A new interfacial-gel copolymerization technique is proposed to prepare steric gradient-index (GRIN) optical waveguides and lens arrays. Since the GRIN profile is obtained from the thin-gel phase formed on the wall of a polymer substrate, many geometrical GRIN materials, such as axial-, radial-, and spherical-GRIN, can be monolithically fabricated. In this paper the principle of GRIN formation is clarified, and a few steric radial -GRIN circuit components are demonstrated.
SynopsisCopolymerization of styrene with acrylamide was carried out in an emulsifier-free aqueous medium. The resulting latex contained an appreciable amount of acrylamide-rich copolymer in the serum. The copolymerization course was divided into three stages on the basis of the main reaction locus. At first, acrylamide polymerized in preference to styrene in the aqueous phase. Water-soluble growing radicals lost hydrophilicity rapidly and nucleated the particles. After particle formation, styrene polymerized exclusively in the particles until styrene droplets disappeared. The decrease in the concentration of residual styrene monomer caused growing radicals to keep the hydrophilicity for a long time, and polymerization of acrylamide was accelerated in the aqueous phase. Polymerizations at higher temperature and lower pH resulted in prolongation of the first stage of the polymerization, that is, preferential polymerization of acrylamide in the aqueous phase. An increase in the acrylamide fraction in monomer feed caused some decreases in the particle size and its uniformity.
ABSTRACT:Precipitation polymerization of acrylamide derivatives in water resulted in the formation of monodisperse submicron particles. Repetitive seeded polymerizations using the product of precipitation polymerization or precipitation polymerization in ethanol-water media gave larger monodisperse particles. Especially, the latter was very effective for the preparation of micro-size particles.KEY WORDS Hydrogel / Microsphere / Precipitation Polymerization / Seeded Polymerization / Swelling / Hydrogel is a subject of great interest in these days due to its characteristic swellingdeswelling behavior in response to changes of temperature, pH, medium components, etc. and applications based on this character in medical, agricultural, and industrial fields. In many cases, quick and uniform responses are necessary for successful applications. The rate of response is inversely proportional to the square of its size. 1 Therefore, hydrogels are often used in small pieces, fine filaments, or thin films. Small pieces of hydrogels are usually prepared by crashing a bulk of gel or by inverse suspension polymerizations. 2 • 3 The particles given by inverse suspension polymerization have a diameter in the range of IO to 100 µm and not necessarily monodisperse.Recently, smaller and monodisperse microspheres were prepared by a novel precipitation polymerization by Pelton and Chibante. 4 They polymerized N-isopropyl acrylamide with N,N' -methylenebisacrylamide in water at 70°C. As the polymerization temperature was much higher than the lower critical solution temperature (LCST) of resulting polymer, ca. 35°C, the reaction accompanied precipitation of polymers and produced a dispersion of polymer particles with submicron diameter. Some other acrylamide derivatives also give polymers with their specific LCSTs. For example, the polymers of acryloyl pyrrolidine and acryloyl piperidine have their LCSTs at 50°C and 5°C, respectively. We have used such monomers with styrene to prepare latex particles having shells composed of them, which exhibited reversible expansion-shrinkage with changing temperature. 5 • 6 The precipitation polymerization of these acrylamide derivatives was found to result in the formation of monodisperse submicron hydrogel microspheres.The most suitable size of hydrogel microspheres in their applications differs from case to case. Submicron-size might be too small to treat in many cases. The smaller the particles t Present address: Mitsui
A -smple method with the use of affinity latex particles has been developed for the fast and efficient Purification of sequence-specific DNA- The concentra ion of covalently bound DNA on the affinity latex particles was 6 times as much DNA per ml as that in the Sepharose resin conventionally used. By sequential batch-wise Procedures with the affinity particles, one of the sequence-specific DNA binding transcription factors, ATF or E4TF3, was quickly and efficiently purified to homogeneity from either a protein fraction in which the factor was enriched or a crude cell extract.
Graded-index plastic optical fiber whose transmission attenuation is 143 dB/km at 651-nm wavelength was fabricated by heat-drawing the corresponding GI preform rod. This rod is prepared by the interfacial-gel copolymerization technique of methyl methacrylate (MMA) and vinyl phenylacetate (VPAc). The total scattering loss of the GI preform rod is ~60 dB/km at 633 nm. The graded-index profiles of the optical fibers are almost the same as those of the corresponding preforms with cladding sheaths. The index distributions of their core regions are quadratic against the distance from the center axis. The numerical aperture estimated from the index difference is ~0.20.
SynopsisAcrylamide derivatives were copolymerized with styrene in an emulsifier-free aqueous medium, and the copolymerization mode and the characteristics of the resulting latices were compared with those of a styrene-acrylamide copolymerization system. In their copolymerization mode, N -(hydroxymethy1)acrylamide and N,N-dimethylacrylamide resembled acrylamide, and their heterogeneous copolymerization course was divided into three stages on the basis of the main reaction locus. Copolymerization of styrene-methacrylamide did not resemble that of the others. The interfacial property and reactivity of acrylamides affected not only the polymerization mechanism but also the latex properties, e.g., particle size, distribution of acrylamides units in the latex, etc. The narrowest distribution of particle size was obtained in styrene-N-(hydroxymethy1)acrylamide copolymerization a t a monomer ratio of 101. Delayed addition of styrene into the aqueous solution of N-(hydroxymethy1)acrylamide prepolymerized to some extent was found to be effective in preparing a latex with nearly monodisperse and large particles.
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