Photochemistry Of Poly Research Articles

Poly(vinyl acetate) paints in works of art: A photochemical approach. Part 1

The photochemistry of poly(vinyl acetate), PVAc, homopolymer, of PVAc mixtures with selected pigments and fillers, and of accurate historic reproductions based on the colours prepared by Portuguese artist Joaquim Rodrigo and on those supplied by the company A Favrel was studied. The systems, applied as films, were irradiated at λ ≥ 300 nm and the changes followed by size exclusion chromatography, infrared spectroscopy, and colorimetry. PVAc as homopolymer or as an emulsion paint proved to be very stable to light, and after 5000 h of irradiation no gel fraction was observed. Φ R ( λ irr = 313 nm) for chain scission for PVAc was determined to be 7 × 10 −8. This value indicates that the mechanism/s operating when irradiating at λ ≥ 300 nm are different from those previously published with irradiation involving 254 nm. No side-group scission was observed, and main chain scission is the foremost photodegradation mechanism. Also, the metal ions present in the pigments do not affect the photochemical stability of the polymer.

Involvement of Singlet Oxygen in the Solid‐State Photochemistry of P3HT

AbstractWe studied the role that singlet oxygen plays in the solid‐state photochemistry of poly(3‐hexylthiophene) (P3HT). The photosensitized formation of singlet oxygen by solid‐state P3HT and its subsequent reactivity on the polymer were investigated. Using a fluorescent probe, it was found that singlet oxygen (1O2) could be produced by irradiation of P3HT by photosensitization, with no oxidation of the polymer. In addition, 1O2 was directly formed on P3HT via a chemical reaction, again with no oxidation of the polymer. These results give strong evidence that 1O2 is not the principal photo‐oxidative degradation intermediate of P3HT, which conflicts with previous reports.magnified image

Investigation of the photochemistry of the poly{p-phenylenevinylene} precursor system: Implications for nanolithography

The photochemistry of poly{p-phenylene[1-(tetrahydrothiophen-1-io)ethylene chloride]} (PPTEC), a water soluble precursor of the semiconducting polymer, poly{p-phenylenevinylene} (PPV), has been studied both under atmospheric conditions and in environments devoid of oxygen. UV-visible spectroscopy and photoluminescence data has been used to provide a picture of the mechanistic pathways involved in UV irradiation of the PPTEC material. A new quantitative model for the effect of UV irradiation upon film morphology is presented, which leads to insights for the improved control of the characteristics of PPV nanostructures produced via near-field scanning optical lithography.

Photophysics and photochemistry of poly (4′-ethoxyacrylophenone)

The photophysics and the long wave ( λ≥300 nm) photochemistry of poly (4′-ethoxyacrylophenone) were investigated. The quantum yield for fluorescence is low (10 −4 mol (einstein) −1), and the principal excited species is the carbonyl triplet. The quantum yield for phosphorescence is greater and the λ max value is 445 nm. The triplet lifetime at 77 K is 0.41 s, but 8.7 μs at 300 K. These observations are consistent with the formation of a low-lying triplet, which, in turn is the result of substitution of the aromatic ring with the electron donating ethoxy group. The principal photoprocess occurring in dilute solution (in CH 2Cl 2) of the polymer is a Norrish Type II decomposition, which results in random chain scission and a rapid decrease in the molecular weight. The relatively low quantum yield (6×10 −2 mol (einstein) −1) for the scission process reflects the low reactivity of a triplet (which has some π, π ∗ character) in abstraction reactions. In the case of PEAP, H-abstraction is a prerequisite for biradical formation, which, in turn leads to chain scission. Chain scission was subject to inhibition by triplet quenchers, such as naphthalene and cis-1,3-pentadiene, and the data conformed to Stern–Volmer kinetics. However, the quenching rate constants, k Q were lower in magnitude than the corresponding diffusion controlled values, and it is proposed that this is principally due to a steric effect, the actual encounter of the quencher with the carbonyl triplet being subject to adverse steric interactions associated with the proximity of the relatively bulky polymer chain.

Unmasking electronic energy transfer of conjugated polymers by suppression of O(2) quenching

The photochemistry of poly[2-methoxy, 5-(2'-ethyl-hexyloxy)-p-phenylene-vinylene] (MEH-PPV) has been found to be highly dependent on the presence of O(2), which increases singlet exciton quenching dramatically. Spectroscopy on isolated single molecules of MEH-PPV in polycarbonate films that exclude O(2) reveals two distinct polymer conformations with fluorescence maxima near 555 and 580 nanometers wavelength, respectively. Time-resolved single-molecule data demonstrate that the 580-nanometer conformation exhibits a "landscape" for intramolecular electronic energy relaxation with a "funnel" that contains a 580-nanometer singlet exciton trap at the bottom. The exciton traps can be converted to exciton quenchers by reaction with O(2). Conformationally induced, directed-energy transfer is arguably a critical dynamical process that is responsible for many of the distinctive photophysical properties of conjugated polymers.

Photochemical reactions of polystyrenes ring‐substituted with thiocyanato groups

AbstractThe photochemistry of poly(2‐vinylphenyl thiocyanate) (P(2‐VPT)), poly(3‐vinylphenyl thiocyanate) (P(3‐VPT)) and poly(4‐vinylphenyl thiocyanate) (P(4‐VPT)) is investigated under 254 nm UV light. Poly(4‐bromostyrene) (P(4‐BrSt)) is used as reference material. Experiments with phenyl thiocyanate show that the main photoreaction is a cleavage into cyano and phenylthio radicals which also occurs in the polymers. Photo‐crosslinking data for the polymers P(2‐VPT), P(3‐VPT) and P(4‐VPT) are evaluated with the Charlesby‐Pinner relation. For P(2‐VPT), P(3‐VPT) and P(4‐VPT) the qunatum efficiencies ΦCL of crosslinking are 0.018, 0.029 and 0.021, the quantum efficiencies ΦCL of chain scission are 9 · 10−4, 37 · 10−4 and 6 · 10−4. P(2‐VPT), P(3‐VPT) and P(4‐VPT) rank among the most sensitive negative resists in the polystyrene series. Hammett's σ constants for SCN substituents are determined (3‐SCN: σ = 0.50, 4‐SCN: σ = 0.45). However, a general correlation between the ΦCL or ΦCS values of ring‐substituted polystyrenes and Hammett's σ constants of the substituents is not found.

Interaction of Oxygen with Conjugated Polymers: Charge Transfer Complex Formation with Poly(3-alkylthiophenes)

Molecular oxygen forms a reversible charge transfer complex (CTC) with poly(3-alkylthiophenes). The complex is weakly bound but possesses a distinct absorption band in the visible region. The electronic properties of the neutral polymer are modulated by the CTC. The extent of modulation of these properties is proportional to oxygen pressure and is fully reversible. Analysis of poly(3-hexylthiophene) field effect transistors under increasing pressures of oxygen shows that the carrier concentration increases, conductivity increases, and the charge carrier mobility is lowered by the formation of the charge transfer complex. The CTC manifests itself as a fluorescence quencher of mobile polaronic excitons, and it explains why oxygen quenches luminescence with much greater efficiency than predicted by a collisional quenching model. Implications of the charge transfer complex on the photochemistry of poly(3-alkylthiophenes) and photosensitization of singlet oxygen are discussed.

Photochemical behavior of poly(organophosphazenes)—XIII. Sensitized photochemistry of poly[bis(4-benzylphenoxy)phosphazene] in solution and in film

In this paper we report the solution and solid-state photochemistry of poly[bis(4-benzylphenoxy)phosphazene] sensitized by benzophenone. u.v. and i.r. spectroscopic characterizations and weight average molecular weight data indicate that the main reaction under irradiation for this polymer dissolved in benzene is the increase in molecular weight due to an efficient crosslinking process. Moreover, gel is formed very rapidly after a few minutes of light exposure, when the polymer is photolyzed in film. These results are attributed to an intermolecular hydrogen atom abstraction reaction that takes place between the electronically excited triplets of the benzophenone photosensitizer and the methylene group present in the side 4-benzylphenoxy substituent of the phosphazene polymer that generates radicals able to couple forming inter-chain links. The different behavior of the poly[bis(4-benzylphenoxy)phosphazene] when the photolysis is carried out in air or in inert argon atmosphere is also described and the presence of a post-photochemical effect in the irradiated phosphazene films is discussed.

Photodegradation of poly(3,5-dimethoxyacrylophenone) in the long-wave UV region

The photophysics and long-wave (λ ≥ 300 nm) photochemistry of poly(3,5-dimethoxyacrylophenone) (P3,5DMAP) were investigated. The quantum yield for fluorescence is low (< 10 −4) and the principal excited species is the triplet carbonyl. Emission (phosphorescence) occurs at 450 nm, the triplet energy (i.e. E T (0-0)) is 270 kJ mol −1 and the phosphorescence lifetime is long (23 μs). These observations are consistent with the formation of a low-lying π,π ∗ triplet which, in turn, is the result of substitution of the aromatic ketone by electron donating methoxy groups. The principal photoprocess is a Norrish type II decomposition which results in random chain scission. The low value of the quantum yield, i.e. Φ cs = 10 4 , is further evidence for a π,π ∗ triplet which is typically unreactive in abstraction reactions. In the case of P3,5DMAP, H-abstraction is a prerequisite for biradical formation (and for chain scission). Inhibition of chain scission was investigated, using naphthalene and cis-1,3-pentadiene as quenchers, and the data could be represented by Stern-Volmer kinetics. However, the quenching rate constants ( k O ) were lower than the corresponding diffusion controlled values, and it was proposed that the actual encounter of triplet and quencher is subject to adverse steric interactions associated with the proximity of the polymer chains.

Photochemistry and photophysics of poly(organophosphazenes) and related compounds: A review. II. Bimolecular reactions

In the second part of this review we highlight the bimolecular reactions (hydrogen abstraction, and energy or electron transfer) that take place in the photochemistry of poly(organophosphazenes). Both inter-molecular interactions (i.e. between excited free chromophores and ground state groups attached to the phosphazenes, or between excited phosphazene substituents and external quenchers) and intra-molecular processes (i.e. between excited and ground state groups geminally attached to the same phosphorus or supported to different phosphorus along the polyphosphazene skeleton) are exploited. Suggestions are given on the possible practical application of these reactions in different photochemical domains, e.g. heterogeneous-phase photosensitization, photocrosslinking, photoconductivity, microelectronics, light-induced radical polymerization of vinyl monomers, etc.

Photochemistry of poly(butyleneterephthalate): 2—Identification of the IR-absorbing photooxidation products

An experimental and analytical study of the photooxidation of poly(butyleneterephthalate), carried out under monochromatic wavelength (254, 365 nm) and under polychromatic wavelength ( λ ≥ 300 nm) is reported. Oxidation products formed by irradiation of films were investigated by FTIR spectroscopy; a series of chemical derivatization reactions were developed in order to identify the photoproducts. Most of them were observed to be analogous to vacuum photolysis species. It has been shown that the repartition of photoproducts in the polymer was heterogeneous. The results of photoproduct identification accounted for the mechanism of photooxidation proposed that implied both pure photolytical processes and photo-induced oxidation route.

Laser ablation of doped polymers: transient phenomena as the ablation threshold is approached

The photochemistry of poly(methyl methacrylate) films dopes with 1,1,3,3-tetraphenylacetone was studied using 266-nm laser excitation at energy doses below and above the ablation threshold. The ressults suggest that transient phenomena appear to remain surprisingly simple in spite of the dramatic change induced by the laser pulse. It is also clear that short-lived reaction intermediates play a key role in controlling the absorption properties of the film during the laser pulse.

Polysilanes: Photochemistry and deep UV lithography

AbstractThe photochemistry of poly(cyclohexylmethylsilane) (PCHMS) has been studied, and PCHMS homopolymer has been shown to be useful for high resolution, deep UV pattern generation either by using a commercial 1:1 projection printer operating in the deep UV or by an excimer laser stepper at 248 nm. In the case of the excimer laser stepper, images 0.5 μm and smaller have been printed, which represents an improvement over the 0.8 μm limit previously reported for polysilane copolymers.

Effects of elongation on the photochemistry of poly(ethylene-co-carbon monoxide) [Erratum to document cited in CA108(24):205354p

Effects of elongation on the photochemistry of poly(ethylene-co-carbon monoxide) [Erratum to document cited in CA108(24):205354p

Effects of elongation on the photochemistry of poly(ethylene-co-carbon monoxide)

Effects of elongation on the photochemistry of poly(ethylene-co-carbon monoxide)

Wavelength effects on the photo-chemistry of poly(vinyl chloride)

The photo-chemical oxidation of poly(vinyl chloride) film has been studied under various conditions of excitation wavelengths. At ‘short’ wavelength (254 nm) under vacuum, two photo-products are observed at 270 and 284 nm. The two photo-products are in photo-chemical equilibrium and accumulate during irradiation. The photo-product which absorbs at 270 nm can be photo-oxidized. Under irradiation at ‘long’ wavelength (365 nm), polyene sequences are formed. Under mixed wavelength radiation (phosphor 310), a combination of these two behaviours occurs and leads to results quite different from those observed under natural conditions of weathering, or under excitation at λ′s > 300 nm in photo-accelerated devices.

The photolysis of poly( p-hydroxystyrene)

The photochemistry of poly( p-hydroxystyrene) (PPHS) has been investigated, thin films being exposed to 254 nm radiation under high vacuum at 298K. H 2 is the principal volatile product, but small amounts of H 2O are also formed. The polymer becomes rapidly coloured, but unlike other styrene polymers, which remain yellow, PPHS undergoes a progressive colour change from yellow through orange to brown. Infrared spectral data indicate the depletion of OH group concentration, and a concomitant formation of carbonyl, possibly quinonoid species. Crosslinking is rapid and no chain scission was detected. It is likely that the polymeric phenoxy radicals formed by photolysis or by subsequent H-abstraction contribute to the formation of both quinonoid species and crosslinks. The mechanism of the photolysis is discussed.

The triplet lifetime of poly(phenyl vinyl ketone). A laser flash photolysis study

The photochemistry of poly(phenyl vinyl ketone) in solution has been examined over a temperature range using nanosecond laser flash photolysis techniques. Experiments were performed at low temperatures to eliminate the interference from biradical signals and allow for the separation in time of the behaviour of quencher-free and quencher-containing polymers. For the former the kinetics of triplet decay in toluene- d 8 lead to log ( A s −1 ) = 9.90 ± 0.50 and E a = (3.56 ± 0.30) kcal mol −1 where A is the preexponential factor and E a the activation energy. The extrapolated triplet lifetime at 20°C is 57 ns.

Characterization of a Dissociative Excited State in the Solid State: Photochemistry of Poly(methyl methacrylate). Photochemical Processes in Polymeric Systems. 5

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCharacterization of a Dissociative Excited State in the Solid State: Photochemistry of Poly(methyl methacrylate). Photochemical Processes in Polymeric Systems. 5Amitava Gupta, Ranty Liang, Fun Dow Tsay, and Jovan MoacaninCite this: Macromolecules 1980, 13, 6, 1696–1700Publication Date (Print):November 1, 1980Publication History Published online1 May 2002Published inissue 1 November 1980https://doi.org/10.1021/ma60078a060RIGHTS & PERMISSIONSArticle Views365Altmetric-Citations84LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (524 KB) Get e-Alerts Get e-Alerts

The photochemistry of ring substituted polystyrenes, 5. Photolysis of poly(p‐amino) and poly(p‐nitrostyrenes)

AbstractThe short‐wave (λ = 254 nm) photochemistry of poly(p‐aminostyrene) (PPAS), and poly(p‐nitrostyrene) (PPNS) films was studied under high vacuum conditions (≈ 10−6 mbar) at 25°C. The principal reaction product in both cases was hydrogen, but both polymers also underwent coloration, crosslinking, and chain scission. Rates of chain scission and hydrogen formation were found to be considerably greater for PPAS, and these was attributed to the stabilizing effect of the p‐amino group (relative to that of the p‐nitro group) on the intermediate free radicals. The very high rate of crosslinking of PPAS would suggest the participation of the p‐amino group in crosslinking reactions.