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Radical Telomerization of Olefin with Lsocyanide

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Radical Telomerization of Olefin with Lsocyanide 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.
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