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Synthesis of Alkoxylated Phenolic Resins Containing an Acetyl Group and Their Functionalization by Grignard Reaction

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Synthesis of Alkoxylated Phenolic Resins Containing an Acetyl Group and Their Functionalization by Grignard Reaction #2009 The Society of Polymer Science, Japan Synthesis of Alkoxylated Phenolic Resins Containing an Acetyl Group and Their Functionalization by Grignard Reaction By Tadamasa NEMOTO, Isamu AMIR, and Gen-ichi KONISHIÃ We successfully synthesized acetyl group-containing phenolic resins as novel reactive polymers. The addition-condensation of 2,4,6-trimethoxyacetophenone (1) with an equimolar amount of formaldehyde catalyzed by 12 mol/L HCl aq. proceeded 1 homogeneously without side reactions to give polymer 3 (Mn 4800, Mw=Mn 1.3) in 32% yield. The FT-IR, H NMR and 13C NMR spectra of 3 revealed that it had arylene-methylene units on the polymer backbones. The terpolymerization from 1, 1,3,5-trimethoxybenzene (2) and formaldehyde was also carried out. When the feed ratio of 1 to 2 was 1:1, the content of 1 in the obtained polymer, 4, was found to be 25% by the 1H NMR spectrum; hence, the reactivity of 1 was lower than that of 2. The reactions of 4 with Grignard reagents were carried out to evaluate the reactivity of acetyl groups in the obtained polymers. Their reactions proceeded at some parts of acetyl groups, so 4 can be applied as novel reactive phenolic resins. From thermogravimetric analyses, thermal stabilities of the functionalized polymers (6a–6d) are similar to that of 4,soitis expected that 4 have characters not only of the phenolic resins but also of the reactive polymers. KEY WORDS: Novolac / Phenolic Resin / Reactive Polymer / Acetyl Group / Grignard Reaction / Addition-Condensation / Phenolic resins (novolacs)1,2 were the first artificial plastics conventional phenolic resins and high functionality, the ap- that were put to practical use in the last century. Furthermore, plicability of novolacs can be enhanced significantly. these resins are one of the most important thermosetting In this study, we carried out the addition-condensation of materials used in industries and have been frequently used as acetylated phenol derivatives with formaldehyde to yield adhesives, curing agents, photoresists, polymer composites, novolacs containing suitable functional groups. In order to etc.3 The significant characteristics of phenolic resins, such as develop a novel phenolic novolac, we focused on carrying out heat stability and mechanical properties, are attributed to their the addition-condensation of an acetyl group-containing phenol rigid rod-like polymer backbone of ‘‘poly(phenylenemeth- derivative, 2,4,6-trimethoxyacetophenone (1). In organic chem- ylene).’’4 Several studies have been conducted on oligomeric istry, an acetyl group often undergoes reactions such as aldol novolac-based resins (Mw < 1000); however, the fabrication of condensation, oxidation, and hydrazone synthesis. Hence, by such novolacs with high molecular weights has been difficult preparing a novolac containing an acetyl group, we can obtain because of their poor solubility in organic solvents.1,2 There- a novel reactive novolac that can be used in the preparation of fore, in order to realize phenolic resins that can be used as new thermally stable materials. Moreover, we demonstrate the engineering plastics, novel phenolic resins with high molecular use of phenol-based novolacs containing a protected hydroxyl weights must be developed via the protection of phenolic group or alkoxylated group as a new class of high-performance hydroxyl groups by converting them to alkoxyl groups.5 phenolic resins. These novolacs exhibit higher solubility in Furthermore, the resins prepared in this manner exhibit better organic solvents, better processability, and higher resistance to reactivities and solubilities and hence have a wide scope of heat than the conventional phenolic resins.5 In our study, we applications. used 1 as the acetylated phenol derivative for copolymerization Reactive polymers have attracted considerable interest of with formaldehyde. We used 1,3,5-trimethoxybenzene (2)as researchers, because their characteristics and functions can be a substrate in the preparation of a terpolymer of 1, 2 and enhanced to develop crosslinking agents, resist materials, formaldehyde; this terpolymer is expected to exhibit the expandable polymers, etc.6 We have already reported the characteristic properties of phenol derivative-based resins, synthesis of formyl group-containing novolacs in another such as good solubility in organic solvents, high thermal paper.7 These novolacs have the potential to be used as reactive stability, and good processability. Furthermore, in order to polymers in the condensation reaction with alkyl amine or investigate the reactivities of the polymers prepared in our diamine that results in imine conformation or gel formation; study and to demonstrate their use as reactive polymers, furthermore, the obtained gel demonstrated reversibility when we carried out the reactions of these polymers with organo- treated with acids. By developing novel reactive novolacs that magnesium bromides (Grignard reagents) derived from exhibit both thermal stability, which is comparable to that of bromobenzene, 2-bromonaphthalene, 4-bromobiphenyl, and Department of Organic & Polymeric Materials, Graduate School of Science & Engineering, Tokyo Institute of Technology, SORST, Japan Science & Technology Agency (JST), 2-12-1-H-134, Ookayama, Meguro-ku, Tokyo 152-8552, Japan ÃTo whom correspondence should be addressed (Tel: +81-3-5734-2321, Fax: +81-3-5734-2888, E-mail: [email protected]). Polymer Journal, Vol. 41, No. 5, pp. 395–401, 2009 doi:10.1295/polymj.PJ2008321 395 T. NEMOTO,I.AMIR, and G. KONISHI 1-bromopyrene. We also investigated the thermal and the methoxybenzene (2) (0.85 g, 5.0 mmol) were continuously solution properties of the obtained polymers. added. After the mixture was stirred at 50 C for 6 h, it was poured into methanol to give the objective product (4)asa 1 EXPERIMENTAL colorless precipitate in 22% yield. H NMR (CDCl3, 400 MHz, , ppm): 2.36–2.50 (Ar–CO–CH3), 3.20–3.63 (Ar–OCH3), Materials 3.67–4.00 (Ar–CH2–Ar), 6.04–6.32 (aromatic H).; FT-IR (KBr, À1 Unless otherwise noted, all reagents and chemicals were cm ): 2941, 2832 (–CH2–), 1700 (C=O), 1597 (aromatic purchased from TCI and utilized without further purification. C=C), 1105 (Ar–O–CH3). 2,4,6-Trimethoxyacetophenone (1) and 1,3,5-trimethoxyben- Typical Procedure for Grignard Reagents (5a–5d). Magne- zene (2) were obtained from Lancaster and Wako Pure Chem., sium turnings (0.74 g, 30 mmol) were taken in a 200 mL three respectively. Magnesium turnings and paraformaldehyde were necked flask and dried under reduced pressure. Dehydrated purchased from Nacalai Tesque. The dehydrated tetrahydro- diethyl ether (Et2O) (50 mL) and 1,2-dibromoethane (2.0 mL) furan without any stabilizers was obtained from Kanto Chem. were added to the flask in an argon atmosphere. After stirring the mixture at room temperature, the dehydrated Et2O (40 mL) Instruments solution of aryl bromide (10 mmol) was added to the reaction All the 1H NMR and 13C NMR spectra were obtained in mixture at 0 C. After stirring the mixture for 1 h at room CDCl3 and recorded by a JEOL LNM-EX 400 instrument with temperature, it was refluxed for 1 h. Finally, the tannish Et2O tetramethylsilane (TMS) as the internal standard. The Fourier solution was obtained and utilized in the Grignard reaction transfer infrared (FT-IR) spectra were recorded by using a without any purification and titration; 5a: phenylmagnesium JASCO FT-IR 460 plus spectrometer. Gel permeation chro- bromide; 5b: 2-naphthylmagnesium bromide; 5c: 4-biphenyl- matography (GPC) was carried out by a JASCO UV-2075 magnesium bromide; 5d: 1-pyrenylmagnesium bromide. detector and a JASCO RI-2031 detector (TOSOH TSKgel Reaction of Polymer 4 with Grignard Reagents (5a–5d). The G3000HXL or G4000HXL column) using tetrahydrofuran (THF) typical Grignard reaction is as follows. Polymer 4 (the content as an eluent after calibration with polystyrene standards. of acetophenone unit is 25% estimated by the 1H NMR Thermogravimetric analysis (TGA) was performed using a SII spectrum) (0.20 g, 0.26 mmol of acetyl group) and THF TG/DTA 6200 (SEIKO Instrument Inc.) with a heating rate of (20 mL) were added to a 100 mL two necked flask in an argon 10 C/min in a nitrogen atmosphere. The solution properties of atmosphere. After adding the Et2O solution of Grignard the polymers were estimated by a Viscotek Triple Detector reagents (6.0 mmol) to the reaction mixture, the solution was TDA302 system and its analysis program (Omni Sec3.0) using stirred continuously for 1 h at room temperature, and then, THF as an eluent. High Pressure Liquid Chromatography stirred for 1 h at 50 C. 5 mol/L NH4Cl aq. (100 mL) and (HPLC) was carried out by an LC-9204 system with a JAI UV- 1.2 mol/L HCl aq. (100 mL) were added to the reaction 3702 detector (Shodex HF-2002) using THF as an eluent. solution in order to quench the non-reacted organomagnesium Addition-Condensation of 2,4,6-Trimethoxyacetophenone (1) reagent. The organic components were extracted by chloroform with Formaldehyde. Paraformaldehyde (0.30 g, 10 mmol as a (300 mL), and the chloroform solution was washed several formaldehyde unit) and THF (10 mL) were added to a 30 mL times with 0.5 mol/L NaHCO3 aq. (100 mL) and water. The round bottom flask. After stirring for a few minutes, 12 mol/L solution was dried over MgSO4 and evaporated to 10 mL. HCl aq. (2.0 mL) was added at 0 C, and then, 2,4,6-tri- Finally, the resulting solution was poured into methanol methoxyacetophenone (2.1 g, 10 mmol) was continuously (100 mL) to obtain the objective product (6a–6d). 1 added. After the mixture was stirred with a reflux condenser 6a: Yield: 40% (colorless powder): H NMR (CDCl3, 400 at 50 C for 15 h, it was poured into methanol to give the MHz, , ppm): 1.82–1.95 (Ar2–C(OH)–CH3), 2.34–2.51 (Ar– objective product (3) as a colorless precipitate in 32% yield.
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