Photochemically reactive polymers

Tyler and co-workers isolated photochemically reactive polymers 30 containing Fe-Fe or Mo-Mo bonds.76-80 Photolysis of polymer 30 resulted in the decomposition of the polymer due to cleavage of the metal-metal bond, yielding 31. The photolysis of polymer 30 could also result in the formation of a metal-metal triple bond to give polymer 32 (Scheme 2.5).76... 

Tyler, D.R. Wolcott, J.J. Nieckarz, G.W. Tenhaeff, S.C. New Class of Photochemically Reactive Polymers Containing Metal-Metal Bonds Along the Polymer Backbone. In Inorganic and Organometallic Polymers II Wisian-Neilson, P.. Allcock, H.R., Wynne, K.J., Eds. ACS Symposium Series 572, American Chemical Society Washington, DC, 1994 481-496. Chapter 36. 

A series of photochemically reactive polymers containing Fp2 and Cp2hfo2( )6 ... 

Tyler and coworkers have developed photochemically reactive polymers (69) by condensation of organic monomers with complexes that incorporated Fe-Fe or Mo-Mo bonds in their structures. On photolysis, the resulting polymers could be depolymerized via cleavage of the metal-metal bonds to produce species such as 70. A polymer with a metal-metal triple bond could also be isolated to give Mo- and W-based polymeric materials (71, Scheme 20). °... 

The prepolymers were then modified by polymer analogous reactions with chromophores to yield photochemically reactive polymers (Figure 1) (79, 23) The compositions and thermal data of two selected pre- and photopolymers are summarized in Table 1. 

New Class of Photochemically Reactive Polymers Containing Metal—Metal Bonds Along the Polymer Backbone... 

Multiphoton processes are also undoubtedly involved in the photodegradation of polymers in intense laser fields, eg, using excimer lasers (13). Moreover, multiphoton excitation during pumping can become a significant loss factor in operation of dye lasers (26,27). The photochemically reactive species may or may not be capable of absorption of the individual photons which cooperate to produce multiphoton excitation, but must be capable of utilising a quantum of energy equal to that of the combined photons. Multiphoton excitation thus may be viewed as an exception to the Bunsen-Roscoe law. 

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). 

A large number of polymeric materials have been developed over the past two decades which are photochemically reactive. In many cases, such polymers are initially soluble in organic solvents prior to exposure with insolubilization accompanying ultraviolet radiation. This often presents a problem in practical applications where handling of organic solvents is objectionable or expensive. A need exists to develop functional polymers which are both water soluble and photochemically labile. 

A number of reports in the literature describe the use of alkyl thiosulfates to modify reactive vinyl type monomers and/or preformed polymers with the expressed goals of producing polymers with enhanced water solubility (1-61. The alkylthiosulfate modified polymers have been shown to be thermally and photochemically reactive and capable of producing crosslinked films with varying degrees of stability (5). 

This article reports on the synthesis of photosensitive polymers with pendant cinnamic ester moieties and suitable photosensitizer groups by cationic copolymerizations of 2-(cinnamoyloxy)ethyl vinyl ether (CEVE) (12) with other vinyl ethers containing photosensitizer groups, and by cationic polymerization of 2-chloroethyl vinyl ether (CVE) followed by substitution reactions of the resulting poly (2-chloroethyl vinyl ether) (PCVE) with salts of photosensitizer compounds and potassium cinnamate using a phase transfer catalyst in an aprotic polar solvent. The photochemical reactivity of the obtained polymers was also investigated. 

Measurement of Photochemical Reactivity. The polymer solution in THF was cast on a KRS plate and dried. The film obtained on the plate was irradiated by a high-pressure mercury lamp (Ushio Electric Co USH-250D) without a filter at a distance of 30 cm in air. The rate of disappearance of the C=C bonds at 1640 cm 1 was measured by IR spectrometry (JASCO A-202 model). 

It was reported (79) that a low Tg value is required from the viewpoint of the photochemical reactivity of pendant cinnamic ester in the polymer film. As summarized in Table I, the Tg of all the copolymers of PCEVE-NPVE and PCEVE-NNVE were in the vicinity of room temperature as expected from the flexible ethoxy chain in the polymer structure. ( j... 

Therefore, we believe that PCEVE-NPVE and PCEVE-NNVE prepared from the reactions of PCVE are better model polymers for the determination of the relationship between the photochemical reactivity and the contents of the photosensitizer units in the copolymers than the copolymers prepared by copolymerization. On the other hand, PCEVE-NPVE and PCEVE-NNVE prepared from the cationic copolymerization seem to be more photosensitive than PCEVE-NPVE and PCEVE-NNVE polymers prepared from the reactions of PCVE and have better properties practical applications since the former copolymers have higher purity than the latter copolymers. 

The relationship between the thickness of polymer films containing about 10 mol-% of pendant photosensitizer groups and the conversions of the —C bonds after 10 min. irradiation is shown in Figure 5. The photochemical reactivity of PCEVE-NNVE decreased slightly with increasing thickness of the film. Interestingly, the reactivity of PCEVE-NPVE was not influenced by the thickness of the film in contrast to the self-sensitized polymers previously... 

From all these results, it was concluded that polymers have high photochemical reactivity and high practical photosensitivity when synthesized by the cationic copolymerizations of CEVE with NNVE or NPVE, or by the reactions of PCVE with potassium cinnamate and PNN or PNP using phase transfer catalyst in DMF. 

In one study,52 the temperature dependence of quantum yields was investigated using polymer 5 (prepared by the route in equation 26). Thin films of polymer 5 are photochemically reactive ( = 532 or 546 nm) in the absence of oxygen, giving the products shown in Scheme 7.19 The reaction is thus similar to the photochemical radical trapping reactions of the Cp2Mo2(CO)6 dimer that take place in solution in the presence of an alkyl halide, and an analogous mechanism was proposed (Scheme 7). 

Figure 13 Temperature dependence of the photochemical reactivity of polymer, 30b. The change in absorbance after 0.5 min of irradiation (A0-AQ5) of the C=C stretching band relative to the initial absorbance (A0) was used to monitor reactivity. (Reprinted with permission from Gangadhara and Kishore [64]. Copyright 1993 American Chemical Society.)...

Liquid crystalline polymers and molecular organic crystals are examples of supramolecular arrays in which long-range order plays an important role in determining the photophysical and photochemical properties of the system. Two chapters in the present volume explore the properties of liquid crystalline polymers and molecular crystals, with an emphasis on understanding how the structure of the supramolecular organization guides the course of the photochemical reactivity and photophysical properties of the component molecular units. 

They are well known as compounds which are photoohemically very reactive. The excited singlet and triplet states are the photochemically reactive states,and they also can participate in energy transfer reactions (2,3i10,11). Some of these compoxmds such as anthracene,phenanthrene,pyrene added to polyethylene effect the photodegradation of polymer (118,... 

The Excited States of Poly(vinyl cinnamate) and their Photochemical Reactivities. The photochemical reaction of PVCi is believed to be Intermolecular crosslinking of the polymer chains by the formation of the four-membered ring from the central double bonds of cinnamoyl-oxy groups( ), and it is known that many experimental results from the photochemical reaction are interpreted well(6) if we can postulate that the reaction is the concerted cycloaddition according to the Woodward-Hoffmann s rule(lB). This means that the four-membered ring... 

Neckers and his co-workers have investigated the photochemical reactivity of ammonium borate salts both in solution and tethered to a polymer substrate as a means of producing free tertiary amines. The reactions are carried out in acetonitrile solution on the benzoylbenzyl molecules (201) using wavelengths > 300 nm. Irradiation of (202) results in the formation of the products shown in Scheme 6. More detailed studies examined the influence of different borate salts as the counterions to the ammonium salts. Some of these results are shown for the decomposition of the salt (201). From these data, it can be seen that the most efficient quantum yield for the release of tri- -butyIamine is obtained with the triphenylbutylborate counterion. 

Photochemical reactivity in the absence of exogenous radical traps is possible in the case of polymers that have carbon-halogen bonds along their backbones. For example, irradiation of... 

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