Association and Structure of Thermosensitive Comblike Block Copolymers in Aqueous Solutions

Authors

Gang Cheng
Fengjun Hua
Yuri B. Melnichenko
Kunlun Hong
Jimmy W. Mays
Boualem Hammouda
George D. Wignall

Date of this Version

2008

Comments

Published in Macromolecules 2008, 41, 4824-4827.

Abstract

The structures and association properties of thermosensitive block copolymers of poly(methoxyoligo( ethylene glycol) norbornenyl esters) in D₂O were investigated by small angle neutron scattering (SANS). Each block is a comblike polymer with a polynorbornene (PNB) backbone and oligo ethylene glycol (OEG) side chains (one side chain per NB repeat unit). The chemical formula of the block copolymer is (OEG₃NB) ₇₉- (OEG_6.6NB) ₆₇, where subscripts represent the degree of polymerization (DP) of OEG and NB in each block. The polymer concentration was fixed at 2.0 wt % and the structural changes were investigated over a temperature range between 25 and 68°C. It was found that at room temperature polymers associate to form micelles with a spherical core formed by the block (OEG₃NB) ₇₉ and corona formed by the block (OEG_6.6NB) ₆₇ and that the shape of the polymer in the corona could be described by the form factor of rigid cylinders. At elevated temperatures, the aggregation number increased and the micelles became more compact. At temperatures around the cloud point temperature (CPT) T ) 60 °C a correlation peak started to appear and became pronounced at 68 °C due to the formation of a partially ordered structure with a correlation length ∼349 Å.