Films and extrusions of cured crosslinked vinyl lactam polymer and method of preparation

This invention relates to a continuous film, coating, membrane or extruded filament of a crosslinked vinyl lactam polymer having excellent substrate adhesion, a glass transition temperature (Tg) above 150.degree. C. and water repellent properties. The invention also relates to the method of preparing and using filaments, coatings and membranes of said crosslinked polymeric product.

BACKGROUND OF THE INVENTION 
Crosslinked vinylpyrrolidone polymeric powder has been prepared by 
proliferous polymerization at high temperatures with vigorous agitation as 
described for example in copending patent application Ser. No. 057,378, 
filed May 6, 1993 for COLORLESS, PURIFIED, POLYMERIZABLE COMPOSITION 
USEFUL FOR THE PRODUCTION OF CROSSLINKED POLYVINYLPYRROLIDONE. U.S. Pat. 
Nos. 5,082,910; 5,130,388 and 5,015,708 also describe processes for 
crosslinking vinyl lactam polymers. However, the powder products obtained 
by these processes are not amenable to extrusion or to the formation of 
membranes or continuous, thin film protective coatings. 
Accordingly, it is an object of this invention to provide a curable 
crosslinked vinyl lactam polymer in the form of a filament or film which 
is coated on a substrate or extruded to form a product having a high Tg 
and water repellency. 
Another object of the invention is to provide microthin protective coatings 
which have superior adhesion to a substrate. 
Still another object is to provide an economical and commercially feasible 
process for preparing the film or filament products of a crosslinked vinyl 
lactam polymer hydrogel. 
Yet another object is to provide a strong, adhesive membrane which is 
non-irritating to the skin and which can be used to cover wounds and the 
like. 
These and other objects of this invention will become apparent from the 
following description and disclosure. 
THE INVENTION 
The crosslinked polymeric products of this invention are prepared by 
(1) forming a uniform liquid mixture of 
(a) between about 2 and about 30 wt. % of a polymerizable reactant 
containing at least 55% N-vinyl lactam monomer; 
(b) between about 0.01 and about 10.0 wt. % crosslinking agent and 
(c) between about 60 and about 90 wt. % water; 
(2) reacting in an inert atmosphere the mixture in the presence of a 
polymerization initiator with agitation by heating the mixture to between 
about 50.degree. and about 80.degree. C. for a period of from about 2 to 
about 5 hours and until a constant viscosity of from about 60 to about 
100K value is obtained; 
(3) applying a coating of the resulting soluble polymer solution as a film 
to a substrate or extruding the soluble polymer in the form of a filament; 
(4) subjecting said film or filament to curing in a closed system in an 
inert atmosphere at a temperature of from about 100.degree. to about 
140.degree. C. for a period of from about 0.5 to 3 hours to produce a 
transparent, water insoluble crosslinked product and then 
(5) digesting the film or filament in water to swell the polymer, extract 
soluble monomer, linear polymer and residuals and to form a hydrogel. 
The hydrogel product of this invention is derived from the 
homopolymerization or copolymerization of N-vinyl pyrrolidone and/or 
N-vinyl caprolactam which is between about 0.01 and about 10% crosslinked, 
preferably between about 0.2 and about 5% crosslinked, with a suitable 
polyfunctional crosslinking agent. 
As indicated, the N-vinyl lactam monomer may be combined with a 
polymerizable comonomer, preferably in an amount not more than 30% 
comonomer. Suitable comonomers are those which are soluble in the reaction 
solvent and include olefinically unsaturated compounds such as another 
N-vinyl amides having the structure CH.sub.2 .dbd.CH--NR.sub.1 
CO--R.sub.2, where R.sub.1 and R.sub.2 are individually hydrogen or lower 
alkyl, e.g. vinyl formamide, vinyl acetate, etc., N,N-dimethylamino 
C.sub.1 to C.sub.4 alkyl acrylate or methacrylate, vinyl acetate, acrylic 
acid, methacrylic acid, styrene, acrylamide, methacrylamide, lower alkyl 
acrylates or methacrylates, hydroxyalkyl acrylates or methacrylates, 
isobutylene, acrylonitrile, vinyl chloride, hydroxyalkyl acrylates or 
methacrylates, ethyl vinyl ether, vinyl ether, quaternized dimethylamino 
lower alkyl acrylates or methacrylates and the like. 
Representative of the crosslinking agents which can be employed are 
diallylimidazolidone; the divinyl ether of diethylene glycol; 
pentaerythritol triallyl ether (PETE); 
triallyl-1,3,5-triazine-2,4,6-(1H,3H,5H)trione (TATT); ethylene glycol 
diacrylate; 2,4,6-triallyloxy-1,3,5-triazine; N-vinyl-3(E)-ethylidene 
pyrrolidone (EVP); 1,7-octadiene; 1,9-decadiene; divinyl benzene; 
methylene bis(methacrylamide); methylene bis(acrylamide); 
N,N-divinyl-imidazolidone; ethylene glycol diacrylate; ethylene 
bis(N-vinylpyrrolidone) (EBVP); etc. 
FNT *as described in copending U.S. patent application Ser. No. 08/025,523; 
filed Mar. 3, 1993, now U.S. Pat. No. 5,274,120; entitled 
1-VINYL-3(E)-ETHYLIDENE PYRROLIDONE, in which EVP is defined by the 
formula: 
##STR1## 
Preferred products of this invention are those derived from N-vinyl 
pyrrolidone homopolymer, N-vinyl pyrrolidone/N-vinyl caprolactam copolymer 
or N-vinyl pyrrolidone/acrylic acid copolymer which are crosslinked with 
EVP, EBVP or N,N-divinylimidazolidone. Most preferred is the EVP 
crosslinked N-vinyl pyrrolidone homopolymer. 
Any of the conventional free radical initiators can be employed in the 
present process. Preferably, the initiator is an organic peroxide such as 
t-butyl peroxy pivalate, t-amylperoxy pivalate, a diacyl peroxide or 
mixtures thereof. 
Water, preferably pure, deionized water is employed as the solvent in the 
system and although the solvent can vary over a wide range; between about 
65% and 75% of the reaction mixture is usually sufficient to dissolve all 
reactive components. If desired, a small amount, e.g. between about 0.001 
and about 1.0 wt. %, of an antiseptic, drug or coloring agent can be added 
to the monomeric component, the solvent or to the water wash in step 5 of 
the process. 
Digestion of the cured polymer in between about 1 and about 500 volumes of 
water takes place at ambient temperature for a period of from about 2 
hours to about 2 days, preferably between about 50 and about 150 volumes 
of water for a period of from about 10 to about 24 hours. This step can be 
carried out with incremental or continuous addition and replacement of 
water. 
The mechanical strength of the hydrogel can be varied within an acceptable 
range by regulating the concentrations of reactive monomer(s) and/or 
crosslinking agent in the initial uniform mixture before casting. Hence, 
the mechanical strength varies directly with the amount of monomer and/or 
crosslinker in the system. 
The non-crosslinked soluble polymer obtained in step (2) contains between 
about 20 and about 98 wt. % water and between about 0 and about 20 wt. % 
innocuous additive or a material which is chemically inactive in the 
polymerization, e.g. antiseptic, drug, colorant, and the like, which 
additives can be added to the feed mixture. 
Upon curing to crosslink the coated or extruded polymer at from about 
100.degree. to about 140.degree. C., a transparent product is obtained 
which is water-insoluble and water swellable. This product is suitably 
employed as a protective coating over wires for rust resistance, over wood 
or metal decks or painted surfaces, as a moisture or fog repellent coating 
over glass, as a water repellent coating on a fabric, etc. since it 
displays superior adhesion to glass, metal, ceramic, plastic, fabric and 
wood surfaces. 
Having generally described the invention, reference is now had to the 
following examples which illustrate preferred embodiments concerning the 
preparation and use of the present formed products, which examples are not 
to be construed as limiting to the scope of the invention as more broadly 
defined above and in the appended claims.

EXAMPLE 1 
A. An aqueous solution of 40 g. of N-vinylpyrrolidone, 0.16 g. of 
1-vinyl-3(E)-ethylene pyrrolidone crosslinking agent, 0.52 g. of 
t-butylperoxy pivalate initiator and 460 g. of water were charged to a 
nitrogen purged Buchi glass reactor equipped with an oxygen analyzer for 
maintaining an oxygen level below 20 ppm. The reactor was sealed under a 
0.14 bar nitrogen pressure and the contents heated to 75.degree. C. with 
agitation at about 150 rpm. Reaction was indicated by an increase in 
viscosity and the viscosity (torque) changes were recorded. After about 1 
hour, the resulting soluble polymer solution containing about 1.8% vinyl 
pyrrolidone monomer and no remaining crosslinking agent was discharged. 
B. The soluble polymer solution obtained above was then coated in a 
thickness of about 25 microns on an aluminum panel and the coated panel 
placed in an oxygen evacuated vacuum oven wherein, under a vacuum of -25 
mm Hg at 115.degree. C. the coating is cured over a period of 1.5 hours. 
Upon cooling the cured, coated panel was soaked in a constant steam of 
distilled water for 16 hours so as to swell the polymer, extract and 
remove unreacted monomer, non-crosslinked polymer and other residuals in 
the water phase and to form a firm hydrogel coating. The panel was then 
dried in air. The resulting panel was covered with a stable, highly 
adhesive, corrosion resistant water insoluble coating. 
Repetition of the above example, except for the substitution of a glass 
plate for the aluminum panel, provided a product having the same strong 
substrate adhesion and water repellency. Also, it was noted that the 
coated glass resisted fogging when exposed to 80% humidity for a period of 
2 hours. 
EXAMPLE 2 
Part A of Example 1 was repeated except that only 25 grams of N-vinyl 
pyrrolidone was used. The soluble polymer product in solution was extruded 
from a syringe into a hot, nitrogen purged oven on a stainless steel 
surface. In the oven, the extruded filaments were heated at 120.degree. C. 
for about 2 hours, then cooled and soaked in a bath of distilled water for 
16 hours to swell the polymer and to extract monomer, non-crosslinked 
polymer and other residuals. The resulting water insoluble filaments were 
then dried in air. The hydrogel filaments of this example can be woven and 
then dried to produce a synthetic water resistant fabric. 
EXAMPLE 3 
Part A of Example 1 was repeated and the soluble polymer product in 
solution was coated in a thickness of about 30 microns on a gauze fabric. 
The coated fabric was then cured in the vacuum oven and subjected to 
treatment as described in Example 1 part B. 
The air dried coated gauze is suitable as a bandage and can be further 
enhanced by incorporating between about 1 and about 10% of an antiseptic 
in the initial feed reaction mixture. 
It is to be understood that many modifications and variations in the above 
examples within the scope of this invention will become apparent from the 
preceding disclosure.