Production of a PMMA foam using cross-linking agents, regulators and blowing agents
The present invention relates to novel types of PMMA foams and also to the production thereof. The recipes used in the production process include particularly crosslinkers and chain transfer agents as recipe constituents, mostly in low concentrations, in addition to suitable blowing agents. It was found that, surprisingly, the invention provides a simple-to-produce stable PMMA foam having very good properties.
1. 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.
2. The process according to claim 1 , wherein the composition comprises
from 0.2 to 1.5 wt % of the initiator,
from 3 to 15 wt % of the blowing agent and
from 80 to 96.8 wt % of the mixture,
wherein
said mixture comprises
from 89.85 to 99.988 mol % of the MMA monomers, polymers, oligomers or combination of polymers and oligomers of MMA,
from 0 to 10 mol % of one or more the MMA-copolymerizable monomers, polymers, oligomers or combination of polymers and oligomers of the MMA-copolymerizable monomers,
from 0.005 to 0.3 mol % of the crosslinker, and
from 0.006 to 1 mol % of the chain transfer agent; and
a total amount of the polymers and/or oligomers of MMA and the polymers and/or oligomers of the MMA-copolymerizable monomers in said mixture is up to 50 wt %.
3. The process according to claim 1 , wherein the temperature is between 30° C. and 70° C. for the polymerization and between 150° C. and 230° C. for the foaming.
4. The process according to claim 1 , wherein the crosslinker comprises a di-, tri- or tetra(meth)acrylate, allyl (meth)acrylate, triallyl cyanurate, triallyl isocyanurate, or a mixture containing two or more thereof.
5. The process according to claim 1 , wherein
the copolymerizable monomers comprise (meth)acrylic acid, methyl acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, styrene, (meth)acrylamide, an N-alkyl(meth)acrylamide having one to 12 carbon atoms in the alkyl group, a hydroxyalkyl (meth)acrylate having one to 4 carbon atoms in the alkyl group, or a mixture of two or more thereof, and
a total fraction of n-butyl (meth)acrylate and n-propyl (meth)acrylate, when present, does not exceed 3 wt %.
6. The process according to claim 1 , wherein the polymerizing and the foaming are effected stagewise at different temperatures.
7. The process according to claim 1 , wherein the polymerizing and the foaming are effected simultaneously to some extent at least.
8. The process according to claim 1 , wherein the blowing agent comprises tert-butyl (meth)acrylate, isopropyl (meth)acrylate, tert-butanol, isopropanol, tort-butyl methyl ether, poly(tert-butyl (meth)acrylate), or a mixture of two or more thereof.