Polycarboxylic acid room temperature process and precautions
Normal temperature polymerization process
The principle of synthesizing polycarboxylic acid water reducing agent at room temperature is that, through the process of dropping reducing agent to the reactor and the oxidant in the reactor to form a redox system, the process of generating oxygen radicals, oxygen radicals in order to achieve a stable structure, seize the electrons of the monomers, so that the monomers become reactive monomers, the reactive monomers repeatedly and monomer molecules are rapidly adducted to form a large monomer and small monomers through the copolymerization of the molecules of the water reducing agent.
Polycarboxylic acid synthesis method at room temperature
01Macromolecule reaction method
In this method, polymerization is carried out first and then esterification, i.e. polycarboxylic acid with known relative molecular mass is prepared first, and then polyether with known relative molecular mass is used to graft the polycarboxylic acid through esterification reaction under the action of catalyst at a higher temperature. However, due to the limited variety and specification of polycarboxylic acid, it is difficult to adjust its composition and relative molecular mass, and at the same time, due to the poor compatibility between polycarboxylic acid and polyether, the esterification is difficult to operate in practice, and as the esterification reaction proceeds, the water is constantly overflowing, and the phase separation phenomenon will occur.
If a polyether monohydric alcohol or diol with good compatibility with polycarboxylic acid can be selected the phase separation problem can be solved. He Jing et al. produced a polycarboxylic acid water reducing agent by using the monomers styrene and maleic anhydride to polymerize first, and then sulfonate and esterify the copolymer, which has high dispersing performance and excellent slump-proof performance.
02 Macromolecular monomer method
The method of esterification followed by polymerization, that is, first of all through the esterification reaction to prepare a polymerization activity of the macromolecular monomer (usually methoxy polyethylene glycol methacrylate), and then a certain ratio of monomers are mixed together, and then directly polymerize the finished product using the method of solution polymerization. This synthesis process seems simple, but the intermediate separation and purification process is cumbersome and costly. Japan catalyst company using short and long chain methoxy polyethylene glycol methacrylate and methacrylic acid three monomers directly co-polymerized into a slump retention of good with polyether side chain concrete admixture. Polycarboxylic acid water reducing agent
03In-situ polymerization and grafting
This method integrates polymerization and esterification, that is, using polyether as the reaction medium of carboxylic acid unsaturated monomers, the polymerization of carboxylic acid unsaturated monomers occurs at the same time as the esterification reaction, thus avoiding the problem of poor compatibility between polycarboxylic acids and polyethers.Shawl et al. added a mixed solution of acrylic acid monomers, chain transfer agent, initiator gradually dropwise into an aqueous solution of methoxypolyglycols with a relative molecular weight of 2000, and after 45 min of reaction at 60℃, the reaction was completed. , which was reacted at 60 °C for 45 min and then heated up to 120 °C, and water was continuously removed under N2 protection (about 50 min), and then the catalyst was added and heated up to 165 °C, reacted for 1 h, and further grafted to obtain the finished product.
Factors affecting the efficiency of normal free radical polymerization at room temperature:
Internal factors: redox system and type, polymerization activity of each material and residual amount of polymerizer; external factors: starting temperature (radical decomposition rate), stirring intensity (oxygen brought in the air will consume radicals).
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