Polymer Photochemistry最新文献

The grafting of styrene/maleic anhydride and maleic anhydride/vinyl acetate onto cellulose from mixed monomer compositions has been studied as a preliminary to the use of the resulting graft copolymers in enzyme immobilisation studies. Grafting has been shown to be effectively non-steady state in character. Attempts have been made to determine initial rates for the grafting reaction so that various dependencies can be ascertained. Values for $\text{k}{}^2{}_{\mathrm{p}}\text{k}{}_{\mathrm{t}}$ have been determined along with the corresponding mean kinetic chain length values. These increase markedly with increase in the bulk concentrations of the monomers used in these combinations.

The dye-sensitized photopolymerization of methyl methacrylate by a Crystal Violet-ascorbic acid system in aqueous solution was investigated. The systems were buffered with phosphate buffer and the effects of monomer, dye, temperature, buffer and ascorbic acid on the reaction system were studied. The rate of polymerization was measured gravimetrically and a suitable kinetic scheme has been proposed.

Fourteen vat dyes from a commercial source were used in this investigation. Their lightfastness was measured by (a) the Blue Scale, (b) the CIE system, and (c) the Hunter L,a,b scale.

From the results obtained, it was found that the Hunter L,a,b scale was easier for evaluating the lightfastness than the CIE system; for individual colours ΔA and ΔE were preferred for measuring the lightfastness, and for different colours ΔL and ΔC were preferred.

New light-sensitive polymer, poly(1-(4-carboethoxyphenyl)-2-propen-1-one), $\text{M}{}_{\mathrm{w}}\text{= 1·3 × 10}{}^6$ Dalton, $\text{M}{}_{\mathrm{w}}\text{M}{}_{\mathrm{n}}\text{= 2·6}$, was prepared. On the basis of fractions prepared by photolysis, Mark-Houwink coefficients (α=0·79 ± 0·02 and K=(2·41 ± 1·4) × 10⁻³) were determined in chlorobenzene at 25°C employing low-angle laser light scattering and automatic viscometry. Quantum yield of main chain scissions (The Norrish Type II Reaction) was 0·45 in benzene solution under 366 nm radiation at room temperature. The Stern-Volmer constant for quenching of photolysis by naphthalene in benzene was 171 mol⁻¹ and 63 mol⁻¹ by 2,5-dimethyl-2,4-hexadiene in chloroform. The OO band of phosphorescence (438 nm) of the polyketone prepared was bathochromically shifted in comparison with poly(1-phenyl-2-propen-1-one), λ_max• = 409 nm. The transient spectrum measured by laser flash photolysis exhibited a maximum at 350 nm with a lifetime of 150 ns. The bimolecular quenching rate constant (k_q) for 2,5-dimethyl-2,4-hexadiene in chloroform was 5·57 × 10⁸ dm³ mol⁻¹ s⁻¹. This value agrees well with k_q = 4·2 × 10⁸ dm³ mol⁻¹ s⁻¹. based on the Stern-Volmer constant of photolysis quenching and lifetime estimated by laser flash photolysis.

The photopolymerization of acrylonitrile and methyl methacrylate in the presence of triphenylamine (TPA) has been performed at 30°C in N,N-dimethylformamide and dimethylsulfoxide under irradiation with light of λ > 300 nm. TPA proved to be very effective for the polymerization of both monomers. An apparent activation energy of 4·3 kcal/mol was recorded for the photopolymerization of acrylonitrile. Equations of polymerization derived from a kinetic study were as follows: $\text{Rate of polymerization=K[TPA]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{[Monomer]}{}^{\mathrm{1·0}}$$\text{Degree of polymerization=K′[TPA]}{}^{\mathrm{<mtext>-</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{[Monomer]}{}^{\mathrm{1·0}}$ From the UV spectrum of photoirradiated TPA in N,N-dimethylformamide solution, the formation of N,N-diphenylamine and aniline was observed, in which the photodecomposition of TPA might result.

Based on these results, it was suggested that radicals formed in the process of photodecomposition of TPA are responsible for the initiation of the photopolymerization, which proceeds through an ordinary mechanism of radical polymerization.

Low-temperature thermooxidation and photooxidation at long wavelengths (λ > 300 nm) of octene-1 linear low density polyethylene have been examined. It is shown that both oxidations proceed according to mechanisms which are very similar to those thought to occur in free radical low density polyethylene presenting a low content of vinylidene unsaturation. Hydroperoxidation in the α-position to the vinylidene groups gives rise to isolated hydroperoxide groups that absorb at 3550 cm⁻¹ and are stable at 85°C. A parallel hydroperoxidation occurs on the saturated chain affording hydrogen-bonded hydroperoxides which are fairly unstable at 85°C. In photooxidation at long wavelengths both hydroperoxides are produced and readily photolysed. Variations in the number of branch points which provoke large variations in density have no significant influence on the photooxidation rate.