科研之友
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摘要
A series of highly purified tadpole-shaped polystyrene (PS) samples were prepared by anionic polymerizations and multistep HPLC fractionations, and their linear melt rheology was investigated. Three tadpole samples were composed of a common ring chain (R-60; M-w = 59.8 kg/mol) and three different lengths of linear chains (L-30, L-70, and L-120; M-w = 27.1, 68.9, and 122 kg/mol, respectively), all of which were longer than the entanglement molecular weight (M-e = 18.0 kg/mol for PS). All tadpole samples revealed remarkably slower terminal relaxation than the constituent ring or linear chains and also than the ring/linear blends. These results are evidently owing to the newly generated characteristic entanglements such as the intermolecular ring linear penetrations. Two rheological parameters, i.e., the zero-shear viscosity, eta(0), and the steady-state recoverable compliance, J(e), were estimated, and their molecular weight dependence was discussed. Tadpoles used in this study exhibited a drastic viscosity enhancement with the increase of the length of the linear tail compared with the simple linear chains. Moreover, the molecular weight dependence of their eta(0) is similar to that of star polymers when plotted against the molecular weight of a tail chain (M-w,M-tail) for tadpoles and that of one arm (M-w,M-arm) for stars. The molecular weight dependence of J(e) for tadpoles was also similar to that of stars rather than the linear chains. These results strongly suggest that the relaxation mechanism of tadpole chains adopted in this study is similar to that of star polymers, being well understood by contour length fluctuations like the arm retraction model. These characteristic rheological properties of tadpoles must originate from their unique architecture where a ring and a linear chain are introduced into one molecule.
- 出版日期2015-12-8
