CA1156032A

CA1156032A - Water absortive composition

Info

Publication number: CA1156032A
Application number: CA000353543A
Authority: CA
Inventors: Kishore R. Shah
Original assignee: Kendall Co
Current assignee: Kendall Co
Priority date: 1979-12-05
Filing date: 1980-06-06
Publication date: 1983-11-01
Also published as: GB2064556B; CH655322A5; NL8002335A; JPS5682839A; BE884287A; BR8003718A; ATA197780A; SE8002537L; AU543598B2; DK192780A; NO156415B; MX153080A; IT8022047A0; FR2470638B1; NO801244L; AU5718780A; AT366080B; FR2470638A1; SE448544B; GB2064556A

Abstract

Abstract of the Disclosure A composition capable of absorbing more than 45% of its weight of water without dissolution at room temperature to form a hydrogel is made by blending (1) 40 to 98% by weight of water-soluble poly(vinyl pyrrolidone) with (2) 2 to 60% by weight of a water-insoluble copolymer formed of 50% to 90%
by weight based on the total copolymer of a hydrophobic water-insoluble ethylenically unsaturated monomer, 2 to 12% by weight of an ethylenically unsaturated monomer containing an acid group, and 0 to 50% by weight of a hydrophilic ethylenically unsaturated monomer free from acidic groups.

Description

lls~a~2 Tl~is invention relates to a composition capable of absorbing more than 45~ of its weiyh-t of water without dissolution at room temperature to form a hydrogel.
According to the present invention, -there is provided a composition capable of absorbing more than 45~ of its weight of wa-ter without dissolution at room temperature to form an optically clear hydrogel consisting essentially oE an op-tically clear blend of (1) 40 to 98% by weight, based on -the total weight of the blend, of a wa-ter-soluble polymer of N-vinyl-2-pyrrolidone, having a molecular weigh-t from 10,000 -to 1,000,000 and (2) 2 to 60% by weight of a water-insoluble polymer consisting essentially at least two monomers selected from the group consisting of 50 to 90% by weight, based on the total weight of the polymer, of a hydrophobic water-insoluble e~hylenically unsaturated monomer,

2 to 12% by weight of an ethylenically unsaturated monomer contain-ing an acid group, and from 15 to 45% by weight of a hydrophilic ethylenically unsaturated monomer free from acidic groups.
The compositions of the present invention may absorb even more than ten times their weight of water. Despite the absorption of such large amounts of water, the compositions retain their coherence and dimensional integrity and do not dissolve.
These characteristics make them particularly useful for several biomedical purpo~es which re~uixe that the hydrogel come into intim~t~ contact wi-th body -ti~sues or cavi-ties. Other u~e~
include non~Eogging coatings for windshlelds.
It h~s previously been propo~Qd to insolubilize poly-meric N-vinyl lac-tams such as poly(vinyl pyrrolidone) by reaction with wat~r-~luble polymers containing carboxyl yroups, the re-action product precipitat:ing ~rom solu-tion when the two are mixed, as described in S-toner Uni-tqd S-tak~ Patent 2,901,457. As pointed out by StQner et al. at column 4, lines 56 - 73, the reaction product there described always has substan-tially the ~ame proper-- 2 - .

ties and contains the two polymeric components in the same propor-tions regardless of the proportions of the two used to make the B - 2a -`:

1l5Ba32 product. rhc compositions of the prescnt invention, on the other hand, vary in properties and in proportions of components ~epending upon proportions of starting materials. It has also bcen proposed in O'l)riscoll et al. Unitcd States Patent 3J700J761, in Gruc~a United States Paten~ 3,807,39~, ancl in Le Boeuf et al. United States Patent 4,018,853 to make coval-ently cross-linked hydrogels by polymerizing hydrophilic meth-acrylate monomers in the presence of poly~vinyl pyrollidone).
The mechanism of interaction between the poly(vinyl pyrrolidone) polymer and the water-insoluble polymer in the blend is not fully understood, but the blend does behave like a physical mixture rather than a chemical reaction product in that it can be separated into the two polymeric components by gel permeation chromatography. The blends are optically clear and substantially free from haziness~ indicating that the blend is homogeneous despite the fac~ that the poly(vinyl pyrrolidone) is water-soluble and the other polymer is water-insoluble. Examination at high magnification under an elec-tron microscope shows the presence o microphase domains (4,000 A or less in diameter) of water-insoluble material dispersed in the continuous phase of water-soluble poly~vinyl pyrrolidone). ~he presence of these microphase domains of the water-insoluble copolymer prevents dissolution of the contin-UOU5 phase polymer in watqr~ hut unlike cQvalent cross~linking o-~ p~lymers d4qs nPt rond~r the blend nPn-thermoplastie. In-stead, -~h~ blend pQssqssQS thq ability ~o b~ repqatedly shap~d or ~ormed under modera~e pr~ssure at a tempqra~uro as 1P~ as 150PC, or in sPme cases even lower. Tho shaped or f~rmed CPmPQ-sltlon rq-tains its sh~pe a~ r~om tanlp~rature subJ~ct to distor-

- 3 -~ ..

1 15~032 tion when swollen with water. rhO compositions oF the present invention in which thc dispersed submicroscopic particles (mi-cro-ph~se clomains) act as multiE~Ie cross-links to prevent dis-solution of the hydrophilic continuo~ls phase (which by itself is water-soluble~, form a new class o hydrogels, distinct from those in whicll the cross-linking is provided by weak co-hesive forces, hydrogen bonds, ionic bonds, or covalent bonds.
The water-soluble poly(vinyl pyrrolidone) polymer employed in the compositions of the present invention may have a molecular weight varying over a wide range from lO,Q00 to 1JOOO~OOO or more, but those polymers having molecular weights from 100,000 to 1,000,000 are preferred.
The water insoluble polymers which can be employecl as blends with the poly(vinyl pyrrolidone) polymer in the com-positions of the present invention include water-insoluble polymers of a hydrophobic water-insoluble ethylenically unsat-urated monomer such as alkyl esters of acrylic or methacrylic acid in which the alkyl group has from 1 to 16 carbon atoms, styrene, acrylonitrile, vinyl acetate, vinyl butyrate, vinyl chloride, vinylidene chloride, ethylene, propylene, butylene, butadiene and other polymerizable alkadienes, vinyl alkyl ethers and vinyl alkyl ketones in which-the alkyls have 3 or more carbon atoms, and the like. The copolymers also include AS another essential monomer an ethylenically unsatura~ed mon-omer containing an a&id ~roup such as a ~arhoxyl:lc, sut~QnicJ
or pho~phonic acid group; among suitable acldic monomers are acrylic acid, me~hacrylic acidJ crotonic acid~ maleic acid, 2-sul~o ethyl methacrylate, l-ph~nyl vinyl phospilonic acid~ and -~h~ like. The third monomer,

- 4 -11560~2 is scl~ctcd ~rom ;l (Jro~l~ o~ hyclroi~hilic e~hylenically unsaturated monomers, po-;scssincJ a solubility parameter in excess o~ 11 [calories/cm3]1~2, free from acidic groups, such as methacrylamide, acryl~mide, hydroxyethyl methacrylate, diethylene or triethylene glycol monomethacrylate, glyceryl methacrylate, etc.
In the cas~ of each of the three types of monomers a mi~ture of two or more indiviclual monomers of the same type can be used.
Compatibility or incompatibility o~ the water insoluble copolymer wikh the water-soluble polymer of N-vinyl-2-pyrrolidone,~
in the hydrated ~orm of the blend, tha~ is, its suitability for use in the present invention, can in each case be readily determined by visual examination of a blend of the two polymers after ,-equilibration in water at room temperature. If the blend is lS transparent and optically clear and remains so after immersion in water at 20C. without dissolution in -the water, it forms a satisfactory hydrogel~ I~ the blend is cloudy or opaque after equilibration in water, or if it dissolves in water at 20C., the blend made ~rom tha-t copolymer is not satis~actory and possesses poor mechanical properties. For a blend composition to possess satis~actory mechanical properties in the hydrated form, the size o~ the microphase domains oF the terpolymer in the hydrogel should no~ be ~rea~r than ~,~00 A, and prc~erably should be below about lQ~Q A.
~5 TI~Q rel~lve propor~ions o~ ~hc ~ r~nk ~nomar~ in ~ha co~lym~r rnay vary ~icl~ly; ~he hydroph~bic w~x-insoluble ~thyl~nicaLly uns~kur~k~cl monomer may amoun~ ~o 5QP~ ~o 90~ by _ 5 ~

~ 1 5~32 weight, based on th~ total weight of copolymer, while the ethyl-enically ~lsaturated monomer containing an acidic group may amount to 2% to 12% by weight; the hydrophilic ethylenically unsaturated monomer may amount to 0 to 50% by weight. The exact proportions of the three types of monomers are determined by the hydrophobic-hydrophilic balance required in each case. ln many cases, for attainment of this balance the incorporation of 15 to 45% of a hydrophilic monomer is required.
Thus, in the case of one preferred class of copolymers the amount of methyl methacrylate tor styrene or 2-ethylhexl acrylato~ is from 55 to 70% by weight based on the total copolymer weight, the amount of acrylîc acid is rom 2 to 12% by weight, and the amount of methacrylamide is from 25-43% by weight.
~n the case of another preferred copolymer, the amount of n-butyl methacrylate is from 65 to 80% by weight based on the total copolymer weightj th~ amount of acrylic acid is from 2 to 12% by weight, and the amount of methacrylamide is from 15 to 35%
by weight.
In the case of still another preferred copolymer, the amount of methyl methacrylate is from 88 to 90% by weight of the total copolymer, while 2-acrylamido-2-methyl propanesulfonic acid, the only other monomer constituent, is from 10-12% by weight. In this case, the prcsence of a non-acidic hydrophilic comonomer is not ~ssential.
In the case of still another pre~qrre~ copolym~r, the asnQunt Oe n-butyl m~h~cryla~e i5 ~r~m S0 to 78% by weight o~ ~he total cQpolymerl the amoun~ o~ acrylic ~cid is from 2 ~o 12~ by weight~ and tlle amo~nt o~ hydrophilic p-s~yrene sulfonamlde ls ~rom 20 to 35% by w~ight. In ano~her pre~Qrred copolym~r, thQ
amount o~ n-butyl m~thacryl~-~e is ~rom 55 to 70~ of tho total ~ - 6 -l 1~6032 copolymer weight, acrylic acid is from 2 to 12%J and hydroxyethyl methacrylate i5 from 25 to 43%.
The relative proportions of poly(vinyl pyrrolidone) and of copolymer in the blend vary over a wide range, from 40 to 98%
by weight, preferably from 50 to 98%J based on the total weight of the blend, of the former and from 2 to 60% by weight, prefer-ably from 2 to 50%, of the copolymer; optimum proportions of each within the range vary depending upon the particu}ar properties de-sired in the blend as well as upon the identity o~ the particular copolymer present in the blend. The greater the proportion of the copolymer in the blend, the lower is the equilibrium water content of the resultant hydrogel. The water content of the PVP-blend hydrogels of this invention can be varied from apprcximately 30%
to 95% or higher by ~udicious selection of the copolymer and its proportion in the blend. In general, the higher the water content of the hydrogel, the poorer become its mechanical properties.
The blend can be made by mixing together solutions or dispersions of the poly(vinyl pyrrolidone) polymer and the water-insoluble polymer in any desired vehicles or solvents which are miscible with each other, then removing the vehicle or solvent, as by evaporation. It may also be~possible to blend the poly-mers on a hot roll mill or in an extruder or in other convention-al mixing equipment. Shaped articles of the blend can be pre-pared by casting rom a suitable solvcnt or ky a moldlng process under ~he in~luence of h~at and pressure.
The th~rmoplas~icity o~ ~hese hydrQgel-~orming hlends confer3 on ~h~m a sp~lal proGe~slng advan~a~e qver covalently cross~llnked syn~hetlc hydrogel~, T~llorlng o~ m~chan:Lcal and physlcal pr~per~ies ~e.~.J wa~er cQn~ent/ solu~e ~nd water per~
3~ m~abili~y, sotness~ flexibility, tensile stren~th, etc.~ of the ~l~drOCJCl i5 readily ~lccomplistlc~d by control of thc~ physico-chemical cllaractcri!;tics. ancl th~ pro~)ortion ln ~le blcncl o~ tho watcr-insoluble copol~mer. Uue to tllese advantages the novel hydrogel compositions o~ this invention lend thernselves to several appli-S cations such as burn and wound dressings, coatings for cathetersand surgical sutures, soft contact lenses, implants ~or delivery of medicaments at controlled ra-tes, and o-ther articles coming into intimate contact with body tissues or cavi-ties (e.g., vitreous and corn~al prosth~s~s).
Thcse new hydrogel-~orming materials can also be used in the manufacture of devices for controlled delivery of drugs ,~
which are sparingly soluble in water. When a drus (soluble in the water-insoluble copolymer) i5 incorporated in these hydrogels, it remains dispersed in hundreds of thousands of "depots" o~ water-insoluble domains. The delivery rate of the drug consequently is governed by partition coefficient of the drug in the aqueous and non-a~ueous phases, membrane geometry, and the size and the number oF the dispersed domains. An advantage of such a device is that a mechanical failure or a pin-hole would not cause any increase in the delivery rate of the drug.
~ non-medical use o~ the novel compositions of this invention is ~or coating glass surfaces, such as inner sides of automQtiv~ ~nd ai~craf~ windshielcls, to rqnd~r khem non~fo9~in~.
~his is accom~lish~d by c~ tinC1 ~rom ~ sui~lc ~lvell~ a khin 2S co~lnc~ o~ ~ blqncl ~mL~ikion, such as th~ desc~i~ed in ~mple 1~, on a gla~s3 surE~cq. P~ma~io~ o~ t~la ~olym~rlc blqnd co~-~inc3 c~n alsQ be a~complishQd hy a sp~y of its diluk~ s~lution in a 1156~)32 sll.ita~lc sc~lvcnt. ~ c coat.illg h.~s a ~ood adllesion to ylass, is colorless, optic~ally cle~r, and non-:EoggincJ upon exposur~ to hot, mo.ist air.
The following specific examples are intended to illustrate more fully the nature of the present invention without acting as limitations upon its scope.
Examples l-13 . . .
Each of the copolymers of these examples was prepared by conventional solution polymer.ization procedure by dissolving the desired proportions of monomers in a suitable solvent and by employiny as an ini~.iator of polymerization a small amount ~0.2-0.4~ by weight of monomers~ of a free rad1cal generator such~
as azobisisobutyronitrile or 2-t-butylazo-2-cyan~opropane.
Polymerization was carri`ed out at 80-95C. to a high degree of lS conversion. The composition of the copolymerization mixtures is ., ::.
described in Table I. Copolymers of the Examples l to 4 were ;: isolated from the reaction mixture by precipitation into methanol, collected by filtration, and dried at 100C. under vacuum, whereas, the copolymer of Example 5 was isolated by removal of the volatiles by heating in vacuum at 100C.

_,............. . ... . . _ . __~

l 156032 ~rl~ur ~; l ()N L~ t~ NO.
IN~RE:DIENT~ 1 2 3 4 5 .... _ _ . . _ CO~tONO~ERS - GR~I~S

~lethyl Methacrylate 65 _ _ 90 Methacrylamide 30 30 15 _ 30 Styrene _ 65 _ ~cxylic Acld 5 5 5 _ 5 n-Butyl Methacryl.lte ~ _ 80 _ 2-Acrylamido-2-mQthyl-propane Sul~onic ~cid _ _ _ 10 2-Ethyll~e~yl Acrylatc _ _ _ _ 65 SOLVENTS-MILLILITERS
___ Ethanol 100 100 100 _ 100 Dioxane 100 100 100 _ N N-Dimethylformamide _ _ _ 100 100 Each of the blend compositions o~ these examples was prcparecl by dissolving in ~ N-dimethylformamide the desired proportions of the water-insoluble copolymer and poly(vinyl pyr-rolidone) (Grade K-90 mol.wt. 360 000) to obtain a solu-tion containing 10-15% by weight oE -the polymeric blend. The solution oE -the blend was then heated at 100C. under vacuum to evaporate ~he solvQn~ }eavinq ~ mass o~ opkically tr~nsp~xqn~ blendecl sQlld m~teEial~ Tll~ t?l~nd which w~s ~h~rmc~Plas~ic was press~d lnto ~ cli3c in ~ rn~ld h~at~d a~ 15~C. Thc mol~ed disc was placed in dQic~nizcd wc~ker ~or 72 hours d~rinc-1 which kimc ik ab-30rbcd water and swelle~d to foxm a hydrogel. The compcJsitions c~f the blc3nclr3 tllcix ph-~3i.c~1 aL~I~qar~nscs ~nd ~ha ~quilihrium watcr con~ent ~e thcir hydroclcl~ ara dcssc~ibed in ~ble II.

_ .. . . . .. _ . .

1~56032 T/~IIL,I, [ I

PTE BI~Il:) or COMPOSITION PHYSIC~L A:PPE~IOE 1~2UILIE~RIUM
. NO. COPOL`l';~ER P~l~rS BY DRY FORM HYDR~`~TED FORM I~TER CONIl~T
OF I3~11?1,E WEIG~IT OF ~æIGElT %
NO. PVP (K-90) __ .......... OP~ LLWD __ ~ 6 1 70 Transpc~ent- Trans~rent, 68 ; Solid Strong , 7 1 90 " .. 31 8 2 70 " , ,. 58 9 2 90 ll " 80 3 90 ll Tr,anslucent, 90 .. Coherent ¦~

11 4 90 'l ~rransparent/ 84 ~¦
Coherent ~l 12 5 70 ll '~ansparent, 77 Strong I, 13 5 90 ll ll 90 ~xamples 14-15 , , A 20.8 g (0.10 mole) portion o~ phosphorous pentachlorid ,was placed in a 500 ml. round-bot-tomed ~lask and 17.4 g (0.084 molq) of pulveri.~ed p-sodium styr~nesulfonate was a~d~d sl~wly with lc~ ba~h coolln~, q'h~ mixtu~e wa~ $tirred cauki~usly wi~h a S magnq~ic stirrQr. ~ r 30 min. ik was h~a~ed ~nder re~lux a~

50~G0C far 2 hrs. r~he prod~c~ was coolqd and po~r~d into lQ0 oE crush~ iCQ ~nd ~x~rac~ed with lQ0 ml o:E chLor4~0rm~ Th~

Org.lrliC' layer COII~aillillCJ p-slyrcncsulfonyl chlori~e was s~E~Ir.ltccl, washed sc!veral tirnes wikh di(;tillecl water, and dried over magrlesiurll ;ulfate.
The chloroorm solution (100 ml) containing p-styrene-sulEonyl chloride was aclded with mechanical stirring into 340 ml of 30~ ammonium hydroxicle (specific gravity 0.90) while cooling with ice over a period of about 30 minutes. The mixture was h~ated to 50C for S hrs. under a reflux condenser and then coolcd to room temperature.
~he or~anic layer was separatedr dried over anhydrous ma~Jncsi~lrl sulfate, and thcn evaporated to dryness to yield a solid white powder of crude p-s-tyrenesulfonamide, which was purified by recrystalliza-tion from ethanol-water mixture to yield about 6.0 g of the sulfonamide, m.p. 130-132C.
lS The infrared spectrum of the sulfonamide showed absorptions at 3350 and 3260 cm 1 (NH stretching), 1600 cm 1 (aromatic c=c~, 1305 and 1160 crn 1 (S=O stre-tching), and 840 cm 1 (p-disubstituted benzene, 2 adjacent CH wagging).
A copolymer o~ 62Q~ n-butyl methacrylate, 30~ p-styrene-sulfonamide prepared as described above, and 8% acrylic acid was prcparecl in the usual way, as described in ~xamples 1-13, ernploying 33~6 concentration of the monomers in a mixture of e~hyl alcohol and dioxane. Th~ copolymer w~s puri~ied by precipi~atlc~n o~ the r~action mixkure in ahloxoformt then isola~ed ~$ by fil~ ion and driqd in va~uo ak 100C.
~ lencls o~ kh~ copolymQr wikh poly(vinyl-pyrrolidorl~ tl'V~ ~rad~ 0, mol.wk. 360,00~) wexe prQpax~cl as de.scrib~(l in ~xamples 1 ko 13, by dissolvlncl the ~opolymer and PVP ill dim~thyl.~orrn~mide ~ncl su~sequqn~ly cva~oxa-~in~ ~hc solvc~ t 100~C in vac~lo. I31ellcls containincJ 10~ and 30~ by wei~Jilt of copolylller, respectively, the b~lance being poly(vinyl-pyrrolidon~) in each case, were found to be optically -transparent solids. Molded discs of the two blends, prepared as described in Examples 1 to 13, were found to absorb water and form transparent hydroc~els containing 84.6~ and 62.5~ water by weight, respectively, when equilibrated with deionized ~ater at room temperature for 72 hours.
rV~an~ :o i6 ~
~Iydroxyethyl methacrylatq (HEMA) was purified by extxactiny (~ -to 6 -times) a 1:1 solution of the polymer in wa-ter with petroleum ether, then saturating the aqueous monomer solution with sodium chloride, and extracting the monomer with chloroform. The combined chloroform extracts were dried over anhydrous magnesium sulfate and the solution distilled ln vacuo (~0.1 mm on Hg) using cuprous chloride as inhibitor. The monomer fraction distilled over at 70-82C.
A copolymer of 52% butyl methacrylate, 4~0% HE~, and ~%
acrylic acid was prepared in the usual way, as described in Examples 1-13, employlng 25% concentration of the monomers in a mixkure of e-thyl alcohol and dioxane.
Optically clear blends of the copolymer in varying proportions with pOly~vinyl pyrrolidone)(PVP, Grade K-90, mol.
Wk. 360,000) werq prqpar~d as dqs~ibed in ~xamples 1-13 hy dissolvincJ th~ ~opolym~ and PVP in dim~hyl~oxlnamid~ and su~c;~qu~n~ly qvclpox~in~J thq solvqn-t at 100qC in vacuo.

App:~ximate1y ~3-12 mi1 thlolc sh~qks oE t:h~ blqnds w~Ie compxas~ion mold~d, a~k~r wlliah kh~y W~Iq qquilibr~ad in doionized wn~er ak room tomp~a~-lra ~or 72 hours. Ik w~s ~ound 115~032 ~lat ~l~nd; COIlt~ (J 70, ~0 an~ 90~ by we.icJIlt, respecl-ively, of l~VI~ Eormc(l llydro-JeLs cont.lini.ll(J 75,8n~ 82.3!1; ancl 88.9~ by weicJht o~ water, respectively.
E.~am~ 20-2G
A copolymer of 62~ butyl methacrylate, 8% acrylic acid, and 30~ methacrylamide was prepared by the same general method as ~escribed in Examples 1-13, and optically clear blends of the resultant copolymer with varyiny amounts of the same poly(Vin~l pyrrolidone), Grade K-90, were prepared as described in Example~ 16-19.
It was ~ouncl that a linear relationship existed between the proportion (10 to 40gO) of the copolymer in the blend and equilibrium water content of the hydrogels as shown in column A
of Table III below. In order to take into account the change in the properties of the PVP in the blend due to incorporatlon of the copolymer, hydration of the PVP fraction alone was calculated assuming that swélling of the copolymer in water is negligible, as shown in the last column of Table III. Once ayain it was found that equilibrium water uptake of the PVP frac~ion was inversely proportional to the amount of copoly~er in the blend.

... , ..... ... _ _ '1'1\~ L.~ :t :1 1 cn~lrocilTro?l _ ~IYDr~OGr,L CO?ll'OSTlON~
Col70i~ ~1t.~ ------ B~ p ,~
~.H20 in llydr:lted P~'P
.. _ ~ _._ .. ~ .__ __ -- ----- :
83.5 16.5 14.85 Rq.90 1'15 79.1 Z0, 9 17 .7GS 81 . 67 2~ 80 77,7 22.3 17.84 8~.. 33 ~ ' 75 69.6 30.4 22.80 75.32 70 64.3 35;7 Z4.99 72.Ql 65 61.7 38.3 2q.895 71,25 ~
~lO 60 55.3 q4.7 26.~2 67.34 ~ ~-: , ~:

n x wll q , ~ .. .. ~

13i~ n X ~ 3l~"~l ~"~ ,y l~

-- lS --1156~)32 The ble~lcl:i of thc presellt invelltion possess the l~ropcrti.cs of thcrmop:Lasticity, usibility, and solubility in ~:
or~anic solvents as well as hydratability. But while they retain the thermoplasticl-ty, fusibility, and solubility in organic i~:
solvents of the PVP portion of the blend, they exhibit varying hydration characteristics of the PVP portion depending upon tha amount of copolymer present. :
What is claimed is: 1 j ~ :
!:
. : ~
~, ~ : - ~
:~

, , . :
:i :
:: : :
I
, 1~:
, . . , 1.6:

`
: : ~

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A composition capable of absorbing more than 45% of its weight of water without dissolution at room temperature to form an optically clear hydrogel consisting essentially of an optically clear blend of (1) 40 to 98% by weight, based on the total weight of the blend, of a water-soluble polymer of N-vinyl-2-pyrrolidone, having a molecular weight from 10,000 to 1,000,000 and (2) 2 to 60% by weight of a water-insoluble polymer consisting essentially at least two monomers selected from the group consisting of 50 to 90% by weight, based on the total weight of the polymer, of a hydrophobic water-insoluble ethylenically unsaturated monomer, 2 to 12% by weight of an ethylenically unsaturated monomer containing an acid group, and from 15 to 45%
by weight of a hydrophilic ethylenically unsaturated monomer free from acidic groups.

2. A composition capable of absorbing more than 45% of its weight of water without dissolution at room temperature to form an optically clear hydrogel consisting essentially of an optically clear blend of (1) 40 to 98% by weight, based on the total weight of the blend, of a water-soluble polymer of N-vinyl-2-pyrrolidone, having a molecular weight from 10,000 to 1,000,000 and (2) 2 to 60% by weight of a water-insoluble polymer consist-ing essentially of 88 to 90% by weight, based on the total weight of the polymer, of methyl methacrylate and 10 to 12% by weight of 2-acrylamido-2-methyl propanesulfonic acid.

3. A composition as claimed in claim 1 in which said water-insoluble polymer consists essentially of 55 to 70% by weight, based on the total weight of the polymer, of a monomer selected from the group consisting of methyl methacrylate, styrene, and 2-ethylhexyl acrylate, 2 to 12% by weight of acrylic acid, and methacrylamide in an amount from 25 to 43% by weight.

4. A composition as claimed in claim 1 in which said water insoluble polymer consists essentially of 65 to 80% by weight of n-butyl methacrylate, based on the total weight of the polymer, 2 to 12% by weight of acrylic acid, and methacrylamide in an amount from 15 to 35% by weight.

5. A composition as claimed in claim 1 in which said water-insoluble polymer consists essentially of 50 to 78% by weight, based on -the total weigh-t of the polymer, of n-butyl methacrylate, 2 to 12% by weight of acrylic acid, and from 20 to 35% by weight of p-styrene sulfonamide.

6. A composition as claimed in claim 1 in which said water-insoluble polymer consists essentially of 55 to 70% by weight, based on the total weight of the polymer, of n-butyl methacrylate, 2 to 12% by weight of acrylic acid, and from 25 to 43% by weight of hydroxyethyl methacrylate.