目前 ,聚羧酸鹽減水劑的合成方法主要有大單體共聚法、聚合后功能化法以及原位聚合與接枝法 3 種,而聚羧酸鹽減水劑合成中所需的不飽和羧酸類單體主要有馬來酸、馬來酸酐、丙烯酸及甲基丙烯酸等,其中馬來酸酐是近兩年來聚羧酸鹽減水劑合成研究中使用較多的一種。本文將對馬來酸酐在聚羧酸鹽減水劑合成中的作用和應(yīng)用情況進(jìn)行分析、論述 ,并對馬來酸酐在合成中的應(yīng)用提出建議。
At present, the synthesis methods of polycarboxylate superplasticizer mainly include macromonomer copolymerization, functionalization after polymerization and in-situ polymerization and grafting. The unsaturated carboxylic monomers needed in the synthesis of polycarboxylate superplasticizer mainly include maleic acid, maleic anhydride, acrylic acid and methacrylic acid, Maleic anhydride is one of the most widely used polycarboxylate superplasticizer in recent two years. This paper will analyze and discuss the function and application of maleic anhydride in the synthesis of polycarboxylate superplasticizer, and put forward suggestions on the application of maleic anhydride in the synthesis.
1 馬來酸酐與(甲基) 丙烯酸在聚羧酸鹽減水劑合成中的差別
The difference between maleic anhydride and (meth) acrylic acid in the synthesis of polycarboxylate superplasticizer
由于馬來酸酐與( 甲基) 丙烯酸分子結(jié)構(gòu)及化學(xué)活性的不同,導(dǎo)致它們在合成聚羧酸鹽減水劑的過程中有很多差別,主要體現(xiàn)在以下 3 方面。
Due to the difference of molecular structure and chemical activity between maleic anhydride and (meth) acrylic acid, there are many differences in the synthesis of polycarboxylate superplasticizer, which are mainly reflected in the following three aspects.
(1) (甲基) 丙烯酸極易發(fā)生均聚,馬來酸酐則不易。(甲基) 丙烯酸在進(jìn)行酯化的過程中,為了防止暴聚必須加入一定量的阻聚劑; 而馬來酸酐在進(jìn)行酯化的過程中則無需考慮。由于各自活性的不同 ,當(dāng)用( 甲基) 丙烯酸進(jìn)行共聚時, 一般不宜一次性投料,因為一次性投料后容易生成大量均聚物,甚發(fā)生暴聚,不利于反應(yīng)進(jìn)行;而當(dāng)用馬來酸酐進(jìn)行共聚時,其投料方式則可以任意選擇。
(1) (meth) acrylic acid is easy to homopolymerize, but maleic anhydride is not. In the esterification process of (meth) acrylic acid, a certain amount of inhibitor must be added in order to prevent the burst polymerization, while maleic anhydride does not need to be considered in the esterification process. Due to their different activities, when (meth) acrylic acid is used for copolymerization, it is generally not suitable for one-time feeding, because a large number of homopolymers are easily generated after one-time feeding, and even burst polymerization occurs, which is not conducive to the reaction; when maleic anhydride is used for copolymerization, the feeding mode can be arbitrarily selected.
(2) (甲氧基) 聚乙二醇與(甲基) 丙烯酸反應(yīng)生成單酯時有水生成,與馬來酸酐反應(yīng)生成單酯時則無水生成。由于酯化反應(yīng)屬于可逆反應(yīng),要想提高酯化產(chǎn)率就必須使其中一種反應(yīng)物過量或者除去副產(chǎn)物。由于(甲基) 丙烯酸與甲氧基聚乙二醇及聚乙二醇反應(yīng)生成單酯時有水生成,要想得到較高的酯化率,除了要調(diào)整酸醇比使其中一種反應(yīng)物過量,還要設(shè)法在反應(yīng)中不斷地排除副產(chǎn)物水;而馬來酸酐的酯化則只需調(diào)整酸醇比,就可以使酯化工藝得到簡化。
(2) When (methoxy) polyethylene glycol reacts with (meth) acrylic acid to form monoester, there is water, when it reacts with maleic anhydride to form monoester, there is no water. Because esterification is a reversible reaction, in order to improve the yield of esterification, one of the reactants must be excessive or the by-products must be removed. Due to the formation of water when (meth) acrylic acid reacts with methoxypolyethylene glycol and polyethylene glycol to form monoester, in order to obtain higher esterification rate, we need to adjust the acid alcohol ratio to make one of the reactants excessive, and try to constantly eliminate the by-product water in the reaction; while the esterification of Maleic anhydride only needs to adjust the acid alcohol ratio to simplify the esterification process.
(3) (甲基) 丙烯酸( 甲氧基) 聚乙二醇單酯活性高,而馬來酸酐(甲氧基) 聚乙二醇單酯活性較低。(甲基) 丙烯酸本身活性就很高,酯化后除了形成酯鍵外,其他結(jié)構(gòu)不變,因而其活性基本不受影響;而馬來酸酐結(jié)構(gòu)對稱，酯化后形成的單酯屬于順式1，2-雙取代，位阻效應(yīng)大，活性較低。同（1）相比，由于馬來酸酐（甲氧基）聚乙二醇單酯的活性低，共聚時其投料方式多種多樣，可以單獨(dú)一次性投料，可以與低活性的小單體一起一次性投料，可以與引發(fā)劑一起一次性投料，還可以與其他單體混合后連續(xù)滴加等。
(3) The activity of (methyl) acrylic acid (methoxy) polyethylene glycol monoester is higher than that of maleic anhydride (methoxy) polyethylene glycol monoester. The activity of (methyl) acrylic acid is very high, and its structure remains unchanged except ester bond after esterification, so its activity is basically unaffected; while the structure of maleic anhydride is symmetrical, and the monoester formed after esterification belongs to cis-1,2-disubstituted, with large steric hindrance effect and low activity. Compared with (1), due to the low activity of maleic anhydride (methoxy) polyethylene glycol monoester, there are various feeding methods during copolymerization, such as single feeding, one-time feeding together with low activity small monomer, one-time feeding together with initiator, continuous dropping after mixing with other monomers, etc.
