Synthesis Of Polycarboxylate Superplasticizer By RAFT Polymerization And Research On The Effects Of Molecular Weight Parameters On Its Application Perfprmance

Polycarboxylate superplasticizer(PCEs) has advantages of high water reducing rate,low slump loss, good designing of molecular structure, energy saving and so on. PCEs getsrapid development after be invented.It has occupied more than half of the superplasticizermarket in China.Synthesis of polycarboxylate superplasticizer has been using the methodof free radical polymerization.Molecular weight of the polymers obtained in this way has awide distribution(PDI>1.5).Lack of convincing when research of the relationship betweenmolecular weight and performance.Reversible addition- fragmentation chain transferpolymerization(RAFT) is a relatively new controlled / living polymerization.Andthe polymers with narrow molecular weight distribution, the molecular weight is easier toadjust. At present,it mainly applied to synthesize water-insoluble polymers with specialstructure of star, comb-shaped, etc. Rarely used in the synthesis of water-solublepolymers.PCEs is a water-soluble polymer with cross-linked branches,it is more special to therequirement of polymerization conditions.In this paper,according to the principle of RAFTpolymerization to synthesize polycarboxylate superplasticizer with different molecular weightand molecular weight distribution.Discussed the influencing factors in production process andstudied on the effect of molecular weight and molecular weight distribution on theperformance of the application.The main research contents and results are as follows:1.Synthesis of S,S′-Bis(a,a′-dimethyl-a′′-aceticacid)-trithiocarbonate(BDATT),andSynthesis of PCEs by the existing general raw material.Investigated the influence ofpolymerization temperature, acrylic acid and RAFT agents jointly droppingtime,initiator feeding time and other parameters on the distribution of molecular weightand the monomer conversion.In this polymerization system,the optimal reactiontemperature is 80℃,which the best time of the initiator aqueous solution dropping togetherwith BDATT in acrylic acid aqueous solution is 3h.Under this condition can obtain polymerswith high polymer monomer conversion rate(more than 75%) and narrow molecular weightdistribution(polydispersity is generally lower than 1.3).2.Studied on the influence of different kinds of initiator,initiator dosage, the ratioof initiator and RAFT agents on synthesis of polycarboxylate superplasticizer.Under thesame conditions,the polycarboxylate superplasticizer synthesis by 2,2’-Azobis(2-methylpropionamidine) dihydrochloride(AIBA) initiator has more narrower molecular weightdistribution and higher monomer conversion than that synthesis by mmonium persulphate(APS) initiator.Under the same RAFT agent dosage, the higher initiator concentration, thewider molecular weight distribution, the higher monomer conversion.Changed the addingproportion of initiator and RAFT agent,found that with the increase of RAFT agentconcentration, narrow molecular weight distribution of polymer and the molecular weightdecreases.3.Make a application performance test for Polycarboxylate superplasticizer withdifferent molecular weight and different molecular weight distribution.Results showed thatthe molecular weight has a significant impact on the fluidity of cement paste, cementmortar dispersion and gas content of cement mortar. PCEs samples were synthesized in thispolymerization system which polydispersity(PDI) were less than 1.35.Under this condition,the weight-average molecular weight of PCEs with the best performance of fluidity andkeeping fluidity was estimated to be between 81000 to 89000.The weight-average molecularweight of PCEs with the biggest water reducing rate of colloidal was estimated to be between80000 to 100000.The weight-average molecular weight of PCEs with best mortar slump flowwas estimated to be between 70000 to 88000.So,it can be sure that the weight-average molarweight of PCEs with the best application performance in the range of 81000 to 88000. Themortar air-containing increased with the molecular weight lower.The bigger the molecularweight of PCEs the smaller the loss of cement mortar.The same molecular weight PCEs, thenarrower molecular weight the better dispersion performance.