Grafting photochromic spiropyran polymer brushes on natural rubber surface via surface-initiated ring-opening metathesis polymerization

The modification of stereoregulated functionalized polymers on the surface of natural rubber (NR) is a challenging task. This work provided a practicable grafting method to design photochromic polymer brushes on the NR surfaces using surface-initiated ring-opening metathesis polymerization (SI-ROMP). The designed photochromic polymer brushes were based on norbornenes with spiropyrin (SP) pendents, and grew from the surface of NR films in the presence of Grubbs 2nd catalyst. The results showed that the grafting rate of polymer brushes with photoisomerization structure reached up to 44.91 %. The modified natural rubber (NR-SP) films exhibited rapid coloring/decolorization property under UV irradiation and visible light. This photochromic property initiated by the light-induced isomerisation of the spiropyran structure and the increased surface energy under light stimuli. NR-SP films exhibited stable photochromic characteristics and outstanding anti-fatigue properties after exposing to over six cycles of consecutive UV/Vis irradiation. A simple and practical strategy for the preparation of highly sensitive photochromic natural rubber materials is proposed and provides a potential application in the fields of information storage and anti-counterfeiting.