Chain extenderIntroduction:
Also known as chain extender, it is a substance that can react with functional groups on linear polymer chains to expand molecular chains and increase molecular weight. Commonly used to improve the mechanical and process properties of polyurethane, polyester and other products.
The synthesis of polyurethane adhesives and sealants is crucial, as it directly affects the mechanical and process properties of the products. Chain extenders are low molecular weight multifunctional alcohol or amine compounds containing hydroxyl or amino groups. Commonly used alcohol chain extenders include 1,4-butanediol (BDO), 1.6 monodiol, glycerol, trimethylolpropane, diethylene glycol (DEG), triethylene glycol, neopentyl glycol (NPG), sorbitol, diethylaminoethanol (DEAE), etc. Amine chain extenders include MOCA and liquid MOCA modified with formaldehyde, ethylenediamine (DA), N, N-dihydroxy (diisopropyl) aniline (HPA), etc. And hydroquinone one and two（β Hydroxyethyl ether (HQEE) is used as a chain extender for polyurethane adhesives, and its product has higher heat resistance, hardness, and elasticity than commonly used chain extenders.
A necessary reagent in the production of polyurethane, which is a prepolymer formed by the reaction of aliphatic and aromatic monomers containing diisocyanate groups with polyesters or polyethers containing binary or polyols. Chain extenders are added during application to shape the resin. The commonly used chain extenders are small molecule alcohols containing binary or multiple hydroxyl groups, compounds containing amino or imine groups, or ether alcohols.
Principle of chain extender:
The principle of chain extender is that in production, some compounds containing active hydrogen are commonly used to react with isocyanate end group prepolymers, causing molecular chain diffusion and elongation, thereby achieving resin curing and forming. 2-Midazolone is a widely used chain extender with imino active hydrogen.
Application of Chain extenders:
In the polyester processing technology, due to thermal degradation and hydrolysis, the molecular weight decreases and the number of carboxyl groups increases, resulting in a decrease in the mechanical and chemical properties of the polymer. Add bifunctional small molecule compounds under reactive blending conditions. For example, bifunctional acid derivatives, isocyanates, anhydrides, and epoxides contain functional groups that easily react with carboxyl, hydroxyl, and amino groups. These bifunctional compounds can directly react with low molecular weight oligomers, forming a "bridge" between the two polymer chains, significantly increasing molecular weight, improving system viscosity, and reducing carboxyl end group content. The end of linear polyester mainly includes hydroxyl and carboxyl groups, so the chain extension of polyester is to select compounds that add to hydroxyl or carboxyl groups.
