Synthesis Of Polyethylene Glycol Methacrylate Macromonomers By Direct Ethoxylation

Polyethylene glycol methacrylate macromonomers are composed of two segments. One of them is polyethylene glycol chain which attributed to the excellent biocompatibility,hydrophilicity and thermosensitivity. Another is unsaturated methacrylate end group which attributed to the good following-up polymerizability with other monomers to form comblike amphiphilic copolymers. The comblike amphiphilic copolymers have been widely used in many fields such as coatings, biosensors, drug deliveries, concrete water reducers and etc. A two-step process is commonly used as the main route to manufacture the above macromonomers, that is, polyethylene glycol mono-methyl ether is first synthesized by etherification, followed by esterification with methacrylic acid or transesterification with methyl methacrylate to get the target macromonomers. The application of these excellent macromonomers is prohibited by the two-step process because of its multi-step operation, many by-products, serious equipment corrosion, lots of waste discharge and etc. Therefore, it is significant to develop a new technology to prepare polyethylene glycol methacrylate macromonomers in one-step process.In this paper, a novel one-step ethoxylation method to synthesize polyethylene glycol methacrylate macromonomers is reported. Two different types of macromonomers, polyethylene glycol monomethyl ether methacrylate (PEEMA) and polyethylene glycol mono-methacrylate (PEGMA) are prepared by the one-step ethoxylation. Meanwhile, polycarboxylate-type high performance water-reducing admixtures (PCA) are synthesized by aqueous free-radical polymerization with the above two as-synthesized macromonomers respectively, and the fluidity of cement pastes containning the polycarboxylate-type PCA are measured and compared with another PCA which was prepared by commerical PEEMA. The main experimental results and conclusions can be listed as followings:(1) A one-step process to synthesize PEEMA was well investigated, in which ethylene oxide (EO) molecules were directly inserted into methyl methacrylate (MMA) over a Al-Mg composite catalyst (MA serial catalyst). The product was characterized by FT-IR, ESI-MS and HPLC, and the target molecular was confirmed. By explorating single inhibitor and complex inhibitors, the quaternary complex inhibitors, TEMPO / acetyl acetone / benzoquinone / sodium nitrite, were suggested. With the composite inhibitors, the double bond retention rate in unsaturated methacrylate segment reached 84.4%, while the average addition number of EO was 20. The catalytic activity reached 0.238 g EO / g Cat / min at the following reaction conditions: reaction temperature 140 oC - 150 oC, reaction pressure 0.8 MPa, catalyst serial MA4.(2) At the simulation reaction conditions of higher temperature and higher pressure, the inhibitors to hydroxyethyl methacrylate (HEMA) and methacrylic acid (MAA) were investigated. It showed that TEMPO had a good effection, which remained 91.7% of HEMA and 96.8% of MAA. Direct ethoxylation of methacrylic acid (MAA) was explored with sorts of catalysts. Characterized by FT-IR and GC, PEGMA with the average addition number of EO 5, was synthesized over calcium acetate catalyst. Some acid or alkli catalysts on the ethoxylation of HEMA were screened. It suggested that PEGMA with average addition number of EO 25 could be synthesized with 4% w/w boron trifluoride-ethyl ether complex catalyst. The product was characterized by FT-IR, ESI-MS and HPLC.(3) Using the ethoxylated products of PEEMA, PEGMA and the industrial product PEEMA macromonomers as raw material, PCA were synthesized by aqueous free-radical polymerization. By measuring the fluidity of cement paste, compared with the industrial product, it showed that the self-made macromonomers can meet the requirement of industry.