Synthesis and End Use Evaluation of Pinene-based Alicyclic Acrylates

__ _._, ,,,..,.....,,..,,._;,_,‘.,,.,,._._-._.,:_s,...., .. . .. W Synthesis and End Use Evaluation of Pinene-based Alicyclic Acrylates V. VIJAYALAKSHMI, J.N. RUPAVANI and N. KHISHNAMURTF Organic Coatings and Polymers, Indian Institute of Chemical Technology, Hyderabad 500 007, India ABSTRACT Alicyclic mono "and diacrylates from or-pinene and B-pinene derivatives were synthesised and characterized spectroscopically. They were then compounded in alkyl 2-cyanoacrylate adhesives as crosslinkers. Their effect on the adhesive bond strengths after exposing the adhesive bonds to various ‘temperatures, was studied. _ Kev Wono: Acrylate ' INTRODUCTION Poor heat resistance of alkyl 2-cyanoacry- late adhesives especially on metal surfaces has prompted a number of attempts to improve this limitation. Various non-cyanoacrylate modifiers were proposed over thelast two decades; they were dialkenyl phthalates, acrylic and methacrylic esters“ 2. * t The improvement in heat resistance ofthe adhesive bonds at depended on the formation of _a't_hree-dimen- sional networkot the additive,‘ which may aiso co-react radically with the 2-cyanoacrylatei Therefore new acrylic esters irom pinenes (Scheme 1) were prepared to study their effects on the heat resistance of 2-cyanoacryiate ad- hesive bonds. ’ EXPERIMENTAL Materials Propyl cyanoacrylate was prepared in our laboratory. The details of the synthesis and its properties are already ' Correspondence author. J. Polym. Mater. 13- (1996) 127-131 © Oxford & IBH Publishing Co. Pvt. Ltd. Journal of Polymer Materials June 1996 elevated temperature. reporteds. . _ Polyethylene glycol 200 dimethacrylate was also prepared by us and its synthesis and properties are reported earlier‘. ' All the rest of the chemicals used in this investigation are of 95 per cent pure. Synthesis of Acrylic Esters from a- and 13- pinenes Mono and diacrylic esters were prepared from u~ and it-pinenes as shown in Scheme 1. ' D _. N _ - ,3-I-Cl-t:CH3 HOMO‘ ‘ o n;c=c_H—c-ncl o '-'--=—C—a _ -—-.—-........y.. (I.-pincne I t‘£._-aénnnarlwtot _l_. 5 £Luur¢,_ 8 A . C-‘CREE N 0’ N2 on PQCIECKCOCE '.E..¢p¢.cNz _.._......_... _ . . ‘ 9 . _ K K-pincnzgtyaohg _§_ ’(Coht.) 128 V. Vijayalakshmi, J.N. Fiupavani and N. Krishnamurti 0 $0" mcncuoocr $/°‘E"¢"=€"1 '----:-1- S5 "°’ it-plume FR‘-oearuol 3 1 new amen); 0 onion C1505-cH=cNz ' 0" 11,c=cn—ooc1 0-¢'¢""¢*'2 __.—-—n- 2,10 ll-r1inone_uiol _L_ I Preparation of ketol (1). Pulverized potassium per- manganate (100 g, 0.63 mol) was added over a period of 10 h to a ice cold stirred solution of a-pinene (50 g. 0.36 mol) in 90% aq. acetone (440 mL). The reaction mixture was stirred at 0-5°C. for an additional 24 h. It was then filtered, distilled to remove acetone and extracted with ether. The combined ethereal extracts were washed with water and saturated aqueous sodium bicarbonate. dried and concentrated to give an oily product, which was then distilled-to give ketol boiling point: 113—115°C (17 mm Hg). Yield (%): 33.5 g (55); lR (neat) (cm“): 3610, 3500. 1720; ‘H-NMR (CDCl;;) 5 (ppm): 2.60-1.65 (m, 7H), 1.38 (s, 3H), 1.32 (s, 3H), 0.88 (s. SH). Preparation of glycol (2). To a solution- of powdered lithium aluminium hydride (1.6 g, 0.042 mol) in ether (90 mL) was added dropwise under nitrogen blanket with stir- ring, a solution of ketol (1). (5.9 g, 0.31 mol) in ether (50 mL) at such a rate so as to maintain a gentle rell_u_x. Alter complete addition, the mixture was heated to reflux for 0.5 h and was allowed to cool. Next, water (5 _mL). and_ aqueous 15 percent Na0H (1.5 mL) solution were added to the mixture and stirred for one hour to ensure decom position of the reduction complex. The mixture was filtered and the granular precipitate was washed with several por- tions of ether. Thecombined extracts were waslfied-with water, dried and concentrated togive a colorless solid. which was purified by eluting with hexane : ethylacetate mixture (75 : 25 v/v) through a silica gel packed column. Yield (%): 2.31 g (43); IR (neat), cm"‘: 3610, 3420; NMR (CDCl3) 5 (ppm): 3.96 (d, 1H), 2.65-1.33 (n1. 6H), 1.29 (s, 3H), 1.26 (s. 3H), 0.93 (s, 3H), Preparation of pinocarveol (3). A solution of selenium dioxide (0.74 g, 0.007 mol) in tart. butane! (150 mL) was taken into a- flask fitted with a mechanical stirrer, ther- mometer, dropping tunnei and retiux condenser. (3-pinene (68 g, 0.5 mol) was then introduced. The resulting mixture was warmed to 40°C. Then aqueous 50% H202 (35 mL, 0.52 mol) was added dropwise over a period of 30 minutes while the mixture was maintained at 40—50°C. After stirring for a period of 2 h, the reaction mixture was diluted with benzene (50 mL), washed with aqueous saturated am- monium sulfate and dried over anhydrous sodium sulfate. A small amount of hydroquinone was added and the sol- Journal of Polymer Materials June 1996 ‘ _ vents were stripped off. The product was then purified by distillation under reduced pressure. Boilling point: 60-70°C (1.5 mm Hg): Yield M): 35 g (46), IR (neat), cm“: 3360, 1650, 1380, 1360, 897; NMR (CDCI3) 5 (ppm): 4.93 (d, 2H), 2.50-2.12 (m, 7H), 1.35 (s, 3H), 0.687 (s, 3H) Preparation of dial (4).. Sodium borohydride (1.014 g, 0.026 mol), diglyme (30 mL) and pinocarveol (10 g. 0.065 mol) diluted with 5 mL or diglyme were placed in a flask equipped with a condenser and titled with a CaCl2 guard tube, a pressure equalizing dropping funnel, a thermometer and a magnetic stirring bar were placed. The flask was immersed in a water bath at 20-25°C. Diborane was generated by dropwise addition ol boron triliuoride ethereate (4_.59 mL, 0.036 mol) to the well stirred reaction mixture over a period of 15 min. The‘ mixture was stirred for an additional hour at 30°C. The excess . sodium borohydride was decomposedby the addition of 8 mL water. "The organoborane thus formed was oxidized at 30°C by adding 3 M aqueous NaOH solution (8 ml.) fol— . lowed by dropwise addition of 30% hydrogen peroxide (7.5 mL) to the well stirred reaction mixture. The reaction mix-‘ ture was stirred for an .additional.h_our and extracted with 70 mL of ether and washed with ice water to remove diglyme. The “ether extract was dried over anhydrous mag- nesium sulfate and the solvent was removed by distillation. The crude product was purified through a silica gel packed column using hexane. ethyl acetate (75:25 v/v) mixture as eluent. 1 . . T Yield (°/..): 8 g (59.2); lR_(n_eat), cm“: 3350, 1330, 1370; ‘H-NMR (CDCl;,). 5 (ppm): 4.87 (d, 2H), 2.5—1.62 (m, 7H), 1.31 (s, 3H), 0.667 (s, 3H), - Preparation of monoacrylates (5, 7). Acryloyl chloride (0.03 mol) ‘was addedgradually to an ice cooled mixture of alcohol (0.03 mol), . triethylamine (0.06 mol), hydro: quinone, and chlorolorm (160 mL). The solution was heated to reflux for 2 h. After cooling, the mixture was poured into cone. l-iCi_ (4.9lml_)_and water (65 mL)_ and extracted three times with petroleum ether (b.pL: 4l}—60°C). The crude product was purified over a column of silica gel (finer than 200 mesh) and oluting with hexane to give the purified product. 7 Preparation of diacryiates (6, 8). Two rhcrylates (6, 8) from diols (2, 4) were prepared by taking alcoholand acryloyl chloride in 1:2 mole ratio and following the prose dure described lor monoacrylates5'7. 6 These alicyclic acrylates were characterized by lFt, NMR and mass spectroscopy. infrared Spectroscopy (ER) The lR spectra were recorded using Perkin-Elmer (Model 221) spectrophotometer. The absorption bands for C=O stretching vibrations at 1725 cm“ and for 0-0 hen purified by Yield (Va): 35 g 360. 897: NMR n, 7H). 1.35 (s, 'dride (1.014 g, ol (10 g. 0.065 aced in a flask a CaCl2 guard a thermometer The flask was Diborane was Jron tritluoride stirred reaction ure was stirred excess sodium dition of 8 mL ‘as oxidized at lion (8 mL) fol- . in peroxide (7.5 :e reaction mix- ! extracted with ater to remove inltydrous mag- d by distillation. llica gel packed vlv) mixture as ": 3350. 1330, _i)_, 2.5—1.s2 (m, lcryloyl chloride cooled mixture 6 mol), hydro- a_ solution was re mixture was ar (65 mt.) "and (b.p.: 40—60°C). imn of silica gel zane to give the «ciacrylabs (6. 8) ng alcohol and wing the proce- tcterized by lR, ) lg Perkin-Elmer rption bands for ‘ and for 0-0 ;.-.-».-;.-.—/9.x.»-t-.-.-.-.t,..-aw.-.-4-.«..~.-.... ... . . . . . Acrylates Synthesis and End Use Evaluation of Pinene-based Alicyclic Acrylares 129 TABLE 1. ‘H—NMR (5 ppm) Values of Acrylates from Pinenes 8 ppm values. of alkyl protons 3-Keto pinyl acrylate (5) 0.37 (s, 3H). 1.37 (5, 31-1), 1.62 (s, 3H), 1.95-3.02 (in, 6H) Pinocarveyl acrylate (7) 0.75 (5, 3H), 1.33 (s. 3H). 4.75 (