Method for the preparation of copolymers of alkyl methacrylates and maleic anhydride

1. A sulfur-free copolymer, consisting of as copolymerized units one or more alkyl methacrylates, maleic anhydride, and from greater than 0 wt % to 10 wt % of an ethylenically unsaturated monomer selected from the group consisting of acrylic acid, methacrylic acid, methacrylamide, hydroxyethyl methacrylate, vinylpyrrolidone, vinylmalonic acid, styrene, vinyl alcohol and vinyl acetate;

wherein

a number average molecular weight of the copolymer is in the range of 3000 to 9000 g/mol,

the number average molecular weight being determined by gel permeation chromatography against poly(methyl methacrylate) standards,

a polydispersity index of the copolymer is in the range of 1 to 5, the polydispersity index being determined by gel permeation chromatography against poly(methyl methacrylate) standards, and

a molar ratio of the one or more alkyl methacrylates to the maleic anhydride in the sulfur-free copolymer is in the range of from 10:1 to 1:1, corresponding to the total molar amounts of the one or more alkyl methacrylates and maleic anhydride used for the preparation of the sulfur-free copolymer; and

a mass fraction of alkyl methacrylates in sequences of three or more consecutive monomer units relative to the total amount of alkyl methacrylates in the copolymer is lower than 10 wt-%;

and

wherein the sulfur free copolymer is obtained by a process, comprising:

a) providing an initial reaction solution comprising a portion of the one or more alkyl methacrylates, a portion of the maleic anhydride, a portion of the initiator and a portion of the solvent;

b) heating the initial solution to a reaction temperature;

c) preparing a reaction mixture by adding a first feed solution comprising a further portion of the maleic anhydride and a further portion of the solvent to the initial reaction solution, and without any initiator;

d) adding a second feed solution comprising a further portion of the one or more alkyl methacrylates, and a further portion of the radical initiator to the initial reaction solution at the reaction temperature, and

e) adding a final portion of the initiator after addition of the feed solutions has been completed;

wherein

the method does not comprise a sulfur chain transfer agent,

a molar ratio of the total of the portions of alkyl methacrylate monomer employed in the reaction to the total of the portions of the maleic anhydride employed in the reaction is from 10:1 to 1:1,

the additions of both first and second feed solutions are started at the same time, and the duration of the additions of the first and second feed solutions are adjusted such that addition of the first feed solution is completed faster than the addition of the second feed solution.

2. The sulfur-free copolymer according to claim 1 , wherein equimolar amounts of the one or more alkyl methacrylates and maleic anhydride are present in the sulfur free copolymer, corresponding to the total molar amounts of the one or more alkyl methacrylates and maleic anhydride used for the preparation of the sulfur-free copolymer.