Acrylic resin takes free radical reaction as the basic reaction, which can be divided into three processes: chain initiation, chain growth, and chain termination. At the same time, the whole process is accompanied by chain transfer. In the process of synthesizing thermoplastic acrylic resin, it is necessary to control the molecular weight and molecular weight distribution. Although the mechanical properties of the paint film will be significantly improved with the increase of the molecular weight, the solution viscosity of the paint film will also be significantly increased and decreased. The solid content, in addition, as the molecular weight increases, it is easy to reduce its solubility. The molecular weight of thermoplastic acrylic resins currently used commercially is around 80,000 to 90,000.

Molecular weight and molecular weight distribution are also easily affected by factors such as monomer feeding method and initiator type. When benzoyl peroxide is selected as the initiator, the benzoyl radical will decompose and become a highly active free radical, which is prone to branching reactions, depriving the hydrogen atoms of the monomer or polymer molecular chain, especially with As the temperature rises, above 130°C, a large number of branches will appear, increasing the molecular weight distribution. In terms of the monomer feeding method, the batch feeding method is selected to obtain a wider molecular weight distribution, and the semi-continuous dripping method and the continuous dripping method are selected.

The dropwise addition method can obtain a narrower molecular weight distribution. Generally, the solvent is first added to the reaction kettle and raised to the reaction temperature, and then the mixed solution is continuously added at a certain rate to maintain the normal concentration of monomer and initiator in the reaction kettle. If the monomer addition rate can maintain the normal polymerization temperature, the monomer concentration in the reactor is basically constant. In the reaction of olefinic monomer copolymers, it is also necessary to consider fully multi-faceted analysis of monomer reactivity ratio. If the reaction rate constants of the various monomers are relatively similar, the molecular chain structure can be regarded as a random distribution. If the reaction rate constants of the various monomers are very different, the batch feeding method will easily affect the uniformity of the molecular chain composition. Choose the semi-continuous dripping method and the continuous dripping method to control the monomer dripping speed and keep it consistent with the polymerization speed to obtain the average composition of the molecular chain.

Having introduced so much, I believe that everyone has a certain understanding of acrylic resins. If you want to know more about and cooperation matters, please contact Heshan KBORON New Material Co., Ltd.

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