Synthesis And Performance Of Polycarboxylate Superplasticizer With β-cyclodextrin Grafted On The End Of Side Chain

Polycarboxylate superplasticizer（PCE）has become the most widely used chemical admixture to improve the comprehensive performance of concrete due to its small dosage,high water-reducing rate,and designable molecular structure.In order to meet the demands of high-performance concrete with complex and low-quality raw materials,further designing the molecular structure of PCE to improve its dispersion performance and compatibility has been a hot topic.PCE modified byβ-cyclodextrin（β-CD）has attracted more and more attention due to its excellent dispersing performance.The high dispersion performance of PCE modified byβ-CD can be attributed to introducing the high steric hindered functional groupβ-CD.However,theβ-CD molecule contains multiple reaction sites,so it is difficult to prepare theβ-CD monomer,introducing the single vinyl functional group toβ-CD;the molecular structure of the existing PCE modified byβ-CD is relatively single and fixed,and theβ-CD is always grafted on the main chain of PCE;PCEs modified byβ-CD usually show strong retardation performance.All of these features limit the further development of PCE modified byβ-CD.In this paper,a novel PCE modified byβ-CD was synthesized through grafting theβ-CD on the side chain by click reaction to solve the existing problems.The novel PCE shows high dispersion,strong clay resistance and less retarding performance.Moreover,the effect ofβ-CD’s grafting position on the performance and mechanism of PCE was also studied.The main research work and achievements are as follows:（1）Theβ-CD monomerβ-P was synthesized through the combination ofβ-CD and polyether macromonomer（HPEG）by click reaction.During the preparation ofβ-P,the steric hindrance of theβ-CD and HPEG was superimposed.The NMR and FT IR were used to verify theβ-CD had grafted on the end of HPEG.The difficulty of introducing the single vinyl functional group toβ-CD has been solved.（2）Through free radical polymerization ofβ-CD monomerβ-P,acrylic acid（AA）and HPEG,the PCE withβ-CD grafted on the end of the side chain was synthsized and it was named PAA-g-（β-P）_nHPEG.Its molecular structure is different from the existing PCEs modified byβ-CD,in which theβ-CD is grafted on the main chain.NMR,FT IR and GPC were applied to confirm the structure of PAA-g-（β-P）_nHPEG.（3）By comparing the PAA-g-（β-P）_nHPEG’s molecular structure and property with traditional polycarboxylate superplasticizer PAA-g-HPEG.It is found that the introduction ofβ-CD prolongs the length of PAA-g-（β-P）_nHPEG’s side chains.Compared with PAA-g-HPEG,the hydrodynamic radius of PAA-g-（β-P）_nHPEG increased by 91%,and PAA-g-（β-P）_nHPEG shows a larger steric hindrance effect;the total organic carbon（TOC）adsorption test results showed that the introducedβ-CD reduced the interaction between montmorillonite and PAA-g-（β-P）_nHPEG.Comprared with PAA-g-HPEG,the surface adsorption and chemical absorption of PAA-g-（β-P）_nHPEG by montmorillonite were decreased significantly.The saturated adsorption of PAA-g-（β-P）_7%HPEG on montmorillonite decreased by 47%compared with that of PAA-g-HPEG on montmorillonite,leaving more PAA-g-（β-P）_nHPEG molecules to disperse cement particles.Therefore,PAA-g-（β-P）_nHPEG showed better dispersion and clay-resistance.（4）The PCE withβ-CD grafted on the main chain[（β-M）_30%-AA-HPEG]was synthesized through free radical polymerization.The properties and mechanism of PAA-g-（β-P）_5%HPEG and（β-M）_30%-AA-HPEG were compared.It is found that the grafting position ofβ-CD significantly affects the PCE’s properties and mechanism.The saturated adsorption of（β-M）_30%-AA-HPEG on cement particle increased by 16%compared with that of PAA-g-（β-P）_5%HPEG;the hydrodynamic radius of PAA-g-（β-P）_5%HPEG improved 51%compared with that of（β-M）_30%-AA-HPEG,both of these two grafting positions achieved the improvement of PCE’s dispersion performance.Theβ-CD grafted on the end of the side chain not only reduced the surface adsorption but also reduced the chemical absorption by montmorillonite,so the PAA-g-（β-P）_5%HPEG showed the better clay-resistance property.Through reducing the adsorption amount by cement particles and weakening the chelation of hydroxyl groups inβ-CD with Ca²⁺dissolved during the hydration of cement paste,less retarding performance of PAA-g-（β-P）_nHPEG was achieved.