Synthesis and properties of viscosity-reducing polycarboxylate superplasticizer in continuous tubular reactor
A viscosity-reducing polycarboxylate superplasticizer VR-PCE-TR with a narrow molecular distribution was synthesized from thermally initiated reversible addition-fragmentation chain transfer(RAFT)polymerization of polyoxyethylene polyoxypropylene isopentenol ether(IPEPPG),2-methyl-2-butylsulfanyl-thiocarbonylsulfanyl-propionic acid and maleic anhydride in a continuous tubular reactor,and characterized by 1HNMR,FTIR and GPC.VR-PCE-TR was then evaluated for its influence on the working performance and rheological properties of concrete,and for performance comparison with viscosity-reducing polycarboxylic acid superplasticizers prepared by conventional aqueous free radical polymerization in tank reactor.The results showed that,when the mass fraction of polycarboxylate superplasticizer solution was 10%,VR-PCE-TR exhibited the lowest surface tension(30.65 mN/m).When the superplasticizer mass fraction was 0.8%,VR-PCE-TR displayed a higher adsorption capacity for cement particles(2.803 mg/g).When the dosage(based on the mass of cement,the same below)of superplasticizer was 0.13%,the cement slurry with VR-PCE-TR showed better dispersion and dispersion retention performance,while when the dosage of superplasticizer was 0.4%,the cement slurry with VR-PCE-TR showed a lower yield stress(1.3 Pa)and lower plastic viscosity(0.26 Pa·s).The continuous tubular reactor avoided the material deoxygenation step and could maintain the polymerization control and polymerization reaction rate,therefore,the prepared VR-PCE-TR had a narrower relative molecular mass distribution(polydispersity index was 1.19),and thus had better viscosity reduction effect and application performance.
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