| A macromonomer(MPEGAA)for preparing polycarboxylate superplasticizer was synthesized by catalytic esterification with methoxy polyethylene glycol(MPEG)and acrylic acid(AA)as the main feeds.The effects of the catalyst kinds and dosage,reaction temperature and molar ratio of the raw materials on the conversion of esterification reaction were investigated and the best reaction conditions were selected as follows:The catalyst was sulfuric acid and its dosage is ca.2.36%of the weigth of MPEG,the molar ratio of MPEG and acrylic acid is n(AA):n(MPEG)=3:1,the polymerization retarder was hydroquinone and its dosage is ca.0.1%of the weigth of MPEG,the reaction temperature is 110℃,and the reaction time is 3 h.The aqueous solution copolymerization of macromonomer(MPEGAA),maleic anhydride(MAD)and acrylic acid(AA)was carried out with the redox system as initiator.The quantitative relationship between the polymerization rate r or polymer intrinsic viscosity[η]and the initiator concentration c_I,total monomer concentration c_M or reaction temperature T were investigated and the copolymerization reaction kinetics equations were obtained as follows:r∝cI0.5 903cM0.8 089e-5 465K/T;[η]∝cI-1.501cM0.6 073e2 587K/T。According to the principle of molecular design,the polycarboxylate superplasticizer was directly synthesized by the aqueous solution copolymeriztion of MPEGAA,MAD and AA.The effect of initiator,molar ratio of monomers and reaction temperature on fluidity of cement paste were investigated and the best reaction conditions were selected as follows:The monomers molar ratios of MPEGAA and AA,MPEGAA and MAD are n(MPEGAA):n(AA)=1:1.5 and n(MPEGAA):n(MAD)=1:0.36 respectively,the reducing agent and oxidizing agent in initiator system are ca.1.25%and 1.0%of the total weight of monomers respectively,the reaction temperature is 60℃,the reaction time is 6 h.The mechanical property and microstructure of the cement materials,and the adsorbant amount of the polycarboxylate superplasticizer on the cement particles in cement materials were studied.The results showed that the polycarboxylate superplasticizer could obviously improve the compression strength and bending strength of cement materials,significantly restrain the early hydration of cement and greatly improve evening property of the cement materials. |
