Thermoplastic elastomers of styrene-butadiene-styrene (SBS) triblock copolymers containing grafts of naphthopyran as side-chain polymer were prepared by polymerization of naphthopyran acrylate monomer with a solution of SBS in tetrahydrofuran. Thin films of all grafted SBS polymers displayed photochromism, the decoloration kinetics of naphthopyran in the films was modeled by fitting biexponential equations to the photochromic decay curves after UV light irradiation. Stretching of the grafted SBS film at room temperature affected the fading rate constant k 1 of the naphthopyran. The length of linker between photochromic naphthopyran moiety and the acrylate unit in monomer also affected the fading rate constant k 1 of the naphthopyran in SBS elastomers. This study presents an example of tuning the photochromic properties of naphthopyran via two approaches, polymer structure, and stretching of films.

Photochromic polymer films were prepared by doping the naphthodipyran into different polymers such as Polyvinylpyrrolidone (PVP), styrene-butadiene-styrene (SBS) triblock copolymer, and polymethyl methacrylate (PMMA) at different concentrations. The kinetics of the photochromism/decoloration in the thin films was quantified by fitting biexponential equations to their photochromic decay curves after UV irradiation. The results show that the fastest decoloration process was in SBS, and the slowest one was in PVP. The DSC results indicate that T g of polymeric matrix has no obvious effect on the decoloration rate of naphthodipyran. The decreasing order of the decoloration constant of naphthodipyran was consistent with increasing polarity of polymer matrixes as PVP > PMMA > SBS.

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Naphthopyran homopolymer and copolymer containing coumarin in side chain were synthesized by atom transfer radical polymerization. Their photochromic properties were investigated using UV-vis absorption spectroscopy and their decoloration kinetics in films was quantified by biexponential fitting of their photochromic decoloration curves after UV irradiation. The results showed that the photochromism and photocrosslinking occurred simultaneously under UV irradiation, and the photocrosslinking of coumarin reduced the decoloration rate of naphthopyran.