3,741,926 United States Patent Office Patented June 26, 1973 2 tillation to provide a concentrated aqueous solution con 3,741,926 taining from about 40 to about 55 weight percent poly CEMENT COMPRISED OF ZINCOXDE AND ACRYLCACD COPOLYMER mer solids, preferably 47 to 52% polymer. Anton Jurecic, Springfield, Del, assignor to Pennwalt The acrylic acid copolymers of this invention have a Corporation, Philadelphia, Pa. molecular weight within the range of about 20,000 to No Drawing. Continuation-in-part of abandoned applica 75,000, preferably about 30,000 to 40,000, as measured tion Ser. No. 18,319, Mar. 10, 1970. This application by capillary viscosity in dioxane solvent at 30° C. July 1, 1971, Ser. No. 159,018 The cement compositions of this invention are pre Ent, C. C08f 45/24, 45/04 pared by uniformly mixing a measured amount of the U.S. C. 260-29.6M 5 Claims O acrylic acid copolymer, preferably in liquid form as a 40 to 55% aqueous solution, with conventional zinc oxide powder (approximately 1 to 50 microns particle ABSTRACT OF THE DISCLOSURE size range). The preferred proportions in parts by weight A copolymer comprised of 10 to 90 mole percent of of the cement ingredients are about 4 to 8 parts acrylic acrylic acid and at least one mono-olefinically unsatu 5 acid copolymer, about 10 to 18 parts zinc oxide and rated polycarboxylic acid selected from the group con about 4 to 9 parts water. Other compatible liquid media sisting of glutaconic acid, aconitic acid, citraconic acid, in which the copolymer is soluble can be substituted for mesaconic acid, itaconic acid, fumaric acid, maleic acid part or all of the water to control viscosity characteris and tiglic acid, is mixed with zinc oxide to prepare im tics of the cement, such as, for example, monohydric and proved cements for dental and orthopedic use. 20 polyhydric alcohols, e.g., ethanol, glycerol, glycols and sorbitol. The zinc oxide constituent can, as is well known This application is a continuation-in-part of Ser. No. in the art, include minor amounts of modifying ingredi 18,319, filed Mar. 10, 1970, now abandoned. ents such as MgO, SiO2, BiO3, BaO, BaSO4, CaO, AlO3, This invention concerns acrylic acid copolymers and NaF, CaWO and the like, as well as chelating agents their use in zinc oxide-based cement compositions for 25 such as eugenol and ethoxybenzoic acid. Other modifying dental and orthopedic use. agents that can be added to the cement mixture are The copolymer of this invention comprises from 10 to monovalent metal salts, e.g., halides, sulfates and phos 90 mole percent of acrylic acid copolymerized with at phates, such as NaCl, Na2SO4 and NaI, for the purpose least one mono-olefinically unsaturated polycarboxylic of improving handling properties and accelerating or de acid selected from the group consisting of glutaconic 30 laying setting time. In general, salt solutions decrease acid, aconitic acid, citraconic acid, mesaconic acid, ita viscosity and extend working time. For example, NaCl conic acid, fumaric acid, maleic acid and tiglic acid. added in about 0.004 wt. percent concentration based on Thus, the copolymers of this invention include not only the polymer makes handling easier and delays setting two component copolymers but terpolymers, quadripoly time for 5 minutes at room temperature. When an equal mers, etc. The preferred acrylic acid proportion in the 35 amount of NaH2PO4 is added, the setting time is ex copolymers is from about 55 to 65 mole percent. In tended to more than 15 minutes. addition to polymerized units of acrylic acid and at least After the cement ingredients are thoroughly mixed, one of said ethylenically unsaturated polycarboxylic the mixture may be easily worked for at least from 2 to acids, the copolymer embodied herein may contain as 5 minutes, after which the cement begins to set in a hard optional components minor amounts, i.e., up to about 5 40 mass, depending on the powder/liquid ratio, added salts, mole percent, of copolymerized alkyl ester of acrylic temperature, and spatulation technique. The resulting acid, e.g., esters wherein the alkyl group has from one cement is employed in dental techniques as a binder, to about eight carbon atoms, such as methyl acrcylate, cementing and luting medium, in hard-set impression ethyl acrcylate, butyl acrcylate and 2-ethylhexyl acrylate. pastes, as an adhesive in orthodontic work, in periodontal Another embodiment of this invention is a dental ce 45 packs, and as restorative filling material. The cement ment composition comprising a mixture of from about compositions embodied herein also are useful as surgical 25 to about 75 parts per weight of the described acrylic and orthopedic cements, for example, in such techniques acid copolymer with 100 parts per weight of zinc oxide. as fusion of metal implants to bone utilizing the cement. The preparation of the acrylic acid copolymers em The dental cement compositions of this invention have bodied herein is carried out using conventional free 50 superior strength and adhesive properties compared to radical catalyzed polymerization techniques in aqueous the acrylic polymer-zinc oxide cements known hereto reaction medium. Suitable free-radical-forming catalysts fore. Other advantages of the new compositions are easier are ammonium persulfate, potassium persulfate, hydro spatulation and workability. gen peroxide, and the like. It is preferred to use the well 55 In the following examples amounts of ingredients and known redox initiator system to facilitate polymeriza reactants are given in parts by weight unless otherwise tion, for example, such additives in small quantities as indicated. The proportions of constituents of copolymers alkali metal sulfites and thiosulfites, ferrous sulfate, di are given in mole percents. hydroxyacetone and ascorbic acid. The quantity of reaction medium for the polymeriza EXAMPLE 1. tion is generally from about 300 to 400 parts of water 60 To a suitably equipped reaction vessel are charged 450 per 100 parts of the acid monomers. The polymerization parts distilled water, 4.5 parts ammonium persulfate and is advantageously carried out in the substantial absence 80 parts itaconic acid. The air in the vessel is evacuated of oxygen and, for best results, the polymerization tem and replaced with a blanket of nitrogen gas. The con perature is within the range of 60° C. to 85° C. About tents of the vessel are heated to 60° C. with stirring, 5 to 8 hours of reaction is generally required to ensure 65 whereupon 80 parts of acrylic acid is added incremen essentially complete conversion of the monomers to co tally. The polymerization temperature rises to 80° C. polymer. where it is maintained during the four hours of acrylic The copolymer products are miscible with and soluble acid addition and for one additional hour thereafter. The in the aqueous reaction medium. For subsequent use as product, a 65% acrylic acid-35% itaconic acid copoly a cement ingredient, a portion of the water may be 70 mer, is recovered as an aqueous solution containing 26% stripped off using sub-atmospheric, low temperature dis polymer. This copolymer solution is a colorless liquid, 8,741,926 3 4 having a relative viscosity of 380 cst., determined in a 88% acrylic acid-12% glutaconic acid Ubelohde viscometer. The polymer solution is evapo 88% acrylic acid-12% mesaconic acid rated under a vacuum (20–30 mm. Hg absolute pressure) 90% acrylic acid-10% aconitic acid at 40° C. for 5 hours to yield a concentrated solution 88% acrylic acid-12% citraconic acid containing 48% polymer solids. 88% acrylic acid-12% tiglic acid The foregoing procedure is repeated using various pro 52% acrylic acid-31% itaconic acid-17% maleic acid portions of acrylic acid and itaconic acid to produce the 64% acrylic acid-34.5% itaconic acid-15% butyl acrylate following copolymers: 64% acrylic acid-35% itaconic acid-1% 2-ethylhexyl 88% acrylic acid-12% itaconic acid acrylate 55% acrylic acid-45% itaconic acid O 50% acrylic acid-30% citraconic acid-15% aconitic acid 37.5% acrylic acid-62.5% itaconic acid 5% maleic acid A dental cement composition is produced by blending 50% acrylic acid-40% glutaconic acid-8.5% itaconic 10 parts of a 48.7% aqueous solution of the representa aicd-1.5% ethyl acrylate tive 37.5% acrylic acid-62.5% itaconic acid copolymer 50% acrylic acid-30% citraconic acid-15% itaconic acid with 15 parts of a powdery 90:10 mixture of ZnO and 5 5% methyl acrylate. MgO containing small amounts of Al2O3, BaSO4 and I claim: CaWO. The compressive strengths of the cement, meas 1. A cement composition comprising a mixture of zinc ured at various time intervals are: oxide and a copolymer having a molecular weight within the range of about 20,000 to 75,000, said copolymer con 24 hours, average --------------------p.s.ill 13,100 20 sisting essentially of copolymerized units of from about 7 days, average --------------------p.s.i.g-- 14,400 55 to 65 mole percent of acrylic acid, 0 to about 5 mole 30 days, average -------------------- p.s.i.-- 13,900 percent of copolymerized units of alkyl ester of acrylic The other copolymers prepared above give comparable acid wherein the alkyl group of the ester has from 1 to results as the polymer component in zinc oxide cements. about 8 carbon atoms, and the remainder copolymerized EXAMPLE 2 25 units of at least one unsaturated polycarboxylic acid se A terpolymer of 54% acrylic acid; 8% maleic acid lected from the group consisting of glutaconic acid, aco and 38% itaconic acid is prepared using the procedure initic acid, citraconic acid, mesaconic acid, itaconic acid, of the previous example.