WO1987007529A1

WO1987007529A1 - Segmented polymers and method for the synthesis thereof

Info

Publication number: WO1987007529A1
Application number: PCT/GB1987/000415
Authority: WO
Inventors: Basil William Brook; William Albert Edward Dunk; Maurice Edward Baguley; Brian Saville
Original assignee: Courtaulds Plc
Priority date: 1986-06-16
Filing date: 1987-06-15
Publication date: 1987-12-17
Also published as: GB8614642D0

Abstract

A surface active agent contains at least one radical generator group in each of its lipophilic and hydrophilic moieties. A water-in-oil dispersion or oil-in-water dispersions contains a first polymerisable monomer dissolved in the oil phase and a second monomer dissolved in the oil phase and a second monomer dissolved in the aqueous phase. A surface active agent as defined above is dispersed across the interface of the oil phase and the aqueous phase with its lipophilic moiety well solvated by the oil phase and its hydrophilic moiety well solvated by the aqueous phase. A segmented polymer comprising such a surface active agent having at least one lipophilic polymer segment attached to its lipophilic moiety and at least one hydrophilic polymer segment attached to its hydrophilic moiety can be formed from the dispersion.

Description

Segmented Polymers and Method for the Synthesis Thereof

This invention relates to segmented polymers and to a method for their manufacture and to novel surface active agents used in their manufacture.

In this specification:-

(a) "segmented polymer" means a molecule in which two or more polymeric segments, at least two of which have different chemical compositions, are each covalently bound at one end to a linking radical.

(b) "radical generator group" means a functional group capable of being decomposed, either by a physical stimulus or by a chemical reaction, to generate a free radical able to initiate the polymerisation of a monomer. Thus the Vradical generator-group" may, for example, be an initiator group which itself generates free radicals in response to a physical stimulus such as heat or light or it may be a source dependent on reaction with another reagent, for example a chain transfer group or a component of redox couple.

Background to the Invention

The most usual method in the prior art for preparing segmented polymers has been anionic polymerisation, as described for example at pages 327 to 336 of "Encyclopaedia of Polymer Science and Engineering". Volume 2 , published by John Wiley and Sons in 1985. Several important classes of addition-polymerised block copolymers now have significant commercial applications as elastomers, fibres, surfactants, adhesives and thermoplastics, notwithstanding the narrow range of largely hydrocarbon monomers, cyclic-ethers and cyclic amides which alone may be employed in the favoured anionic polymerisation process.

There is a need for copolymers having blocks of very different chemical and physical properties, particularly those having lyophilic blocks and hydrophilic (even ionic) blocks, and for an improved process by which they can be made. We have devised such a process for making segmented polymers from monomers.

The Invention

According to the present invention a surface active agent having lipophilic organic moiety and hydrophilic moiety in its molecule is characterised in that the surface active agents contains at least one radical generator group in each of its lipophilic and hydrophilic moieties.

The invention includes a -water-in-oil dispersion or oil-in-water dispersion containing a polymerisable monomer, characterised in that a first monomer is dissolved in the oil phase and a second monomer is dissolved in the aqueous phase, the first monomer being substantially insoluble in the aqueous phase and the second monomer being substantially insoluble in the oil phase, and a surface active agent according to any of claims 1 to 7 is dispersed across the interface of the oil phase and the aqueous phase with its lipophilic moiety well solvated by the oil phase and its hydrophilic moiety well solvated by the aqueous phase.

The invention also includes a process for forming a segmented polymer, characterised in that a dispersion according to claim 8 is treated to initiate polymerisation of the first and second monomers simultaneously or sequentially and to stimulate the radical generating groups of the surface active agent to form polymer segments attached to the lipophilic and hydrophilic moieties of the surface active agent.

One product of this invention is a water-in-oil dispersion of a segmented polymer which comprises a hydrophilic segment which is solvated by the dispersed aqueous phase and a lipophilic segment which is solvated by the continuous oil phase. Alternatively an oil-in-water dispersion of a segmented polymer, comprises a segmented polymer having a lipophilic segment which is solvated by the dispersed oil phase and a hydrophilic segment which is solvated by the continuous aqueous phase.

The invention also included a segmented polymer comprising lipophilic and hydrophilic segments, characterised in that a surface active agent as described above has at least one lipophilic polymer segment attached to its lipophilic moiety and at least one hydrophilic polymer segment attached to its hydrophilic moiety.

It is to be understood that the surface active agent is employed to dispose radical generator groups in both phases of the dispersion. In addition the surfactant may stabilise the dispersion, but this is not essential; and additional commonplace surfactant may be employed for this duty.

We prefer either that the polymerisations are simultaneous or that the polymerisation in the oil phase precedes polymerisation in the water phase.

It is also preferred that the polymer of each monomer is soluble in the liquid used to dissolve the monomer. The Surface Active Agent

The lipophilic organic moiety of the surface active agent can, for example, be a hydrocarbon chain containing at least 8 carbon atoms, for example 8 to 20 carbon atoms. The radical generator group in the lipophilic moiety is preferably separated by at least 6 carbon atoms from the hydrophilic moiety and is most preferably present as a terminal group. The hydrophilic moiety can be an ionic group, for example a carboxylate, sulphonate or quaternary ammonium group, a polar group, for example a tertiary amine group, or a hydrophilic non-ionic organic moiety such as a polyoxthyethylene chain.

The surface active agent for the use in the preferred process may be chosen, according to known principles, to have⁴ an HLB (hydrophile-lipophile balance) appropriate to the liquid components paired in the emulsion or reverse emulsion, so that the surfactant can, in addition to disposing the radical generator groups in the two phases, promote the stability of the dispersion.

The radical generator groups incorporated in the surface active agent may each be either a primary initiator which provides free radicals in response to a physical stimulus (heat or light), or by redox reactions, or a chain transfer group which becomes a free radical only be chemical reaction with a free radical. Examples of primary intiators are azo groups, preferably adjacent to nitrile groups, peroxide, hydroperoxide, peroxyester, persalt and azide groups.

When chain transfer groups are used it is necessary to provide in addition an independent source of free radicals. This independent source may be one of the well-known free-radical initiators for example the peroxide, persalt, azo and redox varieties. Chain transfer groups and their relative reactivities are known (see "Polymer Handbook", second Edition, published by John Wiley and Sons, pp. II 67 to 97). Thiol groups are most reactive for most monomers and are the preferred species, but others, such as polyhalide groups (for example CBr3), tertiary amines having methylene groups adjacent the nitrogen atom and secondary alcohols, are useful. The use of a bifunctional thiol as surface active agent may give the advantage of a narrower molecular weight distribution. In general the water soluble monomer tend to polymerise more rapidly; the use of a more reactive chain transfer group such as a thiol group in the hydrophilic moiety of the surface active agent with a less reactive group such as a secondary alcohol group in the lipophilic moiety may aid in increasing the reactive molecular weight of the lipophilic segment of the block copolymer formed.

Specific examples of such surface active agents are

SH H O SH

I I " I

CH₃ (CH₂)₇ CH (CH₂)₉ N - C - CH - CH₂ - COO- Na⁺

O H

'' ' CH2SH

HS (CH₂)₁₀ C - N -

COO- Na⁺

OH O H

' " ' CH₂SH

CH₃CH(CH₂)₈ C - N -

COO- Na⁺

COO- Na+

HS

(- CH₂)9 -

SH

OH O H

' '

CH₃ (CH₂)₅ CH CH₂ CH=CH(CH₂)₇ C - N - CH₂SH

COO- Na⁺

Surface active agents of the general formula

where R is a thiol-substituted alkyl group containing at least 8 carbon atoms and having at least 6 carbon tacms between the thiol group and the nitrogen atom and M is alkali metal or ammonium, can be formed from an unsaturated fatty amine. The amine can be reacted with an unsaturated dicarboxylic acid anhydride, for example maleic anhydride, to form a half-amide according to the reaction

- CH = CH - COOH

where R' is an unsaturated aliphatic group containing at least 8 carbon atoms. The half-amine can then be resulted with a sulphur containing compound, for example a thiol-carboxylic acid such as thiolacetic acid

₃ to add the sulphur containing compound at the double bonds both in the R' and in the maleic residue. Oleylamine, for example, can be reacted to form the di(thiolester)

C

This can be hydrolysed with base, for example aqueous alkali metal to form the surface active agent

If the group R' is a polyunsaturated grouj. derived for example from linoleyl amine a surface active agent having more than one thiol group (radical generator group) in its lipophilic moiety can be formed.

Surface active agents of the general formula

where R and M are defined as above can be prepared from an unsaturated fatty acid. The fatty acid is treated with a sulphur compound such as thiolacetic acid to cause addition to the double bond. The acid group is then converted to an acyl chloride group, for example by reaction with cyanuric chloride. The resulting acyl chloride is reacted with cysteine ethyl ester hydrochloride

This reaction can be carried out in toluene, with vigorous reflux to drive off hydrogen chloride. The product can be hydrolysed by base, for example aqueous sodium hydroxide, to convert the thiolacetic ether group to a thiol group Starting with 10-undecyclenic acid as fatty acid, the surface active agent ~ ⁺

can be formed.

As an alternative to reaction with cysteine, the acyl chloride can be reacted with the corresponding serine compound

to form an amide group of the form

This can be reacted with thiourea and hydrolysed by base to form the

group,

As an alternative to addition of thiolacetic acid, the double bond of the unsaturated fatty acid can be epoxidised then hydrolysed by base to form a secondary hydroxyl group as chain transfer group in the lipcphilic moiety.

Further examples of surface active agents are

In this latter example two surfactant molecules are joined by an azo group which decomposes forming two surfactant free radicals, which thereafter are independent.

This example is on a surfactant comprising two types of radical generator group which are both initiator centres - the azo group of the lyophilic part and the primary alcohol/cεric ion redox system of the hydrophilic part. An hydroxyl group may be substituted for any thiol group in the hydrophilic part of any of the surfactants listed above and used as a redox couple with eerie ion dissolved in the aqueous phase; for example the surfactant may be

The Segmented Polymer

The hydrophilic segment of the polymer may be ionic or non-ionic. The hydrophilic segments may be homopolymers and copolymers of ethylenically unsaturated acids and their salts, ehtylenically unsaturated tertiary amine acid quaternary ammonium salts, ethylenically unsaturated amides and ethylenically ubsaturated heterocycles. The ethylenically unsaturated acid include, for example, carboxylic acids such as acrylic, methacrylic, maleic and fumaric acids; sulphonic acids such as styrene sulphonic acid, vinyl sulphonic, allyl sulphonic and methallyl sulphonic acids and vinyl phosphonic acis. Methacrylic acid and acrylic acid and their alkali metal salts, for example sodium methacrylate, are particularly preferred. The quaternary ammonium salt monomers include, for example, trialkyl ammonium alkyl acrylate and methacrylate salts, for example trimethyl ammonium ethyl methacrylate hydrochloride and N-alkyl vinyl pyridinium salts. Tertiary amine salt monomers include dialkylaminoalkyl acrylate and methacrylate salts such as dimethylaminoethyl methacrylate hydrochloride. The amilde monomers include N-vinyl acetamide and methacrylamide, ant is N-substituted derivatives including aminoalkyl-substituted derivatives such as dimethylamino- propyl methacrylamide. Acrylamide ans its derivatives can be used but their polymerisation is difficult to control and may lead to polymer segments having too high a molecular weight. The heterocyclic monomers are exemplified by N-vinyl pyrrolidone.

The lipophilic segments may be homopolymers and copolymers of such monomers as styrene, its homologues and derivatives; acrylate esters and their homologues, including methacrylate esters; itacόnate esters; maleate esters, (particularly in combination with monomers which copolymerise in an alternating sequence with such esters), acrylonitrile and its homologues; olefins such as propylene, 1-butene or ethylene; vinyl pyridine and its homologues; vinyl halides such as vinyl chloride or vinylidene chloride; and vinyl esters such as vinyl acetate.

The aqueous phase of any dispersion may optionally contain salts such as sodium chloride, lithium chloride and the like, which have the - effect of promoting the polymerisation of some water-soluble monomers.

The organic solvent used as the oil phase in the dispersions of the invention is preferably a hydrocarbon, for example an aromatic hydrocarbon such as toluene or xylene or an aliphatic hydrocarbon such as hexane, decane, dodecane or white spirit.

Although the polymerisation involving the surface active agent of the invention is carried out using emulsion polymerisation techniques, this system is more correctly described as two simultaneous solution polymerisations in different phases, which are linked by a bridging molecule (the surface active agent). The main difference between this system and a true emulsion polymerisation is that in the former the radical initiating polymerisation is always confined to the same phase and does not cross the interface. The movement of the initiating radical from the continuous to the dispersed phase is a prerequisite of a true emulsion polymerisation. It can be concluded therefore, that the expected kinetics of this system should differ from those of emulsion polymerisation and more closely follow those of solution polymerisation.

The rate of polymerisation in the aqueous solution generally exceeds that in the organic solvent solution. It is often preferred to use a proportion of the solvent soluble monomer in excess of that desired in the segmented polymer, so that the polymerisation of the solvent soluble monomer need not be carried out to completion.

Polymerisation can be initiated by heating the dispersion to activate the free radical initiator groups, whether those are groups present in the surface active agent or in one or more separate initiators. Alternatively the initiator groups can be activated by adding one component of a redox couple. Sulphur dioxide, for example, can be used in this way by bubbling it into the dispersion; it can form a redox couple with peroxy compounds such as hydroperoxides or persulphates. If different initiator groups responsive to different activation processes are present in the aqueous and organic phases, the polymerisation can be carried out in two stages. It is however preferred to carry out polymerisation in both phases simultaneously using thermally activated initiator groups. For example, if the radical generator groups of the surface active agent are chain transfer groups thermal initiators having a similar half-life temperature can be used in the aqueous and organic phases. For example azobisisobutyronitrile or azobisisovaleronitrile can be used in the organic phase with azocyanopentanoic acid in the aqueous phase.

When the radical generator groups of the surface active agent are chain transfer groups it may be necessary to add further free radical initiator during the course of the reaction to ensure that polymerisation continues.

Uses of the Segmented Polymer

Many of the segmented polymers of this invention have the character of polymeric soaps and many uses depend from this character. For example such polymers are useful as dispersing agents and steric stabilisers fo.r pigment and polymer dispersions; as flotation aids and complexing agents for metal ions; as surface modifiers for hydrophcbic polymer articles, particularly films, fibres and coatings, making such surfaces more wettable, printable or antistatic.

The polymers are compatibilising agents for blends of different polymers each having greater compatiblity with one or other of the segments of the segmented polymer than with the other polymer.

A segmented polymer having at least one ionic segment may form a hydrcgen-bonded complex with a complementary polymer. For example a segmented polymer having a polyacrylic or, better still, a polymethacrylic acid segment may form a hydrogen-bonded complex with polyethylene oxide or a block ccpolymer having a polyethylene oxide block, shown schematically in the following figure

Iycphilic segment

Iyophilic block

Such a water-insoluble complex forms when water-containing solutions or dispersions of the two polymers are brought into contact. However, the complex does not form (or is disrupted) in ketone/water mixtures so that a solution is available which may be used to form a film or coating which sets up as the solvent volatilises. Such a reversible complex is useful' for temporary paint protection and as a vehicle for self-polishing, antifouling paints - the slight alkalinity of the seawater being sufficient to disrupt the complex into its water-soluble or water-dispersible parts.

Ionic complexes form from the reaction of anionic segmented polymers and cationic segmented polymers. If each segmented polymer is made as a water-in-oil dispersion with the ionic segments present in the dispersed phase and overcoated with the lipophilic segments, so as to present little - or no ionic character at the surface of the dispersed phase, the dispersions may be mixed without immediate reaction. However, on volatilisation of the continuous phase alone, or by heating the deposited disperse phase above the glass transition temperature (T ) of the lipophilic segments, the two segmented polymers interact to form the polyionic complex.

The invention is illustrated by the following Example.

Example

1. Preparation of Surface Active Agent

Oleylamine (133.75g, 0.5 moles) and maleic anhydride (49g, 0.5 moles) were warmed together in a round bottom flask until a reaction started (30°-40°C), as shown by an exotherm ( T = 80-90°C). The product was a yellowish brown oil which yielded a yellow soap on cooling. "recrystallisation" from propan-2-ol and then acetonitrile gave a white hard soap like material, oleylamidopropenoic acid, in a yield above 90%.

The slow addition of thiolacetic acid (73.3 cm³, 0.821 moles) to the oleylamidopropenoic acid (100g, 0.274 moles) resulted in an immediate exotherm which persisted until the molar ratio had reached 1:1. Further addition of thiolacetic acid caused a cooling of the system. Addition of a peroxide (4 drops), as a source of radicals, gave a second smaller exotherm ( T = 8-9°C). The reaction was maintained at 60°C for 4 hours with the periodic addition of aliquots of peroxide (4 drops); after 2 hours further addition of the peroxide gave no significant exotherm.

The resulting dithiolester (lOg, 0.019 moles) was hydrolysed to the corresponding dithiol by refluxing a methanolic solution (50cm³) of the surfactant with sodium hydroxide (2g, 0.05m) for 2 hours. To avoid oxidation of the thiol to the disulphide, the hydrolysis was performed under an atmosphere of nitrogen and in the present of sodium cyanide (5mg), as a catalytic inhibitor. The precipitate was subsequently filtered and washed with methanol. It comprised

CH₃ (CH₂)₇ CH ₉ ⁺

2. Polvmerisation

N-butylacrylate (91g, 0.71 moles) was dissolved in toluene (202g) and cumene hydroperoxide (0.0154g of 80% pure) were added to the reaction kettle. The solution was then vigorously stirred whilst a mixture of water (76g), sodium methacrylate (32.4g, 0.30 moles), t-butyl hydroperoxide (0.02g of 70% pure) and functionalised surfactant (2.275g, 0.00502 moles) was added, forming an emulsion. The reaction kettle was fitted with a temperature probe, a N₂ purge, an inlet port, an overhead anchor stirrer and a condenser. Once the emulsion has been established the speed of the stirrer was reduced and the system was purged with N₂ for 30 minutes. The polymerisation was subsequently initiated by addition of sulphur dioxide (2 bubble/sec) into the stirred emulsion. There was an initial induction period of 1 minute before the reaction produced an exotherm of 3°C in 4 minutes. The exotherm then plateaued indicating a "dead stop" type polymerisation and that it was necessary to add subsequent aliquots of cumene hydroperoxide to maintain the polymerisation. After approximately 40 minutes and addition of several aliquots of cumene hydroperioxide and sulphur dioxide the rate of temperature increase had become essentially zero. The total temperature rise of the non insulated system was 10°C. The water, toluene and excess monomer were removed under reduced pressure, leaving a hard white polymer. The water soluble fraction was subsequently separated to give a milky solution which would not settle even after prolonged standing. Removal of the water under reduced pressure gave a hard white polymer.

Although the polymer produced was soluble in water the solution was neither homogeneous nor separated into two or more components, which infers that the material was a block copolymer rather than a mixture of the two homopolymers (Poly(sodium methacrylate) forms a clear water solution and poly(butyl acrylate) is water insoluble). The polymer in the bulk state forms an opaque white film, even after prolonged drying. This phenomenon is characteristic of the domain type structure seen in block copoymers containing incompatible segments and results from microphase separation of the blocks, thereby imparting a heterogeneous structure to the sample.

Claims

1. A surface active agent having a lipophilic organic moiety and a hydrophilic moiety in it molecule, characterised in that the surface active agent contains at least one radical generator group in each of its lipophilic and hydrophilic moieties.

2. A surface active agent according to claim 1 characterised in that the hydrophilic moiety is an ionic group.

3. A surface active agent according to claim 1 or claim 2 characterised in that the lipophilic organic moiety comprises a hydrocarbon claim having at least 8 carbon atoms and the radical generator group in the lipophilic moiety is separated from the hydrophilic moiety by at least 6 carbon atoms.

4. A surface active agent according to any of claims 1 to 3, characterised in that the lipophilic moiety contains a thiol group as radical generator group.

5. A surface active agent according to any of claim 1 to 4, characterised in that the hydrophilic moiety contains a thiol group as radical generator group.

6. A surface active agent according to claim 5 having the general formula

O O^{- +}

where R is a thiol substituted alkyl group containing at least 8 carbon atoms and having at least 6 carbon atoms between the thiol group and the nitrogen atom and M is alkali metal or ammonium.

7. A surface active agent according to claim 6, characterised in that the radical R is derived from a oleyl radical by addition of a sulphur containing group at the double bond of the oleyl radical.

8. A water-in-oil dispersion or oil-in-water dispersion containing a polymerisable monomer, characterised in that a first monomer is dissolved in the oil phase and a second monomer is dissolved in the aqueous phase, the first monomer being substantially insoluble in the aqueous phase and the second monomer being substantially insoluble in the oil phase, and a surface active agent according to any of claims 1 to 7 is dispersed across the interface of the oil phase and the aqueous phase with its lipophilic moiety well solvated by . the oil phase and its hydrophilic moiety well solvated by the aqueous phase.

9. A process for forming a segmented polymer, characterised in that a dispersion according to claim 8 is treated to initiate polymerisation of the first and second monomers simultaneously or sequentially and to stimulate the radical generating groups of the surface active agent to form polymer segments attached to the lipophilic and hydrophilic moieties of the surface active agent.

10. A water-in-oil dispersion of a segmented polymer, characterised in that the segmented polymer comprises a hydrophilic segment which is solvated by the dispersed aqueous phase and a lipophilic segment which is solvated by the continuous oil phase.

11. An oil-in-water dispersion of a segmented polymer, characterised in that the segmented polymer comprises a lipophilic segment which is solvated by the continuous oil phase and a hydrophilic segment which is solvated by the continuous aqueous phase.

12. A segmentεd polymer comprising lipophilic and hydrophilic segments, characterised in that a surface active agent according to any of claims 1 to 7 has at least one lipophilic polymer segment attached to its lipophilic moiety and at least one hydrophilic polymer segment attached to its hydrophilic moiety.

13. A segmented polymer according to claim 12 characterised in that the hydrophilic polymer segment is a polymer of acrylic or methacrylic acid of a salt thereof.