Development of polycarboxylate superplasticizer
The African Development Bank will finance $25 billion by 2025 to support Africa's fight against climate change, the bank's president said at the bank's annual meeting in Accra, Ghana.
He noted that climate change has had many negative impacts on the continent, causing natural disasters such as droughts, cyclones, and floods. Climate change costs Africa between $7 billion and $15 billion a year. "Africa has no choice but to address climate change."
To ensure Africa's food supply, the African Development Bank has delivered climate-friendly seeds to 12 million farmers in 27 countries in the past two years under the "Technology for Agricultural Change in Africa" program, he said.
In the area of renewable energy, the African Development Bank is implementing a $20 billion "Desert Power" initiative in the Sahel that is expected to power 250 million people, he said.
US President Joe Biden recently wrapped up his five-day trip to Asia with a summit of leaders of the "Quad" security Dialogue.
Biden has promoted a number of economic and security cooperation initiatives during his visit aimed at deepening ties with Indo-Pacific Allies and partners in response to China's growing influence in the region. Some analysts in the United States believe the most significant announcement may be an initiative to share maritime information to combat illegal activities. But other experts say Biden's move sets a good framework for more security cooperation, though it remains to be seen whether concrete action will follow.
Affected by several factors, the supply of the pce powder is erratic and thus its prices are expected to go higher in the future.
According to the different molecular structure, it can be divided into four generations of polycarboxylate series superplasticizer, the first generation is acrylic acid copolymer, the second generation is propylene ether type, the third generation is amide type, and the fourth generation is polyethylene glycol branched chain type.
First generation: methacrylic acid / enoic acid methyl ester copolymer.
The synthesis of the first generation polycarboxylate superplasticizer has few kinds of raw materials and the process is relatively simple.
Second generation: propenyl ether copolymer.
The second generation polycarboxylate superplasticizer is mainly ether bond in molecular synthesis structure. This synthesis method uses maleic anhydride raw materials, and the units of its branched chains are connected by ether bonds, so it is also called polyether superplasticizer.
Third generation: amide / imide type.
The third generation polycarboxylate superplasticizer began to use amide raw materials.
Fourth generation: polyamide-polyethylene glycol branched chain type.
The fourth kind of polycarboxylate superplasticizer focuses on considering the influence of molecular structure and properties, and polyoxyethylene side chain is introduced into the synthesis process control.
Synthesis method of polycarboxylate superplasticizer
Direct copolymerization of polymerizable monomers.
In this synthesis method, a long polyether side chain is introduced into the main chain, and the key to the preparation is to synthesize macromonomers with polymerization activity (usually methoxy polyethylene glycol acrylate). Then the monomers with a certain ratio are mixed together and the finished product is obtained by solution polymerization. The premise of this synthesis process is that in the stage of synthesis of macromonomers, the catalyst has a great influence on the synthetic products, and there is a tedious process of intermediate separation and purification. The main purpose is to find suitable catalysts and reaction conditions to further increase the yield and shorten the reaction time so as to reduce the production cost. It has been reported that phase transfer catalyst or inorganic salt is a kind of effective reaction catalyst. A kind of concrete admixture with good slump retention was prepared by direct copolymerization of short-chain and long-chain methoxy polyethylene glycol methacrylate and methacrylic acid.
Functionalization after polymerization.
This synthesis method is to first form the main chain and then introduce the side chain, generally using polycarboxylate with constant molecular weight, which is grafted with polyether at higher temperature under the action of catalyst. However, there are some problems in this method: first, the types and specifications of ready-made polycarboxylate products are limited, so it is difficult to adjust their composition and molecular weight; second, the compatibility of polycarboxylate and polyether is not good, and the actual operation of esterification is difficult. Third, water is formed in the process of esterification, and phase separation will occur. Therefore, the selection of a polyether with good compatibility with polycarboxylate has become the key to the synthesis.
In situ polymerization and grafting.
This synthesis method is mainly developed to overcome the shortcomings of post-polymerization functionalization. Side chains are introduced at the same time of main chain polymerization, and polyether is used as the reaction medium of carboxylic acid unsaturated monomers. The reaction integrates polymerization and esterification, which avoids the problem of poor compatibility between polycarboxylate and polyether. Although this method can control the molecular weight of the polymer, the main chain can only choose the monomer containing-C00H group, otherwise it is difficult to graft. And the grafting reaction is a reversible equilibrium reaction, there is a large amount of water in the system before the reaction, and the degree of grafting is not very high and difficult to control. This method has the advantages of simple process and low production cost, but the molecular design is difficult.
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The United States urges the U.N. Security Council to impose additional sanctions on North Korea in response to its latest ballistic missile launch, including a ban on tobacco and oil exports to North Korea and a blacklist of the Lazarus hacking group.
The United States circulated the draft to the 15 members of the Security Council this week. It was not immediately clear if or when a vote would take place. A resolution requires nine "yes" votes and no vetoes from Russia, China, France, Britain, or the United States.
Russia and China have already voiced opposition to tightening sanctions in response to Pyongyang's launch of an intercontinental ballistic missile last month -- the first since 2017.
U.S. and South Korean officials and analysts also say there are growing indications that North Korea may soon conduct its first nuclear weapons test since 2017, too.
The U.S. -drafted U.N. resolution would expand the ban on ballistic missile launches to include cruise missiles or "any other delivery system capable of delivering a nuclear weapon."
The deal would halve crude oil exports to North Korea to 2 million barrels a year and refined oil exports to 250,000 barrels a year. The resolution also seeks to ban North Korea's export of "fossil fuels, mineral oils, and their distilled pce powder are estimated to be influenced by international political situation changes.