Separation of Optical Modes in a Coupler on the Basis of the Bragg One-Dimensional Grating

An integrated narrow-band filter for a wavelength of 1.5 m based on the Bragg Si/SiO₂ one-dimensional grating coupled to a standard waveguide has been designed. Vector simulation of the dispersion properties and calculation of the operational characteristics of the filter using the method of matching in conjugation with the theory of supermodes were carried out. The full width at the half-maximum level (FWHM) of the transmission spectrum gives the subnanometer range at a filter length of about 1 mm.     

Direct two-step synthesis of <Emphasis Type="Italic">n</Emphasis>-butyl acrylate–acrylic acid block copolymer by RAFT polymerization

A series of narrow-MMD polymers with the molecular mass from 33 × 10³ to 123 × 10³ (polydispersity coefficient 1.08–1.16) were synthesized by bulk polymerization of n-butyl acrylate [2,2′-azobis(isobutyronitrile), 60°C] in the presence of a low-molecular-mass RAFT agent, dibenzyl trithiocarbonate. Then, polymerization of acrylic acid was performed in aqueous-alcoholic solution (ammonium persulfate, 70°C) in the presence of the obtained polymers, and a series of n-butyl acrylate–acrylic acid block copolymers with the molecular masses from 22 × 10³ to 81 × 10³ (polydispersity coefficient 1.07–1.13) were prepared. In aqueous-alcoholic solutions of the synthesized copolymers, there are nanoparticles whose size varies from 5 tо 65 nm and increases with an increase in the molecular mass of the copolymer and in the concentration of water in the solvent.     

Photoinitiation of methacrylate polymerization with an o-benzoquinone-amine system

The kinetic features of the photopolymerization of mono- and dimethacrylates in the presence of the binary initiating system comprising a substituted o-benzoquinone and a tertiary amine under the action of visible light are studied. In the case of methyl methacrylate, the limiting conversion of the monomer does not exceed 10%. The photopolymerization of oligo(ester methacrylates) yields a polymer glass with a monomer conversion of 60–90%. As is shown for a series of seven o-benzoquinones, the rate of photopolymerization increases with an increase in the volume of substituents in positions 3 and 6 of the quinoid ring of o-benzoquinone. It found that trialkylamines (dimethylethanolamine and dimethylcyclohexylamine) are more efficient as coinitiators of photopolymerization than N,N-dimethylaniline. For compositions based on 3,6-di-tert-butylbenzoquinone-1,2, the spectral-sensitivity range in the visible region is 400 to 650 nm with a maximum at 600 nm. This value coincides with the maximum of the absorption band of quinone, which corresponds to the S(n → π*) electronic transition of carbonyl groups.     

Synthesis and photoinitiating ability of substituted 4,5-di-tert-alkyl-o-benzoquinones in radical polymerization

New tri- and tetraalkyl-substituted o-benzoquinones were synthesized based on 5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalene-2,3-diol derivatives. The new compounds were characterized by spectroscopic and electrochemical methods. The reactivity of o-benzoquinones was evaluated in the photoreduction and initiation of photopolymerization of oligocarbonate dimethacrylate (OCM-2) in the presence of N,N-dimethylcyclohexylamine and in the inhibition of MMA polymerization. The introduction of the methyl substituent into the benzene ring has a weak effect on the inhibitory activity of o-benzoquinone, whereas the (3,5-dimethylpyrazol-1-yl)methyl substituent enhances the inhibitory effect of 4,5-di-tert-alkyl-substituted o-benzoquinone.

     

Inhibition of polymerization of methyl methacrylate by an ortho-benzoquinone-amine system

The kinetic features of the bulk polymerization of MMA in the presence of sterically hindered ortho-benzoquinones and the tertiary amines N,N-dimethylaniline and N,N-dimethylisopropanolamine have been studied. The irradiation of solutions of quinones and amines in MMA with visible light causes inhibition of the thermal polymerization of MMA, with the effects of quinones and amines being synergistic. The effect of inhibition is enhanced as the steric shielding of carbonyl groups of ortho-benzoquinone by substituents becomes weaker. The dependence of the induction period on the redox potentials of quinones passes through a maximum. It is shown that inhibition involves oxyphenoxyl radicals arising from the interaction of the original quinone with the product of its photoreduction in the presence of amines, pyrocatechol. The inhibiting effect depends on the concentration ratio of quinone and pyrocatechol and the nature of amine. When quinone is in excess with respect to pyrocatechol, additional inhibition of polymerization is observed and the rate of quinone consumption during the induction period is increased.     

Macroinitiators of controlled free-radical polymerization of methyl methacrylate that are based on the tributyl boron-naphthoquinone system

Methods of preparing prepolymers with M = (2–5) × 10⁴ via the free-radical polymerization of methyl methacrylate in the presence of tri-n-butyl boron and 1,4-naphthoquinone at 30–45°C are developed. ¹H NMR spectroscopy measurements show that, in the prepolymer, the ratio between the enchained aromatic structures and the monomer units is 3: 1000. The activation energy for the postpolymerization of MMA initiated by the prepolymer is found to be 39.3 kJ/mol, and the molecular mass of the prepolymer is (0.8–1.2) × 10⁶. The effect of small amounts of acrylates and phosphonium salts on the polymerization of methyl methacrylate and the molecular mass of the polymers is investigated. It is demonstrated that, when polymerization is conducted in the presence of ionic liquids at concentrations commensurable with the concentration of aromatic fragments enchained into the prepolymer, the rate of the process decreases.