DYNAMICS OF THE STRONG POLYMER OF N-LAURYL METHACRYLATE BELOW AND ABOVE THE GLASS-TRANSITION
DYNAMICS OF THE STRONG POLYMER OF N-LAURYL METHACRYLATE BELOW AND ABOVE THE GLASS-TRANSITION
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DOI：
10.1021/ma00124a015
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发表时间：
1995-09-25
期刊：
影响因子：
5.5
通讯作者：
NGAI, KL
中科院分区：
文献类型：
--
作者：
FLOUDAS, G;PLACKE, P;NGAI, KL
采用介电光谱（DS）和动态光散射（DLS）研究了聚n-甲基丙烯酸十二烷基酯（PnLMA） (M（w) 1.1 x 10(5)）在低于和高于玻璃化转变温度T-g （T-g近似于225 K）时的动力学。在实验频率范围内，DS和DLS数据没有显示主弛豫（α -）和次弛豫（β -）分裂的证据。影响DS和DLS的主要过程是混合α - β -弛豫，在弛豫时间的t依赖性方面与单一α -弛豫过程相似。发现两组实验松弛时间非常吻合。弛豫时间的分布表现出明显的温度依赖性：在T近似于T-g时，β (KWW)的Kohlrausch-Williams-Watts （KWW）指数近似于0.25，在T近似于T-g + 100 K时，频率约为1 MHz时，β (KWW)指数近似于1。因此，据我们所知，PnLMA是迄今为止唯一在兆赫频率下具有德拜（β = 1）弛豫时间分布的聚合物。在T-g附近的极宽分布和弛豫时间的弱归一化温度依赖性显然与许多玻璃形成物中两者之间建立的现象学相关性相矛盾。这种矛盾可能是由长烷基链的浓度波动引起的，它会使T-g附近的弛豫谱变宽。除了主要的β -过程外，在两个实验中都可以解决“快速”β -弛豫，并且起源于聚乙烯类烷基链。
Dielectric spectroscopy (DS) and dynamic light scattering (DLS) are employed to study the dynamics of poly(n-lauryl methacrylate) (PnLMA) (M(w) 1.1 x 10(5)) at temperatures below and above the glass transition temperature T-g (T-g approximate to 225 K). The DS and DLS data show no evidence for the splitting between the primary (alpha-) and secondary (beta-) relaxations within the experimental frequency range. The main process affecting DS and DLS is the mixed alpha beta-relaxation which bears similarities to a single alpha-process with regard to the T-dependence of the relaxation times. Excellent agreement between the two sets of experimental relaxation times was found. The distribution of relaxation times exhibits a pronounced temperature dependence: from a Kohlrausch-Williams-Watts (KWW) exponent of beta(KWW) approximate to 0.25 at T approximate to T-g to beta(KWW) approximate to 1 at T approximate to T-g + 100 K and at a frequency of about 1 MHz. PnLMA is therefore, to our knowledge, the only polymer with a Debye (beta = 1) distribution of relaxation times at megahertz frequencies so far. The extremely broad distribution near T-g and the weak normalized temperature dependence of the relaxation time apparently contradict the phenomenologically established correlation between the two in many glass formers. This contradiction might arise from concentration fluctuations of the long alkyl chain which can broaden the relaxation spectrum near T-g. In addition to the main beta-process, a ''fast'' beta-relaxation can be resolved in both experiments and originates from the polyethylene-like alkyl chain.