End-functionalized polymers with zwitterionic end-groups

The synthesis, dilute solution and bulk properties of well-defined polymers with different architectures (linear homopolymers, di- and tri-block copolymers and star homopolymers) having dimethylamine and sulfobetaine end-groups are reviewed. The end functionalized polymers were prepared by means of anionic polymerization using high vacuum techniques. 3-Dimethylaminopropyllithium was used as a functional initiator for the introduction of dimethylamine end-groups. This group was switched to a sulfozwitterionic one by reaction with cyclopropane-sultone. The high molecular and compositional homogeneity of these model materials was confirmed by extensive molecular characterization data. Their aggregation behavior in dilute solutions having different polarities was studied by osmometry, viscometry and static and dynamic light scattering and was compared to predictions derived from theoretical models. The end-functionalized polystyrenes and the block copolymers of styrene possess lower degrees of association than the homopolydienes, probably due to the polarizability of the phenyl groups. The bulk properties of the functionalized homopolymers and diblock copolymers, studied by SAXS, rheology and dielectric spectroscopy, revealed new features of self-organization at this low ionic content and extraordinary phase stability at higher temperatures. The adsorption behavior of linear and star homopolydienes was investigated by ellipsometry and by using a surface-force apparatus. (C) 1999 Elsevier Science Ltd. All rights reserved.