Preparation of Novel Branched Polymer by the Polymerization of Lactide Using Pseudorotaxane as an Initiator

Abstract

Pseudo-polyrotaxane consisting of polyethylene glycol (PEG) and cyclodextrin (CD) was used as an initiator of the polymerization of lactide for the purpose of introducing multiple cross-linking structures as building blocks of a new network polymer. We aim to prepare a new network polymer utilizing the rotaxane and polylactic acid (PLA) stereocomplex as cross-linking sites in the future. Herein, the hydroxyl groups at both ends of PEG, which is the axial component of pseudo-polyrotaxane, and the hydroxyl groups of CD, which is the ring component, were used as the initiation moieties for the polymerization of lactide. The pseudo-polyrotaxane and the branched polymer were separately collected by fractionation with water and acetone. When PEG (M_n = 1500 and 6000) were used, their solubilities were different. We also attempted to change the number of penetrating PEG axes by using α-CD and γ-CD. The structures of these pseudo-polyrotaxanes and branched polymers were confirmed by ¹H NMR and SEC analysis, and their thermostabilities were investigated by thermogravimetric analysis.