WO2015138154A1

WO2015138154A1 - Process for preparing silica/polymer hybrid hollow nanospheres using water-based silica precursors

Info

Publication number: WO2015138154A1
Application number: PCT/US2015/017899
Authority: WO
Inventors: Hau-Nan LEE; Stephanie A BERNARD
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 2014-03-11
Filing date: 2015-02-27
Publication date: 2015-09-17
Anticipated expiration: 2016-09-11

Abstract

The disclosure provides a process for preparing a silica/polymeric hybrid hollow nanosphere comprising: providing a mixture comprising water, at least one non-reactive solvent; at least one acrylic or styrenic monomer; an initiator; and at least one surfactant; shearing the components of the above mixture with high shear energy at an energy density of at least 10^6 J/m^3 to form a mini-emulsion; heating to at least about 50 °C to initiate the polymerization reaction; and at the same time, feeding at least one water-based silica precursor solution to emulsion; and adjusting the pH to about 4 to 10 so that the water-based silica precursor hydrolyzes and condenses to form a silica shell at the oil/water interface resulting in silica/polymeric hybrid hollow nanospheres. Steps (c) and (d) in this process may occur simultaneously.

Description

TITLE

PROCESS FOR PREPARING SILICA/POLYMER HYBRID HOLLOW NANOSPHERES USING WATER-BASED SILICA PRECURSORS BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

The present disclosure relates to a process for making

silica/polymer nanospheres, more particularly to a preparation process for making silica/polymer nanospheres utilizing a mini-emulsion preparation process with water-based silica precursors; and use of the silica/polymer nanospheres in coating compositions.

Description of the Related Art

Nanospheres are submicroscopic colloidal systems composed of a solid or liquid core surrounded by a thin polymer or inorganic shell. This solid or liquid core is removed to form hollow nanospheres. Such core- shell systems may be prepared from micro or miniemulsions via polymerization reaction at the interface of the droplets, the so-called interfacial polymerization reaction. Interfacial polymerization occurs at the interface of two immiscible phases, for example, oil and water, and a thin shell is formed. In the formation of the shell, the monomers are in either oil or water phase to participate in the reaction. Typically, for the preparation of core-shell nanocapsules via interfacial polymerization, an microemulsion or miniemulsion is first prepared, either water in oil or oil in water, wherein in the former nanocapsules with an aqueous core suspended in oil are formed and in the latter nanocapsules with an oily core suspended in water are formed. Existing process for the preparation of hybrid silica/polymeric particles either require a multi-step

polymerization/condensation process to form the hollow nanospheres, or produce particles that are too large.

A need exists for a hollow nanosphere composed of a single silica/polymeric hybrid shell, wherein the silica is derived from a water- based silica precursor. It is also needed that the nanospheres can be prepared through a one step process and provide superior performance for opacity enhancement in architectural and industrial coatings.

SUMMARY OF THE DISCLOSURE

In a first aspect, the disclosure provides a process for preparing a silica/polymeric hybrid hollow nanosphere comprising:

(a) providing a mixture comprising water, at least one non- reactive solvent; at least one acrylic or styrenic monomer; an initiator; and at least one surfactant;

(b) shearing the components of the mixture from (a) with high shear energy at an energy density of at least 10^Λ6 J/m^A3 to form a mini-emulsion;

(c) heating to at least about 50 °C, more typically about 50 °C to about 90 °C; and still more typically about 60 °C to about 80 °C to initiate the polymerization reaction, and simultaneously feeding at least one water-based silica precursor solution, such as sodium silicate, potassium silicate or pre-formed silicic acid, to emulsion; and

(d) adjusting the pH to about 4 to about 10 to form

silica/polymeric hybrid hollow nanospheres.

By non- reactive solvent we mean that the solvent does not substantially react, more typically does not react, with any of the other components added to the reaction.

In the first aspect, steps (c) and (d) may occur simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is the structure of the particles from Example 1 that were analyzed using transmission electron microscopy.

Figure 2 is a TEM image of the hybrid hollow particle for Example 2. DETAILED DESCRIPTION OF THE DISCLOSURE

In this disclosure "comprising" is to be interpreted as specifying the presence of the stated features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps, or components, or groups thereof. Additionally, the term "comprising" is intended to include examples encompassed by the terms "consisting essentially of and "consisting of." Similarly, the term "consisting essentially of is intended to include examples encompassed by the term "consisting of."

In this disclosure, when an amount, concentration, or other value or parameter is given as either a range, typical range, or a list of upper typical values and lower typical values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or typical value and any lower range limit or typical value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the disclosure be limited to the specific values recited when defining a range.

In this disclosure, terms in the singular and the singular forms "a,"

"an," and "the," for example, include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to

"silica/polymeric hybrid hollow nanosphere", "the silica/polymeric hybrid hollow nanosphere", or "a silica/polymeric hybrid hollow nanosphere" also includes a plurality of silica/polymeric hybrid hollow nanospheres.

The disclosure relates to a process for preparing a silica/polymeric hybrid hollow nanosphere, typically a substantially non-porous

silica/polymeric hybrid hollow nanosphere. By substantially non-porous it is meant that the surface area and porosity of the silica/polymeric shell, typically walls, has to be tuned. Whether the silica/polymeric shell is adequate can be determined by comparing the surface area of the particles with surface area of a smooth sphere, typically a polymer shell, of the same diameter. Typically, we consider the shell substantially non- porous if its surface area does not surpass about 130% of the surface area of a smooth sphere of the same dimensions, i.e., it is about 30% or less higher than the surface area of a smooth sphere of the same diameter, more typically about 125% of the smooth sphere surface area, and still more typically about 120% of the smooth sphere surface area of the same dimensions. Controlling the ratio between silica precursor and monomers will lead to more or less porous silica/polymeric layers, which can lead to control of the porosity and surface area of the particles.

These silica/polymeric hybrid hollow nanospheres are useful as hiding or opacifying agents in coating and molding compositions. They are also useful as drug delivery systems in the pharmaceutical and medical industries; in food, personal care and cosmetics; and agriculture.

These nanospheres have a particle size of about 5 nm to about 400 nm, more typically about 50 nm to about 300 nm, and still more typically about 100 nm to about 250 nm.

The silica/polymeric hybrid hollow nanospheres are prepared by a process comprising:

(c) heating to at least about 50 °C, more typically about 50 °C to about 90 °C; and still more typically about 60 °C to about 80 °C to initiate the polymerization reaction; and simultaneously feeding at least one water-based silica precursor solution, such as sodium silicate, potassium silicate or pre-formed silicic acid, to emulsion wherein the concentration of silica precursor is about 0.005 wt% to 5 wt%, more typically about 0.005 wt% to 2 wt%; and

(d) adjusting the pH to about 4 to 10, so that the water-based silica precursor hydrolyzes and condenses to form a silica shell at the oil/water interface resulting in silica/polymeric hybrid hollow nanospheres. Typically steps (c) and (d) may occur simultaneously.

The non-reactive solvent may be an alkane, a hydrocarbon oil, aromatic hydrocarbon or halogenated hydrocarbon liquid, more typically alkane or hydrocarbon oil.

The at least one acrylic or styrenic monomer may be methyl methacrylate, methyl acrylate, n-butyl methacrylate, t-butyl methacrylate, t- butyl acrylate, ethyl glycol dimechacrylate, 3-(Trimethoxysilyl)propyl methacrylate (TMSPM), styrene or divinylbenzene; more typically methyl methacrylate or styrene.

Some suitable initiators include azo compounds such as 2,2'- azobisisobutyronitrile (AIBN) or 2,2'-azobis(2-methylpropionamide) dihydrochloride (AIBA); metal persulfate such as potassium persulfate (KPS) or sodium persulfate; more typically AIBN, AIBA, or KPS. At least one surfactant is part of the mixture in step (a).

Some suitable surfactants include cetyltrimethylammonium bromide (CTAB), lauryltrimethylammonium bromide, dodecyltrimethylammonium bromide, octyltrimethylammonium bromide, sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), dioctylsulfosuccinate , nonionic surfactants such as alkylphenol polyoxyethylene,

polyoxyethylene glycol alkyl ethers, polyoxypropylene glycol alkyl ethers, octylphenol ethoxylates or poloxamers, more typically SDS, SDBS or CTAB. Some useful commercially available surfactants series include Triton X® manufactured by The Dow Chemical Company, Brij®

manufactured by Croda International PLC, or Pluoronic® manufactured by BASF.

Optionally, a polymerizable silane is used to increase the

compatibility between polymeric and silica networks. Some suitable polymerizable silanes include allyltriethoxysilane, allyltrimethoxysilane, diethoxy(methyl)vinylsilane, dimethoxymethylvinylsilane,

triethoxyvinylsilane, trimethoxy(7-octen-1 -yl)silane, 3- (trimethoxysilyl)propyl acrylate, 3-(trimethoxysilyl)propyl methacrylate, or vinyltrimethoxysilane, more typically 3-(trimethoxysilyl)propyl acrylate or 3-(trimethoxysilyl)propyl methacrylate.

The mixture in step (a) may be prepared in any glass container or stainless steel reaction vessel .

The mixture of the above components is then sheared at an energy density of at least 10^Λ6 J/m^A3, more typically about 10^Λ7 J/m^A3 to about 5*10^Λ8 J/m^A3, to form a mini-emulsion. Some useful means for shearing include an ultrasonic disruptor, high speed blender, high pressure homogenizer, high shear disperser, membrane homogenizer or colloid mill, more typically an ultrasonic disruptor, high speed blender, or a high pressure homogenizer. Typically shearing occurs for a period of about 5 to about 120 minutes depending on amount of emulsion needed to be prepared and desired emulsion size range, more typically about 30 minutes to about 60 minutes. Typically, shearing is accomplished at room temperature. Optionally, a defoamer may be needed to avoid foaming during emulsifying. Some suitable defoamers include BASF Foamaster®, Dow Corning® 71 and 74 Antifoams.

The mini-emulsion formed in step (b) is then heated to at least about 50 °C, more typically about 50 °C to about 90 °C; and still more typically about 60 °C to about 80 °C to form, in one step, by a sol gel reaction and polymerization, a silica/polymeric hybrid hollow nanosphere. Heating may be accomplished using hot plate, heating mantle or any other heating method.

The water-based silica precursor in step (c) is sodium silicate, potassium silicate or pre-formed silicic acid; more typically sodium silicate or potassium silicate; still more typically sodium silicate.

The concentration of silica precursor is about 0.005 wt% to about 5 wt%, more typically about 0.005 wt% to about 2 wt%, based on the total weight of the dispersion..

The pH adjustment in step (d) may be achieved using any reasonable choice of acid or base. The process in steps (c) and (d) comprises a sol gel reaction and polymerization that result in the formation of silica/polymeric hybrid nanospheres. Applications:

These silica/polynneric hybrid hollow nanospheres are useful as hiding or opacifying agents in coating and molding compositions. They are also useful as drug delivery systems in the pharmaceutical and medical industries; in food, personal care and cosmetics; and agriculture.

EXAMPLES

Glossary:

AIBN 2,2'-azobisisobutyronitrile

CTAB cetyltrimethylammonium bromide

Example 1 :.

An oily mixture which contained 5.0 g of hexadecane, 36.8 g of octane, 28.8 g of methyl methacrylate, 3.6 g of ethylene glycol

dimethacrylate, 3.6 g of styrene, and 0.798 g of AIBN was first prepared, and added to a water solution which contains 420.0 g of water, 0.9 g of CTAB and 0.5 g of defoamer (Foamaster® 1 1 1 , BASF). Miniemulsification was achieved by shearing the mixture for 30 minutes with a high speed blender at 9500 rpm. After forming a stable miniemulsion, the

polymerization was started by heating the miniemulsion to 70 °C, and then the pH of the emulsion was adjusted to about 7 by adding NaOH solution. Sodium silicate solution (7.2 ml solution silicate in 300 ml water) was added to the emulsion at a feeding rate of 1 .67 ml/min over 3 hours while maintaining the pH of the solution to about 7 by continuously adding HCI solution. After feeding sodium silicate solution, the pH was adjusted to about 9.5, and the mixture was let sit for 3 hours. The sodium silicate hydrolyzed and condensed to form a silica shell at the oil/water interface resulting in a silica/polymeric hybrid network comprising a silica/polymeric hybrid hollow nanosphere. The structure of the resulting particles was analyzed using transmission electron microscopy and shown in Figure 1 . Example 3:. An oily mixture which contained 1 .67 g of hexadecane, 12.3 g of octane, 9.6 g of methyl methacrylate, 1 .2 g of ethylene glycol

dimethacrylate, 1 .2 g of styrene, and 0.266 g of AIBN was first prepared, and added to a water solution which contains 140.0 g of water, 0.17 g of CTAB and 0.3 g of defoamer (Foamaster® 1 1 1 , BASF). Miniemulsification was achieved by shearing the mixture for 30 minutes with a high speed blender at 9500 rpm. After forming a stable miniemulsion, the

polymerization was started by heating the miniemulsion to 70 °C and run overnight. Next, the temperature of the mixture was allowed to lower to room temperature, and then 22.6 g of Sodium silicate solution (26.5 wt% of SiO2) was added to the emulsion, and the pH of the solution was increased to 1 1 .2. The pH of the solution was slowly lowered to about 8 by continuously adding 1 M HCI solution over 4 hours. After lowering the pH, the mixture was let sit at RT for 3 hours. The sodium silicate hydrolyzed and condensed to form a silica shell at the oil/water interface resulting in a silica/polymeric hybrid network comprising a silica/polymeric hybrid hollow nanosphere. The structure of the resulting particles was analyzed using transmission electron microscopy and shown in Figure 2. Example 3:

An oily mixture which contained 1 .67 g of hexadecane, 12.3 g of octane, 9.6 g of methyl methacrylate, 1 .2 g of ethylene glycol

polymerization was started by heating the miniemulsion to 70 °C and run overnight. Next, the temperature of the mixture was raised to 80 °C, and then 22.6 g of sodium silicate solution (26.5 wt% of SiO2) was added to the emulsion, and the pH of the solution was increased to about 1 1 . The pH of the solution was slowly lowered to about 8 by continuously adding 1 M HCI solution over 4 hours. After lowering the pH, the mixture was stirred at 80 °C overnight. The sodium silicate hydrolyzed and condensed to form a silica shell at the oil/water interface resulting in a silica/polymeric hybrid network comprising a silica/polymeric hybrid hollow nanosphere. The structure of the resulting particles was analyzed using transmission electron microscopy and shown in Figure 3.

Example 4. Hiding power performance of selected Examples in coatings formulations

Three hollow particles shown in the Examples above were tested in an acrylic latex paint formulation. Four formulations were prepared (Table 1 ), one without any hollow silica (control), and three with 5 wt% of materials from Examples 1 -3. Thin coating films were made from the four formulations, and they were compared for hiding power (Scoat), using standard protocols of Kubelka-Munk theory of reflectance (Table 2). It is evident that addition of hollow silica particle provides films with superior hiding power. The hollow particles described above are thus seen as good additives for hiding power improvement.

Rheology 3.25 3.25 3.25 3.25 modifier 1

(20wt%)

Rheology 0.33 0.33 0.33 0.33 modifier II

(17.5wt%)

Test material — 2.54 2.54 2.54

Table 1 . Composition of paint formulations with and without hollow silica particle.

Table 2. Dry film PVC and hiding power data from formulations in Table 2. *PVC=pigment volume concentration.

Claims

CLAIMS What is claimed is:

1 . A process for preparing a silica/polymeric hybrid hollow nanosphere comprising:

(c) heating to at least about 50 °C to initiate the polymerization reaction, and simultaneously feeding at least one water-based silica precursor solution to the emulsion; and

(d) adjusting the pH to about 4 to about 10 to form a silica/- polymeric hybrid network comprising a silica/polymeric hybrid hollow nanosphere.

2. The process of claim 1 wherein heating is to about 50 °C to about 90 °C.

3. The process of claim 2 wherein heating is to about 60 °C to about 80 °C.

4. The process of claim 1 wherein the non-reactive solvent is an alkane, a hydrocarbon oil, aromatic hydrocarbon or halogenated hydrocarbon liquid.

5. The process of claim 4 wherein the non-reactive solvent is alkane or hydrocarbon oil.

6. The process of claim 1 wherein the at least one acrylic or styrenic monomer is methyl methacrylate, methyl acrylate, n-butyl methacrylate, t-butyl methacrylate, t-butyl acrylate, ethyl glycol

dimechacrylate, styrene or divinylbenzene.

7. The process of claim 6 wherein the at least one acrylic or styrenic monomer is methyl methacrylate or styrene.

8. The process of claim 1 wherein the water-based silica precursor is sodium silicate, potassium silicate or pre-formed silicic acid

9. The process of claim 8 wherein the water-based silica precursor is sodium silicate or potassium silicate.

10. The process of claim 1 wherein the initiator is an azo

compound; or a metal persulfate.

1 1 . The process of claim 10 wherein the azo compound is 2,2'- azobisisobutyronitrile (AIBN) or 2,2'-azobis(2-methylpropionamide) dihydrochloride (AIBA).

12. The process of claim 10 wherein the metal persulfate is potassium persulfate (KPS) or sodium persulfate.

13. The process of claim 10 wherein the initiator is AIBN or KPS.

14. The process of claim 1 wherein the surfactant is

cetyltrimethylammonium bromide (CTAB), lauryltrimethylammonium bromide, dodecyltrimethylammonium bromide, octyltrimethylammonium bromide, sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), dioctylsulfosuccinate , alkylphenol polyoxyethylene, polyoxyethylene glycol alkyi ethers, polyoxypropylene glycol alkyi ethers, octylphenol ethoxylates, or poloxamers. .

15. The process of claim 14 wherein the surfactant is SDS, SDBS or CTAB.

16. The process of claim 1 wherein steps (c) and (d) occur simultaneously.

17. The process of claim 1 wherein the mixture of the above components is then sheared at an energy density of about 10^Λ7 J/m^A3 to about 5*10^Λ8 J/m^A3 form a mini-emulsion.

18. The process of claim 1 wherein the shearing means is an ultrasonic disruptor, high speed blender, high pressure homogenizer, high shear disperser, membrane homogenizer or colloid mill .