Degradable Amphiphilic End-Linked Conetworks with Aqueous Degradation Rates Determined by Polymer Topology

Abstract

Degradable amphiphilic conetworks, based on end-linked amphiphilic ABA triblock copolymers with a labile fragment in the middle, were synthesized by sequential group transfer polymerization (GTP) of monomers and cross-linker, using a GTP bifunctional initiator containing two hemiacetal ester cleavable groups. The degrees of swelling (DSs) in tetrahydrofuran (a nonselective solvent) of most conetworks span a range of values from 15 to 18, whereas the sol fraction ranged between 27 and 42% in most cases. The labile groups of the initiator fragment allowed for the facile, site-specific conetwork cleavage in pure water and alcohols at a rate that depended on polymer architecture and composition. A systematic investigation was performed by following in detail the temporal evolution of the swollen mass of the conetworks in water and methanol. Most interestingly, a particular conetwork presented a maximum in its swelling profile with time both in water (DSmax ∼ 20) and in methanol (DSmax ∼ 30) due to the simultaneous occurrence of swelling and degradation. A small-angle neutron scattering (SANS) study of the conetworks in deuterated water enabled the independent monitoring of conetwork swelling and degradation as these two processes appeared as two separate peaks in the SANS profiles, the former of which being related to the self-organization of the hydrophobic blocks within the conetworks, whereas the latter being connected with the correlations among the amphiphilic star block copolymers released in solution during the course of conetwork hydrolysis.