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A two-stage transition upon crossing the glass transition of polystyrene with increasing temperature was precisely determined and interpreted by using solid-state nuclear magnetic resonance(SSNMR), ~1H-~1H dipolar couplings based double quantum-filtered(DQF) and dipolar filter(DF) experiments and ~(13)C chemical shift anisotropy(CSA) based centerband-only detection of exchange(CODEX) experiment are used to fully characterize the time scale of molecular motions during the glass transition. While differential scanning calorimetry(DSC) and CODEX experiment predicted the first stage of glass transiton, DQF and DF experiments provided the evidence for the second stage transition during which the time scale of molecular motions changed from very slow(t ms) to very fast(t μs). The first stage of glass transition begins with the occurrence of remarkable slow re-orientation motions of the polymer backbone segments and ends when the degree of slow motion reaches maximum. The onset and endpoint of the conventional calorimetric glass transition of polystyrene can be quantitatively determined at the molecular level by SSNMR. In the second stage, a subsequent dramatic transition associated with the melting of the glassy components was observed. In this stage liquid-like NMR signals appeared and rapidly increased in intensity after a characteristic temperature T_f(~1.1T_g). The signals associated with the glassy components completely disappeared at another characteristic temperature T_c(~1.2T_g). 相似文献
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采用格子自洽场理论计算研究了受限于2个平行板间的对称星形共聚物AmBm(m=1,2,3,4,5)熔体形成的层状相结构.在给定的相互作用下(χNAB不变,χ为Flory-Huggins相互作用参数,NAB=(N?1)/m为单个聚合物分子中一对AB臂的总链节数目),针对平行板间距为体相周期的情况,系统考察了共聚物链长N和单个聚合物分子中A(或B)臂数目m对受限层结构细节及层取向的影响.由计算结果,当N或NAB不变时,受限层的归一化界面宽度随m的增大而减小.受限板为中性时,垂直层结构的单链自由能比平行层结构的低.随着板对共聚物中一种嵌段的选择作用Λ的增大,体系发生垂直层到平行层的转变,该转变为一阶相变.当m不变时,N越小,上述转变出现在越大的Λ值处,体系越容易保持垂直层结构.并且N越小,层状结构周期越小.当N或NAB不变时,m越大体系越容易保持垂直层结构.总之,星形共聚物的链长越短、臂数越多时,垂直层稳定的Λ区间越大、层状结构的界面宽度越小.这些结论可以指导刻蚀应用中对体系参数的选择. 相似文献
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该文以2种不同立构聚丙烯(iPP和sPP)为讨论对象,首先研究了量化计算方法在预测高分子13C各向同性和各向异性化学位移(CSA)中的应用,然后讨论了近年来发展的测定13C CSA粉末线形的2种重要固体NMR实验技术(SUPER和RAI)的特点和实验优化问题.最后,利用可获得接近无扭曲线形的SUPER技术测定了等规立构聚丙烯样品的13C CSA粉末线形,并与量化计算理论结果比较.结果表明:13C各向同性化学位移及CSA粉末线形的理论计算结果均与固体NMR实验结果有很好的符合,预示通过13C CSA量化计算结合固体NMR实验是阐明高分子微观结构的有力工具. 相似文献
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本文使用对二甲胺吡啶为模板剂,在水热条件下合成了一种新型热稳定的微孔磷铝分子筛NK-101,并对其进行了XRD、扫描电镜(SEM)、正己烷吸附、红外吸收光谱(IR)、27Al和31p的固体魔角旋转核磁共振(MAS-NMR)的表征.证明它具有微孔结构,其孔径大于0.43nm.晶粒为大米状多边形,尺寸在几个到十几个微米,命名为NK-101. 相似文献
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