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

The sizes and shapes of star-shaped poly(vinyl ether)s, prepared by li ving cationic polymerization, were studied by dynamic light scattering and molecular mechanics-based computer simulation. The hydrodynamic r adii (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 w ere in the range from 30 to 90 Angstrom in tetrahydrofuran or ethyl ac etate. 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(ar m), the radius increased with f. The relationship between arm number f and the ''shrinking'' factor h [R(h)(star)/R(h)(linear)] was consiste nt with multibranched structures for the star polymers. These results are supported by those for the molecular weight itself; the apparent w eight-average molecular weights by size-exclusion chromatography are l ess than the corresponding absolute values by static light scattering. The dependence of h on f suggests some degree of asymmetry in the sta r shape. Similar results were also obtained by the computer simulation of potential energy-minimized conformations of the arms, which implie d almost spherical but slightly asymmetric shapes. The computer simula tion also demonstrated that the star polymer (4b) with pendant hydroxy l groups in the arms is smaller in size than the corresponding alkyl ( isobutyl) counterpart (4a) with the identical arm number and arm degre e of polymerization. (C) 1995 John Wiley & Sons, Inc.