Photo-crosslinking materials

Different types of gel materials, such as polysaccharides, proteins and synthetic polymers, are now used to entrap biocatalysts. Among them, photo-crosslinkable resin prepolymer ENTP-4000 as shown in Eig. 7 is more useful compared to others. Entrapment of biocatalysts should be carried out under the illumination of near ultraviolet hght within 3-5 min, by which high temperatures, shifts of pH to extremely alkahne or acidic sides are avoided. ENTP-4000, hydrophobic photo-crosslinkable resin prepolymer, is one of the most suitable prepolymers for entrapment of p-glucosidase. Molecular weight of its main chain is about 4000. 

Y. Zhang, R. Hreha, G. Jabbour, B. Kippelen, N. Peyghambarian, and S.R. Marder, Photo-crosslinkable polymers as hole-transport materials for organic light-emitting diodes, J. Mater. Chem., 12 1703-1708 (2002). 

Efforts continue in the Far East, particularly in Japan, by Horie et al., on photosensitive polyimides containing epoxide groups [44,45]. These studies focus on the chemical amplification of photo crosslinks in the resulting materials for use in making mask materials in silicon chip fabrication. 

Polyimides for microelectronics use are of two basic types. The most commonly used commercial materials (for example, from Dupont and Hitachi) are condensation polyimides, formed from imidization of a spin-cast film of soluble polyamic acid precursor to create an intractable solid film. Fully imidized thermoplastic polyimides are also available for use as adhesives (for example, the LARC-TPI material), and when thermally or photo-crosslink able, also as passivants and interlevel insulators, and as matrix resins for fiber-reinforced-composites, such as in circuit boards. Flexible circuits are made from Kapton polyimide film laminated with copper. The diversity of materials is very large readers seeking additional information are referred to the cited review articles [1-3,6] and to the proceedings of the two International Conferences on Polyimides [4,5]. 

The thermally and photo- crosslinking polymers (4) offer probably the Frontiers of Polymers and Advanced Materials... 

Interchain interactions can be suppressed by blending MEH-PPV with small amounts of an inert polymer. Still another route in order to reduce interchain interactions is to fix the units by some extent due to crosslinking [112], In contrast, in PPV types that are capable of photo crosslinking or of thermal crosslinking, the performance decreases due to the existence of residual radicals in the material [113]. 

Also, a European patent was applied for that describes cationic photoinitiators based on 2,4,6-triarylpyrylium salts with nonnucleophilic anions and electron donors. It is claimed that the photoinitiators rapidly photo crosslink mixtures of cycloaliphatic epoxides. Micro encapsulation of the salts in polystyrene was found to increase thermal and photo stability of these photoinitiators.The encapsulation material can be dissolved in monomers when polymerization is desired. 

ROMP and PROMP are very useful methods to synthesize a number of novel materials with unique properties. Poly(cyclooctenes), poly(norbornenes) and poly(acetylenes) were discussed in more details and some of their properties like Tg, cristallinity, oxygen permeability, dielectric properties etc. listed. The polymerization of the cycloolefins was done either thermally or photochemically with the "old" Ru(II)-salts and the later developed Ru-phosphines as catalysts, whereas substituted acetylenes were photo-polymerized with W-, Mo- and Ta-catalysts. In addition, polymeranalogous transformations of the double bonds in ROMP polymers, (additions and cyclo-additions, epoxidation, (photo) crosslinking etc.) were discussed. We are convinced that these materials and systems will find useful applications in the near future. 

The first effect, piezoelectricity, is in principle well known for many types of polar materials [119]. The asymmetry of the switching observed for photo-crosslinked elastomers (see Fig. 15) indicates stabilization of one particular switched state. This means that the sample must have a permanent dipole. If the sample is deformed, the director, and thereby the direction of the polar axis, changes. This effect is detected as an electric signal. Indeed a piezoelectric signal can be measured if the sample is deformed in the direction of the polar axis. As a consequence of the stabilization of the polar state, the sample shows a piezoelectric effect not only in the smectic-C phase, but also in the smectic-A phase [36]. The signal vanishes when the sample becomes isotropic (see Fig. 18). 

QIA 06] Qiang Z., Ma Z., Zheng Z. et al, Novel Photo-crosslinkable light-emitting rod/coil copolymers underlying facile material for fabricating pixelated displays , Macromolecular Rapid Communications, vol. 27, no. 20, pp. 1779-1786, 2006. 

Among unsaturated di-acids, fumaric acid is one of the most useful building blocks, since it is a naturally occurring metabolite. Aliphatic polyesters, poly(propylene fiimarates) have recently been considered as biodegradable and photo-crosslinkable polymeric material used for scaffold applications (15). 

Wang, S., Kempen, D. H. R., Yaszemski, M. J., and Lu, L. 2009. The roles of matrix polymer crystallinity and hydroxyapatite nanoparticles in modulating material properties of photo-crosslinked composites and bone marrow stromal cell responses. Biomaterials 30 3359-70. 

Li, H., Chen, Y, Xie, Y, 2003. Photo-crosslinking polymerization to prepare polyanhydride/ needle-like hydroxyapatite biodegradable nanocomposite for orthopedic application. Materials Letters 57, 2848-2854. 

Tunmer, M.D., Ambrose, C.G., Mikos, A.G., 2003. Evaluation of thermal- and photo-crosslinked biodegradable poly(propylene fumarate)-based networks. Journal of Biomedical Materials Research, PartA 66A, 811-818. 

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