Dendrimer-like star polymers, a novel type of molecular architecture,
have been synthesized. The architecture of the new polymers resembles
that of three-dimensional spherical dendrimers as well as classical st
ar polymers. The controlled structures, based on aliphatic polyesters,
are synthesized by a divergent growth approach. A hexa hydroxy-functi
onal 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) derivative was use
d as the ''initiator'' for the stannous-2-ethylhexanoate (Sn(Oct)(2))
catalyzed living ring opening polymerization of epsilon-caprolactone.
The polymerization generated a six-arm polymer with a molecular weight
of 14 300 (M-n) and a M-w/M-n of 1.06. The new polymer was functional
ized with a protected bis-MPA, deprotected, and used as the ''macroini
tiator'' for the polymerization of a second generation 12 armed poly(e
psilon-caprolactone) (M-n = 42 300, M-w/M-n = 1.16). Another iteration
of the same procedure generated a third generation 24 arm dendrimer-l
ike star polymer with a M-n of 96 000 and M-w/M-n of 1.14. The complet
e initiation and functionalization was carefully investigated by H-1 a
nd C-13 NMR. These novel polymers are different from traditional dendr
itic materials in that this synthetic strategy allows these well defin
ed highly branched polymers to reach a high molecular weight in only a
few steps. In addition these materials are semicrystalline.