Controlling the morphology of (concentric) microtubes formed by in situ free radical polymerization

- Novel template approach for polymer microtube production.
- In situ, one-step synthesis protocol to produce polystyrene and polymethacrylate microtubes.
- Morphological control using volume weighted solvent polarity.
- Concentric polymer microtubes through successive polymerization.
- Multiplex tube formation through microstructured fiber template.

Templates are used extensively for materials synthesis applications. A material, the morphology of which can be controlled by utilizing different material deposition methods, is formed within the template followed by its removal. In this work an in situ, one-step synthesis protocol is employed to produce polystyrene and polymethacrylate microtubes within small-diameter fused silica templates. The versatility of this protocol is also shown by the ability to multiplex tube formation using a microstructured fibre template with 126 individual capillaries. The material synthesis involves functionalizing the inner wall(s) of the template followed by the in situ free radical-initiated polymerization of the pre-polymer solution that contains a radical initiator and monomer/crosslinker mixed with an appropriate porogenic solvent. Distinct morphologies result depending on the template pre-treatment, synthesis temperature, template dimension and the relative polarity of the porogenic solvent. Tubular morphology is promoted through the use of hydrophobic monomers (e.g. benzyl methacrylate or styrene), lower polymerization temperatures and a more polar porogenic solvent mixture. Subsequent polymerizations can be carried out within capillary templates already containing polymer tubes to increase tube wall thickness, or to produce concentric, mixed material tubes (e.g. two- and three-layer combinations of poly-(benzyl methacrylate-co-1,4-butanediol dimethacrylate) and poly-(styrene-co-divinylbenzene) tubes). Morphological control of poly-(benzyl methacrylate-co-1,4-butanediol dimethacrylate) structures, particularly their tubular character and thickness, will prove useful for optimizing their performance as porous-layer open-tubular chromatographic columns, small tubular conduits and high-performance layered materials.