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How does PPG Unsaturation affect the quality of casting urethane prepolymers?

Views: 62 Update date: Oct 21,2020

PPG Unsaturation casting urethaneThe polypropylene glycol used in the polyurethane industry in the past is formed by the ring-opening polymerization of propylene oxide using an anionic catalyst KOH in the presence of polyol or polyamine initiator. Alkali can not only catalyze the formation of polyols from propylene oxide, but also initiate the isomerization reaction of propylene oxide to form allyl alcohol, making part of the PPG molecules become monohydroxy polyethers. With the increase of molecular weight, the monohydroxy polyethers The content increases, the unsaturation increases. When the hydroxyl equivalent reaches 2000, it is difficult to produce bifunctional products. The presence of this monofunctional compound acts as a chain terminator during the PU synthesis process, affecting the polymer chain growth, and at the same time the non-reactive end (C—C double bond) plays a role of internal plasticization, which reduces the performance of the CPU. . Unsaturation also affects the weather resistance of polyurethane, because polymers containing double bonds are very sensitive to ultraviolet light. Under the action of ultraviolet light, the unsaturated groups in polyols produce free radical reactions, which lead to cross-linking and cracking. Reducing the degree of unsaturation of PPG can significantly shorten the demolding time and improve the physical and mechanical properties and dynamic properties of the elastomer. 

 




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