Synthesis of Polyisobutylene with Sec-Arylamino Terminal Group by Combination of Cationic Polymerization with Alkylation*

Synthesis of Polyisobutylene with Sec-Arylamino Terminal Group by Combination of Cationic Polymerization with Alkylation*

Chinese Journal of Polymer Science Vol. 27, No. 4, (2009), 551−559 Chinese Journal of Polymer Science ©2009 World Scientific SYNTHESIS OF POLYISOBUTYLENE WITH SEC-ARYLAMINO TERMINAL GROUP BY COMBINATION OF CATIONIC POLYMERIZATION WITH ALKYLATION* Cheng-long Zhang, Yi-xian Wu**, Xiao-yan Meng, Qiang Huang, Guan-ying Wu and Ri-wei Xu Beijing University of Chemical Technology, State Key Laboratory of Chemical Resource Engineering, Beijing 100029, China Abstract The highly reactive polyisobutylenes (PIBs) with α-double bonds (87.5 mol%) or tert-chloro (tert-Cl) groups (95 mol%) could be prepared via the cationic polymerization of isobutylene (IB) coinitiated by BF3 or TiCl4 respectively. The Friedel-Crafts alkylation of diphenylamine (DPA) with the highly reactive PIB with α-double bonds was further conducted under different conditions, such as at different alkylation temperature, in the mixed solvents of CH2Cl2/n-hexane with different solvent polarity and at DPA concentration ([DPA]). The resultant PIBs with sec-arylamino terminal groups were characterized by GPC with RI/UV dual detectors and 1H-NMR spectrum. The experimental results indicated that alkylation efficiency increased with increases in reaction temperature, solvent polarity and [DPA]. The 77 mol% of sec-arylamino terminated PIBs could be obtained in 10/90 (V/V) mixture of nHex/CH2Cl2 with [DPA]/[PIB] of 3.0 at 60°C for 45 h. Moreover, the alkylation of DPA with highly reactive PIBs with mainly tert-Cl terminal groups was also carried out in 10/90 (V/V) mixture of CH2Cl2/nHex with [DPA]/[PIB] = 3.0 at 60°C for 45 h, and almost monoalkylation with 100 mol% sec- arylamino terminal groups could be achieved. These results will help further explorations of the molecular engineering via combination of cationic polymerization with alkylation. Keywords: Polyisobutylene; Cationic polymerization; Diphenylamine; Alkylation. INTRODUCTION End functional polyisobutylenes (PIBs) constituting numerous industrial polymers are intimately related to improved elasticity, gastight ability, thermal and oxidative stability. Amino-terminated PIBs are important for chain extension and crosslinking reaction and have a potential application in fuel additives. A variety of methods have been used for preparation of functional PIBs including primary, secondary and tertiary amine end groups[1−11]. PIBs with the dichloroboron head group was synthesized by cationic polymerization of isobutylene (IB) via haloboration-initiation with boron trichloride and then reacted with azide by organoborane chemistry to obtain PIBs with functional groups of primary and secondary amine[1−3]. The amino-terminated PIBs were prepared by reaction of hydroxy-terminated PIBs with carbonyldiimidazole to obtain PIBs with imidazolylformate groups and then by coupling with ethylenediamine[4]. The Gabriel synthesis was used to prepare a variety of primary and tertiary amino-telechelic PIBs from α,ω-di(hydroxy)-PIB[5]. Kennedy et al. synthesized the telechelic PIBs with α-phenyl and ω-tert-Cl groups via controlled cationic polymerization in the first step and then obtained PIBs with α,ω-nitroaryl groups by alkylation and nitration of phenyl groups and [6] finally got telechelic PIBs with arylamino groups by quantitative reduction with SnCl2/HCl . The second and * This work was supported by the National Natural Science Foundation of China (No. 20774008) and Ministry of Education (No. IRT0706). ** Corresponding author: Yi-xian Wu (吴一弦), E-mail: [email protected] Received April 10, 2008; Revised May 21, 2008; Accepted May 22, 2008 552 C.L. Zhang et al. tertiary amino-terminated PIBs synthesized by quantitative epoxidation of α-double bond terminated PIBs and [7] the subsequent reaction with excess CH3NH2 . A kind of PIB amines was prepared by reaction of the carbonyl functionalized PIB with amine and then hydrogenation[8]. However, there are few reports on the synthesis of amino-terminated PIBs by directly quenching the cationic polymerization of IB with ammonia since the rapid equilibrium existed between dormant and active species in controlled/living cationic polymerization of IB coinitiated by TiCl4 or BCl3 and PIBs with tert-Cl end groups was normally obtained. Functional PIBs with primary amine could be obtained by capping the living carbocation of polymer chain with 1,1-diphenylethylene and then quenching with dry ammonia[9]. N-methylpyrrole-terminated PIBs could be directly prepared through end-quenching quasiliving cationic polymerization of IB with N-methylpyrrole[10]. Very recently, the arylamino-terminated PIBs were synthesized by alkylation of triphenylamine (TPA) with terminal reactive PIBs containing both α-double bonds and tert-Cl groups and could also be directly prepared by introduction of a certain amount of TPA into the controlled cationic polymerization system of IB without quenching in one pot[11]. In this paper, the alkylation of DPA with highly reactive PIBs with α-double bonds or tert-Cl groups were investigated at different alkylation conditions such as alkylation temperature, solvent polarity and DPA concentration to obtain functional PIBs with sec-arylamino end groups respectively. EXPERIMENTAL Materials 2,4,4-Trimethyl-1-pentene (TMP) (99% purity, Acros Organic Corp. Belgium), 2,6-di-tert-butyl-pyridine (DtBP) (99% purity, Acros Organic Corp. Belgium) and diphenylamine (DPA) (AR, Guangdong Shantou chemical Ltd. Corp) were used as received. Isobutylene (IB) (99.0% purity, Beijing Yanshan Petroleum Chemical Corp.) was cooled to liquid before being charged to test tubes. Dimethylacetamide (DMA) (AR, Beijing Chemical Corp.) was freshly distilled before use. Dichloromethane (CH2Cl2) and n-hexane (nHex) (AR, Beijing Yili Fine Chemical Ltd. Corp.) were distilled from calcium hydride prior to use. TiCl4 (99.9% purity, Yili Fine Chemical Ltd. Corp.) was packaged under nitrogen. Synthesis and Characterization of 2,4,4-Trimethyl-1-pentyl Chloride (TMPCl) 2,4,4-Trimethyl-1-pentyl chloride (TMPCl) was synthesized by hydrochlorination of TMP with HCl[12]. A typical procedure was as follows: neat TMP (30 mL, around 21.5 g) was charged into a 100 mL round-bottomed flask equipped with magnetic rotor, HCl gas inlet and outlet tubes and external ice/water cooling bath. HCl gas produced in a separate reactor by the dropwise addition of 98% concentrated H2SO4 to solid NaCl. HCl gas was passed through a column packed with anhydrous calcium chloride and then bubbled continuously into the agitating TMP liquid for around 8 h at ice bath temperature. Progress of the reaction was monitored using 1H- NMR by observing the disappearance of the vinyl protons of the TMP (δ = 4.62, δ = 4.84). Excess HCl was neutralized by the slow addition of NaHCO3 while magnetic agitating the TMPCl liquid. Anhydrous MgSO4 was added to the TMPCl after all the excess HCl had been neutralized. The liquid product was then filtered, and stored in the refrigerator until use (21 mL, 70% yield). Synthesis of Highly Reactive PIBs Synthesis of PIB with tert-Cl terminal groups was carried out in a three-necked round bottom flask (500 mL) under dry nitrogen atmosphere at −80°C. 156 mL nHex, 104 mL CH2Cl2, and 21 mL IB were added sequentially into a prechilled flask via pipettes. 0.84 mL (4.93 × 10−3 mol) TMPCl, 0.5 mL pure DMA and 1.4 mL (0.1 mol/L) DtBP were airtightly transferred to the flask. The mixtures were stirred for 30 min at −80°C. The polymerization was started by addition of 10.5 mL pure TiCl4 under nitrogen atmosphere and terminated after 90 min by injection of 20 mL ethanol. After evaporation of volatiles, the polymer product was washed with water until neutral and then dried in a vacuum oven at 40°C to a constant weight. Monomer conversion was determined gravimetrically. Synthesis of PIB with 87.5 mol% of α-double bonds and 12.5 mol% β-double bond terminal groups was [13] synthesized by cationic polymerization of IB coinitiated by BF3 in our laboratory . Synthesis of Polyisobutylene with sec-Arylamino Terminal Group 553 Alkylattion of DPA with Highly Reactive PIBs A certain quality of PIBs with 87.5% of α-double bond terminal groups or with 95% of tert-Cl terminal groups was transferred to a large glass ampoule of 500 mL under dry nitrogen atmosphere. nHex and CH2Cl2 were added to dissolve PIB chains completely, and the polymer solution was stirred for 0.5 h. Every 20 mL portion was airtightly transferred to test tube (100 mL) via a 20 mL volumetric pipette, then DPA solution in CH2Cl2 ([DPA] = 0.5 mol/L) was added. Alkylation reaction was started by rapid addition of quantitative TiCl4 solution in CH2Cl2 ([TiCl4] = 5.0 mol/L) at designed temperature and terminated by 10 mL ethanol after 45 h. The Purification of Polymer Products after Alkylation Reaction The polymer solution after alkylation reaction was washed with a series of dissolution-centrifugalization- deposition process to remove impurities and washed with ethanol at 20°C for several times to extract the unreacted DPA completely. The purified products were then dried in a vacuum at 40°C until a constant weight. Characterization [14] The content of H2O in the polymerization system was determined by SF-6 Coulometric Karl Fisher Titrator . Gel permeation chromatography (GPC, Waters 515-2410) with RI/UV dual detectors was performed on samples to determine number-average molecular weight (Mn) and molecular weight distribution (MWD, PDI, Mw/Mn) and UV characteristic absorption at λmax of around 293 nm with elution time at 30°C. Tetrahydrofuran (THF) served as solvent of samples with the concentration of 20 mg polymers per 10 mL of THF and the mobile phase at a flow rate of 1.0 mL/min. Molecular weight calibration was performed by polystyrene standards. 1 H-NMR was performed on DPA, PIB precursors and alkylated products dissolved in CDCl3 to characterize end groups of polymers with a Bruker AV600 MHz at 25°C.

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