WO2003097218A1

WO2003097218A1 - Novel composite tecto-membranes formed by interfacial reaction of crosslinked polymer microspheres with coupling agents

Info

Publication number: WO2003097218A1
Application number: PCT/CA2003/000725
Authority: WO
Inventors: Harald D. H. STÖVER; Lisa M. Croll
Original assignee: Mcmaster University
Priority date: 2002-05-16
Filing date: 2003-05-16
Publication date: 2003-11-27
Also published as: AU2003233276A1

Abstract

This invention provides a process for the preparation of a tecto-membrane which comprises reacting microspheres that bear reactive surface groups with a complementary crosslinking reagent to form the tecto-membrane. This invention also provides the tecto-membrane so formed. The tecto-membranes can be used, for example, to encapsulate volatile liquids, such as pheromones, for controlled release.

Description

Novel Composite Tecto-Membranes Formed by Interfacial Reaction of Crosslinked Polymer Microspheres with Coupling

Agents

FIELD OF THE INVENTION

This invention relates to membranes that comprise microspheres, to the method of making these membranes, and their uses.

BACKGROUND OF THE INVENTION

There is much interest in the development of new nano- and microstructural materials, and in the building blocks used in their construction. Examples of building blocks for such materials include monomers, block copolymers, dendrimers and microspheres, the later of which are also referred to as tectons.

The formation of hollow capsules through electrostatic self-assembly, the formation of composite shells through electrostatic alternating self-assembly and the formation of toner particles involving polymeric particles coated with inorganic materials have been described Velev et al . (Langmuir, 1996, 12:2374; Langmuir, 1997, 13:1856), by Caruso et al . (J. Am. Chem. Soc . , 1998, 120:8523) and by Nakahara, et al . (US Patent No. 4,740,443), respectively.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a process for the preparation of a tecto-membrane which comprises reacting microspheres that bear reactive surface groups with a complementary crosslinking reagent. In a second aspect, the invention also provides a tecto-membrane which comprises microspheres .

In a third aspect, the invention also provides a tecto-membrane which comprises microspheres that are held in ^'■'■5 place within the membrane by a film of crosslinked polymer.

In another aspect, the invention describes the use of the novel membranes for the microencapsulation of volatile organic liquids destined for slow or controlled release into the atmosphere or into a liquid medium. Such 10 volatile organic liquids are sometimes referred to below as "active material" .

In this application, the term "microspheres" encompasses microgels, which are microspheres that have a greater tendency to swell in an appropriate liquid. As

15 well, the term "microspheres" encompasses both porous and non-porous microspheres. Membranes that comprise microspheres (which are also called "tectons" ) are referred to as tecto-membranes, and such membranes that have a substantially spherical shape can also be referred to as

20 tecto-capsules .

DESCRIPTION OF THE FIGURES

Specific embodiments of the present invention are further described with reference to the accompanying Figures :

25 Figure 1 displays an optical microscope image of tecto-capsules formed with poly (ethyleneimine) (PEI) of 1200 number average molecular weight.

Figures 2A-C display Environmental Scanning Electron Microscope (ESEM) (2A and 2C) and Transmission 30 Electron Microscope (TEM) (2B) images of spherical tecto- membranes formed in methylethylketone (MEK) as the first liquid. These bear not only microspheres at the surface but are filled with microspheres.

Figures 3A and 3B display ESEM images and TEM cross-section images of spherical tecto-membranes formed under microsphere loading conditions of 0.04 g particles / mL oil phase (Figure 3A) and of 0.16 g particles / mL oil phase (Figure 3B) . Figures 3C-F display ESEM images of the spherical membrane wall of 3B, at different magnification levels .

Figures 4A-F display ESEM images of composite spherical tecto-membranes comprising divinylbenzene-maleic anhydride (DVB-MAn) microspheres in a polyurea shell. Figures 4A to 4C display composite tecto-membranes made using divinylbenzene/maleic anhydride microspheres that contain about approximately 20% hydrolyzed maleic anhydride, with Mondur ML as the polyfunctional reagent and PEI 1200 as the crosslinking reagent. Figures 4D to 4F display composite tecto-membranes made using divinylbenzene/maleic anhydride microspheres that contain about approximately 3% hydrolyzed maleic anhydride, with Mondur ML as the polyfunctional reagent and PEI 1200 as the crosslinking reagent .

Figure 5A displays a Reflective Optical Microscopy image of a non-spherical composite tecto-membrane comprising DVB-MAn microspheres in a polyurea membrane. Figures 5B-D display the same membrane but as seen using Transmission Optical Microscopy (5C) or ESEM (5B and 5D) . The optical microscope images display the copper loop (1) used as membrane support, and the tecto-membrane (2) .

Figure 6 displays the optical microscopy images taken immediately after the tecto-membrane forming reaction, and after 30s and 10 mins, respectively. A. Capsules formed with propyl acetate. B. Capsules formed with a 50/50 vol% mixture of propyl acetate and xylene.

Figure 7 displays the ESEM images (7A and 7B) and the TEM images (7C and 7D) of a non-spherical composite tecto-membrane with a thin gold coating (approximately 5 nanometer) . The images show the gold layer (1) , the polyurea layer (2) and the microspheres (3) . The aqueous side of the tecto-membrane is also indicated (4) .

Figure 8 displays the optical microscopy image of spherical tecto-membranes made from microgels.

Figure 9 displays the ESEM image of a composite tecto-capsule comprising porous poly (divinylbenzene-55) microspheres surface functionalised with maleic anhydride and maleic acid, in a polyurea shell .

DETAILED DESCRIPTION OF THE INVENTION

The tecto-membranes of the invention are formed by the reaction of microspheres which bear reactive surface groups with a complementary crosslinking agent. In one embodiment, the reaction takes place at or near an interface between two immiscible liquids, with microspheres suspended in a first liquid, and one or more complementary crosslinking reagents dissolved or suspended in a second, immiscible, liquid. To control the rate of reaction, the complementary crosslinking reagent may be added at a controlled rate to the second liquid as the reaction proceeds .

In some embodiments, the one liquid is dispersed in the other liquid by, for example, agitation. It is possible for the microspheres to be present in the dispersed phase and the crosslinking reagent to be present in the continuous phase, or vice versa, depending upon the , _,_ _., . ,_ particular liquids , the reactive groups on the surface or the microspheres and the particular crosslinking reagent.

In other embodiments, the liquids may not be dispersed. For example, one liquid may float on the other, with a horizontal interface.

Usually one of the two immiscible liquids is aqueous, and the other is organic. The reaction starts by diffusion of the more amphiphilic of the two reaction components, usually the crosslinking reagent, from one liquid to the other, where it reacts with the reactive groups on the surface of the other reaction components, usually the microspheres, to form crosslinking bonds. Reaction of the microspheres with the crosslinking reagent usually increases the polarity of the microspheres and thereby facilitates their migration to the liquid/liquid interface. In preferred embodiments, the surface of the microspheres is designed to have polarity suitable to assemble the microspheres at the interface prior to addition of the crosslinking reagent. The microspheres become linked together through the crosslinking reagent, usually via covalent bonds. This results in a network of microspheres interconnected via the crosslinking reagent to form a membrane .

In one embodiment, the microspheres bear reactive succinic anhydride and succinic acid moieties on their surface. Such microspheres can be made, for example, by copolymerization of divinylbenzene (DVB) and maleic anhydride (MAn) and maleic acid (MAc) . Commercial maleic anhydride contains varying amounts of maleic acid. As well, maleic anhydride may partially hydrolyze during the co- polymerization. As well, maleic acid may be deliberately added, in order to adjust the polarity of the microsphere surface. Henceforth, the term "maleic anhydride" encompasses, optionally, maleic acid. In some embodiments, the microspheres of the invention are hydrophobic enough to permit their dispersal in organic solvents, and reactive enough to permit their subsequent reaction with aqueous crosslinking reagents, such as polyamines . In such an embodiment, the chemical reaction involving the reactive groups on the microsphere surface and the amine crosslinking reagent forms amide linkages as follows :

The resulting zwitterionic products have a higher 3.5 hydrophilicity than the unreacted microspheres, which may further facilitate assembly of the microspheres at the organic/aqueous interface.

In another embodiment, the reaction takes place at or near a liquid interface between a first liquid and a 20 second liquid, with the microspheres suspended in one of the liquids, and the complementary crosslinking reagents dissolved or suspended in, or added to, the same liquid. The "same liquid" may be water or may be an organic, water- immiscible phase.

25 A number of factors can be varied in order to control the formation and mechanical stability of the tecto- membranes . Such factors include the polarity of the organic solvent, the microsphere loading, the chemical composition and crosslink density of the microspheres, the molecular weight and the rate of addition of the crosslinking ledyeπ", and the pH value and salinity of the aqueous phase.

The first liquid is usually the liquid in which the microspheres can be dispersed or dissolved and in which any material to be encapsulated can be dispersed or dissolved. It should be immiscible, or at least only partially miscible, with the second liquid. While the limits on what is meant by "partially miscible" are not precise, in general a substance is considered to be water- immiscible (in the case where one of the liquids is water) if its solubility in water is less than about 0.5% by weight. It is considered to be water-soluble if its solubility is greater than 98%, i.e., if 1 gram of the substance is put in 100 grams of water, 0.98 gram would dissolve. A substance whose solubility falls between these approximate limits is considered to be partially water- miscible .

If active material is to be encapsulated for later release it may be dissolved or suspended in the first liquid, and the first liquid may be encapsulated with the active material. If so, the properties of the first liquid may affect the rate of release of the active material.

Selection of a first liquid has to be made with these considerations in mind. Suitable candidates for use as the first liquid include C3-C₁2 alkyl acetates, such as propyl acetate, n-butyl acetate and n-hexyl acetate and the corresponding propionates, C1-C6 alkyl esters of aliphatic diacids, for example adipic acid dimethyl ester, C1-C4 alkyl esters of glycerol such as glycerol tributyrate (tributyrin) , C1-C6 alkyl esters of aromatic acids, for example methyl, ethyl, or butyl benzoate, alkylbenzenes such as toluene and xylene, ethers such as methyl tert. -butyl ether, ketones such as methylisobutylketone, and aliphatic _ _^ ni ri±es suc as utyronitπle . Mixtures of so vents can be used, with 1:1 (vol: ol) mixtures of propyl acetate/p-xylene being particularly preferred. There can also be used co- solvents to change the properties of solvents or solvent mixtures. As co-solvents there are mentioned aliphatic liquids such as kerosene and also cyclic hydrocarbons such as cyclohexane. As well, organic but substantially water- soluble solvents such as methylethylketone may be used as a solvent or co-solvent, though in such cases the final tectoparticles will tend to be dense assemblies of particles without a significant solvent core.

The second liquid, that may form the continuous phase, is preferably water or an aqueous solution with water as the ma or component .

The polarity of the first liquid, if organic, can be used to regulate the diffusion of the reactive species (crosslinking reagent or microsphere) from one phase to the other. If the diffusion of the crosslinking reagent through the microsphere-bearing organic solvent is encouraged by higher polarity and is rapid, the resulting membrane will be thicker but it may have a lower density.

The amount of microspheres in the reaction mixture also has an effect on the thickness of the tecto-membranes produced. Membrane thickness can be affected by the microsphere loading in the first liquid, with higher microsphere loading giving rise to thicker membranes. Microsphere loading may range from 0.001 grams to 0.7 grams per millilitre, preferably ranges from about 0.01 grams to about 0.30 grams per millilitre of solvent in which it is suspended, more preferably from 0.04 grams to 0.16 grams per millilitre of the solvent. .

Using as the sole first liquid a so vent ^■i_< r _ substantially soluble in the aqueous phase, such as MEK, and using a polyamine as the crosslinking reagent, gives a system where the first liquid rapidly diffuses out of the forming tecto-membrane even as the polyamine diffuses into the first liquid containing the microspheres. This leads to thick, porous membranes, and to solid tecto particles having little or no central hollow or solvent-filled core.

The choice of the crosslinking reagent is influenced by the liquid in which it is to be dissolved, by the nature of the complementary solvent which contains the microspheres, and by the nature of the functional groups on the microsphere surfaces. Crosslinking reagents can vary in the length of their backbone and in the number and type of reactive sites per molecule. High molecular weight crosslinking reagents with a large number of reactive sites form stronger linkages between microspheres, while low molecular weight crosslinking reagents form weaker linkages between microspheres . In a preferred embodiment where polyalkyleneimines are used, for example a poly (ethyleneimine) or a poly (propyleneimine) , high molecular weight crosslinking reagents include polyalkyleneimines having weight-average molecular weights of up to 750,000 g/mol . Low molecular weight crosslinking reagents include, for example, tetraethylenepentamines (TEPA) which has a molecular weight of 190 g/mol. The polyalkyleneimines preferably have number average molecular weights of from about 1200 to about 60,000g/mol, more preferable from about 8,000 to about 60,000g/mol. Using PEI of higher molecular weight gave spherical tecto-capsules of similar appearances to those made with PEI of lower molecular weight while wet, but the tecto-capsules retained their spherical shape better upon drying. The rate at which the crosslinking reagent is introduced in the reaction system can also have an effect on the nature of the tecto-membranes produced. If the crosslinking reagent is soluble in the solvent that contains the microspheres, use of a lower rate of addition of crosslinking reagent can decrease the amount of crosslinking reagent that diffuses past the liquid/liquid interface. Carrying out the interfacial reaction at lower (less alkaline) pH, say at pH 8, would be equivalent to adding amine more slowly, since at lower pH less amine would be present in the neutral, non-charged form in which it can best cross the interface.

In cases where the polarity of the microspheres is designed such that they assemble at the interface prior to addition of the crosslinking reagent, the rate of addition of the crosslinking reagent is of minor importance.

Spherical Tecto-Membranes

In order to produce spherical tecto-membranes, an aqueous/organic emulsion is prepared where one solvent contains the reactive microspheres, and the other solvent contains the crosslinking reagent. In order to facilitate the formation of a stable emulsion there may be used a stabiliser, such as polyvinylpyrrolidone (PVP) , or preferably polyvinylalcohol (PVA) . The stabiliser can be used to disperse and stabilise the organic phase in the continuous aqueous phase. Surfactants, such as Igepal CA- 630 or sodium dodecyl sulfonate (SDS) , can also be used to form organic/aqueous emulsions. Use of surfactants tends to give spherical tecto-membranes with smaller diameters. The choice of surfactant or stabilizer may depend on the method of emulsification used. Polymeric stabilisers are generally preferred as they do not tend to facilitate the transfer of organic particles into the aqueous phase.

The spherical tecto-membranes consist of cross- linked networks of microspheres . The outer surface of the tecto-membranes appears smooth, consistent with microspheres assembled and fixed at a distinct liquid-liquid interface. The inner surface of the capsules is rougher, in agreement with a random deposition and anchoring of microspheres. TEM images as well as higher resolution ESEM images show significant free volume between the microspheres that make up the tecto-membrane walls; see Figure 3. This is possibly due to the rapid fixation of microspheres upon deposition at the interface. This free volume may also be due to swelling of the capsule wall during assembly, possibly from adsorption of water into the ionic surface region.

Non-Spherical Tecto-Membranes

Interfacial assembly and fixation, usually covalent fixation, of reactive microspheres may further be used to form non-spherical membranes. One way of forming such non-spherical membranes is by contacting two immiscible liquids, the first containing the reactive microspheres, and the second containing the crosslinking reagent, under conditions whereby they form a non-spherical, for example flat, interface. One approach to making non-spherical membranes is to coat a solution containing a crosslinking reagent onto a macroporous and inert support membrane that has been soaked in a suspension of reactive microspheres, or vice-versa. Another approach is to assemble microspheres in a macroporous support membrane, or on a nanoporous support membrane with the help of a pressure differential across the support membrane [G. Zhu et al, J. Mater. Chem. , 2001, 11:1687-1693], and to fix them by applying the crosslinking solution onto the microsphere layer or bed, followed by rinsing and optional release from the support membrane. in this embodiment in particular, the two solutions containing microspheres or microgels, and the complementary crosslinking reagent, respectively, need not be immiscible as the microspheres or microgels are assembled using a pressure differential rather than interfacial tension. The paper of Zhu et al . is incorporated herein by reference. A third process includes the layering of the two immiscible liquids, each containing the required reactive species to form the tecto-membrane. A tecto-membrane forms at the interface, which in this instance is a flat interface, resulting in a flat membrane. The resulting single or multi-layer tecto-membranes have regular interstitial pores, with the pore diameters decreasing with decreasing microsphere diameter.

Composite Tecto-Membranes

In one embodiment, one or more additional polyfunctional (e.g. difunctional) reagents that are capable of reacting with the crosslinking reagents are added to the membrane-forming reaction mixture. In one example, the polyfunctional reagent is dissolved or suspended in the same liquid as the microspheres, and it also reacts with the crosslinking reagents at the liquid/liquid interface. This produces a composite tecto-membrane in which microspheres are embedded in a polymeric membrane formed by reaction of the polyfunctional reagent and the crosslinking reagent.

In these composite tecto-membranes, the polarity of the microsphere surfaces can be adjusted such that they are located either at the interface between the dispersed and the continuous phases, within the membranes formed between the polyfunctional reagent and the crosslinking reagent, or within the dispersed phase. In those embodiments described earlier where there are no additional polyfunctional reagents, the microspheres present in the membrane are closely adjacent to each other, being separated only by the crosslinking reactant that has reacted with the reactive groups on the surface of the microspheres. In those embodiments where an additional polyfunctional reagent is added, many microspheres will be separated by polymeric chains formed by reaction between the crosslinking reagent and the additional polyfunctional reagent.

Microspheres can be used with known liquid/liquid interface reagents in order to form composite tecto- membranes. Such tecto-membranes comprise microspheres embedded within a polymeric wall structure. For example, if microspheres with surface anhydride moieties are reacted with a polyamine and a polyisocyanate, there will be formed a membrane comprising microspheres embedded in polyurea. As well as reacting with the microspheres, the polyamine reacts with the polyisocyanate to form the polyurea in which the microspheres are embedded.

The polyisocyanate may be a diisocyanate or a triisocyanate, or an oligomer of isocyanate-bearing monomers. The polyisocyanate may be aromatic or aliphatic and may contain two, three or more isocyanate groups. Examples of aromatic polyisocyanates include 2,4- and 2,6- toluene diisocyanate, naphthalene diisocyanate, diphenylmethane diisocyanate (Mondur ML) , and triphenylmethane-p,p' ,p"-trityl triisocyanate.

Aliphatic polyisocyanates may optionally be selected from aliphatic polyisocyanates containing two isocyanate functionalities, three isocyanate functionalities, or more than three isocyanate functionalities, or mixtures of these polyisocyanates. rereraD±y, . e a ip a__ic po .yisocyana_.e con_.ains ^j carbons. More preferably, the aliphatic polyisocyanate comprises one or more cycloalkyl moieties. Examples of preferred isocyanates include dicyclohexylmethane-4 , 4 ' - diisocyanate; hexamethylene 1 , 6-diisocyanate; isophorone diisocyanate; trimethyl-hexamethylene diisocyanate; trimer of hexamethylene 1, 6-diisocyanate; trimer of isophorone diisocyanate; 1, 4-cyclohexane diisocyanate; 1, - (dimethyl - isocyanato) cyclohexane; biuret of hexamethylene diisocyanate; urea of hexamethylene diisocyanate; trimethylenediisocyanate; propylene-1, 2-diisocyanate; and butylene-1,2 -diisocyanate. Mixtures of polyisocyanates can be used.

Particularly preferred polyisocyanates are polymethylene polyphenylisocyanates of formula (I) :

OC

wherein n is from 0 - 4. These compounds are available for example under the general trade-mark Mondur, with Mondur ML being the compound in which n is 0, and Mondur MRS being a mixture of compounds for the majority of which n typically is in the range from 0 to 4.

In addition to isocyanates, other reagents that can be used in composite tecto-membranes include aliphatic acid chlorides such as adipic acid diacid chloride, and aromatic acid chlorides such as terephthalic acid diacid chloride, as well as low molecular weight or polymeric anydrides and polyanhydrides such as terephthalic anhydride or linear poly (styrene-maleic anhydride) copolymers. su a e reac an s a w reac w . isocyanates include water-soluble mixed primary/secondary amines, and mixed primary/secondary/tertiary amines. Mixed primary/secondary amines include those of Formula (II) :

R R

H₂N(CH₂CHNH)_mCH₂CHNH_{2 (II)}

wherein m is an integer from 3 or greater, preferably 30 or greater and R is hydrogen or a methyl or ethyl group. The upper limit on the value of m is not critical; good results have been obtained with polyamines having number average molecular weights of up to about 60,000. Suitable primary/secondary/tertiary amines include compounds like those of formula (II) but modified in that one or more of the hydrogen atoms attached to non-terminal nitrogen atoms of the compound of formula (II) is replaced by a lower aminoalkyl group such as an aminoethyl group . The commercial product of tetraethylenepentamine usually contains some isomers branched at non-terminal nitrogen atoms, so that the molecule contains one or more tertiary amino groups. All these polyamines are readily soluble in water, which is suitably used as the aqueous continuous phase. Other suitable polyamine reactants include polyvinylamine, polyethyleneimine, polypropyleneimine, and polyallylamine. Primary and secondary amino groups will react with isocyanate moieties. Tertiary amino groups catalyse the reaction of the primary and secondary amino groups, as well as the conversion of isocyanate groups into amine groups that can subsequently react further with additional isocyanate groups.

Also suitable are polyetheramines of general formula (III) :

R R

H₂N ( CH₂CHO ) _r ( CH₂CH) NH₂ ⁽in⁾ where r is an integer from 1 to 20, preferably 2 to 15, more preferably 2 to 10, and R is hydrogen, methyl or ethyl. Such compounds, as well as their analogues based on propyleneoxide repeat units, are available under the trademark Jeffamine from Huntsman.

To be useful as a reactant and not merely as a catalyst, the amine must contain at least two amino groups capable of reacting with moieties (a) and (b) , i.e., at least two groups that are primary or secondary amino groups. Hence, the compound must be, at least, a diamine, but it may contain more than two amino groups; see for example compounds of formula (II) . In this specification the term "diamine" is used to indicate a compound that has at least two reactive amino groups, but the term does not necessarily exclude reactants that contain more than two amino groups.

Other suitable crosslinkers include diols and polyols, such as polyalkylene glycols including polyethylene glycol and polypropylene glycol, as well as more hydrophobic diols such as hexanediol . Crosslinking with such systems may be accelerated by adding catalysts such as tertiary amines or tin octanoate.

Spherical tecto-membranes prepared from porous microspheres in the presence of polymeric or low molecular weight interstitial fillers such as acid chlorides, isocyanates, etc. may show release controlled through the pores of the microspheres. The microspheres may additionally contain materials that are responsive to light, to temperature or to humidity and thereby control release . The microspheres further may contain catalytic sites that can modify the active material as it is being released.

Applications The applications of the tecto-membranes disclosed herein include the microencapsulation of volatile or nonvolatile organic fills destined for slow release into the atmosphere or a liquid medium. Examples include the encapsulation of insect pheromones used in insect population control. Other examples include the encapsulation/delivery of perfumes and fragrances. Materials that may be encapsulated for subsequent controlled release are described for example in the PCT international application WO 98/45036, which is incorporated herein by reference.

The described tecto-membranes that solely comprise microspheres held together by a small amount of crosslinking, or coupling, reagent contain large interstitial openings and a high outer surface area. These should facilitate release of the capsule content, especially in case of high boiling pheromones or other marginal volatiles .

Other tecto-membranes described above, which comprise porous microspheres and additional wall forming compounds, such as isocyanates, lead to composite membranes containing porous microspheres embedded in a continuous dense shell, for example a polyurea shell. Release from such capsules takes place through the microspheres, while the continuous polyurea shell matrix serves structural and containment purposes. In conventional encapsulations using just a polyurea shell from isocyanate/amine, the release properties of the polyurea shell are affected by the organic payload, i.e., the active material, which acts as a co- solvent during the formation of the polyurea shell. Hence the organic payload influences the permeability of the polyurea shell formed. In contrast, the permeability of the composite shells described here may be determined by the porosity of the microspheres, which can be controlled independently of the polyurea shell formation. The microspheres may also contain responsive functionalities that respond to temperature, light, or humidity. This would give access to coupling release to environmental conditions, while uncoupling the release from fill composition.

The microspheres may also contain catalytic functions that could modify the active material during release. One example could be an oxidation catalyst or a hydrolytic catalyst that would convert a pre-pheromone into the final pheromone, by either oxidation or hydrolysis, during the release.

Dense tecto-membranes could make useful supports for other interstitial inorganic catalysts, such as described in G. Zhu et al . , J. Mater. Chem. 2001, 11, 1687- 1693.

Preparation of the microspheres

The microspheres (also called tectons) that are used to form membranes in the present invention can be prepared by various known methods, for example precipitation polymerization, emulsion polymerization or suspension polymerization. Precipitation polymerization is a preferred process for forming microspheres, as it offers the advantage of good size control and it does not require the presence of added stabilisers that might interfere with the membrane forming processes. A suitable precipitation polymerisation process is that described by R. Frank and H.D.H. Stover (J. Polym. Sci., Part A., Polym. Chem. (1998), 36:2223-7), which is incorporated herein by reference. Precipitation polymerisation involves autosteric stabilisation of the forming polymer particles in the near-theta polymerisation mixture, and hence does not require addition of either steric or ionic stabiliser to prevent aggregation of the polymer microspheres. As a consequence, the resultant microspheres are free of any residual foreign surfactdU ux stabiliser that might interfere with the subsequent interfacial reaction.

In most cases, the microspheres are formed by the co-polymerization of two or more co-monomers. In one embodiment, one co-monomer is a diolefin. Another co- monomer is usually a mono-olefin that bears another reactive moiety. The mono-olefin undergoes co-polymerization with the di-olefin to form microspheres that bear on their surface the said other reactive moieties. It is these reactive moieties that react with the crosslinking reagent in the formation of the tecto-membranes. Reactive moieties can be, for example, anhydride, glycidyl, haloalkyl or other electrophilic groups. Examples of suitable diolefins include divinylbenzene, ethylenedimethacrylate, ethylenediacrylate and propylenedimethacrylate, for which suitable reactive co- monomers include maleic anhydride, itaconic anhydride, glycidylmethacrylate (GMA) and chloromethylstyrene (CMS) . If divinylbenzene is polymerized with maleic anhydride, there results microspheres having succinic anhydride moieties on their surfaces.

The resulting microspheres are narrow disperse, preferably monodisperse in size, with a diameter of from about 0.1 micrometer to about 10 micrometer, preferably with a diameter of about 0.5 micrometer to about 3 micrometer, and most preferably with a diameter of about 1 micrometer to 2 micrometer. Microspheres are characterized both by their high crosslinking density, and their low ability to swell even in good solvents. Typically, microspheres will comprise between 10 and 99 percent crosslinker, preferably between 20 and 80 percent crosslinker, and most preferably between 25 and 50 percent crosslinker, with the remainder being the functional co-monomer. Similar, but swellable copolymer particles, herein called microgels, of a size ranging from . micrometer __o . microme__er, pre__era y rom . .o- _.^• micrometer, and most preferably from 0.2 to 1 micrometer, are prepared by either reducing the crosslinker density, or increasing the quality of the solvent mixture used for their precipitation copolymerization, or any combination of these two approaches. Examples of their preparation are given in

Example 2, which is based on the article by R.S. Frank, J.S.

Downey, K. Yu, and H.D.H. Stover, Macromolecules, 2002,

35:2728-2735, the contents of which are incorporated herein by reference.

Membranes which are made from these microgels usually have less interstitial porosity than the membranes that are made from larger microspheres.

One preferred type of microspheres is the reaction product of the co-polymerization between divinylbenzene and maleic anhydride. These co-monomers can co-polymerize in an alternating (1:1) sequence to form divinylbenzene-alt-maleic anhydride microspheres. As well, lower concentrations of maleic anhydride can be used in semi-batch co- polymerizations to form, for example, microspheres that have 17% or 32% maleic anhydride.

Microspheres with amine surface active groups can be made, for example, by precipitation polymerization of a diolefin and chloromethylstyrene to make microspheres with surface chlorine atoms. These can be reacted with α,ω- diamines to replace the chlorine atom and result in surface amine groups (see formula IV) .

( IV)

Another approach to obtain microspheres with amine surface groups involves reacting divinylbenzene-maleic anhydride microspheres such as formed in Example 1, with an excess of an α,ω-diamine.

Yet another approach for preparing amine- functionalized microspheres includes the reaction of microspheres prepared by co-polymerization of divinylbenzene with glycidylmethacrylate, with an excess of an α,ω-diamine.

To obtain microspheres with reactive hydroxyl groups there can be carried out similar reactions, but using an α, ω-aminoalcohol instead of an α, ω-diamine .

Other approaches to hydroxyl-functionalized microspheres include co-polymerizing crosslinkers such as divinylbenzene or ethylenedimethacrylate with hydroxyethylmethacrylate .

Microspheres containing isocyanates on their surfaces may be prepared by reacting preformed divinylbenzene-hydroxyethylmethacrylate microspheres dispersed in an inert organic solvent, with an excess of an isocyanate such as Mondur ML or Mondur MRS.

Additives can also be incorporated into the microspheres to alter their characteristics . For example succinic acid groups, can be incorporated in varying amounts, by co-polymerization of maleic acid, or as a consequence of hydrolysis of maleic anhydride to maleic acid before co-polymerization, or by hydrolysis of succinic anhydride after co-polymerization. A certain amount of succinic acid functionality in the microspheres appears to be beneficial in some cases in assembling the reactive microspheres at the interface prior to addition of crosslinking reagent. Up to about 40% of the maleic groups in the microspheres may be present in form of maleic acid, preferably about 10% to 40%, more preferably 15% to 30%. The amount of maleic acid required to impart sufficient polarity to the microspheres to efficiently pre-assemble at the interface depends on the nature and composition of the first liquid, usually the organic phase, and on the nature and composition of the second liquid, usually the aqueous phase.

This produces microspheres that display variations in interparticle adhesion, mechanical properties, polarity, and permeability. As discussed above, other additives contain responsive functionalities that can respond to temperature, for example poly (N-isopropylacrylamide) , to light, for example azobenzene, or humidity, for* example humectants such as polyethyleneglycol-polypropyleneglycol .

Another approach for preparing functionalised microspheres involves functionalising preformed porous microspheres with suitable surface groups. Such surface functionalised microspheres may be used both for the formation of tecto-capsules and composite tecto-capsules. For example, porous, mono-disperse microspheres such as those prepared by precipitation polymerization of divinylbenzene-55, as described by Li et al.(J. Polym. Sci, Polym. Chem., (1998), 36:1543-51) may be subsequently functionalized by reaction with maleic acid, maleic anhydride, or a mixture thereof. Another embodiment includes porous suspension polymer microspheres prepared from divinylbenzene-55 or divinyl-benzene-80, that are also subsequently functionali ed with either maleic acid or maleic anhydride or a mixture thereof .

The invention is further illustrated with reference to the following examples and the accompanying figures . The following examples are offered by way of illustration and not by way of limitation.

Example 1A: Poly (Divinylbenzene-alt-Maleic Anhydride) Microsphere Synthesis

The microspheres were prepared in accordance with the procedure described by R. Frank and H.D.H. Stδver, J. Polym. Sci., Part A. , Polym. Chem. (1998), 36:2223-7, which is included herein by reference. Heptane (12 mL) was added to a solution of maleic anhydride (0.80 g) in methylethylketone (MEK) (8 mL) in a glass scintillation vial (20 mL) . Next, divinylbenzene (DVB-55) (0.73 g) and azobisisobutyronitrile (AIBN) (0.016 g) were added to the vial. The vial was sealed tightly and placed in a polymerization reactor at 70 °C for 24 hours. At the end of the reaction, particles formed were collected by centrifugation, resuspended in MEK and centrifuged again. The resulting particles were then dried at room temperature in a vacuum oven overnight. The size of the microspheres is typically narrow or monodisperse, with number average diameters of 600nm. Their yield typically is from 90 - 98%. By using different ratios of the cosolvents as discussed in the referenced paper, microspheres with diameters as small as 300nm, or as large as 1200 nanometers may be prepared. Example IB: Poly (Divinylbenzene-alt-Maleic Anhydride)

Microgel Synthesis

The same procedure as described in Example 1A was followed, except that a 70/30 volume % mixture of MEK and heptane is used as solvent. This procedure is based on the article by R.S. Frank, J.S. Downey, K. Yu, and H.D.H. Stover, Macromolecules, 2002, 35:2728-2735, which is included herein by reference. This synthesis results in the formation of 100 - 300 nanometer diameter narrow disperse swellable gel particles commonly called microgels. After the reaction, the microgels are solvent exchanged into propyl acetate. To this end, the reaction mixture containing microgels in MEK/heptane mixture was centrifuged, the supernatant decanted and replaced with neat propyl acetate, and the microgels resuspended by shaking and sonication.

This procedure was repeated five times. The microgels were never allowed to dry during this work-up, and were stored as an approximately 0.04g/mL suspension in propyl acetate .

Example 1C: Porous Poly (divinylbenzene-55) microspheres functionalized with Maleic Anhydride and Maleic Acid.

The microspheres were prepared by precipitation polymerization of divinylbenzene-55 in accordance with the procedure described by Li, W.-H., Stδver, H.D.H., J. Polym. Sci, Polym. Chem., (1998), 36:1543-51. The resulting porous microspheres (4g) were dispersed in tetrahydrofuran (100ml) together with maleic acid (2g) and azo-bis isobutyronitrile (AIBN, 1.4g), and heated to 70°C under stirring and under nitrogen atmosphere for 24 hours. The resulting functionalized microspheres were filtered under reduced pressure, washed with tetrahydrofuran, acetone and methanol, and dried in vacuo at 70°C for 3 days. Example 2: Preparation of Non-Spherica Composite Te u- Membranes by incorporation of reactive microspheres into an interfacial membrane formed by reaction of isocyanates with polyamine :

0.02g microspheres from Example 1A were weighed into a 4 mL glass vial fitted with a threaded septum cap. lmL dist. water containing 0.4% polyvinylalcohol (PVA) as stabilizer was added. The vial was placed in an ultrasonic bath for up to 30 seconds to suspend the microspheres in the aqueous phase. A small wire loop was prepared from thin copper wire, and submerged in the aqueous solution in the vial. lmL of the organic phase consisting of 20 vol% isocyanate (Mondur MRS) dissolved in 50/50 v/v propyl acetate/p-xylene was layered on top of the aqueous phase. 0.5mL of a saturated sodium chloride solution was added by syringe to the aqueous phase. After 10 minutes, 0.25 mL of an aqueous solution containing 10 w% TEPA was added by syringe over 30 seconds to the aqueous layer. The system was allowed to sit undisturbed for several minutes, after which the copper wire was slowly lifted out of the vial, capturing the membrane . The captured membrane was dipped into ethyl acetate to remove any residual isocyanate, and dipped into water to remove any residual amine and stabilizer. The resulting membrane is shown in Figure 5.

Example 3: Preparation of Spherical Tecto-Membranes by the Interfacial Reaction of Microspheres with an Aqueous Polyamine Crosslinking reagent, Under Different Microsphere Loading Condition.

An aqueous phase (1 mL, 0.4w/w% PVA) and an organic phase (0.01 or 0.04g divinylbenzene-maleic anhydride (DVB-MAn) microspheres of example 1 suspended in 0.25mL of a 50/50 v/v mixture of propyl acetate and xylene) were combined in a glass vial (4 mL) . The vials were then placed in a laboratory wrist shaker, modified to accept 10, 4 mL vials. Emulsions were formed by shaking the vials at 384 rpm for 30s. After emulsification the shaking rate was reduced to 215 rpm and 0.25mL of a 1 w/w % aqueous amine solution was added by syringe over a period of 10 seconds. The mixture was shaken, samples were withdrawn and observed by optical as well as both scanning and transmission electron microscopy. The resulting membranes are as shown in Figures 3A to 3F.

A similar procedure as described in Example 3 can also be used to prepare larger amounts of tectocapsules . The reagents are scaled up by a factor of 10, and an overhead stirrer fitted with a marine propeller rotating in a small beaker is used. Tecto-membranes formed by interfacial reaction of microspheres with complementary reagents may also be formed using other methods to disperse the first, microsphere containing liquid in the second liquid. For example, agitation by vortex, or by extruding the microsphere containing liquid through a narrow orifice into a stream or reservoir of the second liquid, may be used to form tecto capsules.

Example 4: Formation of Tectocapsules from divinylbenzene- maleic anhydride microgels.

The microgel-based tectocapsules were prepared using the standard tectocapsule method described above in Example 3, using 0.25 mL of the propyl acetate suspension prepared above in Example IB, containing approximately 0.04g microgels/mL. An optical microscope image of a membrane containing the microgels is the subject of Figure 8.

Example 5: Preparation of a Composite Spherical Tecto-

Membrane by the Interfacial Reaction of Microspheres with an Aqueous Polyamine Crosslinking Reagent. 0.02g of divinylbenzene-alt-maleic anhydride (1:1) microspheres of Example 1A were weighed into a 4mL glass vial fitted with a threaded septum cap. 0.25ml of a 20% w/w solution of Mondur ML in propyl acetate / xylene (50/50 v/v) was added. The vial was placed for up to 30 sec in an ultrasonic bath to suspend the microspheres in the organic phase. 1.0 mL distilled water containing 0.4w% polyvinylalcohol (PVA) as stabilizer was then added and the vial shaken at 400 rpm to emulsify the organic phase. Subsequently, the shaking rate was reduced by half, and 0.25 mL of an aqueous solution, containing 1 w% polyethylene imine (number average molecular weight 1200) , was added by syringe directly into the shaking vial . Shaking was continued for 1-3 hours. The resulting capsule membranes are as shown in Figure 4.

Example 6 : Preparation of Composite Spherical Tecto- membranes incorporating porous functionalised poly (divinylbenzene-55) microspheres .

2g of functionalised poly (divinylbenzene-55) microspheres of Example 1C were weighed into a 250mL

Erlenmeyer flask fitted with a rubber stopper, together with 43.5g xylene containing 5g of Mondur ML. 150g of distilled water was combined with 0.15g polyvinylalcohol (PVA) as stabilizer in a 500mL baffled jacketed glass reactor and mixed at 250 rpm to dissolve the stabilizer. Following dissolution of the stabilizer, the above described organic phase was added to the aqueous phase. This biphasic mixture was stirred using an overhead stirrer operating at 400RPM for 10 minutes in order to disperse the organic phase in the aqueous continuous phase. Subsequently, the mixing rate was reduced to 250 rpm, and 50 mL of an aqueous solution containing 5g of diethylenetriamine and 0.05g PVA, was added dropwise to the reactor. The reaction was heated to 70 °C and continued for 4 hours. The resulting capsule membranes are as shown in Figure 9.

All publications, patents and patent applications cited in this specification are herein incorporated by reference as if each individual publication, patent or patent application were specifically and individually indicated to be incorporated by reference. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention.

Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it is readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims .

It must be noted that as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural reference unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs.

Claims

Claims :

1. A process for the preparation of a tecto-membrane, which process comprises reacting microspheres that bear reactive surface groups with a complementary crosslinking reagent .

2. The process according to claim 1, wherein the reactive surface groups are selected from the group comprising anhydride, haloalkyl, glycidyl, activated ester, aldehyde, acid and other electrophile groups.

3. The process according to claim 2, wherein the reactive surface groups are selected from the group comprising of anhydride, chloromethyl styrene and glycidyl.

4. The process according to claim 2 or 3 , wherein the complementary crosslinking reagent is selected from the group consisting of amines and alcohols.

5. The process according to any one of claims 2 to 4 , wherein the reactive surface group is mixture of an anhydride and an acid and the complementary crosslinking reagent is an amine.

6. The process according to any one of claims 2 to 5 , wherein the reactive surface group is a haloalkyl or a glycidyl moiety and the complementary crosslinking reagent is an amine.

7. The process according to claim 1, wherein the reactive surface groups are selected from the group consisting of amine and alcohol.

8. The process according to claim 7, wherein the complementary crosslinking reagent is selected from the group consisting of polyanhydrides, polyisocyanates and other polyelectrophiles .

9. The process according to claim 7 or 8 , wherein the reactive surface group is an amine, and the complimentary

5 crosslinking group is a polyisocyanate.

10. The process according to claim 1, wherein an additional polyfunctional reagent reacts with the crosslinking reagent to form a composite tecto-membrane that comprises microspheres and a polymerized polyfunctional 0 reagent.

11. The process according to claim 10, wherein the polyfunctional reagent is a polyisocyanate.

12. The process according to claim 11, wherein the polyisocyanate is diphenylmethane diisocyanate.

5 13. The process according to claims 1, wherein the reaction takes place at or near a liquid interface, with the microspheres suspended in a first liquid, and the complementary crosslinking reagents dissolved or suspended in a second liquid that is immiscible with the first liquid.

0 14. The process according to claim 1, wherein the reaction takes place at or near a liquid interface, with the complementary crosslinking reagents suspended or dissolved in a first liquid, and the microspheres suspended or dissolved in a second liquid that is immiscible with the *5 first liquid.

15. The process according to claim 1, wherein the reaction takes place at or near a liquid interface, with the microspheres suspended in a first liquid, and the complementary crosslinking reagents dissolved, suspended, or 0 added to the same first liquid.

15, wherein the first liquid is water or an aqueous solution.

17. The process according to any one of claims 13 to

5 15, wherein the first liquid is an organic, water-immiscible phase .

18. The process according to any one of claims 13 to

17, wherein the first liquid is dispersed in the second liquid, which serves as continuous phase.

30 19. The process according to any one of claims 13 to

18, wherein an active material is dissolved or suspended in one of the first liquid and the second liquid prior to the reaction between the microspheres and the complementary crosslinking reagent.

15 20. The process according to any one of claims 13 to 15, wherein the liquid interface is substantially spherical.

21. The process according to any one of claims 1 to 20 wherein the microspheres are non-porous.

22. The process according to any one of claims 1 to _^".'_^■ 20, wherein the microspheres are porous.

23. The process according to any one of claims 1 to 22, wherein the microspheres carry moieties that have a responsive functionality.

24. A tecto-membrane which comprises microspheres that 25 are crosslinked through a complimentary crosslinking reagent .

25. The tecto-membrane according to claim 24, wherein the microspheres are embedded in a film of a crosslinked

^" ' polymer .

26. The tecto-membrane according to claim 24 or 25, wherein the membrane is spherical .

27. The tecto-membrane according to claim 24 or 25, wherein the membrane is non-spherical .

28. The tecto-membrane according to any one of claims 24 to 27, wherein the microspheres carry moieties that have a responsive functionality.

29. Use of a tecto-membrane as claimed in any one of claims 24 to 28, for the microencapsulation of an active material.

30. Use of a tecto-membrane according to claim 29, wherein the active material is selected from a pheromone and a perfume .

31. Use according to claim 29 or 30, wherein the tecto-membrane assists the controlled release of the microencapsulated active material.

32. Use of a tecto-membrane as claimed in any one of claims 24 to 30, as a catalyst support.