CA1303267C - Block copolymer dispersants - Google Patents

Abstract

TITLE

BLOCK COPOLYMER DISPERSANTS

ABSTRACT

Block copolymers composed of similar monomers but which exhibit substantially different polarity provide excellent performance as pigment dispersants. One of the blocks has cationic ammonium, phosphonium or sulfonium moieties. Each of the blocks is formed from monomers of the formulas CH2=CHCO2R and CH2=CCH3CO2R, where R is alkyl or alkyl ether, with one of the blocks containing at least two pendant ionic moieties. The block copolymers may be prepared using group transfer polymerization techniques.

Description

13032~
BLOCK COPOLYMER DISPERSANTS

BACKGROUND OF ~HE INVENTION
Polymeric materials have previously been known wh~ch are effective for dispersing pigments in organic solvents. Such pol~meric dispersant6 are typically of the AB or B~B types, in which a polar group known as th~ A ~egment is present in the m~lecule to f~cilitate attachment to a pigment surface, and at least one non-polar portion known as the B segment is present to enhance stearic stabilization of the pigment particles in a dispersion.

Baker et al, in U~ S. Patent 3,912,677, disclose th~ benefits of polymers containing ionic groups, in specific cases where the ionic groups are in the ~orm of a salt with a salt-~orming component or counterion. ~he salt-forming component has an affinity for the surface of organi~ pigment particles, and is capable of reaction with the polar-bound ionic group so as to form a salt. However, continued effort has been directed to improve the perfo~nance of polymeric d~sper~ants~ and to find effective dispersants that do i not require khe use o~ special salt-forming components, j the u~e of which complicates the manufacture of the I dispereants, and can introduce undesirable color.

S~IMARY OF THE INVENTIOM
The pres~nt invention is based on the dis-! covery that block copolymers composed of similar monomers, but whiah exhibit substantially different polarity, one of the blocks having cationic ammonium,phosphonium, or sulfonium moieties, provide excellent performance as piyment di~p~rsants, without-the need for ~pecial salt-forming components.

- ~ 303~7 Specifically, the instant inYention pr~ides a block copolymer consi~ting e~sentially of (a) about ~rom 0~1 to 50 ~, by weight of the copolymer, of at least one block having a number average molecular weight of about from 200 to 10, 000 and prepared ~rom at least one monomer ~elected from compounds of the general formulas CH2=C~C02R and CH2=CCH3C02R, wherein R is alkyl or alkyl ether of ~-20 carbon atoms, the block further containing at least 2 pendant ionic moieties of the general formula -A(Rl)mX, wherein A is selerted from N , P , and S: Rl ars independently selected ~rom alkyl or alkyl ether of ; 1-20 carbon atoms, phenyl or substituted phenyl, m is 3 when A is N or P, and m is 2 when A is S, and X is selected from halides and conjugate bases of organic acids, the backbone o~ the block being composed of ethylenically unsaturated units, and (b) about from 99.9 to 50 %, by weight of the ! copolymer, o~ at least one blook having a number average molecular weight of about from 500 to 100,000 . and prepared ~rom monomers selected from compounds ofthe general formulas CH2-CHC02R and CH2=CCH3C02R, whereln R is alkyl or alkyl ether of 1-20 carbon atoms.
These compounds can be, and preferably are, prepared by group transfer polymerization techniques, exhibit excellent performance as dispersants and do not require salt-forming counterions for satis~actory performance.

DETAILED DESCRIPTION OF THE INVENTION
Monomers which can be used in the preparation of the dispersants o~ the present invention inolude those a~xylate~ and methacrylates de~cr~bed in Webster, : 35 ~0:~67 ~ 3 -U.S. Patent 4,508,880 at column 8, lines 4 to 58, with the exception of 3-methacryl-oxypropyl acrylate; and 2-methacryloxyethyl acrylate and linalate. Monomers which are preferred ~or the first block of the copolymer, containing the pendant ionic groups, include dimethyl aminoethyl methacrylate and diethyl aminoethyl metha~rylate. Monomers which are pre~erred for the s~cond (b) block ~f the copolymers include methyl meth~crylate, butyl methacrylate and 2-ethylhexyl methacrylate.
The polymers of the present invention can be prepared by conventional anionic polymerization techniqueæ, in which a first block of the copolymer is formed, and, upon complet~on of the ~irst block, ~
~econd monomer 6tream is started to form a ~bsequent block of the pol~mer. However, the react~on temperatur2~ using such technique~ ~hould be maintained at a low level, for example, 0 to -40 degrees Centigrade, ~o that side reactions are minimized and the desired blocks, o~ the speaifled molecular weights, are obtained.
~ o attain the desired mole~ular weight of Qach block as well as uniformity in the blocks, Group Tranefer Polymerizaticn techni~ues are advantageously, and preferably, used, ~uch as those described in the Aforementioned Webster, U.S. Patent 4,508,880.
In accordance with that process, an unsaturated monomer is contacted with an initiator and a catalyst system containing silicon, tin or germanium, undex which the pol~merization proceeds in a controlled manner, as oppos~d the random manner typical o~ polymerization reactions, ~o that a subetantially linear polymer can be prepar~d having )32~7 polymer chains which are uniform and of the desired molecular weight.
In the preparation of dispersants of the present invention, the order in which the blocks are prepared is not critical. Either the block containing the pendant ionic moieties or the blocX not containing the6e moieties can be prepared first.
Catalysts which can be used include those dl~closed in U.S. Patent 4,508,880 at column 11, lines 42 to 68.
Initiators which can be used include those indicated in the aforementioned Webster patent at Column g, line 25 to CQ1Umn 10 line 13. Preferred initiators include 1-(2-trimethyl-siloxyethoxy)-1-trimethyl-siloxy-2-methylpropene; 1-(2-~1-ethoxyethoxy]-ethoxy-l-trimethylsiloxy-2-methylpropene; and l-methoxy-l-trimethylsiloxy-2-methylpropene.
If the dispersant is prepared by ~irst forming the bloak without the pendant ionic groups, then the~e blocks are reacted, u ing the same general procedure~, to form the block~ containing the pendant ionia groups. The same general reactants are used for these ~ec.ond bloaks, except that the monomer~ and their relative quantities are selected to have an average of at least two cationic units, or their precursors, in each block~ The cationic unit~ can be ~n the required quaternary or te~tiary configuration as pol~merized, or, more typi~ally and preferably, can be primary, secondary or tertiary amine~ phosphine or thioether 13~ 7 compounds which are converted to the quaternary or tertiary state after the formation of the basic polymer structure. While a wide variety of monomers can be so used, methacrylates have been found to be particularly satisfactory, including, for example, 2-(dimethylamino) ethyl methacrylate, 2~(diethylamino)ethyl methacrylate, glycidyl methacrylate, and t-butyl aminoethyl methacrylate.
Similar monomers can be used to introduce ionic groups based on phosphorus and sulfur, as will be evident to the skilled artisan.
The pendant ionic moieties have the general formula -A(R1~mX, wherein A is selected from N, P, and S, R1 are independently selected from alkyl or alkyl ether of 1-20 carbon atoms, phenyl or alkyl substituted phenyl, m is 3 when A is N or P, and m is 2 when A is S, and X is selected from halides and conjugate bases of organic acids. Preferably, A is nitrogen, and X is selected from the group consisting o~ carboxylates, sulfonates and phosphates.
After ~ormation of the basic polymer structure, the cationic precursor can be brought into contact with conventional alkylation agents such as an alkyl halide, alkyl sulfonate, alkyl toluene sulfonate, trialkyl phosphate or aralkyl halide.
Alkylation agents which have been found to be particularly satisfactory include methyl toluene sulfonate, dimethyl sulfate, and benzyl chloride.
The physical characteristics of the block copolymers of the present in~ention, including the molecular weight of the blocks and the presence of the ionic moieties on one of the blocks) can be confirmed by conventional analytical techniques, including B

~ ~3~32~7 differential ~canning calorimetry, nuclear magnetic resonance, gas chromatrography and infrared analysis.
For example, the chemical composition o~ the blocks can be determined by proton nuclear magnetic re~onance or infraread analy~i6, or by pyrolysis and gas chromatographic analysis. The block sizes ln the copolymers can be determined by nuclear m~gnetic resonanae, gla~s transition temperature, ~olubility or micella ~ormation a~ measured by ~ua~i elastic light 10 ~cattering.
The resulting block copolymers exhibit excellent parformance as dispersants. Accordingly, they can be used ef~ectiv~ly a~ pigment dispersants in paint formulations and a~ oil additives. Pigment dispersions typically ~omprise pigment, s~lvent and dispersant, and can be prepared, for exampl~, as des~ribed in Baker et al, U.S. Patent 3,912,677.
While similar compounds have been 90 used in the past, the present copolymers are effective without the use of counter-ions such as ionized rosin acid or sulEonated aromatic hydrocarbon that have been previously found necessary for satisfactory dispersant performance~ In addition, the uniform block charaatex in th2 present compounds provides improved and more reliable d~spersant per~ormance.
; In th~ following Examples, dispersant quality ie measured by ~and grinding a mixture o~ pigment, solvent and d~persant and determining what proportion of disper~ant (if any) will give a uniform di~persion, appearing liXe ~tained glass at an optical magnifica-tion Q~ ~50x. In contrast, floccula~ed ~igment has i~land~ of color intersper~ed with areas of relatively clear ~olvent. The degree of dl~persion is evaluated on an arbitrary ~cale of 1 to 4 as follows:
1 - deflocculated dispersion in which pigment particles ~r~ uni~ormly separated and in which brownian motion of parti~les i~ evident.
2 - slightly flocculated dispersion in which pigment parkicles are separated but immobile (no significant evidence of brownian motion).

3 - flocculated disper ions in which pigment lD particles are loosely aggregated wlth 60me voids between aggregates.

4 - severely flocculated dispereions ln which i pigment particles are highly aggregated with larg~
voids between aggregatQs.
The di6per~ants prepared in th~ Examples were evaluated with a variaty of standard pigments and in ~olvents. The solvents used were methylisobutyl ketone (MIBK or M~, toluene tT), xylenes (X), and ~cetone (A).
The ~ollowing ~tandard pigments were used in the evaluation:
W505 - phthalocy~nine blue, red toned I (monastral* blue) W552 - phthaocyanine blue, floaculation re~istant green s~ade, toner WS73 - tetrachloro CPC blue: phthalocyanine ~lue toner, green ~hade, improved rheology W673 - tetraohloro isoindolinone - irgazin yellow W805 ~ monastral magenta - quinacridone type magenta toner W811 - monastral red - quinacridone type red toner * denotes trade mark .

W853 - organic red tone - quinacridone type -monastral transparent red B RT-233 In all Example~ o~ the invention, the blocks : of the copolymers containing the pendant ionic groups had a molecular weight o~ about from 200 to 10,000, and the blocks without the pendant ionic groups had a molecular weight of about ~rom 500 to 100,000. The speci~ic molecular weight~ can be determined by the skilled artisan from the data appearing in the particular Examples. In all Examplas of the invention, an average of at least 2 pendant ionic groups were present in each block (a) o~ the copolymer prepared.
Example 1 A reaction vessel was charged with 316 g tetrahydrofuran ~THF), 0.5 mL xylenes, 4.1 g l~methoxy-l-trimethylsiloxy-~ m~thylpropene ("init.iatox"), and 0.100 mL 1 M tetrabutylammonium 3-chlorobenzoate in ac~tonitrile ("catalyst"). To prepare an A block free from pendant ionic groupd, two feeds were be~un simultaneously; ~1.2 g of methyl methacrylate (MMA) was added in 20 minutes, and 0.350 mL catalysk in 3 ml THF was added over 2 hours. Twenty minutes a~ker the addition o~ the MMA, 28.9 g of 2-N,N-dimethylamlnoethyl methacrylate ~DMEAMA) was added over 10 minutes for the preparation of a block containing pendant ionic groups. Twenty minutes after ; the addition of the ~MAEMA, 91.9 g of MMA was added over 20 minutes. One hour after the second addition of MMAI 5 mL o~ methanol was added. The resin (251 g) was added to heptane (700 mL), the resulting solid was separated from the liquid, and the solid was washPd with 700 mL of heptane and dried.

13~326~

To quaternize the amine groups in the resulting block copolymer, a portion (30.69 g) of the copolymer was dissolved in THF (50.5 g) and benzyl chloride (~.0 ~ wa~ added. The result~ng eolution was refluxed for about 3 hours before the addition of 50.5 g isopropanol. Refluxing was continued for 5 more hours. The resulting resin showed a solids content of 2~ % and an tertiary amine content o~ 0.31 mM~gram, indicating substantially ~omplete quaternization of the amine group~.
The copolymer was evaluated as a pi~ment dispersant, ar.d exhibited a dispersion rating of 1 in MIBK (~1) for standard pigments W505, W552, W573, W673, W805, and W811. The copolymer was also evaluated with 6tandard pigment W8~3 in MIBK, acetone and toluene ~o give ratings of M3, Al and T3, respectively.

Examplas 2-4 and Comparative Example A
In Comparative Example A, an ABA block copolymer was prepared having terlary pendant ionic groups attached to the B ~egment. The general composi-tion o~ the block copolymer was MMA/BMA//DMAEMA//MMA/~MA in expected degrees of polymerization o~ 20/20//8//20/20. In Examples 2-4, thi~ block copolymer wa~ ~uaterized with three different quaternlzing agents to form a composition of the pre~ent invention.
In Comparative Example A, a reaction ~essel was charged with 1361 g THF, 21.5 g initiator, and 1.2 mL catalyst. A feed of 581.5 g of 41.3 wt % MMA in butyl methacrylate was added o~er 20 minutes, while an ice bath was u~ed to m~intain the reaction temperature between 20 and 35 C. Simul~aneously, a 150 minute feed :~l3032~i7 of 2.4 ml catalyst in 2.6 ml THF was started.
Forty-five minutes after the end of the first monomer feed, a twenty minute feed of 173.3 g of 2-N,N-dimethylaminoethyl methacrylat~ wa~ added. Forty minut~s after tha end of the second mono~er feed, a twenty minute feed of 505.1 g of 41.3 wt % MMA in BMA
was added. Ice cooling was again used. A~ter about 16 hours, 40 ml of methanol was added.
The resulting block copolymer with tertiary pendant ionic groups was evaluated as a pigment ~ dispersant, and the results summarized in Table I.
I .In Example 2, a reaction mixture of 513.2 g of the block copolymer of Comparative Example A, 126 g ethanol, and 25.0 g iodomQthane was refluxed ~or three hours. The resulting block copolymer, with quaternized pendant ionic groups, was evaluated as a pigment dispersant, and the results summarized in Table I.
! In Example 3, a reaction mixture of 500.2 g of the block copolymer of Comparative Example A, 125 g ethanol, and 30.3 g benzyl bromide was refluxed for ~ixtean hours. The resulting block copolymer, with q~laternized pendant ionio groups, was evaluated as before, and the results summarized in ~able T.
ln Exampla 4, a reaction mixture of 200.2 g of the block copolymer o~ Comparative Example A, 50.0 g ' isopropanol, and 11.5 g methyl p-toluenesulfonate was refluxed for sixteen hours. The resultlng block copolymar, with quaternized pendant ionic groups, was evaluated as before, and the results summariæed in Table I.

~303~

TABLE I - DISPERSION RATINGS

Example Control A 2 3 4 Pigment W552Al,X4,T4,M3Al,Xl,Tl,Ml Al,Ml,Tl,X1 W573A3 Ml,X3 Ml,X3 1,A3,Tl N673~ ~ M1 W8 05 Al Ml, Xl Ml, Xl Ml W811 . A4 Ml,X3 Ml,X3 Ml W853 Al Ml, X4 M1, X4 Ml ~ .
Example 5 An AB block copolymer was prepared having the general composition EHMA//DEAEMA 42//12. A reaction ve3sel was charged with 205 g toluene, 1. 94 g lnitia-tor, and 0.111 mL catalyst. Simultaneously, a l-hour faed of 0.222 mL catalyst in 5 mL toluen~, and a 20 m~nute feed o~ 92.3 g 2-ethylhexyl methaarylate were ~tarted. After 40 minutes, 0.111 mL catalyst was added. After 3 hours more, 0.111 mL catalyst was added, and a ten-minute feed of Z0.92 g 2-N,N-dimethylamino-2~ ethyl methacrylate was added. A~ter 16 hours fuxther, 5 mL of methanol was added. A portion (150 g) of ths resulting resin was diluted with 37.~1 g ethanol, 9.16 g benzyl bromide was added, and the resulting mixture was refluxed ~or 18 hour~.
The copolymer was evaluated as a dispersant for standard piyments, and found to glve an X4 rating for pigment W505, and Xl rating~ for pigments W573, W805, W811, and W853.
,-~303;~7 Examples 6-7 and Comparative Examples B-H
In Examples 6-7 ~nd Comparative Examples B-H, comparison~ were made between blocked and random copol~mers of similar composition, and with varying degrees of ~uaternization of the pendant ionic moieties on each~
In the preparation of the random copolymer, a xeaction ves~el was charged with 127,2 g toluene, 2.26 g initiator, 74.5 g BMA, 52.6 g MMA, 29.7 g 2-N,N-diethylaminoethyl methacrylate, and 0. 030 mL
catalyst, Cooling wa~ used to maintain the reaction temperatur~ below 40 C. Aft~r 4 hours reaction, 5 mL
methanol was added.
In the preparation of the blocked copolymer, a reaction ves~el was charged with 130.3 g toluene, 0.5 ml xyl~nes, 2.~7 g initiator, 76.4 g BMA, and 54.0 g MMA, and 0.030 mL catalyst. Cooling was used to keep the reaction temperature below 40 C. After 70 minutes reaction, ~imultaneous feeds o~ 29.4 g DEAEMA over 10 minutes and 0.20 mL catalyst in 5 mL toluene over 20 minutes wer~ started. After a further hour of reac-tion, S mL methanol was added.
The re~ulting copolymers, having tertiary pendant ionic groups and representing Comparative Examples ~ and C, were evaluated as dispersants for ~tandard pigm~nt W552, and both exhibited ratings of A3, M4, and T4.
In Comparative Examples D-H and Examples 6 and 7, the block copolymers of Comparative Examples B
and C were each diluted by comhining 65 g resin and 19.5 g ~sopropanol. A 20 g portion of the resulting resin was guaternized using methyl p-toluenesulfonate, u~ing 25 mole %, 50 mole %, 75 mole %, or ~5 mole % of - ~3~3267 methyl p-toluenesulfonate, based on amine content. The rasulting solutions were held at room temperature for 10 day~. The xe~ulting quaternized copolymer6 were evaluatad a~ pigm~nt dispersants and the results 6ummarized below.

2S % QUATERNIZE~

Example D E
(RANDOM) (BLOCKED) Pigment ; W573 A3, M3, X3 A3, Ml, X2 W805 A4, ~4, X4 A4, ~4, X2 ~811 Al, Ml, X2 Al, Ml, Xl W853 Al, Ml, X3 Al, Ml, X2 50 % QUATERNIZED

1 20 Exampla F 6 (~NDOM) (BLOCKED) W573 X3 Xl W805 X4 Xl W811 X3 Xl W853 X3 Xl 75 ~ QUATE~NIZED

Example G 7 (RANDOM3 (BLOCKED) W573 X3 Xl W305 X4 Xl W811 X3 Xl ~3032~;~

W~53 X3 Xl 9 5 % QUAI'ERNI ZED

Example H 8 (RANDOM) (A) (BLOCKED) W573 Al, M2, X2 Al, Ml, Xl W805 Al, M3, X4 A3, M4, X2 W8 11 Al, M1, X3 A1, M1, Xl W8 5 3 Al, ~1, X3 Al, Ml, Xl i .

.. ~

Claims (13)

1. A substantially non-aqueous dispersion comprising pigment, organic liquid, and a block copolymer consisting essentially of (a) about from 0.1 to 50%, by weight of the copolymer, of at least one block having a number average molecular weight of about 200 to 10,000 and prepared from at least one monomer selected from compounds of the general formulas CH2=CHCO2R and CH2=CCH3CO2R, wherein R is alkyl or alkyl ether or 1-20 carbon atoms, the block further containing at least 2 pendant ionic moieties which are pendant from the R
groups and have the general formula - A(R1)mX, wherein A is selected from N, P, and S; R1 are independently selected from alkyl or alkyl ether of 1-20 carbon atoms, phenyl or alkyl substituted phenyl, m is 3 when A is N or P, an m is 2 when A is S, and X is selected from halides and conjugate bases of organic acids, the backbone of the block being prepared from ethylenically unsaturated units, and (b) about from 99.9 to 50%, by weight of the copolymer, of at least one block having a number average molecular weight of about from 500 to 100,000 and prepared from monomers selected from compounds of the general formulas CH2=CHCO2R and CH2=CCH3CO2R, wherein R is alkyl or alkyl ether of 1-20 carbon atoms.

2. A dispersion comprising pigment, organic liquid, and a block copolymer consisting essentially of (a) about from 0.1 to 50%, by weight of the copolymer, of at least one block having a number average molecular weight of about 200 to 10,000 and prepared from at least one monomer selected from compounds of the general formulas CH2=CHCO2R and CH2=CCH3CO2R, wherein R is alkyl or alkyl ether of 1-20 carbon atoms, the block further containing at least 2 ionic moieties which are pendant from the R groups and have the general formula -A(R1)mX, wherein A is selected from N, P, and S; R1 are independently selected from alkyl or alkyl ether of 1-20 carbon atoms, phenyl or alkyl substituted phenyl, m is 3 when A is N or P, and m is 2 when A is S, and X is selected from halides and conjugate bases of organic acids, the backbone of the block being prepared from ethylenically unsaturated units, and (b) about from 99.9 to 50%, by weight of the copolymer, of at least one block having a number average molecular weight of about from 500 to 100,000 and prepared from monomers selected from compounds of the general formulas CH2=CHCO2R and CH2=CCH3CO2R, wherein R is alkyl or alkyl ether of 1-4 carbon atoms.

3. A dispersion of Claim 1 or Claim 2 wherein the block copolymer is of the BAB configuration in which the copolymer contains at least two blocks of the type defined in (b).

4. A dispersion of Claim 1 or Claim 2 wherein A in the pendant ionic groups is N.

5. A dispersion of Claim 1 or Claim 2 wherein the conjugated bases of organic acids are selected from carboxylates, sulfonates and phosphates.

6. A dispersion of Claim 1 or Claim 2 wherein the pendant ionic groups of block (a) are derived from dimethyl aminoethyl methacrylate.

7. A dispersion of Claim 1 or Claim 2 wherein the pendant ionic groups of block (a) are derived from diethyl aminoethyl methacrylate.

8. A dispersion of Claim 1 or Claim 2 wherein block (b) is polymerized from methyl methacrylate.

9. A dispersion of Claim 1 or Claim 2 wherein block (b) is polymerized from butyl methacrylate.

10. A dispersion of Claim 1 wherein block (b) is polymerized from 2-ethylhexyl methacrylate.

11. A dispersion of Claim 1 wherein block (b) is polymerized from butyl methacrylate and 2-ethylhexyl methacrylate.

12. A dispersion of Claim 1 or Claim 2 wherein the block copolymer is prepared by group transfer polymerization techniques.

13. For use in a dispersion according to Claim 2, a block copolymer as defined in Claim 2.