Flexibilizing agents

Flexibilizers based on functionalized, liquid polybutadiene derivatives have been described in several references. Carboxyl-terminated butadiene/acrylonitrile polymers (72), butadiene homopolymers (73), and maleic anhydride/amino acid-grafted butadiene homopolymers (74) (all liquids) have been used as flexibilizers which impart good low temperature strength and water resistance to DGEBA-based epoxy adhesives. These liquid flexibilizers are readily dissolved in epoxy resins and serve to reduce the viscosity of the mixture. 

Polyoxyalkylene ethers, based on propylene oxide or propylene oxide/ethylene oxide copolymers, have also been described as useful flexibilizers. As with the polybutadiene flexibilizers, these materials are typically fairly low-viscosity liquids. DGEBA-terminated 30 70 ethylene oxide propylene oxide polyethers and propoxylated glycerol have been used to modify DGEBA-based adhesives, improving room temperature shear and peel strengths. 

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Flexibilized epoxy resins are important structural adhesives [69]. Liquid functionally terminated nitrile rubbers are excellent flexibilizing agents for epoxy resins. This liquid nitrile rubber can be reacted into the epoxy matrix if it contains carboxylated terminated functionalities or by adding an amine terminated rubber. The main effects produced by addition of liquid nitrile rubber in epoxy formulations is the increase in T-peel strength and in low-temperature lap shear strength, without reducing the elevated temperature lap shear. 

Most epoxy formulations contain diluents, fillers or reinforcement materials, and toughening agents. Diluents may be reactive (mono- and diepoxides) or nonreactive (di-n-butyl phthalate). Toughening (flexibilizing) agents such as low-molecular-weight polyesters or... 

Liquid polymers with terminal mercapto groups (LP-2) are obtained when solid polyolefin poiysulfides are reduced. These liquid polymers may be oxidized to solid polymers in the presence of oxidizing agents, such as lead oxides. The liquid polymers are used in caulking compositions and as reactive flexibilizing agents in epoxy resins. 

Tpo maximize the utility of crosslinked cycloaliphatic epoxy resins in some of the more critical application areas, improved toughness is required. Such improvements can often be made through modification with various flexibilizing agents, but as a rule this improvement is accompanied by a severe degradation of the strength and heat distortion temperature of the cured system. 

Development of epoxidized soya oil, as an acid-absorbing and low-volatile flexibilizing agent, provided the quantum jump in heat stability. High concentrations of epoxidized soya oil could be used as a replacement for much of the primary plasticizers with attendant improvement in the composition s thermal tolerance. 

Soybean fatty acids are conjugated thermally or catalytically to yield dimer and tri-mer polybasic acids (Erhan et al., 2005). Hydrolyzed dimer acids improve color and oxidative stability. These are used in polyamide resins, paints, plastics, and coatings, bodying/curing/flexibilizing agents, corrosion inhibitors, antiwear agents, lubricants, fuel, and lubricant additives (Antonucci et al., 1984 Bhowmick Basu, 1988 Kale et al., 1991 Savastano, 2001 Watanabe et al., 1996). The annual dimer acid production is about 18,000 MT (20,000 t). 

More recent efforts have focused on developments that create true hybrids. For example, blocked isocyanate prepolymers have been mixed with epoxy resins and cured with amines [68-70]. These blocked prepolymers will react initially with the amines to form amine-terminated prepolymers that cross-link the epoxy resin. Several blocked isocyanates are commercially available. The DESMOCAP (Bayer) llA and 12A products are isocyanates (believed to be blocked with nonylphenol) used as flexibilizing agents for epoxy resins. ANCAREZ (trademark. Pacific Anchor, Inc.) 2150 is a blocked isocyanate epoxy blend used as an adhesion promoter for vinyl plastisols. A one-package, heat-cured hybrid adhesive was reported consisting of isophorone diisocyanate, epoxy resin, and a dispersed solid curative based on the salt of ethylenediamine and bisphenol A [71]. Urethane amines are offered commercially that can be used with epoxy resins to develop hybrid adhesive systems [72]. 

Since coatings containing cycloaliphatic epoxides tend to be brittle, other compounds such as oligomeric polyols are frequently added as flexibilizing agents. Alcohols can react with the oxonium ions formed by the addition of protons to epoxide groups (see Scheme 11.2) and are thereby copolymerized with the epoxides. 

Uses Flexibilizing agent in coatings and inks water resist, aid textile release agent dental polymers Manuf./Distrib. Aldrich Monomer-Polymer Dajac Labs Trade Names Photomer 4818 SR 257... 

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