Thiol-acrylate based foam precursor composition

Abstract

A polymeric foam precursor composition including the following components: (a) a di- or tri-functional (meth)acrylate oligomer (2); (b) a di- or higher-functional thiol compound (3); and (c) a borane compound (4) as initiator.
The foam precursor composition can be isocyanate free, and the curing rate is largely moisture independent and can cure at low temperatures, below freezing point.

Claims

1. A polymeric foam precursor composition comprising the following components: (a) A di- or tri-functional (meth)acrylate oligomer; (b) a di- or higher-functional thiol compound; and (c) a borane compound as initiator.

2. The composition according to claim 1, wherein the thiol compound has the structure R(SH).sub.n, with n2.

3. The composition according to claim 1, wherein the thiol compound is Pentaerythritol tetrakis(3-mercaptopropionate) (TKT), trimethylolpropane tris (3-mercaptopropionate), tri[2-(3-mercaptoproprionyloxy)ethyl] isocyanurate or pentaerythritol tetrakis(2-mercaptoacetate).

4. The composition according to claim 1, wherein the borane compound is an alkyl- or alkoxy-borane of formula (alkoxy).sub.3-n-B-(alkyl).sub.n, with n=0 to 3, and wherein alkyl and alkoxy each independently comprise between 1 and 14 C.

5. The composition according to claim 1, comprising no isocyanate group.

6. The composition according to claim 1, further comprising one or more of: (d) A phenolic and/or phosphonic acid compound as stabilizer; (e) A flame retardant; (f) A surfactant; (g) A propellant; and (h) A diluent.

7. The composition according to claim 6, wherein components (a)&(b) (=di- or tri-functional (meth)acrylate oligomer and di- or higher-functional thiol compound) are in the form of a stabilized thiol acrylate blend, further comprising component (d) (=phenolic or phosphonic acid compound) as stabilizer.

8. The composition according to claim 6, wherein at least components (a) to (c) and (g) are stored in an aerosol can, with at least component (c) (=borane compound) being physically separated from components (a)&(b) (=di- or tri-functional (meth)acrylate oligomer and di- or higher-functional thiol compound).

9. The composition according to claim 8, wherein component (c) (=borane compound) is microencapsulated such that the microcapsules are open by bursting and/or tearing upon spraying the composition out of the can through an aerosol nozzle.

10. The composition according to claim 8, wherein components (c)&(h) (=borane compound and diluent) are stored in a separate compartment as half-component, and wherein components (a)&(b) (=di- or tri-functional (meth)acrylate oligomer and di- or higher-functional thiol compound) are stored outside said compartment, and wherein component (c) contacts components (a)&(b) upon spraying the composition out of the can through an aerosol nozzle.

11. The composition according to claim 1, wherein the molar ratio of the total mercaptan units of component (b) (=thiol compound) to the total meth)acrylate units of component (a) (=(meth)acrylate oligomer) is comprised between 50 and 150%.

12. The composition according to claim 1, wherein the borane is present in an amount comprised between 0.5 and 10 wt. %, with respect to the total weight of components (a)&(b).

13. The composition according to claim 2, wherein the thiol compound has the structure R(SH).sub.n, with n=3 or 4.

14. The composition according to claim 13, wherein the borane compound is an alkyl- or alkoxy-borane of formula (alkoxy).sub.3-n-B-(alkyl).sub.n, with n=0 to 3, and wherein alkyl and alkoxy each independently comprise between 1 and 14 C.

15. The composition according to claim 14, comprising no isocyanate group.

16. The composition according to claim 15, further comprising one or more of: (d) A phenolic and/or phosphonic acid compound as stabilizer; (e) A flame retardant; (f) A surfactant; (g) A propellant; and (h) A diluent.

17. The composition according to claim 16, wherein components (a)&(b) (=di- or tri-functional (meth)acrylate oligomer and di- or higher-functional thiol compound) are in the form of a stabilized thiol acrylate blend, further comprising component (d) (=phenolic or phosphonic acid compound) as stabilizer.

18. The composition according to claim 17, wherein at least components (a) to (c) and (g) are stored in an aerosol can, with at least component (c) (=borane compound) being physically separated from components (a)&(b) (=di- or tri-functional (meth)acrylate oligomer and di- or higher-functional thiol compound).

19. The composition according to claim 18, wherein component (c) (=borane compound) is microencapsulated such that the microcapsules are open by bursting and/or tearing upon spraying the composition out of the can through an aerosol nozzle.

20. The composition according to claim 1, wherein the (meth)acrylate oligomer is a polyester (meth)acrylate, a polyurethane acrylate, a bisphenol A based acrylate, or a mixture thereof.

21. The composition according to claim 4, wherein the borane is selected among the group of trimethylborane, triethylborane, tripropylborane, tributylborane, trihexylborane, trioctylborane, tridecylborane, tridecylborane, and methoxydiethylborane.

22. The composition according to claim 6, wherein the flame retardant is TCPP, the surfactant is a silicone surfactant, the propellant is LPG and/or dimethyl ether (DME) and/or the diluent is monoethylene glycol (MEG).

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) For a fuller understanding of the nature of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings in which:

(2) FIG. 1: shows two embodiments of curing reaction of a foam according to the present invention.

(3) FIG. 2: Shows a 1.5K foam system stored in an aerosol can.

(4) FIG. 3: Shows a 1K foam system stored in an aerosol can, with microencapsulated borane initiator.

(5) FIG. 4: Shows various stabilizers, (a) phosphonic acid, and (b) phenolic compounds.

(6) FIG. 5: Shows various boranes suitable as initiator according to the present invention.

(7) FIG. 6: Shows the formula of a preferred thiol compound: TKT.

DETAILED DESCRIPTION OF THE INVENTION

(8) The cross-linking system proposed in the present invention as an alternative route to isocyanate-moisture curing is metal free click chemistry, in particular, it is thiol-X chemistry. The present invention concers a thiol-acrylate reaction system, defined by an acrylate oligomer (di- or tri-functional) to be cured with a di- or higher-functional thiol compound with the aid of an initiator. In particular, the polymeric foam precursor composition of the present invention comprises at least the following components: (a) A di- or tri-functional (meth)acrylate oligomer (2); (b) A di- or higher-functional thiol compound (3); and (c) A borane compound (4) as initiator.

(9) The di- or tri-functional (meth)acrylate oligomer (2) can be a polyester (meth)acrylate or a polyurethane acrylate, or a mixture of both. For example, the (meth)acrylate oligomer can be produced by reacting maleic acid with a fatty acid diol yielding a fatty dimer polyol suitable as (meth)acrylate oligomer for the present invention. Bisphenol A based acrylate oligomers may be used instead or in combination with the foregoing oligomers, such as CN104A75, CN104A60, SR349, CN9167, CN970A60, or CN1963 available from Sartomer, or Bisphenol A glycerolate (1 glycerol/phenol) diacrylate from Sigma-Aldrich (CAS: 4687-94-9).

(10) The di- or higher-functional thiol compound (3), preferably has the structure R(SH).sub.n, with n2, preferably n=3 or 4. For example the following thiol compounds are suitable for the present invention: Pentaerythritol tetrakis(3-mercaptopropionate) (TKT), trimethylolpropane tris (3-mercaptopropionate) (CAS: 33007-83-9), Tris[2-(3-mercaptopropionyloxy)ethyl] isocyanurate (CAS: 36196-44-8), Pentaerythritol tetrakis(2-mercaptoacetate) (CAS: 10193-99-4).

(11) The di- or tri-functional (meth)acrylate oligomer (2) and di- or higher-functional thiol compound (3) are preferably pre-blended together with a stabilizer (5) to obtain a stabilized thiol-acrylate blend (3a), which is easier to handle than the two components separately. Best stabilized blends were obtained by using a phenolic and/or phosphonic acid compound as stabilizer. For example, pyrogallol, vinylphosphonic acid, phenylphosphonic acid, phosphorous acid (CAS: 13598-36-2), (12-phosphonododecyl)phosphonic acid (CAS: 7450-59-1), (3-Bromopropyl)phosphonic acid (CAS: 1190-09-6), ethyl/buthyl phosphonic acid silica (no CAS nr. Sigma-Aldrich product nr:744794) can be successfully used to stabilize the thiol-acrylate blend (3a). FIG. 4 illustrates examples of stabilizers, (a) phoshonic acid wherein R can be H, alkyl (preferably 2-9 C-alkyl), vinyl, or aromatic, and (b) phenolic stabilizers.

(12) Because many applications of such foams are in cavities, sheltered from any light, photo-initiators as proposed in the prior art were discarded as not satisfactory. Various initiators were tested, including peroxides and toluidines. After an extensive screening it was finally found out that best results were obtained with a borane compound as initiator. For example, the borane compound (4) can be an alkyl- or alkoxy-borane of formula (alkoxy).sub.3-n-B-(alkyl).sub.n, with n=0 to 3, and wherein alkyl and alkoxy each independently comprise between 1 and 14 C. In particular the borane compound may be selected among the group of trimethylborane, triethylborane, tripropylborane, tributylborane, trihexylborane, trioctylborane, tridecylborane, tri tridecylborane. Triethylborane, methoxydiethylborane, and tributylborane are preferred borane compounds. Examples of boranes suitable for the present invention are illustrated in FIG. 5.

(13) One of the major advantages of the present invention is that stable foams capable of curing in less than 3 h, even in less than 1 h, regardless of the relative humidity, can be obtained with no isocyanate groups at all. In view of the high toxicity of isocyanate groups, this is highly advantageous. The polymeric foam precursor composition of the present invention may further comprise one or more of the following components: A flame retardant (6), preferably tris(2-chloroisopropyl) phosphate (TCPP); A surfactant (7), such as a non-ionic surfactant, preferably a silicone surfactant, such as Tegostab available from Evonik Industries or Vorasurf available from Dow Chemicals. A propellant (8) such as LPG and/or dimethyl ether (DME). A diluent (9) for the borane compound initiator (4), such as monoethylene glycol (MEG), for the half component (10) in a 1.5K system as will be discussed below.

(14) The acrylate compound (2) and thiol compound (3), preferably in the form of a stabilized thiol-acrylate blend (3a) must be physically separated from the borane initiator (4) until curing is desired. This can be achieved by storing them in two separate containers thus forming a 2K system. 2K systems are, however, cumbersome to use and 1K or 1.5K are preferred, in particular if stored in an aerosol can with a propellent (8) for spraying.

(15) In a 1.5K foam systems the borane initiator (4) is added to the (stabilized) thiol-acrylate blend (2, 3, 3a) shortly or immediately before the composition is dispensed from its container. As illustrated in FIG. 2 the (stabilized) thiol-acrylate blend (2, 3, 3a) is preferably stored in a pressurized aerosol can (1) which further contains a second, smaller pressurized container containing the half component (10) comprising a borane initiator (4) and, if necessary, a diluent (9) such as monoethylene glycol (MEG)). Any other additives such as flame retardants (6) or surfactants (7) may be contained either in the aerosol can or in the second, smaller container. It is generally preferred to store such additives in the main aerosol can. Pressurization of the aerosol can (1) and smaller container requires a propellant (8). Upon actuating the aerosol nozzle of the aerosol can, the half component (10) is released from the second container into the (stabilized) thiol-acrylate blend (2, 3, 3a), simultaneously or shortly before the foam forming composition is to be dispensed and applied. It is clear that once the aerosol nozzle is actuated, the aerosol can must be emptied and cannot be re-used at a later stage, since any composition remaining in the can will cure in the can.

(16) In this respect, 1K foam systems are advantageous since a 1K system can be dispensed from an aerosol can in several shots separated in time. This can be achieved by microencapsulating the borane initiator (4) in microcapsules (11) dispersed in the (stabilized) thiol-acrylate blend (2, 3, 3a). The microcapsules must open upon spraying the composition through the nozzle in order to mix the borane initiator (4) with the (stabilized) thiol-acrylate blend (2, 3, 3a). This can be achieved either by blowing the microcapsule by the pressure difference between the inside of the microcapsules and the atmosphere or by shearing the microcapsules as they pass through the aerosol nozzle to tear them open. Examples of microcapsules which can be used to this purpose are described, e.g., in WO2011003805, US2011/0236498, GB2416524, and WO03/066209. The microencapsulated borane initiator (4, 11) generally does not require any diluent (9) as each particle comprises a small volume of initiator.

(17) The amount of thiol compound (3) relative to the amount of acrylate oligomer (2) depends on the basis of the number of mercaptan units with respect to the number of (meth)acrylate units and therefore depends on the respective functionalities of the thiol and acrylate compounds. In particular, it is preferred that the molar ratio of the total mercaptan units of the thiol compound (3) to the total (meth)acrylic units of the acryliate oligomer (2) be comprised between 50 and 150%, preferably between 90 and 110%, more preferably between 95 and 100%.

(18) For a composition comprising 100 parts of both thiol compound (3) and acrylate oligomer (2) together, the borane initiator (4) is preferably present in an amount comprised between 0.5 and 10 parts, preferably between 1 and 6 parts, more preferably between 3.5 and 4.5 parts.

(19) For 100 parts of both thiol compound (3) and acrylate oligomer (2) together, the composition of the present invention may comprise between 1 and 20 parts, preferably 5 and 15 parts of a flame retardant (6) such as tris(2-chloroisopropyl) phosphate (TCPP). It may comprise between 1 and 10 parts, preferably between 2 and 5 parts of a surfactant such as Tegostab B8871, B84503, B8513, B8517, available from Evonik Industries or Vorasurf 504 available from Dow Chemicals, and between 30 and 60 parts, preferably between 35 and 50 parts of a propellant (8), such as LPG and/or DME, the latter acting also as solvent for the (stabilized) thiol-acrylate blend (2, 3, 3a). In case a stabilized thiol-acrylate blend (2, 3, 3a) is formed, it can be stabilized by adding 10 to 20 parts of a stabilizer (6) such as phenolic and/or phosphonic acid to a 100 parts of both thiol compound (3) and acrylate oligomer (2) together. For 1.5K foam systems, it is important that the viscosity of the half component (10)mainly the borane initiator (4)be sufficiently low to ensure a homogeneous mix thereof with the main componentmainly the thiol-acrylate blend-. The viscosity of the half-component (10) can be controlled with a non reactive diluent (9), such as monoethylene glycol (MEG). The weight ratio diluent (9) to borane (4) can be comprised between 0.5 and 5, preferably between 1 and 3.

(20) Table 1 lists an example of 1.5K foam composition according to the present invention.

(21) TABLE-US-00001 TABLE 1 Typical 1.5K aerosol foam formulation element component description wt. % parts Main component thiol-acrylate TKT + 59% 100.0 blend (2)&(3) bisphenol A based acrylate Surfactant (7) B8871 2% 3.3 (from Evonik) stabilizer (5) phosphonic ac. + 8% 14.0 pyrogallol Half borane TEB 2% 3.9 component (10) initiator (4) Non-reactive MEG 5% 8.5 diluent (9) Propellant (8) Propellant (8) LPG 16% 27.5 Propellant/ DME 7% 11.8 Solvent (8) 100% 168.9

(22) The rigidity and other mechanical properties of the foam can be controlled by an adequate choice of the components. For examples, softer foams can be obtained with ester acrylates and harder foams with urethane acrylates, since the latter form a more rigid backbone than the former.

(23) Unlike isocyanates which are activated by moisture, borane initators are activated with oxygen in the atmosphere. This has the great advantage that the curing kinetics of the foam is not dependent on the weather and climate of the place of application and is constant regardless of the moisture content of the atmosphere. Another great advantage is that the foam can cure also at temperatures below freezing point.

(24) TABLE-US-00002 REF Description 1 aerosol can 2 di- or tri-functional (meth)acrylate oligomer 3 di- or higher-functional thiol compound 3a stabilized thiol-acrylate blend 4 borane compound (initiator) 5 phenolic or phosphonic acid compound (stabilizer) 6 flame retardant (e.g., TCPP) 7 surfactant (e.g., silicone surfactant) 8 propellant (e.g., LPG and/or-dimethyl etherb (DME).) 9 diluent for the half component (e.g., monoethylene glycol (MEG)) 10 half component 11 microcapsules