Bulk viscoelastic contribution to the wet‐sliding friction of rubber compounds

The wet‐sliding friction characteristics of rubber compounds made of high cis‐polybutadiene were examined with a British pendulum skid tester at room temperature. Three series of compounds were prepared—unfilled or filled with carbon black at two different levels. The bulk viscoelastic properties as characterized by the bulk glass‐transition temperature for the compounds were systematically adjusted by changing the crosslinking density via sulfur vulcanization. In fact, the dynamic mechanical glass‐transition temperature for the compounds ranges between approximately ?100 and 20 °C. Consequently, the wet‐sliding friction of these rubber compounds is dramatically affected. With increasing compound glass‐transition temperature, the wet‐sliding friction increases to a maximum and then decreases. However, the rate of increase or decrease varies with the amount of filler in the compounds. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 757–771, 2003     

Synthesis and Properties of Imidazole-Blocked Toluene Diisocyanates

Abstract

Imidazole-, 2-methyl imidazole-, and benzimidazole-blocked toluene diisocyanates (TDI) were prepared and characterized by elemental analysis, IR, and NMR spectroscopy. Simultaneous TGA/DTA results showed that the thermal stability of the adduct decreases in the following order: imidazole-TDI > 2-methylimidazole-TDI > benzimidazole-TDI. Gelation test involving imidazole-blocked adducts and hydroxyl-terminated polybutadiene were also carried out. The cure rate of the adduct increases from the imidazole- to the 2-methylimidazole- and to the benzimidazole-blocked adduct. It is also found that the benzimidazole-blocked adduct shows better solubility in the polyols.     

Comprehensive Microstructure and Molar Mass Analysis of Polybutadiene by Multidimensional Liquid Chromatography

For the first time, polybutadiene is separated according to microstructure using solvent gradient interaction chromatography (SGIC). Superior separation of polybutadienes having different microstructures is obtained on a silica‐based reversed stationary phase and a mobile phase of acetone–hexane. This SGIC system enables the baseline separation of 1,2‐polybutadienes and 1,4‐polybutadienes even in cases where the samples have similar molar masses. 2D liquid chromatography is performed with the SGIC method separating according to microstructure in the first dimension coupled to size exclusion chromatography separating according to molar mass in the second dimension, thus providing comprehensive information on both microstructure and molar mass.

     

Active‐center equilibrium in Ziegler–Natta butadiene polymerization

The Ziegler–Natta‐catalyzed polymerization of 1,3‐butadiene was investigated at a low aluminum alkyl/cobalt (Al/Co) ratio using two different soluble catalyst systems: cobalt(II) octanoate/diethylaluminum chloride/water and cobalt(II) octanoate/methylaluminoxane/tert‐butyl chloride. When the active‐center concentration was determined by the number‐average molecular weight technique, it was found that the percentage of active cobalt depended on the Al/Co ratio. Subsequently, an equilibrium reaction was proposed to be Co + 2Al ? CoAl₂, where Co is cobalt(II) octanoate, Al is either of the aluminum alkyl‐activator species, and CoAl₂ is the active catalyst. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2256–2261, 2001     

An improved method for the diimide hydrogenation of butadiene and isoprene containing polymers

The hydrogenation of unsaturated polymers with diimide generated in-situ by thermolysis of p-toluenesulfonyl hydrazide (TSH) is a commonly used method for preparing laboratory scale quantities of saturated diene based polymers. The by-products from TSH, particularly p-toluenesulfinic acid, can attack at olefinic sites, adding p-tolylsulfone functionality and degrading polymer molecular weight. The addition of tri-n-propyl amine has been found to eliminate these side reactions in butadiene containing polymers and copolymers, enabling the preparation of polymers devoid of backbone unsaturation. No detectable sulfur-containing impurities were indicated by IR, NMR, or elemental analysis, and no chain degradation was observed via GPC analysis of the hydrogenated polymers. cis-Polybutadiene and butadiene containing random and block copolymers with styrene were hydrogenated cleanly using this technique. A ratio of 2 mol TSH and 2 mol amine/mol of olefin was necessary to assure > 99% hydrogenation, and a w/v ratio of 2 parts butadiene/100 parts o-xylene gave the most efficient hydrogenation. Polymers prepared from isoprene were only partially hydrogenated when treated with TSH in the presence of tri-n-propyl amine, and gave evidence of slight degradation of the polymer structure.     

Thermodynamic interactions in blends of poly(4-tert-butyl styrene) and polyisoprene by small-angle neutron scattering

The thermodynamic interactions between poly(4-tert-butyl styrene) [P(4tBS)] and 1,4-polyisoprene (PI; both hydrogenous) were obtained as functions of the temperature, PI molecular weight, and blend composition through the examination of miscible ternary blends of these two components with a common miscible labeled polymer [90% 1,2-deuterated polybutadiene (dPBD)] with small-angle neutron scattering. The thermodynamic interaction parameters between P(4tBS) and dPBD and between P(4tBS) and PI increased with increasing temperature and were consistent with lower critical solution temperature behavior. Although the binary blends of P(4tBS) and dPBD exhibited phase separation at elevated temperatures, the thermodynamic interaction parameters between P(4tBS) and PI remained large and negative and independent of the PI molecular weight. Finally, the thermodynamic interactions for PI and P(4tBS) depended strongly on the ratio of PI to P(4tBS) and were also sensitive to the amount of dPBD present in the ternary blend. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3204–3217, 2004     

Synthesis of polybutadiene‐graft‐poly(dimethylsiloxane) and polyethylene‐graft‐poly(dimethylsiloxane) copolymers with hydrosilylation reactions

We report preliminary results for the synthesis of polyethylene‐graft‐poly(dimethylsiloxane) copolymers obtained by catalytic hydrogenation of polybutadiene‐graft‐poly(dimethylsiloxane) copolymers (PB‐g‐PDMS). These last copolymers were synthesized by hydrosilylation reactions between commercial polybutadiene and ω‐silane poly(dimethylsiloxane). The reaction was carried in solution catalyzed by cis‐dichloro bis(diethylsufide) platinum(II) salt. The PB‐g‐PDMS copolymers were analyzed by ¹H and ¹³C NMR spectroscopies, and the relative weight percentages of the grafted poly(dimethylsiloxane) macromonomer were determined from the integrated peak areas of the spectra. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2920–2930, 2004     

Supramolecular polymer gels formed from carboxy‐terminated telechelic polybutadiene and polyamidine through amidinium‐carboxylate salt bridge

In this article, we report the preparation and properties of the bulk supramolecular polymer gels prepared from a polybutadiene based on the amidinium‐carboxylate salt bridge, highlighting the difference from a well‐established network system based on carboxylic acid and amine. We have prepared the amidinium‐carboxylate salt bridge‐based supramolecular polymer gels from a carboxy‐terminated telechelic polybutadiene and a linear polyamidine having N,N′‐di‐substituted acetamidine group in the main chain. FTIR analysis along with Small angle X‐ray scattering measurements indicated that the salt bridge was attributed to the gelation through three‐dimensional network formation. Virtually no fluidity was observed for the supramolecular gel containing equimolar amounts of the carboxyl group and the amidine group, which showed a high G′ value of about 1 MPa at room temperature and a T_gel of 37 °C. For comparison, the supramolecular polymer gels crosslinked by ammonium‐carboxylate salt were prepared using a linear polyethyleneimine instead of the polyamidine. The gel with equimolar amounts of the carboxyl group and the secondary amino group showed liquid‐like fluidity with a G′ value of about 0.01 MPa at room temperature, which was attributed to the fact that a certain amount of the carboxyl group remained as its free form without salt formation, as evidenced by FTIR analysis. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1815–1824     

Stereoselective Complex Formation between Polybutadiene and Cyclodextrins in Bulk

Polybutadienes (PBs) are found to form inclusion complexes with cyclodextrins (CDs) stereoselectively to give crystalline compounds in bulk. These complexes have been isolated and characterized by means of ¹H NMR and ¹³C CP/MAS NMR spectroscopy, and X‐ray diffraction. Although α‐CD did not form inclusion complexes with any kinds of PBs in aqueous solutions, α‐CD did form inclusion complexes with PBs having 1,4‐cis‐ and 1,4‐trans‐butadiene units in bulk by heating at 100 °C. On the other hand, PB having 79% of a 1,2‐structure did not form inclusion complexes with α‐CD. The yield of the inclusion complexes increases with an increase in the content of the 1,4‐cis‐structure of PB and decreases with the molecular weights of the PBs.

     

季戊四醇型HTPB-PU弹性体的研究

以端羟基聚丁二烯、液化改性MDI为原料,季戊四醇为扩链剂与交联剂制备季戊四醇型聚氨酯,并用IR、TG、DSC和SEM对其进行表征;研究了影响季戊四醇型聚氨酯的力学性能和热性能的因素。结果表明：随扩链剂用量的增大,季戊四醇型聚氨酯的拉伸强度和硬度增大,而断裂伸长率减小,同时热稳定性得到提高。SEM显示此弹性体中存在明显的相分离。