Flame retardant compounds

Abstract

The present invention provides A silsesquioxane of formula: (R1SiO1,5)x (R2SiO1,5)y, wherein x ≥ 2, y ≥ 2, and x + y = 6,8,10 or 12; R1 is L1-phthalimide, wherein L1 is a residue selected from the group consisting of saturated or unsaturated C2-C8 hydrocarbon radicals which may be straight, branched or cyclic; and the phthalimide is optionally substituted by one or more halogen, C1-C6 alkyl, -COOH, -OH or -NO2; and R2 is a residue selected from the group consisting of saturated or unsaturated C1-C8 hydrocarbon radicals, which may be straight, branched or cyclic, phenyl and vinyl; wherein the hydrocarbon radicals, phenyl and vinyl are optionally substituted by one or more halogens.

Description

[0001] Title: Flame retardant compounds

[0002] Field of the invention

[0003] The present invention relates to fire retardants and more specifically to novel functionalized polyhedral oligomeric silsesquioxanes (POSS) and their use as fire retardants in polymeric materials.

[0004] Background of the invention

[0005] Many common polymeric materials used in our daily life are highly flammable thereby increasing their risk as fire hazards when used in practical applications. Consequently, improving polymer fire retardancy is a major challenge for extending polymer use to most applications.

[0006] Halogen-containing compounds are well known to be effective fire retardants for polymers, however, due to environmental concerns the use of halogen-containing fire retardants have been gradually prohibited (Environ Health Perspect., 2004, 112, pages 9-17).

[0007] An alternative to the use of halogen-containing compounds are phosphorus-based fire retardants. However, many phosphorus-based fire retardants will plasticize the polymers, thereby reducing modulus, glass transition temperature and strength. There are also environmental concerns associated with some phosphorus-based fire retardants (Fire Sci. 2004, 22, pages 293-303).

[0008] Further, the occurrence and environmental behaviour of organophosphorus compounds in diverse matrices have been reviewed by Wei et al (Environ Pollut., 2015, 196, pages 29-46)

[0009] Thus, there is a continuous need for developing safe and eco-friendly fire retardants that are compatible with being incorporated into polymer matrices.

[0010] Reinforcing polymers with nanosized fillers, such as carbon nanotubes or nanoclay, represents a promising methodology for providing safe and eco-friendly fire retardants. Following this approach, improvements in fire retardance may be found even at relatively low filler content.

[0011] Montmorillonite is the most commonly used clay because it is naturally ubiquitous, can be obtained at high purity and low cost, and exhibits very rich intercalation chemistry, meaning that it can be easily organically modified. The natural clay surface is hydrophilic, so the clay easily disperses in aqueous solutions but not in polymers. Natural clays are therefore often modified using organic cations such as alkylammonium and alkylphosphonium cations, forming hydrophobic organo- modified clays that can be readily dispersed in polymers. However, there are no covalent bonds between the organic cations and the nanoclay. An alternative to the use of carbon nanotubes and nanoclay is physically or chemically incorporating polyhedral oligomeric silsesquioxanes (POSS) into common polymer systems to offer hybrid composites with improved fire-retardant properties. POSS are a kind of inorganic-organic hybrid compounds which nanostructures have become attractive because of their environmental neutrality, good heat resistance as well as excellent thermoxidative stability (New York: Springer Netherlands; 2011, pages 209-228).

[0012] POSS have the general formula (RSiOi.s)n, where R represents an organic functionality and n is commonly 6, 8 10 or 12. A POSS wherein n is 8 is shown in fig. 1. Although often represented by a single structure as in fig. 1, the product(s) obtained in the synthesis of POSS is usually a mixture of the different closed cage structures according to the general formula, as well as minor amounts of not fully closed structures depending on the nature of the R-groups. These cage structures combine unique hybrid (inorganic-organic) chemical compositions with nanosized cage structures of approximately 1.5 nm in diameter (the R-groups being included). They can be loosely regarded as the smallest possible silica particles. However, unlike silica and nanoclay, each POSS molecule has organic functionalities covalently bound to their outer surface which may provide solubility and compatibility of the POSS with various polymer systems.

[0013] Even though several different polymer POSS-composites have been shown to be associated with enhanced fire retardancy (progress in polymer science, 67, 2017, pages 77-125), it is essential that the incorporation of POSS into the polymer system does not negatively affect the other physical properties of the polymer, in particular the mechanical properties of the polymer system.

[0014] Variations in the POSS R-functionalities have previously been found to determine the interactions between the POSS moiety and the host polymer segments and this, in turn, has been found to impact microstructure and rheology (Journal of Macromolecular Science, Part C: Polymer Reviews, 49: 25-63, 2009). The selection of R-functionalities is essential both with respect to fire retardancy and the other physical properties of the polymer POSS-composite. An important physical property is the tendency of a polymer to sag when on fire.

[0015] The aim of the present invention is to provide novel POSS compounds having excellent properties as fire retardants, while also offering improved properties for alleviating sag in polymers on fire.

[0016] Summary of the invention

[0017] The present invention is defined by the appended claims and in the following:

[0018] In a first aspect, the present invention provides a silsesquioxane of formula: (RiSiOi,s)x (R2SiOi,s)y, wherein x > 2, y > 2, and x + y = 6,8,10 or 12;

[0019] Ri is Li-phthalimide, wherein Li is a residue selected from the group consisting of saturated or unsaturated C2-C8 hydrocarbon radicals which may be straight, branched or cyclic; and the phthalimide is optionally substituted by one or more halogen, Ci-Ce alkyl, -COOH, -OH or -NO2; and

[0020] R2 is a residue selected from the group consisting of saturated or unsaturated Ci-Cs hydrocarbon radicals, which may be straight, branched or cyclic, phenyl and vinyl; wherein the hydrocarbon radicals, phenyl and vinyl are optionally substituted by one or more halogens.

[0021] In an embodiment of the silsesquioxane, Li may be C2-C6 alkyl, phenyl or vinyl, preferably ethyl, propyl or butyl.

[0022] In an embodiment of the silsesquioxane, R2 may be Ci-Cs alkyl, phenyl or vinyl, preferably ethyl, propyl or butyl.

[0023] In an embodiment of the silsesquioxane, x = y.

[0024] In a second aspect, the present invention provides for the use of a silsesquioxane according to any of the embodiments of the first aspect as a flame-retardant additive.

[0025] In a third aspect, the present invention provides a plasticizer composition comprising: a) 50-99 wt% of a plasticizer; and b) 1-50 wt% of a silsesquioxane according to any embodiment of the first aspect.

[0026] In a fourth aspect, the present invention provides a polymeric material comprising a silsesquioxane according to any embodiment of the first aspect or a plasticizer composition according to the third aspect. The polymeric material may be a thermoplastic, thermoset or elastomer, for instance selected from the group comprising polyvinyl chloride (PVC), polyethylene (PE), polyurethane (PU), polyamides (PA), polypropylene (PP), epoxides, various polyesters and polystyrene (PS). The polymeric material may advantageously comprise an inorganic flame retardant additive, such as aluminium trihydrate (ATH) or antimony trioxide. In a fifth aspect, the present invention provides a method of manufacturing a silsesquioxane according to any embodiment of the first aspect comprising the steps of: condensing a compound of formula H2N-Li-Si(ORs)3 and a compound of formula R2Si(OR4)3 in a mole ratio of 0.25 to 4, wherein

[0027] Li is a residue selected from the group consisting of saturated or unsaturated C2-C8 hydrocarbon radicals which may be straight, branched or cyclic;

[0028] R2 is a residue selected from the group consisting of saturated or unsaturated C2-C8 hydrocarbon radicals which may be straight, branched or cyclic; wherein the carbon chains of said residues are optionally substituted by one or more halogens; and each of R3 and R4 are any of -CH3 and -CH2CH3; obtaining an intermediate silsesquioxane of formula (H2N-Li-SiOi,5)x(R2SiOi,5)y, wherein x > 2, y > 2, and x + y = 6,8,10 or 12; reacting the intermediate silsesquioxane with phthalic anhydride optionally substituted by one or more halogen, C1-C5 alkyl, -COOH, -OH or -NO2; and obtaining a silsesquioxane according to any embodiment of the first aspect.

[0029] In an embodiment of the fifth aspect, the mole ratio of the compound of formula H2N-Li-Si(OR3)3 and the compound of formula R2Si(OR4)s is 0.4 to 2.5, preferably 0.75 to 1.25 or 1.0.

[0030] In an embodiment of the fifth aspect, the method comprises a step of adding the obtained silsesquioxane to a suitable plasticizer to obtain a composition according to the third aspect.

[0031] In a sixth aspect, the present invention provides a silsesquioxane obtainable by the method according to the fifth aspect. As used herein, the terms “alkyl” and “alkene” are intended to encompass straight chained, cyclic and branched alkyls and alkenes, respectively.

[0032] In other words, a Ci-Cs alkyl may for instance be a methyl ethyl, propyl, sec-propyl, n-butyl, t-butyl, sec-butyl, pentyl, cyclopentyl, hexyl, cyclohexyl or octyl.

[0033] Description of the invention

[0034] Unless specifically defined herein, all technical and scientific terms used have the same meaning as commonly understood by a skilled artisan in the fields of organic chemistry and polymer technology.

[0035] All methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, with suitable methods and materials being described herein. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will prevail.

[0036] Where a numerical limit or range is stated herein, the endpoints are included. Also, all values and sub ranges within a numerical limit or range are specifically included as if explicitly written out.

[0037] The background for the present invention was the desire to provide novel POSS compounds providing polymers with fire retardancy and improved sag properties. The novel POSS should preferably not have any negative impact upon the mechanical properties of the final polymeric material.

[0038] Experimental procedures

[0039] The synthesis of exemplary POSS compounds according to the invention, as well as comparative POSS compounds are described below.

[0040] As discussed above, the POSS compounds are commonly obtained as mixtures of different closed cage structures.

[0041] A Bruker 400 MHz NB Avance III UltraShielded Plus instrument was used to obtain 'H-NMR,13C-NMR and29Si-NMR spectra for a selection of the isolated POSS compounds. Due to the mixture of compounds the spectra are quite complex, but29Si-NMR showed only shifts belonging to closed cage structures, i.e. no open structures were detected. Exemplary POSS compounds

[0042] Starting compound

[0043] Starting compound 1 (Amino-Propyl-POSS):

[0044] In a 3 L reactor with a temperature adjustable heat jacket, stirrer, thermometer, dropping funnel, vertical cooler with column head for rapid exchange between reflux and distillation, and vacuum connection (membrane pump). A mixture of 625 g (2,82 mol) of (3-aminopropyl) triethoxysilane, 583 g (2,82 mol) triethoxy(propyl)silane, 687 g (11,4 mol) 1-propanol, and 203 g (11,29 mol) water where added to the reaction vessel. The resulting mixture was purged using nitrogen gas and vacuum 3 times. The reaction mixture was then heated with reflux for 16 h (at std. atmospheric pressure). The volatile reaction products and solvents where then removed by distillation. When approx. 1000 g of volatile reaction product and solvents where removed 1200 g xylene was added, and distillation continued until the boiling point of xylene was reached. In total 2138 g of volatile reaction product and solvent was removed resulting in a 581 g (5,65 mol) amino-propyl-POSS and 581 g of xylene in the final mixture, 1162 g of 50 wt% solution of amino-propyl- POSS in xylene.29Si-NMR of the obtained product showed predominantly peaks at - 65 to -70 ppm indicating fully condensed cage structures.

[0045] A similar result was obtained by using l-methoxy-2-propanol as solvent instead of xylene.

[0046] The starting compound could be isolated in close to quantitative yield by distilling / evaporating off the volatiles of the reaction mixture.

[0047] POSS compounds according to the invention

[0048] Inventive compound 1 SF458

[0049] To 5252 g of a solution of starting compound 1 (50 wt. % amino-propyl-POSS in 1- methoxy-2-propanol) obtained as described above, 3780 g (25.52 mol) phthalic acid anhydride was added at 80 °C. An exothermic reaction was observed. When all phthalic acid was dissolved, the mixture was heated to 120 °C to boil off the solvent. After distilling off most of the l-metoxy-2-propanol, 7878 g of xylene was added, and the mixture heated to 140 °C for 5 hours. Isolation of inventive compound 1 was performed using a rotary evaporator to at least 98 % dry matter.

[0050] Yield: 96% (8.23 kg of maximum 8.57 kg).

[0051] 29Si-NMR of the obtained product showed predominantly peaks at -65 to -70 ppm indicating fully condensed cage structures, see fig. 2. Inventive compound 1 as illustrated in fig. 2 may be defined as having the formula (RiSiOi,5)x (R.2SiOi,5)y, wherein Ri is propyl-phthalimide, R2 is propyl and x = y.

[0052] Comparative POSS compound

[0053] To 1162 g of starting compound 1 (50 wt % ammo-propyl-POSS in xylene) obtained as described above, 1500 g xylene and 402 g (1.41 mol) stearic acid were added. The reaction mixture was heated at reflux and water was distilled off as an azeotropic mixture with xylene using a Dean-Stark trap with a volume of 50 ml. When the amount of water distilled off was equal to the calculated yield (25 g), the reaction was cooled to 80 °C, 209 g (1.41 mol) phthalic anhydride chips was added and the reaction mixture heated at 130 °C for 2 h.

[0054] 29Si-NMR of the obtained product showed only peaks between -65 to -71 ppm indicating fully condensed cage structures, see fig. 3.

[0055] The comparative compound, see fig. 3, was isolated in close to quantitative yield by distilling / evaporating off the volatiles of the reaction mixture.

[0056] Determining when reactions where complete:

[0057] The reactions in which amino-groups were reacted with phthalic acid anhydride were considered complete when they reached a residual amine number below 10 but more preferably below 5, as determined by the following method:

[0058] A known amount of the material was dissolved in either 2-butoxy ethanol or chlorobenzene 10 mL and 50 m of glacial acetic acid. This mixture was titrated with a 0.10 molar solution of HCIO4 in acetic acid.

[0059] The below formula is used to calculate the amine number: mi titrated x 5,61

[0060] (Measured sample x TS)

[0061] For example: if the equivalence point is observed when titrated 4.1 ml of the 0,10 M HCIO4 with a POSS sample of 1,203 g and TS% content 51,33% (0,5133)

[0062] 4,1 x 5,61

[0063] TBW = - - - - = 37,2

[0064] 1,203 x 0,5133 Test of exemplary POSS compound as a flame retardant

[0065] The flame retarding properties of the exemplary POSS compound was tested according to the ISO 11925-2 single flame source fire test https: / / www.iso.Org / obp / ui / #iso:std:iso:11925:-2:ed-3:yl:en

[0066] To obtain specimens suitable for the fire test, the exemplary compound was used as additives in PVC to obtain suitable strips of polymeric film having a thickness of 1.3 to 1.6 mm. Each specimen was obtained by curing a mixture of the respective exemplary compound with PVC monomer (Pl 412 E-PVC), diisononyl phthalate (DINP), aluminium trihydrate (ATH) and stabilizer (Baerostab UBZ 660-4 RF) in a weight ratio of 1 :100:50:20:3.

[0067] Both the comparative POSS compound and the inventive compound 1 displayed excellent flame-retardant properties in the ISO 11925-2 test.

[0068] However, the experimental results from the 1SO11925-2 flame test reveals that inventive compound 1, having a combination of n-propyl-phthalimide and short hydrocarbon chains in a 1 :1 ratio has excellent flame retardant properties as well as significantly preventing sag of the fire test specimen during the fire test, see fig. 5.

[0069] While the comparative test compound displays similar flame retardant properties as inventive compound 1, sag of the fire test specimen was significantly higher, see pictures of the fire test strips in fig. 4.

Claims

Claims1. A silsesquioxane of formula:(RiSiOi,s)x (R2SiOi,s)y, wherein x > 2, y > 2, and x + y = 6,8,10 or 12;Ri is Li-phthalimide, wherein Li is a residue selected from the group consisting of saturated or unsaturated C2-C8 hydrocarbon radicals which may be straight, branched or cyclic; and the phthalimide is optionally substituted by one or more halogen, Ci-Ce alkyl, -COOH, -OH or -NO2; andR2 is a residue selected from the group consisting of saturated or unsaturated Ci-Cs hydrocarbon radicals, which may be straight, branched or cyclic, phenyl and vinyl; wherein the hydrocarbon radicals, phenyl and vinyl are optionally substituted by one or more halogens.

2. A silsesquioxane according to claim 1, wherein Li is C2-C6 alkyl, phenyl or vinyl.

3. A silsesquioxane according to claim 1 or 2, wherein R2 is Ci-Cs alkyl, phenyl or vinyl.

4. A silsesquioxane according to claim 1, wherein x = y.

5. Use of a silsesquioxane according to any of the preceding claims as a flameretardant additive.

6. A plasticizer composition comprising: c) 50-99 wt% of a plasticizer; and d) 1-50 wt% of a silsesquioxane according to any of claims 1-5.

7. A polymeric material comprising a silsesquioxane according to any of claims 1-4 or a plasticizer composition according to claim 6.

8. A method of manufacturing a silsesquioxane according to any of claims 1-4 comprising the steps of: condensing a compound of formula H2N-Li-Si(OR3)3 and a compound of formula R2Si(OR4)3 in a mole ratio of 0.25 to 4, whereinLi is a residue selected from the group consisting of saturated or unsaturated C2-C8 hydrocarbon radicals which may be straight, branched or cyclic;R2 is a residue selected from the group consisting of saturated or unsaturated C2-C8 hydrocarbon radicals which may be straight, branched or cyclic; wherein the carbon chains of said residues are optionally substituted by one or more halogens; and each of R3 and R4 are any of -CH3 and -CH2CH3; obtaining an intermediate silsesquioxane of formula (H2N-Li-SiOi,s)x (R2SiOi,s)y, wherein x > 2, y > 2, and x + y = 6,8,10 or 12; reacting the intermediate silsesquioxane with phthalic anhydride optionally substituted by one or more halogen, C1-C5 alkyl, -COOH, -OH or -NO2; and obtaining a silsesquioxane according to any of claims 1-4.

9. A silsesquioxane obtainable by the method according to claim 8.

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