Polymer Journal Vol. 1, No. 5, pp 591-596 (1970)

Radical Telomerization of Olefin with lsocyanide

Takeo SAEGUSA, Yoshihiko !To, and Naohiko YASUDA

Department of Synthetic Chemistry, Faculty of Engineering, Kyoto University, Kyoto, Japan. (Received July 17, 1970)

ABSTRACT: Radical telomerization of olefin with isocyanide was studied. As the isocyanide telogen, t-butyl and benzyl isocyanides were employed. In the telomerizition of ethylene, isobutyl vinyl ether and ethyl trans-crotonate, telomers having degrees of polymerization below four as well as the isomerized product of cyanide were isolated by GLPC, and the structures of oligomers were shown to be expressed by the general formula,

In the case of styrene, acrylonitrile, methacrylate, and 1,3-pentadiene, no low oligomer was isolated and polymers having the above general formula were produced. The chain transfer constant of !-butyl isocyanide in the thermal polymerization of styrene at 100°C was determined to be 0.33x 10-2• The chain transfer reaction of isocyanide was schema­ tized on the basis of the telomer structures and the radical-reaction behavior of isocyanide. KEY WORDS Radical Telomerization / !-Butyl Isocyanide / Benzyl Isocyanide / Chain Transfer Constant / Telogen / Imidoyl Radical/ Ethylene/ Isobutyl Vinyl Ether/ Ethyl Crotonate / Styrene

This paper describes the radical telomerization R-NC + In, - [R-N=C-In] ---"> of olefin with isocyanide. This study is an R-+InN (2) extension of our studies on the free radical re­ (In. from a radical initiator) actions of isocyanide.1- 3 The free radical re­ actions have been schematized by assuming the R· + R-NC ---"> [R-N=C-R] fi-scissio~ corresponding imidoyl radical (I) as the key 1' ! R· + RCN ( 3) intermediate. I i R-NC + R'. - [R+N=C-R'] - It is suggested from the above reaction scheme (I) that t-butyl and benzyl isocyanides may function as a chain transfer reagent in the radical poly­ R- + R'CN ( 1) merization of olefin. In the present study, t­ (R=t-butyl, benzyl) butyl and benzyl isocyanides have been actually agents in In the radical reactions of t-butyl and benzyl found to be powerful chain transfer isocyanides, the imidoyl radicals (I) derived from the radical polymerization of olefins. A mixture these isocyanides undergo .B-scission, resulting of telomers (II) having varying degrees of poly­ in the formation of t-butyl and benzyl radicals, merization was formed along with the cyanide respectively. In particular, the radical isomeri­ (III) of the isomerization product. zations of !-butyl and benzyl isocyanides to the R-NC + )C=C< ,corresponding cyanides (eq 3)4 explicitly present I I characteristic reactivities of N-t-butyl- and R-(-C-C-)-CN + RCN ( 4) the I I " N-benzylimidoyl radicals, as is indicated in the (II) (III) following scheme. (n=l, 2. 3, ···)

591 T. SAEGUSA, Y. ITO, and N. YASUDA

Table I. Telomerization of olefin with isocyanide as telogena DTBP I I R-NC + n )C=C( ------,. R-(C-C);;CN I I Yields of telomers, mmol Recovered Isocyanide, Olefin, Cyanide, isocyanide, 30mmol 45mmol n=l n=2 n=3 n=4 mmol mmol __c 25.0 0 ( CH,-CHO/ro-Bu 6.4 3.6 2.6 _d 17.2 0 t-BuNC _d _d CH3CH=CHCO2Et 11.6 6.8 6.4 2.8 0.7 CH2=CH2° 17.7 6.3 2.2 1.1 _f _f _f 7.4 10.6 PhCH2NC {cH2=CHO;so-Bu 4.8 _d _d _d 9.3 11.6 0.5

a Conditions: Chlorobenzene, 7 ml; di-t-butyl peroxide, 3 mmol; 130°C, 24 hr in a sealed tube. I I b a is the ratio of I; R-(C-C),.CN/RCN n I I c Isomerization reaction of isocyanide under the same conditions except for the absence of olefin. d Not detected. e t-Butyl isocyanide 50 mmol, ethylene 37 atm., 130°C, 24 hr in a stainless steel tube. r Not determined.

RESULTS AND DISCUSSION (n=l-4 in II). However, in this case the fairly high telomer, having an average molecular Telomerization of Olefin weight of 850, was also isolated as a waxy solid The results of telomerizations of olefins with from methanol. In the case of styrene, acrylo­ isocyanide as telogen in the presence of di-t­ nitrile, methacrylate and 1,3-pentadiene, only butyl peroxide (DTBP) are shown in Table I. high polymers were produced, and the amount Telomers having different degrees of polymeri­ of isomerized cyanide was only minute. The zation were isolated separately by GLPC and IR and NMR spectra of these polymers show their structures were adequately determined by the presence of both t-butyl (or benzyl) and NMR and IR spectra as well as by elemental cyanide groups in the polymer chain. analyses. On the basis of the consideration that N-t­ In the reactions of isobutyl vinyl ether and butyl( or benzyl)imidoyl radical readily under­ crotonate with t-butyl or benzyl isocyanide under goes /3-scission to produce the corresponding the conditions indicated in Table I, a telomer cyanide and t-butyl (or benzyl) radical, the fol­ mixture (n= 1-3 in II) was obtained along with lowing reaction scheme will explain the formation the isomerized cyanide. Higher telomers could of the telomer as well as the side reaction of not be detected. The reaction of ethylene with the isomerization to the corresponding cyanide. t-butyl isocyanide also produced a telomer mixture

R-NC + In- - [R-N=C-In] - R- + InCN ( 5) (In· from radical initiator) ~ [R-N=C-R] - R- + RCN (isomerization) ( 6 ) R--I 1 I R-NO I I • I I ----,. [R-C-C-] ----,. [R-C-C-C=N-R] - R-C-C-CN + R· ( 7) )O=C( I I I I ! l ln )C=C< (telomerization)

I I I R-NC I I • [R-(-C-C-);;;-C-C-] ----,. [R-(-C-C-)n+1C=N-R] I I I I I I I ----,. R-(-C-C-Jn+1CN + R- ( 8 ) 1 I

592 Polymer J., Vol. 1, No. 5, 1970 Radical Telomerization of Olefin with Isocyanide

I-Butyl (or benzyl) radical produced via p-scission ed, the polystyrene thus obtained contains both of N-t-butyl(or benzyl)imidoyl radical can add cyano and t-butyl groups in its polymer chain. to either isocyanide or olefin. Therefore, the As another possibility, a N-t-butylimidoyl radical ratio (a) of the total amounts of telomers (II) formed from the reaction of the growing poly­ to that of isomerized cyanide (III) may be taken styrene radical with t-butyl isocyanide may as a measure of the relative reactivity of olefin attack further styrene monomers without under­ toward the t-butyl (or benzyl) radical. As seen going p-scission. This reaction might ultimately in Table I (last column), it is obvious that olefin lead to the formation of a copolymer which having an electron withdrawing substituent, such contains the imino units(-~- )in the polymer as crotonate, has a higher reactivity toward the N-Bu-t I-butyl (or benzyl) radical. This finding is ex­ chain. However, this possibility is quite unlikely plained by both the resonance and inductive from the inspection of the reaction products. effects of the carboxylate substituent. This sub­ The IR spectrum of the polymer did not show stituent stabilizes a neighboring radical by the any absorption of the )C=N- bond. In addition, resonance effect. Moreover, as the t-butyl (or the absence of the isocyanide unit in the polymer benzyl) radical is considered to have a nucle­ was shown by the absence of a carbonyl group ophilic character, the electron-withdrawing group in the acid-treated polymer. The polymer was may also favor the reactivity of olefin. treated with aq HCl solution and then subject­ Chain Transfer Constant of t-Butyl Isocyanide in ed to reaction with 2,4-dinitrophenylhydrazine. the Thermal Polymerization of Styrene The formation of hydrozone was not detected. t-Butyl isocyanide is considered to be a new These findings indicate that the N-t-butylimidoyl type of chain transfer reagent in the radical radical intermediate formed by the reaction of polymerization of olefin. It is interesting to the growing polymer radical with t-butyl iso­ compare it with CC1 4 , one of the typical chain cyanide undergoes p-scission exclusively, result­ transfer reagents. In the former, chain transfer ing in a !-butyl radical which starts a new occurs throught the p-scission of the imidoyl polymerization. The chain transfer constant of radical formed from the reaction of the growing t-butyl isocyanide in the thermal (100°C) poly­ polymer radical with the isocyanide, while in merization of styrene was determined according the latter it occurs through the abstraction of an to Mayo's equation7 (eq 10) atom from CC1 4 by the growing polymer radical. 5 ' 6 -L=c___@l_+-L (10) P [M] P 0

in which P and P0 are the degrees of polymeri­ zation of the styrene polymers formed in the ( 9) presence and absence of t-butyl isocyanide, re­ The reactivity of !-butyl isocyanide as a chain­ spectively, and [SJ and [M] are the concentra­ transfer reagent in the thermal polymerization tions of t-butyl isocyanide and the styrene of styrene was examined by determining the monomer, respectively. chain transfer constant. As previously mention- The conversions % of the styrene polymeri-

Table II. Thermal polymerization of styrene in t-butyl isocyanidea [t-BuNC] CM]) Yield, % [r;], 100 m//g Mx IQ-4 p (1/P)x 104 [Styrene] - [SJ 0.000 9.98 1. 77 36.8 3538 2.83 0.101 9.39 1.15 21.8 2096 4.77 0.202 8.11 0.60 9.7 929 10.76 0.288 6.73 0.53 8.3 797 12.55 0.416 5.83 0.42 6.2 588 16.72 a Reaction conditions: 100°C, 4.5 hr.

Polymer J., Vol. 1, No. 5, 1970 593 T. SAEGUSA, Y. ITo, and N. YASUDA

zation were below 10%. The average molecular a solvent) and 3 mmol of di-t-butyl peroxide weight was calculated from viscosity measure­ (DTBP) was heated under nitrogen in a sealed ment according to the equation8 tube at 130°C in an oil bath for 24 hr. The telomerization of ethylene was carried out in a (11) stainless-steel microautoclave. After the reaction, in which (r;] is intrinsic viscosity in dl/g, and the reaction mixture was subjected to fractional Mis the number-average molecular weight. The distillation, and the distillate was analyzed by results obtained are given in Table II. The GLPC. Each fraction was isolated by preparative chain transfer constant (C) in eq 10) was deter­ GLPC. The structures of the products were mined to be 0.33 x 10-2 from the slope of a examined by IR and NMR spectra and elemental straight line of the plot of 1/ P vs. [S]/[M] analysis.

18 Telomers from Reaction of Isobutyl Vinyl Ether and t-Butyl Isocyanide

15 (CH3)aCCH2CHCN : Bp 87°C (10 mm); IR I OCH2CH(CH3)2 12 (neat) 2280 cm-1 (very weak, 1JceeN); NMR I st • 0 (CDCl3), a 4.10 (triplet, lH, -CHCN), 3.35 - 9 X (multiplet, 2H, -OCH2CH-), 1.5-2.2 (multiplet, -J1a.. 3H, -OCH2CH(CH3)2 and (CH3)3CCH2CH-), 1.00 6 • (singlet, 9H, (CH3)3C-) and 0.95 ppm (doublet, 6H, -CH2CH(CH3)2) 3 Anal. Calcd for C11 H 21 ON; C, 72.08; H, 11.55; N, 7.64. Found: C, 72.14; H, 11.36; N, 0 0.1 0.2 0.3 0.4 0.5 7.55. [Sl/[Ml (CH3)3-(-CH2CH-kCN : It was isolated I Figure 1. The plots of 1/P vs. [S]/[M] (data from OCH2CH(CH3)2 Table II). by the preparative GLPC from the fraction of bp 100-l20°C (3.5 mm); IR (neat) 2280 cm-1 (Figure 1). This value indicates the high re­ (very weak, lJCeeN); NMR (CDCl3), a 4.25 (triplet, activity of t-butyl isocyanide towards a free lH, -CH(CN)O-), 2.9-3.8 (multiplet, 5H, radical. -CH2CHOCH2- and -CH(CN)OCHz-), 1.2-2.2 (multiplet, 6H, (CH3)3CCH2-, 2 x -OCH2CH(CH3)2 EXPERIMENTAL and-CHCH2CH(CN)O-), and 0.8-1.1 ppm (mul­ Reagents tiplet, 21H, (CH3)3CCH2- and 2 x -OCH2CH(CH3)z). Olefinic compounds were commercial reagents, Anal. Calcd for C17H 3p 2N: C, 72.04; H, 11.74; which were purified by the usual procedures N, 4.94. Found: C, 72.17; H, 11.97; N, 4.81. and distilled under nitrogen before use. Styrene (CH3)aC-~CH2CH-)a-CN : It was isolat- 1 was purified in the following way: commercial OCH2CH(CH3)z styrene monomer was washed successively with ed by the preparative GLPC from the fraction sodium thiosulfate aq solution, water, sodium of bp 140-164°C (3.5 mm); IR (neat), 2280 cm-1 hydroxide aq solution and water, dried over (very weak, vceeN); NMR spectrum is very similar barium oxide, and finally distilled under to that of the 1 : 2 telomer (n=2).

nitrogen. Isocyanides were prepared according Anal. Calcd for C 23H 4p 3N: C, 72.01; H, to Ugi's procedure9 and purified by distillation 11.82; N, 3.65. Found: C, 72.24; H, 12.03; N, using a spinning band column under nitrogen. 3.45. General Procedure of Telomerization Telomers from Reaction of Ethyl trans-Crotonate A mixture of 30 mmol of isocyanide, 45 mmol with t-Butyl Isocyanide of olefinic monomer, 7 ml of chlorobenzene (as (CH3)3CCH(CH3)CH(CN)CO2C2H 5 : Bp 104°C

594 Polymer J., Vol. 1, No. 5, 1970 Radical Telomerization of Olefin with Isocyanide

(9.5 mm): IR (neat) 2280 (weak, l.lc=N) and 1750 the preparative GLPC from the fraction of bp cm-1 (strong, l.lc=0); NMR a 4.35 (quartet, 2H, 100-130°C (3 mm); IR (neat) 2270 cm-1 (weak, -CO2CH2CH3), 3.75 (doublet, J=3 Hz, lH, l.lC=N); NMR (CDCI) o 1.35 (triplet, 2H, - , I -CH(CN)CO-), 2.1 (multiplet, lH, -CHCH(CN)-), -CH2CH2CN), 1.8-1.1 (multiplet, JOH, (CH3)3- (-C.Ey:::_!!2-)TCH2CHd, and 0.90 ppm (singlet, 1.35 (triplet, 3H, -CO2CH2CH3), 1.15 (doublet, 9H, (CH3)sC-). 3H, (CH3)3CH(CH3)-) and 1.05 ppm (singlet, 9H, Anal. Calcd for C11H N: C, 78.97; H, 12.65; (CH3)C-). 21 N, 8.37. Found: C, 78.70; H, 12.82; N, 8.43. Anal. Calcd for C11H 19O2N: C, 66.97; H, 9.71; It isolated N, 7.10. Found: C, 67.05; H, 9.74; N, 7.36. (CH3)sC-(-CH2CH2-)4 CN: was from the fraction of bp 140-148°C (3 mm) IR (CH3)3C-(CH-CH-)s-CN : It was isolated I I (neat) 2260cm-1 (weak, l.lc=N); NMR (CDC13) a CH3 CO2CH2CH3 2.30 ppm (triplet, 2H, -CH2CH2CN), 1.8-1.l by the preparative GLPC from the fraction of (multiplet, 14, (CH3 )C-(-CH2CH2-)3 CH2CH2-), bp 100-128°C (3.5 mm); IR (neat), 2280 (weak, and 0.85 ppm (singlet, 9H, (CH3) 3C-). vc=N) and 1730 cm-1 (strong, l.lc=o); NMR (CDC13) Anal. Calcd for C 13H 25N: C, 79.93; H, 12.90; o 4.25 (multiplet, 4H, 2 x-CO2CH2CH3), 3.8 N, 7.17. Found: C, 80.22; H, 12.83; N, 7.01. (broad singlet, lH, -CHCNCO-), 2.5-2.0 I I Telomers from Reaction of Isobutyl Vinyl Ether (multiplet, 2H, -CH-CH(CO2C2H5)CH- and with Benzyl /socyanide I - CH3CHCH(CN)-), and 1.6-0.8 ppm (multiplet, C6H5CH2CH2CH(CN)OCH2CH(CH3)2: Bp 109- I l ll 0C (1 mm); IR (neat) 2240cm-1 (very weak, 22H, (CH3)3C-, (CH3)3CCH(CH3)-, -CHCH(CH3)- 1 l.lc=N); NMR (CDCla) a 7.25 ppm (singlet, 5H, CH- and 2x CO CH CH ). 2 2 3 C 6H5CHd, 4.05 (triplet, lH, -CH(CN)O-), 3.35 Anal. Calcd for C 17H 29 O4N: C, 65.56; H, (multiplet, 2H, -OCH2CH-), 2.85 (triplet, 2H,

9.39; N, 4.50. Found: C, 65.28; H, 9.61; N, C 6H5CH2CHd, 2.4-1.6 (multiplet, 3H,

4.58. C 6H5CH2CH2CH-) and OCH2CH(CH3)2), and 0.95 Telomerization of Ethylene with t-Butyl Isocyanide ppm (doublet, 6H, -CH(CH3) 2). Into a microautoclave (50 ml) containing 50 Anal. Calcd for C14H 19NO: C, 77.38; H, mmol of !-butyl isocyanide and 5 mmol of DTBP, 8.81; N, 6.45. Found: C, 77.15; H, 8.99; N, ,ethylene was charged to 35 kg/cm2. The micro­ 6.49. autoclave was heated at 130°C for 24 hours, and Chain Transfer Constant of t-Butyl Isocyanide in then the reaction mixture was subjected to the Styrene Polymerization. distillation. Preparation of Polystyrene Sample (CH3)3CCH2CH2CN: It was isolated by the The reaction of styrene with !-butyl isocyanide preparative GLPC from the fraction of bp 70- was carried out under nitrogen in a glass tube. 790C (9 mm); IR (neat) 2270 cm-1 (weak, l.lc=N); Weighed amounts of styrene (50-75 mmol) and NMR (CDC13) a 2.1-2.5 (multiplet, 2H, !-butyl isocyanide (5-30 mmol) were placed in -CH2CN), 1.4-1.8 (multiplet, 2H, -CH2CH2CN), the tube, and the tube was attached to a vacuum and 0.95 (singlet, 9H, (CH3)3C-). -- line. The tube was cooled by liquid nitrogen Anal. Calcd for C7H 13N: C, 75.61; H, 11.79; to freeze the contents, and then evacuated. This N, 12.60. Found: C, 75.88; H, 11.55; N, 12.82. proceeure was repeated three times. The tube (CH3)3C-(-CH2CH2-Je-CN: It was isolated by was then sealed and dipped into an oil bath the preparative GLPC from the fraction of bp maintained at 100±0.1 °C. After 5 hr (in order 90-120°C (9 mm); (neat) 2270 Cm-l (weak, l.lC=N); to hold to about 10% conversion), the reaction NMR (CDCl3) a 2.35 (triplet, 2H, -CH2CH2CN), mixture was dissolved in benzene 70 ml and then 1.8-1.1 (multiplet, 6H, (CH3)3CH2CH2CH2CHd, the solution was frozen in Dry Ice and subjected and 0.90 ppm (singlet, 9H, (CH3)3C-). to sublimation under reduced pressure to remove Anal. Calcd for C9H 17N: C, 77.63; H, 12.31; the remaining !-butyl isocyanide and styrene N, 10.06. Found: C, 77.40; H, 12.55; N, 9.93. monomer together with benzene. The obtained (CH3)3C-(-CH2CH2-)3 CN: It was isolated by solid was purified repeatedly by the benzene

'Polymer J., Vol. I, No. 5, 1970 595 T. SAEGUSA, Y. !To, and N. YASUDA freeze-drying method. Finally, the polystyrene 2. T. Saegusa, S. Kobayashi, and Y. Ito, J. Org .. thus obtained was dried in vacuo until constant Chem., 35, 2118 (1970). weight was achieved. 3. T. Saegusa, Y. Ito, N. Yasuda, and T. Hodaka,. J. Org. Chem. in press. Determination of Molecular Weight from Viscosity 4. T. Saegusa, Y. Ito, and N. Yasuda, unpublished. Solution viscosity was determined in toluene 5. R. A. Gregg and F. R. Mayo, J. Amer. Chem. at 30°C using an Ubbelohde viscometer. The Soc., 70, 2373 (1948). intrinsic viscosity, [l'}], was obtained from specific 6. S. L. Kapur, J. Polym. Sci., 11, 399 (1956). viscosities at three polymer concentrations. 7. F. R. Mayo, J. Amer. Chem. Soc., 65, 2324 (1943). REFERENCES 8. T. Alfrey, A. Bartovics, and H. Mark, J. Amer. Soc., 65, 2319 (1943). 1. T. Saegusa, S. Kobayashi, Y. Ito, and N. Yasuda, 9. I. Ugi and R. Meyr, Chem. Ber., 93, 239 (1969). J. Amer. Chem. Soc., 90, 4182 (1968).

596 Polymer J., Vol. 1, No. 5, 1970