SOLID POLYMERS HAVING THE SURFACE PORTION MODIFIED BY REACTION WITH THIOCYANO OR ISOTHIOCYANO GENERATING REACTANTS AND A PROCESS FOR PREPARING SUCH MODIFIED POLYMERS

Abstract: Solid polymers in which the surface portion has been modified by reacting with thiocyano or isothiocyano free radical or ion generating reactants. This invention is also directed to a process for preparing such modified polymers. The polymers of the invention provide improved adhesive strength to laminates prepared therefrom, improved paint adhesion, increased viscosity and alterated gas permeability compared to unmodified polymers.

Description: SOLID POLYMERS HAVING THE SURFACE PORTION MODIFIED BY REACTION WITH THIOCYANO OR ISOTHIOCYANO GENERATING REACTANTS AND A PROCESS FOR PREPARING SUCH MODIFIED POLYMERS The present invention relates to polymeric modification. More particularly, the present invention relates to the modification of polymers by reaction with thiocyano- or isothiocyano-generating reactants. In US 3,607,536 to R. A. Bragole, an organic isocyanate and a photosensitizer are provided at the surface of a body of low surface tension of wetting ' polymer resin material and the surface is subjected to controlled ultraviolet radiation treatment to pro- duce a chemical linkage between the resin material and the organic isocyanate to form an urethane stratum integral with the resin body and capable of being bonded by adhesives. In US 2,781,331 solutions of diene polymers are thiocyanated by reaction with thiocyanogen. By reducing the level of unsaturation through hydrogenation the amount of thiocyanate moieties added to the polymer may be controlled. Similar techniques for thiocyanating solutions of ethylenically unsaturated polymers are disclosed in U.S. 2,287,774 and US 3,867,360. The present invention is directed to a solid polymer having a surface portion and an interior por- tion wherein the surface portion comprises the reaction product of thiocyano or isothiocyano free radical or ion generating reactant and the precursor polymer and the interior portion is substantially devoid of such reaction product. As used herein, the term "surface portion" is defined as the outer most portion of the polymeric solid which may be modified by the thiocyano or isothiocyano free radical or ion generating reactant upon contacting with such reactants in liquid or gaseous reaction medium. The "interior portion" is defined as any remaining portion of the solid polymer. Prefer¬ ably, the surface portion extends no further than about one micron (one micrometre) into the polymeric solid from a point of contacting with such reactant. The present invention is also directed to a process for modifying a solid polymer having a surface portion and an interior portion. The process comprises contacting the surface portion of the precursor polymer with a thiocyano or isothiocyano free radical or ion generating reactant under free radical or ion generat- ing conditions so as to incorporate the reaction products formed by such contact. Modified polymers prepared in the manner of the present invention possess improved physical and chemical properties. By treatment according to the method of the present invention, the modified polymer's resistance to ultraviolet light may be improved over that of an unfunctionalized polymer, antistatic proper¬ ties may be incorporated into polymers otherwise pos¬ sessing little inherent antistatic properties, the dye acceptability of polymers may be altered, permeability of polymeric membranes may be tailored to provide the separation of desirable species from solutions, bonding of otherwise difficultly bondable polymers may be greatly facilitated, and subsequent finishing or treating processes including, for example, painting, metal deposition and plating of polymer surfaces may be improved. Modification of polymers according to the present invention involves at least in part the incor¬ poration of thiocyano or isothiocyano moieties into such polymers by either a homolytic or heterolytic process. However, without desiring to be bound to any particular theory of operation it is also believed that other reaction products besides isothiocyano or thio¬ cyano moieties may be incorporated into the polymers according to the present invention. For example, it is known by means of analysis that certain amounts of amide or sulfonate groups may likewise be present in the resulting polymers, possibly as a result of further reaction of thiocyano or isothiocyano functionality initially incorporated into the polymer, or altern¬ atively such species may form during the modification process, for example in the treating solution, and be incorporated directly into the modified polymer. Such additional functional groups may likewise contribute to the altered physical properties in polymers prepared according to the present invention. Accordingly all such functional groups incorporated into the modified polymers of the invention are included within the term "reaction product of a polymer and a thiocyano or isothiocyano generating reactant" . The process of the present invention may proceed by either homolytic or heterolytic mechanisms. In a preferred embodiment an active hydrogen, especially such a hydrogen that is bound to a carbon moiety of the polymer, is replaced according to a standard substitu¬ tion reaction scheme by reaction with thiocyano or isothiocyano radicals. When the polymer precursor contains ethylenic unsaturation, at least some thio- cyanate or isothiocyanate groups are added across the unsaturated double bond. Alternative mechanisms are also considered possible. For example, the reaction product of the thiocyano or isothiocyano reactant and the precursor polymer may be incorporated into the modified polymer by physical attachment or deposition •onto the polymer surface; or reaction with hydroxyl functionality intentionally or unintentionallypresent on the polymer surface; or by means of a pr ' ocess as yet unknown. Accordingly, the present invented process is not intended to be limited to a particular chemical mechanism or theory of operation it being sufficient that the modified polymers can be prepared according to the procedures hereinafter explained. Polymeric materials suitable for modification according to the present invention include polymeric materials substantially devoid of ethylenic unsaturation which can be modified by reaction with the present thio¬ cyano or isothiocyano generating reactants under homolytic reaction conditions, such as polymers containing hydrogen bound to carbon moieties of the polymer repeating unit such that the hydrogen is available for replacement so as to form reaction products. In addition suitable pre¬ cursor polymers include polymeric materials containing hydrogen that is reactive under catalytic conditions and polymers containing reactive nitrogen moieties. Both aliphatic and aromatic polymers may be modified according to the present invention. Polymeric materials also suitable for modi¬ fication according to the present invention include polymeric materials containing some amount of reactive unsaturation. The unsaturation may be present in the polymer as a consequence of its formation, as where a conjugated diene is polymerized or copolymerized result¬ ing in the presence of residual unsaturation, or unsatu¬ ration may be purposely introduced for example by halogenation of the polymer followed by ydrodehalo- genation according to known techniques. In addition the amount of unsaturation may be reduced if desired by controlled hydrogenation of a portion of such unsatu¬ ration prior to thiocyanation or isothiocyanation according to the present invention. The procedures of halogenation - dehydrohalogenation and hydrogenation are similar to procedures previously known in regards to non-polymeric organic chemical processes. Examples of suitable polymers include, for example, addition polymers, i.e., polymers prepared by reaction of one or more ethylenically unsaturated monomers; ring-opened polymerization products; conden¬ sation polymers; or other suitable polymer. More particularly polymers that may be modified according to the present invention include polymers and copolymers of olefins and substituted olefins, monovinylaromatic monomers (with or without a divinyl comonomer), and ethylenically unsaturated carboxylic acids or esters thereof having up to about 12 carbon atoms. Optionally such copolymers may additionally include a diene monomer. Examples include polyethylene, polypropylene, copolymers of ethylene and one or more α-olefins, polyvinylchloride, copolymers of vinylidene chloride and at least one comonomer, polystyrene, polyvinyltoluene, polymethylm- ethacrylate, polybutylacrylate, polyvinylacetate, styrene/acrylic acid, ethylene/acrylic acid, styrene/- maleic anhydride, and styrene/acrylonitrile. Ring- -opened reaction products include, for example, poly- alkylene oxides, interpolymers of diglycidyl ethers, and polyethyloxazolines. Condensation and addition polymers include, for example, polyesters, polyure- thanes, polyamides, urea/formaldehyde thermosets, poly- phenylene ethers, including ring alkylated or halogen- ated derivatives thereof, epoxy resins, interpolymers of dihydroxybiphenyl, polycarbonates, polysulfones ' , polyimides, and silicone containing polymers, e.g., polydimethylsilane. Also included are blends or mix¬ tures of polymers with or without the presence of a compatibilizer. If not originally present, reactive unsaturation is incorporated into the above polymers by any suitable technique, most preferably by halogenation followed by dehydrohalogenation. In the invention, solid objects of the above polymers are treated so as to incorporate thiocyanate or isothiocyanate functionality only on the available surface of such solid. In this manner, advantageous improvements in physical properties may be obtained without use of excessive amounts of thiocyano or iso¬ thiocyano generating reactant. Preferred polymeric materials for use in one embodiment of the present invention are polyolefins, especially polyethylene. When surface treated accord¬ ing to the present invention, solid polyethylene arti- cles such as films or sheets have been found to be adherable to polymeric materials that are normally difficultly bondable. For example, polyethylene objects treated according to the present invention are readily bonded to other resinous objects such as poly- propylene, polyamides, polyurethanes, and polystyrene. In a preferred embodiment, suitable bonding is achieved merely by contacting the two surfaces to be joined at elevated temperature optionally accompanied by pressure. Accordingly, one advantage of the present invention is that adhesive interlayers for joining differing poly¬ meric materials such as those disclosed in previously mentioned US 3,607,536, may be omitted when joining a modified polymer according to the present invention to another polymeric material. Additionally, cross-linked polymers may be prepared by first modifying a polymer according to the present invention and subsequently processing the modi¬ fied polymer so as to allow bond formation between neighboring functional groups. For example modified polyolefins of the invention can be caused to cross- -link by exposure to elevated temperatures and/or pres¬ sures. The resulting cross-linked polymer may be shown to possess improved dimensional stability and greater melt stability as evidenced by increased intrinsic viscosity of the compound. It is believed without wishing to be bound by such belief that such cross- -linking results through the formation of disulfide, triazine, or dithioether functionality. In another embodiment of the present inven¬ tion, it is preferred to employ polyurethane thermoset- ting resins. It has been found that coatings such as paints applied to reaction injection molded polyure- thane articles that have been surface treated according to the present invention demonstrate significantly improved adhesion compared to coatings applied to untreated reaction injection molded polyurethane arti¬ cles. Suitable coatings include, for example, organic polymer films such as lacquers, alkyl enamels, poly¬ urethanes, epoxies, latex coatings, powder coatings and electrodeposited primers. In still a further embodiment of the present invention, thin films or sheets of permeable polymeric materials such as polyolefins, polyvinyl chloride, vinyiidene chloride copolymers, polystyrene, polyethers or polysulfones are modified to provide selective permeability to -various materials, especially gases such as, for example, carbon dioxide, hydrogen cyanide, methane, and sulfur dioxide. In this manner, a mem¬ brane may be modified so as to selectively separate one or more gases from a mixture of gases. Alternatively, the polymers may be used to ' complex metal ions. Sheets of the modified polymer may be used to selectively extract such metal ions from aqueous streams. The polymeric material treated according to the present invention may be- in any suitable physical shape. Powders, chips, pellets, extrusions, films, as well as solid objects of considerable physical size and complex shape may be satisfactorily treated. Addi¬ tional forming or machining operations such as pellet- izing, stretching, extrusion, compaction, blowing, lamination, pull-trusion, spinning, foaming, painting, plating, vapor deposition or other finishing processes may be performed on polymeric materials modified by the present process. The thiocyano or isothiocyano generating reactant includes any composition capable of generating reaction products through either free radical or ionic charge transfer mechanisms, i.e., by either a homolytic or heterolytic cleavage process. Suitable reactants include, for example, thiocyanochloride, thiocyano- bromide, thiocyanogen, thiocyanocyanate, and thiocy¬ anoisocyanate. Preferably thiocyanate generating reactants, i.e., thiocyanating agents, are employed. The preferred method of operation is to generate the above thiocyano or isothiocyano generating reactant in situ in a dilute solution. When so prepared substantially contemporaneously with use in the present treatment process, losses due to decomposition or polymerization of the radical or ion generating reactant are minimized. The reactant may be prepared by any suitable technique or obtained commercially. Suitable methods of preparation include, for example, oxidation of thiocyanic acid with manganese dioxide or other oxidizing agent; the action of bromine or chlorine on solutions of metal or ammonium salts of thiocyanic acid or isothiocyanic acid; and the electrolysis of ammonium salts such as ammonium thiocyanate. In addition, certain salts, such as ammonium thiocyanate or cupric thiocy¬ anate, may decompose spontaneously in the presence of the polymer to be modified thereby eliminating the need of additional agents to prepare the isothiocyano or thiocyano generating reactant in situ. In the preparation of the modified polymers of the present invention, the thiocyano or isothiocyano radical-generating reactant or thiocyanate or isothio- cyanate ion generating reactant, referred to as "inter- mediate reactant", is preferably prepared by contacting a metal salt of thiocyanic acid or isothiocyanic acid with a halogen. Suitable metal salts include, for example, lead thiocyanate, sodium thiocyanate, and potassium thiocyanate. Suitable halogens include chlorine and bromine. The polymeric substance to be modified may be present in the solution at the time of contacting the halogen and metal salt, or added at a suitable later time. The active species prepared in the above manner may be thiocyanogen, thiocyanogen halide, isothiocyanogen halide or a mixture thereof. The thiocyano or isothiocyano free radical may be prepared from the intermediate reactant by any suitable technique including the use of chemical reac¬ tants, e.g., peroxides; or by the use of electromagnetic radiation; heat; or other suitable means. A preferred method for preparing free radicals is to employ control¬ led amounts of light of a frequency sufficient to cause free radical formation. Generally, light falling into the general description of ultraviolet or visible radiation is sufficiently energetic to initiate free radical formation. Any suitable source of light may be employed such as, for example, mercury lights, electric arcs, sunlight, lasers tuned to a suitable wavelength, and flash tubes. A photosensitizer such as an aromatic quinone, halogenated hydrocarbons or other known sensi- tizers may be employed for efficient generation of thiocyano or isothiocyano free radicals. The photo- sensitizer may be used in minor or major amounts. Gen¬ erally, as little as about 1 percent by weight is effective. Where a halocarbon photosensitizer is employed, large amounts may be employed. In such event, the photosensitizer is also employed as the solvent for the process. In an ionic process the thiocyanate or iso- thiocyante ions are generated by any suitable method including chemical or electrochemical methods. Chemical methods include the use of oxidizing agents such as, for example, chlorine or other halogen, permanganate, or a catalyst. Exemplary catalysts are Lewis acids, especially halogens or the well-known metal halides, such as aluminum trichloride, or ferric chloride. The process may be conducted in an inert sol¬ vent such as, --for example, acetic acid, anhydrous ether or more preferably a halohydrocarbon or halocarbon suck as dichloromethane, chloroform, tetrachloromethane, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1-dichloro- ethane, 1,1,ltrichloroethane, tetrafluoromethane, trichlorofluoromethane, and 1,1,2-trichlorotrifluoro- ethane. Additionally, the process may be conducted in aromatic solvents such as, for example, benzene, toluene, and orthodichlorobenzene. An inhibitor to prevent polymerization of thiocyanate or isothiocyanate moieties may also be included if desired. Generally, temperatures from 0°C to 75°C may be employed for the functionalizing process. Reduced or ambient temperatures are preferred in order to minimize decomposition losses of the thiocyano or isothiocyano generating reactant. A preferred tempera¬ ture is from 20°C to 50°C. The amount of functionality incorporated into the polymer may vary depending on the nature of the polymer, the thiocyano or isothiocyano generating reactant, temperature, and length of reaction. At least a minor amount of functionality is added to the polymer. By the term "a minor amount" is meant that the amount of functionality added is at least an amount effective to provide altered physical properties in the polymer. Examples of suitable means to determine the existence of altered physical properties include the measure of adhesive strength of laminates formed there¬ from; the gas permeability or paint adhesion of treated samples compared to untreated samples; increased intri¬ nsic viscosity compared to unmodified samples or other suitable test. The amount of functionality incorporated into the polymer is expressed as percent thiocyanate (-SCN) or isothiocyanate (-NCS) based on the unfunc- tionalized polymer before functionality is added. The polymer is analyzed for nitrogen and sulfur before and after functionality is added. The increase in the nitrogen and sulfur content is converted to thiocyanate or isothiocyanate. Preferably the amount of function¬ ality is from 0.001 to 10 percent by weight, and most preferably from 0.01 to 1 percent by weight. Prefer- ably the amount of functionality is from 0.001 percent to 10 percent by weight and most preferably from 0.01 percent to 1 percent. Because the added functionality is concentrated at the available surface thereof, even a small added amount is effective to provide greatly altered physical properties. As previously stated such functionality comprises the reaction product of the polymer and the thiocyano or isothiocyano generating reactant. Preferably, such functionality comprises thiocyanate or isothiocyanate groups, most preferably, thiocyanate groups. Having described the invention, the following examples are provided as further illustrative and are not to be construed as limiting inasmuch as variations and modifications within the scope of the present invention will be readily apparent to the skilled artisan. Example 1 - Thiocyanation of Polyethylene Powder In a stirred glass reaction vessel, 100 ml of tetrachloromethane containing 3.23 g of lead thiocya¬ nate, Pb(SCN)-, is cooled by means of an ice bath to a temperature of about 20°C-30°C. Chlorine gas (3.2 g) is introduced into the stirred mixture in two incre¬ ments over a 15-minute period. After additional stir¬ ring for 15 minutes the liquid is filtered to remove lead chloride and the filtrate returned to the flask. A mixture of recrystallized polyethylene powder (DOWLEX 2047, 2.0 g) is added to the flask. The ice bath is removed and a long wave ultraviolet lamp is positioned under the flask. After irradiating for 24 hours at 25°C, stirring is stopped and the polyethylene powder is separated by vacuum filtration, washed with tetra¬ chloromethane two times and aspirated to remove solvent. The recovered sample is digested and analyzed by a colorimetric method for nitrogen content, and a standard mercury titration for sulfur content. Results indicate the presence of 1:1 mole ratio of nitrogen to sulfur representing about 1 percent substitution expressed as thiocyanate functionality. Example 2 The reaction conditions of Example 1 are sub¬ stantially repeated excepting that the polyethylene powder in contact with the thiocyanation solution is maintained at about 50°C by the use of infrared heat lamps. Irradiation is continued for 3 hours. After this time period, the polyethylene is recovered. Analysis in the same manner as previously described indicates the presence of about 1 percent by weight thiocyanate functionality. Example 3 The reaction conditions of Example 1 are sub¬ stantially repeated employing powders of polypropylene and a styrene/acrylonitrile copolymer (Tyril resin available from The Dow Chemical Company). Analysis indicates successful surface incorporation of thiocy¬ anate functionality in each polymeric sample. Example 4 - Bonding of Polyolefins Small samples of polyethylene film are thio- cyanated by treatment substantially according to the. procedure of Example 1. Accordingly, a sheet of poly- (R) ethylene film (DOWLEX 2047) approximately 1.2 g, 0.1 mm thick, is submerged in carbon tetrachloride solution prepared by contacting at 50°C with stirring in 250 ml CC1 4 , lead thiocyanate (3.23 g) and chlorine (2.7 g added over 20 minutes). After reaction for 10 minutes at 50°C, the reaction mixture is filtered and trans¬ ferred to a 1000-ml beaker for treatment of polymer samples. Treatment of films comprises irradiation with ultraviolet light ("long" wavelength) at 50°C placed approximately 10 cm above the beaker containing the polymer film and the thiocyanating solution. After irradiation for 5 minutes, the film is removed, rinsed with CC1 4 and drained on a paper towel. The thiocyanated polymer films are heat sealed to nylon (nylon 6) and to polypropylene films each 0.1 mm thick by heat sealing in a seven point heat sealer. Bond pull-apart strengths are measured using a tensile strength analyzer. Pull strengths and comparative pull strengths of unfunctionalized equal sized and shaped films are contained in Table I. Adhe¬ sion strength is measured as the force required to cause separation at the film bond. TABLE I Bond¬ Bond¬ ing ing Adhesion Temp Time Strength lb/in Film A Film B °C sec (Newton/cm) Thiocyanated Nylon 170 0.64 (1.12) Polyethylene Untreated Nylon 170 <.l (<.175) Polyethylene Thiocyanated Polypro- 104 1 1.74 (2.61) Polyethylene pylene Untreated Polypro- 104 0.02 (0.35) Polyethylene pylene Example 5 Polyethylene powder (DOWLE 2047) prepared substantially according to the procedure of Example 1 is hot pressed for 7 minutes at 157°C onto nylon and polypropylene substrate films. The resulting laminated films are cut into 1-inch (2.5 cm) wide strips and pull- -apart strengths measured by a tensile strength analyzer. Results compared with samples of untreated hot pressed polymer films are contained in Table II. TABLE I I Adhesion Strength lb/in Substance A Substance B (Newton/cm) Thiocyanated Polypropy1ene 0.36 (0.63) Polyethylene Film Powder Untreated Polypropylene 0.0086 (0.02) Polyethylene Film Powder Thiocyanated Nylon Film 0.05 (0.09) Polyethylene Powder Untreated Nylon Film Nil Polyethylene Powder It is seen by comparison of the results of Examples 4 and -5 that laminated layers of'polyethylene and other solid polymers may be obtained without the use of adhesive layers by applying heat and pressure to bond polyethylene having surface thiocyanate func¬ tionality to nylon, polypropylene or other substrate polymers. Example 6 Rigid polyurethane foam is prepared having polyethylene film backing. Accordingly, polyethylene film (DOWLEX 2047) surface treated with thiocyanate functionality substantially according to the technique of Example 4 and comparative samples of unfunctional- ized film are covered with a polyurethane formulation comprising the following ingredients in the indicated parts by weight: polyol: VORANOL ® 360 1 100.0 methylene diphenyl diisocyanate: 89.8 blowing agent: Freon § 11 47.0 surfactant: L-5340 2 1.5 amine catalyst: 33LV 3 2.0 metal catalyst: UL-6 4 0.3 1 available from The Dow Chemical Company 2 available from Union Carbide Corporation 3 available from Air Products Co. available from M and P Chemical Co. After curing for 15 days, the film-backed rigid foams (approximately 10 cm thick) are cut into equal slices approximately 2.5 cm wide and 2.5 cm thick, and the adhesive strength of the films to the rigid foams are measured by a tensile strength analyzer. Compar¬ ative data are contained in Table III. TABLE III Adhesion Strength to Polyurethane Foam Adhesion Strength lb/in Specimen (Newtons/cm) Thiocyanated Polyethylene Film 2.08 (3.64) Untreated Polyethylene Film 0.03 (0.05) It is seen by comparison of the results in Table III that significantly increased adhesion of poly¬ urethane articles to polyethylene may be achieved with¬ out the use of adhesives by surface treating the polyeth¬ ylene to provide thiocyanate functionality and thereafter forming and curing the polyurethane while in contact with the polyethylene film. Example 7 - Membrane Permeability A sample of SARAN polyvinylidene chloride film is surface treated with thiocyanate substantially according to the procedure of Example 4. Thiocyanated films (0.02 mm thick) are contacted with carbon dioxide and methane gases at a differential pressure of approxi¬ mately 5 psi (34 kPa) to measure diffusion rates there- through. Results compared to untreated films are con¬ tained in Table IV. TABLE IV Permeation of C0 2 and CH 4 through SARAN® Film Thiocyanated Film Untreated Film CO- 1.583 mg/min/m 2 6.52 x 10 "1 mg/min/m 2 CH 4 5.43 x 10~ 4 mg/min/m 2 2.0 x lθ "3 mg/min/m 2 It is seen that surface thiocyanated poly- vinylidene chloride films are rendered more permeable to passage of carbon dioxide than untreated film. How¬ ever, surface thiocyanated polyvinylidene chloride is less permeable to passage of methane than is untreated film. Accordingly, carbon dioxide may be selectively separated from a mixture of carbon dioxide and methane by contacting with one or more membranes prepared from thiocyanated films of the present invention. Additional suitable polymers that may be sur¬ face-modified to alter the permeability thereof include polyether sulfone and polystyrene. Additional gases such as, for example, sulfur dioxide, H 2 S, and CO, may also be separated by the films of this invention. Example 8 - Paint Adhesion and Wet Out A thin rectangular shaped polyurethane solid is prepared by reaction injection molding in molds coated with a wax based release compound using a formulation containing an internal mold release agent comprising the following ingredients in the indicated parts by weight: Polyol (XUS14003 available from The Dow Chemical Company) 26.4 D-400 (available from Texaco Inc.) 2.0 zinc stearate 0.8 oleoyl sarcosinic ■ . 0..8 methylene diphenyl diisocyanate modified to be liquid at room temperature (Mondur PF available from Mobay Chemical Company) 64.5 diethyltoluenediamine chain extender <1.0 In a stirred glass reaction vessel 100 ml of tetrachloromethane containing 3.23 g of lead thiocyanate, Pb(SCN),,, is cooled by means of an ice bath to a tempera¬ ture of between 20°C and 30°C. Chlorine gas (3.2 g) is introduced into the stirred mixture in two increments over a 15-minute period. After additional stirring for 15 minutes the liquid is filtered to remove lead chloride and the filtrate returned to the flask. The polyurethane sample is dipped into the thiocyanogen solution for 15 sec. The sample is then heated in an oven for 20 min. at 135°C. After cooling at room temperature a coating of high solids alkyd enamel (PPG 1060 available from PPG Industries) is applied and oven cured at 135°C for 30 minutes. A sample area is marked by scoring and the film is cut leaving grid lines approximately 3 mm separation vertically, horizontally and diagonally in two directions. The cuts were deep enough to cut through the paint film. Specimens prepared as indicated are placed in a stirred water bath at 38°C for a total of 96 hours. Afterwards, the painted surfaces are scraped ten times with a razor blade in each of two directions. The number of cross- hatched sections removed is observed. Failure percent is calculated as the percentage of total cross-hatch flakes removed by the above procedure. Results are contained in Table V. TABLE V Wet Out Relative Total Cross-hatched Scale ( Ξross-hatched Sections with % (1-worst) Specimen Sections Paint Failure Failure (10-Best) Untreated 128 128 100 1 Thiocyanated 171 8 4.7 10 It should be noted that the polyurethane compo¬ sition which normally would possess inferior paint adhesion due to the presence of the internal mold release agent demonstrates greatly improved adhesion as a result of treatment according to the present invention. X-Ray diffraction studies involving acceler¬ ated aging (30 minutes, 135°C) to test for zinc stearate migration indicate substantially no increase in surface zinc stearate levels. This result would suggest improved long-term paint adhesion compared to untreated samples can be expected. Example 9 - Cross-linking of Linear Low Density Poly¬ ethylene Dowlex _ 2047 brand of linear low density poly- ethylene is purified by recrystallization from xylene. The recrystallized polymer is washed with carbon tetra¬ chloride. In a separate flask, lead thiocyanate (3.23 g), is added to 100 ml of carbon tetrachloride (spectro-grade) The resulting slurry is cooled to about -4°C in an ice- bath and chlorine gas (1.6 g) is added. The mixture is stirred for about 10 minutes when an additional amount of chlorine (1.6 g) is added and stirring continued. Remain¬ ing solids are removed by filtration and the recrystal¬ lized linear low density polyethylene powder (1 g) is added. The mixture is maintained at 40°C under a mercury light for 24 hours. After recovery, washing with carbon tetrachloride, and drying, the powder is pressed into a film at 400°C and 0.2 GPa. The recovered polymer film is tested for intrinsic viscosity and compared to a film of unmodified polymer prepared at similar conditions of heat and pres¬ sure. Results are contained in Table VI. TABLE IV Intrinsic Viscosity Specimen Centipoise (Pa-s) thiocyanated polymer 350 (0.350) Untreated polymer 180 (0.180) The results indicate the formation of cross- -linking bonds in the thiocyanate modified polymer. Example 10 - Solution Modification of Polycarbonate A thiocyanogen containing solution is prepared by combining 250 ml of methylene chloride in a 500 ml flask. Lead thiocyanate Pb(SCN)-, (13.2 g) is added with vigorous stirring- Bromine (6.4 g) is added to the suspension. Stirring is continued until loss of color occurs. The resulting solution is filtered and employed without further treatment. Polycarbonate resin (Novarex available from Mitsubishi Chemical Industries Ltd.) (60 grams) is dis¬ solved in methylene chloride (240 g) . The resulting solution is combined with the thiocyanogen containing solution with stirring. The resulting mixture is irradi¬ ated with ultraviolet light for about 90 minutes. The resulting- solution is filtered and a modified polycarbon¬ ate film recovered by evaporation of methylene chloride. When tested for carbon dioxide permeability the treated film demonstrates greatly improved barrier compared to an untreated film. Example 11 - Solution Modification of Chlorinated Polyethyle A thiocyanogen containing solution is prepared substantially according to the procedure of Example 10. After preparation, chlorinated polyethylene powder (1 percen based on solvent weight) is added with stirring. The mixture is heated with continued stirring to 50°C and irradiated with ultraviolet light for one hour. The resulting solution is filtered and a film of modified polymer prepared by solvent evaporation. Analysis of the resulting product confirms the presence of sulfur and nitrogen functionality in about equal molar percentages. Substantially no sulfur or nitrogen functionality is observed in unmodified film. Example 12 - 1,2-dichlorobenzene solvent Lead thiocyanate (13.2 g) and bromine (6.4 g) are combined in 1,2-dichlorobenzene solvent substantial according to the procedure previously described in Example 1 A small amount of the resulting filtered solution (50 g) is combined with polyethylene fibers (1.0 g) in a closed glass bottle. The bottle is exposed to direct sunlight for approximately 30 minutes. The fibers are recovered by filtration and washed with 1,2-dichlorobenzene. Upon drying the fibers are analyzed and shown to contain both sulfur and nitrogen functionality. Infrared spectroscopy indicates the presence of thiocyanate functionality. Example 13 - Vapor Phase Modification A solution of thiocyanogen in tetrachloromethane is prepared substantially according to the procedures employed in Example 1. Approximately 20 ml of the thio¬ cyanogen solution is placed in an uncovered evaporation dish. A film of linear low density polyethylene (Dowlex 2047 available from The Dow Chemical Company) is stretched over the dish leaving a space between the film and the surface of the liquid. A watch glass is placed on top of the film. The apparatus is placed in a 60°C oven and exposed to ultraviolet light for about 7.5 minutes. The film is removed, rinsed with CC1 4 and dried. Analysis indicates the presence of sulfur in the modified film and essentially no sulfur in the unmodified film. Example 14 - Thiocyanation of a Polyethylene Film Having Added Unsaturation. In a one liter resin kettle one gram of liquid bromine is placed in an open beaker. A sheet of linear low density polyethylene film in the form of a cylindrical surface is placed around an ultraviolet fluorescent light tube in the center of the resin kettle. The film is irradiated for 4 hours with long wave length ultraviolet light while being exposed to bromine vapors. Following bromination the film is dehydrohalogenat by contacting with in methanolic sodium methoxide at 20°C for 15 minutes. The resulting film containing unsaturated moieties is thiocyanated by immersion in 0.2 N solution of thiocyanogen chloride at 40°C. The thiocyanating solution is prepared by placing 0101 mole of lead thiocyanat in 200 ml of CCl 4 . Chlorine gas is introduced with agitation into the solution while cooling in an ce bath over a 10 minute period. The chlorine gas is discontinued and the resulting solution filtered. After introduction of the polyethylene film into the solution the film and solution are irradiated with long wavelength ultraviolet light for about 30 minutes- The film is removed and rinsed with carbon tetrachloride then dried at room temperature. Analysis of the film surface by ESCA indicates the presence of sulfur atoms (1.5 percent on a molar basis). Determination of the oxidation state indicates about 53 percent of the sulfur exists as thiocyanate moieties the remainder as sulfonate groups. Similar anaylsis for nitrogen containing groups indicates that 59 percent exist as thiocyanate groups and 41 percent are in the form of amide groups. Samples of the treated unsaturated film are easily bonded to nylon or polypropylene films by simple application of heat and pressure (175°C, 275 kPa, 1 sec contact time). The laminated films prepared by this procedure demonstrate greatly improved adhesion compared to unmodified films.

Claims: 1. A solid polymer having a surface portion and an interior portion, wherein the surface portion comprises the reaction product of a thiocyano or iso¬ thiocyano free radical or ion generating reactant and the precursor polymer and the interior portion is sub¬ stantially devoid of such reaction product. 2. The polymer of Claim 1 wherein the surface portion extends no further than about one micron (one micrometre) into the polymeric solid. 3. The polymer of Claim 1 comprising at least some thiocyanate or isothiocyanate functionality. 4. The polymer of Claim 1 wherein the polymer prior to modification comprises an addition polymer or condensation polymer. 5. The polymer of Claim 4 wherein the polymer prior to modification comprises a polymeric or copolymeric addition product of one or more ethylen- ically unsaturated monomers; a ring opened reaction product; a polyester, a polyurethane, a polyamide, a polyether, a polycarbonate, a polysulfone, a polyimide, a silicone polymer, or a mixture thereof. 6. The polymer of Claim 5 wherein the polymer prior to modification comprises a homopolymer or copoly¬ mer of one or more monomers selected from the group consisting of olefins, substituted olefins, monovinyl aromatics, ethylenically unsaturated carboxylic acids and esters thereof. 7 ' . The polymer of Claim 3 wherein the amount of functionality added to the polymer is from 0.001 percent to 10 percent by weight. 8. The polymer of Claim 1 wherein the polymer is contacted with ' a solution of the thiocyano or isothiocyano free radical or ion operating reactant while simultaneously irradiating the polymer surface with ultraviolet light. ' 9. The polymer of Claim 1 additionally ' com- * prising a surface coating of an organic polymer film. 10. A process for modifying a solid polymer having a surface portion and an interior portion com¬ prising contacting the surface portion of the precursor polymer with a thiocyano or isothiocyano free radical or ion generating reactant under free radical or ion generating reaction conditions so as to incorporate the reaction products formed by such contact. 11. The process of Claim 10 wherein the polymer is contacted with a solution of the thiocyano or isothiocyano free radical or ion generating reagent while simultaneously irradiating the polymer with ultra¬ violet light. 13. The process of Claim 10 wherein at least some thiocyano or isothiocyano functionality is incor¬ porated into the surface portion of the polymer. 14. The process of Claim 13 wherein the amount of functionality incorporated into the polymer is from 0.001 percent to 10 percent by weight. 12. The process of Claim 10 wherein the process is conducted at a temperature of from 0°C to 75°C.

Inventors: KITCHENS JOHN D, NOVAK LEO R, KITCHENS, JOHN, D., NOVAK, LEO, R.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1986
Main classification: C08F8
IPC codes: C08F8, C08G85