A process for the manufacturing of a moulding composition comprising a copolymer, the process comprising the following steps: (a) a polymerisation step, in which a monomer mixture comprising from 80.0 to 99.9 wt.-%, preferably from 85.0 to 98.0 wt.-% of methyl methacrylate; and from 0.1 to 20.0 wt.-%, preferably from 2.0 to 8.0 wt.-% of compound represented by formula the substituent R 1 being a hydrogen atom or a hydrocarbon group having from 1 to 6 carbon atoms, optionally, from 0.0 to 19.9 wt.-%, preferably from 0.0 to 7.0 wt.-% of a monomer selected from methyl acrylate, ethyl acrylate or styrene; a polymerisation initiator; and optionally, a chain transfer agent undergoes radical copolymerisation in a polymerisation reactor to form a copolymer mixture comprising the copolymer and volatile components; (b) optionally, a step of heating the copolymer mixture, obtained in the polymerisation step (a) to a temperature from 100 °C to 300 °C in a heating unit; and (c) a degassing step of removal of the volatile components from the copolymer mixture to form a copolymer melt in a degassing unit, the degassing unit comprising at least one copolymer mixture feed port, at least one degassing device, the degassing device comprising at least one degassing zone, at least one gas outlet at least one copolymer melt outlet, and at least one melt outlet die, wherein temperature of the copolymer melt Tv, °C in the last degassing zone, in relation to the direction of conveying of the copolymer melt, temperature of the copolymer melt To, °C entering the melt outlet die and total residence time t, s of the copolymer melt between the last degassing zone, and the melt outlet die of the degassing unit are adjusted in such a way that the term 4.981 ⋅ 10 − 8 ⋅ t ⋅ exp 0.0517 ⋅ 1.5 ⋅ Tv + 0.5 ⋅ To / 2 is lower than 8, preferably lower than 6, even more preferably lower than 4, particularly preferably lower than 2. (a) a polymerisation step, in which a monomer mixture comprising from 80.0 to 99.9 wt.-%, preferably from 85.0 to 98.0 wt.-% of methyl methacrylate; and from 0.1 to 20.0 wt.-%, preferably from 2.0 to 8.0 wt.-% of compound represented by formula the substituent R 1 being a hydrogen atom or a hydrocarbon group having from 1 to 6 carbon atoms, optionally, from 0.0 to 19.9 wt.-%, preferably from 0.0 to 7.0 wt.-% of a monomer selected from methyl acrylate, ethyl acrylate or styrene; a polymerisation initiator; and optionally, a chain transfer agent undergoes radical copolymerisation in a polymerisation reactor to form a copolymer mixture comprising the copolymer and volatile components; from 80.0 to 99.9 wt.-%, preferably from 85.0 to 98.0 wt.-% of methyl methacrylate; and from 0.1 to 20.0 wt.-%, preferably from 2.0 to 8.0 wt.-% of compound represented by formula the substituent R 1 being a hydrogen atom or a hydrocarbon group having from 1 to 6 carbon atoms, optionally, from 0.0 to 19.9 wt.-%, preferably from 0.0 to 7.0 wt.-% of a monomer selected from methyl acrylate, ethyl acrylate or styrene; a polymerisation initiator; and optionally, a chain transfer agent undergoes radical copolymerisation in a polymerisation reactor to form a copolymer mixture comprising the copolymer and volatile components; (b) optionally, a step of heating the copolymer mixture, obtained in the polymerisation step (a) to a temperature from 100 °C to 300 °C in a heating unit; and (c) a degassing step of removal of the volatile components from the copolymer mixture to form a copolymer melt in a degassing unit, the degassing unit comprising at least one copolymer mixture feed port, at least one degassing device, the degassing device comprising at least one degassing zone, at least one gas outlet at least one copolymer melt outlet, a copolymer melt in a degassing unit, the degassing unit comprising at least one copolymer mixture feed port, at least one degassing device, the degassing device comprising at least one degassing zone, at least one gas outlet at least one copolymer melt outlet, at least one degassing zone, at least one gas outlet at least one copolymer melt outlet, and at least one melt outlet die, wherein temperature of the copolymer melt Tv, °C in the last degassing zone, in relation to the direction of conveying of the copolymer melt, temperature of the copolymer melt To, °C entering the melt outlet die and total residence time t, s of the copolymer melt between the last degassing zone, and the melt outlet die of the degassing unit are adjusted in such a way that the term 4.981 ⋅ 10 − 8 ⋅ t ⋅ exp 0.0517 ⋅ 1.5 ⋅ Tv + 0.5 ⋅ To / 2 is lower than 8, preferably lower than 6, even more preferably lower than 4, particularly preferably lower than 2.