Light-sensitive group

Ishihara [28] synthesized two hydrogel copolymers containing aromatic light-sensitive groups. They were poly(HEMA-co-p-phenylazoacrylanilide (PAAn)). Their structures are shown in Figure 5. 

Intramolecular photochemical reactions need the presence of light sensitive groups such as carbonyls to induce transformations by oc-cleavage (Norrish I reaction) or by y-H-abstraction (Norrish II reaction). 

Ideally the light-sensitive groups absorb strongly in that part of the sun s spectrum which passes through the atmosphere but is not transmitted by window glass, i.e., absorb in the region 290 to 320 nm. The use of a masterbatch is possible with both approaches, and it is claimed that there are no deleterious effects on processing characteristics or on final physical properties. 

The ability of these light-sensitive groups to form crosslinks between polymer chains under the Influence of UV light has been described in paragrah 5. The rate constants of the thermo-reversion for the slow Isomer at 298 K are given in Table 7 for various irradiation times. Also in Table 7 the fractions of the slow Isomer in the polymer film are given. These values could... 

Polar group Light-sensitive group Hydrophobic group... 

Photocrosslinking of Polymers with Light-Sensitive Groups... 

Figure 3.1 Schematic representation of solid phase oligonucleotide synthesis. (A) Glass chip surface. (B) Conjugation of light-sensitive groups. (C) Photomasking. (D) Formation of reactive groups. (E) Binding the first set of nucleotides. (F)...

Incorporation of light-sensitive groups as molecular switches in the polymer networks enabled the development of light-induced SMPs. In this way, SME could be induced independently from any temperature effect [36]. Instead of increasing the sample s temperature, light of different wavelength ranges was used for the fixation of the temporary and the recovery of the permanent shape. CA or cinnamyliden acetic acid (CAA) have been used as photosensitive molecular switches on the molecular level as they are able to form covalent crosslinks with each other in a... 

SCP and SCG, were able to shrink or expand, as long as these materials were stimulated. When light-sensitive groups were incorporated into the material, the thermally-triggered SCC of these systems could be extended to light as stimulus. Here, intelligent gels, polymer networks, in which the photomechanical effect was enhanced, and LCE, in which the SCC was based on the reorientation of macro-scopically ordered LC domains, were differentiated and examples were presented. 

An interesting pathway to telechelics is the synthesis of polymers containing heat- or light-sensitive groups in the main chain, for example, azo groups (432, 433,463). Thus, polycondensation of AIBN with diols yields polyesters (Fig. 17). 

Another interesting pathway to telechelics is to first synthesize polymers containing thermal or light sensitive groups such as azo groups in the main chain. The polyester (70) resulting from the polycondensation of AIBN with diols yields such a structure. Decomposition of the azo function in the presence of styrene yields (AB) block copolymers which can be converted into a,G -dihydroxy (PS) by reductive cleavage of the ester bonds (Scheme 60). 

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