Comparison of the gelation dynamics for polystyrenes prepared by conventional and living radical polymerizations: a time-resolved dynamic light scattering study
Comparison of the gelation dynamics for polystyrenes prepared by conventional and living radical polymerizations: a time-resolved dynamic light scattering study
复制标题
DOI：
10.1016/j.polymer.2004.12.043
复制
发表时间：
2005-02
期刊：
影响因子：
4.6
通讯作者：
T. Norisuye;Morinaga Takashi;Qui Tran‐Cong‐Miyata;A. Goto;T. Fukuda;M. Shibayama
中科院分区：
文献类型：
--
作者：
T. Norisuye;Morinaga Takashi;Qui Tran‐Cong‐Miyata;A. Goto;T. Fukuda;M. Shibayama
通过时间分辨动态光散射（TRDLS）研究了传统和活性自由基聚合制备的两种聚苯乙烯凝胶的结构和动力学。该反应是用含有或不含有可逆加成断裂链转移（RAFT）剂的单体溶液引发的，并通过凝胶化过程进行监测。在不存在交联剂的情况下，反应过程的特征在于当过量散射强度除以浓度绘制为反应时间的函数时出现最大值。强度最大值归因于分子量的增加和随后浓度波动的抑制，这通过弗洛里-哈金斯自由能公式定性地重现。随着浓度变得更高，时间强度相关函数（ICF）表现出两种模式，表明除了合作模式之外还形成了更大的聚集体。通过考虑快模式和慢模式的相对幅度，强度被成功分解为两个分量。通过结合 TRDLS 和凝胶渗透色谱、GPC 数据，可以清楚地检测到两种聚合类型之间的时间进程差异。对于交联体系，其动力学特征在于通用的凝胶机制，即：(1) 慢速模式的发散和 (2) ICF 中在凝胶阈值附近出现幂律，无论聚合方法如何。另一方面，实时强度分解分析揭示了两种聚合类型之间凝胶机制的显着差异。例如，慢模式出现在传统体系的反应早期阶段，并在整个凝胶化过程中维持其幅度。对于活体（RAFT）系统，慢模式的出现仅限于较窄的反应时间范围和较小的幅度。
The structure and dynamics for the two types of polystyrene gels prepared by conventional and living radical polymerizations have been investigated by time-resolved dynamic light scattering (TRDLS). The reaction was initiated with the monomer solutions with and without a reversible addition–fragmentation chain transfer (RAFT) agent and was monitored through the gelation process. In the absence of a cross-linker, the reaction process was characterized by the appearance of a maximum when the excess scattering intensity divided by concentration was plotted as a function of reaction time. The intensity maximum was ascribed to an increase in the molecular weight and subsequent suppression of the concentration fluctuations, which was qualitatively reproduced by the Flory–Huggins free energy formula. As the concentration became higher, the time–intensity correlation functions (ICFs) exhibited two modes, suggesting the formation of larger aggregates in addition to the cooperative mode. The intensities were successfully decomposed into the two components by taking account of the relative amplitude of the fast and slow modes. The difference of the time-course between the two types of polymerizations was clearly detected by combining TRDLS and gel permeation chromatography, GPC, data. For the cross-linking system, the kinetics was characterized by the universal gelation mechanism, namely: (1) divergence of the slow mode and (2) appearance of the power law in ICF around the gelation threshold regardless of the polymerization method. On the other hand, the real time intensity decomposition analysis revealed striking differences in the gelation mechanism between the two types of polymerization. For example, the slow mode appeared at an early stage of reaction for the conventional system and sustained its amplitude through the gelation process. For the living (RAFT) system, the appearance of the slow mode was limited in a narrower range of the reaction time with a much smaller amplitude.