Study On Synthesis Of Y-PEG Of Polycarboxylate And Its Concrete Superplasticizer

Polycarboxylate superplasticizer has the advantages of low dosage,high water reduction rate,high dispersion,high slump retention and good molecular structure designability.It is widely used in the concrete materials.With the development of the concrete industry,it is of great significance to develop new polycarboxylate superplasticizer.Most of the polycarboxylate superplasticizers currently used are with the linear side chain structures.Although this type of structure has the advantages of good dispersibility and strong slump retention,it still has the limitations such as being controlled strictly by invention patents of multinational companies.At the meantime,the dispersion performance of the polycarboxylate superplasticizers with the linear side chain structure is pretty hard to improve.Therefore,in this work,a Y-structure macromonomer（Y-PEG）was synthesized and its synthesis process and its optimization parameters were thoroughly studied.Subsequently we initially explored the synthesis method of polycarboxylate superplasticizer based on the Y-PEG.Firstly,methyl allyl polyethylene glycol ether（HPEG）and tricarballylic acid（TA）are used as raw materials to synthesize Y-type intermediate（m Y-PEG）through the first step of esterification reaction.The influence of reaction time,reaction temperature,catalyst dosage and reactant dosage are studied by single factor optimization.The results turned out that the esterification yield of the m Y-PEG can reach 89.3%when n（TA）/n（HPEG）=3,the dosage of the catalyst kept 2%of the monomers’quality and the reaction temperature and time was 115℃and 6 h.Then,we used water and dichloromethane as solvent and extractant to remove tricarballylic acid in m Y-PEG.Finally,the purified m Y-PEG was obtained after a bit of methylene chloride was removed by reverse extraction.Using purified m Y-PEG and methoxy polyethylene glycol（MPEG）as raw materials,we synthesized Y-PEG through the second step of esterification reaction.¹H-NMR characterization proved that Y-type macromonomer was successfully synthesized.In order to improve the polymerization activity of the Y-PEG,we studied the influence of different dosages,types of polymerization inhibitors and esterification reaction time on the double bond content of the Y-PEG.N₂ was used to isolate the reaction system to prevent the double bond in macromonomer from being oxidized by oxygen in the air,consequently increasing the reaction activity of the double bond in the Y-PEG.Furthermore,Y-type side chain polycarboxylate superplasticizer（Y-PCE）was synthesized by Y-PEG,acrylic acid（AA）and sodium methacrylic acid sulfonate（MAS）.The effects of monomer ratio,chain transfer agent dosage,initiator dosage and reaction temperature on product dispersion performance are studied by single factor optimization.The optimized process conditions for the synthesis of Y-PCE are as follows:the reaction temperature is 80℃,n（AA）/n（Y-PEG）=5,n（MAS）/n（Y-PEG）=1,and dosage of the initiator is 2%of the monomers’quality.The Y-PCE synthesized under optimized conditions showed certain performance.Y-PEG and Y-PCE were successfully synthesized.However,the performance of Y-PCE has not reached the level of commercial polycarboxylate superplasticizer.It still needs further study about the synthesis process and optimization of molecular structure.In spite of the unexpected experimental results,the above research can provide inspiration and theoretical guidance for designing new polycarboxylate molecular structure and improving the performance of polycarboxylate superplasticizer.