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 at least a portion of a composition at a temperature in a range of from 20° C. to 100° C., thereby producing a polymerized composition; and foaming at least a portion of the polymerized composition at a temperature in a range of from 130° C. to 250° C., wherein the composition comprises an initiator in a range of from 0.2 to 2.0 wt. %; an unpolymerizable blowing agent in a range of from 0 to 20 wt. %; a chain-transfer agent in a range of from 0 to 5 wt. %; and a monomer mixture in a range of from 70 to 99.8% by weight, wherein the monomer mixture consists of, optionally in at least partially polymerized form, MMA in a range of from 70 to 95 wt. %, alkyl acrylate(s) having 1 to 12 carbon atoms the alkyl radical in a range of from 0.1 to 5 wt. %, alkyl methacrylate(s) having from 2 to 12 carbon atoms in the alkyl radical in a range from 0 to 10 wt. %, a methacrylamide, an N-alkylmethacrylamide an N,N-dialkylmethacrylamide, or a mixture of two or more of any of these, in a range of from 0.5 to 10 wt. %, crosslinker(s) in a range of from 0 to 10 wt. %, acrylic acid, methacrylic acid, and/or itaconic acid in a range of from 0 to 10 wt. %, and hydroxy functional alkyl (meth)acrylate(s) in a range of from 0 to 10 wt. %.

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

3. The process of 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 of claim 1, wherein the alkyl methacrylate comprises tert-butyl methacrylate and/or isopropyl methacrylate.

5. The process of claim 4, wherein the monomer mixture contains from 5 to 10 wt. % of tert-butyl methacrylate, isopropyl methacrylate, tert-butyl acrylate, and/or isopropyl acrylate, wherein when the monomer mixture contains tert-butyl acrylate, it is present in a mixture with at least one of tert-butyl methacrylate, isopropyl methacrylate, and/or isopropyl acrylate and the tert-butyl acrylate is present in an amount of no more than 5 wt. %, and when the monomer mixture contains isopropyl acrylate, it is present in a mixture with at least one of tert-butyl methacrylate, isopropyl methacrylate, and/or tert-butyl acrylate, and the isopropyl acrylate is present in an amount of no more than 5 wt. %, and the composition does not comprise any uncopolymerizable blowing agent.

6. The process of claim 1, wherein the composition comprises from 0.5 to 1.5 wt. % of the initiator, from 0 to 15 wt. % of the unpolymerizable blowing agent, from 0 to 1 wt. % of the chain-transfer agent, and from 75 to 98.49 wt. % of the monomer mixture, wherein the monomer mixture is present in a range of from 0 to 50 wt. % in at least partially polymerized form, and wherein the monomer mixture contains the MMA in a range of from 75 to 95 wt. %, the alkyl acrylate comprising alkyl acrylate comprising 1 to 12 carbon atoms in the alkyl radical, as an alkyl acrylate comprising from 1 to 8 carbon atoms in the alkyl radical, in a range of from 0.5 to 2.5 wt. %, the alkyl methacrylate comprising from 2 to 12 carbon atoms in the alkyl radical, as an alkyl methacrylate comprising from 2 to 8 carbon atoms in the alkyl radical, in a range of from 0 to 5 wt. %, the methacrylamide, N-alkylmethacrylamide, and/or N,N-dialkylmethacrylamide in a range of from 1 to 8 wt. %, dimethacrylate or trimethacrylate in a range of from 0 to 5 wt. %, and the acrylic acid, methacrylic acid, and/or itaconic acid as the crosslinker(s) in a range of from 0 to 8 wt. %.

7. The process of claim 1, wherein the monomer mixture contains the N-alkylmethacrylamide, wherein the N-alkylacrylamide has from 1 to 12 carbon atoms in the alkyl group, and wherein no methacrylamide or N,N-dialkylmethacrylamide are present.

8. The process of claim 1, wherein the methacrylamide is N-methylolmethacrylamide, 2 hydroxypropylmethacrylamide or N-isopropylmethacrylamide.

9. The process of claim 1, wherein the polymerizing polymerizes the entire composition before the foaming step occurs.

10. The process of claim 1, wherein the polymerizing polymerizes only a portion of the composition, and the foaming step comprises additional polymerization of the composition.

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

12. The foam of claim 11, having a density in a range of from 75 to 250 kg/m.sup.3.

13. The process of claim 1, wherein the monomer mixture is present to an extent of up to 80 wt. % in at least partially polymerized form at the beginning of the polymerizing.

14. The process of claim 1, wherein the monomer mixture is present to an extent of up to 70 wt. % in at least partially polymerized form at the beginning of the polymerizing.

15. The process of claim 1, wherein the monomer mixture is present to an extent of up to 50 wt. % in at least partially polymerized form at the beginning of the polymerizing.

16. The process of claim 1, wherein the alkyl acrylate(s) are a mixture of alkyl acrylates that includes tert-butyl acrylate and/or isopropyl acrylate.

17. The process of claim 1, wherein the alkyl acrylate(s) is entirely tert-butyl acrylate and/or isopropyl acrylate.

18. The process of claim 1, wherein the alkyl acrylate(s) is entirely tert-butyl acrylate.

19. The process of claim 1, wherein the alkyl acrylate(s) is entirely isopropyl acrylate.

20. The process of claim 1, wherein the unpolymerizable blowing agent comprises tert-butanol, n-heptane, MTBE, methyl ethyl ketone, a C1-C4 alcohol, water, urea, methylal, or a mixture thereof.

Description

EXAMPLES

(1) General Method for Producing a PMMA Foam

(2) 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 300×400 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.

(3) 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

(4) 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

(5) 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

(6) 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

(7) 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

(8) 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

(9) 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

(10) 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

(11) 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

(12) 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

(13) 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

(14) 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.