Application of spin trapping technique to radical polymerization, 17.N-hydroxysuccinimide as a radical initiator

N-hydroxysuccinimide (NHS) and N-hydroxyphthalimide were found to initiate effectively vinyl polymerizations of acrylate monomers. The polymerization of methyl methacrylate (MMA) with NHS was investigated in detail. The polymerization rate (R_p) was found to depend highly on the solvents. The over-all activation energy of the polymerization in ethyl acetate was calculated to be 76,2 kJ/mol (18,2 kcal/mol). In the low monomer concentration, R_p can be expressed as R_p = k [NHS]^1/2 [MMA]^3/2. The copolymerization of MMA with styrene, initiated by NHS, could be shown to proceed via radical mechanism. In order to elucidate the initiation mechanism, spin trapping technique was applied to this polymerization system. In the reaction of MMA with NHS in acetone, the 2-carbomethoxypropyl radical was trapped by 2-methyl-2-nitrosopropane, a spin trapping reagent, to give the corresponding aminyl oxide radical 2 . From the results, the initiation mechanism of this polymerization is proposed and discussed.     

Application of spin trapping technique to radical polymerization, 12 The polymerization of N-vinylcarbazole with benzoyl peroxide

To clarify the initiation and propagation mechanisms of the polymerization of N-vinylcarbazole ( 1 ) initiated by benzoyl peroxide ( 2 ), the spin trapping technique using 2-methyl-2-nitrosopropane ( 5 ) was applied. From the ESR spectrum observed from this system, the 1-(N-carbazolyl)-2-benzoyloxyethyl radical ( 6a ) was found to be trapped as its nitroxyl radical 6b , which was confirmed by a comparison with similar nitroxyl radicals ( 7b and 8b ) derived from the systems, di-tert-butyl peroxalate/ 1/5 and 2 /N-ethylcarbazole/ 5 , respectively. Therefore, it was concluded that the 1/2 system produces easily a primary propagating radical of 1 viz. 6a . Further, the monomer 1 was found to show a remarkable accelerating effect on the radical decomposition of 2 . From the copolymerization of 1 with styrene initiated by 2 , it was concluded that 6a propagates by ordinary successive ß-attack to the monomer 1 .     

Application of the spin trapping technique to radical polymerization, 19. Reactions of the tert-butoxyl radical with some N-alkyl-substituted acryl- and methacrylamides

The reactions of tert-butoxyl radical with some N-alkyl-substituted acryl- and methacrylamides were investigated at room temperature in benzene by means of the spin trapping technique. 2-Methyl-2-nitrosopropane (BNO) was used as a spin trapping reagent. The tert-butoxyl radical was found to undergo both hydrogen-abstraction from N-methyl groups and double bond addition in its reactions with N-methylacrylamide (NMAm) and with N,N-dimethylacrylamide. Contrary to this, the benzoylthio radical reacted exclusively with the double bond of NMAm. In the reaction of the tert-butoxyl radical with N-methylmethacrylamide (NMMAm), only double bond addition was observed. However, when the tert-butoxyl radical reacted with N,N-dimethylmethacrylamide (NDMMAm), it mainly attacked the N-methyl group of NDMMAm. The tert-butyl radical abstracted a hydrogen atom from the α-methyl group of NMMAm and NDMMAm, keeping their N-methyl group unreacted. Furthermore, in the reaction of the tert-butoxyl radical with N-propyldimethacryloylamine (NPDMAm) in the presence of BNO, both a methylene radical which was derived from intramolecular cyclopropagation giving a five-membered ring and a radical derived from the addition to the double bond of NPDMAm were trapped as their aminyl radicals.     

Application of spin trapping technique to radical polymerization, 18. Initiation mechanism of vinyl polymerization with N,N-dimethylaniline N-oxide/acid anhydride systems

The mechanism of radical formation from the radical initiator systems N,N-dimethylaniline N-oxide (DMAO)/acid anhydride, was investigated by spin trapping technique. 2-Methyl-2-nitrosopropane (BNO) was used as spin trapping reagent. In the DMAO/acetic anhydride system, both methyl and N-methylanilinomethyl radicals were trapped by BNO as the corresponding amine N-oxyl radicals. However, only ethyl and undecyl radicals were trapped from DMAO/propionic anhydride and from DMAO/lauric anhydride system, respectively. In the DMAO/benzoic anhydride system, the amine N-oxyl radical derived from N-methylanilinomethyl radical and another amine N-oxyl radical were observed. The latter one is likely to be derived from a radical formed by hydrogen abstraction from the methyl group of DMAO by a benzoyloxyl radical. When the concentrations of DMAO and benzoic anhydride were lowered, phenyl radical was also trapped. From these findings, the initiation mechanism of vinyl polymerization with the DMAO/acid anhydride systems was proposed and discussed.     

Application of spin trapping technique to radical polymerization, 14. Initiation reaction of vinyl monomers with the tert-butoxyl radical and evaluation of monomer reactivities

The initiation of various vinyl monomers with tert-butoxyl radicals derived from the decomposition of di-tert-butyl peroxalate (DBPOX) was investigated by using the spin trapping technique with 2-methyl-2-nitrosopropane (BNO), to detect and identify the intermediate radical species, and to evaluate the monomer reactivities toward the tert-butoxyl radical. When the reaction of DBPOX with vinyl monomers, which have no α-methyl group (CH₂?CH(X)), was carried out in the presence of BNO at room temperature, the propagating radical 1 ((H₃C)₃CO? CH₂? CHX) was trapped as its nitroxyl radical. However, in the cases of using α-methylvinyl monomers (CH₂?CH(X)CH₃), such as methyl methacrylate and methacrylonitrile, two kinds of radicals, 6 ((H₃C)₃CO? CH₂? C(X)(CH₃), similar to 1 ) and 8 (CH₂?CH(X)CH₂), were trapped as corresponding nitroxyl radicals. The coupling constants of the nitroxyls obtained from 1 and 6 were determined and discussed on the basis of their structure. When these reactions were performed in a reference solvent, p-xylene, the above radicals, 1 (or 6 ) and/or 8 , together with the p-tolylmethyl radical ( 2 ), were trapped as their nitroxyls. From the ESR peak areas the relative reactivities of vinyl monomers toward the tert-butoxyl radical were evaluated and found to depend not only on the polar nature, but also on the resonance effect of the substituents. In α-methylvinyl monomers such as methyl methacrylate, the hydrogen-abstraction from the α-methyl group by the tert-butoxyl radical was important.     

Application of spin trapping technique to radical polymerization, 13 Polymerization of methyl methacrylate with 1,2,3,10a-tetrahydrophenanthrene-1,2-dicarboxylic anhydride

The polymerization of methyl methacrylate (MMA) with 1,2,3,10a-tetrahydrophenanthrene-1,2-dicarboxylic anhydride (TH) ( 10 ), which is a stable Diels-Alder adduct of α-vinylnaphthalene and maleic anhydride, was investigated by kinetic and spin trapping methods. TH could induce radical polymerizations of MMA and methyl acrylate with a considerably high rate, and the rate of polymerization (R_p) of MMA was found to follow the equation: R_p = k[TH]^0,3 [MMA]^1,6. The overall activation energy and the chain transfer constant to TH for this polymerization were determined to be 47,7 kJ/mol and 0,52, respectively. From these results, an initiation mechanism involving a hydrogen-transfer from TH to MMA was proposed, which is similar to Mayo's initiation mechanism for the thermal polymerization of styrene. To confirm this mechanism, the spin trapping technique was applied. The results obtained regarding the trapping of the initiating radicals supported this hydrogen-transfer initiation mechanism.     

Application of spin trapping technique to radical polymerization, 11. Initiation and propagation mechanisms for alternating copolymerization of styrene with maleic anhydride

The initiation mechanism for spontaneous alternating copolymerization of styrene (St) with maleic anhydride (MAn) was investigated by means of spin trapping technique. using 2-methyl-2-nitrosopropane ( 7 ) as spin trapping agent. By means of ESR spectroscopy of the system St/MAn in ethylbenzene, a cyclic radical ( 13 ), produced via the Diels-Alder intermediate 25 , was detected as its aminyl oxide. A similar radical was also trapped from the system p-methyl-St/MAn and p-dimethylamino-St/MAn. It is formed faster in these systems than in the system St/MAn. In chloroform, however, two types of initiating radicals. 13 and the α-styryl radical ( 15 ), were trapped. This indicates that these radicals are produced via 25 and the charge transfer complex 27 , respectively. From these results an initiation mechanism is proposed. To clarify further the propagation mechanism, the spin trapping technique was applied to the system, which is initiated by tert-butoxyl radical formed from di-tert-butyl peroxalate ( 8 ). The effect of the concentration of 7 on the ESR spectrum of the system St/MAn/ 8 shows that 27 also participates in the propagation of this alternating copolymerization. Finally, the high reactivity of 27 , as compared with free monomers in alternating copolymerization systems, was attempted to be explained on the basis of the Evans-Polanyi theory.     

Application of spin trapping technique to radical polymerization, 15. Photo-decomposition of dibenzoyl disulfide and evaluation of relative reactivities of vinyl monomers toward the benzoylthiyl radical

The mechanism of photo-decomposition of dibenzoyl disulfide (DBDS) in benzene or in monomers, and the evaluation of relative reactivities of various vinyl monomers toward the benzoylthiyl radical ( 4 ) were investigated by means of the spin trapping technique using 2-methyl-2-nitrosopropane (BNO). When DBDS photo-decomposed in benzene at 22±2°C in the presence of BNO, both 4 and benzoyl radicals were trapped as their nitroxyl radicals, indicating that both S? S and C? S bonds in DBDS were decomposed during its photolysis. However, when the photo-decompositions were performed in the monomers, propagating radicals ( 7 ) were trapped, but no allyl-type radicals ( 11 ). The coupling constants of the nitroxyl radicals of various propagating radicals were determined. From the ESR spectra of the systems DBDS/vinyl monomers/methyl methacrylate (as reference)/BNO the relative concentrations of the nitroxyls, [8]/[10, X = COOCH₃], were determined by computer simulation, and the relative reactivities of the vinyl monomers toward 4 were estimated. It was found that the relative reactivities of these monomers are correlated with their e values to give a linear relationship with a negative slope, similar to those toward the tert-butoxyl radical found in the previous paper.     

Application of spin trapping technique to radical polymerization, 16. Photo-decomposition of diphenyl disulfide and initiation mechanism: Evaluation of relative reactivities of vinyl monomers toward phenylthio radical

To clarify the initiation process in radical polymerizations with diphenyl disulfide (DPDS) as initiator, spin trapping technique was applied to the reaction of vinyl monomers with the phenylthio radical ( 1 ), which was produced by photolysis of DPDS. 2-Methyl-2-nitrosopropane (BNO) was used as a spin trapping agent. When DPDS was photo-decomposed in benzene in the presence of BNO radical 1 was trapped as the corresponding aminyl oxide radical 2 , which is unstable at room temperature. The photolysis of DPDS in vinyl monomers of type H₂C?CXY, however, gave only aminyl oxide radicals resulting from their propagating radicals C₆H₅S? CH₂? C˙XY. Contrary to the results obtained with tert-butoxyl radicals, radical 1 was found to undergo exclusively addition reaction to the double bond of the α-methyl-substituted monomers, such as methyl methacrylate or methacrylonitrile, with no hydrogen-abstraction reaction from their α-methyl group. Relative rates of the initiation reactions of vinyl monomers with radical 1 were also determined by spin trapping technique. It was found that the reactivities of vinyl monomers toward radical 1 are controlled by both polar and resonance effects.     

Vinyl polymerization, 307. Polymerization of acrylonitrile initiated by tetramethyl-2-tetrazene

The structure of the aggregates found in dilute solutions of PVC with tacticity 0,53 in THF has been investigated. It is shown that a model of an aggregate describing it as a composition of 10 to 15 single molecules bound together by a crystalline nucleus, is in accordance with the experimental evidence from light-scattering and GPC analysis.     

Vinyl polymerization 270. Polymerization of methyl methacrylate initiated by azibenzil

The polymerization of methyl methacrylate initiated by azibenzil (AB) was studied kinetically. The initial rate of polymerization (R_p) was found to be expressed by the equation R_p = k[AB]^0.47[MMA]^0.97. The polymerization proceeded through a radical mechanism. The overall activation energy for the polymerization was estimated as 16.1 kcal/mole. Furthermore, the rate of decomposition of AB was measured in benzene and the following rate equation was obtained: k_d[sec^?1] = 5.75·10¹⁰ exp(-21.9 kcal/RT). From these results the initiation mechanism was discussed.     

Vinyl polymerization. 186. Polymerization of methyl methacrylate initiated by 9-anthryldiazomethane

A study of the polymerization of methyl methacrylate initiated by 9-anthryldiazomethane (ADM) has been made. The initial rate of polymerization, R_p, followed the equation: This equation may be interpreted by the termination reaction of the growing radical with the primary radical. The rate of decomposition of ADM was measured in bulk or in benzene solution and the following rate equation was obtained:      

Vinyl polymerization. 238. Polymerization of acrylonitrile initiated by tetramethyl tetrazene and benzyl chloride

A study of the polymerization of acrylonitrile (AN) initiated by tetramethyl tetrazene (TMT) and benzyl chloride (BC) system was made. It was found that the polymerization proceeds through a radical mechanism. The initial rate of polymerization, R_p, followed the equation: From the results the initiation mechanism was discussed.     

Vinyl polymerization initiated by the dimethylaniline N-oxide/tosyl chloride system

A study of the vinyl polymerization initiated by the system dimethylaniline N-oxide (DMAO) in conjunction with tosyl chloride (TsCl) has been performed. According to the kinetic results of the polymerization of methyl methacrylate (MMA) and of the copolymerization of MMA with styrene, the polymerization proceeds via a radical mechanism. The rate of polymerization is given by the following equation: and the overall activation energy was calculated to be 14.3 kcal · mole^?1. According to the UV spectrum, the poly-MMA obtained probably contains N-methylanilinomethyl end groups. A graft polymer was obtained by polymerization of MMA with DMAO and partially chlorosulfonated polyethylene (Hypalon-30). From the results an initiation mechanism is proposed and discussed.     

Vinyl polymerization by metal complexes, 17. Effect of nitriles on the vinyl polymerization initiated by imidazole-copper (II) complex

Polymerization of vinyl monomers initiated by the imidazole-copper(II) complex was studied in dimethyl sulfoxide solution. Different from the case of acrylonitrile, the polymerization of styrene and methyl methacrylate did not proceed, even in the presence of various sort of nitriles. From these findings and the copolymerization behaviour of acrylonitrile with styrene and methyl methacrylate, together with the spectroscopic data, the presence of acrylonitrile monomer is essential for generating active species to initiate the polymerization.     

A study on initiation of vinyl polymerization with diacyl peroxide-tertiary amine systems by spin trapping technique

To characterize the intermediate radicals produced in the initiation of vinyl polymerization with binary systems of diacyl peroxides and tertiary amines, spin trapping technique was applied by using 2-methyl-2-nitrosopropane ( 8 ) as a spin trapping reagent. In the reactions of N,N-dimethylaniline ( 2a ) and N-N-diethylaniline ( 2b ) with benzoyl peroxide ( 1a ), N-methylanilinomethyl ( 7 ) and N-ethylanilino-1-ethyl radicals ( 16 ), respectively, were trapped, contrary to benzoyloxyl ( 4a ) and phenyl radicals which were not trapped. This was explained by assuming that benzoyloxyl radicals ( 4a ) react faster with 2a or 2b to give the radicals 7 and 16 , than being trapped with 8 . From this, 4a and 7 or 16 were concluded to be the initiating radicals in these systems. In the reaction of lauroyl peroxide ( 1b ) with 2a or 2b , however, undecyl radicals were trapped together with the radicals 7 or 16 . In the case of N-ethyl-N-methylaniline ( 2c ) both, N-ethylanilinomethyl ( 18 ) and N-methylanilino-1-ethyl radicals ( 20 ), were trapped. Further, it was found that in the reaction of 1a with poly(p-dimethylaminostyrene), both poly{1-[4-(N-methyl-N-methylylamino)phenyl]ethylene} ( 22 ) and phenyl radicals were trapped, contrary to the reaction of 1a with 2a .     

Vinyl polymerization. 284. Polymerization of methyl methacrylate initiated by 4.4′-diazidoazobenzene

The kinetics of the radical polymerization of methyl methacrylate (MMA) with 4.4′-diazidoazobenzene (DAAB) as initiator was investigated in benzene solution. It was found that the initial rate of polymerization (R_p) can be expressed by the equation: The overall activation energy for the polymerization was estimated to be 20.5 kcal/mole. The polymer obtained by the polymerization of MMA initiated by the above initiator was found to contain azobenzene fragment, presumably as endgroup. The thermal decomposition of DAAB was also studied in the temperature range 110 to 130°C. The overall activation energy of the decomposition of DAAB was 35.2 kcal/mole. The polymerization mechanism is discussed on the basis of these results.     

Vinyl polymerization. 235. Free radicals in the polymerization of vinyl monomers initiated by GOMBERG's and its relatad reactions

Free radicals derived from the GOMBERG 's reaction of arylmethyl halides such as benzyldiphenylmethyl-, and tritylbromide and chloride, with silver powder or mercury can initiate the radical polymerization and copolymerization of styrene, methyl methacrylate, acrylonitrile, vinyl chloride, and vinyl acetate. The orders of initiating abilities of halides in the polymerization of styrene and methyl methacrylate were as follows; for bromides, benzyl- > diphenylmethyl- > trityl-, and for chlorides, diphenylmethyl- > benzyl- > trityl-, when silver was used as metal component, while the order for the both halides is diphenylmethyl- > benzyl- > trityl- with mercury. These results were understood by the competition of the reactivities of halides to metal with those of the derived radicals to monomer. The over-all polymerization rate of the system styrene/silver/benzyl bromide was proportional to monomer concentration, square root of halide concentration, and square root of the amount of added but insoluble silver powder. The radical-like composition curves of styrene-methyl methacrylate copolymers and the inhibition of polymerization by verdazyl, a stable free radical, show that these polymerization systems include radical propagation step. Hexaphenylethane and 1.1.2.2-tetraphenylethane were isolated from the reaction systems, trityl halide/silver and diphenylmethyl chloride/silver or mercury, respectively. Recombination products of verdazyl with diphenylmethyl radical and benzyl radical were also isolated, but not N-trityl-verdazyl. Tracer study with benzyl bromide-7?¹⁴C showed the incorporation of benzyl fragments in the obtained polymer.     

Vinyl polymerization, 425. Radical polymerizations of vinyl monomers initiated with diphenyl disulfied and urea

Polymerizations of vinyl monomers initiated with diphenyl disulfide ( 1 ) and urea were carried out in 1,4-dioxane/water (vol. ratio 7:3). Methyl methacrylate (MMA) and methacrylic acid were found to be easily polymerized with this system, whereas the polymerization of styrene and acrylonitrile is not initiated. The polymerization was found to proceed by a radical mechanism. The polymerization of MMA was kinetically investigated.