Production of a PMMA foam using cross-linking agents, regulators and blowing agents

A process for producing a polymethacrylate foam, said process comprising:

• polymerizing at a temperature between 20° C. and 100° C. a composition comprising from 0.01 to 2.0 wt % of an initiator, from 2 to 20 wt % of a blowing agent, and from 75 to 97.9 wt % of a mixture to obtain a polymerized composition, and
• subsequently foaming the polymerized composition at a temperature between 130° C. and 250° C.,
• wherein
• said mixture comprises
• from 79.70 to 99.995 mol % of MMA monomers, polymers, oligomers or a combination of polymers and oligomers of MMA,
• from 0 to 20 mol % of one or more MMA-copolymerizable monomers polymers, oligomers or a combination of polymers and oligomers of the MMA-copolymerizable monomers,
• from 0.002 to 0.5 mol % of crosslinker, and
• from 0.003 to 1.5 mol % of chain transfer agent, and
• a total amount of the polymers, oligomers or combination of polymers and oligomers of MMA and the polymers, oligomers or combination of polymers and oligomers of the MMA-copolymerizable monomers in said mixture is up to 80 wt %,
• wherein the chain transfer agent comprises pentaerythritol tetrathioglycolate.