IMPROVING THE PROPERTIES IN PMMA FOAMS BY USING METHACRYLIC AMIDES

Abstract

The present invention relates to novel PMMA foams and the production thereof. Here, polymers which have been obtained by copolymerization of methacrylamides such as N-isopropylmethacrylamide and without styrene are foamed. It has surprisingly been possible to establish that a stable, simple-to-produce PMMA foam which has very good properties, e.g. a very high compressive strength, and can be joined more simply to covering layers, especially in comparison with known PMMA foams, can be obtained according to the invention.

Claims

1. A process for producing a polymethacrylate foam, the process comprising: polymerizing a composition at a temperature of from 20 C. to 100 C. thereby producing a polymerized composition; and foaming the polymerized composition at a temperature of from 130 C. to 250 C., wherein the composition comprises from 0.2 to 2.0% by weight of an initiator, from 0 to 20% by weight of an unpolymerizable blowing agent, from 0 to 5% by weight of a chain-transfer agent and from 70 to 99.8% by weight of a monomer mixture consisting of from 70 to 95% by weight of MMA, from 0.1 to 5% by weight of an alkyl acrylate having from 1 to 12 carbon atoms in an alkyl radical, from 0 to 10% by weight of an alkyl methacrylate having from 2 to 12 carbon atoms in the alkyl radical, from 0.5 to 10% by weight of a methacrylamide, an N-alkylmethacrylamide and/or an N,N-dialkylmethacrylamide, from 0 to 10% by weight of a crosslinker, from 0 to 10% by weight of acrylic, methacrylic and/or itaconic acid and from 0 to 10% by weight of a hydroxy functional alkyl (meth)acrylate, where an entire monomer mixture or a part of the monomer mixture is optionally present to an extent of up to 80% by weight as polymer and/or oligomer at the beginning of the polymerizing.

2. The process according to claim 1, wherein the polymerization is carried out at a temperature of from 30 C. to 70 C., and the foaming is carried out at a temperature of from 150 C. to 230 C.

3. The process according to claim 1, wherein the crosslinker is at least one selected from the group consisting of a di(meth)acrylate, tri(meth)acrylate or tetra(meth)acrylate, allyl (meth)acrylate, triallyl cyanurate, and triallyl isocyanurate.

4. The process according to claim 1, wherein the alkyl methacrylate is entirely or partly tert-butyl methacrylate, and/or isopropyl methacrylate; and/or the alkyl acrylate is entirely or partly tert-butyl acrylate and/or isopropyl acrylate.

5. The process according to claim 4, wherein the monomer mixture comprises from 5 to 10% by weight of tert-butyl methacrylate, isopropyl methacrylate, tert-butyl acrylate and/or isopropyl acrylate, a proportion of the tert-butyl acrylate and the isopropyl acrylate being no more than 5% by weight, and the composition does not comprise any uncopolymerizable blowing agent.

6. The process according to claim 1, wherein the composition comprises from 0.5 to 1.5% by weight of the initiator, from 0 to 15% by weight of the unpolymerizable blowing agent, from 0 to 1% by weight of the chain-transfer agent and from 75 to 98.49% by weight of the monomer mixture, where the monomer mixture is composed of from 75 to 95% by weight of the MMA, from 0.5 to 2.5% by weight of the alkyl acrylate having from 1 to 8 carbon atoms in the alkyl radical, from 0 to 5% by weight of the alkyl methacrylate having from 2 to 8 carbon atoms in the alkyl radical, from 1 to 8% by weight of the methacrylamide, the N-alkylmethacrylamide and/or the N,N-dialkylmethacrylamide, from 0 to 5% by weight of dimethacrylate or trimethacrylate and from 0 to 8% by weight of acrylic, methacrylic and/or itaconic acid and is present to an extent of from 0 to 50% by weight as polymer and/or oligomer.

7. The process according to claim 1, wherein the monomer mixture comprises the N-alkylmethacrylamide having from 1 to 12 carbon atoms in the alkyl group and no methacrylamide or N,N-dialkylmethacrylamide.

8. The process according to claim 7, wherein the N-alkyl(meth)acrylamide is N-methylolmethacrylamide, 2 hydroxypropylmethacrylamide or N-isopropylmethacrylamide.

9. The process according to claim 1, wherein the polymerizing and/or the foaming are carried out stepwise at different temperatures.

10. The process according to claim 1, wherein the polymerizing and/or the foaming are carried out at least partly simultaneously.

11. A PMMA foam, wherein a solid part of the PMMA foam comprises at least 95% by weight of a polymer produced from a monomer mixture consisting of from 70 to 95% by weight of MMA, from 0.1 to 5% by weight of an alkyl acrylate having from 1 to 12 carbon atoms in an alkyl radical, from 0 to 10% by weight of an alkyl methacrylate having from 2 to 12 carbon atoms in the alkyl radical, from 0.5 to 10% by weight of an methacrylamide, an N-alkylmethacrylamide and/or an N,N-dialkylmethacrylamide, from 0 to 10% by weight of a crosslinker, from 0 to 10% by weight of acrylic, methacrylic and/or itaconic acid and from 0 to 10% by weight of a hydroxy-functional alkyl (meth)acrylate and the foam has a density of from 50 to 350 kg/m.sup.3.

12. The PMMA foam according to claim 11, wherein the PMMA foam has a density of from 75 to 250 kg/m.sup.3.

Description

EXAMPLES

General Method for Producing a PMMA Foam

[0037] The individual components of the formulation (for specific compositions, see the following tables) were weighed out in succession and subsequently mixed for about 20 minutes by means of a stirring motor, optionally with the use of an Ultraturrax, so as to give a homogeneous mixture. The polymerization of the mixture was carried out in a chamber which consisted of two glass plates having a size of 300400 mm and a peripheral seal. The chamber was subsequently heated in a waterbath and the contents were thus polymerized. A heat treatment was subsequently carried out. After polymerization and heat treatment had been concluded, foaming was carried out using the parameters specifically indicated in the tables.

[0038] Rewopol SB-DO 75 is a blowing agent which is added to aid separation of the polymerized PMMA from the glass plates used. This component has no influence on the production of the foam and is used here only for the specific examples to assist the process. Aerosil OX50 is added as nucleating agent. This gives a larger number of smaller pores. However, foams produced without use of a nucleating agent also have very good properties, so that the use of this component should also not be construed as restricting the invention. Pentaerythritol tetrathioglycolate is a chain-transfer agent, while 2,2-azobis(2,4-dimethylvaleronitrile) is an initiator.

Example 1

[0039]

TABLE-US-00001 TABLE 1 Composition and foaming conditions for Example 1 Weight used Composition Mixture [g] [% by weight] PMMA dissolved in MMA (20% by 1114.75 85.75 weight) tert-Butyl methacrylate 91.00 7.0 n-Butyl acrylate 13 1 Glycol dimethacrylate 0.78 0.06 N-Isopropylmethacrylamide 26 2 2,2-Azobis(2,4-dimethylvaleronitrile) 0.65 0.05 Pentaerythritol tetrathioglycolate 0.52 0.04 Rewopol SB-DO 75 1.3 0.1 Aerosil OX50 52 4 Total 1300 100 Plate thickness 10 mm Glass format 400 300 mm Polymerization 24 hours at 42 C. Heat treatment 4 hours at 115 C. Foaming 1 hour at 215 C. in a convection oven Compressive strength 2.7 MPa (density 125 kg/m.sup.3)

Example 2

[0040]

TABLE-US-00002 TABLE 2 Composition and foaming conditions for Example 2 Weight used Composition Mixture [g] [% by weight] PMMA dissolved in MMA (20% by 1075.75 82.75 weight) tert-Butyl methacrylate 91.00 7.0 n-Butyl acrylate 13 1 Glycol dimethacrylate 0.78 0.06 N-Isopropylmethacrylamide 65 5 2,2-Azobis(2,4-dimethylvaleronitrile) 0.65 0.05 Pentaerythritol tetrathioglycolate 0.52 0.04 Rewopol SB-DO 75 1.3 0.1 Aerosil OX50 52 4 Total 1300 100 Plate thickness 10 mm Glass format 400 300 mm Polymerization 24 hours at 42 C. Heat treatment 4 hours at 115 C. Foaming 1 hour at 215 C. in a convection oven Compressive strength 2.8 MPa (density 130 kg/m.sup.3)

Example 3

[0041]

TABLE-US-00003 TABLE 3 Composition and foaming conditions for Example 3 Weight used Composition Mixture [g] [% by weight] PMMA dissolved in MMA (20% by 1075.75 82.75 weight) tert-Butyl methacrylate 91.00 7.0 n-Butyl acrylate 13 1 Glycol dimethacrylate 0.78 0.06 N-Isopropylmethacrylamide 65 5 2,2-Azobis(2,4-dimethylvaleronitrile) 0.65 0.05 Pentaerythritol tetrathioglycolate 1.04 0.08 Rewopol SB-DO 75 1.3 0.1 Aerosil OX50 52 4 Total 1300 100 Plate thickness 10 mm Glass format 400 300 mm Polymerization 24 hours at 42 C. Heat treatment 4 hours at 115 C. Foaming 35 min at 230 C. Compressive strength 0.84 MPa (density 80 kg/m.sup.3)

Example 4

[0042]

TABLE-US-00004 TABLE 4 Composition and foaming conditions for Example 4 Weight used Composition Mixture [g] [% by weight] PMMA dissolved in MMA (20% by 1075.71 82.75 weight) tert-Butyl methacrylate 91.00 7.0 n-Butyl acrylate 13 1 Glycol dimethacrylate 0.78 0.06 N-Isopropylmethacrylamide 65 5 2,2-Azobis(2,4-dimethylvaleronitrile) 0.65 0.05 Pentaerythritol tetrathioglycolate 1.56 0.12 Rewopol SB-DO 75 1.3 0.1 Aerosil OX50 52 4 Total 1300 100 Plate thickness 10 mm Glass format 400 300 mm Polymerization 24 hours at 42 C. Heat treatment 4 hours at 115 C. Foaming Hot air microwave oven (Sharp), 200 C., microwave setting 1 Compressive strength 0.5 MPa (density 57 kg/m.sup.3)

Example 5

[0043]

TABLE-US-00005 TABLE 5 Composition and foaming conditions for Example 5 Weight used Composition Mixture [g] [% by weight] PMMA dissolved in MMA (20% by 1101.75 84.75 weight) tert-Butyl methacrylate 65.00 5.00 n-Butyl acrylate 13 1.00 Glycol dimethacrylate 0.78 0.06 N-Isopropylmethacrylamide 65 5 2,2-Azobis(2,4-dimethylvaleronitrile) 0.65 0.05 Pentaerythritol tetrathioglycolate 0.52 0.04 Rewopol SB-DO 75 1.3 0.1 Aerosil OX50 52.00 4 Total 1300 100 Plate thickness 10 mm Glass format 400 300 mm Polymerization 24 hours at 40 C. Heat treatment 4 hours at 115 C. Foaming 60 min at 215 C. Compressive strength 9.3 MPa (density 300 kg/m.sup.3)

Comparative Example 1

[0044]

TABLE-US-00006 TABLE 6 Composition and foaming conditions for Comparative Example 1 Weight used Composition Mixture [g] [% by weight] PMMA dissolved in MMA (20% by 1406.25 93.75 weight) tert-Butyl methacrylate 75.00 5.00 n-Butyl acrylate 15 1 Glycol dimethacrylate 0.90 0.06 2,2-Azobis(2,4-dimethylvaleronitrile) 0.75 0.05 Pentaerythritol tetrathioglycolate 0.60 0.04 Rewopol SB-DO 75 1.50 0.10 Total 1500.00 100.00 Plate thickness 10 mm Glass format 400 300 mm Polymerization 24 hours at 42 C. Heat treatment 4 hours at 115 C. Foaming 1 h at 215 C. Compressive strength 1.25 MPa (density 112 kg/m.sup.3)

Comparative Example 2

[0045]

TABLE-US-00007 TABLE 7 Composition and foaming conditions for Comparative Example 2 Weight used Composition Mixture [g] [% by weight] PMMA dissolved in MMA (20% by 1140.75 87.75 weight) tert-Butyl methyl ether 91.00 7.00 n-Butyl acrylate 13.00 1.00 Glycol dimethacrylate 0.78 0.06 2,2-Azobis(2,4- 0.65 0.05 dimethylvaleronitrile) Pentaerythritol tetrathioglycolate 0.52 0.04 Rewopol SB-DO 75 1.30 0.10 Aerosil OX50 52.00 4.00 Total 1300.00 100.00 Plate thickness 10 mm Glass format 400 300 mm Polymerization 24 hours at 42 C. Heat treatment 4 hours at 115 C. Foaming 20 min at 215 C. Compressive strength 0.7 MPa (density 90 kg/m.sup.3)

Comparative Example 3

[0046]

TABLE-US-00008 TABLE 8 Composition and foaming conditions for Comparative Example 3 Weight used Composition Mixture [g] [% by weight] PMMA dissolved in MMA (20% by 1140.75 87.75 weight) tert-Butyl methyl ether 91.00 7.00 n-Butyl acrylate 13.00 1.00 Glycol dimethacrylate 0.78 0.06 2,2-Azobis(2,4-dimethylvaleronitrile) 0.65 0.05 Pentaerythritol tetrathioglycolate 0.52 0.04 Rewopol SB-DO 75 1.30 0.10 Aerosil OX50 52.00 4.00 Total 1300.00 100.00 Plate thickness 10 mm Glass format 400 300 mm Polymerization 24 hours at 42 C. Heat treatment 4 hours at 115 C. Foaming 30 min at 230 C. Compressive strength 0.35 MPa (density 61 kg/m.sup.3)

Comparative Example 4

[0047]

TABLE-US-00009 TABLE 9 Composition and foaming conditions for Comparative Example 4 Weight used Composition Mixture [g] [% by weight] PMMA dissolved in MMA (20% by 1404.00 87.75 weight) tert-Butyl methacrylate 80.00 5.00 n-Butyl acrylate 16.00 1.00 Glycol dimethacrylate 0.96 0.06 2,2-Azobis(2,4-dimethylvaleronitrile) 0.80 0.05 Pentaerythritol tetrathioglycolate 0.64 0.04 Rewopol SB-DO 75 1.60 0.10 Aerosil OX50 96.00 6.00 Total 1600.00 100.00 Plate thickness 10 mm Glass format 400 300 mm Polymerization 24 hours at 42 C. Heat treatment 4 hours at 115 C. Foaming Irradiation using IR radiators to the desired density Compressive strength 1.38 MPa (density 140 kg/m.sup.3)

Results

[0048]

TABLE-US-00010 TABLE 10 Comparison of the mechanical properties Compressive Density strength [kg/m.sup.3] [MPa] Example 1 125 2.7 Example 2 130 2.8 Example 3 80 0.84 Example 4 57 0.5 Example 5 300 9.3 Comparative Example 1 112 1.25 Comparative Example 2 90 0.7 Comparative Example 3 61 0.35 Comparative Example 4 140 1.38

[0049] The comparative examples were produced without addition of an (alkyl)methacrylamide to the monomer mixture. The results in Table 10 impressively show, taking into account the respective density, the surprising positive effect which this monomer component has on the compressive strength of the future foam.