Poly phenyl vinyl ketone

Photodegradation of poly(phenyl vinyl ketone) (or poly(phenyl-2-propen-l-one) (3.15) occurs mainly by the Norrish Type II process [521,628,794, 873, 1011, 1312, 1370, 1893]. 

The triplet lifetime in poly(phenyl vinyl ketone) t = 55 ns [628, 1983] is a factor of c. 20 longer than that of monomeric phenylalkyl ketones capable of intramolecular y-hydrogen abstraction, such as y-methylvalerophenone [962], which may reflect the decreased mobility of the benzoyl group with respect to y-hydrogens in the polymer. Energy migration on the poly(phenyl vinyl ketone) reduces their rate of interaction with other substrates [1892], and intramolecular processes such as hydrogen abstraction. The decrease in 

The initial quantum yield for photodegradation of poly(phenyl vinyl ketone) is c. 0.24 [628,649,794,1370] the efficiency of this process decreases rapidly as photodegradation proceeds as a result of the accumulation of oe,j8-unsaturated ketone end groups which act as efficient triplet quenchers [648]. 

Dependence of the quantum yield of chain scission in poly(phenyl vinyl ketone) on the glass transition temperature (Tg) is discussed in section 3.2.5. 

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Frequently B will also undergo a back hydrogen transfer which regenerates the parent ketone, as well as cyclization (in most cases a minor reaction) as a result of this competition the quantum yields of fragmentation are typically in the 0.1-0.5 range in non-polar media. When the Norrish Type II process takes place in a polymer it can result in the cleavage of the polymer backbone. Poly(phenyl vinyl ketone) has frequently been used as a model polymer in which this reaction is resonsible for its photodegradation, reaction 2. 

An apparatus for measuring the time dependence in the xs range of lightscattering intensity has been used to investigate the degradation of poly(phenyl vinyl ketone) (PVK) in solution.205-250 The PVK was irradiated with 25 ns pulses at 347.1 nm, and butyrophenone was also investigated in the same way. In both cases a transient absorption, identified by sensitization measurements as the PVK and butyrophenone triplet state, was shown to have a first-order decay rate-constant of 1.0 0.2 x 107 s-1. The quantum yield of triplet state formation in PVK was estimated to be between 0.1 and 0.3, whereas the quantum yield of main-chain scission was found to be 0.4—0.6, insensitive to the presence of Oa. 

Chart 1.1 Chemical structures of poly (vinyl acetate), PVAc poly (methyl methacrylate), PMMA polystyrene, PSt poly-(methyl vinyl ketone), PMVK poly(phenyl vinyl ketone), PPVK. 

Fig. 1.23 Triplet-triplet absorption spectrum of poly(phenyl vinyl ketone) in benzene solution at room temperature. Recorded at the end of a 15 ns pulse of 347 nm light.

Chart 1.17 Chemical structure of poly (phenyl vinyl ketone). 

Poly(phenyl vinyl ketone) degradation degradation... 

Nearly all the reported attempts at ionic copolymerization of vinyl ketones led to polymers containing very high ketone content, even when the comonomer was known to homopolymerize under the conditions. Copolymerization of phenyl vinyl ketone and styrene in bulk or in tetrahydrofuran initiated with n-butyllithium produced only poly(phenyl vinyl ketone) [341]. The non-incorporation of styrene in the anionic copolymerization was due to the phenyl vinyl ketone enolate anion being sufficiently nucleophilic to add the phenyl vinyl ketone monomer but not the styrene. 

UV and y-radiation of poly(methyl isopropenyl ketone) produced random chain scission at 23 °C. The presence of air increases unexpectedly the main chain scission of the polymer under y-radiation [377]. In a series of publications [378] the radiolysis and photolysis of poly(phenyl vinyl ketone), poly(vinyl benzophenone), and poly(/-butyl vinyl ketone) [357] were described. The authors stated that photodegradation of poly (phenyl vinyl ketone) occurred by the abstraction of a hydrogen in the y-position to a carbonyl group, followed by chain scission by a Norrish type II photoelimination mechanism. 

Poly(l,4-pentadiene-alt-MA), 343, 348, 586 Poly(phenanthrene-alt-MA), 376, 660 Poly(phenylacetylene), MA grafted, 471 Poly(phenylacetylene-co-MA), 335, 660 Poly(2-phenylallyl alcohol-alt-MA), 331, 660 Poly(4-phenyl-l-butene-alt-MA), 340, 341 Poly(/- 1-phenylethyl methacrylate-co-MA), optically active polymer, 383 Poly(/-1-phenylethyl vinyl ether-alt-MA), optically active polymer, 383 Poly(5-phenyl-l-pentene-alt-MA), 340, 341 Poly( l-phenyl-4-pentene- 1-one-alt-MA), 314 Poly(3-phenyl propene-l-alt-MA), 341 Poly(o-phenylstyrene-alt-MA), 373 Poly(2-phenylvinyl alkyl ethers-alt-MA), 318 Poly(2-phenylvinyl alkyl thioethers-alt-MA), 318 Poly(phenyl vinyl ether-alt-MA), 318, 394 Poly(phenyl-o-vinyl formal-alt-MA), 328 Poly(phenyl vinyl ketone-co-MA), physical properties, 290... 

Poly(phenyl vinyl ketone-co-methyl methacrylate)... 

Poly(phenyl vinyl ketone-co-a-methylstyrene) Poly(phenyl vinyl ketone-co-o-tolyl vinyl ketone) Poly(phenyl vinyl ketone-co-)5-phenylpropiophenones) Poly(p-methyl phenyl vinyl ketone)... 

Its formation is favoured over other cyclic conformations by entropy considerations. In solid polymers where certain conformations are more favoured than others, entropy considerations might be less important. It has been shown that the Norrish Type II reaction in poly(phenyl vinyl ketone) occurs via a six-membered cyclic intermediate [510], whereas in poly(methyl methacrylate —CO— methyl vinyl ketone) it occurs via a seven-membered transition state [122]. 

Effects of the glass transition temperature on the photodegradation of poIy(phenyI vinyl ketone) and poly(phenyl vinyl ketone[Pg.116]

The quantum yields of chain scission (s) in poly(phenyl vinyl ketone) (3.15) (Fig. 3.21) and poly(phenyl vinylketone-co-styrene) (Fig. 3.22) show a temperature dependence in the glassy state with a discontinuity near the glass transition temperature (Tg), which is due to changing molecular mobility [510]. 

Fig. 3.22. Quantum yield of Norrish Type II reaction as a function of temperature for 0.5 nm poly(phenyl vinyl ketone) films irradiated with monochromatic radiation of 313 nm as measured by viscometry. (Reprinted with permission from [510]. Copyright (1973) American Chemical Society.)...

Poly(o-tolyl vinyl ketone) (5.20) is much more photochemically stable than poly(phenyl vinyl ketone) (5.15). The o-methylbenzoyl group stabilizes the polymer, which would otherwise undergo the Norrish Type II reaction. The effect is due to the photoenolization of this chromophore, a process which competes favourably with the photofragmentation [197, 198] ... 

Figure 3.4 Absorption spectra of synthetic nonconjugated polymers. PPVK poly(phenyl vinyl ketone) PMVK poly(methylvinylketone) PSt polystyrene PMMA poly(methyl methacrylate) PVAc poly(vinyl acetate). Adapted with permission from Ref [4] 2007, Wiley-VCH.

A macromolecular chain presents a unique reaction situation in which, in certain cases, groups which are potential reactants at elevated temperature are located in close proximity. Thus intramolecular cyclization may occur, which may or may not involve elimination of small molecules. For example, vinyl ketone polymers such as poly(methyl vinyl ketone) (PMVK), poly(methyl isopropenyl ketone) (PMIK) and poly(phenyl vinyl ketone) undergo random cyclization of adjacent monomer units with release of water. The reaction for PMVK is illustrated in Scheme 4. 

Poly(phenyl vinyl ketone) Poly(acrylophenone) 26742-84-7 2-Propen-1 -one, l -phenyl-, homopolymer R (C9H8O),... 

David et al. [9] have studied the photolysis of poly(phenyl vinyl ketone) in detail. Irradiation in solution or in the solid state reduces the molecular weight and was compared with the photolysis of butyrophenone. The principal mechanism was... 

In a later paper, the same authors [10] reported that naphthalene inhibited chain scission by a triplet energy transfer mechanism. Golemba and Guillet [11] determined the 0 of chain scission of poly(phenyl vinyl ketone) to be 0.25 of 313 nm. They determined that the excited state lifetime of the carbonyl group on the polymer was of the same order of magnitude as that of the analogous model compound. 

Energy transfer from solute to polymer has been demonstrated in a number of systems. As mentioned in the section on photodegradation, inclusion of naphthalene in films of poly(phenyl vinyl ketone) reduces to number of chain scissions by a quenching mechanism [10]. 

In another study [42] polystryrene was naphthoylated to give poly(a-naphthoyl-lityrene) and poly(jS-naphthoylstyrene). The solution photoisomerization of stilbene oy the polymer was found to be identical with that resulting from the use of the cor-] esponding ethylnaphylphenyl ketone models. Moser and Cassidy [43] found earlier but reported in an obscure manner that poly(phenyl vinyl ketone) caused the photoisomerization of cw-piperylene. The isomerization proceeded both in solution and by use of solid polymer. The remarkable effect of the solid was attributed to rapid diffusion of c/ -piperylene to the polymer surface. 

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