Controllable Synthesis And Microscopic Mechanism Of Star-shaped Polycarboxylate Superplasticizer

Polycarboxylate superplasticizer?PCE?have attracted wide spread attention as concrete admixtures due to their high water reduction,high slump retention and strong molecular structure design.Many PCEs such as slump retention,viscosity reduction,slow release,early strength,low air-entraining and functional PCE were developed in recent years.These PCEs could be applied in water conservancy project,construction facilities and roadside.However,most of PCEs are less structure integrity,wide molecular weight distribution and many disordered sequence distributions was synthesized through traditional free radical polymerization,and effect their dispersion property,which limit their the further applications as concrete admixtures.Furthermore,with the development of new topological structures such as star-shaped PCE,the precise and controllable synthesis for PCE gradually become a higher requirements to obtain the target material.In this thesis,based on the method of precisely molecular design and synthesis,the star-shaped PCE was synthesized through the steps including the first?core?to obtain initiator of star structure and the?arm?with hydroxyl ethyl acrylate?HEA?,isobutenyl polyethylene glycol?MAPEG?by?living?/controlled atom transfer radical polymerization?ATRP?,respectively.This method avoids the problems of molecular crosslinking and uncontrollable of polymerization process of star-shaped PCE.The main research content of this essay as follows:?1?The star-shaped and comb-shaped PCE were prepared by precise controlled number of functional groups of small monomer and side chain of macromonomer at the the end of star shaped?core?using atom transfer radical polymerization.Furthermore,the star-shaped and comb-shaped PCE were synthesized by the traditional free radical polymerization,and the star-shaped PCE possessing different arm length were synthesized by changing the amount of chain transfer agent.The Fourier Transform Infrared?FTIR?,¹H Nuclear Magnetic Resonance?¹H NMR?were used to prove that the molecular structure of the polymerization product were consistent with the design molecular structure,but also the Gel Permeation Chromatograph?GPC?and particle charge detector PCD 05 have proved same main chain length and charge density of the synthesized product.?2?A quantitative analysis of the PCE polymers via ¹³C Nuclear Magnetic Resonance(¹³C NMR)revealed that the microscopic molecular structure sequence distribution by combined with probability values and Matlab software.The results showed that the three potential structural motifs of the PCE were expressed as EAE,AAE and AAA.Furthermore,the data also suggest that has a higher probability of a structural unit having a feed ratio of molecular structure by the ATRP method.This confirms the achievement of our target structure.?3?The effects of synthesis method and topological structure on the performances of PCE were comparatively studied.The results showed that compared with traditional free radical polymerization,the PCEs were synthesized by ATRP method can exhibit higher rheological properties to cement paste,higher working efficiency and mechanical properties to concrete;comparatively,star-shaped PCE confers higher dispersing efficiency in cement.The results also confirms that the ATRP method can improve the application performance of star-shaped PCE.?4?The micromechanism of star-shaped PCE was synthesized through ATRP method was revealed from the perspective of adsorption amount,zeta potential,adsorbed layer thickness,ion complexation,colloidal interaction force,hydrodynamic radii and hydration behavior.The functional groups of arm adsorbed on the surfaces of cement particles and Ca²⁺complexes in pore solutions,and formed a thinner and more compact adsorbed layer and larger surface coverage with a flat conformation on cement surface to generate stronger steric hindrance or interaction force,leading to a stable suspensions for cement-water system and thus improve the fluidity of cement paste.Furthermore,the ion exchange between the pore solutions and cement particles can be restrained to further delay the progress of cement hydration.Based on the investigation above,the obstacles faced in the application of heterogeneous polymer were discussed and the ATRP methods to solve these problems were proposed.Finally the star-shaped PCE was synthesized by ATRP on the mechanism of cement grains were discussed.This research provides not only a new direction for exploring the method and novel PCE,but also a technical feasibility and a basic theoretical research for optimizing the performance of PCE.