Anionic Synthesis of Macromonomer Carrying Amino Group Using

Chapter 7

Downloaded by UNIV OF SOUTHERN CALIFORNIA on June 18, 2013 | http://pubs.acs.org Publication Date: May 8, 1998 | doi: 10.1021/bk-1998-0704.ch007

Anionic Synthesis of Macromonomer Carrying Amino Group Using Diphenylethylene Derivative 1

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Jungahn Kim , Jae Cheol Cho , Keon Hyeong Kim , Kwang Ung Kim , Won Ho Jo , and Roderic P. Quirk 2

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Division of Polymer, Korea Institute of Science and Technology, Seoul, Korea Department of Fiber and Polymer Science, Seoul National University, Seoul Korea The Maurice Morton Institute of Polymer Science, University of Akron, Akron, OH 44325-3909

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Anionic synthesis of macromonomer of 1,1-diphenylethylene-type unit carrying amino group has been performed in a variety of solvents. The product was characterized by a combination of H NMR spectroscopic and size exclusion chromatographic analysis. Based on the UV/Visible spectroscopic analysis, the crossover reaction ofn-butyllithium(n-BuLi) with 1-[4bis(trimethylsilyl)amino]phenyl]-l-phenylethylene was found to be so slow in benzene, but it was completed in the benzene/THF mixture within 2 h. The synthesis of macromonomer of the 1,1-diphenylethylene-type unit (over 95 %) carryingamine-functionalgroup (maximum 94 %) was successful on the basis of H NMR spectroscopic analysis. Macromolecular monomers have received a great attention in many fields since the synthetic methodology of the Macromer® has been reported in the patent (1) and other literature (2-4). Macromonomer can be defined as polymeric or oligomeric materials carrying some polymerizable functional group at one chain end or at both chain ends (4-6). As a consequence, graft copolymers or network polymers can be produced by post-polymerization or reaction with other reagents (2,3,7). Morphology and physical properties of the graft copolymers are usually dependent of their structural compositions. Thus, the choice of the molecular weights of macromonomers should be carefully considered for the optimization of physical properties of polymers synthesized from a post-reaction using macromonomers. In this respect, the molecular weights of macromonomers should be chosen in the range of 5 x 10 to 2 x 10 g/mol for compromise between copolymerizability and physical property (6). 1

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Macromonomer can be synthesized by a variety of mechanistic reaction types such as free radical transfer (8), anionic polymerization (2,9), cationic polymerization (10), and step-growth polymerization (H). Anionic polymerization provides the best methodology to synthesize a variety of terminally functionalized polymers with well-defined structure and narrow molecular weight distribution (12,13). In order to prepare macromonomers with non-homopolymerizable functional groups such as 1,1-diphenylethylene-type unit using double diphenylethylene derivatives, a new method has been suggested (14-1£). It has been well-known that diphenylethylene derivatives as the terminating agents possess a great potential for the preparation of the aromatic functionalized polymers in anionic polymerization (17-19). Diphenylalkyllithium can reinitiate other vinyl monomers or dienes resulting in the formation of polymers with functional groups at the a-position of the polymer backbone (20). In this respect, macromonomers with functional group can be prepared by a combination of anionic polymerization using functional initiator and the chain-end functionalization method. Herein, we report the results for the preparation of new macromonomer carrying aromatic amine group.

©1998 American Chemical Society In Functional Polymers; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

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Experimental Section Chemicals. Styrene, benzene, and tetrahydrofuran (THF) were purified as described elsewhere (21). /f-Butylkthum (n-BuLi) as initiator was used without further purification. l,3-Bis(l-phenylethenyl)benzene (MDDPE) was prepared using procedures analogous to those reported by Schulz and Hocker (22) and Tung, et al (23). The synthesis of l-[4-[N,N4)is(trimemylsUyl)aminolphenyl]-l-phenylethylene (ADPE) was performed by following the same procedures as reported by Quirk and Lynch (ID. l-(4-Aminophenyl)-l-phenylethylene was first prepared in benzene by the reaction of 4aminobenzophenone with phosphorus ylide formed by the reaction of methyltriphenylphosphonium iodide with methyllithium, followed by protecting amine group using methyllithium and chlorotrimethylsilane. l-(4-[N,N-bis(trirnethylsity^ (ADPE) was then purified by column chromatography and distillation under high vacuum, followed by making ampoule in a high vacuum line using a calibrated cylinder. Synthesis of Amine-functionalized Macromonomer. All experiments were carried out in all-glass, sealed reactors using breakseals and standard high vacuum techniques at room temperature (21). Aromatic amine-functionalized initiator was first prepared by the reaction of n-butyllithium and ADPE in benzene or benzene/THF ([THF]/[n-BuLi] = 20/1, mol/mol). The completion of the reaction of /t-BuLi with ADPE was determined by the UV/Visible spectroscopic analysis. The relative intensities of the UV/Visible absorption bands at specific wavelength were monitored by adding the initiator into the ADPE/benzene solution, for instance, at Kmx = 455 nm and 280 nm in benzene/THF mixture and at ^ = 422 nm and 280 nm in pure benzene. Styrene was then added to the initiator-containing solution. Anionic polymerization of styrene was carried out at 25 °C for 8 h. An aliquot of the polymer solution was taken for the use as the base polymer, followed by reacting the remaining poly(styryl)lithium with MDDPE ([MDDPEJ/fPLi] = 1.5) in benzene/THF mixture ([benzene]/[THF] = 75/25, vol/vol) at room temperature. These reactions were also monitored using the UV/Visible spectroscopic instrument for at least 12 h. The resulting living polymer was quenched with degassed methanol and precipitated severaltimesinto excess methanol to remove the unreacted excess MDDPE, followed byfilteringand drying in vacuum oven at room temperature for at least 48 h. Characterization. Size-exclusion chromatographic (SEC) analysis of polymers was performed at a flow rate of 1.0 rnL/min in THF at 30 °C using a Waters HPLC component system equipped with five Ultra-//-styragel columns (2 x 10 , 10 , 10 , 500 A) after calibration with standard polystyrene samples. 'H NMR spectra were obtained using a Varian Gemini-200 spectrometer with CDC1 as solvent. UV-Visible absorption spectra of the functionalized initiator, living polymer, and macromonomer were obtained using a Hewlett-Packard 8453 diode array spectrophotometer using 0.5 cm UV cell. 5

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Results and Discussion Synthesis of 1-14-INJ^-bisftrimethvlsilvnaminolnlienvll-l-Dhcnvlethvlene. 4-Aminobenzophenone isfirstconverted to l-(4-aminophenyl)-l-phenylethylene by the 'Wittig' reaction using phosphorus ylide. The diphenylethylene derivative still includes active hydrogens which act as reactive impurities in anionic polymerization. Chlorotrimethylsilane effects the protection of the primary amine group after treatment of 2 equivalent of methyllithium (17). The whole reaction processes are shown in Scheme 1. The occurrence of a competitive reaction between the abstraction of the protons on the aromatic amine group and the crossover reaction with the ethylene-unit by methyllithium in the second step reaction in Scheme 1 is inevitable irrespectively of the reactivity of simple alkyllithium showing a dependence on the dissociated state in the reaction medium Q3). The pK. values of the diphenylethylene-unit (estimation for diphenylmethane) and the aromatic amine (estimation for aniline) are 32.2 and 30.6, respectively (24). In our case the protection yield was about 60 mole %. It seems effective for dislylation of the amine using chlorotrimethylsilane in THF

In Functional Polymers; Patil, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

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Scheme 1

after the treatment of l-(4-aminophenyl)-l-phenylethylene with methyllithium because of its lower reactivity compared to /f-butyllithium found to be an efficient substance for protecting the amine group of aniline using chlorotrimethylsilane (25). 'H NMR spectra of the intermediate material (2) and thefinalproduct (3) purified are shown in Figure 1. Specifically, in Figure 1(a) the chemical shift at 5 - 3.8 ppm corresponds to the protons on the aromatic amine (Ph-N// ) and the peak at 5 = 5.4 ppm is assigned to the protons on the methylene unit (CH = CPh ). As shown in Figure 1(b), the chemical shift at 8 = 0.08 ppm corresponds to the protons of trimethylsilyl group (-N-[Si(C// ) ] ) adjacent to nitrogen atom. The integration of the chemical shifts allowed to confirm the successful synthesis of l-[4-[N,N-bis(trimemylsilyl)amino]phenyl]-l-phenylethylene. 2

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Synthesis of Macromonomer carrying Amine-functional Group. Macromonomer of 1,1diphenylethylene-type unit carrying amine-functional group at the chain end can be prepared by following the reaction procedures as shown in Scheme 2. Diphenylalkyllithum with the silylprotected amine group ([1]), as a functional anionic initiator, isfirstsynthesized from the reaction of ft-butyllithium with l-[4-rN,N-bis(trimethylsilyl)amino]phenyl]-l-phenylethylene in benzene or benzene/THF solution ([THF]/[/?-BuLi] = 20/1, mol/mol). Subsequently, polymerization of styrene at room temperature for at least 8 h allows to produce poly(styryl)lithium ([2]) with amine-functional group. Next, macromonomer of the 1,1-diphenylethylene-type unit ([3]) is produced by adding meto-substituted double diphenylethylene (MDDPE)/benzene solution into the poly(styryl)lithium solution in benzene/THF solution ([benzene]/[THF] = 75/25, vol/vol) within 2 h. It has been well-known that 1,1-diphenylethylene is anionically non-homopolymerizable but copolymerizable with other vinyl monomers (26-28). In addition, it has been reported that the diadduct was negligibly small and monoadduct was exclusively obtained from observation through *H NMR and UV/Visible spectroscopic analysis from the reaction of poly(styryl)lithium and l,4-bis(lphenylethenyl)benzene (PDDPE) in hydrocarbon with polar additive (22). This indicates that the addition of polar additive suppresses the formation of diadduct even in benzene solution at room temperature. As shown in Scheme 2, diphenylalkyllithium ([1]) formed from the reaction of ADPE with nbutyllithium revealed the absorption maximum at ^ 455 nm in benzene/THF mixture and at ^ = 422 nm in pure benzene. Specifically, the cross-over reaction wasfinishedin benzene/THF mixture within at least 2 h, which will be discussed in more detail later. The addition of styrene renders the absorption band at = 455 nm disappeared rapidly and simultaneously new absorption =



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Figure 1. 'H NMR spectra of lK4-aminophenyl)-l-phenylethylene (a) and l-[4-[N,N-bis(trimethylsuyl)amino)phenyl]-l-phenylethylene (b).

band appeared at = 344 nm corresponding to the formation of poly(styryl)lithium in benzene/THF mixture. The UV/Visible absorption spectra of active species prepared in this experiment are shown in Figure 2. On adding MDDPE, the fast cross-over reaction from styryl anion to MDDPE is observed without homopolymerization of MDDPE with regard to the reappearance of an absorption band at Kmx = 455 nm and new development of the absorption peak at C = 280 nm corresponding to the unreacted ethylene unit of the MDDPE without formation of diadduct From these observations, the initiation rate of diphenylhexyllithium ([1]) can be deduced in benzene/THF solution. Completion of the cross-over reaction from the substituted diphenylalkyllithium ([1J) to poly(styryl)lithium ([2]) can be also determined by comparison of the relative intensity of the absorption peaks at K*x = 455 nm and 344 nm, as shown in Figure 3. In this respect, the stoichiometric balance between w-BuLi


89 Scheme 2

n-CHgU • CH>


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and ADPE can be readily controlled by adding /f-BuLi dropwise to the ADPE/benzene solution until the ratio (faWnon) of the relative peak intensity at X™« = 455 nm to at Kmx = 280 nm is leveled off. The results of kinetic studies provide an information on the relative reaction rates of the above organolithium compounds with other reagents. Surprisingly, the cross-over reaction of /i-BuLi with ADPE in pure benzene was too slow to complete for a week. The addition of THF was effective to complete the cross-over reaction within 2 h. Thus, from the plot of the UssnJlTsoun against the reaction time, the initial slope is directly related to the rate constant of the cross-over reaction of /i-BuLi with l-[4-[N,N-bis(trimetnylsilyl)amino]phenyl]-l-phenylethylene (ADPE). The key factor to prepare macromonomer quantitatively is how to synthesize effectively diphenylalkyllithium with amine group (ADPELi). Furthermore, the initiation rate of the functional initiator (ADPELi) to styrene is another important variable. It can be deduced by the slope from the plot of the l^m/histm ratio against the reaction time in benzene/THF mixture. From the inflection point in the plot of UssmJI^AAnm ratio against the reaction time, it was found that the initiation was completed within 5 minutes. In addition, the cross-over reaction of diphenylalkyllithium to poly(isoprenyl)lithium was also found to be completed in the mixture of benzene/THF within 5 minutes from the plot of the lAssnJIm™ ratio against the reaction time. It was also found that the cross-over reaction of poly(styryl)lithium to l,3-bis(lphenylethenyl)benzene (MDDPE) was so fast in benzene/THF mixture from the observation on the intensity ratio (hsuJhAAxm) change as shown in Figure 3. The results of these kinetic studies provided a useful information how to control the active species during all reactions. From comparison of 'H NMR spectra of the amine-functionalized polystyrene and the corresponding macromonomer shown in Figure 4, a successful synthesis of macromonomer carrying aminofunctional group can be confirmed. For example, the chemical shift at 5 = 0.08 ppm is assigned to the protons on the trimethylsilyl group of the silyl-protected amine group (-N-lSHC/ZOak), as shown in Figure 4(a). The number average molecular weight of the amine-functionalized polymer was 2300 g/mol by size exclusion chromatographic analysis. It was in accord with that by 'H NMR spectroscopic analysis as shown in Table 1. All functionalized polymers prepared in our experiments are summarized in Table 1.


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ADPE n-BuLi+ADPE PSLi MDDPELi

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Figure 2. UV/Visible absorption spectra of amine-functionalized initiator, poly(styryl)lithium, and macromonomer in benzene/THF mixture (20/1, v/v).

The chemical shift at 8 = 5.4 ppm shown in Figure 4(b) arises from the protons on the methylene group of diphenylethylene-type unit (CH = CPh ) shown in Scheme 2. Simultaneously, from comparison of the chemical shifts at 8 = 0.08 ppm in Figures 4(a) and 4(b), it is clear that macromonomer carrying amine-functional group was successfully synthesized. Comparison of the SECs of the amine-functionalized polystyrene and the corresponding macromonomer inferred that the reaction of MDDPE with poly(styryl)lithium produced mostly monoadduct (below 2 % diadduct) in our experimental condition as shown in Figure 5. As already described, the synthesis of macromonomer was effective in hydrocarbon/THF mixtures with regard to consider the reaction time. The synthesis of macromonomers carrying amine group was meaningless in pure hydrocarbon because the cross-over reaction of w-BuLi with ADPE was too slow to be completed. Thus, the unreacted ADPE may allow to copolymerize with styrene under our reaction conditions with regard to the reaction time. This copolymerization may produce diphenylalkyllithium which can not react with MDDPE. This situation makes efficient synthesis of macromonomer of 1,1-diphenylethylene-type difficult. Thus, Poly 1 and Poly 4 in Table 1 were aamine functionalized polystyrene and polyisoprene excluding the diphenylethylene-type unit. It has been well-known that lithium sec-butoxide was effective to control the 1,4-enchainment of polydienes in the crossover reaction of diphenylalkyllithium with dienes in hydrocarbon (30) while polymerization in THF as solvent produced 59 % of 3,4-enchainment microstructure (31). In this respect, anionic synthesis of macromonomer having the polyisoprene backbone should be performed in hydrocarbon to control the microstructure (30). Although lithium sec-butoxide employed as an additive was effective to control the microstructure of polydienes, it did not effect to the increase of the reaction rate of n-BuLi with ADPE in hydrocarbon. However, in the mixture of benzene/THF, 2

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Figure 3. Kinetic studies of organolithium compounds prepared by the reaction of /i-BuLi with ADPE, styrene, and MDDPE in benzene or benzene/THF mixture ([TOF]/[/i-BuLi] = 20/1).



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Figure 4. *H NMR spectra of amine-functionalized polystyrene (a) and the corresponding macromonomerfromthe reaction with MDDPE (b) (Poly 2 in Table 1).


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Amine-functionalized P S

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Figure 5. Size exclusion chromatograms of amine-functionalized polystyrene and the corresponding macromonomer (Poly 2 in Table 1).

Table 1. The reaction conditions and the results of the characterization of various macromonomers synthesized at 25°C. Solvent

Sample

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Anionic Synthesis of Macromonomer Carrying Amino Group Using

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