Fast Photochromic Dye Response in Rigid Block Polymer Thermosets

Abstract

The behavior of photochromic spiropyran (SP) dyes is greatly affected by the local environment in which they reside. Fluid microenvironments such as liquidlike polymers grant favorably fast dye decoloration whereas rigid microenvironments such as glassy polymers inhibit fast dye response. We study the use of disorganized but microphase-separated block polymer thermosets as photochromic dye hosts. These thermosets incorporate low glass transition temperature (T g) aliphatic polyester domains that facilitate rapid dye decoloration in a rigid poly­(methyl methacrylate) matrix by using a polymerization-induced microphase separation (PIMS) strategy. The spontaneous ring closing of SP was monitored in PIMS materials by UV–vis spectroscopy after irradiation with ultraviolet light. The rate of decoloration was found to be sensitive to a variety of molecular parameters including the molar mass and mass fraction of the polyester block, and the cross-link density of the poly­(methyl methacrylate) block allowing for tunability of the dye performance without changing the chemical identity of the components. Dye decoloration in the PIMS system could be controlled from two extremes: low T g homopolymer (t 1/2 = 170 s) behavior to bulk rigid polymer (t 1/2 = 1400 s) behavior. Through control over a variety of molecular parameters, we have been able to achieve fast decoloration rates in rigid and optically clear thermosets.

Nanostructure Control in 3D Printed Materials

“…Indeed, PIMS performed with low concentrations of macroCTA typically exhibit poor phase separation and discontinuity in the macroCTA domains. [ 39,51 ]…”

“…Indeed, PIMS performed with low concentrations of macroCTA typically exhibit poor phase separation and discontinuity in the macroCTA domains. [39,51] Increasing the weight percentage of PBA 48 -CTA to 28.2 wt% resulted in the formation of 3D printed materials with a bicontinuous morphology, with nanoscopic percolating domains of PBA and net-P(AA-stat-PEGDA) (Figure 2C). The analysis of AFM phase images revealed the average PBA domain size was 7 nm and the average PBA interdomain distance was 18 nm.…”

Highly transparent photochromic films with a tunable and fast solution-like response

“…The second strategy is to facilitate the dye isomerization by providing softer (less steric hindrance) or void (free-volume) matrix environments. This has been accomplished by i) functionalizing the photochromic molecules with flexible tails, [46][47][48][49][50] ii) embedding the dyes in different media such as low glass transition and/or plasticized polymers, 51,52 hybrid organic/inorganic materials, [53][54][55] hydrogels, 56 or organogels, 57 and iii) encapsulating the molecules in the cages of hybrid mesostructured (nano)materials, [58][59][60][61][62] metal-organic frameworks, 63,64 and supramolecular assemblies. [65][66][67] The encapsulation was also explored by our group, which reported tunable photochromic properties (fast or reverse photochromism) in solid materials by embedding core-shell capsules into polymeric films, 20,68,69 a strategy that was also successfully extended to the fabrication of liquid-like thermochromic 70 and white-emitting 71 materials.…”

Thermochromic and/or photochromic properties of electrospun cellulose acetate microfibers for application as sensors in smart packing

“…PhotoLux purple (PL) is a commercial photochromic pigment, with morphology of spherical microcapsules that help to protect the chromic principle, 27 which is why it is widely used in various areas of engineering such as paints, toys, textiles, and so forth, and shows color variations from 3% of the total ultraviolet radiation present in sunlight. 28 Various chemical substances have been used in the production of photochromic pigments. Three different types of photochromic pigments are produced commercially.…”