The commonly used surfactants are mostly low molecular weight compounds with molecular weights of hundreds. With the in-depth research in many hot areas, such as enhanced oil recovery, drug carriers and controlled release, biological simulation, polymer LB films, medical polymer materials (anticoagulant), lotion polymerization, etc., the requirements for surfactants are becoming increasingly diversified and high-performance, and surfactant polymers have become the focus of attention.
Generally, the substances with molecular weight over thousands and surface activity are called macromolecular surfactants. Similar to ordinary surfactants, there is no standard classification for polymeric surfactants. Generally, according to the classification of low molecular surfactants and their ionic properties in water, they can be divided into anionic, cationic, zwitterionic and non-ionic surfactants. According to whether micelle is formed in solution, it can be divided into polysoap and water-soluble polymer surfactant.
Polysoap
The vast majority of polysoaps are charged, which is similar to polyelectrolytes. In fact, most of the polysoaps are the products of hydrophobic modification of polyelectrolytes, which are generally insoluble in water. At present, the following types of polysoaps have been synthesized (in the formula, R represents long chain alkyl):
Water soluble polymer surfactant
The polymer surfactants that do not form micelles in solution are generally water-soluble polymer surfactants. According to its source, it can be divided into natural, semi synthetic and synthetic polymer surfactants.
Natural polymers, such as various kinds of gum, starch, microbial fermentation polysaccharides, etc;
Semi synthetic polymers are various polymers obtained by chemical modification of starch, cellulose and protein, such as cationic starch, methyl cellulose, etc;
Synthetic polymers are polymers obtained by polymerization of petrochemical derived polymerization monomers, such as polyacrylamide derivatives, polyacrylic acid, etc.
Classification of polymeric surfactants
According to their ionic properties in water, they can be divided into anionic, cationic, zwitterionic and non-ionic types.
Anionic polymer surfactant
(1) Typical carboxylic acid type polymers include polyacrylic acid and its copolymer, butyric acid and its copolymer, acrylic acid maleic anhydride copolymer and some of their saponified products.
(2) Typical sulfate type polymers are:
(3) Sulfonic acid type includes partially sulfonated polystyrene, benzenesulfonic acid formaldehyde condensate, naphthalenesulfonic acid formaldehyde condensate, sulfonated polybutadiene, etc. Lignosulfonate is also a kind of sulfonated polymer surfactant. Typical sulfonic acid polymer surfactants are as follows:
Cationic polymer surfactant
(1) Amine salts or polyamines such as polyvinylimine, polyvinylpyrrolidone, polymaleimide and its derivatives. Typical polymers are:
(2) Quaternary ammonium salts such as quaternized polyacrylamide, polyvinylpyridinium salt, polydimethylamine epichlorohydrin, etc. Quaternary ammonium polymer surfactants show positive electricity in acidic, neutral and alkaline aqueous media. Representative products include:
Amphoteric polymer surfactant
The main varieties include acrylic acid vinyl pyridine copolymer, acrylic acid, cationic acrylate copolymer, amphoteric polyacrylamide, etc., such as:
Nonionic polymer surfactant
The main varieties include polyvinyl alcohol and its partially esterified or acetalized products, such as modified polyacrylamide, maleic anhydride copolymer, polyacrylate, polyether, polyethylene oxide propylene oxide, water-soluble phenolic resin, amino resin, etc.
Structure and Properties of Polymer Surfactants
The surface activity of polymer surfactant depends on the macromolecular morphology in solution, and the molecular morphology is closely related to such factors as the amphiphilic chemical molecular structure of polymer, composition ratio and the relative molecular weight of macromolecule.
Block surfactant
Multiblock hydrophobic segments are distributed on the main chain of macromolecules. Proper hydrophobic hydrophilic sequence length will effectively prevent self association (forming single molecular micelles) or intermolecular association (multi molecular association) of hydrophobic segments
Comb surfactant
Comb surfactants have the advantages of easy preparation and variety. For example, the surfactant obtained by homopolymerization or copolymerization of amphoteric and amphiphilic monomers shows different branch chain chemical structures according to different positions of hydrophobic and hydrophilic groups
Because there are hydrophilic groups on the branch chain, which hinder the aggregation and association of hydrophobic chain segments, even in the generated micelles, compared with the micelles with generally formed tight cores, the interior is relatively loose, and there are still a large number of water molecules, so they can have high surface activity; At the same time, due to the configuration, the amphiphilic branched chain can prevent the association of the hydrophobic main chain composed of methylene and methylene, so that it can participate in the adsorption of the interface.
The research shows that any factor that increases the rigidity of molecular chains is conducive to the stretching of macromolecules in solution and may improve the surface activity of polymers on the premise of maintaining solubility.
Application of Polymer Surfactants
Application in pharmaceutical industry:
Because of their excellent surface activity, block and graft polymer surfactants have been widely used in pharmaceutical industry, such as drug carriers, drug emulsifiers, dispersion solubilizers, wetting agents, etc. In addition, polymeric surfactants are also widely used in drug analysis as phase transfer catalysts in drug synthesis.
Application in petroleum industry:
The produced crude oil contains solid paraffin, which leads to poor fluidity of crude oil, and brings certain difficulties to the production, storage, transportation, processing and other processes of this kind of curable high viscosity oil. This problem can be solved by adding pour point depressant or liquidity improver of crude oil. The dispersity of oil soluble polymer surfactant can further improve the flow improver and prevent the formation of precipitation of paraffin in fuel oil during transportation and storage.
Application in textile printing and dyeing industry:
Polyether polymer surfactants are often used as low foam detergents, emulsifiers, dispersants, defoamers, antistatic agents, wetting agents, printing and dyeing agents, etc; Polyvinyl alcohol and other macromolecular compounds are widely used as thickeners and protective colloids in the preparation of lotion printing and dyeing auxiliaries; Cellulose derivatives such as carboxymethyl cellulose are used as detergents to prevent re contamination; Lignosulfonate and phenolic condensate sulfonate are used as dispersants of insoluble dyes.
Application in paper industry:
Polymer surfactant has been paid more and more attention in recent years because of its unique and important role in improving paper properties and improving paper machine efficiency. Some studies have shown that maleic acid monoesters are prepared from polyethylene glycol and maleic anhydride with different relative molecular weights, and then polymerized with acrylic acid to generate maleic acid monoesters and acrylic acid copolymers. The deinking effect is remarkable.