Double Cyclopolymerization of Monoterminal Trienes Using Pd

Note pubs.acs.org/Macromolecules

Double Cyclopolymerization of Monoterminal Trienes Using Pd Catalysis. Polymers Containing Functionallized Cyclic Groups with a Regulated Sequence Kenya Motokuni, Daisuke Takeuchi, and Kohtaro Osakada* Chemical Resources Laboratory R1-03, Tokyo Institute of Technology, 4259 Nagatsuta, Yokohama 226-8503, Japan S Supporting Information *

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INTRODUCTION

Chart 1

Hydrocarbon polymers with a five- or six-membered ring in the repeating unit are expected to show high optical transparency, thermal stability, and mechanical strength.1,2 The common reactions to obtain the polymers are the ring-opening metathesis polymerization of the bicyclic olefins such as norbornene1 and the addition polymerization of the cyclic olefins, including cyclopentene and norbornene, catalyzed by transition metal complexes.2 Copolymerization of acyclic and cyclic olefins provides polymers containing the cyclic groups randomly along the polymer chain.3 Cyclopolymerization of terminal dienes brings about the polymer growth accompanied by the formation of five- to eight-membered rings along the polymer and provides polymers furnished with these cyclic units.4 The cyclopolymerization of the dienes5 and the copolymerization of olefin with the diene,6 giving the polymers with the cyclic groups along the polymer chain, have been generated mainly by using early transition metal complexes as the catalyst. We have studied the cyclopolymerization using late transition metal catalysts and reported the cyclopolymerization of 1,6-heptadiene as well as the copolymerization of ethylene and the diene catalyzed by Fe and Co complexes.7 The polymerization using the Pd−diimine catalysts8 was further applied to the cyclopolymerization of 1,6-dienes containing the functional groups such as Meldrum’s acid and acetal groups, and it produced the polymers having the functionalized cyclic groups (Chart 1, poly-A and poly-B).9 Cyclopolymerization of monoterminal 1,6-dienes having an alkyl substituent at one of the olefinic group yields the product having the five-membered ring and oligomethylene spacer in alternating sequence (Chart 1, poly-C and poly-D) as results of isomerization of the growing polymer end after the ring formation.10 Recently, we reported the first double cyclopolymerization of the triene by using 1,6,11-dodecatriene with Meldrum’s acid groups or cyclic acetal groups at the 4- and 9-positions as the monomer and the Pd−diimine complex as the catalyst (Chart 1, poly-E and poly-F).11 The obtained polymers are composed of the two connected five-membered rings and ethylene spacer. Herein we report that monoterminal trienes polymerize in the presence of the Pd−diimine catalyst to afford the new polymers with the bicyclic groups in a regulated sequence along the polymer chain. © 2014 American Chemical Society

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RESULTS AND DISCUSSION The triene monomers I−IV used in this study are summarized in Chart 2a. The molecules are composed of 13−22 carbons Chart 2

backbone with a 1,6,11-triene structure. Meldrum’s acid group and the six-membered cyclic acetal group are bonded with the carbons at 4- and 9-positions, respectively. Pd complex 1 promoted the polymerization of the trienes in the presence of NaB(C6H3(CF3)2-3,5)4 (NaBARF), according to eq 1. Received: April 27, 2014 Revised: August 21, 2014 Published: September 9, 2014 6522

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and of Meldrum’s acid group at 50.7 ppm. The peak positions are close to the corresponding signals of poly-E and poly-F (50.4 and 39.2 ppm). The signals at 39.5, 39.8, 40.6, 40.8, 46.0, and 46.1 ppm are assigned to the CH2 carbons within the fivemembered rings, as suggested in Figure 2, based on the DEPT mode spectra of poly-I and comparison of the peak positions with the polymers of the corresponding terminal triene (Table 1).

Figures 1 and 2 show the 1H NMR and spectra of poly-I.

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Table 1. 13C{1H} NMR Chemical Shifts of Cyclopentane1,2-diyl Group in Poly-I and Polymers with Similar Structures

C{1H} NMR

polymer poly-I poly-Ea poly-Fa a

CH 45.4, 43.6, 45.0, 44.2,

44.1, 44.0 42.4 44.4, 43.4 42.7, 42.1

CH2

C

46.1, 46.0 40.8, 40.6, 39.8, 39.5 46.0, 39.0 40.6

50.7 39.0 50.4 39.2

Reference 11.

The polymers of 1,6,11-trienes with Meldrum’s acid group and with cyclic acetal group (poly-E and poly-F) show the signals at 46.0, 39.0, and 40.6 ppm. The CH hydrogen signals at 42.4. 43.6, 44.1, 44.0, and 45.4 ppm are at comparable positions with that of poly-E (43.4, 44.4, and 45.0 ppm) and poly-F (42.1, 42.7, and 44.2 ppm). The two polymers with the same functional groups were assigned to have the racemo linkage between the two five-membered rings, and similar peak positions of poly-I suggest the same linkage as the polymer of the symmetrical trienes. Chart 3 shows two possible

Figure 1. 1H NMR spectrum of poly-I in CDCl3 at 50 °C.

Chart 3

sequences of the monomer units having racemo linkage between the five-membered rings. Poly-I contains both of them which causes inequivalency of the peaks of CH (q) and CH2 (p) carbons. Broadened signals at 33.8 (33.7) and 32.6 (32.4) ppm are assigned to the CH2 carbon adjacent to the five-membered rings of the polymer chain, while the corresponding signals of poly-C and poly-D are observed at 34.6 and 32.5−33.0 pm, respectively. The other broadened signal at 26.7 ppm is assigned to the central CH2 carbon of the trimethylene spacer. Figure 3 summarizes the 13C{1H} NMR spectra of poly-II− IV. Signals of the CH and CH2 carbon atoms in the fivemembered ring with the cyclic acetal and cyclic diester groups are observed similarly to poly-I. Thus, the ring moieties of these polymers are regulated to trans-1,2-disubstituted cyclopentane and racemo chemistry of the bond between them. The CH (q) carbon signals of the polymers and CH2 (p) carbon signals of poly-IV are observed as a single peak due to long oligomethylene spacer. Table 2 summarizes the results of the polymerization of the 1,6,11-trienes that contain varied lengths of the alkylene spacer.

Figure 2. 13C{1H} NMR spectra of poly-I in CDCl3 at 50 °C.

The 1H NMR spectrum of the polymer (Figure 1) contains sharp peaks at 1.74 and 1.38 ppm, which are assigned to the methyl hydrogens of Meldrum’s acid group and of the acetal group, respectively, by comparison of the peak positions with poly-C (1.70−1.73 ppm, Chart 1), poly-D (1.38 ppm), poly-E (1.68 ppm), and poly-F (1.35 ppm).10,11 Peaks due to the CH2 hydrogens of the dioxolan ring of poly-I are observed from 3.48 to 3.67 ppm which are at similar positions to that of poly-D (3.53 ppm) and poly-F (3.51 ppm). The 1H NMR spectrum of the polymer contains minor signals due to vinylene hydrogens, which suggests that the growing polymer undergoes β-hydrogen elimination of the alkyl−palladium bond to produce the terminal group containing internal olefin. The 13C{1H} NMR spectrum of poly-I (Figure 2) shows the quaternary carbon signals of the cyclic acetal group at 39.0 ppm 6523

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produce the polymer with Mn of 17 100 and Mw/Mn of 2.15 in 18 h. Scheme 1 shows the proposed mechanism for the polymerization of 1,6,11-trienes with alkyl chains. The 2,1-insertion of a vinyl group of the monomer into the Pd−polymer bond (i) and double cyclization of the diene unit via successive intramolecular insertion of two vinylene (−CHCH−) groups yield a cyclopentylpalladium species (ii). The secondary alkyl− Pd intermediate does not undergo insertion of a new monomer but is isomerized to the intermediate having a primary alkyl− palladium bond via chain walking (iii). The coordination/ insertion reaction of another monomer molecules occurs to the primary alkyl−palladium bond selectively so as to avoid the steric hindrance. The obtained polymers have the two cyclopentane rings having two different substituents with a regulated sequence and the oligomethylene spacer between them. Similar isomerization of the growing polymer end was observed in the polymerization of 4-alkylcyclopentenes catalyzed by the Pd−diimine complexes.12 Differential scanning calorimetric (DSC) measurements of poly-I to poly-IV showed glass transition of these polymers at different temperatures depending on lengths of the oligomethylene spacer. The glass transition temperature was plotted against the number of CH2 groups of the polymer chain per two five-membered rings in Figure 4a. Increase of the alkyl chain lengths of the monomer lowers the glass transition temperature.

Figure 3. 13C{1H} NMR spectra of poly-II−poly-IV in CDCl3 at 50 °C.

Table 2. Isomerization Double Cyclopolymerization of 1,6,11-Trienes with Various Lengths of Alkyl Chains by Pd Complexesa run

monomer

m of (CH2)m

time (h)

convb (%)

Mnc

Mw/Mnc

1 2 3 4

I II III IV

1 2 3 10

18 19 10 18

quant quant quant quant

8100 6300 10800 17100

1.98 2.13 1.90 2.15

a

Reaction conditions: Pd complex = 0.010 mmol, NaBARF = 0.012 mmol, [monomer]/[Pd] = 30, solvent = CH2Cl2 (0.5 mL), at room temperature. bDetermined by 1H NMR. cDetermined by GPC based on polystyrene standard THF as eluent.

These monomers undergo the polymerization reaction and consume the monomers within 20 h. The polymerization proceeds in a higher rate than the cyclopolymerization of isopropylidene allyl(alkenyl)malonate and allyl-5-alkenyl-2,2-dimethyl-1,3-dioxane.10 Especially, the triene with a decyl substituent (IV) undergoes the quantitative double cyclopolymerization catalyzed by Pd complex to

Figure 4. Plots of glass transition temperature versus number of methylene groups of the polymer chain per two five-membered rings (x): (a) poly-I−IV (x = m + 2), (b) poly-D (x = 2(m + 2)), and (c) poly-C (x = 2(m + 2)). Data of (b) and (c) were taken from ref 10.

Scheme 1

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°C): δ 3.63, 3.53 (br, 2H, He), 2.43, 2.13, 1.94, 1.56, 1.32, 1.25, 1.20, 1.00 (br, Ha,Hb, Hc, Hh, Hi, Hj, Hk, Hp, Hq, Hr, Hs), 1.72, 1.71 (Ho and Ho′), 1.39, 1.38 (Hg and Hg′). 13C{1H} NMR (125 MHz, CDCl3, 50 °C): δ 172.1, 171.9 (m and m′), 104.6 (n), 97.6 (f), 70.5, 69.7 (e and e′), 50.8 (l), 46.1, 45.8 (p), 45.4 (j), 43.9, 43.7 (q), 43.5 (i), 42.3, 42.2 (b), 40.6, 39.9, 39.8 (c, h, k), 39.1 (d), 33.4 (a), 32.6, 32.4 (r), 30.2 (t), 28.8 (o and o′), 28.1 (s, u), 24.9, 22.8 (g and g′). Triene IV was polymerized similarly (18 h, 195 mg, yield: 61%, Mn = 10 800, Mw/Mn = 1.90). Poly-IV: 1H NMR (500 MHz, CDCl3, 50 °C): δ 3.61, 3.52, 3.51 (br, 2H, He), 2.43, 2.14, 1.96, 1.58, 1.00, 0.87 (br, Ha,Hb, Hc, Hh, Hi, Hj, Hk, Hp, Hq, Hr, Hs), 1.71 (Ho and Ho′), 1.40, 1.38 (Hg and Hg′), 1.25 (Halkyl chain). 13C{1H} NMR (125 MHz, CDCl3, 50 °C): δ 172.1, 171.9 (m and m′), 104.6 (n), 97.6 (f), 70.5, 69.8 (e and e′), 50.9 (l), 46.1, 45.8 (p), 45.5 (j), 43.9 (q), 43.6 (i), 42.3 (b), 40.5, 40.0, 39.8 (c, h, k), 39.1(d), 33.7, 33.5 (a), 32.8, 32.4 (r), 29.9, 29.7, 29.6 (alkyl chain), 28.2, 28.1 (o and o′), 27.9 (s, u), 24.6, 23.0 (g and g′) Assignment of the NMR signals is based on the formula in the figures.

The glass transition temperatures of the obtained polymers are between the plots for poly-D having the cyclic acetal groups only (Figure 4b) and poly-C with Meldrum’s acid groups only (Figure 4c). In summary, monoterminal 1,6,11-trienes undergo the Pdcomplex-catalyzed double cyclopolymerization to produce the polymers with racemo bis-cyclopentane groups. The obtained polymers have a regulated sequence of the substituents containing the functional groups along the polymer chain. The kind of functional groups or lengths of alkyl group of the monomers influence the glass transition temperature of the resulting polymers.

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EXPERIMENTAL SECTION

General Method. All manipulations of air- and water-sensitive compounds were carried out with standard high-vacuum or Schlenk techniques. NMR spectra were recorded on a Varian Mercury 300 and JEOL JNM-500 spectrometers. 1H and 13C{1H} NMR chemical shifts were referenced to the signals of solvents. Gel permeation chromatography (GPC) measurement was conducted at 40 °C on a JASCO high-speed liquid chromatograph system equipped with a differential refractometer detector and a variable-wavelength UV−vis detector, using THF as eluent at a flow rate of 0.6 mL min−1 with TSKgel Super HM-L and Super HM-M columns Molecular weights were calculated relative to polystyrene standards. DSC and TG were recorded on Seiko DSC 6200R and TG/DTA 6200R, respectively. Materials. Dry solvents were purchased and used as received unless otherwise noted. CDCl3 was dried over CaH2, vacuum-transferred, and degassed by repeated freeze−pump−thaw cycles was used for kinetic studies. Diimine ligands, Pd complexes, and NaBARF were synthesized according to the literature method.13 The monomers were newly synthesized by modifying those to prepare analogous diene or trienes, and the procedure and the analytical data are in the Supporting Information. Polymerization of 1-{5-(2E)-Butenyl-2,2-dimethyl-4,6-dioxo1,3-dioxan-5-yl}-4-(5-allyl-2,2-dimethyl-1,3-dioxan-5-yl)-(2E)butene (I). Typically, to a 25 mL Schlenk flask containing a CH2Cl2 solution (0.5 mL) of Pd complex 1 (0.01 mmol, 5.7 mg) was added NaBARF (0.012 mmol, 10.6 mg) under Ar. After stirring for several minutes, 1-{5-(2E)-butenyl-2,2-dimethyl-4,6-dioxo-1,3-dioxan-5-yl}-4(5-allyl-2,2-dimethyl-1,3-dioxan-5-yl)-(2E)-butene (I, 109.3 mg, 0.30 mmol) was added, and the reaction mixture was stirred at room temperature. The portion of the reaction mixture was taken out from the flask and subjected to 1H NMR and GPC analysis to determine conversion of I and molecular weight of poly-I (18 h, quantitative conversion). After the polymerization was quenched by adding a few drops of pyridine, the reaction mixture was poured to hexane, and the separated solid was dissolved in CH2Cl2 and reprecipitated from hexane to afford poly-I as white powder (70 mg, 64% yield, Mn = 8100, Mw/Mn = 1.98). 1H NMR (500 MHz, CDCl3): δ 3.67, 3.54, 3.48 (br, 2H, He), 2.42, 2.14, 1.94, 1.54, 1.26, 1.18, 1.02, 0.89 (br, Ha,Hb, Hc, Hh, Hi, Hj, Hk, Hp, Hq, Hr, Hs), 1.74, 1.73 (Ho and Ho′), 1.40, 1.38 (Hg and Hg′). 13C{1H} NMR (125 MHz, CDCl3, 50 °C): δ 171.9 (m and m′), 104.7 (n), 97.6 (f), 70.5, 69.6 (e and e′), 50.7 (l), 46.1, 46.0 (p), 45.4 (j), 44.1, 44.0 (q), 43.6 (i), 42.4 (b), 40.8, 40.6 (c and h), 39.8, 39.5 (k), 39.0 (d), 33.8, 33.7 (a), 32.6, 32.4 (r), 28.8 (o and o′), 26.7 (s), 25.2, 22.5 (g and g′). Triene II was polymerized similarly (19 h, 344 mg, yield: 91%, Mn = 6300, Mw/Mn = 2.13). Poly-II: 1H NMR (500 MHz, CDCl3, 50 °C): δ 3.64, 3.54 (br, 2H, He), 2.44, 2.14, 1.95, 1.58, 1.26, 1.02 (br, Ha,Hb, Hc, Hh, Hi, Hj, Hk, Hp, Hq, Hr, Hs), 1.73, 1.72 (Ho and Ho′), 1.40, 1.39 (Hg and Hg′). 13C{1H} NMR (125 MHz, CDCl3, 50 °C): δ 172.1, 171.9 (m and m′), 104.6 (n), 97.6(f), 70.5, 69.8 (e and e′), 50.8 (l), 46.1, 45.8 (p), 45.5 (j), 43.8, 43.7 (q), 43.5 (i), 42.4, 42.2 (b), 40.6, 39.9, 39.7 (c, h, k), 33.7, 33.5 (a), 32.6 (r), 28.9 (o and o′), 28.7, 28.5, 28.3 (s, t), 24.8, 22.9 (g and g′). Triene III was polymerized similarly (10 h, 194 mg, yield: 74%, Mn = 10 800, Mw/Mn = 1.90). Poly-III: 1H NMR (500 MHz, CDCl3, 50

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ASSOCIATED CONTENT

S Supporting Information *

Preparation procedure and spectroscopic data of the monomer compounds. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail [email protected] (K.O.). Notes

The authors declare no competing financial interest.

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REFERENCES

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