Simple, Yet Powerful Reactions for Polymer Crosslinking and Functionalization

摘要

Cross-linking is of crucial importance to endow enhanced thermal stability, mechanical properties and solvent resistance to polymeric materials. While many methods exist to prepare cross-linked materials, they can be largely divided into two separate categories: (1) copolymerizing monomers with a small fraction of multifunctional monomers to directly prepare cross-linked materials and (2) inducing covalent cross-linking of preformed polymer chains in a secondary step. The second method allows facile materials processing as well as spatio-temporal control of the cross-linking reaction; however, methods generally used for such a procedure are often harsh, triggered by excess heat, light, or reactive intermediates. We have devised an approach that combines the best of each established strategy, where well-defined chemistry induced under mild conditions without any small molecule additives is used to prepare functional cross-linked materials. Our method relies on a system that employs mild, orthogonal chemistries to both cross-link and functionalize polymer structures in a controlled manner. The thermal azide-alkyne cycloaddition (TAAC, Figure 1) is used for this process, in which linear polystyrene bearing random incorporation of azido and alkynyl groups undergoes effective crosslinking at temperatures above 60 oC. The residual azide and alkyne groups are then used to orthogonally covalently tether small molecules to the surface and throughout the bulk of the material in defined patterns.