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21.
A generalized equation was derived to calculate the melting temperatures of homopolymers and copolymers. The Gibbs‐Thomson equation for homopolymers and a modified application to copolymers were derived using the proposed equation. The melting temperature Tm0 in the Flory equation corresponds to the melting temperature TmC,∞ of copolymer crystals with stems of infinite length. Also, TmC,n*, the melting temperature for copolymer crystals with stems containing the maximum possible number of structural units, n*, should be used instead of Tm0 as the basis of supercooling in crystallization. The proposed equation shows good agreement with experimental data for α‐alkene‐ethylene homogeneous copolymers. 相似文献
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A series of polyurethane block copolymers based on hydroxy-terminated polydimethylsiloxane and poly(propylene glycol) soft segments of molecular weights 1818 and 2000, respectively, were synthesized. The hard segments consisted of 4,4′-diphenylnethane diisocyanate and 1,4-butanediol as the chain extender. Samples with different molar ratios were prepared. We tried to synthesize polydimethylsiloxane-based polyurethanes (PDMS-PU) containing a hard block as major fraction and a soft block as minor fraction for preparing toughened rigid systems. After a study of the pure polydimethylsiloxane-based polyurethane and poly(propylene glycol)-based polyurethane (PPG-PU), (mixed polyol)-based block copolymers and blends of PDMS-PU and PPG-PU were synthesized, and characterized by means of differential scanning calorimetry, tensile testing and scanning electron microscopy. In (mixed polyol)-based copolymers and lower hard-segment content blends, macro-phase separation occurred, but blends with higher hard-segment contents showed significant reduction in amounts of phase separation. 相似文献
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高聚物共混物及嵌段共聚物熔体的流变性(Ⅰ)共混物熔体的流动特性 总被引:1,自引:0,他引:1
综述了高聚物二元共混物及嵌段共聚物熔体的静态流变性,分析了不同共混体系的流动曲线,总结了共混物的流动特性及规律 相似文献
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马来酸及其酐和衣康酸与PP熔体接枝反应机理的研究 总被引:13,自引:0,他引:13
以马来酸酐作对照,用热分析、流变、化学分析等方法,研究了马来酸和衣康酸在非隔氧条件下与PP熔体催化接枝反应的特点和规律,阐述了单体结构-单元反应相对速率--接枝产物结构之间的关系,提出了3种接枝物的结构模型。 相似文献
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Core–shell type nanoparticles of poly(L ‐lactide)/poly(ethylene glycol) (LE) diblock copolymer were prepared by a dialysis technique. Their size was confirmed as 40–70 nm using photon correlation spectroscopy. The 1H‐NMR analysis confirmed the formation of core–shell type nanoparticles and drug loading. The particle size, drug loading, and drug release rate of the LE nanoparticles were slightly changed by the initial solvents that were used. The drug release behavior of LE core–shell type nanoparticles showed an initial burst during the first 12 h and then a sustained release until 100 h. The degradation behavior of LE block copolymer nanoparticles was divided into three phases: the initial rapid degradation phase, the stationary phase, and the rapid degradation phase until complete degradation. It was suggested that lidocaine release kinetics were predominantly governed by the diffusion mechanism in the initial burst phase and after that by both of the diffusion and degradation mechanisms. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2625–2634, 2002 相似文献
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化学氧化法制备的聚苯胺表面的亲水性差,本文在本征态和不同酸掺杂志聚苯胺的表面上接枝共聚丙烯丙烯酸和丙烯酰胺,明显地改善了聚苯胺的表面亲水性。结果显示,聚苯胺表面经过等离子体处理后,有利于丙烯酸和丙烯酰胺在聚苯胺表面上的接枝共聚,随着接枝量增多,导电率则随之有所下降,此外,利用SEM和反射IR表征了改性反聚苯胺表面的形态和结构。 相似文献