Polymers with Pendant Azide Groups

Both azide and sulfonyl azide groups are photo-reactive and decompose into active nitrene groups and nitrogen upon irradiation. The dissociation of the azide moiety follows almost every transition from an excited n → π* state to a high vibrational level of the ground state [170, 171]. Introductions of pendant azide and sufonyl azide groups into polymeric structures are possible in a variety of ways and many publications describe different approaches. Thus, Tsuda and Yamaoka [81] introduced azide groups into a phenolic novolac resin by the following scheme:

Tsunoda and Yamaoka [173, 174] also condensed formyl-1-naphthyl azide with poly (vinyl alcohol). All steps in the synthesis were not disclosed. The preparation was illustrated as follows:

Preparations of azide derivatives from styrene-maleic anhydride copolymers, cellulose, and gelatin by attaching aromatic azide compounds are described in the literature [175]. Most of the resultant polymers cross-link rapidly when exposed to light of 260 mm wavelength. Also, as much as 90% of the hydroxy groups of poly (vinyl alcohol) can be esterified with p-azido-benzoyl chloride. These reactions must be carried out in mixtures of chloroform and aqueous sodium hydroxide [175]. Earlier, Merrill and Unruh [175] described formation of derivatives from poly (vinyl alcohol) and attachment of aromatic azide groups. Most of the seazide polymers photocross-link at a faster rate than does poly (vinyl cinnamate), when exposed to light of 260 mm. In addition, they responded well to photosensitization. Also, it was observed [50] that the 4-isomer of azido phthalate shows greater speed increase than does the 3-isomer. In general, the poly (vinyl alcohol) derivatives were reported to exhibit higher cross-linking speeds than do other azide functionalized polymers [176]. The reaction product of p-azido benzoyl chloride with polyvinyl alcohol was investigated by Tsuda and coworkers [179]. In the polymer studied by them, over 90% of the hydroxy groups were esterified. The photocross-linking reaction was followed by observing changes in the ultraviolet and infra-red absorption spectra. It was shown that the simple photochemical reaction occurs stochiometrically upon irradiation. Also, an absorption band was observed at 1,500/cm in the infra-red region of the irradiated and cross-linked polymer. This band is due to N¼N stretching vibration of the azo group. Based on that, Tsuda concluded the cross-linking reaction takes place by dimerization, as expected [179]. There are reports in the literature that photosensitive azide polymers formed from polymers substituted with isocianate groups [176, 177]. The preparation and properties of many other polymers containing pendant aryl azide groups were described by Delzenne and Laridon [178]. The polymers were prepared by interfacial polycondensation of azido-substituted acid chlorides with diols and diamines. Also, in one experiment, a cinnamate moiety was combined with an azide group, together in one pendant functional structure [178]. It was found, however, that addition of the azide groups to the cinnamate side chain does not increase reactivity. A marked wavelength dependence was observed on π → π* and n → π* transitions that occurs in both functional groups [179].

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مواضيع ذات صلة

Polymers Designed to Cross-link Upon Irradiation with Laser Beams

Polymers with Pendant Abietate and Dibenzazepine Groups

Polymers with Pendant Maleimide Groups

Polymers with Pendant Furan Groups

Polymers with Functional Groups Similar to Cinnamates

Polymers with Functional Chalcone Groups

Polymers with Pendant Cinnamoyl Functional Groups

Polymers That Photocross-link by Formation of Cyclobutane Rings

Photocross-linkable Polymers

Photosensitizers

The Charge Transfer Processes in Polymers

The Electron Transfer Process