宽分子量分布聚合物的制备

分别对采用物理共混法、自由基聚合、配位聚合和离子聚合法制备宽分子量分布聚合物进行了综述。指出目前应用较为广泛的是物理共混法，配位聚合容易实现分子量和分子量分布宽度可控，近几年已成为研究热点。     

宽峰聚乙烯／蒙脱土纳米复合材料的制备

利用2种不同的方法制备了2种氢调敏感性不同的蒙脱土／氯化镁／四氯化钛（MMT／MgCl2／TiCl4）催化剂,利用这2种催化剂及其混配催化剂,通过原位聚合法,制备出一系列宽峰聚乙烯纳米复合材料,采用X_射线衍射仪（XRD）、凝胶色谱测试分析（GPC）及力学性能测试等方法对催化剂及聚合产物进行分析,结果表明,2种催化剂以及按照不同比例混合的混配催化剂均表现出较高的聚合活性,XRD测试结果表明,蒙脱土片层在乙烯聚合过程中发生了插层及剥离,以单片层或几层共存的形式分散于聚乙烯基质中;用混配催化剂可制得宽峰聚乙烯纳米复合材料,Mw／Mn=7．23,并且聚合物的堆积密度达到工业生产的标准,宽峰聚乙烯纳米复合材料的综合力学性能较工业产品5000S及工业上应用的管材料有很大的提高。     

窄分布低乙烯基线型液体聚丁二烯的环氧化反应

采用负离子聚合法设计合成了分子量分布(MWD)窄、乙烯基含量低的线型液体聚丁二烯(NDLPB),然后用过氧甲酸原位法制备了不同环氧度的环氧化线型液体聚丁二烯(ENDLPB),并以其为偶联剂合成了梳状聚丁二烯,通过核磁共振法对ENDLPB的环氧度和结构进行了表征,考察了ENDLPB环氧度的影响因素.结果表明,随着ENDLPB环氧度的增加,环氧基特征峰逐渐增强,顺式-1,4-结构和反式-1,4-结构含量减小,1,2-结构含量不变;随着NDLPB数均分子量(~￣M_n)的增加,ENDLPB的环氧度减小,且~￣M_n略有增大,MWD约为1.08;以~￣M_n为2 450、MWD为1.07的NDLPB为反应物,在H_2O_2/NDLPB(摩尔比)为0.5、甲酸/NDLPB(摩尔比)为 0.4、反应温度为50 ℃的条件下反应2 h,可获得环氧度约为33%的ENDLPB,且实验的重复性良好;改变ENDLPB用量可获得不同偶联度的梳状聚丁二烯.     

Synthesis and characterization of pendent hydroxy fluoroesters of secondary high molecular weight guayule rubber

The epoxidation of secondary high molecular weight guayule rubber (SHMWGR) and subsequent ring opening with fluoroacids to give hydroxyfluoroesters (FGR) is reported. Structural characterization was performed with FTIR; ¹H-, ¹³C-, and ¹⁹F-NMR; and DSC. The percent epoxidation was quantitatively determined by ¹H-NMR. It was noted that the glass transition temperatures (T_g) of the FGR polymers increased with increasing fluoro acid content; however, reactions with longer chain, highly fluorinated acids lowered the T_g. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1077–1089, 1997     

Anomalies in the rheological behavior of polyethylene with very broad molecular weight distribution

The rheological behavior of high density polyethylenes with very broad molecular weight distribution is studied in the molten state starting from freshly synthesized powders. The complex viscosity increases slowly up to a limiting value as a function of ageing of the polymer and faster when the molten polymer is stirred. The phenomena are explained by an heterogeneous distribution of very high molecular weight nodules in the polymer arising from the synthesis and is proved by the preparation and characterization of polymers presenting the opposite heterogeneity and behavior (very low molecular weight nodules).     

相对分子质量及其分布对高反式1，4-丁二烯-异戊二烯共聚橡胶性能的影响

研究相对分子质量(门尼粘度)及其分布对反式1,4-丁二烯-异戊二烯共聚橡胶(TBIR)性能的影响。结果表明,TBIR的塑炼、混炼性能随着门尼粘度的减小逐渐改善,门尼粘度大于60的TBIR混炼难度增大、加工性能变差;TBIR的综合物理性能随着门尼粘度的增大而提高,但当门尼粘度大于55之后胶料物理性能和动态性能改善效果不显著,TBIR胶料综合性能在门尼粘度为50～60时达到最佳。相对分子质量分布呈双峰的TBIR生胶和硫化胶的强伸性能、磨耗性能和生热性能较优;相对分子质量分布呈单峰的TBIR硫化胶耐屈挠性能得到很大提高。     

星形中乙烯基聚丁二烯橡胶的合成与表征

以多官能团有机锂为引发剂，四氢呋喃为微观结构调节剂，在抽余油中一步法合成了星形中乙烯基聚丁二烯橡胶（S-MVBR），并对其结构进行了表征。结果表明，在2L聚合釜中，聚合单体质量浓度为0.08-0.09g/mL,50℃下反应2h后，再在80℃下反应1.5-2h；通过调节四氢呋喃用量和改变温度可调节S-MVBR中的1，2-结构质量分数为35%-55%；通过调节多官能团有机锂引发剂所含的活性中心数及繁臂的相对分子质量来控制S-MVBR的相对分子质量；通过多官能团有机锂引发剂的官能团分布来调节S-MVBR的相对分子质量分布；S-MVBR中的凝胶质量分数小于1%。     

单反应器法生产宽/双峰聚乙烯催化剂研究进展

系统介绍了国内外用于单反应器法生产宽/双峰聚乙烯的催化剂,主要包括混合催化剂、双/多金属催化剂、双载体催化剂和其它催化剂体系;阐述了各类催化体系的优缺点及研究现状;评述了各种催化剂的工业化应用前景。     

Unusual stress-strain properties of natural rubber vulcanizates with high primary molecular weight

Summary Natural rubber vulcanizates with high primary molecular weight were prepared by mixing raw rubber and dicumyl peroxide in benzene followed by freeze-drying. The stress-strain properties of these vulcanizates were quite different from those prepared by conventional mastication method. The important characteristics of these vulcanizates is high tensile modulus, high tensile strength, large hysteresis loss, and higher degree of strain-induced crystallization. The difference in the stress-strain behavior between these rubbers and conventional vulcanizates are discussed from the standpoint of the network structure.     

The modification of secondary high molecular weight guayule rubber with metachloroperoxybenzoic acid

The epoxidation of secondary high molecular weight guayule rubber has been accomplished. The reaction is performed using metachloroperoxybenzoic acid as the epoxidation agent in various stoichiometric ratios including 5, 10, 20, and 50 mol %. The products were characterized by infrared spectroscopy, ¹H- and ¹³C-nuclear magnetic resonance (NMR), differential scanning calorimetry, and elemental analysis. ¹H-NMR is used quantitatively to calculate epoxidation levels that are compared to stoichiometry. DSC results record a linear relationship between percent epoxidation and T_g. © 1993 John Wiley & Sons, Inc.     

锂系高门尼粘度丁二烯橡胶的环氧化

对高门尼粘度锂系丁二烯橡胶进行了环氧化研究。用IR和NMR对聚合物微观结构进行表征时发现,在810～890cm-1和(1.0～2.0)×10-6处出现环氧基峰。环氧化程度(E)较高时,X—C键断裂,造成Mn和Mw减小,Mw/Mn变窄。Tg随E增大而升高。     

官能化高乙烯基聚丁二烯橡胶与丁腈橡胶共混胶的性能

以氢化钠为活性剂、马来酸酐为改性剂,通过负离子反应对高乙烯基聚丁二烯橡胶(HVBR)进行官能化改性制备了官能化HVBR(FHVBR)。考察了FHVBR与丁腈橡胶(NBR)共混的质量比对FHVBR/NBR共混胶硫化特性、力学性能、耐热氧老化性能和电性能的影响,并通过差示扫描量热仪和扫描电子显微镜探讨了共混胶的两相相容性。结果表明,随着NBR用量的增加,FHVBR/NBR共混胶的硫化时间缩短、硫化效率提高,定伸应力和硬度增大,耐老化性能得以改善。NBR用量的增加使得FHVBR/NBR共混胶对不同频率下的微波吸收能力增强,共混胶的电阻率下降,导电性增强。然而,NBR用量增加导致共混胶的拉伸强度略有下降。     

Molecular weight and molecular weight distribution from dynamic measurements of polymer melts

A method for determining the molecular weight distribution (MWD) of a polymer melt has been developed using the dynamic elastic modulus (G'), plateau modulus (G), and zero shear complex viscosity (η). The cumulative MWD was found to be proportional to a plot of (G'/G)^0.5 vs. measurement frequency (ω). Frequency (ω) was found to be inversely proportional to (MW)^3.4, as expected. Results were scaled to absolute values using the empirical relationship η ∝ (M?_w)^3.4, where M?_w is the weight-average MW. M?_w, M?_n (number-average MW) and M?_w/M?_n calculated from melt measurements were found to agree with size exclusion chromatography usually well within 10 percent for broad and bimodal distribution samples. M?_w/M?_n tended to be approximately 20 percent higher for narrow distribution samples (M?_w/M?_n < 1.2) because we did not account for a finite distribution of relaxation times from a collection of monodisperse polymer chains. We also did not account for the plasticizing effect of short chains mixed with long ones which caused peak positions to be closer together for Theological vs, size exclusive chromatography (SEC) determinations of MW for bimodal distribution blends.     

Some properties of low molecular weight polybutadiene and polytetrahydrofuran

The proposition, that low molecular weight polymer fractions in good solvents behave as if they were under ? conditions, has been examined experimentally. Series of monodisperse hydroxy-terminated polytetrahydrofuran (PTHF), 82% 1,4-polybutadiene (PBD), and 30% 1,4-PBD were prepared, and values of M?_n obtained by vapor-pressure osmometry and endgroup analysis. The Mark–Houwink viscosity parameters K and ν were determined in a number of solvents. The general conclusion is that the proposition is invalid for these systems notwithstanding the fact that ν = 0.50 for one of them [82% 1,4-PBD in methyl ethyl ketone (MEK) at 25°C]. For this particular case, the following evidence suggests that these are actually ? conditions so that the apparent fulfilment of the proposition is fortuitous. (1) Cloud-point precipitation yields ? = 26 ± 3°C in MEK. (2) The value of K is close to that of K_? found elsewhere for PBD in a different solvent at a similar temperature. (3) Application of the Kurata-Stockmayer iterative procedure for estimating K_? from data in good and bad solvents yields a reasonably small discrepancy (10%) between the K_? values from data in toluene and MEK at 25°C for this polymer and only a 3% difference in the unperturbed dimensions (〈r₀²〉/M)^1/2 derived from them. Measured melting points T_m of PTHF (M?_n = 1000–13000), plotted as a function of chain length Z, viz., 1/T_m = 1/T_m0 + 2R/ZΔH_f, yield 43 ± 3°C and 1.6 kcal/submole, respectively, for the limiting melting point T_m0 and the heat of fusion ΔH_f. The former is in good agreement with the value obtained dilatometrically for high molecular weight polymer, while the latter indicates a degree of crystallinity of ca. 54%.     

Z-N催化剂生产宽/双峰MWD聚乙烯的研究进展

介绍了Ziegler-Natta(Z-N)催化剂在单反应器中生产宽,双峰相对分子质量分布(MWD)聚乙烯(PE)的最新研究进展,概括了Z-N催化剂制备宽／双峰MWDPE的主要方法及特点,即传统的Ti系催化体系生产的双峰PE的MWD较窄,改进的Ti-V双金属催化体系活性高,可以调节MWD,但反应操作难度大。通过加入不同的配合物,调节并改进PE的MWD,取得了较好的实验结果。宽/双峰MWDPE的生产和开发是PE工业发展的一个重要方向。     

Synthesis and characterization of high molecular weight water-soluble polymers

The synthesis of high molecular weight acrylic water-soluble polymers in heterophase water-in-oil polymerizations is discussed. A mechanism has been elucidated which includes elementary reactions in the continuous (organic) and dispersed (aqueous) phases, as well as the interfacial layer. The latter allows for the identification of interfacially active species which can concurrently enhance stability and increase the linear molecular weight of the polymer. Suitable species are found to contain multiple radically active functional groups on either the hydrophilic or hydrophobic moieties. A one-point light-scattering method is also developed which improves the accuracy in molecular-weight estimation to /pi5%. compared with /pi10% for the conventional dilution procedure. This is demonstrated for high molecular weight polyacrylamides and is found to reduce the sample measurement time fourfold, to 20 min.     

Preparation and characterization of high molecular weight novolak resins

Summary High molecular weight novolak resins were prepared from phenol and paraformaldehyde in organic solvents, e.g., 2-propanol, ethyl propionate, 2-methoxyethanol, 4-methyl-2-pentanone, dioxane and acetic acid. The molecular weights were estimated by gel permeation chromatography (GPC) and solution viscosity measurement and it was confirmed that high molecular weight resins were formed in organic solvents. The structure was determined by¹³C-NMR measurements, and it was found that the resin obtained in organic solvent was a random novolak with higher molecular weight than a conventional novolak.     

铁系高乙烯基聚丁二烯橡胶的性能

研究了高乙烯基质量分数大于80%的铁系聚丁二烯橡胶(FVBR)的生胶性能、混炼行为、硫化特性、硫化胶性能、黏弹性能以及耐热老化性能,并与溶聚丁苯橡胶(SSBR)的性能进行了比较。结果表明,FVBR的混炼行为良好,添加适量的操作油,可得到性能理想的硫化胶。FVBR硫化胶的拉伸强度、撕裂强度以及耐热老化性能等与SSBR相当。此外,FVBR在60℃下的tanδ较低,表明其具有较低的滚动阻力。     

Segregation behavior of polyethylene with broad molecular weight distribution by annealing procedure in temperature gradient

An annealing treatment in a molten state, in which temperature of the top plate is different from that of the bottom one in a compression-molding, leads to molecular weight segregation of high-density polyethylene (HDPE) prepared by mixture of two types of HDPE with different molecular weights (Mw = 1.8 × 10⁵ and 2.9 × 10⁴). Low molecular weight fraction tends to localize at the surface attached to the higher temperature and vice versa. The segregation behavior is obvious at a large temperature gradient. Although the accuracy and mechanism of the phenomenon have not been clarified yet, this could be applied as a new fractionation method, which does not use a solvent.