聚丙烯熔体的零切变粘度与粘均分子量的关系

<正> 零切变粘度η_0是聚丙烯熔体流变性能的一个基本物理量,零切变粘度-分子量关系不仅具有理论上的兴趣,而且也有较大的实用意义。在文献中零切变粘度通常都是用毛细管粘度计数据外推求得的,但是由于聚丙烯熔体有较强的非牛顿性,即使在毛细管粘度计测量下限测得的粘度仍表现出明显的切变速率依赖性。因此,难于用外推的方法     

分子量分布对双烯聚合物粘弹性能的影响——Ⅱ.顺-1,4-聚异戊二烯的粘弹性能对分子量及其分布的依赖关系

本文利用凝胶渗透色谱和应力松弛方法研究了顺-1,4-聚异戊二烯的粘弹性能对分子量及分布的依赖性。实验结果表明,生胶的松弛模量和最长松弛时间与分子量和分子量分布都有依赖关系,主要是改变τ_m=KM_w~6关系中的K值,对β值的影响甚小。由于本体聚合物的链缠结而导致的非牛顿效应使生胶的τ_m与M_w的关系偏离3.4法则,这可用缠结网络密度来校正。探讨了生胶的应力松弛过程是橡胶分子链的滑移和解缠结兼有的两种运动。低分子量级份对链缠结网络有显著影响,起稀释剂作用,使网络的临界缠结分子量增高。     

丁苯橡胶甲苯溶液粘度的切变速度依赖性

对低温聚合丁苯橡膠一个级分(M=1.0×10~6)的甲苯溶液在切变速度 D=10—20,000秒~(-1)范国内测定了五种浓度溶液的粘度数据(25.0℃)。粘度计采用 Tsuda 的水平毛细管水平流出体积计量管的设计,且在全部切变速度范围内都从同一毛细管流出,使不同范围内的数据很好衔接。实验结果证明在低切变速度区域牛顿粘度η(?)(0)的存在。并且从lnη(?)—ln D 曲线的反曲点(?)值不依赖于浓度和对反曲点的对称性估计η(?)(∞)值和整个切变速度范国内的粘度行为。取几个等 D 值时的 lnη(?)按(lnη(?)/C)-C 的线性外推得到[η]_D,明确表示在低切变速度区域[η](?)的存在。两种牛顿流动间转变区域的实难数据可以采用下列两公式线性化:x(D)=(1/2)[1-erf(kln(?))],x(D)=(1/1+(?))~n,式中x=(lnη(?)-lnη(?)(∞)/lnη(?)(0)-lnη(?)(∞)),erf(z)=(?)-u~2du,k 和 n 是依赖于浓度的参数,但在较高浓度时均趋向一恒定值。([η]_D/[η]_0)-ln D 曲线相当符合于刚性橢球轴比 p=4—5间的理论曲线,这样得到的转动扩散系数(?)_(rot)=6.6×10~2秒~(-1),但是从(?)_(rot)和[η]_0值按 Scheraga-Mandelkern 方法计算得到的分子量值与实际不符,所以丁苯橡膠分子线团不是刚性结构;而以1/(?)值作为高分子线团弹性变形的松弛时间,按 Bueche 理论计算得到的分子量值与实际极相一致。     

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。     

星形聚苯乙烯的链缠结和松弛过程

本工作用应力松弛仪测定了一组等支链长不同支化度星形聚苯乙烯的松弛谱,探讨了支化结构对松弛谱橡胶平台区粘弹行为的影响,用“管子”模型对松弛谱进行了计算机模拟,从分子运动观点上解释了星形聚合物的粘弹特性:     

十二烷基聚氧乙烯硫酸钠胶束体系的流变性质研究

用流变学方法研究了无机电解质KBr存在时,阴离子表面活性剂十二烷基聚氧乙烯(3)硫酸钠(SDES)水溶液中胶束的生长和结构。通过测量体系的稳态剪切粘度(η)和应力(σ)关系,得到零剪切粘度(η0)、复合粘度(|η^*|)、动态模量[储能模量(G')和损耗模量(G")、平台模量(G0)、结构松驰时间(τ)等流变学参数,并应用Cox-Merz规则和Cole-Cole图,发现在SDES/KBr体系中可以形成蠕虫状胶束网络结构,体系为假塑性流体,偏离Maxwell模型,具有非线性粘弹性,没有单一的结构松驰时间。     

十二烷基聚氧乙烯硫酸钠胶束体系的流变性质研究

用流变学方法研究了无机电解质KBr存在时,阴离子表面活性剂十二烷基聚氧乙烯(3)硫酸钠(SDES)水溶液中胶束的生长和结构。通过测量体系的稳态剪切粘度(η)和应力(σ)关系,得到零剪切粘度(η0)、复合粘度(|η^*|)、动态模量[储能模量(G')和损耗模量(G")、平台模量(G0)、结构松驰时间(τ)等流变学参数,并应用Cox-Merz规则和Cole-Cole图,发现在SDES/KBr体系中可以形成蠕虫状胶束网络结构,体系为假塑性流体,偏离Maxwell模型,具有非线性粘弹性,没有单一的结构松驰时间。     

冷态模型系统模拟介质糖浆溶液粘弹性的分析

利用旋转流变仪和毛细管流变仪研究了不同葡萄糖浆溶液的粘弹性,结果表明:不同除水量的糖浆溶液的零剪切粘度(η0)呈现指数增长规律;不同PAM添加量对糖浆溶液的储能模量(G′)和损耗模量(G″)影响较大,且对G′的影响较为显著;随着PAM(聚丙烯酰胺)含量的增加,松弛时间和挤出胀大比(B)逐渐增大,糖浆溶液弹性越来越明显;其它条件相同,零剪切粘度越大,糖浆溶液的弹性效应越明显;糖浆溶液在20~80℃温度范围内粘度可逆,温度对糖浆溶液粘度的影响非常显著,且粘度变化相差可达1000倍。     

聚电解质──壳聚糖浓溶液流变学性质研究：浓度、温度、溶剂pH值和外加盐对粘度及流动性的影响

本工作用日本岩本ＲＰＸ－７０５多功能流变仪测定了在不同浓度、温度、溶剂ｐＨ值和外加盐浓度对壳聚糖在甲酸水溶液中其浓溶液粘度η随剪切速率γ的变化关系．讨论了浓度、温度等对溶液粘度、流动活化能Ｅ_γ和流动指数ｎ的影响．发现溶剂ｐＨ值减小或溶液中外加盐浓度增加，溶液粘度变小，ｎ增大，表明非牛顿流动性减弱，并且进一步讨论了零剪切粘度η_０和外加盐浓度Ｃ_ｓ的依赖关系．     

星形SIS嵌段共聚物的动态力学性能

本文报导了用粘弹谱仪对组成相同、支链分子量相同而支化度不同的,以及支化度相同、支链分子量不同的系列星形SIS嵌段共聚物的测试结果,实验发现:支链分子量是影响各相玻璃化转变温度和动态杨氏模量E′的主要因素,支化度对各相玻璃化温度影响很小,但是对E′影响是明显的。     

Synthesis and solution properties of star‐shaped poly(tert‐butyl acrylate)

A series of star polymers consisting of poly(tert‐butyl acrylate) arms and an ethyleneglycol dimethacrylate (EGDMA) microgel core were synthesized using anionic polymerization. The effect of various parameters (precursor length, ratio [[EGDMA]/[Initiator], reaction time, and overall concentrations) on the average number of arms was investigated. Molecular weights were determined using GPC coupled with an online viscometer and MALLS. The exponents for the relation between intrinsic viscosity or radius of gyration and molecular weight, respectively, are extremely low, indicating that the dimensions of the star polymers only slightly increase with the number of arms. After a certain number of arms is reached the intrinsic viscosity even decreases with molecular weight. Computer simulations for star polymers were carried out where the radius of gyration was calculated as a function of the number of arms. The results are in good agreement with the experimental data.     

Normal stress and shear stress in a viscoelastic liquid under steady shear flow: Effect of molecular weight heterogeneity

Under steady shear flow, the normal stress and the shear stress in both dilute and concentrated solutions of monodisperse poly-α-methylstyrenes and their blends were measured. It was confirmed that the molecular theories of Rouse and Zimm extended to concentrated solutions can explain the relation between the zero-shear normal stress coefficient and the zero-shear steady-flow viscosity for both monodisperse and polydisperse systems. Shear-rate dependence of steady-flow viscosity can be understood fairly well by the molecular entanglement concept proposed by Graessley so long as the polymer is monodisperse or the amount of the higher molecular weight component is high. However, zero-shear viscosity of blended systems cannot be explained quantitatively by the theory of Graessley. The shear-rate dependence of steady-state compliance of blended systems was also observed, and it can well be explained by the theory of Tanaka, Yamamoto, and Takano which interpreted the shear rate-dependent steady-state compliance in terms of the relaxation time spectrum and its variation with shear rate.     

Synthesis of methyl methacrylate star-branched polymer with divinylbenzene as a linking agent via controlled/living photopolymerization

HTEMPO-functionalized central cores were formed with divinylbenzene in ’’core first’’ method,and the four or five arms star polymers were built via controlled/living free radical photopolymerization.The four arms star polymers were also prepared with controlled/living free radical photopolymerization in ’’arm first’’ method.The resulting polymers had been confirmed by GPC and 1 H NMR.It showed that the star polymers had low polydispersities and molecular weight(M n) with the 85,000-560,000 g/mol range.     

Arm‐first synthesis of star polymers with polywedge arms using ring‐opening metathesis polymerization and bifunctional crosslinkers

This work presents a two‐step, one‐pot process to make star polymers with polywedge arms. In a one‐pot reaction, after the polywedge arms are synthesized, crosslinker species are added to the reaction, rapidly forming star polymers. Crosslinker species with different degrees of conformational freedom were designed and synthesized and their capacity to generate star polymers was evaluated. Mass conversions up to 92% and stars with up to 17 arms were synthesized with the most rigid crosslinker. The effects of arm molecular weight and molar ratio of crosslinker to arm on mass conversion and arms per star were explored further. Finally, the size‐molecular weight scaling relationship for polywedges with linear and star architectures was compared, corroborating theoretical results regarding star polymers with arms much larger than their core. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 732–740     

Synthesis and characterization of star-shaped polytetrahydrofuran

Star polymers of tetrahydrofuran (polyTHF) were prepared by reaction of living polyTHF with diethylene triamine (DETA) in the presence of 2,2,6,6-tetramethylpiperidine (TMP) as proton trap. The influence of several reaction parameters on the end-capping reaction was studied in order to produce stars having varying number of arms. With a starting living polyTHF with a molecular weight of 1600, star-shaped polymers containing up to seven polymer chains could be prepared. When the molecular weight of the living polyTHF was 8000, at most five polymer chains could be grafted on the DETA. Some physical properties of the star polymers were compared with those of their linear counterparts of the same molecular weight.     

Synthesis of low polydispersity polybutadiene and polyethylene stars by convergent living anionic polymerization

Star‐shaped polybutadiene stars were synthesized by a convergent coupling of polybutadienyllithium with 4‐(chlorodimethylsilyl)styrene (CDMSS). CDMSS was added slowly and continuously to the living anionic chains until a stoichiometric equivalent was reached. Gel permeation chromatography‐multi‐angle laser light scattering (GPC‐MALLS) was used to determine the molecular weights and molecular weight distribution of the polybutadiene polymers. The number of arms incorporated into the star depended on the molecular weight of the initial chains and the rate of addition of the CDMSS. Low molecular weight polybutadiene arms (M_n = 640 g/mol) resulted in polybutadiene star polymers with an average of 12.6 arms, while higher molecular weight polybutadiene arms (M_n = 16,000 g/mol) resulted in polybutadiene star polymers with an average of 5.3 arms. The polybutadiene star polymers exhibited high 1,4‐polybutadiene microstructure (88.3–93.1%), and narrow molecular weight distributions (M_w/M_n = 1.11–1.20). Polybutadiene stars were subsequently hydrogenated by two methods, heterogeneous catalysis (catalytic hydrogenation using Pd/CaCO₃) or reaction with p‐toluenesulfonhydrazide (TSH), to transform the polybutadiene stars into polyethylene stars. The hydrogenation of the polybutadiene stars was found to be close to quantitative by ¹H NMR and FTIR spectroscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 828–836, 2006     

星形偶联反应的动力学分析

<正> 链端带有一个官能团的聚合物与多官能团偶联剂之间的反应,是合成星形聚合物的主要途径之一。一些研究者已对上述反应作了统计分析。本文则严格求解了星形偶联反应的动力学微分方程组,得到了星形聚合物的各种分子参数与被偶联聚合物的分子参数之间的关系。     

Synthesis of cleavable multi-functional mikto-arm star polymer by RAFT polymerization: example of an anti-cancer drug 7-ethyl-10-hydroxycamptothecin (SN-38) as functional moiety

Multi-functional mikto-arm star polymers containing three different arms [hydrophilic, SN-38-P(OEGMA_8–9)₁₁, cationizable, SN-38-P(DMAEMA)₃₈ and hydrophobic, SN-38-P(BMA)₂₆] were prepared by RAFT polymerization via an arm-first approach using a cleavable cross-linker. The star polymers were cleaved to the linear arms with tributylphosphine as a reducing agent. The decrease in molecular weight observed is consistent with the initial stars having approximately five arms. Blue fluorescence was observed when a solution of mikto-arm star was irradiated under a 365 nm light proving the retention of the SN-38 moiety during star formation by RAFT polymerization. Thus these polymer-drug conjugates can be considered as potential delivery vehicles for cancer therapy. The P(DMAEMA) arms can be quaternized using iodomethane, allowing star polymers to bind negatively charged small interfering RNA (siRNA) and potentially be used as a carrier for that material.     

利用混合溶剂消除ATRP反应制备多臂星形聚合物的凝胶现象

研究了带有苄氯基团的超支化聚苯乙烯引发苯乙烯和甲基丙烯酸甲酯的ATRP反应的动力学,在良溶剂氯苯中,该反应很容易发生凝胶.如果在氯苯溶剂中反应一段时间后,加入1,4-二氧六环作为不良溶剂,则能有效阻止凝胶反应,最终得到分子量超过百万的星形聚合物.