MOLECULAR-DYNAMICS IN LINEAR AND MULTIARMED STAR POLYMERS OF CIS-POLYISOPRENE AS STUDIED BY DIELECTRIC-SPECTROSCOPY

Dielectric spectroscopy from 10-1 to 109 Hz was used to investigate bulk amorphous multiarmed stars of cis-polyisoprene and their linear counterparts, both having narrow molecular weight distributions. The star polymers resemble the linear polymers in showing two distinct regions of dielectric dispersion. A molecular weight independent segmental process occurs at nearly the same frequency as in the linear polymer due to dipole moments perpendicular to the chain backbone. The second process is caused by the parallel dipole moments and exhibits a pronounced molecular weight dependence. The relaxation time of the molecular weight dependent normal-mode process for linear polymers can be described according to the Rouse theory below the critical molecular weight, Mc (≅104), but above Mc it corresponds to the 3.7 power of Mw, which is characteristic for entangled macromolecules. A similar dependence of the relaxation time is observed for the many armed star polymers. It is interpreted by means of the conformational scaling properties of Daoud and Cotton and compared with theoretical and computational approaches. © 1990, American Chemical Society. All rights reserved.