, Fig. 1b. In all cases the
MarkeHouwink a-values as determined in MEK are significantly
lower for all three hyperbranched polymers compared with linear
PMMA 310 kDa, a ¼ 0.4 compared with a ¼ 0.69, indicating a more
compact structure and higher molecular density. Branching was
calculated using a Zimm-Stockmeyer model first reported by Frechet
and co-workers which relates the intrinsic viscosities of the
branched fractions to that of the linear reference materials [30],
with the highest molecular weight fractions for the hyperbranched
polymers being the most highly branched through successive
generation