Preparation of an Acrylic Copolymer in Methyl Ethyl Ketone

Benzoyl peroxide is dissolved in a mixture of methyl methacrylate and ethyl acrylate. 

40% of the monomer mixture and methyl ethyl ketone are charged to a reactor set for reflux. 

The reactor is heated to 9CP C and ten minutes after reflux starts, the balance of the monomer mixture is added at a constant rate over a period of two and a half hours. 

Reflux is maintained for a further two hours when a polymer with a solids content of 58% is obtained, corresponding to a conversion of 98.5%. If the non-volatile content is less than 58%, then additional shots of benzoyl peroxide are added. 

The use of a delayed addition of part of the monomer is very common in industrial practice. In this instance it allows a relatively constant monomer concentration to be maintained. The addition of initiator over the same two and a half hour period gives a slight increase in the rate of radical production, which will increase the rate of polymerisation whilst reducing the molecular weight. The reactivity ratios of 2.0 and 0.26, for methyl methacrylate and ethyl acrylate respectively, means that the initial copolymer will be rich in methyl methacrylate. The delayed addition of monomer mixture means that the range of copolymer distribution will be narrower than would be the case if all the monomer were added initially. The initial reflux temperature is about 85 C and will rise slightly to about 90°C towards the end of the polymerisation. 

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