Effect of dicumyl peroxide on photo-oxidation of polystyrene films: 2

The effect of dicumyl peroxide on the photo-oxidation of polystyrene film has been studied using light of a wavelength absorbed by the polystyrene—oxygen complex. Energy transfer from the excited polystyrene—oxygen complex to the peroxide present in polystyrene film was considered to be the process of most importance in the initiation of polystyrene long-wave photo-oxidation.     

Polystyrene and polyether polyurethane elastomer blends compatibilized by SMA: Morphology and mechanical properties

Blends of polystyrene (PS) and the polyether polyurethane elastomer (PU‐et) were prepared by melt mixing using poly(styrene‐co‐maleic anhydride) (SMA) containing 7 wt % of maleic anhydride as a compatibilizer. The polyurethane in the blends was crosslinked using dicumyl peroxide or sulfur. The content of maleic anhydride was varied in the blends through the addition of different SMA amounts. The morphology of the blends was analyzed by SEM and a drastic reduction of both the domain size and its distribution was observed with increase of the anhydride content in the blends. The morphology of the PU‐et blends also showed dependence on the crosslinker agent used for the elastomer, and larger domains were obtained for the elastomer phase crosslinked with dicumyl peroxide. The mechanical properties of the blends were evaluated by flexural and impact strength tests. The blend containing 0.5 wt % of maleic anhydride and 20 wt % of PU‐et crosslinked with sulfur showed the highest strength impact, which was three times superior to the PS strength impact, and the blends containing 20 wt % of PU‐et crosslinked with dicumyl peroxide showed the highest deflection at break independent of the anhydride content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 830–837, 2002     

Modification of polystyrene by reactive extrusion with peroxide and trimethylolpropane triacrylate

Polystyrene (PS) was modified by reactive extrusion with trimethylolpropane triacrylate (TMPTA) and dicumyl peroxide (DCP). The coupling reaction caused by TMPTA increased the molecular weight of PS, and this coupling reaction was enhanced in the presence of DCP at high TMPTA/DCP ratio. The rheological properties of the extrudate were examined. The impact strength of PS improved as the molecular weight increased by the coupling reaction. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1672–1679, 2004     

Thermal and mechanical properties of microcellular thermoplastic SBS/PS/SBR blend: effect of crosslinking

This study investigates the effect of peroxide crosslinking on the structure and mechanical properties for SBS/PS/SBR foams composed of polystyrene (PS), poly(styrene-b-butadiene) diblock copolymer (SBR-1502), and poly(styrene-b-butadiene-b-styrene) triblock copolymer (SBS). The cell size and its distribution of SBS/PS/SBR foams were investigated by SEM images, showing the smaller and denser of hollow cells for the SBS/PS/SBR foam containing the higher concentration of DCP (dicumyl peroxide). As expected, the density of the SBS/PS/SBR foams increases with increasing the content of DCP. The high density of polymeric foams exhibits the high mechanical properties such as hardness, shrinkage, tensile strength, tear strength, elongation at break, and compression set.     

Crystalline crosslinked microparticles from immiscible blends of polyethylene and polystyrene

Crystalline crosslinked polyethylene microparticles with size distribution averages ranging from 0.374 to 0.944 μm were prepared from immiscible PS and PE blends in the melt phase for microgel applications. The particles were crosslinked either concurrently while blending using dicumyl peroxide or post blending via electron-beam irradiation. The effects of varying the processing temperature, blend duration, and block copolymer compatibilizer content on the particle morphology were studied and it was found that only a decrease in processing temperatures (increase in continuous-to-dispersed phase viscosity ratio) resulted in finer particles for the range of variables tested. The chemical composition of the isolated particles was determined using infrared and nuclear magnetic resonance spectroscopy while the particle morphology was investigated using electron microscopy image analysis in conjunction with thermogravimetric analysis. It was determined that particles produced with and without the block copolymer contained a small amount of PS even after meticulous extraction with a PS solvent (THF). However, the exact location of PS on the PE particles remains obscure.     

多功能单体对反应共混PP／PS合金的影响

研究了在聚现烯／聚苯乙烯／过氧化二异丙苯（ＰＰ／ＰＳ／ＤＣＰ）反应挤出共混过程中,不同分子结构的多功能单体添加剂对共混物降解的抑制及增容作用的影响。研究发现,多功能单体所含的双键越是靠近分子末端,分子链越长,结构越简单,增容效果越好;若多功能单体分子中含有一定含量的碳－碳双键,则能很好地抑制降解。     

LDPE熔融接枝丙烯酸的研究

本文选择丙烯酸作为接枝单体与过氧化二异丙苯、低密度聚乙烯混合，在单螺杆挤出机中进行熔融接枝反应。实验研究了挤出条件、ＤＣＰ用量以及丙烯酸单体用量对熔融接枝的影响。     

ESR study of vulcanizates under the deformed state

Electron spin resonance (ESR) measurements under the tensile deformation of cross‐linked polyisoprene were examined by the combination of home‐built stretching machine with commercially available ESR spectrometer. The changes of radical concentration during tensile deformation were successfully determined by this technique. It was found that the number of radicals produced by the stretching process decreased during the retraction of stretched sample. In addition, at a given strain, the decrease of radical concentration with time was accompanied by the increase of stress. Such changes were more prominent in the cross‐linked sample by sulfur PS sample (PS) than by dicumyl peroxide (PCP), PD sample (PD). The tensile modulus of the samples after the one cyclic deformation increased with increasing the keeping time at room temperature after the cyclic deformation. The increase was larger for the PS than for the PD. These results suggest that the broken cross‐linking structure induced by the stretching process was partly reconstructed during and after the retraction with this tendency more prominent in the PS than in the PD. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

新型橡胶密封件交联体系的研究

在橡胶密封件硫化体系中,由于硫磺硫化体系压缩永久变形性能比较差,而最常用的过氧化物交联剂过氧化二异丙苯的硫化胶容易产生刺鼻的异味,从而限制了它在高档制品中的用途。本实验使用1,4-双叔丁基过氧异丙基苯做为丁腈橡胶交联剂。实验结果表明:使用1,4-双叔丁基过氧异丙基苯做为交联剂的硫化胶不仅在综合性能上优于过氧化二异丙苯,而且也避免了刺鼻异味的产生。并且和硫磺硫化体系相比它也大大改善了硫化胶的压缩永久变形性能,从而拓宽了过氧化物交联体系在密封制品中的用途。同时,本文还研究了双组分补强填料对丁腈橡胶的补强效果。     

Reactive extrusion of polystyrene/polyethylene blends

The feasibility of inducing beneficial changes to polystyrene/polyethylene (PS/PE) blends via reactive extrusion processes is considered. Experiments have been conducted on 50:50 wt.% PS/PE blends that were treated with different levels of dicumyl peroxide and triallyl isocyanurate coupling agent. Both a low molecular weight and a high molecular weight blend series have been investigated. A “more reactive” polystyrene was synthesized by incorporation of a minor amount of ortho-vinylbenzaldehyde. Blends containing this modified polystyrene were subjected to identical processing' conditions on a counter-rotating twin screw extruder. Examination of the tensile properties of the extrusion products suggested that a judicious level of peroxide and coupling agent additives would be beneficial to the ultimate physical properties. The quantity of styrenic phase becoming chemically grafted to the polyethylene matrix was influenced most strongly by the level of the chosen coupling agent. As determined by scanning electron microscopy, the phase morphologies of the tensile test fracture surfaces were strongly dependent upon the reaction extrusion process; those extruded blends that had been exposed to the additive pre-treatment displayed substantially finer microstructure. The enthalpy of fusion of the polyethylene melting endotherm was likewise influenced by both the presence or absence of the additives as well as the molecular weight nature of the blend series.     

马来酸二乙酯熔融接枝聚丙烯蜡的研究(Ⅰ)

用马来酸二乙酯接枝改性聚内烯蜡,在烃链上导入极性基团,目的是以此做为第三组分用于改进聚丙烯与含极性基团聚合物,如聚酰胺、聚氯乙烯等的相容性。通过对引发剂用量、单体用量、反应温度和反应时间等条件的研究,制得接枝率为17％的接枝改性聚丙烯蜡。     

Chemorheological studies on polymer degradation

The degradation of dicumyl peroxide-cured natural rubber was studied by the stress relaxation method. Experiments were carried out in air, in nitrogen, and by irradiation of UV light in the temperature range of 30–200°C. We attempted to divide factors of the degradation into two parts: that caused by heat and that by light, and to study the respective degradation quantitatively. The degradation caused by UV light in nitrogen was almost independent of temperature. However, the degradation caused by UV light in air increased with temperature and the rate of degradation caused by the interaction between light and oxygen was greater at high temperature than at low temperature. It was found that scission along main chains occurs for dicumyl peroxide-cured natural rubber by photo-oxidation as well as thermal oxidation.     

Rheological properties of polyethylenes modified with dicumyl peroxide

Low- and high-density polyethylenes were modified using dicumyl peroxide. The modified polyethylenes were subjected to steady and oscillatory shearing flows. The viscous and elastic properties determined with a cone-and-plate rheometer are correlated to the molecular weight of the materials, which was determined with the aid of size exclusion chromatographic analysis. It was found that both the melt viscosity and elasticity increase with the amount of dicumyl peroxide used, and shear-thinning behavior becomes more intense. The Bueche master curve of viscosity is constructed by using a relaxation time based on the weight-average molecular weight for both virgin and modified resins.     

Morphology,mechanical properties,and failure topography of semi‐interpenetrating polymer networks based on natural rubber and polystyrene

Semi‐interpenetrating networks (semi‐IPNs) were prepared from natural rubber (NR) and polystyrene (PS) by the sequential method. In these semi‐IPNs the NR phase was crosslinked while the PS phase was uncrosslinked. Different initiating systems such as dicumyl peroxide (DCP), benzoyl peroxide (BPO), and the azobisisobutyronitrile (AIBN) system were used for polymerizing the PS phase. The blend ratio was varied by controlling the swelling of NR in the styrene monomer. The mechanical properties of the semi‐IPNs, namely, density, tensile strength, tear strength, elongation at break, tension set, tensile set, impact strength, and hardness, were determined. The morphology of different IPNs was studied using scanning electron microscopy. A compact morphology with a homogeneous phase distribution was observed in the semi‐IPNs. The properties of the semi‐IPN do not change much with the initiating system. However, in most cases, the DCP initiating system showed slightly superior performance. The tensile and tear‐strength values of the IPNs were found to increase with increasing plastomer content. The crosslink density of the semi‐IPNs also increased with increase in the polystyrene content. The experimental values were compared with theoretical models such as series, parallel, Halpin Tsai, Coran, Takayanaki, Kerner, and Kunori. The tensile and tear‐fracture surfaces were examined using a scanning electron microscope. The fracture patterns were correlated with the strength and nature of the failure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2327–2344, 2000     

Free-Radical Graft Copolymerization of Polar Monomers on Low-Density Polyethylene Under Melt-Processing Conditions

Free-radical graft co polymerization of acrylic acid and ethyl methacrylate on low-density polyethylene (LDPE) was studied under simulated melt-processing conditions. Initiators benzoyl peroxide and dicumyl peroxide were evaluated for their grafting efficiency. Benzoyl peroxide was found to be an excellent catalyst for the grafting of both monomers, whereas dicumyl peroxide was quite ineffective. Effect of reaction time, initiator concentration, and reaction temperature was studied for benzoyl peroxide initiated graft co polymerization of the two monomers. The changes in the torque and temperature of the reaction melt in the course of the reaction were recorded. More or less quantitative grafting of both monomers could be achieved, using low initiator concentrations, in very short reaction times. The possibility of modifying LDPE during melt extrusion in the extruder itself has been clearly demonstrated. This would be a highly cost-effective way of diversifying the properties and applications of LDPE. Cross linking was found to be relatively higher in the graft co polymerization of acrylic acid but within acceptable limits. Possible mechanisms of this are discussed.     

炭黑填充PE-HD/EVA/PE-LD导电发泡复合材料的阻温特性

以高密度聚乙烯（PE-HD）为聚合物基体材料,乙烯-乙酸乙烯酯（EVA）为增韧剂,低密度聚乙烯（PE-LD）为增塑剂,乙炔炭黑(ACET)为导电填料,偶氮二甲酰胺（AC）为发泡剂,过氧化二异丙苯（DCP）为交联剂制备了PE-HD/EVA/PE-LD /ACET导电发泡复合材料。结果表明,PE-HD/EVA/PE-LD＝50/30/20（质量比,下同）,ACET填加量为35 % (质量分数,下同)、发泡剂AC的添加量为4 %、交联剂DCP填加量为0.5 %时,制备的导电泡沫具有比较理想的闭孔泡孔结构。经过升温电阻测试,发现PE-HD/EVA/PE-LD/ACET导电发泡复合材料具有良好的开关特性,呈现明显的正温度系数特性（PTC）特性;AC发泡剂用量为4 %时,PTC效应最强。     

PPC/PDAP共混膜的制备和性能

将过氧化二异丙苯(DCP)置于特定温度下,引发邻苯二甲酸二烯丙酯(DAP)在聚碳酸亚丙酯(PPC)溶液中聚合,制备得到聚碳酸亚丙酯/聚邻苯二甲酸二烯丙酯(PPC/PDAP)共混膜。采用红外光谱仪(FTIR)、X射线衍射仪(XRD)、差示扫描量热仪(DSC)、热重分析仪(TGA)、万能试验机和水蒸气透过率测试仪对共混膜的红外吸收、结晶性、热、力学和阻隔性能进行了表征。结果表明,通过DAP的聚合,提高了PPC的结晶性,使PDAP在PPC基体中形成交联网络,提高了共混膜的热、力学和阻隔性能。相比纯PPC,当DAP含量为20%时,共混膜的玻璃化转变温度和拉伸强度分别提高了5.3℃和266%;当DAP含量为40%时,共混膜的失重5%热分解温度提高了50.9℃,透湿系数下降了25%,因此,阻隔性能得到了提升。     

挤出过程中交联聚氯乙烯的研究

应用过氧化二异丙苯 /苯乙烯 /三乙醇胺体系在挤出过程中实现了聚氯乙烯的一步交联 ,研究了三乙醇胺和过氧化二异丙苯用量对交联产物力学性能及交联凝胶率的影响。研究发现 ,三乙醇胺对PVC交联结构的形成具有明显的促进作用。在苯乙烯用量 5 phr,三乙醇胺用量为 0 33phr时 ,过氧化二异丙苯在 0 15phr取得最佳值 ;当苯乙烯用量 5 phr,过氧化二异丙苯用量 0 15 phr时 ,三乙醇胺用量在 0 4hpr取得最佳值。交联可以使聚合物材料的力学强度得到提高     

聚苯乙烯光氧老化行为及其模型研究

研究了自然曝晒试验后的聚苯乙烯(PS)样品结构和性能的变化,同时对其拉伸强度保持率的变化进行回归拟合,并建立了光氧老化模型。结果表明:太阳辐照是影响PS光氧老化的主要因素,水分对其起促进作用;PS老化过程中有羰基基团生成;老化模型可以反映光、热、水综合作用的强弱。     

A kinetic study on the reaction of dicumyl peroxide with some low-olefin rubbers

The viscosity lowering of toluene solutions of isobutylene-isoprene rubber, polyisobutylene, and ethylene-propylene rubber in the reaction with dicumyl peroxide was investigated. By using the kinetic equations for the reaction of rubber with peroxide which had been derived previously by KIRIYAMA et al. the results of the experiments are discussed.