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     

Molecular weight characterization of polybutadiene rubber with high molecular weight and broad molecular weight distribution

Following the molecular weight characterization of two polybutadiene samples, it was found that M _w from gel permeation chromatography with universal calibration and light scattering were in agreement, but M _n by gel permeation chromatography was less than M _n from membrane osmometry. A more detailed analysis revealed that the high molecular weight and broad molecular weight distribution of the two samples forced two corrections to the membrane osmometry results for (a) diffusional layer effects caused by high solution viscosities, and (b) solute permeability of the membrane. In the latter effect, the high viscosities of the solutions prevented actual diffusion through the membrane, but “reflection” of these species as defined by the Staverman coefficient prevented an accurate M _n determination. After making these corrections, it was found that M _n from membrane osmometry using a very tight membrane was in very good agreement with M _n from gel permeation chromatography. A method is demonstrated for obtaining M _n from a combination of membrane osmometry and gel permeation chromatography, where membrane osmometry data from membranes of different porosities (after corrections for diffusional layers and membrane reflection) are used to verify the accuracy of the gel permeation chromatography data as representing the true molecular weight distribution, allowing the gel permeation chromatography data to be used to calculate M _n.     

Synthesis and characterization of maleinized‐silylated low molecular weight guayule rubber (MASiGR)

Maleinization followed by silylation of low molecular weight guayule rubber was accomplished for the first time via a two‐step process. Maleinization was first effected by grafting maleic anhydride onto guayule rubber under the influence of benzoyl peroxide catalyst to give maleinized guayule rubber (MAGR). The maleinized rubber was then further derivatized via hydrosilylation with dichloromethyl silane and chloroplatinic acid (Speier's catalyst) to give maleinized‐silylated guayule rubber (MASiGR). The silylated polymer (MASiGR) was further functionalized by reaction with ethanol or aqueous ammonia to produce ethoxysilane and silanol moieties, respectively. The products were characterized by Fourier transform infrared spectroscopy (FTIR), ¹H‐, ¹³C‐, and ²⁹Si‐ nuclear magnetic resonance spectroscopy (NMR). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 754–761, 2001     

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.     

Applications of epoxidized and hydroxy‐fluoroester pendent secondary high‐molecular‐weight guayule rubber in coatings

The epoxidation of secondary high‐molecular‐weight guayule rubber to yield epoxidized guayule rubber (EGR) and the subsequent opening of the oxirane rings by fluoroacids to yield fluorinated guayule rubber (FGR) were reported in an earlier article. 1 The oxirane and hydroxyl groups that occur in EGR and FGR, respectively, enable these derivatives to be integrated into the binder system of coatings. The coating industry has long been interested in nontoxic multifunctional crosslinking agents that do not emit volatile organic compounds (VOCs). Ring‐opening reactions of epoxides and reactions between hydroxyl and isocyanate groups are prime examples of crosslinking that do not emit VOCs. This study was conducted to ascertain the viability of guayule rubber derivatives that contain epoxide and hydroxyl groups as crosslinking agents in solvent‐based coatings and powder coatings. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1718–1724, 2001     

The degradation of guayule rubber and the effect of resin components on degradation at high temperature

Degradation of pure guayule rubber and rubber in the presence of stearic, oleic, linoleic, and linolenic acid, has been studied at high temperatures (from 150°C to 600°C) using thermogravimetric analysis (TGA). On-line mass spectrometric analysis of the products of decomposition has also been done to understand the mechanism of degradation. Degradation of rubber starts around 230°C in air and 330°C in nitrogen. Presence of acids changes the onset of degradation, because of low decomposition temperature of the acids. In the derivative curve, there is one T_max for degradation in nitrogen; two for rubber; and three for rubber containing acids are observed for degradation in air. The activation energy of degradation, as observed by isothermal kinetics, in the 1–10% weight loss region, is 225 kJ/mol in nitrogen and 167 kJ/mol in air. In the 10–100% region, however, the activation energy of degradation measured by the Freeman and Carroll method using dynamic thermogravimetry, is 239 kJ/mol in both nitrogen and air atmosphere. The main products of pyrolysis in inert atmosphere are propylene, propane, isobutylene, methyl butene, isoprene, 2,3-dimethyl cyclopentene, octene, 2,4-dimethylcyclohexene, dipentene, etc. Isoprene is found to be the most abundant. Fragments having m/e values of 136, 121, 107, 93, 79, and 53 are also produced in large quantities. The ratio of concentration of dipentene to isoprene increases marginally with temperature. The concentration of other fragments however increases drastically with temperature. The additives have no effect on the nature of products obtained. The conversion to different fragments depends upon the temperature of degradation and the stability of intermediate products. All smaller molecules are obtained from either dipentene or isoprene. A mechanism of formation of these products has been suggested.     

超高相对分子质量聚乙烯纤维改性方法

简介了超高相对分子质量聚乙烯纤维的性能与应用,重点阐述了低温等离子处理法、辐照接枝改性法、化学氧化法和电晕放电法4种常用的对超高相对分子质量聚乙烯纤维改性方法的研究情况。综述表明,无论采用以上任何一种改性方法,都能相应有效改善纤维的表面性能,提高纤维与其它材质间的粘接性。     

Mechanism of secondary crystallisation in irradiated and aged ultra high molecular weight polyethylene

Ultra high molecular weight polyethylene has been irradiated in air and aged for 168 months. On melting and recrystallisation in the differential scanning calorimeter a secondary crystallisation event is observed around 80 °C. This event has been studied using isothermal crystallisation and the results analysed using the Avrami equation and the Lauritzen-Hoffman approach. This suggests that during this event growth occurs through regime II kinetics whereby large numbers of surface nuclei form on the substrate, with multiple nucleations acts commencing before the previous ones have finished. It is postulated that this secondary crystallisation event involves the development of a diffuse semi-ordered interface between the well-developed lamellae and the amorphous phase.     

双螺杆反应器制备高分子量聚乳酸的研究

利用双螺杆挤出机将低分子量的乳酸预聚物在挤出机上进一步缩聚,制备出较高分子量的聚乳酸.研究了反应挤出温度、催化剂用量及螺杆转速等因素对该缩聚反应的影响.结果表明,当反应温度为160℃,催化剂用量为0.5％,螺杆转速为30 r/min时,聚乳酸的分子量能得到最大程度的提高.     

The forming properties of high molecular weight polyethylene

The formabilities of cold-rolled high molecular weight polyethylene (HMWPE) sheets have been studied by measuring their plastic anisotropy ratio (R value), strain-hardening exponent (n value), strain distribution, and the forming limit diagram (FLD). The deep drawability of the polymer is improved by rolling. After 40% or more reduction in thickness by cold rolling, the HMWPE sheet could be deep-drawn into a cylindrical cup. The results of R value measurement indicate that the R value is responsible for improved drawability. Cold rolling also increases the n value but decreases the strain gradient. Stretch forming tests have also been carried out, and the results show that cold working could also improve the stretchability of this polymer. The results of the FLD are in agreement with the other properties studied. The mechanical properties, environmental stress cracking resistance, and shape, size, and property stability of the deep-drawn HMWPE cups have also been investigated.     

Effects of environment and composition on degradation of guayule rubber

Bales of antioxidant-stabilized guayule rubber underwent significant losses in bulk viscosity when stored under ambient conditions at an Arizona processing facility. Previous work implicated the unsaturated fatty acid esters present in entrained resin as promoters of such degradation. Aging studies as functions of storage temperature and unsaturated acid ester content were carried out on both bulk rubber and rubber-resin solution (miscella) for cultivar AZ-101. The rate of thermooxidative degradation, determined as a function of Mooney viscosity, was increased by the addition of unsaturated ester. Anaerobic degradation was not affected in this way. The activation energy of chain thermolysis was found to be 116 ± 6 kJ/mol (28 ± 1 kcal/mol). At temperatures above 60°C, chain recombination successfully competed with chain scission in lower viscosity rubber. The rate of thermoox-idative degradation was substantially higher in a typical process miscella. A hindered amine antioxidant significantly reduces chain scission under these conditions. © 1996 John Wiley & Sons, Inc.     

Effect of resin components on the degradation of guayule rubber

All natural rubbers are likely to contain some long chain fatty acids or their esters. The individual effect of the four C₁₈ fatty acids (stearic, oleic, linoleic, and linolenic acid) present in the guayule resin on the degradation of guayule rubber has been investigated concurrently by stress–relaxation of radiation cured rubber networks and by gel permeation chromatography studies on the raw rubber in the temperature zone 70–125°C. C₁₈ unsaturated fatty acids enhance the degradation of rubber several fold. The rate of degradation follows the order: rubber ≤ rubber + stearic acid < rubber + oleic acid < rubber + linoleic acid < rubber + linolenic acid. The thermal degradation is slower than the thermooxidative. The rate of degradation monotonically increased with the number of conjugated double bonds and is first order with respect to acid concentration. The activation energy for the chain scission for both thermal and thermooxidative degradation has been found to be 95 ± 10 kJ/mol. The mechanism of degradation of guayule rubber in the presence of fatty acids is discussed.     

双组分室温硫化硅橡胶相对分子质量测定

对双组分室温硫化硅橡胶相对分子质量进行测定.根据双组分室温硫化硅橡胶粘度测定数据,分别用外推法、一点法和算图法计算其平均相对分子质量.一点法计算简单,但误差较大;外推法误差较小;算图法准确性最高,但耗时长.粘度测定结果的影响因素包括粘度计结构和材料以及温度、外界震动和溶剂纯度等.     

超高分子量聚乙烯纤维的表面处理

综述了超高分子量聚乙烯（UHMWPE）纤维复合材料界面的重要性,总结了表面改性方法对UHMWPE纤维以及UHMWPE／树脂界面的影响。     

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。     

超高分子量聚乙烯纤维防切割手套应用与市场分析

阐述了超高分子量聚乙烯(UHMWPE)防切割手套的加工及性能特点,并分析了市场发展趋势,对市场前景进行了展望。     

The analysis of high molecular weight quaternary ammonium chlorides

Summary Commercial production of high molecular weight quaternary ammonium chlorides has necessitated methods for their analysis. Available methods were found to be lacking in completeness. A successful scheme of analysis was worked out for determining quaternary ammonium chloride, amine hydrochloride (or free alkali), amine, and sodium chloride. The analytical procedures as described are straightforward and suitable for routine product and process control. Paper No. 129, Journal Series, General Mills Inc., Research Department.     

Effects of various factors on the formation of high molecular weight polyamic acid

The reaction of pyromellitic dianhydride (PMDA) and aromatic diamine in an aprotic solvent such as dimethylacetamide (DMAc) gives a solution of poly(amic acid). The effects of certain variables on the polymerization and some additives on the stability and imidization of the poly(amic acid)s were studied. It was found that the addition of PMDA portionwise to the solution of diamine always keeps the excess diamine in solution and enables one to obtain the highest molecular weight of poly(amic acid). When the addition process was reversed, either by the change or dehydration of solvent, a high molecular weight was not attained. The inevitable water in the solvent or the reaction medium is the major factor, and the more the water content in the solvent or the reaction medium, the larger is the probability of destruction of PMDA during the reaction and hence low molecular weight is obtained. If very pure monomers were used in the polymerization, the 1:1 of molar ratio is the optimum value. Excess diamine or dianhydride results in the exchange reaction with poly(amic acid) and causes a rapid degradation of polymer chain. This exchange reaction was proved by NMR measurements. The presence of electrophilic agents or the nucleophilic agents containing active protons in the poly(amic acid) solution promotes the decomposition of polymer and causes the brittleness of polyimide film in the curing process. Using acetic anhydride (A) to convert the poly(amic acid) to polyimide, pyridine (P) can protect the polymer chain from the nucleophilic attack by the anhydride. The mixture with proper ratio of A/P (1/1–15/1) can be used as good dehydrating agents. Meanwhile, according to the results to the results of experiments, we suggested the probable reaction mechanisms about how the water, amine, and anhydride destroy the polyamic acid chains.     

用门尼粘度仪测试天然橡胶的相对分子质量

研究了门尼粘度仪测试的门尼粘度和凝胶渗透色谱仪测试的相对分子质量的关系。结果表明,Mark-Houwink方程η=kMa可以描述复数粘度与相对分子质量间的关系,并有较好的相关性。用门尼粘度值计算的数均相对分子质量和重均相对分子质量与凝胶渗透色谱仪测试的相对分子质量的相对误差分别为11.3%和2.4%。