Selective determination of glass transition temperature and vibrational properties at the chain end of polystyrene by Fourier transform infrared measurement in combination with deuterium-labeling
Selective determination of glass transition temperature and vibrational properties at the chain end of polystyrene by Fourier transform infrared measurement in combination with deuterium-labeling
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DOI：
10.1016/j.polymer.2015.01.021
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发表时间：
2015-02
期刊：
影响因子：
4.6
通讯作者：
Yohei Miwa;O. Urakawa;S. Nobukawa;S. Kutsumizu
中科院分区：
文献类型：
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作者：
Yohei Miwa;O. Urakawa;S. Nobukawa;S. Kutsumizu
采用傅里叶变换红外光谱法（FT-IR）对聚苯乙烯（PS）的玻璃化转变温度（Tg）和链端振动性质进行了选择性测定。在该方法中，合成了具有几乎相同的数均分子量（Mn）但选择性地在不同位置（中间链（M-PS，Mn= 10.7 kDa）或链末端（E-PS，Mn= 10.3 kDa））氘代的PS，并详细分析了主链CD 2的不对称伸缩振动（νas（CD 2））。我们发现，νas（CD 2）频率的温度依赖性在PS的量热Tg处显示出明显的拐点。拐点温度定义为Tg，FTIR，它代表氘代位周围局部区域的Tg。虽然在我们的前期工作中发现了在链端有较高的链段迁移率，但本研究发现M-PS和E-PS的Tg、FTIR是相同的。从这个结果，可以得出结论，链端移动与许多相邻的其他部分合作，平均出这些流动性在温度约Tg。另一方面，在任何温度下，E-PS的νas（CD 2）频率都比M-PS高几cm-1。这可以用链末端重复单元的不连续性来解释，导致沿着链的重复单元之间的相互作用减少。
Glass transition temperature (Tg) and vibrational properties at the chain end of polystyrene (PS) were selectively determined by a novel method utilizing Fourier transform infrared (FT-IR) spectroscopy. In this method, PSs having almost the same number average molecular weight (Mn) but selectively deuterated at different sites, midchain (M-PS,Mn= 10.7 kDa) or chain end (E-PS,Mn= 10.3 kDa), were synthesized and the asymmetric stretching vibration of the main chain CD2(νas(CD2)) were analyzed in detail. We found that the temperature dependence of theνas(CD2) frequency shows a clear inflection at the calorimetricTgof PS. The inflection temperature was defined asTg,FTIR, which represents theTgat the local region around the deuterated sites. Althoughhighersegmental mobility at the chain end had been shownabovetheTgin our earlier work, this study found that theTg,FTIRs of the M-PS and E-PS are the same. From this result, it was concluded that the chain ends move cooperatively with numerous neighboring other segments, averaging out those mobilities at temperatures around theTg. On the other hand, theνas(CD2) frequency of the E-PS was by a few cm−1higher than that of the M-PS for any temperature. This was explained in terms of the discontinuity of the repeat unit at the chain end resulting in reduced interactions between repeat units along the chain.