Foaming of polycarboxylate based superplasticizers (PCEs) is a widely known problem in concrete applications.Strong foaming action introduces high air content into the concrete,which greatly reduces its final strength.This is the reason why polycarboxylates commonly require a defoamer to prevent this highly undesirable effect.It is known that industrially manufactured allyl ether-based polycarboxylates can contain 5% ~ 10 % of residual unreacted allyl ether macro monomer.It has been found that neither the pure allyl ether monomer nor the completely purified allyl ether-co-maleic acid based PCE superplasticizer exhibit foaming.Whereas, the combination of PCE polymer and allylether monomer shows strong foaming action.Even very small amounts of unreacted macro monomer in the final PCE product instigate the need for a defoamer.This was confirmed by adding a small amount of pure allyl ether macro monomer to the purified PCE polymer.This mixture showed comparable foaming like industrially manufactured PCE superplasticizers.The conclusion is that minimizing the amount of unreacted allylether monomer in commercial PCEs is the way to obtain a less foaming product.