Thermally stable bromobutyl rubber with a high crosslinking density based on a 4,4′‐bismaleimidodiphenylmethane curing agent

The development of thermally stable bromobutyl rubbers has been a challenge in rubber chemistry and engineering. In this circumstance, 4,4′‐bismaleimidodiphenylmethane (BMI) was newly applied as a novel crosslinking agent for thermally stable brominated isobutylene–isoprene rubber (BIIR) with a high crosslinking density. With oscillating disk rheometry and differential scanning calorimetry, the curing characteristics of BIIR were systematically investigated with respect to the content of BMI. We found that BMI alone could crosslink BIIR at higher temperature, and a corresponding possible chemical reaction mechanism was proposed. With the introduction of zinc oxide, the curing reaction of BIIR with BMI was significantly accelerated, and the resulting vulcanizate provided a higher state of curing with excellent overcure reversion stability even at a temperature of 190 °C for 2 h. The content of the dicumyl peroxide (DCP) reaction accelerator was also optimized to be BMI/DCP = 1:0.05 on the basis of considerations of the curing rate, scorch safety, maximum rheometric torque, and reversion resistance at 160 °C. Compared with the conventional sulfur‐cured BIIR, the BMI‐cured BIIR exhibited a higher crosslinking density with a superior low compression set property at elevated temperatures and an excellent thermal stability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44092.     

Influence of pendent groups on the tensile properties of polyisoprene vulcanizates

Gum compounds of polyisoprene were vulcanized with a number of different curing systems to give networks with crosslink densities in two different ranges. Stress–strain curves were obtained upon rapid (500 mm/min) and slow (0.5 mm/min) extension. In tetramethylthiuram disulfide (TMTD)/sulfur and zinc dimethyldithiocarbamate/sulfur vulcanizates, which crystallize readily, failure occurred at higher tensile values upon rapid than upon slow extension and this is attributed to a greater contribution to tensile strength by a larger amount of stress‐induced crystallites. X‐ray diffraction showed that 2‐benzothiazole‐2,2′‐disulfide (MBTS)/sulfur vulcanizates did not stress‐crystallize and failure occurred at lower tensile values. Furthermore, samples extended rapidly failed at lower tensile values than did slowly extended samples. These differences, compared to TMTD vulcanizates, are attributed to extensive main‐chain modifications (pendent groups), causing delays in the movement of sections of the chain, leading to the load being unequally distributed between chains. The fewer load‐bearing chains ensure earlier failure. The addition of zinc stearate to TMTD/sulfur and MBTS/sulfur formulations increases the ability of vulcanizates of similar crosslink density to crystallize and enhances tensile properties of vulcanizates with similar crosslink densities, outcomes that are attributed to zinc stearate's promoting crosslinking of pendent groups and reducing impediments to crystallization and chain movement. Dicumyl peroxide–cured networks crystallize readily and exhibit a very rapid upturn in the stress–strain curve. However, failure occurs at lower stress values than apply to accelerated sulfur networks and it is suggested that the distribution of subchain lengths between crosslinks may contribute to their inferior properties. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2587–2596, 2001     

Effect of C5 petroleum resin content on damping behavior,morphology, and mechanical properties of BIIR/BR vulcanizates

In this work, the white‐silica‐filled vulcanizates of brombutyl rubber (BIIR)/cis 1,4 polybutadiene rubbers (BR) with hydrogenated aromatic hydrocarbon (C5) petroleum resins were prepared by compression molding, and the effects of C5 petroleum resin content on the damping behaviors and mechanical properties of BIIR/BR vulcanizates were investigated by foam force rheometer, dynamic mechanical analysis (DMA), scanning electron microscopy, and mechanical measurements. The results of this study showed that, the C5 resins could retard the vulcanization, and reduce the crosslink density and Mooney viscosity of vulcanizates. The DMA curves exhibited two independent peaks of loss factor (tanδ) corresponding to the glass transition of BR and BIIR vulcanizates, respectively. The addition of C5 resin had a positive impact on the damping of BIIR/BR vulcanizates, with the increment content of C5 resin, the main tanδ peaks shifted significantly to higher temperature and the effective damping temperature range was broadened remarkably, especially in the range of the BIIR glass transition. The mechanical properties such as tensile strength and abrasion performance were influenced by the C5 resin and the changes in mechanical properties were mainly due to the decline of crosslink density and the improvement of filler dispersion. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Properties of EVM vulcanizates reinforced by in situ prepared sodium methacrylate

Ethylene–vinyl acetate copolymer (EVM) vulcanizates with good mechanical properties and high transparency were obtained using sodium methacrylate (NaMAA) as a reinforcing agent. Sodium methacrylate was in situ prepared through the neutralization of sodium hydroxide (NaOH) and methacrylic acid (MAA) in an EVM and used to reinforce the EVM cured by dicumyl peroxide (DCP). Different factors such as the DCP content, NaMAA content, and the mol ratio of NaOH/MAA were included to study their effects on the mechanical properties, optical properties, stress‐relaxation behavior, and crosslink structure of the EVM vulcanizates. The rheological behavior of the EVM compounds was also investigated and compared with that of the high abrasion furnace carbon black (HAF)/EVM compounds. The experimental results show that with an increase of the NaMAA content the curing rate index (C_R) of the EVM compounds is greatly speeded up, while the Mooney viscosities of the compounds remain nearly unchanged. The mechanical properties and optical properties of the NaMAA‐reinforced EVM vulcanizates depend on the NaMAA content and the mol ratio of NaOH/MAA. The formulation of DCP of 3 phr and a NaOH/MAA mol ratio of 1.0 is recommended for the EVM vulcanizate with high mechanical properties. At a given NaOH/MAA mol ratio of 1.0, all the EVM vulcanizates are transparent and the light transmission is over 76% in the NaMAA content range of 10–50 phr. The NaMAA/EVM vulcanizates show faster stress relaxation and more obvious stress‐softening effects than those of the HAF/EVM vulcanizates. Crosslink density analysis indicated that the EVM vulcanizates contain both covalent and ionic bonds. The ionic crosslink densities greatly increase with an increasing NaMAA content. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2192–2200, 2003     

Influence of internal strain on change of crosslink density of natural rubber vulcanizates by thermal ageing

Change of crosslink density of natural rubber (NR) vulcanizates by thermal ageing at 60 °C has been studied under swollen conditions in solvents to investigate the influence of internal strain applied to the vulcanizate on the crosslink density change. The internal strain was controlled by swelling with various solvents such as n‐hexane, toluene, tetrahydrofuran (THF), methanol and water. The order of degree of the swelling is toluene ≈ THF > n‐hexane > methanol > water. The influence of curing system has been investigated with the vulcanizates cured by the conventional and EV cure systems. After thermal ageing, the apparent crosslink densities of the swollen vulcanizates in n‐hexane, toluene and THF decrease irrespective of the cure systems, while that of the swollen vulcanizate in water increases. For the swollen vulcanizates in methanol, the apparent crosslink density of the vulcanizate with the conventional cure system after thermal ageing increases while that of the vulcanizate with the EV cure system decreases. The decrement of the apparent crosslink density of the vulcanizate after thermal ageing becomes larger and larger upon increasing the internal strain. © 2001 Society of Chemical Industry     

Cure characteristics and physical properties of ground‐rubber‐filled natural rubber vulcanizates: Effects of the curing systems of the ground rubber and rubber matrix

Recycling discarded rubber is important for both environmental and economic reasons. One of the most attractive methods of recycling rubber waste is to use ground rubber (GR) as a compounding ingredient or as a replacement for raw polymers. In this study, ground natural rubber was prepared with different curing systems and compounded into the parent compounds. The cure behaviors and physical properties of the GR‐filled vulcanizates were investigated, and they were largely affected by the curing systems of the rubber matrix and GR. GR‐filled vulcanizates with GR and the rubber matrix, having a conventional curing system, showed the largest changes in the cure characteristics. The greatest decrease in the physical properties was observed for peroxide‐cured‐GR‐filled vulcanizates. The addition of GR decreased the crosslink density of the GR‐filled vulcanizates. This was thought to be the main reason for the reduction of the mechanical properties of the GR‐filled vulcanizates. However, the adhesion between the GR and rubber matrix may also have caused the differences in the physical properties of the GR‐filled vulcanizates with respect to the curing systems of the rubber matrix and GR. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

The tensile properties of strain‐crystallizing vulcanizates. III. The superiority of conventional over peroxide vulcanizates in terms of network microstructure

It is proposed that, when vulcanization is performed using peroxides, crosslinking leads to a simple network, whereas in conventional vulcanization crosslinking a partially interpenetrating polymer network (PIPN) is formed. Two unfilled polyisoprene networks of similar crosslink density, produced with dicumyl peroxide and 2‐bisbenzothiazole‐2,2′‐disulfide/sulfur formulations, were compared with respect to the effect of strain rate on their stress–strain and hysteresis curves at room and elevated temperatures. At high elongations, the stress–strain curves for peroxide vulcanizates show a steeper upturn than for conventional vulcanizates, but have lower tensile strength and elongation at break. On increasing the extension rate, stress–strain curves for peroxide vulcanizates rise less steeply, while conventional vulcanizates rise more steeply. For both vulcanizates the hysteresis ratio decreases on increasing the rate at which samples are extended and retracted. The effect on conventional vulcanizates is less than on peroxide vulcanizates. It is suggested that chains in peroxide networks disengage increasingly rapidly at higher strains, allowing increased strain‐induced crystallization. Rapid strain‐induced crystallization leads to low ultimate tensile strength (UTS). In more complex PIPNs, the disengagement and alignment of chains are retarded. The increased nonuniform extension of chains promotes early strain‐induced crystallization at low extensions, but overall it reduces the rate of crystallization, which occurs over a wider range of strains. This improves UTS and elongation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 876–884, 2006     

In situ preparation of magnesium methacrylate to reinforce NBR

Magnesium methacrylate (MDMA) was in situ prepared in nitrile rubber (NBR) by reacting magnesium hydroxide (Mg (OH)₂) with methacrylic acid (MAA) during the mixing step. The formation of MDMA in NBR was proved by the wide‐angle X‐ray diffraction analysis (WAXD). The mechanical properties, crosslinking structure, and morphology of the resulting peroxide‐cured NBR vulcanizates were studied. Results showed that Mg (OH)₂/MAA mixtures had a great reinforcing effect for NBR, and their amounts and ratio played important roles in influencing the ultimate properties. Both the covalent crosslink density and ionic crosslink density of the vulcanizates were measured. And the nano‐composite morphology of such vulcanizates was also observed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1403–1408, 2002; DOI 10.1002/app.10323     

Effect of crosslinking on the conductivity of conductive silicone rubber

We investigated the effect of polyvinylsilicone oil (C gum) as a crosslinker and 2,5‐bis(tert‐butyl peroxy)‐2,5‐dimethyl hexane (DBPMH) as a curing agent on the conductivity of conductive silicone rubber with two different kinds of conducting mechanisms. The experimental results show that the volume resistivity of conductive silicone rubber changed with its degree of crosslinking. When the carbon black loading was 25 parts per hundred rubber (phr) and a completely continuous conducting network had not formed, the volume resistivity of the vulcanizates decreased with increasing crosslink density. The volume resistivity of the vulcanizate with a suitable amount of C gum decreased to 53%, and the tensile strength increased by 0.8 MPa compared to the vulcanizate without C gum. When the carbon black loading was 40 phr and a completely continuous conducting network had formed, the crosslink density of vulcanizates changed as the amount of DBPMH changed. The volume resistivity of vulcanizates first decreased and then increased with increasing crosslink density. There was a valley value in the resistivity–crosslink density curve. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3471–3475, 2003     

Effect of a small amount of sulfur on the physical and mechanical properties of peroxide‐cured fully saturated HNBR compounds

Sulfur can be used as crosslink coagent in unsaturated elastomer. In this work, a fully saturated HNBR with 39 wt % nitrile content was selected to investigate the effect of a small amount of sulfur acting as crosslink coagent on the physical and mechanical properties of peroxide‐cured vulcanizates. First, selective cleavage of polysulfide (? Sx? ) and monosulfide(? S? ) bond by combined thiol‐piperidine treatment were performed and the existence of poly/monosulfide bond in sulfur‐contained HNBR compounds was verified. Then, no‐filler HNBR compounds with various content of sulfur were investigated to detect the influence of sulfur on the crosslink density and cure kinetics. The MDR results showed that the crosslink density of HNBR compounds reduced only when the amount of sulfur is 0.25 phr and above. Besides, the curing rate of no‐filler HNBR compounds increased with the increasing of the amount of sulfur and reached a maximum at a dosage of 0.25 phr sulfur. Finally, physical and mechanical properties of fully formulated compounds were evaluated and it was found that the addition of small amounts of sulfur in fully saturated HNBR compounds could improve the dynamic properties of peroxide‐cured HNBR compounds remarkably but at a cost of slightly higher compression set values and a small loss in heat aging resistance. In a conclusion, small amount of sulfur can impart the peroxide vulcanizates some “sulfide properties” like dynamic property, tensile strength, but at the same time, due to the introduction of sulfur, some “peroxide vulcanizates property” like heat‐resistance property, hot air resistance were weakened slightly. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41612.     

Effect of norbornyl modified soybean oil on CB‐filled chloroprene rubber

Carbon black (CB)‐filled chloroprene rubber (CR) compounds and vulcanizates containing naphthenic oil (NO), soybean oil (SO), and two different levels of norbornyl modified soybean oil (MSO) were prepared and investigated. The MSO was prepared through the reaction of SO and dicyclopentadiene (DCPD) at different ratios. Various properties including gel fraction, crosslink density, bound rubber fraction, curing behavior, thermal, mechanical, and aging properties of CB‐filled CR containing different oils were compared. It was observed that the addition of SO and MSO could benefit the dispersion of the filler, lower the glass transition temperature, and increase the thermal stability of the CB‐filled CR/MSO compounds and vulcanizates, and also slightly decrease the crosslink density of the CB‐filled CR/MSO vulcanizates compared to that of the CR/NO vulcanizate. With the increase of the modification level of the MSO, the curing time of the CB‐filled CR/MSO compounds was found to be decreased, the tensile property, tear strength, abrasion resistance, and aging resistance of the CB‐filled CR/MSO vulcanizates were improved compared with those of the CB‐filled CR/NO vulcanizate. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43809.     

Effects of hot‐air aging and dynamic fatigue on the structure and dynamic viscoelastic properties of unfilled natural rubber vulcanizates

The effects of hot‐air aging and dynamic tensile fatigue on the network structure and dynamic viscoelastic properties of unfilled natural rubber (NR) vulcanizates were investigated with magnetic resonance crosslink density spectrometry, Fourier transform infrared spectroscopy/attenuated total reflection (FTIR–ATR), and dynamic mechanical analysis. The results showed that there was a carbonyl weak absorption peak at 1723 cm^?1 in the FTIR–ATR spectra of unfilled NR vulcanizates after hot‐air aging; The crosslink density decreased continuously as the aging time increased. The dynamic modulus of an aged specimen declined considerably, and the value of tan δ after 72 h of aging greatly increased. There was a large difference in the FTIR–ATR spectra of unfilled NR vulcanizates before and after tensile fatigue. The peaks at 1597, 1415, and 1015 cm^?1 increased concurrently with the tensile fatigue time. Initial analysis suggested that structures such as conjugated dienes appeared in the network structure. The modulus declined sharply, whereas the value of tan δ increased noticeably, after tensile fatigue. The effects of hot‐air aging and tensile fatigue on the crosslink density and FTIR–ATR spectra of unfilled NR vulcanizates were different, but both affected the viscoelastic properties dramatically. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Microcellular foaming of chlorosulfonated polyethylene rubber and its kaolin‐filled compounds with supercritical nitrogen

The microcellular foaming of vulcanizates made from chlorosulfonated polyethylene (CSM) rubber and its kaolin‐filled compounds was carried out with supercritical nitrogen. The effects of various curing times, temperatures of the vulcanizates, and kaolin filler contents in the vulcanizates on the prepared foams were studied. The foaming of the vulcanizates with various crosslinking densities revealed the critical effect the crosslinking density of the CSM matrix played on its foaming. A certain sufficient level of crosslinking density was most effective for the foaming of the matrix; a higher crosslinking density led to a decreased cell size, increased cell density, and decreased matrix expansion in the foams. The effect of the crosslinking density was due to its effect on the free volume of the elastomeric matrix, which controlled the gas diffusion from the matrix during the pressure‐release stage of the foaming operation. The incorporation of kaolin decreased the cell size and increased the cell density of the foams; the decreased free volume and the heterogeneous cell nucleation effect of the kaolin contributed to this. The tensile strength of the foams significantly improved with increasing kaolin content in the foams. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45656.     

Dimethylammonium dimethyldithiocarbamate‐accelerated sulfur vulcanization. II. Vulcanization of rubbers and model compound 2,3‐dimethyl‐2‐butene

Rubber and model compound 2,3‐dimethyl‐2‐butene were vulcanized for various times with dimethylammonium dimethyldithiocarbamate [(dma)dmtc]‐accelerated sulfur formulations in the absence of ZnO. Model compound systems were analyzed by HPLC, and no reaction intermediates containing pendent groups were found. Crosslinked sulfides, characterized by ¹H‐NMR, were found to be essentially bis(alkenyl). Residual curatives were extracted from rubber compounds vulcanized for various times and analyzed by HPLC. Compounds, cured to various crosslink densities, were found to crystallize readily in a density column at subambient temperatures. This supports evidence from model compound systems that pendent groups are largely absent from vulcanizates. It is suggested that a reaction mechanism, similar to that applicable to zinc dimethyldithiocarbamate‐accelerated sulfur vulcanization, may be applicable with (dma)dmtc accelerated formulations. Very limited crosslinking occurred on heating compounds under vacuum, and this can be attributed largely to the rapid loss of (dma)dmtc from rubber at elevated temperatures. However, the slower rate of crystallization on cooling of the gels, compared to the rate in press‐cured vulcanizates of similar crosslink density, was interpreted as evidence that some pendent groups did form during heating with (dma)dmtc/sulfur. Crosslinking of such pendent groups may be inhibited by the loss of (dma)dmtc, that, like zinc dimethyldithiocarbamate, may catalyze their crosslinking, and/or to the loss under vacuum of dimethyldithiocarbamic acid that would form thiol pendent groups that would rapidly crosslink with thiuram pendent groups. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3074–3083, 2001     

Curing of a tetrafluoroethylene–propylene elastomer with high-vinyl polybutadiene rubber and peroxide

A cocuring agent is necessary for tetrafluoroethylene–propylene elastomer (FEPM), which cannot be cured by peroxide alone. We observed that high-vinyl polybutadiene rubber (HVBR) could be used as a cocuring agent for FEPM. The structure and properties of FEPM–HVBR blend vulcanizates were investigated by ¹³C-NMR, differential scanning calorimetry, swelling tests, tensile tests, dynamic mechanical analysis, and thermogravimetric analysis. This research showed that HVBR significantly improved FEPM by conferring a high crosslink degree to the FEPM–HVBR blends. When the HVBR concentration was 25% without any filler reinforcement, the tensile strength of the FEPM–HVBR blend vulcanizate reached 11.6 MPa, and the crosslinking density reached 171 μmol/cm³. In addition, HVBR improved the thermal stability of FEPM and changed the glass-transition temperature (T _g) of the blend; as the HVBR content increased, the T _g of the blend also increased. ¹³C-NMR analysis confirmed that crosslinks existed between the HVBR and FEPM macromolecules. When the blends contained trace amounts of HVBR, free-radical reaction was more preferred between FEPM and HVBR, whereas when HVBR was 15% or more, crosslinking between HVBR was predominant. These findings expand the choices for the curing of FEPM. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47836.     

Mechanical properties of deproteinized natural rubber in comparison with synthetic cis‐1, 4 polyisoprene vulcanizates: Gum and black‐filled vulcanizates

Gum and black‐filled vulcanizates having various crosslink densities were prepared from 2 types of rubber, namely, deproteinized natural rubber (DPNR) and synthetic cis‐1, 4 polyisoprene vulcanizates (IR). Their mechanical properties, such as tensile strength, tear strength, abrasion loss, and heat buildup resistance, at various crosslink densities as well as at similar optimum crosslink density were compared. For both gum and black‐filled systems, IR possessed a higher crosslink density than that of DPNR at a fixed curative content. Tensile and tear strength of all vulcanizates passed through a maximum with increasing crosslink density. For gum vulcanizates, tensile and tear strengths of DPNR and IR below the maximum were not much different. However, IR had a narrower tear strength peak relative to DPNR. At a comparable optimum crosslink density, DPNR exhibited higher tensile strength and crack growth resistance than IR. For black‐filled vulcanizates, tensile and tear strengths, and heat buildup resistance of DPNR and IR at a given crosslink density were similar. The results revealed that the properties of gum samples were more dependent upon crosslink density than the black‐filled ones because the reinforcement by carbon black overshadowed the intrinsic properties of the rubbers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1139–1144, 2005     

Crosslinking of poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] using dicumyl peroxide as initiator

In order to modify poly [(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] (PHBV), the crosslinking of this copolymer was carried out at 160 °C using dicumyl peroxide (DCP) as the initiator. The torque of the PHBV melt showed an abrupt upturn when DCP was added. Appropriate values for the gel fraction and crosslink density were obtained when the DCP content was up to 1 wt% of the PHBV. According to the NMR spectroscopic data, the location of the free radical reaction was determined to be at the tertiary carbons in the PHBV chains. The melting point, crystallization temperature and crystallinity of PHBV decreased significantly with increasing DCP content. The effect of crosslinking on the melt viscosity of PHBV was confirmed as being positive. Moreover, the mechanical properties of PHBV were improved by curing with DCP. When 1 wt% DCP was used, the ultimate elongation of PHBV increased from 4 to 11 %. A preliminary biodegradation study confirmed the total biodegradability of crosslinked PHBV. Copyright © 2004 Society of Chemical Industry     

Crystallization of vulcanizates. II. Low‐temperature crystallization as a function of extent of cure for polybutadiene vulcanized with dicumyl peroxide,tetramethylthiuram disulfide, 2‐bisbenzothiazole‐2,2′‐disulfide,and zinc–accelerator complexes

Polybutadiene compounds, vulcanized to various degrees of cure, were crystallized in a density column at ?16°C. The percentage crystallinity of vulcanizates was also determined by differential scanning calorimetry where samples, precooled at a programmed rate, were reheated. Curing with peroxides has little effect on either the rate or the extent of crystallization, except at very high crosslink densities, although the induction period prior to crystallization increases progressively with increased crosslink density. Tetramethylthiuram disulfide (TMTD)/sulfur and 2‐bisbenzothiazole‐2,2′‐disulfide (MBTS)/sulfur vulcanizates, cured for progressively longer periods, were found to have lower densities, a result attributed to an increase in free volume occasioned by the formation of accelerator‐terminated pendent groups on the polymer chain. The induction period for crystallization increases and both the rate and the extent of crystallization decrease with extent of cure. These changes are more marked for MBTS vulcanizates that do not crystallize once a gel has formed. Formulations with zinc stearate develop higher crosslink densities and crystallize to a greater extent on cooling, showing the effect of zinc stearate in the crosslinking of pendent groups. The densities of both zinc dimethyldithiocarbamate [Zn₂(dmtc)₄]– and zinc mercaptobenzothiazole [Zn(mbt)₂]–accelerated sulfur vulcanizates increase with cure time, a result attributed to the formation of ZnS in the compounds. Zn₂(dmtc)₄ compounds crystallize extensively on cooling, pointing to limited main‐chain modification. It is suggested that main‐chain modification in these vulcanizates may comprise cyclic sulfide formation. Zn(mbt)₂ compounds crystallize less readily than Zn₂(dmtc)₄ compounds, but to a greater extent than MBTS/sulfur compounds. The crystallization of the vulcanizates is discussed in terms of vulcanization reactions that give rise to crosslinking with the different formulations used. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2573–2586, 2001     

硫化体系对动态硫化EPDM/POE热塑性弹性体性能的影响

采用动态硫化的方法在Haake转矩流变仪上制备了三元乙丙橡胶/聚烯烃(EPDM/POE)热塑性弹性体(TPV),并分别对不同硫化体系和硫化剂用量对TPV交联密度和性能的影响进行了研究。结果表明,随硫化剂用量的增加,TPV的交联密度增大,其中硫黄硫化体系的TPV变化最明显;采用硫黄硫化体系和酚醛树脂硫化体系制备的TPV性能优于过氧化物硫化体系,并且DCP和硫黄分别在用量为0.5份,酚醛树脂在1.0份时性能较佳。     

Effects of polymeric curing agent modified with silazanes on the mechanical properties of silicone rubber

Polymeric curing agent modified with hexamethyldisilazane (PCA‐D), or with hexamethylcyclotrisilazane (PCA‐T), was used to improve the mechanical properties of hydroxyl‐teminated polydimethylsiloxane (PDMS) rubber. The structure and the gel time of PCA were characterized by ²⁹Si NMR and shear viscosity measurement, respectively. The PCA modified with silazanes was more stable in storage than that without treatment (PCA‐0). Chemical bonds were formed during the reaction of silazanes and PCA according to ²⁹Si NMR results. The crosslink density (γ_e) and the mechanical properties of PCA/PDMS rubber were determined by swelling equilibrium and stress–strain tests. It was found that PCA treated with both silazanes could better enhance the mechanical properties of PCA/PDMS rubber compared with PCA‐0. PCA‐T/PDMS rubber, with additional crosslinks, was the best among the three types of PCA/PDMS rubber on the mechanical properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009