The Synthesis,Properties And Mechanism Of Isopentenol Polyether Polycarboxylate Superplasticizer

Isopentenol polyether polycarboxylate superplasticizer was synthesized using free radical copolymerization with isopentenol polyoxyethylene ether（TPEG）as the polymerization macromonomer,and acrylic acid,maleic anhydride as tiny monomers.The effects of acid/ether molar ratio,oxidant,and chain transfer agent on the properties of the synthesized superplasticizer were studied,and the samples with the best properties were chosen.The infrared spectroscopy,nuclear magnetic resonance hydrogen spectroscopy and time-flight mass spectrometry were used to characterize the molecular structure of superplasticizer,and the action mechanism of superplasticizer on cement paste was investigated further.Finally,the copolymerization behavior of the superplasticizer raw material monomer was thoroughly investigated.The following are the specific outcomes:（1）The fluidity of initial paste is best when the molar ratio of acid to ether is 3.85:1,the amount of oxidant is 0.8%（the same below,expressed as a share of the mass of macromonomers）,the amount of chain transfer agent is 0.5%,the dosage of sodium gluconate（SG）is 0.07%,and the mass ratio of superplasticizer to slump-proof agent is 4:6.When the superplasticizer content in cement paste is 0.15%（percentage of cement mass）,the initial fluidity of HP-1 is 324 mm,the fluidity of HVS 2 h is345 mm,and the slump protection performance is the best.Under the conditions of 0.15%（as a percentage of total rubber material mass,see below）superplasticizer and 0.07%auxiliaries,the initial slump of concrete mixed with HP-1 is 220 mm,and the slump after 3 h is 200 mm,with the best water-reducing performance.The initial expansion of concrete mixed with HP-2 is 605 mm and increases to 630 mm after 3 h,with outstanding slump retention performance.When compared to the blank control in the compressive strength test of concrete,the addition of HP-2 has little effect on the compressive strength（13.4 MPa）in the early stage（3 d）,but clearly improves the compressive strength（47.2 MPa and55.0 MPa,respectively）in the middle and later stages（7 d and 28 d）.（2）The superplasticizer PCE2 has a weight-average molecular weight of 6517,a solid content of 38.98%and an acid value of 1.4496mol/g with a molar ratio of n（TPEG）:n（AA）:n（MA）=1:3:1.The initial fluidity of PCE2 cement paste can reach 323 mm when the admixture content is 0.25%（as a percentage of cement mass）,its saturated adsorption capacity can reach 5.43 mg/g,the fluidity and adsorption capability are the highest among PCE samples.And its corresponding Zeta potential is-0.349 mv,it is the most negatively charged.It can be seen that PCE2 has good foam stability since it can reach the foam height peak of 105 mm within 30 s at a superplasticizer concentration of 0.2 g/L and defoam in just 78 s from the foam height peak to 40 mm.When the pH of PCE is 11.0 and the volume of Ca Cl₂is 3.00 m L,compared with other PCE samples,the conductivity of PCE2 is the lowest,which is 6350μs/cm,this demonstrates that PCE2 and Ca²⁺have a high complexing ability on cement paste.The largest increase in hydrodynamic radius（Rh）among all PCE samples occurs in PCE2 when the concentration of superplasticizer is increased from 0.5 g/L to 5.00 g/L.This indicates that PCE2 is simple to cause the extension conformation of the main chain,which results in the increase in Rh.The surface tension of PCE2 fell from55.55 m N/m to 42.10 m N/m when the concentration of PCE2 grew from1.0 g/L to 50.0 g/L,indicating that PCE2 was highly hydrophilic.（3）Copolymers with varying molar ratios of HEA and MA were created using hydroxyethyl acrylate（HEA）and maleic anhydride（MA）as the primary raw materials.The HEA and MA reactivity ratios were determined to be r₁=2.3797 and r₂=0.0192,respectively.Based on the microstructure of the copolymer with a molar ratio of HEA to MA of 7:3,the average chain length of HEA and MA was 6.55 and 1.01,respectively.It demonstrates that MA is more difficult to homopolymerize than HEA.To improve maleic anhydride conversion and obtain a uniform copolymer,HEA should be slowly added to MA and the p K_avalue at this molar ratio was determined by potentiometric titration,and its two p K_a1,p K_a2were4.33 and 7.59,respectively,which were higher than maleic acid.