Photopolymerization-Powder

Methods are used to produce the more costly rapid prototypes include those that produce models within a few hours. They include photopolymerization, laser tooling, and their modifications. The laser sintering process uses powdered TP rather than chemically reactive liquid photopolymer used in stereolithography. Models are usually made from certain types of plastics. Also used in the different processes are metals (steel, hard alloys, copper-based alloys, and powdered metals). With powder metal molds, they can be used as inserts in a mold ready to produce prototype products. These systems enable having precise control over the process and constructing products with complex geometries. 

Polymer and copolymer. Polymer and copolymer were prepared in our laboratory for strict control of purity, branching content and molecular weight. All monomers and solvents were carefully purified. PVC samples were prepared as powders in bulk using free radical photoinitiation with either AIBN or uranyl nitrate as initiators. The AIBN/UV initiation was used for photopolymerization at temperatures of 50°, 25°, and 0°C. 

Transmission of directional properties from the monomer lattice reveals that many photopolymerizations of the four-center type are topotactic, but this information is insufficient to determine whether the reactions occur via homogeneous or heterogeneous phase-separation mechanisms. Powder x-ray studies done in... 

In the first, Fe(CO)5 and distilled methylacrylate were sonicated as a mixture of neat liquids. During the sonication, the glass cell was wrapped in a dark cover to avoid photopolymerization. After 30 min of irradiation (avoiding degradation) at a dry ice-acetone temperature, the solution was treated with cold methanol, precipitating the polymeric product. In the second method, amorphous iron nanoparticles were prepared following Suslick s recipe [6]. The dried amorphous iron powder was introduced into the sonication cell without exposure to air and mixed with a solution of the methylacrylate monomer in N,N -dimethylformamide (DMF). The concentration of the methylacrylate solution in DMF was 5.5 M. 35 ml of this solution was mixed with various amounts of amorphous iron nanoparticles. The amounts of the iron powder were changed from 50 mg to 200 mg. The chemical analysis of polymers prepared by the two methods is presented in Table 6.1. 

Photopolymerization of Powder Formulations Powder coatings are very attractive [314]. The powder is applied on the substrate and exposed to an IR source to get the coalescence of the solid particules then, the cross-linking reaction is carried out under UV (or visible) light in a very short time and at a temperature about 100-120°C. Largely encountered systems are based on, for example, polyesters (with maleates or fumarates unsaturations) and polyurethane vinyl ethers that copolymerize according to a radical process, amorphous polyesters and functionalized polyesters (with allyl ethers). 

In a similar approach, Saigo et al. have prepared a chiral columnar LC structure [2] using the same benzoic acid derivative and a chiral amino alcohol (Fig. 2.13) [64-66]. The columnar phase could be photopolymerized and powder X-ray... 

Addition of aluminum powder was not effective this probably is related to the increasing optical density of the photopolymerization composition layer as a results of the lower rate the polymerization process near the metallic surfaces as compared to the polymerization in the volume. As a result, the monolayer near a surfece is weakta- and the explosion proceeds in the place of a fnetal -polymer contact. 

Saturated solutions of acetylene in water were irradiated for several hours by a 125-W UV lamp [83]. Photopolymerization was followed by UV-vis spectroscopy and different polymerization pathways involving diacetylene, vinylacetylene, and cumulene formation were discussed. The evaporation of the solvent from the resulting milky white solution of photopolymer resulted in the isolation of a cream-colored powder of acetylene photopolymer that was insoluble in common solvents. This photopolymer was characterized by elemental analysis, FTIR, and UV spectroscopy and was found to incorporate about 18% oxygen (probably from water) in the form of ketone, carboxyl, hydroxyl, and ether derivatives. FTIR spectroscopy revealed the structural similarity of acetylene photopolymer and a linear PA oxi-... 

Recently, the spectroscopic identification of carbonyl teUuride, obtained by photolysis of H2Te in CO or 1 % CO/Ar matrices at 10 K, was reported. Carbonyl selenide is readily synthesized in situ from R2NC(0)Se R2NH2+ and acids, but little of its chemistry is known. Poly(carbon diselenide) is obtained as a black powder by thermal polymerization or photopolymerization of carbon diselenide. The obtained polymer is highly disordered, and it has a head-to-head polymer structure". 

T. Wu, T. Alabi, W. Baker, D. Legdzina, D. Wolski, W. Zimbeck, and D. Long. 2010. Photopolymerization of powder suspensions for shaping ceramics. Journal of the European Ceramic Society 31(14) 2613-2619. 

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