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From potassium alkalide and benzyl glycidyl ether to crown-like macroinitiator with alkoxide active centres
REACTIVE & FUNCTIONAL POLYMERS
Reactive & Functional Polymers 67 (2007) 120–126
www.elsevier.com/locate/react
From potassium alkalide and benzyl glycidyl ether to crown-like macroinitiator with alkoxide active centres Andrzej Stolarzewicz a,*, Barbara Morejko a, Zbigniew Grobelny a, Barbara Trzebicka b, Wiesław W. Sułkowski c a
c
Institute of Materials Science, University of Silesia, 40-007 Katowice, Poland b Institute of Coal Chemistry, Polish Academy of Sciences, Gliwice, Poland Department of Environmental, Chemistry and Technology, Institute of Chemistry, University of Silesia, 40-006 Katowice, Poland Received 17 December 2005; received in revised form 4 June 2006; accepted 19 October 2006 Available online 28 November 2006
Abstract Cyclic oligoether with alkoxide groups is obtained in the reaction of alkalide K , K+(15-crown-5)2 with benzyl glycidyl ether. This oligoether contains potassium glycidoxide units and benzyl glycidyl ether units. Its use as a macroinitiator should lead to star-shaped polymers with a cyclic core. 2006 Elsevier B.V. All rights reserved. Keywords: Alkalide; Benzyl glycidyl ether; Potassium glycidoxide; Macroinitiator
1. Introduction Synthesis and structure of polyethers have been studied for many years. An important progress was observed in the case of polymers obtained from oxiranes. Homopolymers and copolymers of ethylene oxide and propylene oxide were particularly interesting from the practical point of view. The most of routes to those and other polyethers were based on anionic processes. Various initiating systems were used for that purpose. Potassium hydroxide [1–3], alkali metal alkoxides [4–6], alkalides [7– 10], potassium hydride [11,12] and bimetal cyanides [13,14] belonged to them. Polyetherdiols and polyethertriols with a very low content of aliphatic car*
Corresponding author. Tel./fax: +48 32 259 69 29. E-mail address: [email protected] (A. Stolarzewicz).
bon–carbon double bonds were synthesized from propylene oxide with bimetal cyanides. Polyurethane elastomers obtained from those polymers showed mechanical properties much better than known earlier ones [15]. Some initiating systems led to star-shaped polyethers [16,17]. Cyclic products were obtained from glycidol without the initiator [18,19]. Recently, potassium glycidoxide activated 18crown-6 was applied for the polymerization of propylene oxide [20,21]. This alkoxide is an inimer [22]. It can initiate the polymerization as well as take part in the propagation step as a monomer because it possesses both the alkoxide group and the oxirane ring. Its use results in a polyether having a cyclic core and one or more arms. Potassium glycidoxide can be obtained in several ways, however, two of them seem to be the most
1381-5148/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.reactfunctpolym.2006.10.003
A. Stolarzewicz et al. / Reactive & Functional Polymers 67 (2007) 120–126
important. In the first one, it is synthesized from potassium hydride and glycidol in the presence of 18-crown-6 [20]. Potassium hydride reacts exclusively with the hydroxyl group of glycidol and the oxirane ring opening does not occur. However, potassium glycidoxide complexed 18-crown-6 starts to oligomerize spontaneously after some time [23]. This process results in a crown-like oligomer with several alkoxide active centres. The number of the latter depends on the concentration of crown ether. Hexamers and heptamers are mainly formed at the equimolar amounts of reagents. The trimer is almost exclusively obtained at threefold excess of crown ether in relation to potassium hydride. The second method is based on the reaction of alkalide K , K+(15-crown-5)2 with benzyl glycidyl ether, i.e. with an oxirane possessing cyclic and linear ether bonds [24]. Unexpectedly, only the linear bond is cleaved in this process giving potassium glycidoxide and benzyl radical. The strongly strained three-membered oxacyclic ring remains undisturbed. That process has been studied at the benzyl glycidyl ether to alkalide molar ratio equal to 5:1. The reaction has been quenched with butyl bromide immediately after mixing of the reagents. Therefore, it was not explained whether potassium glycidoxide oligomerized in the presence of 15-crown-5 in the similar manner as with 18-crown-6 and what structure had the reaction product or products. In the present work we try to answer these questions. 2. Experimental 2.1. Synthesis Benzyl glycidyl ether (Aldrich) was heated over CaH2 for 6 h and then distilled under dry argon atmosphere; the fraction boiling at 70 C/11 mm Hg was collected. Tetrahydrofuran and 15-crown-5 (both Aldrich) were purified as in Ref. [25]. Preparation of alkalide K , K+(15-crown-5)2 tetrahydrofuran solution was performed at ambient temperature in an apparatus presented in Ref. [25]. Potassium (about 1.5 g) was distilled into a reactor under a high vacuum. Then, 0.2 M 15-crown-5 solution in tetrahydrofuran (10 mL) was dropped on the metal mirror. After 25 min of mixing in an ultrasonic bath a deep blue 0.1 M solution of alkalide was obtained. That solution was then filtered off through the glass frit and introduced into a 50 mL reactor containing 0.5 M tetrahydrofuran solution of benzyl glycidyl ether (10 mL). The reactor was thermostatted at
121
25 C. It was equipped with a magnetic stirrer and teflon valves enabling substrates delivery and sampling under dry argon atmosphere. Initial benzyl glycidyl ether concentration in the reaction mixture was equal to 0.25 M whereas the concentration of K of alkalide to 0.05 M. The dark blue alkalide solution became colourless instantaneously after mixing with benzyl glycidyl ether. Methyl iodide was added at 95% conversion of oxirane compounds. Insoluble K+(15-crown-5)2I and KI salts were formed in that case. They had been removed from the mixture and the oligomer was precipitated with hexane. Finally, it was dried to a constant mass yielding a viscous liquid product free of bibenzyl. The latter remained in hexane solution. 2.2. Measurements MALDI-TOF measurements were performed with a Voyager-Elite mass spectrometer (Perseptive Biosystems, Framingham, MA, USA) equipped with a pulsed nitrogen laser (337 nm, 4 ns pulse width) and a time delayed extraction ion source. An accelerating voltage of 20 kV was used. Mass spectra were obtained in the reflection mode. 2,5Dihydroxybenzoic acid was used as a matrix. It was dissolved in tetrahydrofuran (10 mg/mL) and the solution was mixed with tetrahydrofuran solution of the oligomer (10 mg/mL). The samples were mixed additionally with LiCl acetone solution (10 mg/mL). Nevertheless, potassium adduct ions were mainly observed in the spectra. 1 H and 13C NMR spectra were recorded at 20 C on a Bruker multinuclear spectrometer at the 1H resonance frequency of 400 MHz, and the 13C resonance frequency of 100 MHz. Deuterated acetone was used as the solvent. Chemical shifts were referenced to tetramethylsilane (TMS) serving as an internal standard. Infra-red (IR) spectra were acquired using a BIO-RAD FTS-40A Fourier transform infrared spectrometer in the range of 4000– 700 cm 1 at a resolution of 2 cm 1, and for an accumulated 32 scans. The number-average molecular mass (Mn) and dispersity (Mw/Mn) of the oligomer were determined by gel-permeation chromatography (GPC) using polymer standard service (PSS) column SDV ˚ columns. GPC system 1 · 105 + 1 · 103 + 2 · 102 A contained differential refractive index detector dn1000 RI WGE Dr. Bures and a multiangle light scattering (MALLS) detector DAWN EOS of Wyatt Technologies. Measurements were performed
122
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using tetrahydrofuran as the solvent at 30 C with an anominal flow rate of 1 mL/min. Results were evaluated using the ASTRA software from Wyatt Technologies. Refractive index increments used in calculations were measured in a separate experiment and calculated from the concentration dependence of RI signals. The results were also evaluated using polystyrene calibration and WINGPC software from PSS. Mn values resulting from polystyrene calibration were lower than the absolute ones from GPC-MALLS. The concentration of oxirane compounds in the reaction mixture was estimated using the dioxane method [26].
with the same peak-to-peak increment of 164.2 equal to the molecular mass of benzyl glycidyl ether. The main set A is observed at m/z 708.1, 872.2 and 1036.4. The most abundant peak of this series at m/z 872.2 represents adduct ions of macromolecules consisting of two propane-1,2-dioxide units (73.2, Scheme 1) formed from potassium glycidoxide incorporated into the polymer chain, four benzyl glycidyl ether units (Scheme 2) and two methyl end groups (Mcalc = 872.2). Thus, these macromolecules contain six oxygen atoms in the main chain.
O
3. Results and discussion
CH2
CH
CH2 O
Scheme 1.
The oligomerization of the reagents was carried out at the benzyl glycidyl ether to alkalide molar ratio equal to 5:1. A product with Mn = 1600 was formed in this process as measured by GPCMALLS (Mn = 1400 for PS calibration). A representative part of its MALDI-TOF spectrum (Fig. 1) shows four series of potassium adduct ions
CH2OCH2Ph CH2
CH
O
Scheme 2.
A 872.2
A 1036.4
A B
708.1
B
796.2
873.2
960.4
1037.4
E
1124.6
E
766.2
1004.4
840.2 709.1
C
748.1
720.1 694.0 695.0
700
762.1
838.2
750
841.2 794.2
800
961.4
C
797.2
767.1
734.1
B
1002.4
F
884.3 885.3
914.3
958.4
D 962.4
926.3
854.3
850
F
912.3
900
C 1048.5
1005.4
1049.5
1018.4 1050.5
1000
1094.5 1090.5
973.4
950
F
1050
1125.6
D 1136.6
1093.5
1137.6
1100
1150
m/z Fig. 1. MALDI-TOF spectrum of the oligomer obtained in the reaction of alkalide K , K+(15-crown-5)2 with benzyl glycidyl ether in tetrahydrofuran solution at 25 C. Peaks of potassium adduct ions of macromolecules with two, three, four and five propane-1,2-dioxide units are denoted as A, B, C and D, respectively. Peaks of lithium adduct ions of macromolecules with two and three propane-1,2-dioxide units are denoted as E and F, respectively.
A. Stolarzewicz et al. / Reactive & Functional Polymers 67 (2007) 120–126
Macromolecules with three, four and five propane-1,2-dioxide units are also found in this sample. Their peaks are seen in series B at m/z 796.2, 960.4 and 1124.6, in series C atm/z 720.1, 884.3 and 1048.5, and in series D atm/z 973.4 and 1136.6, respectively. The former, i.e. the most abundant peak in series B represents potassium adduct ions of macromolecules containing three propane-1,2-dioxide units, three benzyl glycidyl ether units and three methyl end groups (Mcalc = 796.2). It means that these macromolecules also contain six oxygens in the main chain.
Macromolecules with one propane-1,2-dioxide unit were not identified. Moreover, two series of lithium adduct ions are observed in the spectrum. They are adducts ions of macromolecules with two propane-1,2-dioxide units present at m/z 840.2 and 1004.4 denoted as series E, and with three propane-1,2-dioxide units at m/z 766.2, 926.3 and 1094.5 denoted as series F. The last peak, for example, was assigned to macromolecules containing three propane-1,2-dioxide units, five benzyl glycidyl units and three methyl end groups (Mcalc = 1092.6).
K , K
OCH2Ph O
K0
O
CH2Ph
K0
, K
O
O , K O
PhCH2
1 K0
PhCH2 , K
OCH2Ph O
O ,K
PhCH2CH2Ph
O
2 where
123
K+ denotes the complex with two 15-crown-5 molecules. Scheme 3.
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A. Stolarzewicz et al. / Reactive & Functional Polymers 67 (2007) 120–126
be assumed that the oxirane ring was really opened during the oligomerization. Moreover, no signals of any other starting group were observed in the spectra and the signal of methyl end groups was identified at 59.91 ppm in the 13C NMR spectrum of the methylated sample. Taking into account all these facts a following mechanism of the oligomerization is proposed. At first potassium glycidoxide with and without crown ether, denoted as 1 and 2, respectively, is obtained in the reaction of alkalide with benzyl glycidyl ether as described in Ref. [24] (Scheme 3). Alkoxide 1 can serve as the inimer and 2 only as an oxirane co-monomer because it is not activated. Therefore, the oligomerization has to be initiated by 1 (Scheme 4). This alkoxide adds one or more benzyl glycidyl ether molecules as well as potassium glycidoxide ones. If one of the latter is 2 then its ‘‘free’’ K+ can be enclosed step by step with the growing chain. A free anion, i.e. an additional active centre is formed at the same time. On the other hand, the surrounded potassium cation can originate from its complex with 15-crown-5 if the growing chain does not possess ‘‘free’’ K+. The intramolecular cyclization is expected to occur mainly when the oligomer possesses six oxygen atoms in the main chain. Cyclic hexamer 3 being in this case the final reaction product is
The results of MALDI-TOF analysis correlate very well with works on the anionic polymerization of ethylene oxide presented by Kazanskii [4,5]. It was shown that the counter-ion is surrounded gradually by the growing oligoether chain. Reaction rate constants of the ethylene oxide addition to the alkoxide active centre with K+ increased substantially until the incorporation of sixth monomer molecule. The chain with six oxygen atoms was preferred to form a complex with the potassium cation. Its stability was similar to that of 18-crown-6. If potassium glycidoxide activated 15-crown-5 initiates the oligomerization then the oxirane ring becomes the starting group, i.e. that situated at the beginning of the polymer backbone. Unfortunately, the MALDI-TOF technique does not give information whether this starting group after incorporation of some benzyl glycidyl ether molecules and/or potassium glycidoxide molecules reacts with the end of its own chain, i.e. with the alkoxide active centre. A linear macromolecule with the oxirane starting group and a cyclic macromolecule with the propane-1,2-dioxide unit formed after the oxirane ring opening possess the same molecular masses. NMR and IR techniques were employed to solve that problem. No signal of the oxirane ring was found in the spectra of the oligomer. Thus, it could
O , K
O ,K O
OCH2Ph
O , K O
OCH2Ph
O
O
1
O
OCH2Ph K
K
, O O
, O
K
O
OCH2Ph
3
O
K O
PhCH2O
PhCH2O O
OCH2Ph
, O
O
O
O
O
2
K O
O
OCH2Ph O
O OCH2Ph O
O
OCH2Ph
Ph CH2O
O
O OCH2Ph O
3 Scheme 4.
O
K
A. Stolarzewicz et al. / Reactive & Functional Polymers 67 (2007) 120–126
bifunctional even if the second potassium glycidoxide is not activated crown ether. The molecular mass calculated for its methylated derivative is equal to m/z value of the most abundant peak in Fig. 1. Thus, the oligoether obtained at fivefold excess of benzyl glycidyl ether in relation to alkalide is a mixture of substituted crown ethers of the irregular structure containing a few alkoxide active centres. Their irregularity is connected with a different number of carbon atoms localized between two neighbouring oxygen atoms. This oligoether can be used as a macroinitiator of the polymerization of oxiranes, lactones or some other monomers able to polymerize with potassium alkoxides. A starshaped polymer with an oxacyclic core and with several arms is expected to form in its presence. The number of the arms will depend on the number of activated alkoxide groups. It is shown that the macromolecules with two alkoxide groups are always bifunctional. The macromolecules containing three alkoxide groups can be bifunctional or trifunctional. From the statistical point of view the functionality of the macromolecules with four and five alkoxide groups can range between two and four and two and five, respectively. Intensity of the peaks derived from the macromolecules with two and three methoxy groups obtained after methylation is greater then those with four and five ones. However, in such cases the MALDI-TOF technique usually does not give quantitative results. The quantitative analysis of polymers or copolymers have been demonstrated only for a limited number of systems [27,28]. The estimation was found to be near to real terms when the polymer was composed of similar monomers [29]. It means that the average functionality of the new macroinitiator can be equal to about three and this macroinitiator is expected to produce star-shaped polymers possessing mainly three arms. 4. Conclusions Substituted crown-like oligoether of the irregular structure possessing alkoxide groups is prepared in the reaction of alkalide K , K+(15-crown-5)2 with an excess of benzyl glycidyl ether. The number of alkoxide groups is equal to two to five. Some of them are activated by 15-crown-5 and some others by the cyclic oligoether itself. They should become
125
active centres after the addition of a monomer. A star-shaped polymer containing the cyclic core and arms built from the selected monomer can be obtained in this case. Acknowledgement This work was supported with the Committee of Scientific Research in Poland (Project no. 4 TO9A 036 25). References [1] L.E.St. Pierre, C.C. Price, J. Am. Chem. Soc. 78 (1956) 3432. [2] E.C. Steiner, R.R. Pelletier, R.O. Trucks, J. Am. Chem. Soc. 86 (1964) 4678. [3] J. Plucin´ski, H. Matyschok, R. Janik, H. Prystasz, Angew. Makromol. Chem. 97 (1981) 35. [4] K.S. Kazanskii, in: N.S. Enikolopov (Ed.), Khimija i tekhnologija vysokomolekularnykh soedinenij, VINITI, Moskva, 1977, p. 35. [5] K.S. Kazanskii, Y.Ya. Kaminskii, N.V. Ptitsyna, V.S. Romanova, I.N. Topchieva, Vysokomol. Soedin. Sect. A 10 (1987) 2219. [6] A. Stolarzewicz, D. Neugebauer, Z. Grobelny, Macromol. Chem. Phys. 196 (1995) 1301. [7] Z. Grobelny, A. Stolarzewicz, B. Morejko-Bu_z, G. Buika, J.V. Grazˇulevicˇius, A. Maercker, Eur. Polym. J. 38 (2002) 2359. [8] A. Stolarzewicz, Z. Grobelny, Makromol. Chem. 193 (1992) 531. [9] H. Janeczek, Z. Jedlin´ski, Polish J. Appl. Chem. 41 (1997) 377. [10] Z. Grobelny, A. Stolarzewicz, D. Neugebauer, B. MorejkoBu_z, Eur. Polym. J. 38 (2002) 1065. [11] A. Stolarzewicz, D. Neugebauer, J. Grobelny, Macromol. Rapid. Commun. 17 (1996) 787. [12] A. Stolarzewicz, D. Neugebauer, Macromol. Chem. Phys. 200 (1999) 2467. [13] J. Milgram, USA Pat. 3,278,457 (11.09.1966). [14] J. Kuyper, G. Boxhoorn, J. Catal. 105 (1987) 163. [15] S.D. Seneker, C.C. Shen, N. Barksby, Polyurethanes World Congress (1993) 568. [16] G. Łapienis, S. Penczek, Macromolecules 33 (2000) 630. [17] A. Dworak, A. Kowalczuk-Bleja, B. Trzebicka, W. Wałach, Polym. Bull. 49 (2002) 9. [18] A. Sunder, R. Hanselmann, H. Frey, R. Mu¨llhaupt, Macromolecules 32 (1999) 4240. [19] A. Sunder, R. Mu¨lhaupt, H. Frey, Macromolecules 33 (2000) 309. [20] A. Stolarzewicz, B. Morejko-Bu_z, Z. Grobelny, W. Pisarski, M. Lanzendo¨rfer, A. Mu¨ller, Rapid Commun. Mass Spectrom. 18 (2004) 716. [21] A. Stolarzewicz, B. Morejko-Bu_z, Z. Grobelny, W. Pisarski, H. Frey, Polymer 45 (2004) 7047. [22] A.H.E. Mu¨ller, D. Yan, M. Wukow, Macromolecules 30 (1997) 7015.
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[23] A. Stolarzewicz, B. Morejko-Bu_z, Z. Grobelny, W. Pisarski, React. Funct. Polym. 65 (2005) 259. [24] Z. Grobelny, A. Stolarzewicz, B. Morejko-Bu_z, A. Maercker, J. Organomet. Chem. 660 (2002) 6. [25] A. Stolarzewicz, Z. Grobelny, J. Grobelny, Spectrochim. Acta Part A 56 (2000) 1257. [26] S. Siggia, Quantitative Organic Analysis via Functional Groups, J. Wiley, New York, 1963, p. 241.
[27] R. Abate, A. Ballistreri, G. Montaudo, D. Garozzo, G. Impallomeni, G. Crichley, K. Tanaka, Rapid Commun. Mass Spectrom. 7 (1993) 1033. [28] G. Wilczek-Vera, P. Danis, A. Eisenberg, Macromolecules 29 (1996) 4036. [29] R. Chen, N. Zhang, A. Tseng, L. Li, Rapid Commun. Mass Spectrom. 14 (2000) 2175.
Reactive & Functional Polymers 67 (2007) 120–126
www.elsevier.com/locate/react
From potassium alkalide and benzyl glycidyl ether to crown-like macroinitiator with alkoxide active centres Andrzej Stolarzewicz a,*, Barbara Morejko a, Zbigniew Grobelny a, Barbara Trzebicka b, Wiesław W. Sułkowski c a
c
Institute of Materials Science, University of Silesia, 40-007 Katowice, Poland b Institute of Coal Chemistry, Polish Academy of Sciences, Gliwice, Poland Department of Environmental, Chemistry and Technology, Institute of Chemistry, University of Silesia, 40-006 Katowice, Poland Received 17 December 2005; received in revised form 4 June 2006; accepted 19 October 2006 Available online 28 November 2006
Abstract Cyclic oligoether with alkoxide groups is obtained in the reaction of alkalide K , K+(15-crown-5)2 with benzyl glycidyl ether. This oligoether contains potassium glycidoxide units and benzyl glycidyl ether units. Its use as a macroinitiator should lead to star-shaped polymers with a cyclic core. 2006 Elsevier B.V. All rights reserved. Keywords: Alkalide; Benzyl glycidyl ether; Potassium glycidoxide; Macroinitiator
1. Introduction Synthesis and structure of polyethers have been studied for many years. An important progress was observed in the case of polymers obtained from oxiranes. Homopolymers and copolymers of ethylene oxide and propylene oxide were particularly interesting from the practical point of view. The most of routes to those and other polyethers were based on anionic processes. Various initiating systems were used for that purpose. Potassium hydroxide [1–3], alkali metal alkoxides [4–6], alkalides [7– 10], potassium hydride [11,12] and bimetal cyanides [13,14] belonged to them. Polyetherdiols and polyethertriols with a very low content of aliphatic car*
Corresponding author. Tel./fax: +48 32 259 69 29. E-mail address: [email protected] (A. Stolarzewicz).
bon–carbon double bonds were synthesized from propylene oxide with bimetal cyanides. Polyurethane elastomers obtained from those polymers showed mechanical properties much better than known earlier ones [15]. Some initiating systems led to star-shaped polyethers [16,17]. Cyclic products were obtained from glycidol without the initiator [18,19]. Recently, potassium glycidoxide activated 18crown-6 was applied for the polymerization of propylene oxide [20,21]. This alkoxide is an inimer [22]. It can initiate the polymerization as well as take part in the propagation step as a monomer because it possesses both the alkoxide group and the oxirane ring. Its use results in a polyether having a cyclic core and one or more arms. Potassium glycidoxide can be obtained in several ways, however, two of them seem to be the most
1381-5148/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.reactfunctpolym.2006.10.003
A. Stolarzewicz et al. / Reactive & Functional Polymers 67 (2007) 120–126
important. In the first one, it is synthesized from potassium hydride and glycidol in the presence of 18-crown-6 [20]. Potassium hydride reacts exclusively with the hydroxyl group of glycidol and the oxirane ring opening does not occur. However, potassium glycidoxide complexed 18-crown-6 starts to oligomerize spontaneously after some time [23]. This process results in a crown-like oligomer with several alkoxide active centres. The number of the latter depends on the concentration of crown ether. Hexamers and heptamers are mainly formed at the equimolar amounts of reagents. The trimer is almost exclusively obtained at threefold excess of crown ether in relation to potassium hydride. The second method is based on the reaction of alkalide K , K+(15-crown-5)2 with benzyl glycidyl ether, i.e. with an oxirane possessing cyclic and linear ether bonds [24]. Unexpectedly, only the linear bond is cleaved in this process giving potassium glycidoxide and benzyl radical. The strongly strained three-membered oxacyclic ring remains undisturbed. That process has been studied at the benzyl glycidyl ether to alkalide molar ratio equal to 5:1. The reaction has been quenched with butyl bromide immediately after mixing of the reagents. Therefore, it was not explained whether potassium glycidoxide oligomerized in the presence of 15-crown-5 in the similar manner as with 18-crown-6 and what structure had the reaction product or products. In the present work we try to answer these questions. 2. Experimental 2.1. Synthesis Benzyl glycidyl ether (Aldrich) was heated over CaH2 for 6 h and then distilled under dry argon atmosphere; the fraction boiling at 70 C/11 mm Hg was collected. Tetrahydrofuran and 15-crown-5 (both Aldrich) were purified as in Ref. [25]. Preparation of alkalide K , K+(15-crown-5)2 tetrahydrofuran solution was performed at ambient temperature in an apparatus presented in Ref. [25]. Potassium (about 1.5 g) was distilled into a reactor under a high vacuum. Then, 0.2 M 15-crown-5 solution in tetrahydrofuran (10 mL) was dropped on the metal mirror. After 25 min of mixing in an ultrasonic bath a deep blue 0.1 M solution of alkalide was obtained. That solution was then filtered off through the glass frit and introduced into a 50 mL reactor containing 0.5 M tetrahydrofuran solution of benzyl glycidyl ether (10 mL). The reactor was thermostatted at
121
25 C. It was equipped with a magnetic stirrer and teflon valves enabling substrates delivery and sampling under dry argon atmosphere. Initial benzyl glycidyl ether concentration in the reaction mixture was equal to 0.25 M whereas the concentration of K of alkalide to 0.05 M. The dark blue alkalide solution became colourless instantaneously after mixing with benzyl glycidyl ether. Methyl iodide was added at 95% conversion of oxirane compounds. Insoluble K+(15-crown-5)2I and KI salts were formed in that case. They had been removed from the mixture and the oligomer was precipitated with hexane. Finally, it was dried to a constant mass yielding a viscous liquid product free of bibenzyl. The latter remained in hexane solution. 2.2. Measurements MALDI-TOF measurements were performed with a Voyager-Elite mass spectrometer (Perseptive Biosystems, Framingham, MA, USA) equipped with a pulsed nitrogen laser (337 nm, 4 ns pulse width) and a time delayed extraction ion source. An accelerating voltage of 20 kV was used. Mass spectra were obtained in the reflection mode. 2,5Dihydroxybenzoic acid was used as a matrix. It was dissolved in tetrahydrofuran (10 mg/mL) and the solution was mixed with tetrahydrofuran solution of the oligomer (10 mg/mL). The samples were mixed additionally with LiCl acetone solution (10 mg/mL). Nevertheless, potassium adduct ions were mainly observed in the spectra. 1 H and 13C NMR spectra were recorded at 20 C on a Bruker multinuclear spectrometer at the 1H resonance frequency of 400 MHz, and the 13C resonance frequency of 100 MHz. Deuterated acetone was used as the solvent. Chemical shifts were referenced to tetramethylsilane (TMS) serving as an internal standard. Infra-red (IR) spectra were acquired using a BIO-RAD FTS-40A Fourier transform infrared spectrometer in the range of 4000– 700 cm 1 at a resolution of 2 cm 1, and for an accumulated 32 scans. The number-average molecular mass (Mn) and dispersity (Mw/Mn) of the oligomer were determined by gel-permeation chromatography (GPC) using polymer standard service (PSS) column SDV ˚ columns. GPC system 1 · 105 + 1 · 103 + 2 · 102 A contained differential refractive index detector dn1000 RI WGE Dr. Bures and a multiangle light scattering (MALLS) detector DAWN EOS of Wyatt Technologies. Measurements were performed
122
A. Stolarzewicz et al. / Reactive & Functional Polymers 67 (2007) 120–126
using tetrahydrofuran as the solvent at 30 C with an anominal flow rate of 1 mL/min. Results were evaluated using the ASTRA software from Wyatt Technologies. Refractive index increments used in calculations were measured in a separate experiment and calculated from the concentration dependence of RI signals. The results were also evaluated using polystyrene calibration and WINGPC software from PSS. Mn values resulting from polystyrene calibration were lower than the absolute ones from GPC-MALLS. The concentration of oxirane compounds in the reaction mixture was estimated using the dioxane method [26].
with the same peak-to-peak increment of 164.2 equal to the molecular mass of benzyl glycidyl ether. The main set A is observed at m/z 708.1, 872.2 and 1036.4. The most abundant peak of this series at m/z 872.2 represents adduct ions of macromolecules consisting of two propane-1,2-dioxide units (73.2, Scheme 1) formed from potassium glycidoxide incorporated into the polymer chain, four benzyl glycidyl ether units (Scheme 2) and two methyl end groups (Mcalc = 872.2). Thus, these macromolecules contain six oxygen atoms in the main chain.
O
3. Results and discussion
CH2
CH
CH2 O
Scheme 1.
The oligomerization of the reagents was carried out at the benzyl glycidyl ether to alkalide molar ratio equal to 5:1. A product with Mn = 1600 was formed in this process as measured by GPCMALLS (Mn = 1400 for PS calibration). A representative part of its MALDI-TOF spectrum (Fig. 1) shows four series of potassium adduct ions
CH2OCH2Ph CH2
CH
O
Scheme 2.
A 872.2
A 1036.4
A B
708.1
B
796.2
873.2
960.4
1037.4
E
1124.6
E
766.2
1004.4
840.2 709.1
C
748.1
720.1 694.0 695.0
700
762.1
838.2
750
841.2 794.2
800
961.4
C
797.2
767.1
734.1
B
1002.4
F
884.3 885.3
914.3
958.4
D 962.4
926.3
854.3
850
F
912.3
900
C 1048.5
1005.4
1049.5
1018.4 1050.5
1000
1094.5 1090.5
973.4
950
F
1050
1125.6
D 1136.6
1093.5
1137.6
1100
1150
m/z Fig. 1. MALDI-TOF spectrum of the oligomer obtained in the reaction of alkalide K , K+(15-crown-5)2 with benzyl glycidyl ether in tetrahydrofuran solution at 25 C. Peaks of potassium adduct ions of macromolecules with two, three, four and five propane-1,2-dioxide units are denoted as A, B, C and D, respectively. Peaks of lithium adduct ions of macromolecules with two and three propane-1,2-dioxide units are denoted as E and F, respectively.
A. Stolarzewicz et al. / Reactive & Functional Polymers 67 (2007) 120–126
Macromolecules with three, four and five propane-1,2-dioxide units are also found in this sample. Their peaks are seen in series B at m/z 796.2, 960.4 and 1124.6, in series C atm/z 720.1, 884.3 and 1048.5, and in series D atm/z 973.4 and 1136.6, respectively. The former, i.e. the most abundant peak in series B represents potassium adduct ions of macromolecules containing three propane-1,2-dioxide units, three benzyl glycidyl ether units and three methyl end groups (Mcalc = 796.2). It means that these macromolecules also contain six oxygens in the main chain.
Macromolecules with one propane-1,2-dioxide unit were not identified. Moreover, two series of lithium adduct ions are observed in the spectrum. They are adducts ions of macromolecules with two propane-1,2-dioxide units present at m/z 840.2 and 1004.4 denoted as series E, and with three propane-1,2-dioxide units at m/z 766.2, 926.3 and 1094.5 denoted as series F. The last peak, for example, was assigned to macromolecules containing three propane-1,2-dioxide units, five benzyl glycidyl units and three methyl end groups (Mcalc = 1092.6).
K , K
OCH2Ph O
K0
O
CH2Ph
K0
, K
O
O , K O
PhCH2
1 K0
PhCH2 , K
OCH2Ph O
O ,K
PhCH2CH2Ph
O
2 where
123
K+ denotes the complex with two 15-crown-5 molecules. Scheme 3.
124
A. Stolarzewicz et al. / Reactive & Functional Polymers 67 (2007) 120–126
be assumed that the oxirane ring was really opened during the oligomerization. Moreover, no signals of any other starting group were observed in the spectra and the signal of methyl end groups was identified at 59.91 ppm in the 13C NMR spectrum of the methylated sample. Taking into account all these facts a following mechanism of the oligomerization is proposed. At first potassium glycidoxide with and without crown ether, denoted as 1 and 2, respectively, is obtained in the reaction of alkalide with benzyl glycidyl ether as described in Ref. [24] (Scheme 3). Alkoxide 1 can serve as the inimer and 2 only as an oxirane co-monomer because it is not activated. Therefore, the oligomerization has to be initiated by 1 (Scheme 4). This alkoxide adds one or more benzyl glycidyl ether molecules as well as potassium glycidoxide ones. If one of the latter is 2 then its ‘‘free’’ K+ can be enclosed step by step with the growing chain. A free anion, i.e. an additional active centre is formed at the same time. On the other hand, the surrounded potassium cation can originate from its complex with 15-crown-5 if the growing chain does not possess ‘‘free’’ K+. The intramolecular cyclization is expected to occur mainly when the oligomer possesses six oxygen atoms in the main chain. Cyclic hexamer 3 being in this case the final reaction product is
The results of MALDI-TOF analysis correlate very well with works on the anionic polymerization of ethylene oxide presented by Kazanskii [4,5]. It was shown that the counter-ion is surrounded gradually by the growing oligoether chain. Reaction rate constants of the ethylene oxide addition to the alkoxide active centre with K+ increased substantially until the incorporation of sixth monomer molecule. The chain with six oxygen atoms was preferred to form a complex with the potassium cation. Its stability was similar to that of 18-crown-6. If potassium glycidoxide activated 15-crown-5 initiates the oligomerization then the oxirane ring becomes the starting group, i.e. that situated at the beginning of the polymer backbone. Unfortunately, the MALDI-TOF technique does not give information whether this starting group after incorporation of some benzyl glycidyl ether molecules and/or potassium glycidoxide molecules reacts with the end of its own chain, i.e. with the alkoxide active centre. A linear macromolecule with the oxirane starting group and a cyclic macromolecule with the propane-1,2-dioxide unit formed after the oxirane ring opening possess the same molecular masses. NMR and IR techniques were employed to solve that problem. No signal of the oxirane ring was found in the spectra of the oligomer. Thus, it could
O , K
O ,K O
OCH2Ph
O , K O
OCH2Ph
O
O
1
O
OCH2Ph K
K
, O O
, O
K
O
OCH2Ph
3
O
K O
PhCH2O
PhCH2O O
OCH2Ph
, O
O
O
O
O
2
K O
O
OCH2Ph O
O OCH2Ph O
O
OCH2Ph
Ph CH2O
O
O OCH2Ph O
3 Scheme 4.
O
K
A. Stolarzewicz et al. / Reactive & Functional Polymers 67 (2007) 120–126
bifunctional even if the second potassium glycidoxide is not activated crown ether. The molecular mass calculated for its methylated derivative is equal to m/z value of the most abundant peak in Fig. 1. Thus, the oligoether obtained at fivefold excess of benzyl glycidyl ether in relation to alkalide is a mixture of substituted crown ethers of the irregular structure containing a few alkoxide active centres. Their irregularity is connected with a different number of carbon atoms localized between two neighbouring oxygen atoms. This oligoether can be used as a macroinitiator of the polymerization of oxiranes, lactones or some other monomers able to polymerize with potassium alkoxides. A starshaped polymer with an oxacyclic core and with several arms is expected to form in its presence. The number of the arms will depend on the number of activated alkoxide groups. It is shown that the macromolecules with two alkoxide groups are always bifunctional. The macromolecules containing three alkoxide groups can be bifunctional or trifunctional. From the statistical point of view the functionality of the macromolecules with four and five alkoxide groups can range between two and four and two and five, respectively. Intensity of the peaks derived from the macromolecules with two and three methoxy groups obtained after methylation is greater then those with four and five ones. However, in such cases the MALDI-TOF technique usually does not give quantitative results. The quantitative analysis of polymers or copolymers have been demonstrated only for a limited number of systems [27,28]. The estimation was found to be near to real terms when the polymer was composed of similar monomers [29]. It means that the average functionality of the new macroinitiator can be equal to about three and this macroinitiator is expected to produce star-shaped polymers possessing mainly three arms. 4. Conclusions Substituted crown-like oligoether of the irregular structure possessing alkoxide groups is prepared in the reaction of alkalide K , K+(15-crown-5)2 with an excess of benzyl glycidyl ether. The number of alkoxide groups is equal to two to five. Some of them are activated by 15-crown-5 and some others by the cyclic oligoether itself. They should become
125
active centres after the addition of a monomer. A star-shaped polymer containing the cyclic core and arms built from the selected monomer can be obtained in this case. Acknowledgement This work was supported with the Committee of Scientific Research in Poland (Project no. 4 TO9A 036 25). References [1] L.E.St. Pierre, C.C. Price, J. Am. Chem. Soc. 78 (1956) 3432. [2] E.C. Steiner, R.R. Pelletier, R.O. Trucks, J. Am. Chem. Soc. 86 (1964) 4678. [3] J. Plucin´ski, H. Matyschok, R. Janik, H. Prystasz, Angew. Makromol. Chem. 97 (1981) 35. [4] K.S. Kazanskii, in: N.S. Enikolopov (Ed.), Khimija i tekhnologija vysokomolekularnykh soedinenij, VINITI, Moskva, 1977, p. 35. [5] K.S. Kazanskii, Y.Ya. Kaminskii, N.V. Ptitsyna, V.S. Romanova, I.N. Topchieva, Vysokomol. Soedin. Sect. A 10 (1987) 2219. [6] A. Stolarzewicz, D. Neugebauer, Z. Grobelny, Macromol. Chem. Phys. 196 (1995) 1301. [7] Z. Grobelny, A. Stolarzewicz, B. Morejko-Bu_z, G. Buika, J.V. Grazˇulevicˇius, A. Maercker, Eur. Polym. J. 38 (2002) 2359. [8] A. Stolarzewicz, Z. Grobelny, Makromol. Chem. 193 (1992) 531. [9] H. Janeczek, Z. Jedlin´ski, Polish J. Appl. Chem. 41 (1997) 377. [10] Z. Grobelny, A. Stolarzewicz, D. Neugebauer, B. MorejkoBu_z, Eur. Polym. J. 38 (2002) 1065. [11] A. Stolarzewicz, D. Neugebauer, J. Grobelny, Macromol. Rapid. Commun. 17 (1996) 787. [12] A. Stolarzewicz, D. Neugebauer, Macromol. Chem. Phys. 200 (1999) 2467. [13] J. Milgram, USA Pat. 3,278,457 (11.09.1966). [14] J. Kuyper, G. Boxhoorn, J. Catal. 105 (1987) 163. [15] S.D. Seneker, C.C. Shen, N. Barksby, Polyurethanes World Congress (1993) 568. [16] G. Łapienis, S. Penczek, Macromolecules 33 (2000) 630. [17] A. Dworak, A. Kowalczuk-Bleja, B. Trzebicka, W. Wałach, Polym. Bull. 49 (2002) 9. [18] A. Sunder, R. Hanselmann, H. Frey, R. Mu¨llhaupt, Macromolecules 32 (1999) 4240. [19] A. Sunder, R. Mu¨lhaupt, H. Frey, Macromolecules 33 (2000) 309. [20] A. Stolarzewicz, B. Morejko-Bu_z, Z. Grobelny, W. Pisarski, M. Lanzendo¨rfer, A. Mu¨ller, Rapid Commun. Mass Spectrom. 18 (2004) 716. [21] A. Stolarzewicz, B. Morejko-Bu_z, Z. Grobelny, W. Pisarski, H. Frey, Polymer 45 (2004) 7047. [22] A.H.E. Mu¨ller, D. Yan, M. Wukow, Macromolecules 30 (1997) 7015.
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