Polymer photocrosslinkable

Tsafack V.C., Marquette C.A., Pizzolato F., Blum L.J., Chemiluminescent choline biosensor using histidine-modified peroxidase immobilized on metal-chelate substituted beads and choline oxidase immobilized on anion-exchanger beads co-entrapped in a photocrosslinkable polymer, Biosens. Bioelectron, 2000 15 125-133. 

It is known that aromatic azides are photodecomposed to give active nitrenes as the transient species, which react with the environmental binder polymers to crosslink them. However, the mechanism of these photocrosslinking polymers has not been studied in detail. L.S.Efros et al. have proposed that the rubber polymer is crosslinkes in such a way that the aromatic nitrene inserts into an unsaturated bond of the polymer to give an aziridine ring. The experimental evidence for this, however, has not been given (8). 

Chemisorption. A key step in the development of a successful membrane modified FET is the adherence and longevity of the membrane and the success of the encapsulation procedure. Sudholter et al (35) have proposed a method for the attachment of the ion selective membrane to a silylated SiC>2 gate oxide. An organofunctional silane, for example methacryloxypropyl trimethoxysilane, forms a bond between the surface and a photocrosslinkable polymer (eg polybutadiene). The ionophore would be directly bound to the polymer backbone, thus eliminating the need for plasticiser. Without any further modification with ionophore the membrane is sensitive to pH and shows a long life time (some months). Similar approaches have also been proposed by other workers, eg (36)... 

Yamaki, S., Nakagawa, M., Morino, S-, and Ichimura, K. Surface relief gratings generated by a photocrosslinkable polymer with styrylpyridine side chains. Appl. Phys. Lett. 2000, 76, pp. 2520-2522. 

The increasing utility of photocrosslinkable polymers in microelectronics, printing, and UV-curable lacquers and inks is providing an incentive for development of new varieties of photopolymers. After a brief overview of some of the commonly used materials, some of the interesting recent developments in this... 

Synthesis of New Photocrosslinkable Polymers Derived from Cinnamic Acid... 

Introduction of these photocrosslinkable structures in macro-molecular chains can be performed by esterification of hydroxyla-ted polymers with cinnamoyl chloride. Cellulose Q).condensation products (4, ) and mainly poly(vinyl alcohol) have Been treated( by this method. Other chemical modifications have been studied as ester interchange of poly(vinyl acetate) 7) and Knoevenagel reaction on polyesters (8). Very few results on the synthesis of such photocrosslinkable polymers by polymerization have been reported. Therefore free radical polymerization of cinnamic acid vinyl derivatives did not lead to the expected polymers, but to insolubilization reactions. Howewer cationic procedure can be a good way in some cases since Kato et al. could polymerize by this way with high yields p-vinyl phenylcinnamate (9) and B-vinyloxyethyl cinnamate (10). 

Electronic Structures in the Excited States of the Photosensitive Groups of Photocrosslinkable Polymers. (I) Polyvinyl dnnamate... 

Photocrosslinkable polymers are macromolecules which can become cross-linked by formation of interchain bonds under the influence of light ... 

By photocrosslinkable polymers are meant macromolecules which bear photoreactive groups capable of forming crosslinks between their respective chains. A typical photocrosslinkable polymer is poly(vinyl cinnamate) 6>. The photocrosslinking occurs when a network of crosslinks is built up between adjacent chains of poly (vinyl cinnamate). The mechanism of crosslinking will be described in detail in a later section. 

Intermediate species such as macromolecules bearing acrylate-type residues represent a cross between photopolymerizable monomers and photocrosslinkable polymers. The gap between photopolymerizable systems and photocrosslinkable polymers is closed since the two systems are basically the same. A photocrosslinkable polymer can be considered the extreme case of a macromolecular photopolymerizable monomer. 

Natural polymers such as albumin, gelatin, fish glue, shellac, and gum arabic received attention up to the early 1900 s, after which time other materials such as bichromate, diazo compounds, iron salts, and silver halides were added to resins in order to hasten or accomplish their crosslinking. These systems were neither photopolymerization nor photocrosslinkable polymers. Instead, the added second component, when excited by light, produced a species which itself caused the formation of radical sites on a prepolymer or polymer chain which then led to cross-linking. 

Extension of the use of the cinnamoyl unit to photocrosslinkable polymers is found in the numerous chalcone-type polymers prepared by Unruh and Smith 34>. Typical is a group of chalcone polymers which were prepared by reaction of poly(4-vinylacetophenone) with aromatic aldehydes such as benzaldehyde. 

Another quite different group of photocrosslinkable polymers synthesized by Merrill and Unruh 35> was based on the azide group. In this case, an azide group usually attached to an aromatic nucleus is appended to, or incorporated within, a polymer chain. Typical is poly(4-azidosty-rene). 

The range of the spectral sensitivity of light-absorbing photocrosslinkable polymers can be extended in two ways (a) by modification of the range of light absorption of the crosslinking chromophore in the polymer, or (b) by inclusion of spectral sensitizers. 

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