Self-Threading-Based Approach for Branched and/or Cross-linked Poly(methacrylate rotaxane)s

Abstract

Physically branched and cross-linked polymeric structures were produced for the first time by rotaxane formation during reaction of a pendant group of a preformed macromolecule. The rotaxane structure is believed to form from a hydrogen-bonded bimolecular complex of 5-(hydroxymethyl)-1,3-phenylene-1‘,3‘-phenylene-32-crown-10 ( 16 ) by esterification of the hydroxy group of one macrocycle through the cavity of the second in its reaction with poly(methacryloyl chloride) ( 12 ). For esters formed in model reactions of 12 with methanol and with 5-(hydroxymethyl)-1,3-phenylene-16-crown-5 ( 14 ), which is too small to be threaded, the degrees of polymerization were identical; however, the polymer from reaction of 12 and 16 under the same conditions had a significantly higher degree of polymerization and polydispersity, i.e., was highly branched via rotaxane formation. Increasing the concentration in the reaction of 12 with 16 led to the formation of a gel fraction along with a high molecular weight sol fraction; the gel represents a novel network structure based on mechanical interlocking via rotaxane structures. 2D NOESY NMR experiments clearly demonstrated the rotaxane structure as manifest in the through-space correlation of the benzylic protons of the “thread” with the intra-annular protons of the “bead”.