .但支链的存在对结晶行为却有很大的影响 ,主要是由于支链的存在降低了晶体的结晶速率从而影响结晶过程 ,使得低分子量的支化聚乙烯的结晶行为与高分子量线性聚乙烯的结晶行为相似而与低分子量的线性聚乙烯不同 .动力学分析表明 ,低分子量的支化聚乙烯的结晶生长方式的转变温度比同等分子量的线性聚乙烯降低了约 2 0℃     

茂金属聚乙烯的非等温结晶行为及其动力学研究

为探索分子量和支链含量对聚乙烯非等温结晶过程的影响,选用3组样品:(1)不同分子量的无支链线形聚乙烯;(2)低分子量的支链含量不同的试样;(3)高分子量的支链含量不同的试样.用DSC研究了这3组样品的非等温结晶动力学.结果表明:(1)与支链含量相比,分子量大小对结晶的影响是次要的,但高分子量样品的结晶度比低分子量样品低;(2)支链对聚乙烯的非等温结晶有重要影响,在支化聚乙烯中起决定作用;(3)无论是高分子量试样还是低分子量试样,支化含量增加,聚乙烯的结晶温度、结晶度、结晶动力学以及晶体的熔点等显著降低.     

苯乙烯-异戊二烯星形嵌段共聚物的玻璃化转变温度及中间相松弛

用线膨胀仪和动态粘弹谱仪测定了具有不同分子量和不同支化度的规则星形苯乙烯-异戊二烯嵌段共聚物的玻璃化转变温度。T_g(s)和T_g(I)值均依赖于共聚物的形态结构、支化度和分子量。其中分散相的玻璃化转变温度T_g(s)所受影响更为显著。中间相松弛被确认。     

窄分子量分布茂金属短链支化聚乙烯结晶动力学

本工作用DSC方法对三种不同支化度的茂金属短链支化聚乙烯的等温、非等温结晶行为进行了研究 .样品为乙烯和己烯 1的共聚物 ,短支链主要为正丁基 ,分子量Mw =2 0 ,0 0 0 ,Mw/Mn<1 15 ,支化度 (每10 0 0C中CH3 数目 )分别为 1 6、10 4、40 .实验结果表明 ,茂金属短链支化聚乙烯结晶方式Ⅰ Ⅱ转变温度随支化度增加而降低 ,分别为 119 8℃、115 9℃、113 3℃ ;同时支链的存在降低了二次成核速率 ,增大了方式Ⅰ的结晶范围 ,总的结晶速度随支化度增大而减小     

活性正离子聚合及原位制备聚醋酸乙烯酯-g-聚四氢呋喃共聚物/纳米银复合材料

通过将烯丙基溴/高氯酸银引发体系引发四氢呋喃活性正离子开环聚合与"grafting onto"合成方法相结合,原位制备了不同接枝密度和接枝链长度的新型聚醋酸乙烯酯-g-聚四氢呋喃接枝共聚物(PVAc-g-PTHF)及其与纳米银(Ag)的复合材料.采用傅里叶变换红外光谱(FTIR)、核磁共振波谱(1H-NMR)和多角度激光光散射-黏度-凝胶渗透色谱仪(MALLS-VIS-GPC)分别表征了该接枝共聚物的化学结构、共聚组成、分子量、分子量分布、接枝支链数目及支化度,采用原子力显微镜(AFM)、示差扫描量热分析(DSC)、偏光显微镜(POM)研究了接枝共聚物中接枝支链数目及支链长度对其微观形态、单端受限链段结晶行为的影响,并探讨了该纳米复合材料的抗菌性能.结果表明:所制备的不同支链数目和支链长度的PVAc-g-PTHF/Ag纳米复合材料,均表现出良好的抗菌性能;接枝共聚物PVAc-g-PTHF的重均分子量可达4.52×10~5,分子分子量较窄(M_w/M_n~1.8),支化因子可达0.19.接枝共聚物PVAc-g-PTHF可形成明显的相分离结构,其微观形态与接枝支链数目有关;相比相同分子量的双端不受限的PTHF链,PVAc-g-PTHF接枝共聚物中单端受限PTHF支链的结晶速率明显降低;在确定接枝支链数目的情况下,随着支链中PTHF链段长度增加,其结晶逐渐增强,结晶熔融温度及熔融焓均稍有增加.     

梳形支化聚苯乙烯的支化结构对其溶液形态和性质的影响

通过氮氧稳定自由基聚合和原子转移自由基聚合制备出不同支化结构的梳形支化聚苯乙烯.使用示差折光指数-多角激光光散射-毛细管黏度三检测联用凝胶渗透色谱对不同链结构梳形支化聚苯乙烯在四氢呋喃(THF)中的形态和性质进行了研究.结果表明,梳形支化PS在THF中的均方根回转半径(Rg)和特性黏数([η])均随支链长度和支链数目的增加而增大,但是在支链长度较长或者支链数目较大时,Rg和[η]随分子量增加而增大的趋势逐渐放缓,而且支链数目对梳形支化PS在溶液中的均方根回转半径和特性黏数的影响程度要大于支链长度.梳形支化聚苯乙烯在四氢呋喃中的MHS方程特性参数K、α随支链长度和支链数目的增加不断变化.     

带支链感光性环氧肉桂酸酯的合成和性能研究

本文对带支链感光性环氧肉桂酸酯的支化度和感光度以及耐溶剂性能之间的关系进行了研究。结果表明,在缠结链的临界分子量以下,随着环氧树脂支化度的增加,环氧肉桂酸脂的感光度和耐溶剂性能都会有较大幅度的提高。     

星形聚苯乙烯本体粘弹性对结构的依赖性

用应力松弛法研完了一组4—12支链星形聚苯乙烯本体的粘弹性。从应力松弛主曲线测定了零切变粘度η_0、稳态柔量J_e~o和其它流变学参数。结果发现,零切变粘度和最大松弛时间τ_m强烈地依赖于聚合物的分子尺寸,并且可以用无扰特性粘度或折合分子量来描述。η_0和τ_m随支化度增大而增大。实验还直接证实了支链长度相同的星形聚合物的J_e~o与支链数目无关,但是星形聚合物的稳态柔量比具有和支链间分子量相同的线形聚合物的稳态柔量大。     

超支化聚醚的支化度对玻璃化转变温度的影响

聚合物的分子结构对聚合物性能影响很大.支化度不同的同种聚合物,必须通过不同的催化体系合成,很难得到既具有相近分子量又具有不同支化度的系列聚合物样品,因此对聚合物性能与支化度的依赖关系的研究报道不多.     

The Glass Transition Temperature and Liquid1-Liquid2 Relaxation of Star-Shaped Polystyrene

The glass transition temperature T and relaxation temperature T11 of a series of regular star-shaped polystyrenes were measured by using torsional braid analyzer(TEA) and linear dilatometer.The results showed that Tg for star-shaped polymer increases with increas-ing branching degree whan the molecular weights of branch chains arethe same,but it is lower than that of linear polystyrene with the same molecular weight.The liquid 1iquid relaxation temperature T11 and the intensity of loss peak of star polystyrene also depend on branching degree.Two-Tg transitions in star polystyrenes with DVB microgel nodule were proved by comparing two types of star polystyrenes.     

电子束辐射固化环氧树脂的动态力学分析——树脂化学结构、分子量及其分布的影响

应用不同化学结构、分子量及其分布的环氧树脂进行了电子束辐射固化实验 ,对固化物进行了动态力学分析 ,研究了不同样品凝胶含量、内耗tanδ及动态模量的变化规律 .分析结果表明环氧树脂辐射反应活性与其化学结构有很大关系 ,酚醛型环氧树脂的辐射反应活性高 ,固化后高温模量及玻璃化温度较高 ,而脂环族环氧树脂反应活性小 .在低辐射剂量下 ,环氧树脂的固化度随分子量增大略有下降 ,但固化物的玻璃化温度随分子量增加而升高 .增大辐射剂量 ,树脂固化度的提高受分子量大小的影响很小 ,分子量较大样品的网络均匀程度有所提高 ,在较高反应程度下 ,玻璃化温度主要受固化度影响 .树脂固化程度也是决定其模量高低的主要因素 ,而在固化程度相近的情况下 ,分子量的影响作用很大 .在同样辐射剂量下 ,分子量分布宽的树脂固化反应程度高 ,但交联网络均匀性低 .     

拟合粘度曲线法研究高聚物的长链支化

本文介绍了用计算机试误法拟合粘度曲线,讨论支化参数的方法,本法可以同时确定支化临界分子量和支化程度,在此基础上可以同时得到支化参数及平均分子量、分子量分布.以聚乙烯标准参考物:SRM 1475(线型)、1476(支化物)及镍催化顺式聚丁二烯为对象介绍了上述方法.     

Architectural control of polystyrene physical properties using branched anionic polymerization initiated at ambient temperature

Ambient temperature-initiated anionic polymerization has generated branched polystyrenes of varying molecular weights and architectures by inclusion of a distyryl branching comonomer into a conventional sec-Butylithium-initiated polymerization of styrene. Primary chain length control within the branched polymers, and restriction of the branching points to varying segments of the primary chains, led to variations of glass transition temperature with no direct correlation to the branched polymer molecular weight but a strong relationship to the length of individual chains comprising the branched macromolecules.     

无乳化剂乳液聚合制备高分子量聚乙烯醇

通过无乳化剂乳液聚合方法, 采用氧化还原引发体系制备了超高分子量的聚醋酸乙烯酯(PVAc), 继而醇解为超高分子量的聚乙烯醇(PVA). 研究了聚合温度、引发剂浓度、单体转化率对PVA的分子量和分子结构的影响. 探讨了线性高分子量PVA结构的控制方法. 结果表明, 利用无乳化剂乳液聚合可以实现在室温(14~20 ℃)制备出聚合度为9899的高分子量的PVA, 聚合过程对PVA的分子量和结构均有显著的影响. 在无乳化剂乳液聚合恒速聚合区得到的聚合物分子量较高, 分子量分布窄, 且结构比较规整, 而在加速区, PVAc的支化和交联现象显著, 最终会对PVA的线性程度产生很大影响. 因此, 可以通过聚合过程来控制PVA的分子量和链结构.     

Method of determination of dielectric relaxation characteristics of plasticized polystyrenes on the basis of calorimetric glass temperature

The dielectric loss measurements of different polystyrenes (fractions and blends) with different molecular weights (M _n 2000–125000 g/mol) were carried out in the frequency range 10^–2–10⁶ Hz and the temperature range of the glass process (60°–135°C, depending on the molecular weight). The measurements of the pure fractions showed that the half-width of the glass relaxation process of the different polystyrenes can be correlated by a straight line, if they are plotted versus the relaxation frequency maxima of the glass process, regardless of the difference in both their molecular weight and glass transition temperature. Moreover, the fine structure of the shape of the glass process of polystyrenes with different molecular weights was found to be the same when the glass process appears at the same relaxation frequency range. The addition of oligostyrenes or low molecular <10% wt additives to the high molecular weight polystyrene did not influence the shape of the glass process. The calorimetric glass transition temperature of polystyrene was found to be only dependent on the number average molecular weight as well as on the number of end groups, but not on the molecular weight distribution. The obtained experimental results were correlated to develop a method for the estimation of the dielectric relaxation characteristics (relaxation frequency as well as the shape parameters) of the glass process of plasticized polystyrenes based on the calorimetric glass transition temperature. A method for the analysis of the dielectric relaxation curves of mixtures of label and polymer is suggested.     

Influence of polydispersity and long chain branching on the melt viscosity of polycarbonate

The Newtonian and non-Newtonian melt viscosities of bisphenol A polycarbonate (PC) at 280°C were treated according to the generalized multivariable power function, where the average molecular weights, polydispersity degree and branching degree are considered as variables. The shear rate was also considered as a variable for non-Newtonian conditions. In the same way, the melt fluidity was treated as a multivariable power function. It has been found that the same melt flow properties of polymer can be obtained by an appropriate combination of Newtonian melt viscosity (being a function of molecular weight) and long chain branching. The experimental data on PC agree with the theoretical approach of Bucche and Graessley.     

A theoretical investigation of the production of branched copolymers in continuous stirred tank reactors

A comprehensive mathematical model for free-radical copolymerization reactions has been developed for a homogeneous continuous stirred tank reactor. The present model is based on a fairly general copolymerization scheme accounting for the formation of linear and branched copolymer chains. Both chain transfer to polymer and terminal double bond reactions are considered in order to predict the long chain branching frequency. Changes in molecular weight, composition and degree of branching occurring during the copolymerization reaction are modelled using the method of moments. To break-down the dependence of the moment equations on higher order moments two different closure methods are considered. The predictive capabilities of the model are examined in relation to the solution copolymerization of methyl methacrylate with vinyl acetate. It is shown that both chain transfer to polymer and terminal double bond reactions significantly contribute to the broadening of the molecular weight and degree of branching distributions. Furthermore, the terminal double bond reaction effects significantly the copolymer number-average molecular weight and the concentration of terminal double bonds.