RAFT chemistry and Huisgen 1,3-dipolar cycloaddition:: A route to block copolymers of vinyl acetate and 6-O-methacryloyl mannose?

The present communication explores a novel avenue to glycopolymer-block-poly( vinyl acetate) polymers by a combination of reversible addition fragmentation chain transfer ( RAFT) chemistry and Huisgen 1,3-dipolar cycloaddition (i.e., so-called 'click' chemistry) under mild reaction conditions. Such block copolymers are - because of the strongly disparate reactivity of the two monomers - otherwise not obtainable. Poly( vinyl acetate) that has an azide end group (M-n 6800 g mol(-1), PDI 1.15) was treated with poly(6-O-methacryloyl mannose) (M-n 7600 g mol(-1), PDI 1.11) in the presence of 1,8-diaza[5,4,0] bicycloundec-7-ene and copper(I) iodide. The resulting poly( vinyl acetate)- block-poly( 6-O-methacryloyl mannose) had a number-average molecular weight of 15 400 g mol(-1) and a PDI of 1.48, which indicates that while the cycloaddition had occurred the resulting polymer distribution featured a considerable width. The resulting slightly amphiphilic block copolymer was subsequently investigated with regard to its self-assembly in aqueous solution. Dynamic light scattering studies indicated a hydrodynamic diameter of close to 200 nm. Transmission electron microscopy studies indicate the formation of rods as well as spheres with transitions between these two phases. However, the segregation between core and shell in the spheres is not pronounced; such behaviour is expected for weakly amphiphilic block copolymers.