polyvinylbutyral resins are commercially available materials , which usually range in molecular weight from 35 , 000 to 150 , 000 . they generally contain some level of hydroxyl functionality and for the purposes of the present invention this is not critical . changes in hydrophilic character of the blend resulting from variations in hydroxyl content of the pvb can be countered by adjustments in the amount of poly ( n - vinyl lactam ). polyvinylbutyral resins are further described in the encyclopedia of polymer science and technology , mark , et al ., ( eds . ), wiley , 1969 , which is incorporated herein by reference . although the useful polymers are essentially linear in order to provide solubility , they can be crosslinked following blending with the poly ( n - vinyl lactam ) component , e . g ., by adding a sufficient quantity of crosslinking agent to a solvent solution of the polymers . examples of crosslinking agents which can be utilized for this purpose are isocyanates , polycarboxylic acids , peroxide and organotitanates . the term &# 34 ; poly ( n - vinyl lactam )&# 34 ; as used herein shall be understood to include homopolymers and copolymers of such n - vinyl lactams as n - vinylpyrrolidone , n - vinylbutyrolactam , n - vinylcaprolactam , and the like , as well as the foregoing prepared with minor amounts , for example , up to about 20 weight percent , of one or a mixture of other vinyl monomers copolymerizable with the n - vinyl lactams . of the poly ( n - vinyl lactams ), the polyvinylpyrrolidone ( pvp ) homopolymers are preferred . a variety of polyvinylpyrrolidones are commercially available from several sources and of these , a polyvinylpyrrolidones having k - values of about 30 to 90 are especially preferred . the polyvinylbutyral and poly ( n - vinyl lactam ) components of the blend can be combined by dissolving them in solvent which is subsequently evaporated to yield the blend . if the latter procedure is selected , the choice of solvent is important . thus , the solvent must be capable of dissolving both polymer components in a single - phase solution and the relative volatilities must be such that at no point during evaporation and drying , the resulting mixture will tend to precipitate either pvb , poly ( n - vinyl lactam ) or an association complex of these polymers which may have different solubility characteristics than either material by itself . solvents which are suitable include isopropanol , methyl ethyl ketone , diacetone alcohol , ethyl lactate , methylene chloride , trichloroethylene , n - methyl pyrrolidone and mono and di - ethylene glycol ethers . other solvents can be added to accelerate drying , reduce solvency toward particular substrates , etc ., provided the aforestated conditions are met . an improper combination of solvents will result in coatings which are not homogeneous in composition , and which will soften and swell so much as to be useless . for example , even though both polymers are soluble in isopropanol , this solvent yields weak , watery coatings when used alone . the same composition with added diacetone alcohol affords coatings with a high degree of lubricity plus surprising abrasion resistance . the blends can contain from about 10 to about 80 percent , and preferably from 25 to about 60 weight percent , of pvb , the balance being made up of the poly ( n - vinyl lactam ) component . minor quantities , for example , up to about 20 weight percent , of one of a mixture of other compatible polymers can be incorporated into the blends , e . g ., any of the polymers disclosed in general aniline & amp ; film corporation technical bulletin 7583 - 033 . the blends can be formed into a variety of shapes and , if desired , can be fabricated into foams employing known and conventional techniques including the use of chemical and / or physical blowing agents . the solid blends can also be extruded as fibers , rods , sheets , and so forth . many different types of additional materials can be incorporated into the polymer blends herein including organic and inorganic salts , alcohols , amines , acids , polymer latices , resin or wax dispersions , fillers , fibers , cellulosics , surfactants , pigments , dyes , fragrances , and so forth . the blends of this invention are especially useful as carriers for a wide variety of releasable materials including biologically active substances having curative or therapeutic value for human beings or non - human animals . included among the biologically active materials which are suitable for incorporation into the blends of the present invention are : hypnotics , sedatives , tranquilizers , anti - convulsants , muscle relaxants , antiparkinson agents , analgesics , antipyretic agents , antiinflamatory agents , local anesthetics , antispasmodics , antiulcer agents , antivirals , antibacterials , antifungals , antimalarials , sympathomimetic agents , cardiovascular agents , diuretics , antiparasitic agents , antitumor agents and hypoglycemic agents , and so forth . in the form of a sheet or film or as a coating , the blends can be combined with and adhered to a virtually unlimited variety of substrates including metal and resin foils , woven and non - woven webs of natural and synthetic fibers , etc . the following examples are further illustrative of the blends of this invention . to a mixture of 20 g isopropanol , 40 g methyl ethyl ketone and 20 g diacetone alcohol was added 0 . 8 g polyvinylbutyral ( xyhl resin , union carbide corp .) and 2 . 4 g polyvinylpyrrolidone ( povidone 90 , gaf corp .). the resulting clear solution was applied to a length of pvc tubing and dried in an oven at 60 ° c . for 15 min . the dried coating was hard , clear and colorless , and absorbed water becoming highly lubricious ( coefficient of friction = 0 . 039 ). the lubricity was unchanged after soaking in water for 72 hrs . ( coefficient of friction = 0 . 039 ). rubbing briskly with a paper towel did not remove the coating or alter its slippery nature . similar results are obtained when the coating solution is applied to a polyurethane catheter and an acrylic coated steel plate . to the solvent mixture of example 1 was added 1 . 5 g polyvinylbutyral resin and 1 . 5 g polyvinylpyrrolidone . coatings deposited from this solution were also hard , clear and colorless when dry . exposure to water resulted in noticeable lubricity , though significantly less than in example 1 ( coefficient of friction = 0 . 09 ). this coating is useful as an anti - fog or anticondensation coating on lenses , mirrors and films where it must resist smudging from handling abuse . it would also be suitable for numerous applications which require repeated use , or exposure to abrasive elements . the coating &# 39 ; s hydrophilic behavior was unchanged after soaking in water for 3 days . to the composition of example 2 was added a polyethylene glycol distearate surfactant , 0 . 3 g ( 10 % based on non - volatile weight ). coatings prepared from such a mixture have improved wetting properties which are not lost by extended exposure to condensation ; as in a greenhouse . to 80 g of isopropanol were added 0 . 8 g polyvinylbutyral resin and 2 . 4 polyvinylpyrrolidone . coatings deposited from this clear solution on a pvc tube were hard , clear and colorless when dry . however , after soaking in water for 1 hr ., the coating was extremely soft and watery and was easily abraded from the surface . on drying , the coating had a whitish appearance suggesting microvoids from leaching of a soluble component . to a mixture of 50 g methyl ethyl ketone , 25 g isopropanol and 25 g diacetone alcohol was added 1 g polyvinyl butyral and 3 g of polyvinylpyrrolidone / 2 acrylamidopropylmethylsulfonate copolymer ( 98 / 2 ). coatings formed on a pvc substrate were clear and colorless . when wetted with water , the coatings became highly lubricious ( coefficient of friction 0 . 022 ), with no evidence of soluble material or change in character . the lubricity was unchanged after soaking 3 days in water . to a mixture of 50 g methyl ethyl ketone , 25 g isopropanol and 25 g diacetone alcohol was added 1 g polyvinyl butyral and 3 g of polyvinylpyrrolidone / 2 ethylhexylacrylate copolymer ( 95 / 5 ). coatings formed on a pvc substrate were clear and colorless . when wetted with water , the coatings became highly lubricious ( coefficient of friction 0 . 059 ), with no evidence of soluble material or change in character . the lubricity was unchanged after soaking 3 days in water . to the solution in example 1 was added 8 g of a 10 % solution of estane 5703 polyurethane resin in diacetone alcohol solvent . a clear solution resulted which yielded clear coatings on pvc and polyurethane films . when wetted with water , the coatings were determined to have slightly less lubricity versus those of example 1 ( coefficient of friction =. 072 ), but considerably more abrasion resistance . after 3 days &# 39 ; soaking in water , the coefficient of friction had decreased to 0 . 05 , representing an increase in hydrophilic character . the solution in example 1 was modified by adding 4 g 20 % polyvinyl chloride ( union carbide vmch ) in methyl ethyl ketone solvent . coatings deposited from this composition on polycarbonate were clear and colorless when dry , but slightly hazy when wet . lubricity was much reduced and abrasion resistance greatly improved versus the properties observed in example 1 . however , the coatings were still sufficiently hydrophilic to function well as anti - fog treatments when exposed to warm , moist air . coefficients of friction were 0 . 15 initially , and 0 . 18 after soaking in water for three days . thus , while there have been described what are presently believed to be the preferred embodiments of the present invention , those skilled in the art will realize that other changes and modifications can be made without departing from the spirit of the invention , and it is intended to include all such changes and modifications as come within the true scope of the invention .