Grafted chloroprene adhesives are formulated by graft copolymerization of chloroprene rubber, methyl methacrylate and other monomers, initiators, antioxidants in a solvent, with a terminator and tackifying resin.
Chloroprene Rubber
Ordinary chloroprene rubber is not effective for graft copolymerization, so specialized chloroprene rubbers are available. Examples include CR2481 and CR2482 from China, and A-90, A-30, and G40 from Japan.
Methyl Methacrylate (MMA)
Methyl methacrylate is a colorless, transparent, volatile liquid with a strong, pungent odor. Its relative density is 0.932–0.942. Its boiling point is 100–1010°C, and its freezing point is -48.20°C. It is soluble in ether, acetone, chloroform, and benzene, and slightly soluble in water and ethylene glycol. It is flammable. Methyl methacrylate contains polymerization inhibitors, which should be removed during grafting reactions. However, some polymerization inhibitors can decompose spontaneously at temperatures above 600°C.
Benzyl peroxide (BPO)
Industrial benzoyl peroxide contains 28%–32% water. Before use, it must be thoroughly dried, either by air drying, washing with anhydrous ethanol, or oven drying. During drying, extreme safety precautions must be taken to prevent explosions. A vacuum oven or steam oven is best, and the temperature should not be too high (50–600°C).
Hydroquinone (HQ)
Hydroquinone is a grayish-white or slightly yellow crystalline powder. It easily discolors when exposed to air. Its relative density is 1.358. Melting point is 170.5–1740°C. It is readily soluble in hot water, ethanol, and ether, and slightly soluble in benzene. It is moderately toxic and corrosive to skin contact.
Tackifying resins
Most grafted chloroprene adhesives require the addition of tackifying resins, such as terpene resins (molecular formula (C10H16)), terpene phenolic resins, and 2402 resin. These resins exhibit good solubility and compatibility in grafted chloroprene adhesives, significantly improving initial adhesion. Poly(α-methylstyrene) resin, when used in grafted chloroprene adhesives, can significantly improve bond strength and toughness, as well as increase the adhesive's transparency and stability.
