|296. Walther, A.; Göldel, A.; Müller, A.H.E.: Controlled crosslinking of polybutadiene containing block terpolymer bulk structures: A facile way towards complex and functional nanostructures, Polymer 49, 3217 (2008) -- DOI: 10.1016/j.polymer.2008.05.023 -- PDF|
The controlled crosslinking of polystyrene-block-polybutadiene-block-poly(tert-butyl methacrylate) (SBT) terpolymers in their microphase-segregated bulk state is investigated. Two different methods, the cold vulcanization and the 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) morphologies of SBT templates. It was found that the microphase-separated structures of the terpolymers react very sensitive 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 the cold vulcanization, 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 turns out 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 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.
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