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Designed Monomers and Polymers
ISSN: (Print) 1568-5551 (Online) Journal homepage: https://www.tandfonline.com/loi/tdmp20
Synthesis of polytetrahydrofuran
macromonomeric peroxy initiators via cationic
polymerization
Sevil Savaskan , Cüneyt Volga & Baki Hazer
To cite this article:
Sevil Savaskan , Cüneyt Volga & Baki Hazer (1998) Synthesis of
polytetrahydrofuran macromonomeric peroxy initiators via cationic polymerization, Designed
Monomers and Polymers, 1:1, 111-119, DOI: 10.1163/156855598X00161
To link to this article: https://doi.org/10.1163/156855598X00161
Published online: 02 Apr 2012.
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Short communication
Synthesis of polytetrahydrofuran macromonomeric peroxy initiators via cationic polymerization
SEVIL SAVA�KAN,1 CÜNEYT VOLGA1 and BAKI HAZER2
1 Karadeniz Technical University, Department of Chemistry, Trabzon 61080, Turkey
2Zonguldak Karaelmas University, Department of Chemistry, Zonguldak 67100 and TUBITAK-Marmara Research Center, Food Science and Technology Research Institute, Gebze 41470, Kocaeli, Turkey Received 13 June 1997; accepted 3 October 1997
Abstract-Polytetrahydrofuran macromonomeric initiators (poly-THF-inimer) were synthesized via cation- ic polymerization of THF, initiated by the combination of AgSbF6 and mono-, di-, or tetra-bromomethyl benzoyl peroxides, followed by termination with methacrylate anion. The macroinimers were character- ized by 1H-NMR and GPC techniques. Copolymerization of poly-THF-inimers with methyl methacrylate (MMA) gave crosslinked block copolymers. Sol-gel analysis and swelling measurements of the crosslinked product are also reported.
Keywords: Macroinimer; cationic polymerization; crosslinked block copolymer.
1. INTRODUCTION
Macromonomeric initiators which behave as a macromonomer, a macroinitiator, and a macrocrosslinker have attracted great interest because they lead to crosslinked or branched block copolymers [1-3] (Scheme 1).
Macroinimers can be divided into two classes, according to the free radical initiator group: (1) macroazoinimers, and (2) macroperoxy inimers. We have recently reported the synthesis of these two types of macroinimers [2-5]. As a typical macroazoinimer, polyethylene glycol (PEG)-azo inimers are synthesized by the reaction of 4,4'-azobis- (4-cyano-pentanoyl chloride) (ACPC) with PEG, followed by reaction with methacry- loyl or 4-vinyl benzyl chloride [2, 3]. Poly-THF peroxy inimer as a macroperoxy in- imer was previously obtained by the reaction of poly-THF-diol, isophorandiisocyanate, 2,5-dimethyl-2,5-dihydroperoxyhexane, and isocyanatoethyl methacrylate [4, 5] as de- scribed in Scheme 2. Ba§kan et al. [6] have very recently reported on the poly-THF azo inimer via the cationic route. Combination of AgSbF6 and ACPC initiates the cationic polymerization of THE Termination of the growing poly-THF-azoinitiator with methacrylate anion yields poly-THF-azo inimer.
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Scheme 1.
The present paper describes the synthesis of poly-THF-peroxy inimer obtained by the cationic polymerization of THF with bromomethyl benzoyl t-butyl peroxy ester (t-BuBP) or bis-(4-bromomethyl benzoyl) peroxide (BBP) or bis-(3,5-dibromomethyl benzoyl) peroxide (BDBP) in the presence of AgSbF6, followed by termination with the sodium salt of methacrylic acid as shown in Scheme 3.
2. EXPERIMENTAL
2.1. Materials
THF was refluxed and distilled over a sodium and benzophenon mixture after pro- ducing a purple color, just before use. MMA was purified in a conventional manner. AgSbF6 and Na202 were used without further purification. Sodium salt of methacrylic acid was obtained by the reaction of equimolar amounts of methacrylic acid and aque- ous NaOH solution. It was purified by reprecipitation from methanol solution into excess acetone [6].
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Scheme 2.
2.2. Synthesis of bromomethyl functional peroxide initiators (t-BuBP, BBP, and BDBP)
As a typical example, in order to prepare the monofunctional peroxide initiator t-BuBP, 4.67 g (21.5 mmol) of 4-bromomethyl benzoyl bromide, 2.4 g (21.5 inmol) of t-butyl hydroperoxide, 10 ml of 30% aqueous NaOH solution, and 50 ml of diethyl ether were stirred at 0°C for 1 h. The organic phase was washed with distilled water and dried over anhydrous sodium sulfate. White crystals were obtained by three-times crystallization from a mixture of chloroform and n-hexane ( 1 : 1). Melting point of the product: 94°C. H-NMR (8 ppm): 1.5 (9H, methyl protons). Peroxygen analysis was
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done using potassium iodide and isopropyl alcohol reflux and the thiosulfate titration method [7]. The peroxygen content was found to be 11.1 wt%, in agreement with the theoretically calculated value (11.2 wt%). BBP and BDBP were synthesized by the procedure reported in [7, 8].
2.3. Synthesis of poly-THF-inimers
Living poly-THF was prepared by the polymerization of THF (50 ml) initiated by the AgSbF6 and mono-, di-, or tetra-bromomethyl benzoyl peroxide initiator system at 0°C, according to the described procedure [7]. At the end of the given time, the sodium methacrylate suspension of THF was added to the polymerization mixture at 0°C. It was stirred for 3 h, separated from AgBr (s), and the poly-THF-inimer solution was then poured into 0.5 1 of cold 0.1 M NH3 solution. Poly-THF inimer was purified by reprecipitation from diethyl ether solution into petroleum ether. The results and polymerization conditions are listed in Table 1.
2.4. Copolymerization of MMA with poly-THF inimer
Bulk polymerization of MMA initiated by poly-THF inimer was carried out under argon at 80°C. After the desired time, the reaction mixture was poured into excess methanol to precipitate the block copolymer. Soluble and insoluble fractions were separated by extracting with chloroform. The swelling ratio, qv, of the crosslinked
Table 1.
Cationic polymerization of THF with the AgSbF6 and mono-, di- or tetra-bromomethyl benzoyl peroxide initiator system at 0°C
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Table 2.
Copolymerization of MMA (0.47 g) with poly-THF inimers at 80°C for 10 h
block copolymers was calculated by the following equation:
where polymer and Vsoivcnt are the volumes of dry polymer and solvent, respectively. The copolymerization results and conditions are listed in Table 2.
2.5. Polymer characterization
1 H-NMR spectra were taken on a Bruker instrument with solvent CDCI3 and tetra- methyl silane as the internal standard. IR spectra of the sample were taken on a Perkin Elmer 983 Model FT-IR instrument. GPC chromatograms were taken on a Shimadzu gel permeation chromatograph instrument including a CR-4A chromatopac computer and printer, a CTO-6A colon furnace, an RID-6A detector, and an LC- 9A liquid pump. THF was used as the eluant at a flow rate of 0.75 ml/min. A calibration curve was generated with three polystyrene standards: 250000, 90000, 50000 Daltons, of low dispersity from Polyscience. DSC and TGA curves were recorded on a Du Pont 910 differential scanning calorimeter. Measurements were carried out from -90°C to 140°C under nitrogen at a scanning rate of 10°C/min. Specimen sizes were of the order of mg.
3. RESULTS AND DISCUSSION
Mono-, di-, and tetra-functional initiators [7-9] were used in the synthesis of the living poly-THF-containing peroxygen group (active poly-THF), which was terminated by the sodium salt of methacrylic acid to prepare poly-THF inimer. The conditions and results of the polymerization are listed in Table 1. An equimolar ratio of bromomethyl functional groups to the silver salt as the initiator system was chosen. There was no measurable polymer after polymerization for 1.5 h at 0 °C (run No. 1), indicating that there is an induction period at around 1.5 h for the monofunctional peroxide initiator
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system. Low conversion of THF between 2.9 and 5.7 wt% was observed because bromomethyl initiators are slow initiators in cationic polymerization [10]. This low conversion also helps to keep the solution at a low viscosity to react with methacrylate anion completely. The Mn and Mw/ Mn values are also listed in Table 1. When we compare these values, it can be seen that the Mn of poly-THF inimer increases with increasing initiator functionality. These results are in good agreement with the results obtained by Cai and Yan for cationic polymerization with di-, tri-, and tetra- bromomethyl benzene [I I ]. The chemical shifts of the vinylic protons and phenyl protons of poly-THF inimer were observed at 5.6 and 7.4-8.1 ppm, respectively (Fig. I ). The IR spectra of the poly-THF-inimer samples exhibited characteristic peaks at 1720 (ester carbonyl), 1608 cm-1 (vinylic aromatic groups), and 1100 cm-1 (etheric groups of poly-THF).
Copolymerization of MMA with poly-THF inimer demonstrated the macroinimer characteristic behavior [2, 3] resulting in a crosslinked product. The poly-THF-inimer samples listed in Table I were used in the copolymerization. Poly-THF inimer ob- tained by using t-BuBP led to completely soluble branched block copolymer (run
Figure 2. DSC curves of pure poly-THF inimer (run No. 5, Table 1) and poly(THF-b-MMA) crosslinked block copolymer (run No. 21, Table 2).
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No. 22), while those obtained by using BBP or BDBP resulted in crosslinked copoly- mers with a swelling ratio between 2.40 and 5.56. The first three runs 16-18 and the second three runs 19-21 show a smooth decrease in which means that the poly-THF inimer obtained after a longer polymerization time (6 h) has a smaller One can conclude that a higher bromomethyl functionality in the peroxidic initiator produces more active cationic sites as the polymerization proceeds [10].
Thermal analysis of crosslinked block copolymers was carried out by taking DSC and TGA curves. All samples exhibited glass (7g) and melting transitions (T",) arising from the poly-THF units (Fig. 2). Peroxygen decomposition of sample 5 in Table 1 around 125 °C was confirmed by the peroxide group in the poly-THF-inimer samples. It disappeared in the second cycle as expected. Poly-THF units undergo very fast crystallization because they have a melting transition around 25-30°C in the first and even in the second cycle. Notably, it was observed that the Tg shifted to 72°C in comparison with the pure homo PMMA (Tg at 110°C), because of the miscibility of poly-THF units with PMMA units in the crosslinked copolymer.
The poly-THF content in the crosslinked block copolymer was calculated as 30- 50 wt% from the TGA curves, which have two weight loss temperatures, 370°C (poly-THF units) and 400 °C (PMMA units).
REFERENCES
1. B. Hazer, in: Polymeric Materials Encyclopedia, J. C. Salamone (Ed.), Vol. 6, pp. 3911-3918. CRC Press, New York (1996);
M. K. Mishra and Y. Yagci, in: Macromolecular Design Concept and Practice, M. K. Mishra (Ed.), pp. 499-506. Polymer Frontier International, New York (1994);
B. Hazer, J. Macromol. Sci. Chem.: Pure Appl. Chem. A32, 889-895 (1995). 2. B. Hazer, Macromol. Chem. 193, 1081-1086 (1992).
3. B. Hazer, B. Erdem and R. W. Lenz, J. Polym. Sci. A: Polym. Chem. 32, 1739-1746 (1994). 4. S. Sava�kan and B. Hazer, Angew. Makromol. Chem. 239, 13-26 (1996).
5. B. Hazer and S. Sava�kan, Eur. Polym. J. (accepted).
6. A. Ba�kan, S. Denizligil and Y. Yagci, Polym. Bull. 36, 27-34 (1996). 7. B. Hazer, Eur. Polym. J. 26, 1167-1170 (1990).
8. B. Hazer, Eur. Polym. J. 27, 975-978 (1991).
9. B. Hazer, I. Çakmak, S. Küçükyavuz and T. Nugay, Eur. Polym. J. 28, 1295-1297 (1992). 10. E. Franta and L. Riebel, in: ACS Symposium Series, J. E. McGrath (Ed.), pp. 183-194. American
Chemical Society, Washington, DC (1985).
