Facile Synthesis and Polymerization of Ether Substituted Methacrylates
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Polymer Journal, Vol. 27, No. 4, pp 325--338 (1995) Facile Synthesis and Polymerization of Ether Substituted Methacrylates Robert D. THOMPSON, Thomas B. BARCLAY, Kumar R. BASU, and Lon J. MATHIAS* Department of Polymer Science, University of Southern Mississippi, Hattiesburg, MS 39406-{)076, U.S.A. (Received May 12, 1994) ABSTRACT: New difunctional methacrylate monomers containing f3 heteroatoms have been synthesized from o:-hydroxymethylacrylate esters or o:-chloromethylacryloyl chloride. These monomers are more reactive than their alkane counterparts (e.g., ethacrylates), giving polymers with molecular weights comparable to poly(itaconate)s. The simple synthetic approach described allows a wide range of difunctionalized acrylate monomers to be produced. Variations in both ester and ether substituents were explored for ease of synthesis and polymerization. KEY WORDS Beta-Substituted Methacrylates / Disubstituted Ethylene / Functionalized Acrylates / Water-Soluble Acrylates / Poly(methacrylate)s / Ceiling Temperature/ Chain Transfer/ Acrylate monomers containing hydrocarbon alkyl ix-hydroxymethylacrylates8 with yields chains at the ex-position, such as the ethyl and ranging up to approximately 50% of readily propyl derivatives (1 and 2, Figure 1), display purified monomer. Reaction of the hydroxy very poor or no free radical polymerizability methyl group with appropriate reagents gives at room temperature. 1 Incorporation of an reactive ally! halides 7 •9 •10 capable of high oxygen atom fJ to the double bond (as in 3) yield conversion to a range of derivatives makes monomers which are much more reac (Figure 2). The ether's flexibility imparts tive. For example, the methyl ester of the ex unique properties to the monomer compared hydroxymethyl compound polymerizes faster to similar, more rigid ester derivatives; for than methyl methacrylate in free radical poly example, the ally! ether of ethyl ix-hydroxy merization, 2 although ether derivatives give methylacrylate undergoes efficient cyclopo molecular weights only up to ca. sixty thou lymerization to high molecular weight solu sand. 3 This is comparable to itaconate mono ble polymers, 11 in contrast to ally! acrylate mers. Apparently, chain transfer to monomer and methacrylate. limits molecular weight for the ethers. 4 Characteristics of the polymers obtained Our group and several others have been from these monomers include the fact that the exploring the chemistry of 1, 1-disubstituted ether linkage is inherently more stable than vinyl monomers based on esters of ex-hydroxy an ester linkage and should not be easily methylacrylate for several years. 5 Earlier work in this area involved complicated or low yield syntheses of hydroxymethyl compounds and natural product syn derivatives for use as 2 3 thons. 6·7 We have pursued a simple, clean Figure 1. Examples of o:-alkyl acrylates (1 and 2) which synthetic approach involving the DABCO give low molecular weight polymers and ethyl oi:-hydroxy catalyzed insertion of paraformaldehyde at methylacrylate (3) which gives high molecular weight the ex-position of acrylic esters to produce polymer. 325 R. D. THOMPSON et al. hydroxyethyl)-2-pyrrolidinone, N-(2-hydroxy DABCO 'i---.,,-o'-l + a, n y R ethyl)morpholine, t-butyl acrylate, and ethyl 0 10% solvent acrylate were used as received from Aldrich Chemical Company. Triethylamine (TEA, SOCl 2 R'OH Aldrich) was dried over calcium hydride for or PBr 3 TEA 24 h, then distilled into a dry vessel which was sealed and stored. Calcium sulfate (Fisher) was 3: R = Et; X: a = OH, 4, 5 b = Cl, used in air-drying tubes for reaction vessel c = Br outlets. 2,2'-Azobis(isobutyronitrile) (AIBN) 4: R = Et; R': a = Me, b = Benzyl, c = 3-Propionitrile, was recrystallized from methanol before use. d = N-(2-Hydroxyethyl)pyrrolidinone, a = N-(2-Hydroxyethyl)morpholine, Monomer syntheses and purities were mon f = N-(2-Hydroxyethyl)phthalimide itored by gas chromatography (GC) using a 5: R =I-Bu; R' = Me Hewlett-Packard 5890 Gas Chromatograph Figure 2- Synthetic scheme for intermediates and ether equipped with an FID detector, 95% dimethyl/ derivatives. 5% diphenyl polysiloxane column, and an HP 3396a Integrator. Monomers and polymers thermalized or hydrolyzed. In addition, steric were characterized by 13C NMR spectroscopy inhibition at the carbonyl carbon through the with Bruker AC-300 or AC-200 spectrometers. neopentyl effect should also reduce hydrolysis Thermal analyses were done on a Du Pont of the ester group in the polymers obtained. 9900 analyzer with a 910 or 912 DSC module. Examples of previous research on a-hy Viscosities were determined at 30°C using droxymethylacrylates include evaluating the Cannon-Ubbelohde microviscometers and ini kinetics of polymerization of these monomers tial polymer concentrations of ca. 0.5-0.85 as 1, 1-disubstituted ethylenes. 3 We have been g dL - 1 in tetrahydrofuran (THF). Intrinsic studying these materials with regard to their viscosity values were obtained by extrapolating utility in liquid crystalline monomers (fluoro least squares fits of both reduced and inherent alkyl ethers), 12 cyclopolymers, 11 and wood values to zero concentration. Size-exclusion polymer composities via monomer impregna chromatography (SEC) was carried out with tion and polymerization. 13 Several of the alkyl THF solvent, American Polymer Standard ethers of ethyl a-hydroxymethylacrylate have Company columns of 500, 10 3 , 104 , and 10 6 A been reported by others, including the methyl, packing, and polystyrene calibration standards ethyl, propyl, isopropyl, dodecyl, 3 and phe ranging from 17.5 x 10 3 to 3 x 106 . nyl 14 ethers. We describe here several new ether derivatives of the ethyl, methyl, and t Intermediate Syntheses butyl esters (Figure 2) as examples of the The synthesis of the alkyl a-hydroxymethyl versatility of this overall synthetic approach acrylates (RHMAs) has been previously de along with an improved method for obtaining scribed (R=ethyl and t-butyl). 5 •15 We have the chloromethyl intermediates. improved the yield to approximately 50% through the use oft-butyl alcohol or dimethyl EXPERIMENTAL sulfoxide (10vol%) as cosolvent. Purity of all monomers was determined by GC before Methanol, hexane, ethyl ether, and t-butyl polymerization. alcohol were used as received from Fisher Ethyl a-Hydroxymethylacrylate (EHMA, Chemical Company. Paraformaldehyde, l,4- 3a). Ethyl acrylate (20.0 mL, 0.188 mol), para diazabicyclo[2.2.2.]octane (DABCO), phos formaldehyde (2.82 gm, 93.9 mmol), t-butyl phorous tribromide, 2-pyrrolidinone, N-(2- alcohol (2 mL, 10 vol-%), 1,4-diazabicyclo- 326 Polym. J., Vol. 27, No. 4, 1995 Ether Substituted Methacrylates [2.2.2.]octane (DABCO) (1.05 gm, 9.36 mmol), alcohol (4.6 mL, 113 mmol), ethyl ix-chloro and a teflon-coated stirring magnet were added methylacrylate (8.37 g, 56.3 mmol), and a to a round-bottomed flask. The flask was fitted teflon-coated magnetic stir bar were placed in with a condenser and drying tube and placed a IO0mL single-neck round-bottom flask. The into an oil bath preheated to 55°C. After flask was placed in an ice bath and, with rapid approximately 8 h the vessel was removed from stirring, TEA (1 l.6mL, 83.2mmol) was added the heat and cooled. Ethyl ether (20mL) was to the flask slowly via addition funnel. The added to the solution which was then washed solution was allowed to come to room tem three times with 1 wt% aqueous HCl (l0mL). perature and stirred for an additional 8 h. The The combined aqueous layers were back TEA/HCI salt and excess TEA were extracted extracted with l 0 mL ethyl ether. Organic by washing three times with 1 wt% aqueous layers were combined, and solvents and un HCl solutions (IOmL portions). The aqueous reacted ethyl acrylate removed using a rotary layers were combined and back-extracted with evaporator. Copper(II) chloride was added CH2Cl2 (IOmL portions). The organic layers as a free-radical inhibitor and the solution were combined and dried with magnesium vacuum distilled to give 96% pure ethyl ix sulfate. Copper(II) chloride was added as a hydroxymethylacrylate; 50% overall yield. free-radical inhibitor, and solvent and excess Ethyl a-Chloromethylacrylate (ECMA, 3b). reactants were removed by rotary evaporation. Ethyl ix-chloromethylacrylate has been syn Vacuum distillation gave 98% pure ethyl thesized previously by our group. 10•16 Pure ix-methoxymethylacrylate; 41 % yield. EHMA (vacuum-distilled from the crude Ethyl a-Benzyloxymethylacrylate (EBzMA, hydroxymethyl monomer synthesis mixture 4b). Benzyl alcohol (4.15mL, 40.1 mmol) and (77.7 g, 0.596mol)) and a teflon-coated magne ECMA (2.88 g, 19.4mmol) were added to a tic stir bar were added to a three-neck round 50mL round-bottom flask in an ice bath. TEA bottom flask in an ice bath. A nitrogen purge (3.5 mL, 25.1 mmol) was added dropwise with was used to remove HCl gas evolved, which rapid stirring via magnetic stir bar and the re was then trapped in a basic solution. Thionyl actants heated to 68°C and allowed to stir for chloride (78.0 g, 0.656 mol) was added slowly 21 h. Ethyl ether (40mL) was added and the to the flask. After complete addition, the mixture extracted and worked up as above. solution was allowed to warm to room tem Vacuum distillation gave 98% pure ethyl ix perature and refluxed for one hour to con benzyloxymethylacrylate; 69% yield. vert the chlorosulfite intermediate to the pri Ethyl a-(3-Propionitrile)oxymethylacrylate mary chloride. Gas chromatographic (GC) (4c). ix-bromomethylacrylate (7.25 g, 37.6 analysis of the reaction mixture does not give mmol) was placed in a 50 mL round-bottom correct identification of intermediates; there flask in an ice-bath. 3-Hydroxypropionitrile fore, to ensure complete conversion, the (3.lmL, 45.4mmol) and TEA (10.5mL, 75.3 reaction was monitored by 13C NMR. Excess mmol) were added dropwise to the flask with thionyl chloride was removed by rotary evap rapid stirring via magnetic stirring bar.