Adhesive controlled polymerization

Novel, flexible, completely organic, polymer dispersed liquid crystal (PDLC) "light valves" were fabricated using two flat pieces of commercial overhead transparency substrates (Nashua j -20) coated with polypyrrole between which a film of commercial PDLC material (Norland Products Co. NOA 65 optical adhesive and BDH Ltd. E7 liquid crystal fluid together with EM. Ind. 15 micron polystyrene spacers) was sandwiched. The optical adhesive was polymerized by exposure to UV light. Thin conducting polypyrrole films of varying controllable thickness were deposited on the overhead transparency. 

Gosselin, C.A. Effect of surface preparation on the durability of structural adhesive bonds, polymeric materials for corrosion control. In ACS Symposium 322 180-193 (1986)... 

This glue, first used for bleeding control, has been successfully utilized for preoperative portal vein embolization [15]. This adhesive, that polymerizes on contact with blood and endothelium, does not affect the peribiliary arterial plexus, and this property led to the assumption that it can be used for transcatheter arterial embolization [55]. Mixed with radiopaque lipiodol, the polymerization time can be prolonged to 10-15 s, depending on dilution. Therefore, a more peripheral and permanent embolization can be achieved. 

Fumio Sanda is associate professor at Kyoto Univereity. His research interests include amino add-based polymere, optically active conjugated polymers, and precisely controlled polymerization. So far he has published about 310 original papere and about 50 review artides. He has been given several awards induding the Young Investigator Award of The Adhesion Sodety of Japan in 2005. He is the editor of Polymer Reviews and Journal of the Adhesion Society of Japan, and he is on the editorial advisory board of ACS Applied Materials Interfaces. 

The main components of adhesives are polymeric materials such as elastomers or synthetic polymers. The main component type for a certain adhesive is decided hy the designer considering the type of adherends and use conditions. Control items to he considered is as follows solubility parameters, average molecular weights, Mooney viscosity, crystallinity, and existence or nonexistence of functional groups. Materials that can be used as main components of elastomer adhesives are polychloroprene rubbers, nitrile rubbers (butadiene-acrylonitrile copolymer), SBR (styrene-butadiene copolymer), thermoplastic elastomers (SBS, SIS, SEBS, SEPS etc.), butyl rubbers, acryhc rubbers, sUicone rubbers, polysulfides, modified polysulfides, modified silicone rubbers, and silyl urethanes. 

Emulsion Adhesives. The most widely used emulsion-based adhesive is that based upon poly(vinyl acetate)—poly(vinyl alcohol) copolymers formed by free-radical polymerization in an emulsion system. Poly(vinyl alcohol) is typically formed by hydrolysis of the poly(vinyl acetate). The properties of the emulsion are derived from the polymer employed in the polymerization as weU as from the system used to emulsify the polymer in water. The emulsion is stabilized by a combination of a surfactant plus a coUoid protection system. The protective coUoids are similar to those used paint (qv) to stabilize latex. For poly(vinyl acetate), the protective coUoids are isolated from natural gums and ceUulosic resins (carboxymethylceUulose or hydroxyethjdceUulose). The hydroHzed polymer may also be used. The physical properties of the poly(vinyl acetate) polymer can be modified by changing the co-monomer used in the polymerization. Any material which is free-radically active and participates in an emulsion polymerization can be employed. Plasticizers (qv), tackifiers, viscosity modifiers, solvents (added to coalesce the emulsion particles), fillers, humectants, and other materials are often added to the adhesive to meet specifications for the intended appHcation. Because the presence of foam in the bond line could decrease performance of the adhesion joint, agents that control the amount of air entrapped in an adhesive bond must be added. Biocides are also necessary many of the materials that are used to stabilize poly(vinyl acetate) emulsions are natural products. Poly(vinyl acetate) adhesives known as "white glue" or "carpenter s glue" are available under a number of different trade names. AppHcations are found mosdy in the area of adhesion to paper and wood (see Vinyl polymers). 

Polychloroprene rubber (CR) is the most popular and versatile of the elastomers used in adhesives. In the early 1920s, Dr. Nieuwland of the University of Notre Dame synthesized divinyl acetylene from acetylene using copper(l) chloride as catalyst. A few years later, Du Pont scientists joined Dr. Nieuwland s research and prepared monovinyl acetylene, from which, by controlled reaction with hydrochloric acid, the chloroprene monomer (2-chloro-l, 3-butadiene) was obtained. Upon polymerization of chloroprene a rubber-like polymer was obtained. In 1932 it was commercialized under the tradename DuPrene which was changed to Neoprene by DuPont de Nemours in 1936. 

An example of this improvement in toughness can be demonstrated by the addition of Vamac B-124, an ethylene/methyl acrylate copolymer from DuPont, to ethyl cyanoacrylate [24-26]. Three model instant adhesive formulations, a control without any polymeric additive (A), a formulation with poly(methyl methacrylate) (PMMA) (B), and a formulation with Vamac B-124 (C), are shown in Table 4. The formulation with PMMA, a thermoplastic which is added to modify viscosity, was included to determine if the addition of any polymer, not only rubbers, could improve the toughness properties of an alkyl cyanoacrylate instant adhesive. To demonstrate an improvement in toughness, the three formulations were tested for impact strength, 180° peel strength, and lapshear adhesive strength on steel specimens, before and after thermal exposure at 121°C. 

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