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

Abstract

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.

Claims

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.

Description

EXAMPLES

Comparative Example 1

(1) In this example, a PMMA foam was produced from a composition containing a chain transfer agent but no crosslinker.

(2) A mixture of 281.13 g of a polymethacrylate prepared exclusively from MMA, 1124.52 g of MMA, 0.75 g of 2,2-azobis(2,4-dimethylvaleronitrile), 3.60 g of pentaerythritol tetrathioglycolate as chain transfer agent, 15.00 g of n-butyl acrylate and 75.00 g of tert-butyl methacrylate was polymerized at 42 C. for 24 h between two 400 mm*300 mm glass plates separated from each other by 10 mm and laterally sealed off by a rubber strip. This was followed by 4 h conditioning at 11500. After removal of the glass plates, the PMMA slab obtained was finally foamed in an oven at 215 C. for 1 h. A coarse-cell, very irregular foam was obtained.

Example 1

(3) In this example, which is in accordance with the present invention, a PMMA foam was produced from a composition containing a relatively small amount of chain transfer agent and a relatively small amount of crosslinker.

(4) A mixture of 281.25 g of a polymethacrylate prepared exclusively from MMA, 1125.00 g of MMA, 0.75 g of 2,2-azobis(2,4-dimethylvaleronitrile), 0.60 g of pentaerythritol tetrathioglycolate as chain transfer agent, 15.00 g of n-butyl acrylate, 75.00 g of tert-butyl methacrylate, 1.50 g of Rewopol SB-DO 75 release agent and 0.90 g of ethylene glycol dimethacrylate as crosslinker was polymerized at 42 C. for 24 h between two 400 mm*300 mm glass plates separated from each other by 10 mm and laterally sealed off by a rubber strip. This was followed by 4 h conditioning at 115 C. After removal of the glass plates, the PMMA slab obtained was finally foamed in an oven at 215 C. for 1 h. The mixture foamed very well and the cells were considerably finer than in the foam obtained in according to Comparative Example 1.

(5) The release agent is known from experience not to affect the polymerization or the foaming operation, and solely serves to facilitate removal of the glass plates from the polymer slab.

Examples 2 to 5

(6) In this example, which is in accordance with the present invention, a PMMA foam was produced from various compositions containing varying amounts of chain transfer agent as well as a relatively small amount of crosslinker.

(7) Mixtures consisting in each case of a polymethacrylate (see table 1 for the amount) prepared exclusively from MMA, MMA (see table 1 for the amount), 0.75 g of 2,2-azobis-(2,4-dimethylvaleronitrile), pentaerythritol tetrathioglycolate as chain transfer agent (see table 1 for the amount), 15.00 g of n-butyl acrylate, 75.00 g of tert-butyl methacrylate, 1.50 g of Rewopol SB-DO 75 and 0.90 g of ethylene glycol dimethacrylate as crosslinker were polymerized at 42 C. for 24 h between two 400 mm*300 mm glass plates separated from each other by 10 mm and laterally sealed off by a rubber strip. This was followed by 4 h conditioning at 115 C. After removal of the glass plates, the PMMA slab obtained was finally foamed in an oven at 205 C. for 1 h. All the four mixtures foamed up very well. The greater the amount of chain transfer agent used, the faster the foaming.

(8) The cells were distinctly finer than in the foam obtained as per Comparative Example 1.

(9) TABLE-US-00001 TABLE 1 Component Example 2 Example 3 Example 4 Example 5 PMMA 281.25 g 281.19 g 281.13 281.01 g MMA 1125.00 g 1124.76 g 1124.52 1124.04 g Pentaerythritol 0.60 g 0.90 g 1.20 g 1.80 g tetrathioglycolate

Example 6

(10) In this example, which is in accordance with the present invention, a PMMA foam was produced from a composition containing a chain transfer agent and a crosslinker. No blowing agent was used here that is released from a copolymerizable constituent of the composition, but is freely present therein.

(11) A mixture of 281.25 g of a polymethacrylate prepared exclusively from MMA, 1125.00 g of MMA, 0.75 g of 2,2-azobis(2,4-dimethylvaleronitrile), 0.60 g of pentaerythritol tetrathioglycolate as chain transfer agent, 15.00 g of n-butyl acrylate, 75.00 g of isopropanol, 1.50 g of Rewopol SB-DO 75 and 0.90 g of ethylene glycol dimethacrylate as crosslinker was polymerized at 42 C. for 24 h between two 400 mm*300 mm glass plates separated from each other by 10 mm and laterally sealed off by a rubber strip. This was followed by 4 h conditioning at 115 C. After removal of the glass plates, the PMMA slab obtained was finally foamed in an oven at 215 C. for 1 h. Avery efficiently foamed material having rather coarse cells was obtained.

Comparative Example 2

(12) In this example, a PMMA foam was produced from a composition containing a chain transfer agent but no crosslinker.

(13) A mixture of 162.21 g of a polymethacrylate prepared exclusively from MMA, 648.56 g of MMA, 0.85 g of 2,2-azobis(2,4-dimethylvaleronitrile), 0.68 g of pentaerythritol tetrathioglycolate as chain transfer agent and 37.40 g of tert-butyl methyl ether was polymerized at 50 C. for 3 h between two 400 mm*300 mm glass plates separated from each other by 10 mm and laterally sealed off by a rubber strip. This was followed by 4 h conditioning at 115 C. After removal of the glass plates, the PMMA slab obtained was finally foamed in an oven at 215 C. for 1 h. The sample could not be foamed. All that happened is that small bubbles developed in the polymer.

Comparative Example 3

(14) In this example, a PMMA foam was produced from a composition containing smaller amounts of chain transfer agent than in Comparative Example 2 and no crosslinker. The further change from Comparative Example 2 was a distinct increase in the amount of blowing agent.

(15) A mixture of 162.00 g of a polymethacrylate prepared exclusively from MMA, 648.00 g of MMA, 0.85 g of 2,2-azobis(2,4-dimethylvaleronitrile), 0.34 g of pentaerythritol tetrathioglycolate as chain transfer agent and 65.50 g of tert-butyl methyl ether was polymerized at 50 C. for 3 h between two 400 mm*300 mm glass plates separated from each other by 10 mm and laterally sealed off by a rubber strip. This was followed by 4 h conditioning at 115 C. After removal of the glass plates, the PMMA slab obtained was finally foamed in an oven at 215 C. for 1 h. The sample could not be foamed. All that happened is that small bubbles developed in the polymer.

Comparative Example 4

(16) In this example, a PMMA foam was produced from a composition containing smaller amounts of chain transfer agent and no crosslinker. The blowing agent was varied as compared with Comparative Example 2.

(17) A mixture of 167.00 g of a polymethacrylate prepared exclusively from MMA, 668.00 g of MMA, 0.85 g of 2,2-azobis(2,4-dimethylvaleronitrile), 0.34 g of pentaerythritol tetrathioglycolate as chain transfer agent and 31.88 g of tert-butanol was polymerized at 50 C. for 3 h between two 400 mm*300 mm glass plates separated from each other by 10 mm and laterally sealed off by a rubber strip. This was followed by 4 h conditioning at 115 C. After removal of the glass plates, the PMMA slab obtained was finally foamed in an oven at 215 C. for 1 h. The sample could not be foamed. All that happened is that small bubbles developed in the polymer.