Facile UV-induced covalent modification and crosslinking of styrene-isoprene-styrene copolymer Paterno-Büchi [2 + 2] photocycloaddition

The chemical functionalization or modification of polymers to alter or improve the physical and mechanical properties constitutes an important field in macromolecular research. Fabrication of polymeric materials via structural tailoring of commercial or commodity polymers that are produced in vast quantities especially possess unique advantages in material applications. In the present study, we report on benign chemical modification of unsaturated styrene-isoprene-styrene (SIS) copolymer using available backbone alkene groups. Covalent attachment of aldehyde functional substrates onto reactive isoprene double bond residues was conveniently carried out using UV-induced Paterno-Büchi [2 + 2] cycloaddition. Model organic compounds with different structures were utilized in high efficiency chemical modification of parent polymer chains via oxetane ring formation. Functionalization studies were confirmed via 1 H NMR, FT-IR and SEC analyses. The methodology was extended to covalent crosslinking of polymer chains to obtain organogels with tailorable crosslinking degrees and physical characteristics. Considering the outstanding elastic properties of unsaturated rubbers and their high commercial availability, abundant reactive double bonds in backbone chains of these polymers offer easy to implement structural modification via proposed Paterno-Büchi photocycloaddition. Paterno-Büchi reaction is reported as a convenient chemical reaction tool to modify unsaturated copolymer elastomers.