Conformational analysis of alternating copolymers and their association into nanoarchitectures
A.S.W. Chan, M. Groves, C. Malardier-Jugroot
Royal Military College of Canada, CA
Keywords: alternating, amphiphilic, copolymer, IMA, geometric optimization, pH dependent, nanostructure
Abstract:Our research focuses on the characterization of the association and the properties in aqueous solution of nano-structures, particularly on nanotubes composed of amphiphilic alternating copolymers. These copolymers constitute a pH sensitive hydrophilic group (maleic anhydride) alternating with a hydrophobic group. To investigate the role of the nature of the hydrophobic groups on the association, the self-assembly of two different polymers are compared: poly(isobutylene-alt-maleic anhydride) (IMA) and poly(styrene-alt-maleic anhydride) (SMA). It has been well reported that, at pH7, SMA forms stable nanotubes by association through a linear conformation due to H-bonding and pi-cation interactions. The linerarity favours the association of the chains by decreasing the entropic cost. A theoretical approach was chosen to investigate and characterize the behavior of IMA chains at different pH values. To optimize IMA at different pH values, a complete conformational method was applied using both semi-empirical and ab initio molecular modeling methods. The present paper will describe in detail the conformational analysis of IMA, the association among IMA chains to form nanotubes and discuss the influence of the nature of the hydrophobic group on the association. The theoretical prediction will also be compared to experiment (dynamic light scattering, small angle neutron scattering, cryo-transmission electron microscopy).