Polymer Journal, Vol. 32, No. 2, pp 140~146 (2000)

Cyclopolymerization XXVIII. Radical Polymerizations of N-Substituted N-Methallyl-2-(methoxycarbonyl)allylamines : Polymerizability ofUnconjugated Dienes with Functional Groups with Low Homopolymerization Tendency

Toshiyuki KoDAIRA t, Michio URUSHISAKI, and Norio KAsAJIMA

Department of Materials Science and Engineering, Faculty of Engineering, Fukui University, 3-9-1 Bunkyo, Fukui 910-8507, Japan

(Received July 8, 1999)

ABSTRACT : Radical cyclopolymerizations of N-substituted-N-methallyl-2-(methoxycarbonyl)allylamines (1) were studied to compare their cyclopolymerizabilities with those of N-substituted-N-allyl-2-(methoxycarbonyl)allylamines (2). Monomers 1 with a phenyl(la) and a t-butyl(lb) group as an N-substituent were employed. The phenyl group was cho­ sen, since 2 with an N-phenyl group(2a) was reported to have exceptionally low polymerization tendency among 2. Monomer lb was polymerized to see whether the bulky N-t-butyl group enhances the cyclization tendency of 1 or not, since 1 with an N-methyl group(lc) was reported to yield polymers with pendant unsaturations, though their content is low. It was found that polymerizations of la proceed very slowly like 2a, but the reason for their slow polymerizations was left unsolved. Polymers with high degree of cyclization, 96% for poly(la) and 100% for poly(lb), were obtained even in their bulk polymerizations. This could be an additional support for the proposal made previously. It states that uncon­ jugated dienes, for which monofunctional counterparts do not have homopolymerization tendency yield highly cyclized polymers. This is because both the monofunctional counterparts of 1 are considered to have essentially no homopolym­ erization tendency. The bulky t-butyl group was found to be effective to enhance cyclization tendency also in 1. Struc­ tural studies showed that poly(la) and poly(lb) contain both six- and five-membered rings as repeat cyclic units. Mecha­ nism for intramolecular cyclization was discussed. KEY WORDS Radical Cyclopolymerization I 1,6-Diene I a-Substituted Acryloyl Group / Methallyl Group I Repeat Cyclic Unit / Degree of Cyclization I

Cyclopolymerizations of N-phenyl- and N-t-butyl-N­ methallyl-2-(methoxycarbonyl)allylamines (la and lb, respectively)(see Scheme 1) were undertaken to see the effect of the N-substituents on their cyclopolymerization behavior. The reasons why these groups were chosen as N-substituents are as follow. It has been proposed that the use of functional groups with a higher conjugative nature together with no homopolymerization tendency is R 2 essential for the design of 1,6-dienes with not only a high cyclization tendency but also high polymerizability. 1 N­ 1a 2a Substituted-N-allyl-2-(methoxycarbonyl)allylamines 0 1 2 · al­ (2) and N-methyl-N-methallyl-2-(methoxycarbonyl) 1b C(CH3b 2b lylamine (le) 3 are the monomers that were synthesized and polymerized to establish the validity of the proposal. 1c CH 3 2c Their a-substituted acryloyl groups were found to have a high conjugative nature, though they do not show ho­ Scheme 1. mopolymerization tendency when they exist as monoene 1 2 compounds. • However, polymerization behavior of 2 changed considerably depending on their N-substituents. Another interesting point of this study is structural in­ For examples, 2a polymerized exceptionally slowly de­ vestigations on repeat cyclic units of poly(l). The struc­ spite the fact that its a-substituted acryloyl group has a tures of the polymers derived from various diallyl com­ 7 high conjugative nature. Polymerizations of la were un­ pounds were compared in the previous paper. It showed dertaken to see how is the effect of N-phenyl group on that the substituents on their olefinic double bonds tend the polymerizations of 1, because le polymerized rapidly to favor the formation of a six-membered ring probably in accordance with the proposal.3 Bulky substituents due to the steric and radical stabilizing effect. Monomers have been known to enhance the cyclization tendency of 1 which have a structure with an additional methyl 4 6 unconjugated dienes. - This led us to the studies of cy­ group on the allyl group of 2 are supposed to yield poly­ clopolymerizations of lb to see whether the bulky N-t­ mers with a considerable amount of a six-membered ring butyl group enhances the cyclization tendency of 1 or not, as a repeat cyclic unit, different from poly(2) which con­ 1 2 since le yielded polymers with a small amount of pen­ sist exclusively of a five-membered ring. • In fact, le dant methallyl groups. yielded polymers which consist almost exclusively of a six-membered ring as a repeat cyclic unit.3 Present in­ tTo whom correspondence should be addressed. vestigation may provide us valuable information on how

140 Design of 1,6-Dienes with High Cyclization Tendency the influence of the N-substituents on the structures of placed in glass ampoules, which were then subjected to the repeat cyclic units ofpoly(l) is. several freeze-pump-thaw cycles and sealed. After poly­ merization in a constant-temperature bath, the polymer­ EXPERIMENTAL ization mixtures were poured into excess petroleum ether. Conversion of the monomer was calculated from Materials the weight of the polymer along with the residual mono­ Monomers 1 were synthesized by the equimolar reac­ mer concentration measured by gas chromatography tion between methyl a-(bromomethyl)acrylate (BMA) (GC) with tetralin as the internal standard, since some and corresponding amines based on the procedure for portion of their polymers was found to be soluble in pe­ 1 2 the preparation of 2. · Crude products obtained were troleum ether. The polymers were reprecipitated from subjected to repeated distillations to give pure liquids. benzene solution into petroleum ether to obtain pure Yields of the final stage of the synthesis of these mono­ polymers for measurements. mers were from 40 to 60% after distillations two times. Group-transfer polymerizations were carried out ac­ 8 11 The supposed structures were confirmed by NMR. The cording to the procedure reported, • using MTMP and boiling points and chemical shifts of the characteristic TBABB as initiator and catalyst, respectively. absorption peaks of 1H and 13C NMR spectra of 1 are as follow. Boiling point of la: 124°C/0.4 mmHg. 1H NMR Measurements 1 13 for la : o= 7.17 (m, m-C6H5), 6.67 (t, p-C6H5), 6.60 (d, o• H NMR and C NMR spectra were taken on a JEOL 1 13 or a C6H5), 6.26 (s, CH2 =, acryloyl), 5.55 (s, CH2 =, acryloyl), JNM-GX-270 (270 MHz for H and 68 MHz for C) 1 125 MHz for 13C) FT 4.86 (s, CH2 =, methallyl), 4.80 (s, CH2 =, methallyl), JEOL LA-500 (500 MHz for H and 4.19 (s,>N-CHd, 3.80 (s,>N-CHd, 3.79 (s,-O-CH3), NMR spectrometer using CDC13 and tetramethylsilane 13 Size and 1.73 (s, CH2 =C (C!!a) -) ppm. C NMR for la : o = as a solvent and an internal standard, respectively. 166.9 (>C=O), 148.2 (>N-C=), 140.2 (CH2 =_Q (CH3)-), exclusion chromatography (SEC) was performed on a equipped 135.3 (CH2 =Q<, acryloyl), 129.0 (m-C6H5), 124.9 (_QH 2 Shimadzu LC-lOAD liquid chromatograph =C<, acryloyl), 116.5 (p-C6H5), 111.9 (o-C6H5), 110.6 with three polystyrene gel columns (Shodex K-804L) using (_QH 2 =C (CH3) -), 56.2 ( > N-CHd, 51.8 (-O-CH3), 51.3 and ultraviolet/refractive index dual-detectors (>N-CHd, and 20.0 (CH2 =C (CH3) -) ppm. Boiling chloroform as eluent. A molecular weight calibration point oflb: 82°C/0.l mmHg. 1H NMR for lb : o=6.16 (s, curve was obtained by using standard polystyrene. GC GC-8A gas chroma­ CH2 =, acryloyl), 5.94 (s, CH2 =, acryloyl), 4.84 (s, CH2 =, was carried out on a Shimadzu methallyl), 4.69 (s, CH2 =, methallyl), 3.73 (s,-O-CH3), tograph equipped with a silica gel column (Shimadzu 3.32 (s, > N-CHd, 3.00 (s, > N-CHd, 1.68 (s, CH2 = C DC-11). Viscosity was measured using a Ubbelohde vis­ 13 (C!:!3) -), and 1.08 (s, (C!!3)aC-) ppm. C NMR for lb : cometer at 30°C in N, N-dimethylformamide. 0=167.7 (>C=O), 145.7 (CH2 =_Q (CH3)-), 141.3 (CH2 =_Q<, acryloyl), 125.5 (_QH 2 =C<, acryloyl), 111.7 (_QH2 RESULTS =C (CH3) -), 57.3 ( > N-CHd, 55.2 ((CH3)a_Q-), 51.5 (-0 lb CH3), 50.8 (> N-CHd, 27.0 ((_QH3)aC-), and 20.7 (CH2 = Polymerizations of la and C (_QHa)-) ppm. The results of the polymerization of la and lb are Bis(2-methoxycarbonylallyl)aniline (10) was prepared summarized in Table I along with the reported results of 1 2 by the reaction of BMA with aniline based on the proce­ le and 2 · that are given for comparison. The degrees of 1 dure reported for a similar compound.8 White crystal cyclization determined based on H NMR spectra were with mp 67-68°C was obtained in 80% yield by recrys­ found to be 96% for poly(la) and 100% for poly(lb) (see tallization from methanol. 1 H NMR for 10 : o= 7 .18 (t, next section). In accordance with these structural char­ samples are sol­ m-C6H5), 6.71 (t,p-C6H5), 6.59 (d, o-C5H5), 6.28 (s, CH2 =, acteristics, both poly(la) and poly(lb) assumed acryloyl), 5.59 (s, CH2 =, acryloyl), 4.19 (s,>N-CHd, uble in common solvents. It can be reasonably 13 of 1, N-substituted and 3.80 (s,-O-CH3) ppm. C NMR for 10 : o= 166.8 ( > that both the monoene counterparts C=O), 147.6 (>N-C=), 134.9 (CH2 =_Q<), 129.2 (m-C6 N-isobutyl-2-(methoxycarbonyl)allylamines(3) (see Sch­ N-substituted N-methallyl-2-(methoxycar­ H5), 125.1 (_QH 2 =C<), 116.9 (p-C6H5), 111.8 (o-C6H5), eme 2) and 51. 9 ( > N-CHd, and 51.2 (-O-CH3) ppm. bonyl)propylamines (4), have extremely low homo­ BMA was prepared by the reported procedure.9 N-t­ polymerizability. This is because N-substituted N-propyl- Butyl-, and N-phenylallylamines were synthesized ac­ 2-(methoxycarbonyl)allylamines (5) which have almost cording to the procedure reported for the synthesis of N, the same structure as 3, have been reported to have es­ 1 2 N-diethylallylamine.10 sentially no homopolymerization tendency • and ex­ Commercial 2,2' -azobisisobutyronitrile (AIBN) was tremely low homopolymerizabilities of methallyl com­ recrystallized from ethyl alcohol. 1-Methoxy-1-(trimeth­ pounds is well-known. For this reason, high cyclization ylsiloxy)-2-methyl-1-propene (MTMP, Tokyo Kasei) was tendency of these monomers could be an additional sup­ used as received. Tetrabutylammonium bibenzoate port for the principle for the monomer design for the syn­ (TBABB) was synthesized based on the reported proce­ thesis of highly cyclized polymers. It states that the bi­ dures.11 All common solvents were purified by the usual functional monomers, for which monofunctional counter­ methods. parts do not polymerize are likely to give rise to highly 12 13 cyclized polymers, if they polymerize at all. • However, Polymerization the results of the polymerizations of 1 show that the cy­ Radical polymerizations were performed in sealed clization tendency of 1 is slightly lower than that of 2. tubes. A given amount of monomer and initiator were This is because le investigated previously yielded poly-

Polym. J., Vol. 32, No. 2, 2000 141 T. KoDAIRA, M. URUSHISAKI, and N. KASAJIMA c~} c~} c:tF N N I 3 I 4 I 5 R R R

Seheme2. 6

Table I. Polymerizations of 1 and related compounds in bulk at 60 °C IAIBN]o Time [11] DC" Conversion/ % No. Monomer(MX !03) -h~ Mn Mw!Mn dL g-1 % Preb GC' l~~o 1 la 112 24 5100 2.3 96 11 23 2 lb 112 12 100 32 49 ---- :l~J: 5 N 2 3 lb 28 4 100 5 I I 4 lb 28 12 0.08 100 16 R R 5d le 112 1.2 6400 2.5 0.22 97 74 9 6d le 28 4 9300 2.3 0.24 71 78 8 5 7• 2a 28 2 20000 2.0 100 Seheme3. 7• 2a 28 10 100 36 8• 2b 28 4 0.16 100 73 9d 2e 112 0.3 100 80 lQf 2e 6 0.7 0.28 100 22 llg 10 5 5900 1.5 97 84 "Degree of cyclization. bDetermined by weight. 'Determined by GC.

mers with degree of cyclization of 97%,3 while all 2 in­ C vestigated afforded completely cyclized polymers irre­ 1 2 spective of the N-substituents. • The results summarized in Table I show that polym­ D erization tendency of 1 decreases with a following order, a b lc>lb>la. It is clear that N-substituents influence in a similar manner for both 1 and 2. This is because 2c po­ lymerizes most rapidly and 2a most slowly among 2. When polymerizabilities of 1 are compared with those of 2 with a same N-substituent, the former are always 8 7 6 5 4 3 2 lower than the latter. b (ppm)

1H NMR spectra of poly(l) and 1. (A) Poly(l Pendant Unsaturations of Poly(la) and Poly(lb) Figure 1. 270 MHz a) (No. 1 in Table I); (B) olefin protons of la; (C) poly(lb) (No. 2 2-(methoxycarbonyl)al­ A methallyl group (6) and a in Table I); (D) olefin protons of lb. lylamino group (7) are the pendant unsaturations which appear in poly(l) (see Scheme 3). 1H are expected to 13 NMR spectra ofpoly(l) are illustrated in Figure 1 along illustrated in Scheme 3. Proton noise decoupled C with absorptions due to olefin protons of 1. Comparison NMR spectra of poly(la) for higher and lower magnetic of these spectra clearly indicates that poly(la) contains field regions are depicted in Figures 2A and 3A, respec­ small amount of pendant methallyl groups, while the tively. The spectra shown in Figures 2B and 3B were ob­ spectrum of poly(lb) shows formation of completely cy­ tained by DEPT (Distortion Enhancement by Polariza­ clized polymers. Degrees of cyclization of poly(la) listed tion Transfer) measurements of poly(la) under the con­ up­ in Table I were determined based on the signal intensi­ ditions where methyl and methine carbons appear ties of methallyl protons detected at around 4. 7 ppm and wards and methylene carbons downwards. Comparison the absorptions due to phenyl protons detected over the of these spectra allows the assignment of the absorption 13 region from 6.3 to 7.5 ppm. signals of C spectrum of poly(la) shown in Figure 2A. However, the complicated spectral pattern does not al­ Repeat Cyclic Units of Poly(la) low detailed assignment of the each peak. Further, the is Extremely lower contents of pendant unsaturations appearance of the absorptions due to phenyl carbons of indicate that repeat cyclic units of poly(l) are 8 and/or 9 also complicated, as can be seen from the observation Polym. J., Vol. 32, No. 2, 2000 142 Design of 1,6-Dienes with High Cyclization Tendency

rNCH3 3. 2' I D -C- 1 (C5 l D -c-I ( '(C3) 4' 4' 1'

B

B

4' 3,3' A 2'

1' A >C=O 4

I -C- 180 160 140 120 & (ppm) Figure 3. 125 MHz 13C NMR spectra. (A) Poly(la) (No. 1 in Ta­ ble I ) ; (B) DEPT spectrum of poly(la) measured under the condi­ upwards and CH 70 60 50 40 30 20 tions where CH3 and CH carbons are detected 2 carbons downwards; (C) poly(lO) (No. 11 in Table I ) ; (D) stick (ppm) o spectrum of poly(ll) depicted based on the spectrum reported for Figure 2. 125 MHz 13C NMR spectra. (A) Poly(la) (No. 1 in Ta­ the polymer. ble I ) ; (B) DEPT spectrum of poly(la) measured under the condi­ CH tions where CH3 and CH carbons are detected upwards and 2 carbons downwards; (C) poly(lO) (No. 11 in Table I); (D) poly(lc) (No. 5 in Table I). 2A. Considerable differences can be seen between the spectral patterns of the phenyl carbons of poly(lO) and two peaks for a quaternary carbon adjacent to nitrogen poly(ll) which are illustrated in Figures 3C and 3D, re­ 13 (peaks 1 and 1' in Figure 3A). For this reason, the spec­ spectively. Substituent effect on C chemical shifts of 16 tra of polymers derived from compounds with similar monosubstituted benzenes was studied extensively. It structures to la were compared with those of Figures 2A revealed that they are influenced strongly by electron and 3A. 13C NMR spectra for higher and lower magnetic withdrawing or electron donating power of the substitu­ field regions of a polymer obtained by a group transfer ents. The assignment for the phenyl carbons shown in polymerization (GTP) of bis(2-methoxycarbonylallyl) Figure 3C was made based on these reported results. aniline(lO) are shown in Figures 2C and 3C, respectively. Appearances of the absorption signals of poly(lO) and Its repeat cyclic unit is supposed to be a six-membered poly(ll) indicate that conjugation between the lone pair 8 11 ring, judging from the mechanism of GTP. • Figure 2D electrons on nitrogen and the benzene ring is more effi­ 16 is the spectrum of a higher magnetic field region ob­ cient in the latter than in the former. This suggests served for poly(lc) which consists almost exclusively of that a bulkier six-membered ring than a five-membered six-membered rings.3 Figure 3D shows the stick spec­ ring interferes with the coplanar conformation between trum of phenyl carbons of a polymer derived from N­ piperidine and benzene rings. Comparison of the spectra phenyldiallylamine(ll). It was depicted based on the of Figures 3 indicates that poly(la) contains both five­ spectrum of poly(ll) and its peak analysis reported by and six-membered rings as repeat cyclic units and the Johns et al.14 The polymer was obtained by a radical po­ former is the main component. This structural charac­ lymerization and its repeat cyclic unit has been identi­ teristic can also be recognized from the spectral analysis fied to a five-membered ring. 13C Chemical shifts re­ at higher magnetic field. Methylene carbons detected at ported for model compounds with piperidine and pyr­ the region from 26 to 37 ppm in Figure 2A are attribut­ rolidine ring structures (Scheme 4) are listed in Table able to those of main chain attached to five-membered 7 15 chain lI , • which were used to assign the spectrum of Figure rings (C6 and C7 carbons of 9), because main

Polym. J.. Vol. 32, No. 2, 2000 143 T. KDDAIRA, M. URUSHISAKI, and N. KASAJIMA

Table II, 13C NMR chemical shifts of 12," 13, a and poly(2c)h in ppm Model compounds C2 C3 C4 C5 C6 N-CH3 12 69.1 31.5 50.4 31.5 69.1 47.1 13 69.8 44.1 44.1 69.8 42.6 poly(2 c) 61.6-64.3 54.6, 56.8 46.7, 50.6 61.6-64.3 42.4 "Quoted from ref 15. hQuoted from ref 7. methylene carbons (C4 and C7) of poly (le) (Figure 2D) that consists of six-membered rings were detected at H3C 4 CH3 definitely different chemical shifts. A quaternary carbon H3CUCH3 detected at 59 ppm in Figure 2A can be attributed to C3 5 N 2 6 N 2 This is because C3 carbon of poly carbon of 9 of poly(la). I I CH (2c) (Scheme 4) was detected at around 55 ppm (Table 3 CH 3 in this region for II). No quaternary carbon was observed poly(2c) 12 13 the spectrum of poly(lc) (Figure 2D). The peaks due to Scheme 4. quaternary carbons can also be seen at around 36 and 46 ppm in Figure 2 A The former can be attributable to a C5 carbon of 8, since C3 and C5 carbons of 12 are ob­ at served at 31.5 ppm, while C3 and C4 carbons of 13 are carbons of 8 in poly(la) and poly(lc) are detected detected at 44.1 ppm. The peaks at around 46 ppm are around 46 and 36 ppm, respectively, almost the same assigned to a C3 carbon of 8 according to the spectral chemical shifts as those of these two polymers. This sug­ analysis ofpoly(lc) (Figure 2D) and poly(lO) (Figure 2C). gests that poly(lb) also contains a six-membered ring as However, the peak detected at around 36 ppm is signifi­ a repeat cyclic unit. However, the peak intensity at cantly weak as compared with that observed at around around 36 ppm is considerably weak as compared with 46 ppm. The ratio, 3 to 5, was obtained for the former to that at around 46 ppm, which indicates the presence of a the latter, based on the peak intensities determined by considerable amount of a five-membered ring as a repeat the measurements under suppressed NOE as described cyclic unit as in the case ofpoly(la). Peak analysis at the below. Furthermore, the signal at 36 ppm is overlapped region from 52 to 54 ppm also supports this considera­ with that of methylene carbons as can be seen from the tion. This is because two peaks due to quaternary car­ comparison with DEPT spectrum (Figure 2B). The peaks bons, one at 52 and the other at 54 ppm, are detected. observed at around 46 ppm are considered to be contami­ The one should be attributed to the C3 carbon of 9 and nated with signals due to the C4 carbon of 9. The chemi­ the other to>N-Q (CH3) 3. The absence of the character­ cal shifts of C3 and C4 carbons of 13 given in Table ill ra­ istic peaks attributable to the two repeat cyclic units tionalize this consideration. The methylene carbons ad­ does not allow to estimate accurately the contents of jacent to nitrogen of poly(la) were detected at consider­ these two rings. The observations of> N-CH2- carbons of ably higher magnetic field than those of poly(lc). One poly(lb) at considerably high magnetic field as com­ reason for this might be ascribed to the effect of benzene pared with those ofpoly(lc) can be interpreted by taking ring through diamagnetic anisotropy and the other to y­ they-gauche effect into considerations. These N-methy­ gauche effect. Two ortho carbons could be gauche to lene carbons have possibility to be gauche to the three these methylene carbons. In the polymers derived from methyl carbons in the t-butyl group of poly(lb). No such N-substituted diallylamines, it was reported that> N­ carbon exists for N-methylene carbons ofpoly(lc). It has methylene carbons of poly(ll) were shifted to higher been reported that signals due to N -methylene carbons 9 ppm as compared with those of of poly(2 b) are observed at higher magnetic field than magnetic field by about 7 N-methyl derivative.14 those of poly(2 c) by about 10 ppm. This result also ra­ Two factors influence seriously on the peak intensities tionalizes the rather large difference between the chemi­ of 13C NMR spectra. One is nuclear Overhauser effect cal shifts of the N-methylene carbons of poly(lb) and 17 and the other is spin-lattice relaxation time (T1) . The poly(lc). longest T value determined using a progressive satura­ 1 13 tion method was 2.8 s for the carbonyl carbon of poly(l C NMR Studies of 1 and Related Compounds 13 a). 13C NMR spectrum of poly(la) was measured under C Chemical shifts ofC=C double bonds (C~H2 =Ca<) the suppressed Overhauser effect adopting 24 s for pulse of the acryloyl groups of 1 and related compounds are delay time which is long enough for the spins to recover. summarized in Tableill. Oca and OcB values shift to a The five-membered ring content was determined to be higher and lower magnetic field, respectively, with a lin­ 72% based on the peak intensities of the phenyl carbons ear relationship when e values of the monomers become adjacent to nitrogen (peaks 1 and 1' in Figure 3A). larger with increasing electron-attracting power of sub­ stituents.18 This means that the stronger the electron­ Repeat Cyclic Units of Poly(lb) attracting power of the substituents, the smaller the ~o A 13C NMR spectrum of poly(lb) is illustrated in Fig­ values, which was obtained by subtracting oc, from Oca ure 4. The assignment given in the figure was made by values. Comparison of the ~o of 1 indicates that conju­ comparing its spectral pattern with that of poly(la) and gation between the olefin and carbonyl double bonds in poly(lc). A spectrum obtained by DEPT measurements these compounds changes depending on the substituents also supported the assignment. Characteristic peaks on nitrogen according to the same trend as in the case of which have been attributed to C3 and C5 quaternary 2. The extent of conjugation between C = C and C = 0 J., Vol. 32, No. 2, 2000 144 Polym. Design of 1,6-Dienes with High Cyclization Tendency

Table III. 13C Chemical shifts of C~H2 =Ca< carbons of acryloyl groups of 1 and related compounds in CDCb >C=O oc, Oc., M" Compound ppm ppm ppm la 126.2 138.2 12.0 lb 125.5 141.3 15.8 Icb 124.9 135.3 10.4 180 170 MMA' 125.5 136.3 10.8 2ad 126.8 137.8 11.0 Ii, ppm 2bd 125.7 141.1 15.4 2ce 125.0 135.6 10.6 la 112.71 143.61 30.9 ",fo,-oc,. bQuoted from ref 3. 'Methyl methacrylate. aQuoted 1 from ref 2. eQuoted from ref 1. Chemical shifts of methallyl car­ bons.

I -C- has high conjugative nature. In the case of 2, the lowest I 1 -C- polymerizability was also observed for 2a, though the 1 conjugative nature of its a-substituted acryloyl group was found to be as effective as that of 2c which has the highest polymerization tendency.2 One possible reason for their slow polymerizations might be ascribed to lower conjugation between an unpaired electron and a C = 0 is brought 70 60 50 40 30 20 double bond in a propagating radicals, which reac­ ii, ppm about by conformational change during addition 19 tions of the monomers to polymeric chain ends. An­ 4. 68MHz 13C NMR spectrum ofpoly(lb) (No. 4 in Table I). Figure other is side reactions which are common to both la and 2a. They might be playing important roles to suppress rate in these two monomers, double bonds decreases, as the bulkiness of N-substitu­ the overall polymerization at present. Anyhow further ent on nitrogen increases. However, the conjugation of though they are unknown elucidate the cause for the slow po­ the acryloyl groups of 1 is considerably effective even in study is necessary to 2a. lb, judging from /10 of these compounds and methallyl lymerization of la and groups. High cyclization tendency of la and lb can be ex­ groups, the one of typical unconjugative 3 plained by a similar manner to that of lc. The intra­ (eq 1 and eq 1') pro­ DISCUSSION molecular cyclization reactions of 14 ceed preferentially over the intermolecular propagation form cyclized radicals 15 and 15' be­ The results obtained indicate that N-substituents in­ reaction (eq 2) to homopolymerization tendency of 3 fluence polymerizabilities of 1 in a similar manner to cause extremely low assumed. The methyl group on the those of 2. Steric hindrance of the bulky t-butyl group of can be reasonably to interfere slightly with the cy­ lb distorts the coplanarity between the C=C and C=O methallyl group seems these monomers, which results in double bonds of its a-substituted acryloyl group. This clization reactions in of the uncyclized radical (14) to would be the reason for a lower conjugative nature of its lowering the reactivity reactions (eq 1 and eq 1'). a-substituted acryloyl group. Monomers 1 are consid­ the intramolecular cyclization reason why slower polymerizations ered to be incorporated into the polymeric chain at first This could be the when their polymerizabilities were through their acryloyl groups, since their conjugative proceed in 1 than 2, with a same N-substituent. Only nature is higher than that of methallyl groups even in compared among those radical related to the a­ lb. The fact that only methallyl group was detected as the uncyclized propagating group was considered in the reac­ pendant unsaturations in poly(la) and poly(lc) supports substituted acryloyl in Scheme 5, since the first at­ this consideration. For this reason, the polymerization tion scheme illustrated radical to 1 is considered to be rate would decrease, as the conjugative nature of the tack of a propagating group as mentioned above. acryloyl groups decreases. Bulky substituents that de­ made on the acryloyl that differentiate the polym­ crease the extent of conjugation might also be unfavor­ One of the characteristics those of 2 exists in their repeat cyclic able sterically for the addition of the attacking radical to erizations of 1 from examination on the influence of the a-substituted acryloyl group. structures. Detailed compounds on the repeat cyclic Bulky substituents have been known to enhance the substituents of diallyl 4 6 therefrom revealed that these cyclization tendencies of unconjugated dienes. - This units of polymers derived form a six-membered ring, as sub­ can also be seen in the polymerization of 1. Completely 1,6-dienes tend to on olefinic double bonds.7 Based cyclized polymers were obtained from lb, while la and stituents are introduced 1 have been expected to yield poly­ le yielded polymers with a small amount of pendant un­ on the investigation, amount of a six-membered ring saturations. It can be understood that bulky substitu­ mers with a considerable different from 2 that formed selec­ ents can generally be utilized to enhance the cyclization as a repeat cyclic unit five-membered rings for their re­ tendency of 1,6-dienes. tively polymers with This is what has really been observed. The reason for the lowest polymerization tendency of 1 peat cyclic units. that the 2-methyl group of the a among 1 is not clear at present, since its acryloyl group It can be understood 145 Polym. J., Vol. 32, No. 2, 2000 T. KoDAIRA, M. URUSHISAKI, and N. KASAJIMA

dency, though the conformations of uncyclized radicals leading to five-and six-membered rings are considerably if· ___ it4"} different. N N N 1 I I 15 R R R REFERENCES AND NOTES

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146 Polym. J., Vol. 32, No. 2, 2000