Polymer Journal, Vol. 28, No. II, pp 1000-1005 (1996)
Cyclopolymerization XXIII. Design of Unconjugated Dienes with High Polymerizability Using Functional Groups with No Homopolymerization Tendency and Synthesis of Completely Cyclized Polymers Therefrom: Radical Polymerizations of N-Substituted N-Allyl-2-(methoxycarbonyl)allylamines
Qing-Qing LIU, Toshiyuki KoDAIRA,t Michio URUSHISAKI, and Tamotsu HASHIMOTO
Department of Materials Science and Engineering, Faculty of Engineering, Fukui University, Fukui 910, Japan
(Received June 19, 1996)
ABSTRACT: N-Substituted N-allyl-2-(methoxycarbonyl)allylamines (SAMC) were synthesized and polymerized to estab lish a methodology for designing unconjugated dienes with not only a high cyclization tendency but also high polymerizability. The N-substituents investigated were methyl, propyl, tert-butyl, and phenyl groups. Detailed examination of the properties of the unconjugated dienes reported so far indicated the use of functional groups with a higher conjugative nature together with no homopolymerization tendency to be essential to achieve this purpose. SAMC were designed since oc-substituted acrylates have a considerably higher conjugative nature, even if they do not have homopolymerization tendencies. In fact, conjugation between C=C and C=O double bonds of the acryloyl groups of SAMC and N-substituted N-propyl-2-(methoxycarbonyl) allylamines (SPMC), one of the monofunctional counterparts of SAMC, were found to be considerably effective. No detectable homopolymer could be obtained from SPMC. It is well known that ally! compounds, the other monofunctional counterparts of SAMC, have extremely lower polymerization tendencies. SAMC were converted to completely cyclized polymers by use of a radical initiator with a high polymerization rate, especially in the case of methyl and propyl derivatives. Their polymerizabilities were correlated with the conjugative nature of C = C and C = 0 double bonds of their acryloyl groups, except for the phenyl derivative. ESR studies on the methyl derivative suggested that its polymerization initiates through the acryloyl group. KEY WORDS Radical Cyclopolymerization / 1,6-Diene / oc-Substituted Acryloyl Group/ Ally! Group / Propagating Radical / High Cyclopolymerizability /
The principle for monomer design for the synthesis of cyclopolymerizabilities have not been investigated in highly cyclized polymers from bifunctional monomers terms of the polymerizabilities ofmonofunctional counter has been established. 1 - 5 It states that the bifunctional parts. Preliminary results reported on N-methyl-N-allyl- monomers whose monofunctional counterparts do not 2-(methoxycarbonyl)allylamine (MAMC) suggest the polymerize are likely to give rise to highly cyclized poly validity of the idea proposed. 6 The goal of this work mers, if they polymerize at all. However, the problem is to establish the concept with additional evidence has been the lower polymerization tendencies of the provided. ESR studies on MAMC and N-methyl-N-pro unconjugated dienes synthesized under this principle. pyl-2-(methoxycarbonyl)allylamine (MPMC) were also For this reason, we searched for monomers which not undertaken to obtain information on the mechanism of only have a high cyclization tendency but also high polymerization of these monomers. polymerizability. Detailed examination of the properties of unconjugated dienes designed under the principle suggested that the main reason for low polymerizability stems from the unconjugative nature of the functional c:rr groups and steric hindrance of substituents which inter N fere with the addition of an attacking radical. The use SAMC of functional groups with a higher conjugative nature together with no homopolymerization tendencies would thus appear essential to achieve the purpose. 6 N-Sub SAMC R SPMC stituted N-allyl-2-(methoxycarbonyl)allylamines (SA MC) were designed as monomers which fulfill the con MAMC CH3 MPMA ditions, since a-substituted acrylates have considerably PAMC CH2CH2CH3 PPMC higher conjugative nature, even if they do not have homopolymerization tendencies. 7 Their polymerization BAMC C(CH3h BPMC behavior was studied along with that of N-substituted PhAMC PhPMC N-propyl-2-(methoxycarbonyl)allylamines (SPMC), a 0 class of monofunctional counterparts of SAMC. Cyclo Scheme 1. polymerizations of several symmetrical and unsymmet rical unconjugated dienes having a-substituted acryloyl EXPERIMENTAL groups have already been reported. s- 16 However, their Materials t To whom correspondence should be addressed. SAMC and SPMC were synthesized by the equimolar 1000 Completely Cyclized Polymers from Unsymmetrical 1,6-Dienes
Table I. Boiling points and elementary analysis
bp• C/% H/% N/% Monomer Calcd Found Calcd Found Calcd Found
PAMCb 62/2 66.97 66.86 9.71 9.63 7.10 7.11 BAMCC 78/2 68.21 67.95 10.02 9.94 6.63 6.57 PhAMCa 105/0.2 72.39 72.23 7.81 7.51 6.03 5.95 PPMCe 88/3 66.30 66.03 10.62 10.54 7.03 7.05 BPMC' 65/0.1 67.57 67.52 10.87 10.86 6.57 6.61 PhPMC• 123/0.2 71.76 72.03 8.60 8.42 5.98 5.90
• Not corrected. b N-Propyl-N-allyl-2-(methoxycarbonyl)allylamine. c N-tert-Butyl-N-allyl-2-(methoxycarbonyl)allylamine. a N-Phenyl-N-allyl-2- (methoxycarbonyl)allylamine. e N,N-Dipropyl-2-(methoxycarbonyl)allylamine. 'N-tert-Butyl-N-propyl-2-(methoxycarbonyl)allylamine. • N-Phenyl N-propyl-2-(methoxycarbonyl)allylamine. reaction between methyl a-(bromomethyl)acrylate (BMA) Polymerization and corresponding amines based on the procedure for Polymerizations were performed in sealed tubes. A the preparation of MAMC and MPMC. 6 Crude products given amount of monomer and initiator were placed in obtained were subjected to repeated distillations to give glass ampoules, which were then subjected to several pure liquids. Yields of the final stage of the synthesis of freeze-pump-thaw cycles and sealed. After polymeriza these monomers were from 40 to 60% after distillations tion in a constant-temperature bath, the polymerization two times. The supposed structure was confirmed by mixtures were poured into excess petroleum ether. The NMR and results of elementary analyses. The boiling polymers were reprecipitated from benzene solution into points (bp) and results of the elementary analyses are petroleum ether to obtain pure polymers for measure shown in Table I. Chemical shifts of the characteristic ments. Conversions of the monomer for PAMC were absorption peaks of 1 Hand 13C NMR spectra of SAMC calculated from the weight of the polymer. In the case and SPMC other than MAMC and MPMC are as follow. of BAMC and PhAMC, they were determined from the 1HNMRforPAMC: 6=6.22(s, lH), 5.82(m, lH), 5.81 residual monomer concentration measured by gas chro (s, lH), 5.12 (t, 2H), 3.75 (s, 3H), 3.25 (s, 2H), 3.07 (d, matography with tetralin as the internal standard, since 2H), 2.39 (t, 2H), 1.46 (sextet, 2H), and 0.86ppm (t, 3H). some portion of their polymers was found to be soluble 13C NMR for PAMC: 6= 167.6, 138.7, 136.1, 125.9, in petroleum ether. Monomer conversions determined 116.9, 57.1, 55.8, 54.2, 51.7, 20.4, and 11.8 ppm. 1H NMR by the precipitation method for PAMC were essentially for PPMC: 6=6.19 (s, lH), 5.81 (s, lH), 3.75 (s, 3H), the same as those by gas chromatography. The absence 3.22 (s, 2H), 2.36 (t, 4H), 1.44 (sextet, 4H), and 0.85 ppm of polymer in the polymerization systems of PPMC, (t, 6H). 13C NMR for PPMC: 6= 167.8, 139.1, 125.6, BPMC, and PhPMC was confirmed by the precipitation 56.2, 55.0, 51.6, 20.4, and l 1.9ppm. 1HNMRforBAMC: method using petroleum ether as the non-solvent along 6=6.21 (s, lH), 6.03 (s, lH), 5.80 (m, lH), 4.86 (m, 2H), with 1H NMR using tetralin as an internal standard. 3.74 (s, 3H), 3.33 (s, 2H), 3.19 (d, 2H), and 1.08ppm (s, 9H). 13C NMR for BAMC: b= 167.7, 141.1, 138.7, 125.7, Measurements 115.2, 55.0, 53.3, 51.5, 49.2, and 27.3 ppm. 1H NMR for The molecular weight distribution of poly(PhAMC) BPMC: 6=6.22 (s, lH), 6.10 (s, lH), 3.75 (s, 3H), 3.31 was determined by size-exclusion chromatography (SEC) (s, 2H), 2.45 (t, 2H), 1.29 (sextet, 2H), 1.04 (s, 9H), and in tetrahydrofuran on a Shimadzu chromatograph equip 0.80ppm (t, 2H). 13C NMR for BPMC: 6= 167.8, 142.0, ped with three polystyrene gel columns (Shodex 80M x 125.5, 54.8, 53.4, 41.5, 51.1, 27.1. 23.6, and 11.9ppm. 2 and KF-203.5) and ultraviolet/refractive index dual 1H NMR for PhAMC: 6= 7.18 (m, 2H), 6.67 (m, 3H), detectors. The number-average molecular weight (M.) 6.26 (s, lH), 5.86 (m, lH), 5.60 (s, lH), 5.19 (m, 2H), and ratio of weight- to number-average molecular weight 4.16 (s, 2H), 3.93 (d, 2H), and 3.79ppm (s, 3H). 13C (Mw/ M.) were calculated on the basis of polystyrene NMR for PhAMC: 6= 166.9, 148.2, 135.6, 133.4, 129.1, calibration. 1 H NMR and 13 C NMR spectra were taken 125.0, 116.6, 116.4, 112.0, 52.9, 51.8, and 51.2ppm. 1H on a JEOL JNM-GX-270 FT NMR spectrometer using NMR for PhPMC: 6 = 7.20 (m, 2H), 6.63 (m, 3H), 6.23 CDC13 and tetramethylsilane as solvent and internal (s, lH), 5.53 (s, lH), 4.16 (s, 2H), 3.79 (s, 3H), 3.26 (t, standard, respectively. The ESR spectra were recorded 2H), 1.65 (sextet, 2H), and 0.93 ppm (t, 3H). 13C NMR using a flow system with a TE0l 1 mode cylindrical cavity for PhPMC: 6= 167.0, 147.8, 135.4, 129.2, 125.0, 116.0, of a JEOL JES-FElX spectrometer. The flow rate used 111.7, 52.9, 51.8, 51.6, 20.5, and 11.4ppm. was 2.5 cm 3 s - 1. This flow rate corresponds to the time BMA, 17 N-methylallylamine, 18 and N-methylpropyl lag before measurement of about 0.03 s. The method amine18 were prepared by the reported procedure. N• used for the generation of amino radicals was similar Propyl-, N-tert-butyl- and N-phenylallylamines, and N to that previously described. 20 The pH was adjusted to tert-butyl- and N-phenylpropylamines were synthesized 1.4 by adding sulfuric acid. The monomer concentration according to the procedure reported for the synthesis of used was usually 0.05 mol dm - 3. All measurements were N,N-diethylallylamine. 19 made at room temperature (25 ± 2°C). Viscosity was Commercial 2,2'-azobisisobutyronitrile (AIBN) was measured using a Ubbelohde viscometer at 30°C in N,N recrystallized from ethyl alcohol. All common solvents dimethylformamide. were purified by the usual methods. Polym. J., Vol. 28, No. 11, 1996 1001 Q.-Q. LIU et al.
Table II. Polymerizations of SAMC and related compounds at 60°C
[MJo [AIBN] 0 Time oc· [11] Conv. No. Monomer M M X 10 3 h % dLg- 1 %
I b MAMC bulk 6.06 0.3 100 0.24 7 2b MAMC bulk 6.06 0.7 100 0.28 20 3b MAMC 2.32 6.06 I 100 21 4 PAMC bulk 28.0 0.5 100 0.14 15 5 PAMC bulk 28.0 0.8 100 36 6 PAMC bulk 28.0 1 100 77 7 BAMC bulk 28.0 2 100 45 8 BAMC bulk 28.0 4 100 0.16 78 9c PhAMC bulk 28.0 2 100 5 10 PhAMC bulk 28.0 10 100 36 11 b MPMC bulk 112 48 0 12 PPMC bulk 112 48 0 13 BPMC bulk 112 48 0 14 PhPMC bulk 112 48 0 15d MAMA bulk 143 15 93 35 16' BAMA bulk 110 12 100 41 17' PhAMA bulk 99 12 94 33 18' MAA 2.31 6.06 I 60 23
• Degree of cyclization. b Quoted from ref 6. c M. = 2 x 104 , M w! M. = 2.0 determined by SEC. d Quoted from ref 2. 'Quoted from ref 22. r Quoted from ref 21.
RESULTS RAMA R
Polymerization of SAMC and SPMC :{r MAMA CH3 The results of the polymerization of SAMC and SP I R RAMA BAMA C(CH3)g MC are summarized in Table II. Reported results of N methylacrylamide (MAA)21 and N-substituted methac ~) PhAMA rylamides (RAMA) such as N-methyl-, 2 N-tert-butyl-, 22 0 N 0 I MAA and N-phenylmethacrylamides22 (MAMA, BAMA, and CH3 PhAMA, respectively) are also given in Table II for Scheme 2. comparison. SAMC yielded high polymers, while no detectable polymer could be obtained from SPMC, even polymerized to high polymers. Accordingly, RAMA are after prolonged polymerization time. This leads to the polymerized to yield highly cyclized polymers but with conclusion that the monoene counterparts of SAMC a lower polymerization rate, 2 •22 while MAA has high have essentially no homopolymerization tendency, be polymerizability but its cyclization tendency is low. 21 cause it may be reasonably assumed that the other mono Higher polymerizabilities in addition to higher cycliza functional counterparts of SAM C, ally! derivatives, have tion tendencies could be achieved in SAMC especially in extremely low polymerizability based on 13C NMR the case of methyl and propyl derivatives, irrespective of studies of the ally! group of SAMC shown later. The the fact that both of their monofunctional counterparts poly(SAMC) samples are soluble in common solvents, have extremely low polymerization tendencies as in RA which suggests the formation of highly cyclized poly MA. Another characteristic feature of polymerization mers. In fact, no pendant double bonds could be detected behavior of SAMC is that N-substituents influence sig in 1 H NMR spectra of poly(SAMC) (see next section). nificantly the polymerization of SAMC different from That the polymerizations were carried out in bulk is in that of RAMA as can be seen from Table II. 2 •22 dication of how high the cyclization tendency of SAMC is. These results could be additional support for the Structure of Poly(SAMC) principle for the monomer design for the synthesis of The repeating units which are expected to appear in highly cyclized polymers mentioned above. Molecular poly(SAMC) are 1--4 shown in Scheme 3. 1 H NMR weights and their distribution of poly(SAMC) obtained spectra of poly(SAMC) are illustrated in Figure I along could not be determined by SEC except for poly(PhA with absorptions due to olefin protons of SAMC. These MC), since they were not detected under the conditions described in the experimental section. For this reason, viscosities were measured to obtain information on mo ) lecular size. R-N It can be seen from Table II that polymerization l=o N N tendencies of SAMC are much higher than those of I I R-N R R RAMA2 ·22 and almost comparable to that of MAA21 except for PhAMC. The monofunctional counterparts ) 0 of RAMA do not polymerize, while one monoenconter 2 3 1°4 part of MAA, N-methyl-N-propylacrylamide, can be Scheme 3.
1002 Polym. J., Vol. 28, No. II, 1996 Completely Cyclized Polymers from Unsymmetrical 1,6-Dienes
1 3 Table III. C Chemical shifts of CµH 2 = C, < and carbonyl carbons of acryloyl groups of SAMC D A and related compounds in CDCl3 ------·----- a "c, 0c,
8 7 6 54 3 2 O stituents on nitrogen decreases the extent of conjugation b (ppm) between C = C and C = 0 double bonds. Coplanarity of Figure 1. 1 H NMR spectra of poly(SAMC) and SAMC: A, poly these double bonds is considered to be distorted prob (PAMC) (No. 5 in Table I) measured at 50°C; B, poly(BAMC) (No. ably due to steric strain caused by bulky substituents. 7 in Table II); C, poly(PhAMC) (No. IO in Table II); D, E, and Fare However, the conjugation of the acryloyl groups of olefin protons of PAMC, BAMC, and PhAMC. respectively. SAMC and SPMC is considerably effective even in tert-butyl derivatives, judging from Lib of these com polymers do not contain practically any pendant un pounds and methallyl chloride (MA), the one of typical saturations. This means that repeating units of poly unconjugative monomers. Similar dependence of Lib on (SAMC) consist of structures 1 and/or 2. For the present, substituents was also observed in a series of ether dimers we do not have sufficient data to determine the repeating of ix-(hydroxymethyl)acrylic acid esters, though sub unit, 5- and/or 6-membered rings, and further study is stituents investigated in this case were those of ester necessary. groups. 8 •9 Chemical shifts of the carbonyl carbons also provide information on the conjugation between C = C NMR Studies of SAMC and Related Compounds and C = 0 double bonds, since the effective conjugation Chemical shifts of C = C double bonds (CµH 2 =Ca<) moves electrons in the olefin double bond into the car and carbonyl carbons of the acryloyl groups of SAMC bonyl group and shifts the chemical shifts of the carbonyl and related compounds obtained by measuring 13C carbons to higher magnetic fields. This can be under NMR spectra are summarized in Table III. be. and stood from the largest chemical shift of the carbonyl bep values shift to a higher and lower magnetic field, carbon of methyl isobutyrate (MI) among the com respectively, with a linear relationship when e values of pounds listed in Table III. The chemical shifts of the the monomers become larger with increasing electron methacryloyl carbons of RAMA are listed in Table III. attracting power of substituents. 23 This is because ef These values indicate that the conjugative nature of their fective conjugation between C = C and C = 0 double methacryloyl groups is extremely low even in MAMA bonds reduces the electron density on C = C double and it is almost comparable to that of MA. bonds. This means that Lib obtained by subtracting bep Radical polymerizabilities of ally! monomers were from be. reflect the influence of substituents more ef correlated to LI b to show that those with a value of more fectively than their respective values. The stronger the than 6 ppm for Lib are reluctant to polymerize. 24 This electron-attracting power of the substituents, the smaller clearly indicates that the polymerization tendency of the the value. Comparison of the Lib of SAMC indicates that allylic monofunctional counterparts of SAMC may be conjugation between olefin and carbonyl double bonds extremely low because of the large Lib values (Table IV) in these compounds changes depending on the sub observed for the ally! groups of SAMC. stituents on nitrogen. Their variation suggests that Lib increase with bulkiness of substituents except for the ESR Studies of MAMC and MPMC phenyl group. This means that bulkiness of the sub- The elemental reactions related to radical cyclopo-
Polym. J., Vol. 28, No. 11, 1996 1003 Q.-Q. LIU et a/.
13 Table IV. C Chemical shifts of ally! (CpH 2 =C,H-) 1mT carbons of SAMC in CDCl3 A - ric, ric. ,1/j• SAMC ppm ppm ppm
MAMC I 17.4 135.7 18.3 PAMC 116.9 136.1 19.2 BAMC 115.2 138.7 23.5 PhAMC 116.4 133.4 17.0 B
a ric.-ric,· lymerization of symmetrical unconjugated dienes are il lustrated schematically in reactions (1)-(5). The prop- Figure 2. ESR spectra of MAMC (A) and MPMC (B).
is the double bond of higher reactivity between the two double bonds of MAMC. 6 This is because the conjuga tive nature of the acryloyl group is much higher than that of its ally! group as can be seen from the chemical t (1) shifts of their C = C double bonds summarized in Tables (5) III and IV. These ESR studies confirm this assumption. V - Observation of only the uncyclized radical suggests that the rate-determining step for the cyclopolymerization (2) VJ MAMC ! of is intramolecular cyclization. Completely cyclized polymers can be obtained, even if intramolec t)· (4) ular cyclization (6 and/or 7) is slower than intermolec - tyV ular propagation (8 and/or 9), because intermolecular Scheme 4. propagation (10) between the uncyclized radical and monomer never occurs in this polymerization system. agating radicals that may appear during the polymer izations are two cyclized radicals and an uncyclized DISCUSSION radical. Either radical or a mixture of them would be detected on ESR measurements depending on the rate The effects of N-substituents on polymerization and determining step of cyclopolymerization and the cyclic conjugation between C = C and C = 0 double bonds of structure formed. In the case of the unsymmetrical un a-substituted acryloyl groups of SAMC and SPMC can conjugated dienes, the situation is rather complicated, be clearly seen from the data summarized in Tables II because the number of radicals detected would be twice and III. The results obtained suggest that non-homo as high. However, if the interpretation of the results polymerizability of SPMC is mainly due to steric factors, obtained is valid, the information on the reactivity of the since their acryloyl groups have considerably higher two double bonds involved could be available in addition conjugative nature. The definitely lower polymerizability to that of the rate-determining step. of SPMC indicates that the probability of the formation Figure 2(A) shows the ESR spectrum of MAMC of sequence 8 during the polymerization of SAMC is obtained using · NH2 as an initiating radical. Low signal quite low and a chain end 7 may react with its own to noise ratio of this spectrum does not allow un double bond to yield cyclized unit 9 and/or 10. Higher ambiguous identification. Therefore, ESR of MPMC cyclopolymerization tendencies of SAMC indicate that was measured under the same conditions. A spectrum the steric factors fatal to intermolecular propagation obtained is illustrated in Figure 2(B). This is also com (10) leading to the sequence 8 are not unfavorable to plicated but comparison of these spectra suggests that intramolecular cyclization (6 and/or 7). Information on they are due to essentially the same radical species. The the rate constants for the elementary reactions on the extremely low homopolymerization tendency of MPMC polymerization of SAMC is essential to gain insight on indicates that radical 5 is the only possible radical which polymerization. However, some characteristic features forms from this compound. This consideration permits of their polymerizations can be pointed out, based on us to attribute the spectrum shown in Figure 2(A) to these results. Bulky substituents seem to prevent effec radical 6. It has been assumed that the acryloyl group tive conjugation and retard polymerization. SAMC are considered to be incorporated into the polymeric chain mainly through their acryloyl groups, since their con jugative nature is higher than for ally! groups. In ac cordance with these considerations, ESR studies on MAMC revealed that the first step in the polymeriza tion of MAMC predominantly involves the acryloyl group. For this reason, the polymerization rate would 5 6 decrease, as the conjugative nature of the acryloyl groups Scheme 5. decreases. Bulky substituents which decrease the extent 1004 Polym. J., Vol. 28, No. 11, 1996 Completely Cyclized Polymers from Unsymmetrical 1,6-Dienes
tendency, but also high polymerizability. The arguments made above are concerned only with ~-__(B_)_hlf SAMC with substituents other than the phenyl group. The reason for slow polymerization of PhAMC is not N SAMC N N clear at present. The conjugative nature of the acryloyl 9 A A A groups of PhAMC and PhPMC might not be argued based on the same ground as that of SAMC and SPMA l(6) without the phenyl group, since strong influence of the benzene ring on the chemical shifts through diamagnetic anisotropy is well known. Other factors such as chain transfer reactions to monomers might play important -ff.r roles to suppress the overall polymerization rate in PhAMC. Further study is necessary to determine the ") . ' effect of the phenyl group on the polymerization be 1(7) havior of SAMC. Acknowledgment. This work was supported partly by a Grant-in-Aid for Scientific Research (No. 07651079) (9) ~- from the Ministry of Education, Science, and Culture of N SAMC Japan, for which we are grateful. 10 A
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