Description of Acrylic Resin
1 Introduction
Since the introduction of acrylic polymers, after decades of efforts, people have made great progress in the coatings and related industries. This is because acrylic polymers have improved flexibility and adhesion compared to polyvinyl acetate emulsions, phenolic resins, and styrene-butadiene latex, and are moderate in cost. In addition, its outdoor durability, including resistance to UV degradation, has been significantly improved, and thus has been applied in many fields. In many ways, "acrylic polymers" are completely comparable to many high-performance polymers.
2, chemical properties and manufacturing
2.1 monomer
Acrylic monomers include acrylates and methacrylates. Methyl esters, ethyl esters, isobutyl esters, n-butyl esters, 2-ethylhexyl esters, octyl esters, lauryl esters and octadecyl esters are commonly used varieties. These esters may include such functional groups as hydroxyl (eg, hydroxyethyl methacrylate), amino (eg, dimethylaminoethyl methacrylate), amide (acrylamide), and the like. In addition, it also contains unesterified carboxylic acid functional monomer, acrylic monomer may be multifunctional (such as trimethylolpropane triacrylate, butenyl diethylene glycol diacrylate, etc.). When designing a special polymer system, polymer chemists have many choices of monomers.
In general, the choice of comonomer depends on the properties it imparts to the polymer. For example, a monomer with a low glass transition temperature is used to increase the bond strength, such as butyl acrylate or 2-ethylhexyl acrylate. Acrylic and methacrylic carboxyl groups also tend to increase the polymer's adhesion. Cohesive strength is usually conferred by harder acrylic monomers such as methyl methacrylate and methyl acrylate. In addition, the molecular weight is also an important factor affecting the performance of the polymer, and the two parameters of adhesive strength and cohesive energy must be carefully regulated by the polymer chemist.
When subsequent reactions require functional groups, monomers such as hydroxyethyl methacrylate or N-methylolacrylamide must be added. Hydroxyl groups can be cross-linked with melamine and epoxy curing agents. Likewise, other functional groups (acid groups, amino groups, amide groups, etc.) can be added.
2.2 Polymerization method
2.2.1 Bulk polymerization
As the name suggests, bulk polymerization initiates the polymerization of acrylic monomers in the absence of a solvent and only the monomers themselves. Peroxides and azo initiators are generally used. The main problem in the reaction process is a significant increase in viscosity after the conversion rate approaches 30%. In general, the viscosity is controlled using a vigorously agitated mixer and a temperature in excess of 150°C.
The well-known Tromssdirf gel effect can be observed at high conversion rates, which can lead to an exothermic increase in molecular weight and polydispersity.
2.2.2 Solution Polymerization The addition of a solvent to the bulk polymerization formulation makes it easier to control the viscosity at high conversions. In addition, peroxides (such as benzoyl peroxide, lauroyl peroxide) or (azobisisobutyronitrile) initiators are used, and mercaptans and halogenated hydrocarbons are used to adjust the molecular weight. To a certain degree, most solvents also play a role. The role of chain transfer agent. The acrylic polymer, which is usually prepared by solution polymerization, has a molecular weight of less than 100,000.
2.2.3 Suspension Polymerization
As the name implies, the suspension polymerization process uses a suspending agent to stabilize the monomer droplets in the continuous phase, which is usually water. With continuous stirring, polymerization is carried out in suspended droplets using oil-soluble initiators such as peroxides and azo compounds. In fact, the droplets of polymerization show the kinetics of bulk polymerization because each droplet is actually a small bulk reactor with an aqueous phase, and the continuous aqueous phase of the species acts as a heat sink. Typical suspending agents include polyvinyl alcohol, polyacrylic acid, and hydroxyethyl cellulose. As expected. Suspension polymerization often limits the monomer composition of the glass whose Tg is near or greater than room temperature. Otherwise, gels are easily generated in small monomer beads. After polymerization, the suspension polymerized particles are dehydrated, washed to remove impurities such as suspending agents and electrolytes, and then dried.
2.2.4 Emulsion polymerization
Emulsion polymerization may be the most complicated polymerization process, and it has received a lot of research and description. As the name implies, emulsion polymerization uses an emulsifier to suspend the acrylic monomer in a continuous aqueous phase and use a water-soluble initiator to initiate polymerization. Some common initiators are redox systems such as ammonium persulfate, potassium persulfate, hydrogen peroxide, and tert-butyl hydroperoxide-sodium formaldehyde sulfoxylate.
Polymerization is generally thought to begin in the aqueous phase, and the growing free radicals enter the monomer-containing micelles to continue polymerization. The diffusion of the growing micelle* monomer droplets then feeds the new monomer.
Source: China Tobacco Packaging Ink Information Network
