Ivan Lukáč

Photosensitized cationic polymerization using N-ethoxy-2-methylpyridinium hexafluorophosphate

Abstract The cationic polymerization of cyclohexene oxide is initiated at room temperature upon irradiation at λinc > 350 nm of CH2Cl2 solutions containing N-ethoxy-2-methylpyridinium hexafluorophosphate (EMP+PF6−) and one of the following compounds: thioxanthone, anthracene, perylene or phenothiazine. Poly(cyclohexene oxide) of molar mass exceeding 105 is produced. In the absence of EMP+PF6−, which is transparent at λinc > 350 nm, these sensitizers are ineffective. Acetophenone and benzophenone do not act as sensitizers. An initiation mechanism involving electron transfer from the excited sensitizers to EMP+ ions is proposed. In flash photolysis experiments, electron transfer was evidenced by the formation of radical cations in the cases of anthracene, perylene or phenothiazine.

Synthesis, photochemical and photoinitiation activity of water soluble copolymers with pendent benzil chromophores

In the present paper the synthesis of three novel water soluble copolymers with benzil pendant groups are described. The new polymers have been prepared by copolymerization of the obtained benzil acrylate, 1-phenyl-2-[4-(2-methacroyloxyethoxy)phenyl]ethandione-1,2 (MBz) with three water soluble comonomers: acrylamide, 2-acrylamido-2-methylpropane sulphonic acid and 2-acryloxyethyl trimethylamonio iodine. The absorption, luminescence, photoreduction and microsecond flash photolysis characteristics of the new copolymers were examined in water and methanol and the results compared to the corresponding low molecular weight compound. The photoinduced polymerization activities of the new products have been determined by photodilatometry in the presence of a tertiary amine. The copolymers exhibit polymerization rates and quantum yields similar to those of the low molecular weight model compounds.

Preparation and photochemical properties of polymers containing 1-(4-benzylphenyl)-2-propen-1-one or 1-(4-benzoylphenyl)-2-propen-1-one structural units☆

Abstract The new monomers 1-(4-benzylphenyl)-2-propen-1-one (4) and 1-(4-benzoylphenyl)-2-propen-1-one (6) and their homopolymers P4 and P6 and copolymers with styrene P4/S and P6/S were prepared. The polymers exhibit an n—π* band in their UV spectra and vibrationally well-resolved low-temperature phosphorescence. Both properties are characteristic of photoreactive polyketones. Polymers containing structure 6 show greater near-UV absorption and lower triplet energy in films at 77 K than the photoreactive polyvinylketones. The absorption and emission spectra of the transients, their lifetimes and their quenching by triplet quenchers in benzene at 300 K were determined by laser flash photolysis. Lamp photolysis of the title polymers at 366 nm in benzene results in a decrease in the molecular mass due to the Norrish type II reaction. The quantum yields of main-chain scission are comparable with those of other reactive polyvinylketones (around 0.2). The Stern—Volmer constants based on photolysis and transient quenching indicate the involvement of the long-lived triplet state in the chain scission process.

The photolysis of polymers with benzoyl and para methoxybenzoyl structural units

Abstract The emission spectra of polyacrylophenone, copolymers styrene/acrylophenone (28.6, 19.0, 10.2 wt/wt% poly-p-methoxyacrylophenone and copolymer styrene/p-methoxyacrylophenone (22.7 wt/wt%) were measured for films at liquid nitrogen temperature. The emission spectra indicated a weak interaction between benzoyl structural units and a strong interaction in poly-p-methoxyacrylophenone. Photolysis in solution was not affected by these interactions. Quantum yields of main chain scissions in chlorobenzene by 366 nm radiation were about 0.2 for polyacrylophenone and copolymers styrene/acrylophenone and about 0.1 and lower for poly-p-methoxyacrylophenone and copolymer styrene/p-methoxyacrylophenone. The Stern-Volmer constants for photolysis quenching for styrene/acrylophenone copolymers increased in solution and decreased in film. The presence of oxygen lowers the quantum yield and Kw constant of poly-p-methoxyacrylophenone and styrene/p-methoxyacrylophenone copolymer. GPC measurements show that the molecular weight distribution widens during photolysis of styrene/acrylophenone copolymer (28.6 wt,/Wt %) indicating inhomogeneity in the copolymer.

Photolysis and emission spectra of substituted polyacrylophenones

Abstract Poly-[3′,4′-dimethoxyacrylophenone], poly-4′-phenylacrylophenone, poly-2′-acrylonaphthone and copolymers of acrylophenone monomers with styrene and methyl methacrylate were prepared. Quantum yields of main chain scission in chlorobenzene by 313 nm radiation were 10 3 times lower for all homopolymers and copolymers studied than for polyacrylophenone. The emission spectra of the polymers, copolymers and model compounds were taken for films at 77 K. The 3′,4′-dimethoxyacrylophenone, 4′-phenylacrylophenone and 2′-acrylonaphthone structural units exhibited poorly resolved emission spectra in homopolymer, copolymer and model compound. No difference in the emission spectra of films and dispersed homopolymer or copolymer in a poly(methyl methacrylate) matrix was observed. The decay of the emission of all homopolymers and copolymers under study was exponential, the life-time exceeding 0.20 sec.

Relative rates of photooxidation of benzil to benzoyl peroxide in various polymer matrices

Benzil (BZ), 16 wt.-%, has been irradiated (>400 nm) at ambient temperature in aerated polystyrene (PS), poly(methyl methacrylate) (PMMA), polycarbonate (PC), polysulfone (PSF) and poly(vinyl chloride) (PVC) films. The rate of BZ consumption, leading primarily to the formation of benzoyl peroxide, was followed by infrared spectroscopy. The rate of reaction is sensitive to the nature of the glassy polymer matrix and decreases in the order: PS > PC > PVC > PSF > PMMA. The dependence of the rate of BZ consumption on the concentration of dissolved molecular oxygen in the polymer matrices is rather complex. A kinetic treatment, assuming steady-state conditions, leads to the conclusion that the sum of the rates of bimolecular formation of benzoyl peroxide and quenching of BZ triplets by molecular oxygen, (k ox + k q )[ 3 O 2 ], represents only 0.8-13% of the sum of the unimolecular rates of radiationless and radiative deactivation (including k p , the pseudo first-order rate constant for reaction of BZ triplets with the polymer), (k d + k ph + k p ), in the various polymer matrices.

The determination of Stern-Volmer constants in polymer systems

Abstract The inhibition of main chain scission of carbonyl polymers and sensitization of biacetyl phosphorescence by carbonyl polymers were employed for determination of Stern-Volmer quenching constants. Fairly good agreement was found between these two methods. Both methods are sensitive to impurities especially when Stern-Volmer constants exceed 1000 l/mole. The differences between quenching of the excited state of the chromophore bound in high polymers and in low molecular substance are discussed.

Preparation and emission spectra of polymeric 1,2-diketones

Abstract Monomers of the methacrylate type, viz. 1-[4-(2-methacroyloxyethoxy)phenyl] propandione-1,2 (7a) and 1-phenyl-2-[4-(2-methacroyloxyethoxy)phenyl] ethandione-1,2 (7b) having the 1,2-dicarbonyl chromophore in the side-chain, were synthesized. The soluble homopolymer of monomer 76 and copolymers of both monomers 7a and 7b with styrene and methyl methacrylate were prepared by radical polymerization in solution. The absorption and emission spectra of a model compound and the homopolymer showed that the 1,2-dicarbonyl chromophore behaved as an isolated unit. No fluorescence was observed for the model compound or the homopolymer in emission spectra of poly(methyl methacrylate)-doped films. Phosphorescence of low- and high-molecular carbonyls was quenched by ferrocene in solution. Comparison of Stern-Volmer constants indicates partial steric hindrance of energy transfer for high-molecular donor.

The influence of alkyl substituents on norrish type II reactions for poly-4′-alkylacrylophenones

Abstract Poly-4′-alkylacrylophenones were prepared and their emission spectra and photolysis were studied. In low temperature emission spectra of poly-4′-alkylacrylophenones a bathochromic shift with respect to low molecular weight compounds was observed. The largest bathochromic shift, which was observed for poly-4′-methylacrylophenone, is caused by hypercojuggation. The quantum yield of main chain scission of poly-4′-alkyl-substituted acrylophenones lies in the range 0.2 – 0.4. Stern—Volmer constants indicate longer lives for the lowest triplet states compared with polyacrylophenone. It seems that an electron-donating effect of alkyl substituents is decisive in this prolongation. The bulkiness of alkyl substituents in the 4′ position does not influence the lifetime in solution and they do not produce any effects in emission spectra.

The study of degradable polystyrene: Photolysis in solution and photo-oxidation in films

Abstract Radical copolymerization of styrene with benzalacetophenone or benzalacetone in bulk or in suspension yielded copolymers with as much as 10 wt% of carbonyl monomer. They were characterized by GPC, viscometry and spectroscopy. Photolysis of copolymers was investigated in benzene at 313 nm. Quantum yields for main chain scissions were about 0.005 and the life-time of the triplet state was 5 nsec. Photo-oxidation in films was followed by monitoring the decrease in molecular weight and by i.r. and emission spectra. Quantum yield for main chain scission in films was about 0.0002. During photooxidation in film, the molecular weight distribution widened. A new i.r.-band appeared at 3580 cm −1 and the carbonyl band was spread between 1700 and 1800 cm −1 . In the emission spectra, the vibrational resolved emission (typical of the carbonyl chromophore) disappeared.