RHEOLOGY OF SMALL SPHERICAL POLYSTYRENE MICROGELS - A DIRECT PROOF FOR A NEW TRANSPORT MECHANISM IN BULK POLYMERS BESIDES REPTATION
RHEOLOGY OF SMALL SPHERICAL POLYSTYRENE MICROGELS - A DIRECT PROOF FOR A NEW TRANSPORT MECHANISM IN BULK POLYMERS BESIDES REPTATION
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DOI：
10.1021/ma00116a025
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发表时间：
1995-06-05
期刊：
影响因子：
5.5
通讯作者：
BREMSER, W
中科院分区：
文献类型：
--
作者：
ANTONIETTI, M;PAKULA, T;BREMSER, W
最近开发的一种合成技术--微乳液聚合--提供了一种新型的模型聚合物--球形微凝胶或“橡胶纳米球”。这些聚合物分子分布窄，尺寸在5 nm<；R<；50 nm。在这篇文章中，我们研究了这些微凝胶在其玻璃化转变上方的块体中的粘弹性行为。与所有预期相反的是，这些微凝胶表现出高达M(W)=2×10(6)的粘性流动或相应的R=9 nm的硬球半径，并且零剪切粘度显著低于相同分子量的直链。同样令人惊讶的是，结果表明，机械响应的频率依赖性看起来类似于众所周知的Zimm或螺动类型的响应，尽管可以严格排除Zimm或螺动类型的迁移率被分子的球形结构所排除。这些结果支持除了旋转外，还存在一种较强的次要类型的聚合物流动性，这种流动性本质上比单链流动性更具协同性。这种迁移性应该在所有本体聚合物系统中发挥重要作用，并可能解释在许多复杂程度较高的聚合物系统中报告的相当高的传输速率和偏离旋转的情况。
A recently developed synthetic technique, the polymerization in microemulsions, gives access to a new type of model polymer, spherical microgels or ''rubbery nanospheres''. These polymer molecules are narrowly distributed and have sizes in the range of 5 nm < R < 50 nm. In this paper, we report the examination of the viscoelastic behavior of these microgels in the bulk above their glass transition. Opposite to all expectations, these microgels show viscous flow up to molecular weights of M(W) = 2 x 10(6) or related hard-sphere radii of R = 9 nm, and the zero-shear viscosity is remarkably lower than the one of linear chains of the same molecular weight. Similarily surprising, it is shown that frequency dependence of the mechanical response looks like the well-known Zimm- or reptation-type response, although a Zimm- or reptation-like mobility can be strictly excluded by the spherical architecture of the molecules. These results support the existence of a strong, secondary type of polymer mobility besides reptation which is more cooperative in its nature than a single-chain mobility. This mobility should play an important role in all bulk polymer systems and might explain the rather high transport rates and deviations from reptation reported in many polymer systems with higher complexity.