Water retention type polycarboxylic acid water reducer and preparation method thereof

The invention relates to a water-retaining polycarboxylic acid water reducer, which is prepared from the following raw materials in parts by weight: 300 to 400 parts of polyether macromonomer, 5 to 20 parts of unsaturated water-retaining functional monomer, 25 to 50 parts of unsaturated acid, 2 to 8 parts of oxidizing agent, 0.8 to 2.0 parts of chain transfer agent, 0.1 to 1.0 part of reducing agent, 300 to 760 parts of water and 5 to 20 parts of alkali liquor, the unsaturated water retention type functional monomer is prepared from the following raw materials in parts by weight: 20 to 30 parts of konjac glucomannan, 2 to 20 parts of maleic anhydride, 0.2 to 0.5 part of catalyst and 200 parts of water; the structural general formula of the konjac glucomannan is (C6H10O5) n, wherein n is 2-10. Konjac glucomannan is introduced into a molecular chain of the water-retaining polycarboxylate superplasticizer, so that the prepared water-retaining polycarboxylate superplasticizer is good in water-reducing rate, water