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

Home , Boron trichloride

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. Chemical shifts were referenced to tetramethylsilane (TMS).

Alkylation degree (Ad) is defined as describing the degree from monoalkylation of DPA to dialkylation with 1 PIB chains. On the basis of H-NMR characterization of phenyl moiety and the corresponding assignments, Ad was calculated according to the following equation.

Sb,b' − 2Sc Alkylation degree (Ad ) = Sb,b'

Sb,b' — the integral value of around δ = 7.06; Sc — the integral value of around δ = 6.93.

Theoretically, the corresponding Ad is equal to 0.5 and 1.0 when monoalkylation and dialkylation take place respectively.

RESULTS AND DISCUSSION Alkylation of DPA by PIB with α-Double Bond Terminal Groups The alkylation reaction of DPA with PIB with 87.5% of α-double bonds and 12.5% of β-double bonds catalyzed by Lewis acid TiCl4 was carried out at different temperatures from −14°C to 60°C for 45 h in nHex/CH2Cl2 (60/40, V/V) mixed solvent. As well known, the α-double bond is much more reactive than the β-double bond. The GPC traces of the products after alkylation by RI/UV dual detectors are shown in Fig. 1. UV detector is only sensitive to phenyl groups in PIB chains, and RI detector is sensitive to both phenyl groups and PIB chains. It can be seen from Fig. 1 that all the GPC traces by RI detector presented unimodal molecular weight distribution, and molecular weights increased slightly by comparing with that of the unreacted PIB precursor. All the GPC traces recorded by UV detector were nearly identical with those by RI detector, indicating that sec- arylamino terminated PIB chains could be prepared by the alkylation of DPA with the highly reactive PIB with 87.5% of α-double bonds. The UV absorption intensity increased from 1.55 × 10−4 to 2.31 × 10−3 with increasing reaction temperature from −14°C to 60°C at the same concentration of polymers in THF, which indicated that the alkylation could be facilitated at relatively high reaction temperatures. Furthermore, it can be seen from Fig. 1 that the RI trace of polymer after alkylation at 60°C evidently shifted to the left, and thus the

Mn of polymer increased from 3400 before alkylation to 4900 after alkylation, which is most likely due to the dialkylation to some extent. 554 C.L. Zhang et al.

No. Ta (°C) Mn Mp PDI Intensity (UV) B8 60 4900 5300 1.36 2.31 × 10−3 B7 50 3400 4700 1.80 1.42 × 10−3 B5 40 3100 4700 1.75 8.03 × 10−4 B4 30 3300 4700 1.65 6.80 × 10−4 B3 15 3400 4700 1.72 5.78 × 10−4 B2 −4 3600 4900 1.53 5.21 × 10−4 B1 −14 3200 4700 1.67 1.55 × 10−4 PIB 3000 4600 1.72

Fig. 1 RI traces (RI detector) and UV traces (inverted curves by UV detector) of PIBs obtained at different reaction temperatures nHex/CH2Cl2 = 60/40 (V/V), [DPA]/[PIB] = 0.65, [TiCl4]/[PIB] = 40.9, ta = 45 h

The effect of solvent polarity on alkylation of DPA with PIB with 87.5% of α-double bonds catalyzed by

TiCl4 at 60°C was further investigated in different volume ratios of nHex to CH2Cl2 while holding other conditions constant. The GPC traces of the corresponding products after alkylation recorded by RI/UV dual detectors are given in Fig. 2. As shown in Fig. 2, all the GPC traces by RI or UV detector presented unimodal molecular weight distribution, and the corresponding RI and UV curves were nearly identical with each other. The results indicate that the sec-arylamino terminated PIB chains could be prepared by alkylation of DPA with highly reactive PIB at different ratios of nHex/CH2Cl2 solvent mixture with different solvent polarity. However, the UV absorption intensity was relatively weak when the percentage of CH2Cl2 in mixed solvent was less than

50%, while it was relatively strong when the volume percentage of CH2Cl2 in mixed solvent (ϕ(CH2Cl2)) was equal to or more than 50%. According to the data of UV absorption intensity in Fig. 2, the intensity increased −2 with an increase in the solvent polarity and reached 1.43 × 10 when ϕ(CH2Cl2) = 88%, and then decreased to −2 1.28 × 10 when ϕ(CH2Cl2) = 97% since CH2Cl2 is not a good solvent for the PIB chains. Therefore, the 10/90

(V/V) nHex/CH2Cl2 mixed solvent had better be used in the alkylation for both solubility of PIB and DPA. The effect of [DPA] on alkylation of DPA with PIB was further investigated by varying DPA concentrations in 10/90 (V/V) nHex/CH2Cl2 mixed solvent at 60°C and while keeping other conditions the same. The experimental results are shown in Fig. 3. The corresponding GPC traces recorded by dual RI/UV detectors were unimodal and coordinated with each other for every set of conditions. The UV absorption intensity of PIB solution in THF by UV detector of GPC is also given in Fig. 3. The intensity increased from 3.65 × 10−3 to 5.43 × 10−2 when [DPA] increased from 2.4 × 10−3 mol/L ([DPA]/[PIB] = 0.5) to 1.4 × 10−2 mol/L ([DPA]/[PIB] = 3), which was attributed to an increase in collision probabilities between reactive terminal groups in polymer chains and DPA molecules.

Synthesis of Polyisobutylene with sec-Arylamino Terminal Group 555

Intensity No. ϕ(CH Cl ) (%) M M PDI 2 2 n p (UV) B1 98 4300 4800 1.60 1.28 × 10−2 B2 88 4200 5300 1.76 1.43 × 10−2 B4 69 4200 5300 1.58 8.19 × 10−3 B6 50 4000 5100 1.64 7.86 × 10−3 B7 41 3800 5200 1.77 1.62 × 10−3 B8 31 3600 4900 1.73 1.98 × 10−3 B9 21 3800 4700 1.51 6.37 × 10−4 B10 12 3800 5000 1.84 2.44 × 10−4 B11 3 3800 4900 1.65 1.28 × 10−4 PIB 3100 4500 1.88 Fig. 2 RI traces (RI detector) and UV traces (inverted curves by UV detector) of PIBs obtained at different solvent polarity [DPA]/[PIB] = 1.0, [TiCl4] = 40, Ta = 60°C, ta = 45 h

No. [DPA] (mol/L) Mn Mp PDI Intensity (UV) B6 1.8 × 10−2 4100 5200 1.59 4.77 × 10−2 B5 1.4 × 10−2 4100 5200 1.59 5.43 × 10−2 B4 9.4 × 10−3 4100 4900 1.78 2.96 × 10−2 B3 4.8 × 10−3 4100 4900 1.73 1.29 × 10−2 B2 2.4 × 10−3 4100 5700 1.92 3.65 × 10−3 PIB 3600 5000 1.68 Fig. 3 RI traces (RI detector) and UV traces (inverted curves by UV detector) of PIB and alkylated products at different [DPA] nHex/CH2Cl2 = 10/90 (V/V), [TiCl4]/[PIB] = 43.5, Ta = 60°C, ta = 45 h 556 C.L. Zhang et al.

The 1H-NMR spectrum of DPA in Fig. 4 indicates that the integrals of peaks at around δ = 7.27, δ = 7.06,

δ = 6.93 and δ = 5.48 have a relative integral ratio of 4:4:2:1 (Ha:Hb:Hc:Ht), which are assigned to meta-, ortho- and para-proton (Ha, Hb, Hc) in phenyl groups and sec-amino proton (Ht) connected to N atoms respectively. The 1H-NMR spectrum of PIB precursor with 87.5% of α-double bonds and 12.5% of β-double bonds is shown in Fig. 4, and the characteristic protons of tert-butyl head groups, repeat isobutyl units, α-double bonds and β-double bond terminal groups are attributed to corresponding resonance signals. The 1H-NMR spectrum of polymer after alkylation (Run B5 in Fig. 3) is also given in Fig. 4. It can be seen that the signals of α-double bonds at δ = 4.85 and δ = 4.64 obviously decreased after alkylation of DPA with PIB precursors, and the corresponding signals of phenyl groups from δ = 7.32 to δ = 6.88 increased greatly at the same time. The inert β-double bond did hardly take part in the alkylation reaction. Interestingly, the signals of tert-Cl terminal groups at δ = 1.96 and δ = 1.69 (2H, 6H, －CH2C(CH3)2Cl) emerged after alkylation of DPA with the PIB only with α- and β-double bonds, which may be attributed to the transformation of carbocation to tert-Cl structure via abstraction of electronegative chlorine atoms from counterions. When the para-hydrogen (Hc) of DPA was substituted by PIB chain, the ortho-protons (Hb') moved upfield by around 0.03, resulting in an overlap of the signals of the product’s ortho-protons (Hb') and residual ortho-protons (Hb) actually. According to theoretical [15, 16] evaluation of the meta-protons (Ha') which would move downfield by around 0.02 , the meta-protons

(Ha & Ha') of the phenyl group where whether para-hydrogen substituted or not were essentially overlapped with the signal of CDCl3 at around δ = 7.26. Therefore, the signals (a, a') at around δ = 7.30 and signals (b, b') at around δ = 7.06 were assigned to the meta-protons (Ha & Ha') and ortho-protons (Hb & Hb') of phenyl groups respectively in which whether para-proton (Hc) was substituted or not. The signal (c) at around δ = 6.91 was assigned to the para-protons (Hc) of phenyl groups in which the para-proton (Hc) was not substituted. The signals (b, b') at δ = 7.06 and the signal (c) at δ = 6.93 can be used for calculation of alkylation degree (Ad).

Fig. 4 1H-NMR spectra of DPA, PIB precursor with α-double bonds and run B5 product in Fig. 3

On the basis of structural analysis and corresponding integral data, the terminal groups in PIB chains after alkylation consist of 1.7 mol% of α-double bonds, 11.1 mol% of β-double bonds, 10.2 mol% of tert-Cl terminal and 77.0 mol% of DPA terminal groups respectively. Theoretically, when mono- or di-alkylation took place, Ad would be 0.5 or 1.0 respectively. According to chemical shifts and corresponding integrals of protons in phenyl rings, the Ad of sample (Run B5) was calculated to be 0.64. If x% was defined as the content of monoalkylation Synthesis of Polyisobutylene with sec-Arylamino Terminal Group 557

(Ad = 0.5), and (1 − x%) represents the content of dialkylation (Ad = 1.0), then

Ad = 0.5 × x% + 1.0 × (100% − x%) Therefore, x% was calculated to be 72%, indicating that PIBs with sec-arylamino terminal groups consists of around 72% monosubstituted and 28% disubstituted chain end groups. Alkylation of DPA by PIBs with tert-Chloro Terminal Groups The cationic polymerization of IB ([IB] = 0.8 mol/L) was conducted by using TMPCl as initiator −2 ([TMPCl] = 1.68 × 10 mol/L) and TiCl4 as coinitiator ([TiCl4] = 0.32 mol/L) in the presence of DMA ([DMA] −2 = 1.84 × 10 mol/L) in the mixture of nHex and CH2Cl2 (60/40, V/V) at −80°C for 90 min. The GPC trace of the resulting PIB is shown in Fig. 5. The controlled cationic polymerization of IB could be achieved at high 1 concentration of initiator, and PIB with Mn of 2700 and with Mw/Mn of 1.48 was obtained. The H-NMR spectrum of the above PIB precursor is given in Fig. 6. The head group of tert-butyl and two kinds of end groups of tert-Cl and α-double bond are also presented in Fig. 6. The formation of end group tert-Cl in polymer chains is attributed to the rapid equilibrium of dormant species with active species. The formation of end groups of double bonds is due to β-proton elimination. On the basis of the assignments and corresponding integral data, the terminal groups in PIB chains consist of 95 mol% of tert-Cl and 5 mol% of α-double bond, both of which are reactive in Friedel-Crafts alkylation reaction.

No. Mn Mp PDI Precursor 2700 3700 1.48 Alkylated 3400 4100 1.34 preduct

Fig. 5 RI traces (RI detector) and UV traces (inverted curves by UV detector) of PIB and alkylated products at different [DPA] −2 Precursor: nHex/CH2Cl2 = 60/40 (V/V), [IB] = 0.83 mol/L, [TMPCl] = 1.68 × 10 mol/L, −2 −4 [TiCl4] = 0.32 mol/L, [DMA] = 1.84 × 10 mol/L, [H2O] = 3.7 × 10 mol/L, [DtBP] = 4.78 × −4 10 mol/L, Tp = −80°C, tp = 90 min, Conv% = 98.9%; Alkylated product: nHex/CH2Cl2 = 10/90 (V/V), [DPA]/[PIB] = 3.1, [TiCl4]/[PIB] = 80.4, Ta = 60°C, ta = 45 h

The alkylation reaction of DPA by the above reactive PIB with 95% tert-Cl terminal groups and 5% of α- double bonds catalyzed by Lewis acid TiCl4 was carried out at 60°C for 45 h in nHex/CH2Cl2 (10/90, V/V) mixed solvent. The GPC trace with RI/UV dual detectors of the alkylated product is shown in Fig. 5. It can be seen that the GPC traces by RI/UV dual detectors presented unimodal molecular weight distribution (Mw/Mn =

1.34) and were identical each other, and Mn increased slightly from 2700 of the PIB precursor to 3400 of the polymer product after alkylation.

558 C.L. Zhang et al.

Fig. 6 1H-NMR spectra of DPA, tert-Cl terminated PIB precursor (A) and alkylated product (B)

The 1H-NMR spectrum of the polymer product after alkylation is given in Fig. 6. It indicates that the signals of tert-Cl groups at δ = 1.96 and δ = 1.69 (2H, 6H, －CH2C(CH3)2Cl) were almost undetectable after alkylation of DPA with PIB precursor with tert-Cl terminal group while the corresponding signals of phenyl groups from δ = 7.32 to 6.88 increased greatly. There are no signals of α-double bonds left in the spectrum. Therefore, all the tert-Cl and α-double bond terminal groups in PIB chains took part in the electrophilic substitution with DPA. According to chemical shifts of characteristic protons in phenyl groups and corresponding integral data, the Ad was calculated to be 0.52 and thus almost only monoalkylation occurred under these reaction conditions.

Scheme 1 The possible mono-alkylation mechanism of DPA with PIBs with α-double bond or tert-Chloro terminal group Synthesis of Polyisobutylene with sec-Arylamino Terminal Group 559

As described above, both the highly reactive PIBs with α-double bonds and tert-Cl end groups can be used for alkylation of DPA catalyzed by Lewis acid TiCl4 in 10/90 (V/V) mixture nHex and CH2Cl2 at 60°C. Although DPA is a weak Lewis base, it can be neutralized with strong acid[17]. The possible monoalkylation or dialkylation of DPA with highly reactive PIB containing α-double bond terminated PIB or tert-Cl terminated one was proposed in Scheme 1 since Friedel-Crafts alkylation theoretically processed via cationic mechanism.

CONCLUSIONS A facile synthetic route to PIBs with sec-arylamino terminal groups had been established by alkylation of DPA with highly reactive PIBs with end groups of α-double bonds or tert-Cl respectively. The experimental results indicate that the alkylation efficiency increased with increases in alkylation temperature, solvent polarity and DPA concentration, and the optimum alkylation could take place at relatively high temperature of 60°C, in highly polar mixed solvent of 10/90 (V/V) nHex/CH2Cl2 and with [PIB]/[DPA] of 3.0. PIBs with 77.0% of sec- arylamino terminal groups and with 100 mol% sec-arylamino terminal groups could be synthesized respectively by alkylations of DPA with α-double bond terminated PIB and tert-Cl terminated one. The possible monoalkylation mechanism of DPA with highly reactive PIB with α-double bonds or tert-Cl terminal groups may be processed via cationic mechanism.

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