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61.
Strain-induced ordering of microdomain structures in cross-linked polystyrene-block-polybutadiene-block-polystyrene (SBS) triblock copolymers was examined by the small-angle X-ray scattering technique. To stretch the SBS samples at elevated temperature above the glass transition temperature of polystyrene, polybutadiene blocks were chemically cross-linked in the disordered state. The initial morphology was disorder-like or bicontinuous due to incompletion of microphase separation in the presence of the chemical cross-links. When the cross-linked SBS samples were mechanically stretched at 130 °C and were further annealed for 24 h under a stretched state, the random domain structures ordered gradually and lamellar-like regularity was finally attained. It was found that the ordering proceeded more for the case of the higher strain. 相似文献
62.
Structure–property relationships in poly(urethane urea)s synthesized with ultra‐low monol content poly(propylene glycol) soft segments were investigated as soft segment molecular weight (2000, 4000, and 8000 g/mol) and hard segment content (6.3 and 9.0 wt %) were varied. Morphological features such as interdomain spacing and interphase thickness were quantified and revealed with small‐angle X‐ray scattering (SAXS) and atomic force microscopy (AFM). The thermal and mechanical behavior was assessed with a dynamic mechanical analyzer (DMA) and by differential scanning calorimetry (DSC) and stress‐strain tests. Hard segment content, over the limited range studied, had little effect on the morphology and soft segment thermal and mechanical properties. The molecular weight of the soft segments had considerably more influence on the morphology and mechanical properties. Increasing soft segment molecular weight resulted in greater interdomain spacings, as shown by SAXS, and a noticeable change in the structure, as shown by AFM. Additionally, as soft segment molecular weight decreased the soft segment glass transition broadened and rose to higher temperatures. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 229–243, 2002; DOI 10.1002/app.10168 相似文献
63.
The reactive compatibilization of syndiotactic polystyrene (sPS)/oxazoline‐styrene copolymer (RPS)/maleic anhydride grafted ethylene‐propylene copolymer (EPR‐MA) blends is investigated in this study. First, the miscibility of sPS/RPS blends is examined by thermal analysis. The cold crystallization peak (Tcc) moved toward higher temperature with increased PRS, and, concerning enthalpy relaxation behaviors, only a single enthalpy relation peak was found in all aged samples. These results indicate that the sPS/RPS blend is miscible along the various compositions and RPS can be used in the reactive compatibilization of sPS/RPS/EPR‐MA blends. The reactive compatibilized sPS/RPS/EPR‐MA blends showed finer morphology than sPS/EPR‐MA physical blends and higher storage modulus (G') and complex viscosity (η*) when RPS contents were increased. Moreover, the impact strength of sPS/RPS/EPR‐MA increased significantly compared to sPS/EPR‐MA blend, and SEM micrographs after impact testing show that the sPS/RPS/EPR‐MA blend has better adhesion between the sPS matrix and the dispersed EPR‐MA phase. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2084–2091, 2002 相似文献
64.
采用极限氧指数法、热重分析和差示扫描量热分析等研究了碳酸钙(CaCO3)对乙烯-丙烯酸丁酯共聚物(EBA)阻燃及热降解行为的影响,探讨了CaCO3对EBA力学性能和熔体流动速率的影响。结果表明,CaCO3降低了EBA的拉伸强度、断裂伸长率和熔体流动速率,但复合阻燃材料仍具有良好的加工性能;当CaoCO3含量为60%(质量分数,下同)时,阻燃材料的极限氧指数可达28.5%。CaCO3通过EBA在热降解过程中与之发生化学反应来改变EBA的热降解行为,提高在高温下的热稳定性,降低EBA的热降解速率,促进高温下成炭在凝缩相中发挥阻燃作用。此外,CaCO3与EBA在热降解过程中形成隔热、隔氧的多孔泡沫膨胀结构,可进一步加强阻燃效果。 相似文献
65.
Two series of siloxane-urethane copolymers were prepared from polydimethylsiloxane (PDMS) with a molecular weight of 1000 or 1800 which was used as a soft segment, 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (1,4-BD). Differential scanning calorimetry (DSC) demonstrated that the position (Tgs) and breadth (ΔB) of soft-segment glass transition of copolymers remained constant as the hard-segment content increased. Heat capacities at soft-segment glass transition of the copolymer (ΔCp) were 0.195∼0.411 J/g○C and heat capacities of pure PDMS (ΔCp0) were 0.571∼0.647 J/g○C, leading to the various ΔCp/ΔCp0 ratios. The ΔCp/ΔCp0 ratios decreased as the increasing of hard-segment content, showing poor phase separation. The FTIR spectrum confirmed the occurrence of hydrogen bonding in ether end-group of pure PDMS. The ether group of the soft segment led to interfacial mixing between soft and hard segments. The tan δ of the soft segment determined by dynamic mechanical testing (DMA) also identified the mixing of soft and hard segments. The mechanical properties of the copolymer were directly related to either the soft and hard segment contents or the chain lengths of soft and hard segments. The hard segment that reinforced the soft segment and interfacial thickness between soft and hard segment dominated the mechanical properties. 相似文献
66.
New organodilithium initiators were prepared in a hydrocarbon solvent in the absence of any polar additive. Although these initiators are insoluble when they are synthesized, they may be easily purified and reacted with dienes to give perfectly telechelic polydienes having unimodal distributions and low dispersity. A good agreement between experimental and theoretical molecular weights was observed. The polymer microstructures were similar to those of polymers initiated by butyllithium in the same solvent. Triblock thermoplastic elastomers were also prepared, the characteristics of which are given. The mechanical properties of a S.B.S. sample support also the claim of a good initiating ability and difunctionality of these initiators. 相似文献
67.
68.
Soap‐free emulsion copolymerization of perfluoroalkyl acrylate (FA)/methyl methacrylate (MMA)/n‐butyl acrylate (n‐BA) was carried out in the presence of sodium 2‐acrylamide‐2‐methyl propanesulfonate (AMPSNa) as a reactive surfactant and potassium persulfate (KPS) as an initiator. An analysis of the effects of concentration of AMPSNa, KPS, FA as well as polymerization temperature on the kinetic features (rate of polymerization) and colloidal characteristics (mean particle diameter, particle disperse index, particle numbers, and surface charge density) was followed. NMR, FTIR, AFM, and fluorine‐selective electrode analysis were used to characterize the composition and morphology of the FA copolymers. Both AFM analysis and contact angle measurements strongly implied that the fluorinated segments migrated to the outmost surface and created films with lower surface energy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2438–2444, 2007 相似文献
69.
We employ self-consistent mean-field (SCMF) theory in studying the body-centered cubic (bcc) spheres of block copolymers in the presence of a neutral solvent. First we examine the accuracy of the dilution approximation then analyze the dependence of the bcc structural sizes with copolymer volume fraction ?, the interaction parameter χAB, and degree of copolymerization N. Our results reveal that both distribution of each component and the micro-structural length scales are greatly influenced by each parameter ?, χAB, and N. As expected, with decreasing ?, more solvent distributes non-uniformally in the segregated domains, therefore deviation from the dilution approximation increases. This also suggests that when the effective segregation parameter ?χABN is fixed, a larger deviation is expected as χABN increases (i.e. ? decreases). Although when both χABN and ? are fixed, decreasing N (i.e. increasing χAB) enlarges the deviation from the dilution approximation. Furthermore, this solvent non-uniformity behavior is so significant that it even affects the dependence of the domain spacing L* and the matrix length Λ* with respect to (χAB)effN=?χABN near the ODT. When the systems are in molten state and/or in the concentrated regime, both L* and Λ* exhibit a sharp increase behavior as ODT is approached, due to many of the minority blocks being pulled from the spherical domains and swelling the matrix. With increasing solvent amount and/or χABN, we observe that the increase of the degree for the minority blocks pulled from the spheres into the matrix near the ODT is not as significant as that in the melt. As such, the sharp increase behavior in L* as well as Λ* near the ODT smoothens and even disappears. 相似文献
70.