Preface
At present, water reducing agent has become the indispensable concrete component. On concrete superplasticizer research also is all-time and active, and many of the new water reducing agent has been developed. High efficiency water reducing agent is also called super plasticizer, compared with the ordinary water-reducing agent, it can greatly reduce the water cement ratio, increased mobility, has the advantages of high efficiency water reducing, the improvement of concrete pore structure and the degree of compaction, saving cement, controlling the slump loss of concrete function, can improve the workability of concrete, the concrete air entraining, retarding and other issues, enhance the concrete strength and durability of high performance concrete, is a kind of indispensable core material. At present, in the domestic and international common superplasticizer mainly naphthalenesulfonic acid formaldehyde condensate, melamine formaldehyde condensates and polycarboxylic acid copolymer three categories. Naphthalene series superplasticizer water-reducing agent is currently on the market using the most common class of superplasticizer, its market share of more than 90%, but this kind of high efficiency water reducing agent because of its existing high slump loss, the water reducing rate is relatively low, environmental pollution is serious wait for a series of defects. Therefore, in order to adapt to the early strength, high strength, high impermeability, self-leveling concrete needs, the development of a new generation of high performance water-reducing agent be imperative. But at present, polycarboxylate superplasticizer has gradually become the industry at home and abroad superplasticizers research hotspot. Poly carboxylic acid water reducing agent has high water reducing rate, and good, no collapse of chloride, ammonia, low alkali, the production process without the "three wastes" emissions, on human health is not a threat, and the molecular structure can be modulated by sex is strong wait for a series of advantages. Therefore, has a very good application prospect.
In this paper, with methoxy polyoxyethylene methyl acrylate and methyl acrylic acid, methyl allyl sulfonate, acrylic acid as raw materials, the persulfate and peroxide dual initiator system under, through free radical polymerization, synthesis of a series of with different composition and chain structure of comb type copolymer, and mainly on the polymerization of the monomer type and proportion on cement paste and concrete are studied the dispersion performance.
1 Experimental section
1.1 experimental equipment and raw materials
1.1.1 experimental apparatus
Four mouth flask; condenser; constant temperature water bath pot; thermometer; polytetrafluoroethylene slurry mixer.
TLJ2 type electronic electric stirrer: Jiangyan City Tianli medical instrument limited company;
ZNHW type electronic energy saving control instrument: Gong on the valley of China Instrument factory;
BT00100M peristaltic pump: Baoding's constant flow pump limited company;
1.1.2 experimental materials
Methoxy poly methyl acrylate ( homemade): molecular weight 1000, monomer melt after the color was red. Methacrylic acid ( analysis of pure ): Beijing Yi Li fine chemicals company limited; acrylic acid ( analysis of pure ): Beijing Yi Li fine chemicals company limited; methyl allyl sulfonate, industrial ( 98%); chain transfer agent; initiator; sodium hydroxide solution; (30% ): baseline, the Taihang Cement cement cement;
1.2 polycarboxylic acids comb type copolymer molecular structure

1.3 polycarboxylate superplasticizer preparation
As shown below, with water bath pot, thermometer, stirrer, a peristaltic pump and a reflux condensation tube glass reaction vessel, adding a certain amount of deionized water, stirring while heating to 75 degrees C, the temperature is stable, then the polyester, acrylic, acrylic acid, methyl allyl sulfonate, and chain transfer agent with a certain concentration of the solution, as component A; the same is also the initiator solution of certain concentration, recorded as component B, respectively, in 1 hours and 1.5 hours slow drip to the 500ml reactor, after finishing dropping, insulation for half an hour, and then at 10min drops and residual initiator solution, then heat 1 hours after, cooling to 3040 C, with 20% sodium hydroxide solution to neutralize, finally with deionized water to the reaction solution is diluted to 30%, the end of the reaction.

1.4 performance test
1.4.1 raw material
( 1): Taihang Cement (C) P.O 42.5 ordinary Portland cement;
( 2) fly ash ( FA ): mountain I grade fly ash;
( 3) powder: Tianjin Tang dragon;
( 4) ( S ); sand medium sand, fineness modulus for: 3.0-2.3
( 5) stone ( G ): particle size 5mm-20mm;
1.4.2 cement paste fluidity determination
In accordance with the GB8077-2000 on different kinds of monomers and the proportion of synthesis of polycarboxylic acid water reducing agent for cement paste fluidity test, water cement ratio of 0.29, unless otherwise specified, are used in China Research Inst of building material production base cement.
Determination of 1.4.3 concrete performance
Concrete water reducing rate determination according to GB8076-1997, adding certain water-reducing agent after reduction of the corresponding water use, and keep the concrete with superplasticizer and blank concrete slump the same ( 80+10 ) mm, calculate the corresponding water reducing rate and the detection of the workability of concrete testing concrete compressive strength"
2 results and discussion
2.1 polymerization monomer type on the fluidity of cement paste effect
Polymerization of the monomer type is the influence of the polycarboxylate superplasticizer dispersion performance is an important factor, the different polymerization monomer addition to comb copolymers provide rich backbone structure, can also be changed to some extent polymer surfactant electrostatic repulsion, and the dispersed particles suction the number of dots, but, in the free radical polymerization process, as a result of all sorts of polymerization monomer activity are different, this will lead to the grafting process difficult easy degree the difference as well as the final conversion rate of monomer size, but also to a certain extent in the chain structure rationality. And ultimately affect the synthesis of polycarboxylic acid and dispersion properties of size.

Table 1 polymerization of monomer mass ratio

From table 1, table 2 and figure 1 of the experimental results showed that: polymerization monomer type on Synthesis of polycarboxylic acid superplasticizer dispersion properties have important effects. When using methacrylic acid and polyester copolymerization, methacrylic acid content can not be too large, when the methacrylic acid and polyester ratio exceeds a certain value, the preparation of the reaction solution can delaminate, at the same time can be detected by the two monomer synthesis of high efficiency water reducing agent in low amount of cases, will exhibit good dispersion performance; when the selection of acrylic and polyester polymerization of acrylic acid, due to a high polymerization activity, therefore in the polymerization process is prone to aggregation or critical aggregation phenomenon, so when using acrylic acid as a comonomer, must strictly control the polymerization conditions, while the data in Table 2 also shows that through this group of monomer synthesis of polycarboxylic acid water reducing agent in the 0.3% volume will exhibit good dispersion performance. In the polyester and methacrylate polymerization reaction system, the introduction of methyl allyl sulfonate can significantly reduce the copolymer dispersion property, which may be associated with sodium methylacrylsulfonate itself has since inhibition related. So when the system by adding sodium methylacrylsulfonate should be appropriate to reduce the amount of chain transfer agent. On the other hand, when the polymerization system with ethyl acrylate, can to some extent to improve the dispersing performance of product.

Table 2 polymerization monomer type on the fluidity of cement paste initial effects (mm )

Fig 1 polymerization monomer type on cement paste fluidity loss effect

( Note: This article uses superplasticizer are 20% solid content polycarboxylic superplasticizer)

Table 4 made of poly carboxylic acid water reducing agent on dispersion properties of concrete

Table 4 experimental data can be seen: the polymerization of monomer type on the synthesis of polycarboxylic acid copolymer dispersion influences the performance of the polyester and, when using methyl methacrylate as a comonomer, the synthesis of polycarboxylic acid copolymer has good dispersing performance, its volume is 1% ( solid content is 20%.), concrete prepared by initial slump can reach more than 220mm, and its 1 hour and 1.5 hour slump no loss or loss is very small. When using acrylic acid instead of methyl acrylate as monomer, in the same polymerization conditions on the synthesis of poly carboxylic acid water reducing agent for concrete although early has good dispersion performance, but its dispersion maintaining performance is poor, their mobility is usually in half an hour would be completely lost. This may be associated with acrylic polymerization activity is too high, the polymerization process is difficult to form the hydrophilic carboxyl groups and polyether long side chain in the molecular structure on the reasonable distribution; when in methacrylic acid and polyester based molecular chain on the introduction of methyl allyl sulfonate, the composite poly carboxylic acids on the dispersion performance of concrete and cement paste experimental results were similar, whether it is the initial slump or late slump maintaining are very poor, theoretically, the introduction of sulfonic group can to some extent to improve the dispersing performance of poly carboxylic acid water reducing agent, but because the process of polymerization, polymerization of monomer grafted hard to varying degrees, as well as sodium methylacrylsulfonate itself from the polymerization effect, so in the actual reaction is difficult to form the theory of molecular structure. At the same time the third monomer into the May to some extent destroyed two copolymer structure rationality.
2.3 domestic and abroad polycarboxylate superplasticizer performance comparison

Table 5 Effect of poly carboxylic acid water reducing agent on concrete performance comparison of dispersion

Table 5 in the experiment of several groups of poly carboxylic acid water reducing agent on the same concrete mix ratio of concrete prepared by dispersion experiment. From the experimental results it can be seen, with a Shandong product prepared concrete performance the worst, when its content is 1%, its initial slump and slump maintaining and several other products will be reduced in different degree, and a South Korean products in this mix shows best dispersion properties, and found in the experiments, the use of this product prepared the workability of concrete is one of the best. Homemade polycarboxylate superplasticizer and other two kinds of water-reducing agent, also exhibit good dispersion performance.
3 conclusion
(1 ) based on the polyester, acrylic, methyl allyl sulfonate as raw materials, the pair of initiator and chain transfer agent role, by water bath heating way, the synthesis of a series of having good dispersion effect of polymeric surfactant.
( 2) proved by the experiment, during the polymerization, polymerization of the monomer type on the product performance influence.
( 3) in the process of polymerization, using methyl acrylic acid polyester and preparation of polycarboxylic acid water reducing agent comprehensive performance is more superior, but if in this system, by introducing a small amount of ethyl acrylate can to some extent to improve its performance, however, when using acrylic acid instead of methacrylic acid, the synthesis of polycarboxylic acid high efficiency water reducing agent in dispersion properties remain will show great defects. While in the polyester and methyl acrylic acid copolymerization system introduced in two sodium methylacrylsulfonate, would greatly reduce product dispersibility, so before joining this kind of monomer, should adjust the amount of chain transfer agent.
( 4) at the same time, through to the domestic and foreign different polycarboxylate superplasticizer contrast, can be found a homemade polycarboxylate superplasticizer has excellent comprehensive properties.