WO2024082028A1

WO2024082028A1 - Encapsulation and controlled release of liquid polyurethane catalysts

Info

Publication number: WO2024082028A1
Application number: PCT/AU2023/051053
Authority: WO
Inventors: Christophe Jean Alexandre BARBÉ; Kathryn Jordan
Original assignee: Encap Hive Pty Ltd
Priority date: 2022-10-21
Filing date: 2023-10-20
Publication date: 2024-04-25

Abstract

The invention provides a method of preparing silica particles encapsulating a liquid polyurethane catalyst, the method comprising: providing a hydrophilic phase comprising water and a surfactant; providing a hydrophobic phase comprising an organosilane and the liquid polyurethane catalyst; forming an oil-in-water emulsion comprising the hydrophobic phase dispersed in the hydrophilic phase; aging the emulsion, forming the silica particles encapsulating the liquid polyurethane catalyst in the hydrophobic phase; and recovering the formed silica particles encapsulating the liquid polyurethane catalyst There is also provided silica particles encapsulating a liquid polyurethane catalyst prepared by the method and use of the silica particles to control the speed of formation of polyurethanes by controlling the kinetics of the polymerisation of isocyanates with diols.

Description

ENCAPSULATION AND CONTROLLED RELEASE OF LIQUID POLYURETHANE CATALYSTS FIELD OF INVENTION The present invention relates to a method of preparing silica particles encapsulating a liquid polyurethane catalyst and silica particles prepared by the method. BACKGROUND ART Organometallic catalysts, such as tin, zinc and mercury organometallic catalysts, and amine catalysts are well known catalysts for polycondensation reactions and are used extensively in the production and stabilisation of many plastics, particularly polyurethane. While particular mention is made to tin catalysts in the discussion below. The present invention equally applies to other organometallic and amine liquid polyurethan catalysts. Tin catalysts are suitable alternatives to other products in a wide range of industries and can meet requirements met by other options, such as zinc or bismuth catalysts. From an organometallic perspective, the handling of Tin catalysts may be more demanding, but that may come with significant performance benefits, such as considerably faster reaction times. Tin catalysts are generally valued in industries that produce products in a controlled environment. For example, adhesive and sealant production industries, the pharmaceutical industry and glass coating industries. Further applications can be found in oleo chemistry, in paints and coatings or in polymer processing. As a stabilizer, Tin compounds prevent reactions that are undesirable, such as the decomposition of plastics under the influence of the weather, or the self- decomposition of substances without external influence. One of the most commonly used organotin compound is Dibutyltin Dilaurate (DBTDL), (CH3CH2CH2CH2)2Sn[OCO(CH2)10CH3]2. This is a water insoluble oily liquid which is produced by the heating of lauric acid with dibutyltin oxide. It has been extensively used as a stabilizer for polyvinyl chloride (e.g., plastisol), preventing the accumulation of HCl. It is also used as an accelerator in the production of isocyanate containing polymers and polysiloxanes, and acts as a catalyst in castor oil diisocyanate reactions for the preparation of polyurethane foams and coatings (E.S. Lower Pigment & Resin Technology 1980: 10-11). An emulsion system for the production of particles encapsulating releasable dopants is described in International Patent Publication No. WO 2006133519, “Particles Comprising A Releasable Dopant Therein”. According to this system, the particles comprising a dopant are produced by providing an emulsion comprising a hydrophilic phase and a hydrophobic phase dispersed in the hydrophilic phase, the hydrophobic phase comprising a precursor material and the dopant. The precursor material is then reacted in the presence of a catalyst, generally an aminoorganotrialkoxysilane such as 3-aminopropyltriethoxysilane (APTES), to form the particles. As will be discussed below, while the present invention follows similar methodology to that seen in WO 2006133519, the present invention does not involve the use of an amino silane catalyst to form the product particles. Rather, it has been surprisingly found that the addition of the active organotin catalyst induces the formation of spherical microparticles without the requirement for an extra step involving the addition of a catalyst such as APTES or other amino silanes. Moreover, with reference to Figure 1A, DBTDL appears to react with the aminosilane catalyst of WO 2006133519 leading to the formation of a precipitate. Specifically, the encapsulation of DBTDL using the process outlined in WO 2006133519 leads to the formation of a milky solution which does not separate efficiently using centrifugation, with the collected dried materials being crumbly in nature and presenting significant size variations. This suggests an uncontrolled reaction, and therefore the process described in WO 2006133519 is considered unviable for the industrial production of encapsulated organotin catalysts as reproducible performance may not be possible. Surprisingly, with reference to Figure 1B, when APTES is not added to the emulsified mixture and the emulsion is aged for 4h, the product collected by centrifugation presents spherical discrete particles ranging from 10-30 microns in diameter. The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate exemplary technology areas where some embodiments described herein may be practiced. Various aspects and embodiments of the invention will now be described. SUMMARY OF INVENTION As mentioned above, the present invention relates generally to a method of preparing silica particles encapsulating a liquid polyurethane catalyst and silica particles prepared by the method. According to one aspect of the invention there is provided a method of preparing silica particles encapsulating a liquid polyurethane catalyst, the method comprising: providing a hydrophilic phase comprising water and a surfactant; providing a hydrophobic phase comprising an organosilane and the liquid polyurethane catalyst; forming an oil-in-water emulsion comprising the hydrophobic phase dispersed in the hydrophilic phase; aging the emulsion, forming the silica particles encapsulating the liquid polyurethane catalyst in the hydrophobic phase; and recovering the formed silica particles encapsulating the liquid polyurethane catalyst. The surfactant in the hydrophilic phase is preferably a nonionic alcohol alkoxylate surfactant. For example, preferred surfactants include Ecosurf EH9, Ecosurf EH14 and Tergitol CA 90 produced by Dow. The organosilane is preferably a trialkoxysilane, more preferably selected from phenyltriethoxysilane, phenyltrimethoxysilane, octyltriethoxysilane and vinyltrimethoxysilane. The hydrophobic phase more preferably comprises a mixture of the trialkoxysilane and a tetraalkoxysilane, preferably tetraethoxysilane. Preferably, the mixture has a molar ratio of tetraalkoxysilane;trialkoxysilane of from 15:85 to 45:55, preferably about 30:70. The liquid polyurethane catalyst may be selected from an organotin catalyst, organozinc catalyst, organomercury catalyst, organobismuth catalyst, or alternatively an amine catalyst. For example, the liquid polyurethan catalyst may be selected from Dioctyltin dithioglycolate, Dioctyltin dilaurate, Monobutyltin tris - (2-ethylhexanoate), Dioctyltin diacetate, Dibutyltin diacetate, Dioctyltin dicarboxylate, Dioctyltin carboxylate, Dioctyltin diacetyl acetonate, Dioctyltin bis-(isooctyl mercaptoacetate), Dibutyltin bis-(1-thioglycerol), Dimethyltin Dioleate, Dibutyltin bis-(2-ethylhexyl maleate), Dibutyltin Dilauryl Mercaptide, Dioctyltin Dilauryl Mercaptide, Dibutyltin bis-(2-ethylhexyl mercaptoacetate), Dimethyltin Dineodecanoate, Dioctyltin bis-(2-ethylhexyl mercaptoacetate), Dibutyltin bis-(isooctyl mercaptoacetate), Tin Ricinoleate, Tin neodecanoate, Zinc neodecanoate, Zinc octoate, Zinc 2-ethylhexanoate, Zinc isooctanoate, Bismuth neodecanoate, Bismuth octoate, Bismuth methanesulfonate, Bismuth 2-ethylhexanoate, Potassium Octoate, Lead 2- ethylhexanoate, Mercury neodecanoate, Phenylmercury neodecanoate, N,N,N-dimethylaminopropyl hexahydrotriazine. The liquid polyurethan catalyst is preferably a dibutyltin catalyst, more preferably selected from dibutyltin dilaurate, dibutyltin dioctanoate, dibutyltin diacetate and dibutyltin oxide. The liquid polyurethane catalyst may be added directly to the organosilane or may be dissolved in a solvent, preferably selected from ethanol and acetone. The emulsion may be aged for any suitable time period. Generally, the emulsion is aged for a period of up to 24 hours, preferably from about 2 to 4 hours. The molar ratio of liquid polyurethane catalyst:silicon in the hydrophobic phase is preferably 4 to 9:91-96 liquid polyurethane catalyst:silicon. The method preferably further comprises stirring said hydrophobic phase, more preferably for at least 5 minutes, prior to addition to the hydrophilic phase. In a preferred embodiment the hydrophobic phase is added to the hydrophilic phase under vigorous stirring or agitation to form the emulsion. The formed silica particles encapsulating the liquid polyurethane catalyst are preferably recovered by centrifugation, for example at 3000-4000rcf for 20-30 minutes. The method may further comprise drying the formed silica particles encapsulating the liquid polyurethane catalyst, for example in an oven at 40°C for 12 to 24 hours. According to another aspect of the invention there is provided silica particles encapsulating a liquid polyurethane catalyst prepared by a method as described above. According to a further aspect of the invention there is provided silica particles comprising a silica matrix and an encapsulated liquid polyurethane catalyst, wherein the liquid polyurethane catalyst is releasable from the silica matrix in a controlled manner by diffusion. As with the method discussed above, the silica matrix is preferably formed from a trialkoxysilane precursor, more preferably selected from phenyltriethoxysilane, phenyltrimethoxysilane, octyltriethoxysilane and vinyltrimethoxysilane In another embodiment, the silica matrix is formed from a mixture of a trialoxysilane and a tetraalkoxysilane. In this embodiment, the trialoxysilane is preferably selected from phenyltriethoxysilane, phenyltrimethoxysilane, octyltriethoxysilane and vinyltrimethoxysilane and the tetraalkoxysilane is preferably tetraethoxysilane. The mixture preferably has a molar ratio of tetraalkoxysilane;trialoxysilane of from 15:85 to 45:55, preferably about 30:70. The liquid polyurethane catalyst may be selected from an organotin catalyst, organozinc catalyst, organomercury catalyst, organobismuth catalyst, or alternatively an amine catalyst. For example, the liquid polyurethan catalyst may be selected from Dioctyltin dithioglycolate, Dioctyltin dilaurate, Monobutyltin tris - (2-ethylhexanoate), Dioctyltin diacetate, Dibutyltin diacetate, Dioctyltin dicarboxylate, Dioctyltin carboxylate, Dioctyltin diacetyl acetonate, Dioctyltin bis-(isooctyl mercaptoacetate), Dibutyltin bis-(1-thioglycerol), Dimethyltin Dioleate, Dibutyltin bis-(2-ethylhexyl maleate), Dibutyltin Dilauryl Mercaptide, Dioctyltin Dilauryl Mercaptide, Dibutyltin bis-(2-ethylhexyl mercaptoacetate), Dimethyltin Dineodecanoate, Dioctyltin bis-(2-ethylhexyl mercaptoacetate), Dibutyltin bis-(isooctyl mercaptoacetate), Tin Ricinoleate, Tin neodecanoate, Zinc neodecanoate, Zinc octoate, Zinc 2-ethylhexanoate, Zinc isooctanoate, Bismuth neodecanoate, Bismuth octoate, Bismuth methanesulfonate, Bismuth 2-ethylhexanoate, Potassium Octoate, Lead 2- ethylhexanoate, Mercury neodecanoate, Phenylmercury neodecanoate, N,N,N-dimethylaminopropyl hexahydrotriazine. In a preferred embodiment, the liquid polyurethane catalyst is a dibutyltin catalyst, more preferably selected from dibutyltin dilaurate, dibutyltin dioctanoate, dibutyltin diacetate and dibutyltin oxide. Preferably, the liquid polyurethane catalyst is substantially homogeneously distributed inside the silica matrix. According to a further aspect of the invention there is provided use of the silica particles as described above to control the speed of formation of polyurethanes by controlling the kinetics of the polymerisation of isocyanates with diols. BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS To further clarify various aspects of some embodiments of the present invention, a more particular description of the invention will be rendered by references to specific embodiments thereof, which are illustrated in the appended drawings. It should be appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting on its scope. The invention will be described and explained with additional specificity and detail through the accompanying drawings in which: FIGS.1A and 1B illustrate SEM images of the differences in morphology and size for particles produced by WO2006133519 and by the method of the invention respectively. FIG. 2 illustrates a flowchart of a method of producing particles including encapsulated organotin catalyst according to an embodiment of the invention. FIG. 3 illustrates the FT-IR spectrum of released DBTDL in CHCl3 following leaching. FIG.4 illustrates a graph of DBTDL calibration in chloroform. FIG.5 illustrates SEM micrographs of samples aged for a period of: a) 1 hour, b) 2 hours, and c) 24 hours. FIG.6 illustrates SEM micrographs of samples synthesized with: a) PTES, and b) PTMS. FIG.7 illustrates SEM micrographs of samples synthesized with: a) 1x, b) 1.25x, c) 1.5x, and d) 2x normal quantity of DBTDL. FIG.8 illustrates SEM micrographs of samples synthesized with: a) Ethanol, b) Acetone, and c) No solvent. FIG. 9 illustrates SEM micrographs of samples synthesized with: a) 20% increase in EH9 amount, b) 10% increase in EH9 amount, c) 10% decrease in EH9 amount and d) 20% decrease in EH9 amount. FIG. 10 illustrates SEM micrographs of samples synthesised using different surfactants. FIG. 11 illustrates SEM micrographs of samples synthesised using different PTES molar ratio. FIG. 12 illustrates SEM micrographs of samples synthesised using different organosilane precursors: a) OTES, b) VTMS, and c) TPOS. FIG.13A illustrates an SEM micrograph of Sample ES23-0073 – EH9 produced sample. FIG.13B illustrates an SEM micrograph of Sample ES23-0084 – EH9 produced sample. FIG.13 C illustrates an SEM micrograph of Sample ES23-0084, EH9 produced sample, at higher magnification. FIG.14 illustrates a Nitrogen Isotherm of DBTDL sample, produced with EH-9. FIG.15 illustrates a influence of precursor on DBTDL loading in chloroform. FIG.16 illustrates influence of precursor on release percentage of DBTDL over time, in 50/50 acetone/ chloroform. FIG.17 illustrates a graph of influence of PTES molar % on DBTDL loading, leached in chloroform. FIG.18 illustrates influence of PTES molar % on the release of DBTDL over time. FIG.19 illustrates the Infrared spectrum of Castor Oil. FIG.20 illustrates the Infrared spectrum of DBTDL. FIG.21 illustrates Infrared spectrum of DBTDL in Castor Oil, with DBTDL peak present at 1600cm-1. FIG.22 illustrates the Comparison of 1600cm^-1 peak at 0, 1 and 24 hours. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, this specification will describe the present invention according to the preferred embodiments. It is to be understood that limiting the description to the preferred embodiments of the invention is merely to facilitate discussion of the present invention and it is envisioned without departing from the scope of the appended claims. Referring to Figure 2, a simple flow chart of an embodiment of the method of the invention is illustrated. On the left side of the flowchart, a hydrophilic phase comprising water and surfactant is prepared. On the right side of the flowchart, a hydrophobic phase comprising a silicon precursor and dibutyltin dilaurate (DBTDL) is prepared. The hydrophobic phase is stirred prior to addition to the hydrophilic phase, to which it is added under vigorous stirring. This forms an oil-in-water (O/W) emulsion as illustrated, with droplets of the hydrophobic phase dispersed throughout the hydrophilic phase. The resulting emulsion is left to age under agitation, for example for 2-24 hours, and the solid particles recovered by centrifugation. Examples General procedure General synthetic scheme A certain quantity of surfactant (typically 2.5 g of Ecosurf EH9 purchased from Dow) is dissolve in de-ionised water (typically 50 ml) to produce the water phase of the emulsion. Then DBTDL (typically 1g) is dissolved in a solvent (typically 1ml of ethanol) and then added to a mixture of tetra ethoxy silane (TEOS) and Phenyl Triethoxy silane (PTES) with a typical molar ratio of 30:70 respectively. This mixture, which forms the oil phase, is further stirred for 5 minutes prior to being added to the continuous water phase under vigorous stirring. After a certain time (typically 4h), the particles formed are separated by centrifugation (3000 rcf for 20 minutes) before being dried in an oven at 40˚C overnight. Loading measurements Loading measurement of actives in hybrid silica particles are typically performed by dissolution of the matrix in strong base and quantification of the actives by analytical method such as UV-visible spectrophotometry, HPLC or ICPEOS in the case of organometallic such as DBTDL. The alternative method is to leach out the active in an appropriate solvent (in which the active is highly soluble). Although this method does not take into account the active which is either physically or chemically entrapped in the silica matrix, the loading figure it provides represent the total utilisable amount of active and is thus acceptable from an application point of view. Due to failures in assessing the loading of the encapsulated organotin catalyst particles in both strong acid or base, the above leaching methodology was used to assess the DBTDL loading. The loading is defined by the amount of DBTDL leached divided by the weight of the initial dry particles. The encapsulation efficiency is defined by the amount of DBTDL in the particles divided by the amount of DBTDL introduced into the system to synthesise the particles. Referring to Figure 3, FT-IR analysis was used to monitor the presence and quantity of DBTDL in the leached samples. Ethanol, acetone and chloroform were tested for release of DBTDL. Figure 3 indicates that DBTDL has been encapsulated into the particles due to the presence of identical peaks of the DBTDL in the range of 1400-1600 cm^-1. Calibration using ethanol did not provide a meaningful trend or results. In contrast, acetone and chloroform were able to provide linear calibration curves. A medium sharp peak at 1600 cm^-1 was considered for the calibration in acetone and chloroform. Figure 4 presents the calibration of DBTDL in chloroform and the obtained formula is y = 8281.5x – 58.042, R² = 0.9984. Comparison of the loading of the two samples using acetone and chloroform at two different leaching times shows that leaching of DBTDL using chloroform for 24 hours aging yielded a higher loading value and thus a more efficient extraction. In the following examples the leaching time has been fixed at 24h. Influence of Various Synthetic Parameters Influence of Aging Time (EH9) The general synthesis described above was used to prepare samples. The influence of the aging time on the morphology and loading was studied by aging the emulsions for either 1, 2, 16 or 24h prior to centrifugation. The SEM micrographs are presented in Figure 5 and loadings are outlined below in Table 1. Table 1: Influence of the aging time on the Loading and Encapsulation efficiency. Samples Loading Error EE %

Influence of precursor PTES vs PTMS (EH9) The general synthesis described above was used to prepare the following samples. The influence of the nature of the alkoxy group from the silane on the morphology and loading was studied by substituting phenyltriethoxysilane with phenyltrimethoxysilane. The SEM micrographs are presented in Figure 6 and loadings are outlined below in Table 2. Figure 6 shows that particles produced by PTES are significantly larger than the those produced by PTMS and their appearance is more faceted than the particles produced by PTMS, which are more spherical. Table 2 also reveals that the use of PTES as a precursor leads to a significant increase in loading as well as encapsulation efficiency. Table 2: Influence of the nature of the alkoxy group of the phenyl silane on the Loading and Encapsulation efficiency. Samples Loading Error EE %

Influence of increasing amount of Active The general synthesis described above was used to prepare the samples. The influence of increasing the amount of DBTDL on the morphology and loading of particles was studied by multiplying the amount of DBTDL used in the standard recipe by 1, 1.25, 1.5 and 2 times. The amount of ethanol used to dissolve the active was adjusted accordingly. The SEM micrographs are presented in Figure 7 and loadings are outlined below in Table 3. Increasing the amount of DBTDL introduced in the synthesis leads to an increase in particle size as well as an increase in polydispersity. The loading is also increased with the amount of DBTDL introduced. Interestingly, maximum encapsulation efficiency is observed for an amount of DBTDL at 1.5x times higher than that used in the standard preparation. Table 3: Influence of amount of DBTDL on the Loading and Encapsulation efficiency. Loading

Influence of the solvent (EH9) The samples were synthesised using the general synthesis above except that the DBTDL is dissolved in acetone rather than ethanol. When no solvent was used, the DBTDL was added neat to the alkoxide/silane mixture in which it dissolved. The SEM micrographs are presented in Figure 8 and loadings are outlined below in Table 4. Use of Ethanol appears to produce particles with the best morphology (see Figure 8) with the smallest dispersion in size and well-formed spherical particles. Interestingly, however, the particles made using acetone have a higher loading and better encapsulation efficiency than the particles synthesised using ethanol or no solvent. Table 4: Influence of Solvent on Loading and Encapsulation efficiency. Samples Loading Error EE %

Influence of the amount of Surfactant (EH9) Synthesis according to the general synthesis described above was conducted using varying amounts of EH9 surfactant. Samples were produced using the following variations in the surfactant amount: ● 20% increase in EH9 quantity ● 10% increase in EH9 quantity ● 10% decrease in EH9 quantity ● 20% decrease in EH9 quantity The water phase was produced by stirring EH9 surfactant in 50 ml of water. The below amounts were used: ● 20% increase – 3g of EH9 ● 10% increase – 2.75g of EH9 ● 10% decrease – 2.25g of EH9 ● 20% decrease – 2g of EH9 The SEM micrographs are presented in Figure 9 and loadings are outlined below in Table 5. Table 5: Influence of Solvent on Loading and Encapsulation efficiency. Samples Loading Error EE %

Increasing the surfactant amount does not appear to significantly affect the particle size or dispersity. In contrast, decreasing the surfactant seems to lead to a higher polydispersity, which could be explained by a lower stability of the emulsion system. Influence of the nature of the surfactant Synthesis according to the general synthesis outlined above was conducted using various surfactants. The surfactants were selected based on their HLB values which are in the range of the HLB for EH9 i.e., 12.5. ● Tergitol NP9 – HLB: 12.9 ● Tergitol CA 60 – HLB: 11-12 ● Tergitol CA 90 – HLB: 13-14 ● Tergitol NP 10 – HLB: 13.2 ● Tergitol NP8 – HLB: 12.6 ● Tergitol 15-S-7 – HLB: 12.1 ● Ecosurf EH14 – HLB: 14 The water phase was prepared by stirring the surfactants in 50 ml of water. The amounts used were: ● 2.5g of CA 60 ● 2.5g of CA 90 ● 1.5g of CA60 + 1g of CA 90 ● 6.92 g of NP10 ● 6.16g of NP 8 ● 5.47g of 15-S-7 ● 2.5g of EH9 ● 6.63g of NP9 ● 2.5g of EH14 The SEM micrographs are presented in Figure 10 and loadings are outlined below in Table 6. The samples synthesised with NP8, NP9, NP10 tend to form capsules, i.e., core-shell structures, which have different mechanical resistance depending on the surfactant used, and after drying appear to be in the form of shards (NP8), doughnuts or half shells (NP9), or fused hollow spheres (NP10). The EH series produces particles, albeit with different morphologies. CA 90, though, in contrast with CA 60, produces nice particles with a loading significantly higher than EH9. There does not appear to be a clear correlation between the HLB of the surfactant and either the shape or the loading of the particles. Viable samples, from morphology perspective, were prepared by CA90, EH9 and EH14. Table 6: Influence of different surfactants on Loading and Encapsulation efficiency. Samples Loading Error EE %

Influence of the molar ratio of PTES (EH9) Synthesis according to the general synthesis outlined above was conducted using differing ratios of PTES and TEOS. The water phase was prepared in accordance with the general synthesis, and differing amounts of PTES and TEOS were used, based on the molar ratio of the two precursors. Samples were produced using: ● PTES – 55%: 45% - TEOS ● PTES – 60%: 40% - TEOS ● PTES – 65%: 35% - TEOS ● PTES – 75%: 25% - TEOS ● PTES – 80%: 20% - TEOS ● PTES – 85%: 15% - TEOS ● PTES – 90%: 10% - TEOS The SEM micrographs are presented in Figure 11 and loadings outlined below in Table 7. Increasing the molar ratio of PTES/TEOS increases the hydrophobicity of the hybrid silica network as the molar ratio of Phenyl group/silicon atoms increases. This increase in network hydrophobicity seems to increase the particle size to the point where the emulsion becomes unstable and a significant fusing between the particles occurs (molar ratio of 90/10 PTES/TEOS). The loading remains relatively stable until the PTES/TEOS ratio goes beyond 80/20, where it starts to decrease. Table 7: Influence of different precursor molar ratios on Loading and Encapsulation efficiency. Samples Loading (%) Error EE %

Influence of the nature of the organosilane precursor (EH9) Synthesis according to the general synthesis scheme outlined above was conducted using various organosilane precursors to investigate the effect of changing the lipophilicity through functionalisation of the siloxane network. The general synthesis was used to prepare the following samples. The organosilane precursor (PTES) was replaced with Octyltriethoxysilane (OTES), Vinyltrimethoxysilane (VTMS) and Tetrapropoxysilane (TPOS). The SEM micrographs are presented in Figure 12 and loadings outlined below in Table 8. Substitution of the phenylsiloxane by long chain alkyl siloxane like octyltriethoxysilane or smaller double bond group such as vinyl led to particle formation. Substitution of the tri alkoxy silane (PTES) by a tetra-alkoxy silane (TPOS) does not result in the production of particles, thus highlighting the need to have a trialkoxysilane as one of the precursors for successful encapsulation. It is noted that even if particles are formed, the loading of OTES and VTMS particles remain significantly lower than the PTES particles. Table 8: Influence of different organosilane precursors on Loading and Encapsulation efficiency. Loading

Further Examples Microstructure and Porosity of encapsulated DBTDL particles Particle Synthesis: Particles were synthesized using 3 different types of surfactants according to the following procedure: Reaction Mixture Preparation: 2.5g of surfactant (EH9, X114 or 15-S-9) was solubilised in 50ml of deionised water. Separately, 1g DBTDL was solubilised in 1g ethanol by stirring with a magnetic stirrer for 3-5 minutes. The solubilised DBTDL was then added to a mixture of 5.39mL PTES and 2.14mL TEOS (in a molar ratio of 70:30, respectively), and this precursor mixture was stirred for a further 5 minutes before being added to the water phase of the reaction. Ageing: The resulting reaction mixture was left to age for 4 hours, before being spun down at 4400 rpm for 20 minutes. Drying: Samples (particle pellets) after discarding the supernatant were then dried at 40^oC overnight. Characterization: The structures of the particles were analyzed using Scanning Electron Microscopy (SEM). SEM of samples ES23-0073 & ES23-0084, produced with EH9, show a matrix with large vacuoles present inside, as shown in Figures 13A-13C. Porosity and Surface area: Determination of pore size, volume and particle surface area was carried out using N2 sorption using a Micromeritics TriStar II 3020 system. Comparison of the BET surface areas showed very similar values for surface areas and pore volumes in various DBTDL particle samples (Table 9). Further, little difference was shown between the particles produced different surfactant preparations (Table 9). The very low surface area and absorption/desorption isotherm suggests that the particles are dense and non-porous (see Figure 14). Interestingly, this contrasts with particles produced using a mixture of organo-silane using amino- silane as a catalyst as described in Kong et al. J Sol-Gel Science and Technology DOI 10.1007/s10971-012-2859-7 and International Patent Publication WO 2006133519. Comparison of the DTBDL particle samples, produced using PTES and TEOS, to that of the Organosilane sample, produced using PTMS and TEOS, shows that the DBTDL particles have a much smaller internal structure when measured using this method, despite having a larger pore width. This result also contrasts with the microstructure observed in particles synthesized by double emulsions as reported in International Patent Publication WO 2006133518 which exhibited large surface areas (100-500m²/g) and pore volume from 0.1 to 1 cm³/g. This suggests that despite the presence of vacuoles in both cases, for the present invention the walls are dense, in contrast to the micro- and meso-porous walls synthesized in WO 2006133518. The difference in the shape of the nitrogen adsorption-desorption isotherm (type II in the present invention versus type 4 in WO 2006133518) confirms the drastic difference in their porous structures despite similar morphology. Table 9: BET measurements for DBTDL and Organosilane samples. PTES & TEOS Kong et Al

DBTDL loading from samples produced using different precursors Particle Synthesis: The samples were produced using various precursors: Octyl Tri Ethoxy Silane (OTES CAS# 2943-75-1), Vinyl Tri Methoxy Silane (VTMS CAS# 2768-02-7), Phenyl Trimethoxy Silane (PTMS CAS# 2996-92-1) and Phenyl triethoxy silane (PTES CAS# 780-69-8), according to the following procedure. 2.5g of surfactant (in this case Ecosurf EH9) was solubilised in 50ml of de- ionised water. Separately, 1g DBTDL was solubilised in 1g ethanol with stirring for 3-5 minutes (as previous). The solubilised DBTDL was then added to a mixture of TEOS and either PTMS, PTES, VTMS or OTES (in amounts as listed below). Table 10: Sample preparation amounts. Silane Amount silane (ml) Amount TEOS (ml)

Ageing and Drying: The reaction mixture for PTMS, PTES and OTES were left to age for 4 hours before being spun down at 4400 rpm for 20 minutes. The pelleted DBTDL particles were then dried at 40^oC overnight. In the case of VTMS samples, the reaction mixture was left to age over 24 hours, as full particle production was not seen at 4 hours. The sample mixture was then spun down at 4400rpm for 20 minutes and left to dry at 40^oC overnight. Characterization: Loading percentage of DBTDL in particles was determined by leaching in chloroform for 24 hours as follows: Roughly, 120mg powder was stirred in 5ml chloroform for 24 hours, before filtering through a 0.2um filter. The chloroform was evaporated, and the remaining DBTDL was read using IR, with the characteristic peak at 1600cm^-1 used for concentration determination (Table 11, Figure 15). It was clear that type of precursor had an impact on the DBTDL loadings in different samples, with best loading seen in the PTES/DBTDL particles. Table 11: Influence of precursor on DBTDL loading in chloroform Loading Error

Influence of the nature of the silane precursors on the DBTDL release The influence of the nature of the silane precursors used in the preparation of the particles on the release kinetics of DBTDL was investigated over a period of 24 hours. The release was carried out in a 50/50 mixture of acetone and chloroform. The release study was carried out using a procedure identical to the one described above for the loading determination. The release was determined as a percentage of the DBTDL loading value obtained for each precursor. The results are summarized in Table 12. Figure 15 shows a comparison of release profiles from VTMS and PTES samples, showing significant differences in the manner of release, with VTMS samples showing slower release at early times (59.8%) vs. higher release rates from PTES samples (up to 95.7% by 10 minutes). Table 12: Influence of precursor on release percentage of DBTDL over time, in 50/50 acetone/ chloroform Mins OTES OTES VTMS VTMS PTMS PTMS PTES PTES –

1 71.7 ±0.09 57.2 ±0.21 86.6 ±0.06 72.6 ±0.38

DBTDL Loading of samples synthesized with different PTES molar ratio Particle Synthesis: DBTDL samples were produced using molar ratio of PTES: TEOS of 55:45%, through to 90:10% according to the following procedure: 2.5g of surfactant (in this case Ecosurf EH9) was solubilised in 50ml of de- ionised water. Separately, 1g DBTDL was solubilised in 1g ethanol by stirring for 3-5 minutes. The solubilised DBTDL was then added to a mixture of PTES and TEOS (in differing molar ratios as listed below). Table 13: Sample preparation molar ratios. Silane Molar Ratio PTES amount (ml) TEOS amount (ml)

This precursor mixture was then stirred for a further 5 minutes before being added to the water phase of the reaction. Ageing and Drying: The reaction mixture was left to age for 4 hours, before being spun down at 4400 rpm for 20 minutes. Pelleted DBTDL particles were then dried at 40^oC overnight. Characterization: Loading determination was carried out in the same was as described above, by leaching in chloroform for 24 hours. Table 14: Influence of PTES molar % on DBTDL loading, leached in chloroform. PTES molar percent Loading Error

Comparison of the loading values for the different PTES molar percentages shows an slight overall decrease in the loading of DBTDL in the particles with increasing PTES content (Table 14 and Figure 17). Influence of the PTES/TEOS molar ratio on the DBTDL Release Release of DBTDL was investigated with different precursors, over a period of 24 hours, in a 50/50 mixture of acetone and chloroform using the procedure described above. The results are summarized in Figure 18. Comparison of release kinetics over 24 hours for differing PTES molar percentages shows an overall decrease in the rate of release with increasing PTES content, This confirms our initial hypothesis that increasing the hydrophobicity of the silica network does decrease the release of the active from the particles. It also demonstrates the capability to control the release by controlling the organosilane/TEOS molar ratio. Testing of the DBTDL Release in a Polyol This testing was carried out to identify the suitability of castor oil as a storage medium for encapsulated DBTDL. This would be critical for the use of these catalyst as accelerant for resin and paints such as poly urethane coatings. To verify the detactabilitty of DBTDL in polyol by FTIR, a sample was prepared by mixing pure DBTDL with castor oil using a 1:1 weight ratio. The individual FTIR spectra of plain castor oil, and pure DBTDL are shown below in Figures 19 and 20 respectively. The combination sample is shown in Figure 21. The presence of the DBTDL peak at 1600cm-1 is clearly visible in the combination sample confirming the potential to detect leached DBTDL in castor oil. Testing of an encapsulated DBTDL particles prepared using EH9 (prepared as described in section 1) was carried out in castor oil. The amount of sample was calculated to provide a 1.2% weight quantity of DBTDL within the mixture. The sample was mixed periodically to prevent settling of the particles. Infrared spectra were collected at 0-, 1- and 24-hour time points using a Themo Scientific Nicolet iS5 model FTIR. Comparison of the sample reading at 24 hours shows no difference to that at the 0-minute time point, and the absence of a peak at 1600 cm^-1 demonstrates that there is no release of the DBTDL from the particles into the castor oil (see Figure 22). Hence demonstrating the suitability of castor oil for storage of DBTDL particles. Prediction on the impact on catalytic behaviour of Encapsulated DBTDL A study of the impact of DBTDL on the polymerisation of polyurethane from isocyanates and polyols is planned. Typically, a low amount of DBTDL can significantly accelerate the polymerisation rate with a set time decreasing from 2h to about 1-2 minutes with around 1% of DBTDL. Although fast polymerization is an advantage, in some applications such as floor coating, one wants to be able to increase the applicability/workability of the paint without compromising the mechanical properties and strength of the final coating. The workability is characterised by the working time which is the time at which the paint no longer levels or heals. It is envisaged that: ● Varying the quantity of surfactant will have an impact on the emulsion droplet size and the size of the particles but will not affect the internal structure of the particles. Therefore, it is not expected that the molar ratio of surfactant to silane will impact the release and the working time. ● The use of PTES will significantly increase the working time compared to PTMS. It is thought that the fact that both precursors have the same alkoxy group (i.e., epoxy) will lead to comparable hydrolysis and condensation rate and the formation of a more homogeneous hybrid which is able to slow down the release more effectively. ● The molar ratio of PTES/TEOS will influence the hydrophobicity of the silica matrix and thus will influence the release of DBTDL and the working time. ● There will be no significant influence of the nature of solvent on the working time. The polar solvent used in the synthesis to dissolve DBTDL will rapidly migrate from the oil (i.e., silane) droplet to the aqueous continuous phase and thus is not thought that it will significantly affect the polymerisation of the silane and hence, the internal structure of the particles, which are the key to controlling the release of the actives from the particles. Throughout this specification, unless the context requires otherwise, the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated step or element or integer or group of steps or elements or integers, but not the exclusion of any other step or element or integer or group of steps, elements or integers. Thus, in the context of this specification, the term “comprising” is used in an inclusive sense and thus should be understood as meaning “including principally, but not necessarily solely”. Unless the context requires otherwise or specifically stated to the contrary, integers, steps or elements of the invention recited herein as singular integers, steps or elements clearly encompass both singular and plural forms of the recited integers, steps or elements. It will be appreciated that the foregoing description has been given by way of illustrative example of the invention and that all such modifications and variations thereto as would be apparent to persons of skill in the art are deemed to fall within the broad scope and ambit of the invention as herein set forth.

Claims

CLAIMS 1. A method of preparing silica particles encapsulating a liquid polyurethane catalyst, the method comprising: providing a hydrophilic phase comprising water and a surfactant; providing a hydrophobic phase comprising an organosilane and the liquid polyurethane catalyst; forming an oil-in-water emulsion comprising the hydrophobic phase dispersed in the hydrophilic phase; aging the emulsion, forming said silica particles encapsulating the liquid polyurethane catalyst in the hydrophobic phase; and recovering the formed silica particles encapsulating the liquid polyurethane catalyst.

2. The method of claim 1, wherein said surfactant in the hydrophilic phase is a nonionic alcohol alkoxylate surfactant.

3. The method of claim 1 or 2, wherein the organosilane is a trialkoxysilane, preferably selected from phenyltriethoxysilane, phenyltrimethoxysilane, octyltriethoxysilane and vinyltrimethoxysilane.

4. The method of claim 3, wherein said hydrophobic phase comprises a mixture of said trialkoxysilane and a tetraalkoxysilane, preferably tetraethoxysilane.

5. The method of claim 4, wherein said mixture has a molar ratio of tetraalkoxysilane;trialkoxysilane of from 15:85 to 45:55, preferably about 30:70.

6. The method of any one of claims 1 to 5, wherein said liquid polyurethane catalyst is selected from an organotin catalyst, organozinc catalyst, organomercury catalyst, organobismuth catalyst, or alternatively an amine catalyst, for example, the liquid polyurethan catalyst is selected from Dioctyltin dithioglycolate, Dioctyltin dilaurate, Monobutyltin tris - (2-ethylhexanoate), Dioctyltin diacetate, Dibutyltin diacetate, Dioctyltin dicarboxylate, Dioctyltin carboxylate, Dioctyltin diacetyl acetonate, Dioctyltin bis-(isooctyl mercaptoacetate), Dibutyltin bis-(1-thioglycerol), Dimethyltin Dioleate, Dibutyltin bis-(2-ethylhexyl maleate), Dibutyltin Dilauryl Mercaptide, Dioctyltin Dilauryl Mercaptide, Dibutyltin bis-(2-ethylhexyl mercaptoacetate), Dimethyltin Dineodecanoate, Dioctyltin bis-(2-ethylhexyl mercaptoacetate), Dibutyltin bis- (isooctyl mercaptoacetate), Tin Ricinoleate, Tin neodecanoate, Zinc neodecanoate, Zinc octoate, Zinc 2-ethylhexanoate, Zinc isooctanoate, Bismuth neodecanoate, Bismuth octoate, Bismuth methanesulfonate, Bismuth 2-ethylhexanoate, Potassium Octoate, Lead 2-ethylhexanoate, Mercury neodecanoate, Phenylmercury neodecanoate, N,N,N-dimethylaminopropyl hexahydrotriazine.

7. The method of claim 6, wherein said liquid polyurethane catalyst is a dibutyltin catalyst, preferably selected from dibutyltin dilaurate, dibutyltin dioctanoate, dibutyltin diacetate and dibutyltin oxide.

8. The method of any one of claims 1 to 7, wherein said liquid polyurethane catalyst is dissolved in a solvent, preferably selected from ethanol and acetone.

9. The method of any one of claims 1 to 8, wherein said emulsion is aged for a period of up to 24 hours, preferably from about 2 to 4 hours.

10. The method of any one of claims 1 to 9, wherein the molar ratio of liquid polyurethane catalyst:silicon in the hydrophobic phase is 4 to 9:91-96 liquid polyurethane catalyst:silicon.

11. The method of any one of claims 1 to 10, further comprising stirring said hydrophobic phase, preferably for at least 5 minutes, prior to addition to the hydrophilic phase.

12. The method of any one of claims 1 to 11, wherein said hydrophobic phase is added to said hydrophilic phase under vigorous stirring or agitation to form said emulsion.

13. The method of any one of claims 1 to 12, wherein said formed silica particles encapsulating the liquid polyurethane catalyst are recovered by centrifugation, for example at 3000-4000rcf for 20-30 minutes.

14. The method of any one of claims 1 to 13, further comprising drying the formed silica particles encapsulating the liquid polyurethane catalyst, for example in an oven at 40°C for 12 to 24 hours.

15. Silica particles encapsulating a liquid polyurethane catalyst prepared by a method of any one of claims 1 to 14.

16. Silica particles comprising a silica matrix and an encapsulated liquid polyurethane catalyst, wherein the liquid polyurethane catalyst is releasable from the silica matrix in a controlled manner by diffusion.

17. The silica particles of claim 16, wherein the silica matrix is formed from a trialkoxysilane precursor, preferably selected from phenyltriethoxysilane, phenyltrimethoxysilane, octyltriethoxysilane and vinyltrimethoxysilane 18. The silica particles of claim 16, wherein the silica matrix is formed from a mixture of a trialoxysilane and a tetraalkoxysilane. 19. The silica particles of claim 18, wherein the trialoxysilane is selected from phenyltriethoxysilane, phenyltrimethoxysilane, octyltriethoxysilane and vinyltrimethoxysilane and the tetraalkoxysilane is tetraethoxysilane. 20. The silica particles of claim 18 or 29, wherein said mixture has a molar ratio of tetraalkoxysilane;trialoxysilane of from 15:85 to 45:55, preferably about 21. The silica particles of any one of claims 15 to 19, wherein said liquid polyurethane catalyst is selected from an organotin catalyst, organozinc catalyst, organomercury catalyst, organobismuth catalyst, or alternatively an amine catalyst, for example, the liquid polyurethan catalyst is selected from Dioctyltin dithioglycolate, Dioctyltin dilaurate, Monobutyltin tris - (2- ethylhexanoate), Dioctyltin diacetate, Dibutyltin diacetate, Dioctyltin dicarboxylate, Dioctyltin carboxylate, Dioctyltin diacetyl acetonate, Dioctyltin bis-(isooctyl mercaptoacetate), Dibutyltin bis-(1-thioglycerol), Dimethyltin Dioleate, Dibutyltin bis-(2-ethylhexyl maleate), Dibutyltin Dilauryl Mercaptide, Dioctyltin Dilauryl Mercaptide, Dibutyltin bis-(2-ethylhexyl mercaptoacetate), Dimethyltin Dineodecanoate, Dioctyltin bis-(2-ethylhexyl mercaptoacetate), Dibutyltin bis-(isooctyl mercaptoacetate), Tin Ricinoleate, Tin neodecanoate, Zinc neodecanoate, Zinc octoate, Zinc 2-ethylhexanoate, Zinc isooctanoate, Bismuth neodecanoate, Bismuth octoate, Bismuth methanesulfonate, Bismuth 2-ethylhexanoate, Potassium Octoate, Lead 2-ethylhexanoate, Mercury neodecanoate, Phenylmercury neodecanoate, N,N,N-dimethylaminopropyl hexahydrotriazine. 22. The silica particles of claim 21, wherein said liquid polyurethane catalyst is a dibutyltin catalyst, preferably selected from dibutyltin dilaurate, dibutyltin dioctanoate, dibutyltin diacetate and dibutyltin oxide. 23. The silica particles of any one of claims 16 to 22, wherein the liquid polyurethane catalyst is substantially homogeneously distributed inside the silica matrix. 24. Use of the silica particles of any one of claims 15 to 23 to control the speed of formation of polyurethanes by controlling the kinetics of the polymerisation of isocyanates with diols.