Photochemical behaviour of poly(organophosphazene)s, 12. Photo‐oxidation of catena‐poly[bis(4‐benzylphenoxy)‐λ⁵‐phosphazene] at short and long wavelengths under accelerated conditions

Abstract

In this paper the mechanism of the thermo‐and photo‐oxidation of catena‐ poly[bis(4‐benzylphenoxy)‐λ5‐phosphazene] films at short and long wavelengths has been followed under accelerated conditions using FTIR and UV‐visible spectroscopic techniques. The decrease of the band at 1453 cm−1 and the simultaneous appearance of new bands at 3400 and 3481 cm−1, due to free and bonded hydroperoxides, show that the primary hydroperoxidation in this polymer occurs at CH2 groups belonging to benzylic moietics. According to our previous paper, the bands observed in the carbonyl region at 1657, 1704 and 1725 cm−1 during photo‐oxidation have been assigned to the formation of benzophenone, benzaldehyde and benzoic acids (dimmers), respectively. The formation rate of benzophenone groups increases during irradiation at long wavelengths (λ > 400 nm). Under thermo‐oxidative condition (90°C), the benzophenone groups are the main oxidation products derived from hydroperoxide decomposition. In addition, the photooxidation of a film pre‐thermo‐oxidized for 500 h shows clearly that the benzophenone groups can generate aldehydes, benzoic acids and peracids. Crosslinking takes place in high yields by hydrogen abstraction occurring at both benzylic and secondary alcohol units. The regeneration of benzophenone groups has been evidenced during the photo‐oxidation.

Photochemical and Photophysical Studies of and in Bulk Polymers

“…An example of a commercial photodegradable polymer is Ecolyte, which has large amounts of carbonyl groups BZ + hν k ph 3 BZ + polymer adducts k p copolymerized with ethylene and propylene. 114 Sunlight -induced excitation to n, π * electronic states initiates Norrish type I and Norrish type II reactions that cleave the polymer chains in these polymers and facilitate their ingestion by microorganisms. 114 Aliphatic ketones undergo some dissociation by Norrish type I cleavage processes, and ketones containing γ -hydrogen atoms undergo type II cleavage processes, also, via formation of truncated ketones and alkenes.…”

“…114 Sunlight -induced excitation to n, π * electronic states initiates Norrish type I and Norrish type II reactions that cleave the polymer chains in these polymers and facilitate their ingestion by microorganisms. 114 Aliphatic ketones undergo some dissociation by Norrish type I cleavage processes, and ketones containing γ -hydrogen atoms undergo type II cleavage processes, also, via formation of truncated ketones and alkenes. 39 In an ethylene -carbon monoxide copolymer, CO -poly1 , at near -ambient temperatures, the quantum yield of the type II reaction ( Φ II ∼ 0.02; path b) is higher than the quantum yield of the type I reaction ( Φ I ∼ 0.001; path a) (Scheme 11.5 ).…”

“…39 In an ethylene -carbon monoxide copolymer, CO -poly1 , at near -ambient temperatures, the quantum yield of the type II reaction ( Φ II ∼ 0.02; path b) is higher than the quantum yield of the type I reaction ( Φ I ∼ 0.001; path a) (Scheme 11.5 ). 114 However, Φ II is nearly zero below the glass transition temperature because the restrictions to molecular movements do not allow the requisite six -membered transition state for the initial type II reaction step to be attained.…”

“…Photooxidation of polyolefi n -based plastics leads to cleavage reactions at unsaturated positions and formation of hydroperoxides at allylic positions. 114 The mechanism of the cleavage reactions in hexadiene copolymers has been studied by analyzing photolabile intermediates and photoproducts. Upon photooxidation of poly(propylene -co -hexadiene) copolymers, FT -IR spectra show a broad band at 3450 cm − 1 (from alcohols and hydroperoxides) and concomitant disappearance of a band at 966 cm − 1 (attributed to double bonds).…”

Poly(organophosphazenes) containing azo dyes

“…This is due to the possibility of changing 3-5), co-substituting6) or chemically functionalizing ' 3 8, the side residues "R" easily, thus allowing a fine tuning of the chemical and physical properties of POPs to be reached9) and the potential applicability of these substrates in different fields of science and technoFrom a photochemical point of view, the importance of poly(organophosphazenes) is related to the great transparency of their inorganic backbone, up to 200-220 nm I 1 -l 3 ) and to the chance of appending selected chromophores to the -P=N-chain easily j4). In this way polyphosphazenes containing phenol j5), &naphthol j6), 4-methylaniline j6, j7), 4-isopropylphenol j9), 4-sec-butylphenol 19), 21) Special interest in the photochemical domain is offered by POPs substituted with organic dyes. This interest is due to their potential applicability as polymeric photosensitizer~ 26,27), polymer-supported photoinitiators ,*), photographic dyes bonded to macromolecular matrices 29), or materials for non-linear optics ,O).…”