Synthesis of a Novel Kind of Amphiphilic Graft Copolymer with Miktoarm Star-Shaped Side Chains

ReceiVed January 17, 2008 ReVised Manuscript ReceiVed February 21, 2008 Introduction. In recent years, much attention is paid to the synthesis of copolymers with different compositions and chain architectures, such as linear, grafted, comb-shaped, star-shaped, hyperbranched, and dendrimeric chains with the purpose to establish architecture-property relationships in bulk and in solution. Of these various architectures, the graft copolymers, especially the amphiphilic graft copolymers, are attractive materials because of their unique chemical and physical properties as well as their potential applications in drugs, bimomaterials, nanotechnology, polymer-hybrid nanocomposites, and supermolecular science. Generally, three strategies were used for the preparation of amphiphilic graft copolymers: (i) grafting onto, in which side chains are preformed and then attached to the main chain; (ii) grafting from, in which the monomer is grafted from the main chain; and (iii) grafting through, in which the macromonomers are copolymerized. It is well-known that controlled polymerizations such as anionic, ATRP, and RAFT are powerful tools for the synthesis of linear polymers with well-controlled molecular weight and polydispersity, and it is possible to make topological tailoring on polymer by the reactions of anion with some functional compounds or modification of the end groups. And “click” reactions, as termed by Sharpless et al., are widely used in polymer chemistry during the past few years due to their high specificity, quantitative yields, and near-perfect fidelity in the presence of most functional groups. Therefore, it is promising to combine the click reaction with controlled polymerization methods to synthesize the graft copolymers with complex structure. Miktoarm star polymer is a kind of copolymer in which the arms with same or different chemical structure were connected at one junction point. They showed quite different microdomain morphologies in bulk and self-assembly behavior in solution compared with the comb-shaped, block-grafted, cyclic, arborescent, and hyperbranched copolymers. In the investigation of ABC 3-miktoarm star-shaped terpolymers polystyrene-poly(ethylene oxide)-poly(ethoxyethyl glycidyl ether) (PS-PEO-PEEGE), it was found that the hydroxyl end group of PEEGE block could be modified further, and then the miktoarm star copolymers with functional group as alkyne group were obtained. If these star copolymers could be fastened onto a polymer chain by reaction of functional groups between graft and main chains, then these graft copolymers with complex structure may provide new models for the investigation of morphologies and self-assembly of copolymers. Up to now, few publications are reported about the synthesis of the amphiphilic graft copolymer with miktoarm star side chains; only Yu et al. reported recently the synthesis of hydrophobic graft polymers with Y-shaped branches. In this paper, a novel kind of graft copolymers composed of the copolymers of EO and EEGE as main chains and starshaped functionalized ABC copolymers of PS-PEO-PEEGE as side chains were described. The copolymers main chains with pending functional groups were modified to azide groups first by a series of reactions, and then the coupling reaction of the azide groups on main chain with alkyne group at PEEGE chain end of miktoarm star copolymers could be easily carried out.