Controlled crosslinking of polybutadiene containing block terpolymer bulk structures: A facile way towards complex and functional nanostructures

The controlled crosslinking of polystyrene-block-polybutadiene-block-poly(tert-butyl methacrylate) (SBT) block terpolymers in their microphase-segregated bulk state is investigated. Two different methods, cold vulcanization and free radical crosslinking as well as its optimized procedure, the thiol-polyene method, are applied for crosslinking the lamellar polybutadiene microdomains within the lamella-lamella (ll) morphology of SBT bulk structures. It was found that the microphase-separated structures of the block terpolymers react very sensitively towards the addition of swelling solvents and crosslinking agents. The changes in the microphase-segregated morphologies are followed at all stages with transmission electron microscopy to give an in-depth view of the nanoscopic transformations. These partially unexpected changes in the morphologies make a careful adjustment and optimization of the reaction conditions necessary. For cold vulcanization, i.e. the reaction of double bonds with sulphur monochloride, several swelling solvents and concentrations of crosslinking agents are explored. In the case of free radical crosslinking, it is found that an increase of the radical initiator concentration above 5 wt% does not lead to an increase of insoluble material as radical chain cleavages occur as side reactions, thus limiting the amount of the desired gel fraction. However, the addition of a trifunctional thiol can further increase the desired network formation. By means of this procedure and a subsequent homogenization, it is possible to create novel disc-like Janus particles. Dynamic light scattering and scanning force microscopy are used to highlight the flat nanoparticle structure and to demonstrate the influence of the crosslinker on the formed structures.