Polymers photochemical cross-linking

Sulfurized olefins (S2CI2 plus isobutene) are further reacted with S and Na2S to give products useful as extreme pressure lubricant additives (144,145). The reaction of unsaturated natural oils with sulfur monochloride gives resinous products known as Factice, which are useful as art-gum erasers and mbber additives (146,147). The addition reaction of sulfur monochloride with unsaturated polymers, eg, natural mbber, produces cross-links and thus serves as a means for vulcanizing mbber at moderate temperatures. The photochemical cross-linking of polyethylene has also been reported (148). 

Of great importance for both the formation and photochemical cross-linked of organotin oligomers and polymers is the tin atom in the coordination-bound state. 

It follows from these findings that the simultaneous presence of both anhydride and organotin groups in the copolymer structure and their regular distribution among the macromolecular chain is a prerequisite for photochemical cross-linking of a polymer. 

The photochemical reactivity of 1,2,3-thiadiazoles has been utilized in the formation of cross-linked polymers <1996CHEC-II(4)289>. No new developments in this area have been reported since the publication of CHEC-II(1996). 

In arrays of closely packed nucleosomes composed of all four core histones, strands of H2A-H2B dimers could be incorporated in the grooves between the two H3-H4 strands, producing a four-stranded polymer. Alternatively, they could bind to the H3-H4 double-stranded fiber to give an octamer of the histones per nucleosome. This latter model is supported by the photochemical cross-linking of histones to DNA which have shown that within the nucleosome core the four core histones are not equivalently positioned with respect to... 

The result of a photochemical reaction involving monomers, oligomers, and polymers depends on the chemical nature of the material, wavelength of the light, and other components of the system. Ultraviolet, visible, and laser light can polymerize functional monomers, cross-link polymers, or degrade them, particularly in the presence of oxygen. ... 

Post-Treatment of Hollow Fibers. End use of ihe hollow-fiber membrane dictates the ty pe of post-tre.iiment. if any There are three main categories fibers thal are spun, fibers that vv ill be chemically or physically modified, and fibers that will serve as a porous matrix lor support ol another lactivc) polymer deposited (nr entrapped) upon (or within) its walls. There is no theoretical impediment to the inclusion of all conventional treatments in the spinning line photochemical cross-linking, llmirinniion, and anliplaslici/ers have been successful. 

Cinnamates occupy an important place in the history of photochemistry. Schmidt and his co-workers [18] used the solid state photochemistry of cinnamic acid and its derivatives to develop the idea of topochemical control of photochemistry in the crystalline state. Minsk [19] developed poly(vinyl cinnamate) as the first polymer for photoimaging. The cinnamate chromophore is still commonly incorporated in photopolymers of all types, including LC polymers, to enable them to be photochemically cross-linked [20], and a number of reports of the photochemistry of such MCLC and SCLC polymers are summarized below. 

Tazuke, Ikeda, and their co-workers [53,54] were the first to use phenylene-diacrylate (PDA) as a mesogen and chromophore to explore the possibility of forming two-dimensionally reinforced polymer materials by photochemical cross-linking of a thermotropic LC polymer. Polyesters, 23, of para-phenylene-diacrylic acid and several diols were synthesized and found to exhibit LC behavior upon annealing above Tg. Polymer 23a exhibited [53] the texture of a N meso-... 

Photopolymerization, that is, a polymerization process initiated by photochemical production of the reactive species initiators (Section 6.8.1), is largely used in industry. Polymers can be synthesized by photoinitiation, but can also be modified by photochemical cross-linking (photochemical hardening or UV curing photoimaging photolithography see Special Topic 6.27). 

Polymerization of reactive monomeric liquid crystals is one method for stabilizing the liquid-crystalline thin films. Another approach is to form chemical gels of liquid crystal molecules with low molecular weight by construction of a polymer network. This method has been investigated for the stabilization of ferroelectric liquid crystal displays. Guymon et al. reported that a polymer network produced by photochemical cross-linking accumu-... 

Films of lithium triflate salt of [NP(0CH2CH20CH2CH20CH3) (MEEP) can be photochemically cross-linked. This inhibits slow loss of electrolyte from the cell. similar results are obtained from [NP[ (0CH2CH20)7R]2] (R=Me, CH2CH=CH2). °° The polymer electrolyte, MEEP/poly(propylene oxide), combined with several lithium salts has been employed as an electrolyte and conductivities have been... 

When free-radical polymerization is employed, polymerization can be initiated either thermally or photochemically, thus starting the cleavage of the initiator to generate free radicals. This radical formation then initiates the polymerization of the functional monomers and the crosslinker, which leads to the formation of a cross-linked polymer network. Note that polymerization is carried out in the presence of the template molecules, and therefore, the template molecules are trapped inside the polymer network at the end of this process. 

Reactive noncanonical amino adds have also been integrated into elastin-like protein polymers to enhance their application as biomaterials. The Tinell laboratory has used the photoreactive amino add p-azidophenylalanine to pattern elastin-like protein polymers on surfaces. " Zhang et d. used p-azidophenylalanine to photochemically cross-link an elastin-leudne zipper protein to a glass surface. A target protein linked to a second leudne zipper domain can then be captured from solution and patterned on the surface by dimerization of the leucine zipper domains. Carrico et al. used similar p-azidophenylalanine-fiinctionalized elastin protein polymers... 

A. Led with. Photochemical cross-linking in polymer-based systems, Dev. Polym. 3, 55 (1982). W. L. Dining, Polymerization of unsaturated compounds by photocycloaddition reactions, Chem. Revs. 83, 1 (1983). 

---