STAR-SHAPED POLYMERS BY LIVING CATIONIC POLYMERIZATION .8. SIZE AND SHAPE OF STAR POLY(VINYL ETHER)S DETERMINED BY DYNAMIC LIGHT-SCATTERING AND COMPUTER-SIMULATION

Abstract

The sizes and shapes of star-shaped poly(vinyl ether)s, prepared by living cationic polymerization, were studied by dynamic light scattering and molecular mechanics-based computer simulation. The hydrodynamic radii (R(h)) Of Star poly(isobutyl vinyl ether)s (4a; ($) over bar M(w) = 2.2 X 10(4) - 1.7 X 10(5)) determined by dynamic light scattering were in the range from 30 to 90 Angstrom in tetrahydrofuran or ethyl acetate. Consistent with the expected multiarmed architecture of 4a, the radius for a given number (f) of arms per molecule increased with the degree of polymerization [DP(arm)] of the arms, and for a fixed DP(arm), the radius increased with f. The relationship between arm number f and the ''shrinking'' factor h [R(h)(star)/R(h)(linear)] was consistent with multibranched structures for the star polymers. These results are supported by those for the molecular weight itself; the apparent weight-average molecular weights by size-exclusion chromatography are less than the corresponding absolute values by static light scattering. The dependence of h on f suggests some degree of asymmetry in the star shape. Similar results were also obtained by the computer simulation of potential energy-minimized conformations of the arms, which implied almost spherical but slightly asymmetric shapes. The computer simulation also demonstrated that the star polymer (4b) with pendant hydroxyl groups in the arms is smaller in size than the corresponding alkyl (isobutyl) counterpart (4a) with the identical arm number and arm degree of polymerization. (C) 1995 John Wiley & Sons, Inc.