Photochromic polymers: the application and control of photochromism through its interaction with polymers

摘要

The research highlights the application of polymer conjugation as a way to tailor photochromic performance. The technology is based on controlling the mobility of the dye by targeting its local environment.ATRP was initially applied to synthesize naphthopyran dye-polymer conjugates of a range of polymer types and chain lengths, to allow comprehensive tuning of their switching behaviour in a lens matrix. With control over the average molecular weight and their distributions, the photochromic-polymer conjugates inherit uniform characteristics which can therefore be targeted in order to control photochromic performance.An investigation of various ATRP-produced naphthopyran-poly(n-butyl acrylate) conjugates showed that the geometry of the polymer chain and the location of the dye in the chain are also important considerations. This included random copolymers and a gradient copolymer system which incorporated pendant photochromic monomer units along the chain. A Y-branching approach which locates the dye both pendant and exactly in the middle of two polymer chains provided superior kinetics per chain length of conjugated polymer. Films composed of ABA triblock copolymers which contained the photochromic units within the soft central section (B) also showed enhanced tuning of decolouration response. Another simple conjugation strategy was presented, which involves the direct attachment of hydroxyl naphthopyrans to acid end-functionalized PDMS. In another study, PEG oligomers were also conjugated to dyes in the same manner. The important chemical strategies to generate the relevant starting materials were described. The oligomeric dye-conjugates showed optimized performance in a lens matrix.A brief study was conducted to investigate and compare the behaviour of different branched and matrix-bound photochromic systems. Various polymerizable naphthopyran monomers were synthesized and reacted firstly within the curable lens composition to become part of the final network structure. Then, various crosslinked hyperbranched polymer structures were synthesized via RAFT, which also incorporated photochromic dyes either as mono-bound pendant units or as bis-tethered crosslinking agents. The strong sensitivity of photochromic dyes to their surroundings highlighted the use of photochromic dyes as probes for monitoring the characteristics of their local environment. This approach was used to monitor the formation of amphipilic block copolymer micelles in water, a process that leads to measurable changes in the dye’s decolouration behaviour.