Analysis of network structure formed in styrene–butadiene rubber cured with sulfur/TBBS system

Several styrene–butadiene rubber (SBR) compounds were prepared with different cure systems based on sulfur and TBBS (N‐t‐butyl‐2‐benzothiazole sulfenamide), varying the amount of sulfur and accelerator between 0.5 and 2.5 phr in the formulation. Torque curves, measured with a moving die rheometer at temperatures at 433 K, were used to characterize the vulcanization. The time to achieve the maximum torque, t_100%, was evaluated for each sample, and this time was set to vulcanize sheets at 433 K. The density and type of elastically active crosslinks of each cured sample were evaluated by means of swelling measurements and were related to the vulcanizing system. Finally, the rheometer data were analyzed considering the network structure formed during vulcanization. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1105–1112, 2007     

Structure and properties relationships of epoxy resins part 1: Crosslink density of cured resin: (I) model resins synthesis

Two model epoxy resin precursors based on the N-glycidyl derivatives of 4.4'-diaminodiphenylene methane (DDM) were prepared: N,N bis-(2,3-epoxypropyl)-N′,N″-dimethyl-4.4'-diaminodiphenylene methane (G2A); N.N′ bis-(2,3-epoxypropyl)-N,N′-dimethyl-4,4'-diaminodiphenylene methane (G2S). To prepare these, aniline or N-methyl aniline was reacted with epichlorohydrin, using acetic acid as catalyst. The products were coupled via acid-catalysed condensations in the presence of formaldehyde or with N,N-dimethylaminobenzyl alcohol. The coupled chlorohydrins formed were then dehydrochlorinated to form the desired product. All reactions were monitored and purifications of the crude products were effected by high pressure liquid chromatographic techniques. The products were characterised by proton and carbon-13 nuclear magnetic resonance, infrared and mass spectroscopy, elemental and titrametric analysis. Results were compared with those obtained for tetra-N-glycidyl-4,4'-diaminodiphenylene methane (TGDDM). All the data confirmed the structures of the model resins. These, together with TGDDM. will be used to prepare epoxy resin networks of controlled crosslink density and chemical homogeneity.     

甘露醇交联的聚丙烯酸钠吸水树脂综合应用性能的测试

采用溶液聚合法合成了甘露醇交联的聚丙烯酸钠吸水树脂。用红外光谱和热重分析方法对聚丙烯酸钠超强吸水树脂产品进行了表征,测定了该树脂的溶胀动力学、耐热、耐寒、耐光性能及不同pH溶液对树脂吸水率的影响,分析了该树脂的羧酸根和凝胶含量,测试了不同温度下的吸水率、保水率。结果表明,该树脂在蒸馏水中的吸水率为1 750mL/g,在0.9%NaC l水溶液中的吸盐水率为130mL/g。利用热重分析法对该树脂的热分解动力学过程进行研究,并计算了热分解的活化能及指前因子。实验结果表明,该树脂的溶胀动力学扩散摸模型为non-Fickon扩散;热分解过程为一级反应。该树脂具有较好的综合应用性能。     

Functionality distribution and crosslink density of hydroxyl-terminated polybutadiene

A novel approach is proposed for estimating the average molecular weight between crosslinks (M?_c) from the functionality distribution of hydroxyl-terminated polybutadiene ( HTPB ). The functionality distribution of four free-radically polymerised HTPB prepolymers of varying hydroxyl content and molecular weight was determined by a combination of preparative and analytical gel permeation chromatography. The gumstock properties of the samples cured with stoichiometric amounts of toluene diisocyanate were not correlatable with the relative amounts of difunctional chain extender and multifunctional crosslinker present, unlike the case of HTPB with similar hydroxyl content and molecular weight. However, the mechanical properties and sol content could be correlated with the average molecular weight between crosslink sites, M?_c, of the cured polymer. The M?_c values derived by our method compare well with those of classical methods, and the observed differences are attributed to segmental entanglement. These M?_c values give consistently good correlation with all the gumstock properties, confirming the validity of our approach and the soundness of the techniques developed for the determination of the functionality distribution of HTPB .     

Preparation and characterization of collagen‐based composite conduit for peripheral nerve regeneration

Collagen‐based composite nerve conduit scaffold was prepared by freeze‐drying steam‐extrusion method and modified chemically with glutaraldehyde (GTA) by adding chitosan into collagen. Fourier transform infrared spectroscopy showed that the collagen and chitosan are certainly crosslinked through GTA. It was observed under scanning electron microscope that the modified nerve conduit material is a porous three‐dimensional crosslinked structure and the quantity ratio of the collagen to chitosan has influence on the morphology. The cell proliferation experiment results showed that the collagen‐based composite scaffold prompts the adhesion and proliferation of cells, but as the chitosan increasing, the cell proliferation decreased slightly. The swelling property, the collagenase degradation, and the mechanical property of the scaffold are tested at the quantity ratios of collagen to chitosan 4 : 3, 3 : 1, and 4 : 1 and crosslinking time 0.5 and 1.0 h. The experiments show that the stability of the scaffold is enhanced with decreasing the quantity ratio of collagen to chitosan and increasing crosslinking time. Through the experimental investigations, the modifying technique parameters are discussed and the scaffold exhibits better physical and chemical properties at the quantity ratio of collagen to chitosan 3 : 1 and crosslinking time 0.5 h. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Swelling kinetics of linseed oil‐based polymers

Kinetics of swelling and sorption behavior of copolymers (based on linseed oil, styrene, divinylbenzene, and acrylic acid via cationic and thermal polymerization) is studied in tetrahydrofuran (THF) at different temperatures. The values of n in the transport equation are found to be below 0.4, showing non‐Fickian or pseudo‐Fickian transport in the polymers. The dependence of diffusion coefficient on the composition and temperature has also been studied for the linseed oil‐based polymers. The diffusion coefficient in cationic samples decreases with an increase in the oil contents in the samples. In case of thermal samples, the diffusion coefficient first increases up to 30% oil contents and then decreases. The diffusion coefficient decreases with an increase in temperature for all of the linseed oil polymer samples. The sorption coefficient increases with an increase in the oil contents for all samples. The crosslink density (calculated from the THF swelling) ranges from 20.16 to 92.34 × 10⁶ mol/cm³ for cationic samples and 20.62 to 86.01 × 10⁶ mol/cm³ for thermal samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

离子液体改性炭黑增强丁腈橡胶的研究

先采用离子液体（1-丁基-3-甲基咪唑六氟磷酸盐BMIM.PF6,IL）处理炭黑,而后进行微波处理得到改性炭黑（m-CB）,将m-CB用于增强丁腈橡胶（NBR）。研究了m-CB的结构、混炼胶的硫化特性和补强效果。结果表明,IL可吸附到炭黑表面,而且部分IL强烈吸附于炭黑表面,微波处理之后,IL会发生部分分解;m-CB使混炼胶的硫化延迟;NBR/m-CB硫化胶的断裂伸长率、拉伸和撕裂强度相对于未改性炭黑均有较大提高,而模量和硬度略有下降。通过对硫化胶的交联密度、动态力学分析（DMA）、形态学等研究,探讨了改性炭黑补强橡胶机理。     

一种丙二酸衍生物的制备及其对胶原膜的改性应用

将丙二酸与N-羟基琥珀酰亚胺(NHS)在二环己基碳二亚胺(DCC)催化下反应得到丙二酸NHS酯。以丙二酸NHS酯为交联剂对胶原膜进行交联改性,考察不同交联剂浓度对胶原膜物理化学性能的影响,通过测试其变性温度、吸水率、酶解率和机械强度等,来表征交联前后膜性能的改变。结果表明:经过丙二酸NHS酯交联改性后的胶原膜热稳定性、形态稳定性增强,抵抗酶解的能力增加,机械强度有所提高。说明丙二酸NHS酯作为一种交联剂,可有效改善胶原膜的物理化学性能。     

SBS Thermoplastic Elastomer Based on Dynamic Metal-Ligand Bond: Structure,Mechanical Properties,and Shape Memory Behavior

A Cooper(II) (Cu²⁺)-nitrogen coordination-crosslinked network is designed in poly(styrene-co-butadiene-co-styrene) (SBS) to change commercial elastomers into advanced soft materials. Herein, ligand groups into SBS molecular chains by the 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (DPT) click reaction are first introduced. The results from fourier transform infrared (FT-IR), 1H-nuclear magnetic resonance, and X-ray photoelectron spectroscopy (XPS) are verified the successful modification of SBS. The DPT-grafted SBS could then coordinate with copper sulfate (CuSO₄) to form a Cu²⁺-nitrogen bond, which is further characterized using FT-IR, XPS, atomic force microscope, scanning electron microscope, and geometric structure calculations. After modifying SBS to form an SBS-DPT/CuSO₄ composite (SBS-DPT2-Cu10), the tensile stress is improved from 11.43 to 23.25 MPa, while the elongation at break is remained almost unchanged, and the corresponding toughness is increased from 33.21 to 63.26 MJ m^–3. Moreover, the dynamic nature of the Cu²⁺-nitrogen coordination bonds enables the SBS-DPT/CuSO₄ composite to exhibit sustained thermoplastic performance and excellent shape memory behavior under an external thermal stimulus.     

Synthesis and properties of polyurethane elastomers based on renewable castor oil polyols

In this contribution, castor oil polyols with functionality of f = 2.7 and f = 2 are used as soft segments (SS) for synthesizing polyurethane elastomers (PUEs) without addition of petroleum-based polyol. The effect of molar ratio of castor oil polyols on structure and properties of PUEs has been investigated by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, X-ray diffraction, tensile, swelling, and water absorption tests. The results reveal that hydrogen bonding mainly exists in hard segments (HSs) and weakens with decreasing the molar percentage of castor oil polyol (f = 2.7) in SS. T _g of SS decreases while T _g of HS remains constant as molar percentage of castor oil polyol (f = 2.7) decreased. The initial degradation temperatures (T_5%) are above 300 °C and independent of the molar ratio of castor oil polyols. However, the temperature at 50% weight loss (T_50%) decreases significantly as molar percentage of castor oil polyol (f = 2.7) decreased. Moreover, PUEs exhibit very low water absorption rate, <1%, after immersing in water for 140 h at room temperature. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47309.