Real time SANS study on head group self-assembly for lithium based anionic polymerizations
Real time SANS study on head group self-assembly for lithium based anionic polymerizations
复制标题
锂基阴离子聚合头基自组装的实时 SANS 研究
DOI：
10.1016/s0032-3861(02)00450-0
复制
发表时间：
2002
期刊：
影响因子：
4.6
通讯作者：
L. Fetters
中科院分区：
文献类型：
--
作者：
J. Stellbrink;J. Allgaier;L. Willner;D. Richter;T. Slawecki;L. Fetters
利用小角中子散射原位研究了丁二烯和异戊二烯在氘代正庚烷中聚合过程中形成的聚集结构。样品被设计为具有相同的聚合度。这些测量表明，在低 Q 值下，丁二烯传播事件的开始伴随着高度延伸的大规模结构的存在。随着传播的进行，这些初始结构的尺寸逐渐减小，并至少部分被星状聚集体取代。在聚合反应停止时，星形胶束，中等Q状态，表现出8.4的平均聚集状态。在较低的转化率（因此较低的链分子量）下，表明存在大的三维聚集体。相反，异戊二烯系统在传播的初始时刻并未显示出相同程度的大规模结构，尽管低 Q 数据确实表明形成了比星状聚集体更大的结构。星形胶束的平均聚集度为 4。这些结果表明，这些极性二烯基锂头基的缔合行为比当前“教科书”机制所允许的变化更大，其中单独允许的聚集态为 4。这些发现与最近基于半经验和从头算量子化学的一系列计算得出的结论一致。
Small angle neutron scattering was used to in situ study the aggregated structures formed in the course of the polymerization of butadiene and isoprene in deuterated n-heptane. The samples were designed to have equal degrees of polymerization. These measurements showed, at low Q, that the start of the butadiene propagation event was accompanied by the presence of highly extended large-scale structures. As propagation progressed these initial structures diminished in size and were replaced, at least in part, by star-like aggregates. At the cessation of the polymerization reaction the star micelles, mid-Q regime, exhibited a mean aggregation state of 8.4. At lower conversions (and thus lower chain molecular weights) the presence of large three-dimensional aggregates was indicated. Conversely, the isoprene system in its initial moments of propagation did not show the same extent of large-scale structures although the low Q data did indicate the formation of architectures larger than the star-like aggregates. The star shaped micelles exhibited the mean degree of aggregation of 4. These results demonstrate that the association behavior of these polar dienyllithium headgroups is more varied than permitted by the current ‘textbook’ mechanism where the solitary permissible aggregation state is four. These findings concur with those suggested from a recent semi-empirical and ab initio quantum chemistry based series of calculations.