Dalsin Samuel J, Hillmyer Marc A, Bates Frank S
Department of Chemical Engineering and Materials Science and ‡Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455-0431, United States.
Department of Chemical Engineering and Materials Science and Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455-0431, United States.
ACS Macro Lett. 2014 May 20;3(5):423-427. doi: 10.1021/mz500082h. Epub 2014 Apr 15.
A series of bottlebrush polymers with atactic polypropylene side chains were synthesized via ring-opening metathesis polymerization using Grubbs' third-generation catalyst (HIMes)(3-BrPy)(Cl)Ru═CHPh. Polymers were prepared with fixed side chain length and variable backbone degree of polymerization (DP) ranging from 11 to 732 ( = 22-1500 kg/mol) and include the largest reported polyolefin-based bottlebrush polymers. The zero-shear viscosity of each polymer sample was measured using small-amplitude oscillatory shear measurements. Power law fits of zero-shear viscosity (η) versus weight-average molar mass (η ∼ ) revealed distinct regimes with differing molecular weight dependences. A weak dependence (α < 0.5) was observed at low molecular weight due to the increasingly compact nature of short bottlebrush polymers with the continued addition of side chains. The scaling transitioned to Rouse-like dynamics (α = 1.2) at high molecular weight as a consequence of a sphere-to-cylinder conformational change with increasing DP of the bottlebrush backbone.
使用Grubbs第三代催化剂（HIMes）(3-BrPy)(Cl)Ru═CHPh，通过开环易位聚合反应合成了一系列带有无规聚丙烯侧链的刷状聚合物。制备的聚合物具有固定的侧链长度和可变的主链聚合度（DP），范围从11到732（ = 22 - 1500 kg/mol），包括已报道的最大的基于聚烯烃的刷状聚合物。使用小振幅振荡剪切测量法测量了每个聚合物样品的零剪切粘度。零剪切粘度（η）与重均摩尔质量（η ∼ ）的幂律拟合显示出具有不同分子量依赖性的不同区域。由于随着侧链的持续添加，短刷状聚合物的结构越来越紧凑，在低分子量时观察到较弱的依赖性（α < 0.5）。随着刷状主链DP的增加，由于球体到圆柱体的构象变化，在高分子量时标度转变为类Rouse动力学（α = 1.2）。
