Study On The Synthesis And Properties Of Polycarboxylate Ether Superplasticizer

In recent years,polycarboxylate ether superplasticizer（PCEs）have been widely used in concrete industry ando become a research hotspot at home and abroad due to their excellent performance,environmental protection,and strong design capabilities of molecular structure.Reversible addition-fragmentation chain transfer（RAFT）polymerization,as a controllable/“living”polymerization,is an efficient polymerization method for the synthesis of polymers with narrower the molecular weight distribution and refined structure than those prepared by conventional free radical polymerization（FRP）.In this paper,PCEs with different functions,such as water-reducing type,slump preserving and early-strength types,were synthesized by FRP and RAFT polymerization,respectively.The main research contents and results are as follows:1.Water-reduced PCEs were synthesized by FRP and RAFT polymerization in aqueous solution employing acrylic acid（AA）and allyl alcohol polyoxyethylene ether（TPEG）as monomers,thioglycolic acid（TGA）and S,S′（α-α′-dimethyl-α″-acetate）-trithiocarbonate（BDMAT）as chain transfer agent,respectively.The thermal initiator,VA0-44,was used to synthesize the symmetric gradient structure PCEs in which AA monomer units gradually increased from the two ends to the middle and TPEG monomer decreased from the two ends to the middle by RAFT polymerization.The effect of the molecular weight and acid-ether ratio on the performance of gradient PCEs were investigated.It was found that gradient PCEs showed better performance than the products synthesized by FRP in a wide range of molecular weight（22,600 g/mol～34,000 g/mol）and acid-ether ratio（4～6）.Furthermore,the properties of sulfate resistance of gradient PCEs were especially excellent.In addition,PCEs with gradient structure were synthesized by RAFT polymerization initiated by redox initiator VC-H₂O₂in aqueous solution,it also shows excellent performance in the fluidity of cement.2.Two kinds of water-reducing PCEs with block structure,P（AA-grad-TPEG）-b-PAA-b-P（AA-grad-TPEG）and PAA-b-P（AA-grad-TPEG）-b-PAA were synthesized by RAFT polymerization method in aqueous solution.By comparing the fluidity of cement paste with PCEs of different structures,it is found that the performance of gradient PCEs was better than that of random structure,while the performance of block PCEs is the worst.Especially,the fluidity of cement paste added with P（AA-grad-TPEG）-b-PAA-b-P（AA-grad-TPEG）was the lowest.The mechanism of the excellent dispersion of the gradient products prepared by RAFT polymerization was discussed and analyzed.3.Using AA,hydroxyethyl acrylate（HEA）and TPEG as monomers,FRP and RAFT polymerizations were carried out in aqueous solution to synthesize slump preserving PCEs.In FRP polymerization,the molecular weight of the polymer was adjusted from 26,500 g/mol to 66,200 g/mol,and the sample with molecular weight as 33,000 g/mol showed the best the slump retention performance.In RAFT polymerization,PCE presents a symmetrical gradient structure in which TPEG monomers gradually decrease from both ends of the molecular chain to the middle;the molecular weight of the polymer was adjusted from 22,400 g/mol to 35500 g/mol.The PCEs product with the molecular weight of as 33,000 g/mol also exhibited the best performance.The gradient PCEs prepared by RAFT can achieve better performance than the FRP products in a larger molecular weight range（26,400 g/mol～33,100g/mol）.4.Early-strength PCEs were synthesized by FRP and RAFT polymerization using TPEG macromonomers,AA and functional monomers selected from HEA,acrylamide（AM）and sodium methacrylate sulfonate（SMAS）.It was found that the PCE containing HEA and AM prepared by RAFT polymerization showed the best performance.