0 Introduction
Modern concrete admixtures for the development of about 60 years of history. A naphthalene sulfonate as the main component of the dispersant on 1938 in the United States of America obtained patents, marks of various additives of patent products start and rapid development. In the early 30 century, the United States of America and other developed countries have in highway, tunnel, underground engineering application the chemical additive, the early use of admixtures are mainly abietic acid sodium lignosulfonate air-entraining agent, plasticizer, stearic acid waterproofing agent and calcium chloride and other early strength agent.
During the nineteen sixties to naphthalene sulfonate formaldehyde condensate ( PNS ) and sulfonated melamine formaldehyde resin ( PMS ) as the main component of the high efficiency water reducing agent ( also known as super plasticizer ) laid the foundation for modern concrete materials and construction methods of modernization, therefore, concrete high efficiency water reducing agent in the invention and Application of being recognized as the world development of concrete technology in a technological breakthrough. The high efficiency water reducing agent in our annual production has more than 1 million tons per year, for more than 400000000 cubic meters of concrete in engineering construction.
Faced with environment, resource and the sources of energy a lot of new problems, cement concrete industry must get rid of the traditional pattern of industry sustainable development. Since the nineteen ninties presented high performance concrete ( High Performance Concrete, referred to as HPC ) concept, concrete material has excellent mechanical properties, should also meet the good work performance, durability, volume stability and economy of a variety of requirements. High performance concrete in twenty-first Century to become the various countries to develop new building materials. High performance concrete and the development of new materials for better performance of superplasticizer, polycarboxylic high performance is more excellent performance on the new water reducing agent, with PNS and PMS superplasticizer incomparable advantages: low dosage and high performance admixture for cement ( weight 0.2% ~ 0.5%, reduce water rates can be high up to 30% ~ 40% ); fluidity keeping ability ( 1-2 h in fresh concrete slump has lost ); good adaptability ( a variety of cement and admixture ); green pollution-free ( synthesis process without the use of formaldehyde and other pollutants in the environment ); performance strong designability ( can realize molecular structure and properties of the design ). Due to its good comprehensive benefits, therefore polycarboxylate superplasticizer worldwide attention, is called the third generation high performance water-reducer [1 ].
1 domestic and foreign research status and existing problems
Study abroad polycarboxylate water reducing agent for longer periods of time, its production process and technical control is relatively mature, the industrialization has products in many engineering applications. According to the report, in 1998 Japan poly carboxylic acid series products accounted for all the high performance AE water-reducing agent products more than 60% of the total, the major manufacturers have Kao, Takemoto oil, Nippon paper, Teng Ze drugs [2, 3, 4]. The North American and European countries in recent years, the research focus has gradually to the polycarboxylic acid transfer is the main commercial development and promotion, such as
Grace Construction Asva series, MBT Pheomix 700 FC Rheobuild 3000FC brand, super early strength water-reducing agent, Sika's Visconcrete 3010 has a good performance [5 ]. Polycarboxylate superplasticizer has become a worldwide hotspot [7, 8, 9], polycarboxylate superplasticizer in our country has also become admixtures industry focus of study, many of the units are polycarboxylate superplasticizer synthesis research, of which the Shanghai region some units have industrialized production products, and in the building on the successful use of [2, 5], but its comprehensive performance compared with foreign products there is still a considerable gap. Beijing surrounding areas of polycarboxylate superplasticizer research has made great progress, laboratory synthesis products have been tested, I believe will soon realize industrialized production application.
Due to technical confidentiality reasons, master of polycarboxylic high performance complete production technology is not much, especially the production of polycarboxylic high performance the key raw materials and process control, such as catalyst, defoaming agent, stabilizer. Although our country has a lot of University and research departments are engaged in research in this area [2, 5], but the current domestic synthesis of polycarboxylic acid superplasticizer selection key raw material is limited, from raw material selection to production processes, reduce costs, improve performance and other aspects, there are a lot of infrastructure work needs to carry out.
2 structure of polycarboxylic acid type water-reducer characteristics and the main synthesis method
Polycarboxylate superplasticizer molecular structure was a comb type, main chain having a plurality of active groups, a strong polarity, a side chain having a hydrophilic polyether segment, and the chain is longer, the number of hydrophobic radicals, molecular chain segment is shorter, less quantity. Typical high performance polycarboxylate water reducing agent of the molecular structure is shown in figure 1:

Fig 1 polycarboxylic molecular structure
Fig.1 Molecular structure of the polycarboxylic acid superplasticizer
R1, R2, R3, R5, R6, R7 represents H or CH3; R4 represents with 1 to 3 carbon atoms of the alkyl group; M1, M2 represents an alkali metal, alkaline earth metal or ammonium or amine groups such as a, B, C; N, D,, m as integer
The polycarboxylic acid polymer is obtained by free radical polymerization, including chain initiation, chain, chain transfer and chain termination four processes, reaction under the protection of nitrogen atmosphere. Polymer on cement particle dispersing ability depends on the sequence structure of copolymers, molecular weight and its distribution, functional groups, species and quantity of side chain length, polar and nonpolar groups in the proportion of [8, 10], the effects of these factors on structure parameters of water-reducing ability effect of. The domestic and foreign research shows, monomer feed ratio and the dosage of initiator on the dispersion properties of the impact is particularly evident. Due to the high performance polycarboxylate water reducing agent of the relationship between molecular structure and properties of understanding is not comprehensive, preparation of high performance polycarboxylate water reducing agent of raw material, synthetic process, product composition and molecular structure of great change. Europe, very few countries can achieve the molecular structure and performance design. Generally polycarboxylate superplasticizer preparation methods can be divided into the following several kinds:
2.1 active monomer copolymerization
This synthetic process has the advantages of molecular structure can be well designed, its main chain and side chain length can be obtained by reactive monomer and preparation of copolymerization monomer ratio and reaction condition control. This synthetic method is the key to prepare macromer polymerization activity ( usually methoxy polyethylene glycol methacrylate ), and then the certain proportion of monomers are mixed together to obtain the finished product directly by solution polymerization. But to synthetic reactive macromer, the existence of intermediate purification process is complex, the problem of high cost. In addition, active block preparation process to prevent acid polymerization, choose the suitable polymerization agent and catalyst, try to improve productivity.
Traditional functional macromolecular monomer preparation process is using methanol as initiator, in the autoclave and flammable and explosive of the epoxy ethane addition reaction for preparing methoxy polyethylene glycol, then in organic solvents and ( meth) acrylic acid or ( meth ) acrylic ester reaction. This technology not only in the production process has a strong irritating smell, difficult process control, complex equipment, but also increase the solvent recovery process and cost, limit their application, reaction process is as follows.

R1, R2 represents H or CH3

There are also reported in the autoclave with acrylic acid as initiator in propylene oxide adduct synthesis of macromonomer. Beijing City Building Material Science Research Institute used to have irritant smell methacrylate excess synthesis of macromonomer [6 ], after full reaction with distillation distillation excess methacrylate and fatty alcohol, and its essence is the organic solvent as reaction medium, in the actual production process is very difficult to achieve.
Tsinghua University used to direct air heating bath synthesis of side chain of the polymer monomer, but the premise is must limit the preparing single-pipe can reunite glycol [11 ].

R1 represented with 1 to 3 carbon atoms of the alkyl group; R2 represents H or CH3;
2.2 after the polymerization function method
This method is to form a backbone and then introduced into the side chains. The general is the use of existing known molecular weight of poly carboxylic acid, under the action of catalyst and polyether at high temperature by esterification reaction. This method saves the problem is polycarboxylic acid and polyether compatibility is not good, but also in the esterification process generates water appeared phase separation, esterification and difficult operation. Therefore, selection of good compatibility with polycarboxylic acid polyether has become the key work of synthesis.
2.3 in situ polymerization and graft
This method is also introduced into the side chains in the main chain polymerization. Polyether as the carboxylic acid type unsaturated monomer in the reaction medium, to overcome the polycarboxylic acid and polyether incompatible problem. The method is that the acrylic monomer, chain transfer agent, initiator mixture gradually dropping with methoxy polyethylene glycol aqueous solution, under certain conditions in the reaction of. Although this method can control the molecular weight of the polymer backbone, but in general can only choose COOH group containing monomer, otherwise very difficult to graft, and the graft reaction is reversible equilibrium reaction, reaction system has a large number of water, the grafting degree is not high and it is difficult to control. This method has the advantages of simple process, low production cost, but the molecular design is more difficult.
The 3 domestic high performance polycarboxylate water reducing agent problems and problems
3.1 polycarboxylate superplasticizer research task
Although there have been a lot of polycarboxylic acid water reducing agent research report, but the polycarboxylate superplasticizer synthesis, action mechanism and application, there are still many problems to be further studied [ 12-20]:
(1 ) studied first with the polymerization activity of polyoxyethylene ( or propylene ) class of macromonomer synthesis technology, especially the different molecular weight polyoxyethylene end capping groups choice and end sealing method and detection method. With the polymerization activity of macromonomer synthesis by the use of raw materials, safe and reliable technique and detection method;
( 2) a clear polymer molecular structure and molecular arrangement and the relationship between performance, thereby realizing the molecular structure and properties can be designed; for example Europe have developed for precast concrete products with polycarboxylate superplasticizer, it has high water reducing rate and early strength admixture amount, low, concrete products can save the steam maintenance, saves energy and improves the performance of the purpose of;
( 3) high performance polycarboxylate water reducing agent in the application of technical problems. The research of this respect is very few, including the application of polycarboxylate superplasticizer performance and cost, as well as the polycarboxylate superplasticizer admixture with other compatibility problems, these problems are high performance polycarboxylate water reducing agent in a large number of projects application premise;
( 4) high performance polycarboxylate water reducing agent in the production of quality and stability of product storage stability problem.
In 3.2 studies the problems existing in the course of
Concrete admixture manufacturing is the synthesis of fine chemical engineering category, and the products are used in construction of the building materials, the concrete chemical admixture of research and development is the chemical and building materials industries in the shared task. Therefore, concrete admixture is a cross discipline, requires a different discipline research co-operation to achieve the ideal effect. But the study on the main problems existing in domestic admixture:
( 1) the lack of cooperation and the coordination of different industries. In a laboratory study level, synthetic polymer cement concrete and professional and technical personnel did not fully cooperate, limits the high performance polycarboxylate water reducing agent research and development speed. Even though the research in laboratory, the industrial production level without large chemical enterprises, the production of polycarboxylic acid superplasticizer has stable quality and equipment problems.
( 2) the lack of the necessary capital investment and government support. Our country of polycarboxylate superplasticizer research basically no original results, mostly in imitation tracking foreign research results, the use of domestic raw materials developed similar products performance.
( 3) the lack of application performance, especially high performance polycarboxylate water reducing agent for concrete special properties ( Volume Stability Research on ). At present, most of our research work is focused on the synthesis and preparation process thereof, in the application of performance studies is few, limiting the polycarboxylic acid products to promote the application, so the engineering units to use on these new product performance advantage also no basic knowledge, not to mention the extensive use.
4 countermeasures and development trend
Different industries and units through collaborative research to accelerate new polycarboxylate superplasticizer synthesis process performance and applied research, first in the university or research institute engaged in internal branch of polymer and cement concrete researchers can realize the cooperation study, it can implement complementary course, and can guarantee the integrity of intellectual property, easy to achieve. Different industries and enterprises cooperation requires association or the government departments to promote. Through the high performance polycarboxylate water reducing agent to promote interdisciplinary research and development, but also promote the concrete materials to high technology direction of development, as soon as the new high performance polycarboxylate water reducing agent to the market, for China's huge construction market services. Can foresee, along with the domestic and international polycarboxylic high performance chemical study on the structure and properties of constant depth, polycarboxylic high performance will be widely applied, and promote the development of concrete material toward the functional, ecological and high performance of direction.