Synthesis Of Carboxyl-terminated Polyether Macromonomer And Novel Polycarboxylate Superplasticizer And Their Properties

As the third-generation plasticizer,polycarboxylate has the advantages of high water-reducing rate,good slump retention and strong structural design.Recently,it has attracted plenty of domestic manufacturers to put into production,while competition among low-level homogeneity is getting fiercer.Most of the polycarboxylate superplasticizer currently are linear side chain structures,which show good dispersibility and strong slump retention.However,problems such as "neck sucking" of raw materials by the property rights of multinational companies,and difficulties in further improving of dispersion performance still remain.In this paper,a batch of carboxyl-terminated polyoxyethylene ether macromonomers(HPES and HPET)were designed and synthesized,and the synthesis process and optimization parameters were thoroughly explored,synthesis of the traditional polycarboxylate superplasticizer(HPES-AA,HPET-AA),and carboxyl-terminated polycarboxylate superplasticizer(HPEG-HPES,HPEG-HPET,HPEG-HPET500)based on the macromonomer were initially explored.The monocarboxyl-terminated polyoxyethylene ether macromonomer HPES was synthesized by esterification with HPEG and succinic anhydride as raw materials,the esterification reaction was obtained,and the effect of temperature,time and the dosage of catalyst on the esterification yield was explored.Optimized conditions are: 85℃,6h,1.5 wt%of catalyst.Under the optimized conditions,the yield of esterification can reach 96.7%.Then HPES was extracted with water and dichloromethane as solvent and extractant to remove succinic acid in the crude product,and then dichloromethane was distilled off under reduced pressure to obtain purified HPES.The purified HPES was first used to copolymerize with acrylic acid(AA)to synthesize the traditional polycarboxylate superplasticizer(HPES-AA),the effect of monomer ratio and dosage of initiator on its intrinsic viscosity and dispersion performance were studied,and the optimized condition of the synthesis of HPES-AA was obtained: the reaction temperature is 80℃,n(AA):n(HPES)=3:1,the amount of initiator is 1.0 wt% of the total monomer.The fluidity of HPES-AA synthesized under the optimized conditions was up to 310 mm at a water-cement ratio of 0.29.Then HPES was used to replace acrylic acid to synthesize HPEG-HPES,and the overall fluidity of the pure pulp was maintained at 100～110mm.The results of adsorption capacity test show that the adsorption capacity of the HPEG-HPES is much weaker than that of HPES-AA.The reason is the small monomer used to connect the two types of macromonomers has a much stronger grafting capacity than the macromonomers,resulting in the HPEG-HPES providing less adsorption sites than that of HPES-AA,with the performance getting worse.In order to increase the adsorption sites,bicarboxyl terminated polyoxyethylene ether macromonomer(HPET)was synthesized by esterification of HPEG and tricarballylic acid(TA)with DMAP as catalyst.The effects of reaction temperature,time and amount of catalyst on esterification yield were investigated.The optimized conditions of esterification reaction were as follows: temperature 115℃,reaction time 5h,dosage of catalyst 1.50 wt%,esterification rate 97.0%,double bond retention rate 98.3%.The traditional polycarboxylic acid(HPET-AA)with double carboxyl groups was prepared by copolymerization of HPET and acrylic acid.The effects of monomer ratio and initiator dosage on its intrinsic viscosity and paste fluidity were studied.The optimized synthesis condition of HPET-AA was as follows: reaction temperature 80℃,n(AA):n(HPET)= 4:1,initiator dosage 1.00 wt% of total monomer.Under the optimized conditions,the fluidity of HPET-AA cement paste is295 mm when the content of HPET-AA is 0.20 wt% and the water cement ratio is 0.29.Then,novel polycarboxylate superplasticizer(HPEG-HPET and HPEG-HPET500)with molecular weights of 2400 and 500 were synthesized.The fluidity of the slurry at 0.37 water cement ratio and 3 wt% content was more than 120 mm,which was higher than 100-110 mm of HPEG-HPES at the same water cement ratio and dosage of PC.The results of adsorption capacity test showed that the adsorption capacity of HPEG-HPET and HPEG-HPET500 was doubled than that of HPEG-HPES.However,there is still a big gap between HPEG-HPET,HPEG-HPET500 and HPET-AA,in terms of dispersibility and adsorption capacity of cement particles,which needs further improvement.In this paper,carboxyl terminated polyether macromonomer was synthesized,which formed independent intellectual property rights.It can not only replace IPEG,HPEG and other macromonomer to synthetize traditional polycarboxylate superplasticizer,but also can be used as adsorption chain to try to synthetize modified polycarboxylate and explore the structural design and synthesis of new polycarboxylate superplasticizer.