Synthesis Of Polycarboxylate Superplasticizers With Different Topology Structure

In modern construction engineering, superplasticizer is an indispensable admixture inconcrete technology. If the amount of cement is fixed, the strength of concrete hasimproved by reducing the mixing water. And if the concrete strength is kept unchanging,the low dosage of cement was required, thus can lower the costs and bring less pollution.Polycarboxylate superplasticizer (PC) is the third-generation superplasticizers, the newsuperplasticizer has good dispersion for the electrostatic repulsion effect of the mainchain and the electrostatic repulsion of side chains. The structure of molecular has asignificant impact on the performance of PCs. In this paper, PCs with differenttopologies were prepared by using various polymerization methods, the influence ofmolecular structure on the performance were also studied.1. A new monomer, named sorbitol acrylates (ASB), was prepared by a esterificationmethod using sorbitol (SB) with acryloyl chloride in the presence of N,N-dimethylformamide (DMF) as solvent. The obtained product from the monomers wasfollowed by radical copolymerization with acrylic acid (AA), methacrylic sodium(SMAS), methoxy polyethylene glycol methaerylate (MPA). Product characterizationsshowed that the SB-modified comb-type PCs were synthesized successfully, andpresented better dispersion and better capacity retention compared with unmodifiedcomb superplasticizer.2. High performance of PCs with a suitable structure was achieved by moleculardesign. Since there have a plurality of hydroxy groups on the surface of β-cyclodextrin(β-CD)，which can introduce double-bond with acryloyl chloride by a condensationreaction, then the hyperbranched polycarboxylic superplasticizers (ACD-PC) waspolymerized with AA, SMAS, MPA in the presence of aqueous solution. The influenceof many factors, such as the reaction time, the usage of initiator, polyethylene glycol(PEG) chain lengths, and the dosage of β-CD were studied to the performance of PCs,then derived the optimal conditions. We synthesized the ACD-PC under the optimalconditions and make comparisions with the performance of comb-type PCs, which iswidely sold in the market. The obtained product showed more advantages because ofgood adaptability and the steric resistance effect, then enhance the cement dispersionand dispersed retention，eventually can meet the requirement of high-performanceconcrete.3. β-CD-core star macroinitiator was synthesized by means of acetyl bromide reaction from2-bromoisobutyryl bromide (BIBB) and β-CD, using triethylamine (TEA)as a deacid reagent and DMF as the solvent. Then the macro-product wasliving-polymerized by atom transfer radical polymerization (ATRP) using β-CD-corestar macroinitiators to initiate DMAEMA under nitrogen protection in themethanol-water solvent, the system containing the ligands2,2’-bipyridine (2,2’-bpy) incombination wih copper chloride (CuCl) catalys. Then PCs with controllable structureswere obtained using the product as macro-initiator to initiate sodium acrylate andethoxylated isoamyl alcohol in deionized water under the same reaction conditions.Each step product is showed success after tests, and the structural of final product isstar-shaped PCs. Compared to comb-type PCs, it has better adsorption capacity ofcement pastes and better dispersion.