Photo-responsive polymers copolymers

Figure 4.7 exhibits examples of diblock copolymers with irreversible photo-response. Polymer 30 contains photolabile protecting groups attached to carboxylic groups in the side chains. Upon UV irradiation, photosolvolysis of the pyrenylmethyl ester occurs, 1-pyrenemethanol is cleaved from the polymer chain and carboxylic add groups are released. As a consequence, the hydrophobic block turns into a hydrophilic PMAA block. Core-shell micelles formed by 30 disappeared after irradiation with UV light at 365 nm. This design was further validated with other chromophores (polymers 31-34). °... 

Yamane H, Kikuchi H, Kajiyama T. 1999. Laser addressing rewritable optical information storage of (liquid crystalline side chain copolymer/liquid crystals/photo responsive molecule) ternary composite systems. Polymer 40(17) 4777 4785. 

In general, it was observed that the higher the acrylate content of the copolymer, the more photo-response is observed. Rigid homopolymers can easier transmit the work than soft materials. It was also demonstrated that the spatial disruption generated by the photo-transformation of the photochrome is not the main driving force for the photo-mechanical and photo-optical effects. It is important to take into account that stereo-electronic interactions between the polymer matrix and the photochrome exist, mainly for the merocyanine form. 

Another example of self-assembly of porphyrin-containing polymer was illustrated by Li et al.73 Polyacetylene functionalized with fullerene and zinc porphyrin pendant groups were synthesized by polymerizing the corresponding fullerene/porphyrin substituted alkyne monomers with rhodium(I) norbomadiene catalyst (Scheme 5.5).74 Polymers with different ratio of C60 and porphyrin were synthesized. The polymers showed photocurrent response when the thin films were irradiated with white light, which was due to the electron transfer from the photo-excited porphyrin to the C60 units. In addition, the copolymers aggregated into ellipse-shaped nanorod structures with a diameter of approximately 100 nm and a length of... 

Kuckling D, Hoffman J, Plotner M, Ferse D, Kretschmer K, Adler HJP, Arndt KF, Reichelt R (2003b) Photo cross-linkable PNIPAAm copolymers 3 microfabricated temperature responsive hydrogels. Polymer 44 4455 462... 

Like a bulk responsive material, surface of a substrate can be responsive upon electrochemical, photo, temperature, pH, mechanical, or electrical stimuli (Lahann Langer, 2005). Researchers are developing different ways to make these smart surfaces such as self-assembled monolayers (SAMs), polymer brushes, or copolymer coatings. A classic example is a switchable SAM surface in responsive to electric potential, which achieve hydrophobic-hydrophilic transition on a gold substrate. The switchable surfaces provide an idea platform to smdy surface-biological system interactions (Lahann et al., 2003). Polymer brushes and copolymers are more practical avenues to be applied with long-term performance. 

---