Crosslinked absorbent pressure sensitive adhesive and wound dressing

Crosslinked, absorbent pressure sensitive adhesive compositions are disclosed comprising an acrylate or methacrylate ester of an alcohol, a hydrophilic alkylene oxide acrylate, a hydrophilic N-vinyl lactam, and an effective amount of a crosslinking agent. The compositions have an enhanced skin adhesion profile and are moderately absorbent. Also disclosed are precursor adhesive compositions and low-profile wound dressings.

FIELD OF THE INVENTION 
The invention broadly relates to pressure sensitive adhesive compositions, 
precursor compositions for such adhesives, and wound dressings using such 
adhesive compositions. More specifically, the invention relates to 
biologically compatible, absorbent, pressure sensitive adhesive 
compositions, precursor compositions for such adhesives, and wound 
dressings using such adhesive compositions. 
BACKGROUND OF THE INVENTION 
Pressure sensitive adhesives have long been used in the manufacture of 
medical tapes and dressings intended for attachment to the skin. 
Pressure sensitive adhesives intended for use in attaching tapes and/or 
dressings to the skin must possess a number of physical, chemical and 
biological characteristics including (i) biological compatibility with 
skin over extended periods of continuous contact, (ii) biological 
compatibility with surgical incisions and lesions, and (iii) a bonding 
strength sufficient to prevent premature peeling of the tape/dressing from 
the skin but low enough to prevent skin irritation upon removal of the 
tape/dressing. 
Acrylate-Based Pressure Sensitive Adhesives 
Acrylate-based pressure sensitive adhesive tapes have been used for many 
years in medical and surgical applications. Acrylate-based pressure 
sensitive adhesive tapes are generally biologically compatible and provide 
acceptable adhesion to the skin. One such acrylate-based pressure 
sensitive adhesive tape having acceptable skin adhesion performance is 
disclosed in U.S. Pat. No. 3,121,021 issued to Copeland. 
Acrylate-based pressure sensitive adhesive tapes are known to suffer from 
adhesion buildup after extended contact with the skin. Excessive adhesion 
buildup causes the tape to strip skin from the body upon removal from the 
skin to the point of producing moderate pain and prolonged skin 
irritation. U.S. Pat. No. 3,321,451 issued to Gander discloses that the 
inclusion of certain amine salts into an acrylate-based pressure sensitive 
adhesive facilitates the removal of pressure sensitive adhesive tape from 
the skin by permitting the bonding strength of the tape to be reduced by 
soaking the tape with water. U.S. Pat. No. 3,475,363, also issued to 
Gander, attempts to overcome the objectionable adhesion buildup associated 
with acrylate-based pressure sensitive adhesives by including the 
crosslinking agent dimethylaminoethyl methacrylate into the adhesive. 
U.S. Pat. No. 3,532,652 issued to Zang discloses that the adhesion buildup 
observed with acrylate-based pressure sensitive adhesives is caused by the 
migration of body fluids, such as skin oils, into the adhesive. Zang 
discloses that partially crosslinking an acrylate-based pressure sensitive 
interpolymer adhesive with polyisocyanate overcomes the adhesion buildup 
problem. 
U.S. Pat. No. 4,140,115 issued to Schonefeld discloses that the 
skin-stripping irritation associated with the removal of acrylate-based 
pressure sensitive adhesive tapes can be alleviated by blending an 
unreacted polyol having a fatty acid ester pendant moiety into the 
acrylate-based pressure sensitive adhesive. We observe that such an 
adhesive would tend to leave objectionable residue on the skin after 
removal of the tape. 
Crosslinking of Pressure Sensitive Adhesives 
The crosslinking of acrylate-containing polymers using a photosensitive 
crosslinking agent, such as a benzophenone, is taught by U.S. Pat. No. 
4,181,752 issued to Martens et al. 
U.S. Pat. No. 4,165,266 issued to Stueben et al. discloses a pressure 
sensitive adhesive composition synthesized from a poly(vinyl alkyl ether), 
a monoacrylate monomer and a photoinitiator, such as benzophenone. 
A solvent and heat resistant pressure sensitive adhesive is disclosed in a 
Japanese language review article authored by Toshio Okada entitled 
Radiation Curing of Pressure sensitive Adhesives, Volume 20, No. 611984. 
The pressure-sensitive adhesive is a copolymer of benzoin acrylate and an 
acrylate monomer, such as 2-ethylhexylacrylate, cured by exposure to 
ultraviolet radiation. We believe that the degree of crosslinking in such 
a composition would result in an adhesive having unacceptably low adhesion 
strength for use in securing a tape or dressing to the skin. 
While the varied adhesives disclosed above provide a wide range of 
beneficial properties, a substantial need still exists for a low-cost, 
absorbent, biologically compatible, pressure sensitive adhesive useful in 
the manufacture of a low-profile wound dressing having a moderate capacity 
for absorbing wound exudate. 
SUMMARY OF THE INVENTION 
Pressure-Sensitive Adhesive 
The invention is a moderately absorbent, biologically compatible, pressure 
sensitive adhesive useful in the manufacture of a low-profile wound 
dressing with an acceptable adhesion to skin arid a moderate capacity for 
absorbing wound exudate without objectionable adhesion, buildup after 
extended contact: with the skin. The adhesive may be formulated to provide 
a substantially transparent dressing so that the wound may be inspected 
and monitored without removing the dressing. 
A first aspect of the invention is an absorbent, biologically compatible, 
pressure sensitive adhesive comprising a crosslinked copolymer of (a) an 
acrylate monomer selected from the group consisting of (i) an acrylate or 
methacrylate ester of a non-tertiary C.sub.4-12 alcohol, and (ii) an 
acrylate or methacrylate ester of a mixture of non-tertiary C.sub.1-14 
alcohols with a resultant average of between about 4-12 carbon atoms per 
alcohol molecule; (b) a hydrophilic alkylene oxide acrylate monomer having 
an average of about 3 to 40 alkylene oxide units; (c) a hydrophilic 
N-vinyl lactam monomer; and (d) a crosslinking agent effective for 
crosslinking the copolymer. 
The pressure sensitive adhesive can be chemically tailored, within 
physically defined parameters, to produce a skin compatible adhesive 
having a unique combination of properties. The properties of the novel 
pressure sensitive adhesive include (i) biological compatibility with 
human skin over extended periods of continuous contact, (ii) biological 
compatibility with surgical incisions and lesions, (iii) a bonding 
strength sufficient to preventing premature peeling of the tape/dressing 
from the skin but low enough to prevent skin irritation upon removal of 
the tape/dressing, (iv) a moderate absorbency sufficient to permit use of 
an otherwise low-absorbent tape/dressing over a surgical incision or 
lesion producing a moderate amount of fluid exudate, (v) a conformability 
sufficient to permit a tape/dressing to follow to the contours of the 
body, and (vi) a cohesive strength effective for maintaining the adhesive 
in position between the skin and the backing of the tape/dressing during 
application and use. 
Precursor Composition for Manufacture of a Pressure-Sensitive Adhesive 
A second aspect of the invention is a precursor composition useful for 
making an absorbent, biologically compatible, pressure sensitive adhesive. 
The precursor composition comprises an uncrosslinked copolymer of (a) an 
acrylate monomer selected from the group consisting of (i) an acrylate or 
methacrylate ester of a non-tertiary C.sub.4-12 alcohol, and (ii) an 
acrylate or methacrylate ester of a mixture of non-tertiary C.sub.1-14 
alcohols with a resultant average of between about 4-12 carbon atoms per 
alcohol molecule; (b) a hydrophilic alkylene oxide acrylate monomer having 
an average of about 3 to 40 alkylene oxide units; (c) a hydrophilic 
N-vinyl lactam monomer; and (d) a crosslinking agent effective for 
crosslinking the copolymer. 
Wound Dressing 
A third aspect of the invention is a wound dressing comprising (i) a 
substrate (ii) an absorbent pressure sensitive adhesive coated upon a 
major surface of the substrate, and (iii) a release liner protectively 
sandwiching the adhesive between the substrate and the liner. The pressure 
sensitive adhesive comprising a crosslinked copolymer of (a) an acrylate 
monomer selected from the group consisting of (i) an acrylate or 
methacrylate ester of a non-tertiary C.sub.4-12 alcohol, and (ii) an 
acrylate or methacrylate ester of a mixture of non-tertiary C.sub.1-14 
alcohols with a resultant average of between about 4-12 carbon atoms per 
alcohol molecule; (b) a hydrophilic alkylene oxide acrylate monomer having 
an average of about 3 to 40 alkylene oxide units; (c) a hydrophilic 
N-vinyl lactam; and (d) a crosslinking agent effective for crosslinking 
the copolymer. 
Copolymerizing of a crosslinking agent into the backbone of the pressure 
sensitive adhesive copolymer greatly increases crosslinking efficiency and 
permits the copolymer to be crosslinked after formation of the copolymer. 
The increased crosslinking efficiency permits very minor amounts of 
crosslinking agent to achieve useful degrees of crosslinking. 
Use of the preferred photosensitive crosslinking agent in the copolymer of 
this invention allows the use of solventless coating techniques because 
the copolymer need not be crosslinked until after it is coated upon a 
support member. 
These and various other advantages and features of novelty which 
characterize the invention are pointed out with particularity in the 
claims annexed hereto and forming a part hereof. However, for a better 
understanding of the invention, its advantages, and objects obtained by 
its use, reference should be had to the accompanying descriptive matter, 
in which there is illustrated and described preferred embodiments of the 
invention. 
Detailed Description of Embodiments of the Invention 
The first aspect of the invention is a biologically compatible, moderately 
absorbent, pressure sensitive adhesive composition which is a crosslinked 
copolymer of (a) a hydrophobic acrylate monomer (monomer A), (b) a 
hydrophilic alkylene oxide acrylate monomer (monomer B), (c) a hydrophilic 
N-vinyl lactam (monomer C), and (d) a mono-ethylenically unsaturated 
crosslinking agent (monomer PX). The PX monomer is preferably a 
photosensitive crosslinking agent effective for crosslinking the copolymer 
upon exposure to ultraviolet radiation. 
A second aspect of the invention is a precursor composition useful for 
manufacturing the pressure sensitive adhesive composition described above. 
The precursor composition comprises the copolymer of A, B, C and PX 
described above prior to crosslinking of the copolymer. 
A third aspect of the invention is a wound dressing for use over surgical 
incisions or lesions exuding a moderate amount of fluids. The dressing 
comprises a substrate coated on a major surface with the absorbent 
pressure sensitive adhesive composition described above, and a release 
liner protectively sandwiching the adhesive between the substrate and the 
liner. 
The properties and characteristics of the adhesive compositions of this 
invention are based upon a synergistic interaction of the various 
individual components. Consequently, efforts to describe the attributes 
contributed and/or influenced by each of the individual components is not 
necessarily indicative of the attributes possessed by the final adhesive 
composition. Such descriptions should therefore be used only as an 
indication of general trends and as a guide to those attributes which 
should be carefully considered when selecting the other components of the 
composition. For example, monomer B impacts absorbency such that 
incorporation of a minor proportion of monomer B in the adhesive would 
tend to produce an adhesive having reduced absorbency. However, the 
overall absorbency of the adhesive may be returned to an acceptable level 
by selecting a highly absorbent monomer C, increasing the amount of 
monomer C in the adhesive, etc. 
The Monomers 
Monomer A 
Monomer A is a hydrophobic acrylate monomer which contributes to the 
visco-elastic properties of the copolymer. The monomer is selected from 
the group consisting of (i) an acrylate or methacrylate ester of a 
non-tertiary C.sub.4-12 alcohol, and (ii) an acrylate or methacrylate 
ester of a mixture of non-tertiary C.sub.1-14 alcohols with an average of 
between about 4-12 carbon atoms per alcohol molecule. Useful acrylate and 
methacrylate alcohol esters include specifically, but not exclusively, the 
acrylic acid and methacrylic acid esters of 1-butanol, 1-pentanol, 
3-pentanol, 2-methyl-1-butanol, 1-methyl-1-butanol, 1-methyl-1-pentanol, 
2-methyl-1-pentanol, 3-methyl-1-pentanol, 2-ethyl-1-butanol, 
2-ethyl-1-hexanol, 3,5,5-trimethyl-1-hexanol, 3-heptanol, 2-octanol, 
1-decanol, and 1-dodecanol. Mixtures of these alcohols are available from 
Exxon under the Exxal family mark. A preferred alcohol mixture for use in 
synthesizing monomer A is Exxal-8. 
The copolymer includes about 30 to 70 wt %, preferably about 40 to 50 wt % 
monomer A based upon the total weight of all monomers in the copolymer. 
Inclusion of less than about 30 wt % monomer A tends to produce an 
adhesive which is excessively hydrophilic to the point of losing cohesive 
strength when exposed to more than modest amounts of fluid. Inclusion of 
greater than about 70 wt % monomer A tends to produce an adhesive with 
insufficient absorbency. 
Monomer B 
Monomer B is a hydrophilic alkylene oxide acrylate. The synthesis of 
monomer B employs commercially available starting materials and widely 
known and accepted conventional techniques. For example, monomer B may be 
prepared by reacting an .alpha.,B-unsaturated carboxylic acid, such as 
acrylic acid or methacrylic acid, with an equimolar amount of a 
monoalcohol of a poly(lower alkylene oxide). The esterification reaction 
is generally conducted under anhydrous conditions in an organic solvent, 
such as toluene, which preferably forms an azeotropic mixture with the 
water which is generated by the esterification reaction. Typically, the 
alcohol is combined with the organic solvent and the unsaturated 
carboxylic acid is then added. 
The reaction is conducted in the presence of an acid catalyst, such as 
para-toluenesulfonic acid, and a free-radical inhibitor, such as copper 
powder. The reaction mixture is refluxed for several hours under a 
nitrogen atmosphere and the resultant water removed by azeotropic 
distillation. 
Suitable polyalkylene oxides which may be used to prepare the preferred B 
monomers using the above-described procedure include Carbowax.TM. 350, 
Carbowax.TM. 550, Carbowax.TM. 750, Carbowax.TM. 2000 and Carbowax.TM. 
5000 (i.e., the methoxypoly(ethylene oxide) ethanols of about 350 MW, 550 
MW, 750 MW, 2000 MW and 5000 MW, respectively, which are commercially 
available from Union Carbide Corp. The polyalkylene oxide of choice is 
polyethylene oxide having an average of from 3 to 40 polyethylene (EO) 
units, preferably 5 to 20 EO units, per molecule. 
The copolymer includes about 15 to 40 wt %, preferably about 20 to 30 wt % 
monomer B based upon the total weight of all monomers in the copolymer. 
Inclusion of less than about 15 wt % monomer tends to produce an adhesive 
having reduced absorbency and reduced transparency. Inclusion of greater 
than about 40 wt % monomer B tends to produce an adhesive having reduced 
tack. 
Monomer C 
Monomer C is a hydrophilic N-vinyl lactam which is copolymerizable with 
monomers A, B and PX. The monomer reinforces the adhesive and contributes 
modest absorbency and improved cohesiveness to the adhesive composition. 
Monomer C is an N-vinyl lactam. Preferred N-vinyl lactams are 
N-vinylpyrrolidone and N-vinyl-2-caprolactam. 
The copolymer includes about 15 to 50 wt %, preferably about 20 to 30 wt % 
monomer C based upon the total weight of all monomers in the copolymer. 
Inclusion of less than about 15 wt % monomer C tends to produce an 
adhesive having a reduced cohesiveness observed as an unsatisfactory "skin 
adhesion profile". Inclusion of greater than about 50 wt % monomer C tends 
to produce an adhesive with reduced tack and reduced conformability. 
Crosslinking Monomer PX 
Crosslinking monomer PX is a copolymerizable, monoethylenically unsaturated 
crosslinkable monomer. The ethylenically unsaturated group is 
copolymerizable with the A, B and C monomers to form the backbone of the 
polymer chain. The PX monomer is preferably one which may be crosslinked 
after coating of the adhesive composition upon a support such as by 
exposure to ultraviolet radiation. 
A preferred PX monomer is a monoethylenically unsaturated aromatic ketone. 
Such PX monomers are known to absorb ultraviolet radiation and form a 
triplet excited state through intersystem crossing. The excited-state 
molecules abstract hydrogen radicals from the polymer chain leaving free 
radical sites which combine to form crosslinks. The semi-pinacol radical 
on the aromatic ketone can also produce crosslinking. 
A hydroxyl group positioned ortho to the carbonyl group on the aromatic 
ring is known to inhibit the ability of aromatic ketones to effect 
crosslinking. Accordingly, the aromatic ketone monomer must be free of 
ortho-aromatic hydroxyl groups to be effective as a photosensitive 
crosslinking agent. 
Suitable PX monomers are represented by the general formula: 
##STR1## 
wherein: R: is a lower alkyl or phenyl which may be substituted with one 
or more halogen atoms, alkoxy groups or hydroxyl groups except that when R 
is a hydroxy substituted phenyl the hydroxyl group(s) must be positioned 
meta or para to the aromatic carbonyl; 
X: is halogen, alkoxy or hydroxyl provided that when X is a hydroxyl group 
it is positioned meta or para to the aromatic carbonyl; 
Y: is a divalent linking group which is preferably a covalent bond, an 
oxygen atom(--O--), an amino group (--NR.sup.1 -- wherein R.sup.1 is 
hydrogen or lower alkyl), an oxyalkyleneoxy group (--O--R.sup.2 --O-- 
wherein R.sup.2 is an alkylene group), a carbamoylalkyleneoxy group 
(--O--R.sup.2 --O--(O)--N--(R.sup.1)--R.sup.3 -- wherein R.sup.3 is a 
covalent bond or an alkyleneoxy group such as --R.sup.2 --O--); 
Z: is alkenyl or ethylenically unsaturated acyl group; and 
n: is an integer from 0 to 4. 
Particularly preferred PX monomers are the acryloxybenzophenones such as 
4-acryloxybenzophenone. 
The copolymer includes about 0.01 to 2 wt %, preferably about 0.025 to 
about 0.5 wt % PX monomer based upon the total weight of all monomers in 
the copolymer. A PX content of less than about 0.025 wt % tends to produce 
an adhesive with reduced cohesive strength while a PX content of greater 
than about 2 wt % tends to produce an adhesive with reduced tack. 
It will be understood that other forms of radiation can be used to 
cross-link the pressure sensitive adhesive of the present invention. For 
example, electron beam radiation can be used to cross-link the adhesives 
of the present invention. In such an instance, the PX monomer would become 
an optional component in the pressure sensitive adhesive composition. 
Properties and Characteristics 
Inherent Viscosity 
Inherent viscosity (IV) is recognized as a relative measure of polymer 
molecular weight. In order to achieve the desired creep compliance and 
skin adhesion profile the inherent viscosity of the uncrosslinked 
copolymer of this invention should be between about 0.5 to 1.4 dl/g when 
measured in tetrahydrofuran (THF). More preferably, the inherent viscosity 
is between about 0.5 to 1.1 dl/g, most preferably between about 0.6 to 
0.95 dl/g when measured in THF. 
Creep Compliance 
The fundamentals of creep compliance (J.sub.3) as they relate to polymeric 
materials and, in particular, to viscoelastic polymers is covered in 
"Viscoelastic Properties of Polymers", John D. Ferry, 3rd Edition, John 
Wiley and Sons, 1980, Chapter 1; "Treatise on Adhesion and Adhesives", R. 
L. Patrick--Editor, Volume 2, Marcel Dekker Inc., 1969, Section entitled 
"Materials"/"Pressure Sensitive Adhesives"; Properties and Structure of 
Polymers, Tobolsky, John Wiley and Sons, 1960, Chapter II, Section 6; and 
"Handbook of Pressure Sensitive Adhesive Technology", C. A. Dahlquist, 
Donatas Satas--Editor, Van Norstrand Reinhold Company, 1982, Chapter 5. 
The creep compliance of the adhesive composition of this invention is 
dependent upon several factors including the specific type and relative 
amounts of monomers A, B, C and PX in the copolymer and the degree to 
which the copolymer is polymerized. Generally, an increase in the amount 
of PX monomer will result in an increase in the degree of crosslinking 
within the copolymer and thereby decrease the creep compliance of the 
copolymer. Similarly, an increase in the degree to which the copolymer is 
polymerized will increase the length of the polymer chains and thereby 
decrease the creep compliance of the copolymer. These two factors may be 
adjusted as necessary to produce an adhesive having the desired creep 
compliance. 
Moisture Vapor Transmission Rate 
Adhesives preferred for use as a pressure sensitive adhesive in wound 
dressings are those which permit passage of moisture vapor such as 
perspiration. Accordingly, the preferred materials are those with a twenty 
four hour moisture vapor transmission rate (MVTR T.sub.24) of at least 
about 500 g/m.sup.2, most preferably at least about 1000 g/m.sup.2, when 
measured in accordance with ASTM E 96-80 at 40.degree. C. with a humidity 
differential of 80%. 
Skin Adhesion 
The adhesive of this invention exhibits an initial skin adhesion (T.sub.0) 
of between about 8 to 80 g/cm width, preferably between about 12 to 60 
g/cm width; and a twenty four hour skin adhesion (T.sub.24) of between 
about 8 to 160 g/cm width, preferably between about 12 to 80 g/cm width. 
Adhesives with an adhesion of less than about 8 g/cm width at any time 
during normal periods of use will result in premature peeling from the 
skin while adhesives with an adhesion of greater than about 160 g/cm width 
at the time of removal will produce significant skin irritation upon 
removal. 
In addition, the adhesive exhibits a (T.sub.WET) of at least about 8 g/cm 
width, preferably at least about 12 g/cm width. 
Adhesive Lift 
An adhesive which prematurely peels or delaminates from the skin is 
commercially unacceptable for use as a skin adhesive. Generally, an 
adhesive must exhibit an average adhesive lift rating (Lift) of less than 
about 2.5 to be useful as a skin adhesive. 
The adhesive of this invention can be reproducibly synthesized with an 
acceptable adhesive Lift rating of less than about 2.5, typically below 
about 2, without interfering with the ability of the adhesive to meet the 
other characteristics required for consideration of the adhesive as an 
acceptable skin adhesive. 
Adhesive Residue 
An adhesive which leaves excessive residue behind is commercially 
unacceptable for use as a skin adhesive. Generally, an adhesive must 
exhibit an average adhesive residue rating (Residue) of less than about 
2.5 to be useful as a skin adhesive. 
The adhesive of this invention can be reproducibly synthesized with an 
acceptable Residue rating of less than about 2.5, typically below about 2, 
without interfering with the ability of the adhesive to meet the other 
characteristics required for consideration of the adhesive as an 
acceptable skin adhesive. 
Skin Adhesion Profile 
The "Skin Adhesion Profile" of an adhesive is a combination of the Skin 
Adhesion, Adhesive Lift and Adhesive Residue characteristics of the 
adhesive. A satisfactory "Skin Adhesion Profile" is a combination of Skin 
Adhesion, Adhesive Lift and Adhesive Residue which is subjectively 
acceptable to consumers. For example, an adhesive having superior skin 
adhesion but modest adhesive lift and adhesive residue may possess an 
unsatisfactory Skin Adhesion Profile while an adhesive having fair skin 
adhesion but superior adhesive lift and adhesive residue may possess a 
satisfactory Skin Adhesion Profile. 
Immersion Absorption 
The adhesive of the present invention possesses a twenty-four hour immersed 
absorption capacity (Imrs.sub.24) of at least about 200%, preferably about 
300% to 450%. This level of absorption capacity makes the adhesive well 
adapted for use in wound dressings intended to cover surgical incisions 
and lesions expected to exude moderate amounts of body fluids. For 
example, a ten centimeter square wound dressing having a 1 mil (0.025 cm) 
thick film of the adhesive of this invention rated at (Imrs.sub.24) of 
300% can be expected to absorb and retain about 7.5 ml of fluid in the 
adhesive. 
Demand Absorption 
The adhesive of the present invention possesses a demand absorption 
(Dmnd.sub.15) (measured as the slope of the line through the point of the 
curve at 15 minutes and through the origin) of at least about 1.5 g/hr, 
preferably about 2.0 g/hr. This rate of absorption demand makes the 
adhesive well adapted for use in wound dressings intended to cover 
surgical incisions and lesions expected to exude moderate amounts of body 
fluids within a relatively short time span. 
Polymerization Process 
Monomers A, B, C and PX are free radical polymerized to form the precursor 
composition of this invention which may then be crosslinked to form the 
adhesive. 
Solvent 
The A, B, C and PX monomers may be dissolved in a suitable inert organic 
solvent for polymerization. The solvent must be effective for dissolving 
monomers A, B, C and PX as well as the resultant uncrosslinked copolymer. 
Suitable solvents include specifically, but not exclusively, single 
solvent systems, such as ethyl acetate; and cosolvent systems, such as 
mixtures of ethyl acetate/toluene and ethyl acetate/toluene/isopropyl 
alcohol. Other solvent systems are also believed to be useful. 
The amount of solvent used must be sufficient to achieve intimate contact 
between the polymerization reactants including monomers A, B, C, and PX as 
well as the polymerization initiator and initiated polymer chains. 
Typically, use of about 30-80 wt % solvent, based on the total weight of 
reactants and solvent, is sufficient to achieve substantially complete 
polymerization within a reasonable time period. 
In addition to the solvent-based technique, copolymerization of the 
monomers may be completed by other well known techniques such as 
suspension polymerization, emulsion polymerization, and bulk 
polymerization. 
Polymerization Initiator 
Polymerization of the solvent dissolved monomers is effected by standard 
free radical polymerization utilizing a suitable free radical initiator. 
Numerous free radical initiators are well known in the industry. Exemplary 
of those free radical initiators suitable for use in the present invention 
are those described in U.S. Pat. Re. No. 24,906 issued to Ulrich, the 
disclosure of which is herein incorporated by reference. Suitable 
thermally activated initiators include specifically, but not exclusively, 
azo compounds such as 2,2'-azo-bis(isobutyronitrile), tert-butyl 
hydroperoxide, benzoyl peroxide, and cyclohexanone peroxide. Generally, 
about 0.01 to 1 wt %, preferably about 0.01 to 0.5 wt %, initiator, based 
upon the total weight of all monomers in the copolymer, is effective for 
initiating polymerization. 
Coating onto Substrate 
The adhesive precursor may be coated onto a substrate to form various 
articles intended for adhesion to skin including tapes, patches, strips, 
wound dressings, monitoring or neuro-stimulating electrodes, drapes, etc. 
Without intending to be unduly limited thereby, the remainder of the 
discussion will be presented with respect to the manufacture of a wound 
dressing. 
Wound Dressing Backings 
Substrates suitable for use in the manufacture of a wound dressing intended 
for attachment to the skin include woven, nonwoven and knit fabrics and 
conformable synthetic films such as polypropylene, polyethylene, polyvinyl 
chloride, polyurethane, polyester, and ethyl cellulose. 
Suitable woven and nonwoven fabrics include those formed from threads of 
synthetic or natural materials including cotton, nylon, rayon, polyester, 
and the like. Synthetic films suitable for use are those having a tensile 
modulus of less than about 400,000 psi (2758.8 MPa), preferably less than 
about 300,000 psi (2069.1 MPa), measured in accordance with ASTM D-638. 
The fabric should be sufficiently continuous to prevent the passage of 
pathogens such as bacteria from entering the wound. 
The preferred substrates are those which permit visual inspection of the 
wound without removal of the dressing and permit passage of body fluids 
such as perspiration and wound exudate. Accordingly, preferred materials 
are those which are transparent and possess a twenty four hour moisture 
vapor transmission rate (MVTR T.sub.24) of at least about 500 g/m.sup.2, 
most preferably at least about 1000 g/m.sup.2 when measured in accordance 
with ASTM E 96-80 at 40.degree. C. with a humidity differential of 80%. 
A continuous polyurethane film sold by B. F. Goodrich under the trademark 
"Estane.TM." and a continuous polyester film sold by E. I. Dupont 
DeNemours sold under the trademark "Hytrel.TM." each have an MVTR T.sub.24 
value of about 1000 to 1500 g/m.sup.2. Woven substrates, such as that sold 
by Minnesota Mining and Manufacturing Company and used in "Durapore.TM." 
surgical tape possess even higher MVTR T.sub.24 values. 
Coating Techniques 
The copolymer precursor can be coated onto the substrate by any of a 
variety of conventional techniques such as roll coating, spray coating, 
extrusion coating, coextrusion, hot-melt coating and the like. The process 
of choice depends upon the nature of the substrate employed. For example, 
a preferred method for coating the adhesive upon a nonwoven fabric is to 
dissolve the adhesive copolymer in an organic solvent, spread the 
copolymer solvent onto a release liner, and then laminate the adhesive 
coating onto the nonwoven fabric before the adhesive is completely dry. 
As mentioned previously, use of the preferred photosensitive crosslinking 
agent in the copolymer of this invention allows the use of solventless 
coating techniques because the copolymer need not be crosslinked until 
after it is coated upon a support member. For example, the adhesive may be 
coated without the aid of a solvent by (i) stripping solvent remaining 
from polymerization by any of the well known conventional techniques, (ii) 
coating the dried, uncrosslinked polymer onto a suitable substrate by any 
of the well known conventional "hot melt" techniques such as an extrusion 
or rotogravure process, and then (iii) crosslinking the coated polymer to 
form an absorbent pressure sensitive adhesive film. 
Crosslinking 
The coated adhesive precursor is then crosslinked by contacting or exposing 
the precursor to the appropriate crosslinking initiator such as 
ultraviolet radiation at an intensity and for a duration sufficient to 
crosslink the copolymer by means of the PX monomer. 
The extent to which the copolymer is crosslinked depends upon both the 
amount of PX monomer in the copolymer and the intensity of the treatment. 
For purposes of quality control, the degree to which the copolymer is 
crosslinked is preferably controlled by treating the copolymer so as to 
effect substantially complete crosslinking of the PX monomer and adjusting 
the amount of PX monomer as necessary. 
When a photosensitive PX monomer is employed, ultraviolet radiation 
treatment is conveniently effected using medium-pressure mercury lamps 
providing an output of about 80 watts per cm (200 watts per inch) and 
having a spectral output over a range of about 180 to 430 nanometers. 
Sterilization 
When the adhesive is intended for use in a wound dressing, the adhesive 
must be sterilized. A widely accepted method of sterilizing wound 
dressings is to subject the dressing to about 2.5 to 5 megarads of gamma 
radiation. 
Testing Protocols 
Inherent Viscosity (IV) (Degree of Polymerization) 
The inherent viscosity of a polymer is measured in accordance with the 
protocol described by Fred W. Billmeyer, Jr. at pages 84-85 of the 
textbook entitled Textbook of Polymer Science, Second Edition, published 
by Wiley-Interscience, (1971). Briefly, solution viscosity is measured by 
comparing the efflux time (t) required for a specified volume of polymer 
solution to flow through a capillary tube with the corresponding efflux 
time (t.sub.0) for the solvent. The measured variables t, t.sub.0, and 
solute concentration (c) are then used to calculate inherent viscosity 
(also known as Logarithmic Viscosity) using the equation: 
EQU .eta.=(ln t/t.sub.0)/c 
Creep Compliance 
The adhesive to be tested is knife-coated onto a smooth film of 
polytetrafluoroethylene to a thickness of 150 micrometers. The adhesive 
coating is dried to constant weight in an air-circulating oven (at least 
five minutes at 110.degree. C.). The dried adhesive is stripped from the 
polytetrafluoroethylene support to form a dried adhesive film. 
Two identical test specimens are die-cut from the dried adhesive film and 
positioned on a Parallel Plate Creep Compliance Rheometer. One of the 
specimens is laminated to each side of a rigid metal center plate and then 
sandwiched between rigid metal outer plates to form a 
plate/adhesive/plate/adhesive/plate laminate. Screws connecting the outer 
plates are tightened to compress the interposed test specimens 
approximately 10%. 
The specimen-containing plates are positioned horizontally within the 
rheometer with one end of the center plate electronically connected to a 
chart recorder and the other end attached to a flexible wire. The flexible 
wire is extended horizontally from the center plate, directed downward 
around a pulley, and connected to a 500 gram weight. The outer plates are 
held in a fixed position. 
The size of the weight is selected to measurably deform the test specimen a 
distance no greater than its thickness. 
A strip chart recorder is started and the variables of time (t), 
displacement (Strain) and applied force (Stress) are recorded. The creep 
compliance of the tested adhesive is then calculable in cm.sup.2 /dyne 
using the equation: 
EQU J.sub.(t) =(2AX)/(hf) 
where: 
(t) is the time at which the measurement is taken (hrs), 
(A) is the area of one major surface of the adhesive sample (cm.sup.2), 
(h) is the thickness of the adhesive sample after compression (cm), 
(X) is the displacement at time t (where X is less than h) (cm), and 
(f) is the force exerted on the center plate by the weight attached to the 
end of the flexible wire (dynes). 
Moisture Vapor Transmission Rate (Upright) 
The Moisture Vapor Transmission Rate (MVTR.sub.Up) is measured in 
accordance with ASTM E 96-80 as modified below. 
Thirty five millimeter diameter samples of a 0.025 cm thick film of the 
adhesive is laminated to a 0.0275 cm thick polyurethane web having a 
MVTR.sub.up T.sub.24 of 2,000 to 2,400 g/m.sup.2 measured at 40.degree. C. 
and a relative humidity differential of 80%. 
The laminated samples are sandwiched between the adhesive surfaces of two 
axially aligned foil adhesive rings having 2.54 cm diameter holes. Each 
sample is pulled to ensure a flat, wrinkle-free and void-free 
foil/sample/foil laminate. 
A four-ounce (0.14 kg) glass jar is filled half-full with distilled water. 
The jar is fitted with a screw-on cap having a 3.8 cm diameter hole 
concentrically aligned with a rubber washer having a 4.445 cm 
outside-diameter and a 2.84 cm inside-diameter. 
The foil/sample/foil laminate is concentrically positioned on the rubber 
washer and the sample-containing sub-assembly screwed loosely onto the 
jar. 
The assembly is placed into a chamber maintained at a temperature of 
40.degree. C. and 20% relative humidity. The assembly is removed from the 
chamber after four hours, weighed to the nearest 0.01 gram (W.sub.1), and 
immediately returned to the chamber. The cap is now screwed tightly onto 
the jar without bulging of the sample. The assembly is again removed from 
the chamber after an additional eighteen hours and weighed to the nearest 
0.01 gram (W.sub.2). 
The MVTR.sub.up T.sub.24 of the adhesive (measured in grams of water 
transmitted per square meter of sample area over a twenty four hour 
period) may then be calculated according the formula set forth below: 
EQU MVTR.sub.up T.sub.24 =(W.sub.1 -W.sub.2)(4.74.multidot.10.sup.4)/t 
where: 
(W.sub.1) is the initial weight of the assembly (grams) 
(W.sub.2) is the final weight of the assembly (grams), and 
(t) is the time period between W.sub.1 and W.sub.2 (hrs). 
Three samples of each adhesive were run and the average of the three 
samples reported. 
Moisture Vapor Transmission Rate (Inverted) 
The protocol for measuring MVTR.sub.invt is the same as the "Upright" 
protocol except that the assembly is inverted inside the chamber once the 
cap is tightly screwed onto the jar so that the water within the jar 
directly contacts the foil/sample/foil laminate while the assembly is 
within the chamber. 
Skin Adhesion 
Evaluation of the adhesiveness of a composition to human skin is an 
inherently temperamental determination. Human skin possesses wide 
variations in composition, topography, and the presence/absence of various 
body fluids. However, controlled and comparative values of adhesion are 
attainable by employing a select panel of individuals trained to recognize 
the normal skin variations encountered in medical practice. 
Initial skin adhesion (T.sub.0), skin adhesion after 24 hours of continuous 
contact with the skin (T.sub.24), and skin adhesion to wet skin 
(T.sub.WET) is measured in accordance with the widely accepted PSTC-1 Peel 
Adhesion Test for single coated adhesive tape conducted at a removal angle 
of 180.degree.. The PSTC-1 Peel Adhesion Test is a testing protocol 
established by the Specifications and Technical Committee of the Pressure 
Sensitive Tape Council located at 5700 Old Orchard Road, Skokie, Ill. The 
test is modified for our purposes by applying the tape to the skin of a 
living human. 
The adhesive is tested as a 0.025 cm film coated onto a 0.0275 cm thick 
polyurethane web having a MVTR.sub.up T.sub.24 of 2,000 to 2,400 g/m.sup.2 
measured at 40.degree. C. and a relative humidity differential of 80%. 
Three samples measuring 2.5 cm wide by 7.6 cm long are applied to the back 
of each of six human subjects (three men and three women). The subjects 
are placed in a prone positioned with arms at their sides and heads turned 
to one side. Samples are applied to both sides of the spinal column with 
the length of each sample positioned at a right angle to the spinal 
column. The samples are applied without tension or pulling of the skin. 
Those samples tested for wet skin adhesion are applied to skin which had 
been moistened with a water saturated cloth, leaving visually observable 
drops of standing water, immediately before application of the sample. 
The samples are pressed into place with a 2 kg roller moved at a rate of 
approximately 2.5 cm/sec with a single forward and reverse pass. No manual 
pressure should be applied to the roller during application. 
The samples are then removed either immediately after application (T.sub.0) 
or after 24 hours of continuous contact with the skin (T.sub.24), at a 
removal angle of 180.degree. and removal rate of 15 cm per minute, using a 
conventional adhesion tester equipped with 25 lb (11.4 kg) test line 
attached to a 2.5 cm clip. The clip is attached to the edge of the sample 
furthest from the spinal column by manually lifting about 1 cm of the 
sample from the skin and attaching the clip to the raised edge. The 
adhesion tester is a strain-gauge mounted on a motor-driven carriage. 
The measured force required to effect removal is reported in grams per cm. 
Adhesive Lift 
Evaluation of the adhesive tenacity of a composition to human skin is an 
inherently temperamental determination for the same reasons established 
above in connection with evaluation of the adhesiveness of a composition 
to human skin. 
However, the observational values as to adhesive tenacity (Lift) are 
generally reproducible and in accord with subjective assessments of 
similar properties which are widely accepted in the art as meaningful, 
reliable and reproducible. 
The Adhesive Lift Test is a subjective assessment of the extent to which 
adhesive tape prematurely separates from the body after application of a 
sample in accordance with the Skin Adhesion Test. The applied samples are 
visually inspected just prior to testing for Skin Adhesion (i.e. twenty 
four hours after application) to determine the extent to which the edges 
of the sample have separated from the skin. Each sample is assigned a 
numerical rating from 0 to 5 based on the following observation: 
______________________________________ 
Rating Definition 
______________________________________ 
0 No visible separation. 
1 Separation at edges of tape only. 
2 Separation of 1% to 25% of tape area. 
3 Separation of 26% to 50% of tape area. 
4 Separation of 51% to 75% of tape area. 
5 Separation of 76% to 100% of tape area. 
______________________________________ 
Each sample is assigned a single whole number from the list established 
above by each panel member. The assigned values from the panel members are 
then averaged and reported to the tenths position. Due to the subjective 
nature of the test, differences of less than 0.5 in averaged residue 
values should be considered substantially the same. 
Adhesive Residue 
As with the rating of Adhesive Lift, an assessment of the Adhesive Residue 
Rating (Residue) of a composition to human skin is an inherently 
temperamental but reproducible determination. 
The Adhesive Residue Test is a subjective assessment of the amount of 
adhesive left upon the skin after removal of an adhesive sample in 
accordance with the Skin Adhesion Test. The skin directly underlying each 
sample was visually inspected to determine the extent to which the area 
contacted by the adhesive contains residual adhesive. Each sample was then 
assigned a numerical rating from 0 to 5 based on the following 
observation: 
______________________________________ 
Rating Definition 
______________________________________ 
0 No visible residue. 
1 Residue at edges of tape only. 
2 Residue covering 1% to 25% of tested area. 
3 Residue covering 26% to 50% of tested area. 
4 Residue covering 51% to 75% of tested area. 
5 Residue covering 76% to 100% of tested area. 
______________________________________ 
Each sample was assigned a single whole number from the list established 
above by each panel member. The assigned values from the panel members 
were then averaged and reported to the tenth position. Due to the 
subjective nature of the test, differences of less than 0.5 in averaged 
residue values should be considered substantially the same. 
Preferred skin adhesives will generally exhibit an average residue rating 
below about 2.5. 
Absorption (Immersion) 
The Water absorptive capacity of an adhesive is measured by immersing the 
adhesive into buffered water and measuring the weight of water absorbed. 
Round test samples having a 5 cm.sup.2 surface area are preweighed 
(W.sub.i) and placed into a 180 ml bottle containing 30 ml of phosphate 
buffered saline solution having a pH of 7.2 purchased from Sigma Chemical 
Company. The bottles are capped and allowed to stand without agitation. 
The samples are removed 24 hours after initial immersion in the bottle and 
weighed (W.sub.f). The Absorbency Value is calculable using the following 
formula: 
EQU Imrs.sub.24 =[(W.sub.f -W.sub.i)/W.sub.i ].times.100 
Absorption (Demand) 
The initial rate at which an adhesive is able to absorb water is measured 
by contacting a sample of the adhesive with buffered water, periodically 
measuring the weight of water absorbed, plotting the weight of water 
absorbed verses time, and measuring the slope of a line through the origin 
of the plot and the data point at 15 minutes. 
Equipment 
Feeding Plate 
A water feeding plate is constructed from (i) a 5/8 inch thick six inch 
diameter plexiglass base plate, (ii) a 1/2 inch thick six inch diameter 
plexiglass top plate, (iii) a sixty mm diameter Corning 60C.TM. fritted 
glass disc, (iv) two, two-way valves, and (v) one 31/2 inch and one 4 inch 
diameter O-ring. 
The base plate is machined to provide (a) a 1/2 inch deep, three inch 
diameter, central cylindrical reservoir, (ii) a pair of radially opposed 
passages extending completely through the sides of the plate into 
communication with the reservoir, and (c) concentric 31/2 inch diameter 
and 4 inch diameter grooves. The two-way valves are sealing fitted into 
the bores and the O-rings positioned within the grooves. 
The top plate is machined to provide a sixty mm central hole into which the 
glass frit is sealed with silicone adhesive. The top surface of the glass 
frit is positioned flush with the top surface of the plate. 
The top plate is secured over the base plate using four machine screws 
spaced along the periphery of the plates which pass through orifices 
drilled in the top plate and extend into axially aligned bores within the 
bottom plate. 
Supply Tank 
A 19 cm diameter supply tank of phosphate buffered saline solution is 
connected with rubber tubing to a first of the valves attached to the 
Feeding Plate. The tank is covered to prevent evaporation of the saline 
solution but is NOT sealed. The tank is placed upon a standard Lab Jack so 
that the vertical position of the tank may be raised and lowered as 
necessary to generate zero head pressure at the surface of the glass frit 
in the feeding plate. 
Balance 
The feeding plate is placed upon the pan of a standard electronic balance 
to permit changes in the weight of the feeding plate to be measured and 
recorded. 
Procedure 
The reservoir is filled with saline solution from the supply tank and 
bubbles removed by opening the second of the two-way valves connected to 
the feeding plate. The tank is then vertically positioned to provide zero 
head pressure within the reservoir. 
A six centimeter diameter disc of Whatmann No. 1 filter paper is positioned 
on the glass frit to prevent the adhesive from bonding to the frit. 
An oversized sample of the adhesive to be tested (one which more than 
covers the glass frit) is centered over the glass frit. The balance is 
tared to zero and the cumulative weight of saline solution absorbed by the 
adhesive sample weighed over time. 
The height of the supply tank is NOT readjusted during the experiment 
unless more than 20 grams of saline solution is removed from the tank due 
to absorption or evaporation. Should more than twenty grams of saline be 
removed from the tank the vertical height of the tank is repositioned once 
immediately after the twenty grams have been removed to compensate for the 
decrease in head pressure generated by the saline solution within the 
tank. 
The increased weight is plotted against time and a "Demand Absorption 
Value" (Dmnd.sub.15) determined by measuring the slope of a line through 
the origin of the plot and the curve at fifteen minutes.