Polymers with pendent functional groups

Polymers with pendent functional groups

European Polymer Journal 36 (2000) 221±224 Short communication Polymers with pendent functional groups IV. The reaction of chloromethylated polystyr...

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European Polymer Journal 36 (2000) 221±224

Short communication

Polymers with pendent functional groups IV. The reaction of chloromethylated polystyrene with N-phenacyl-4,4 '-bipyridinium bromides Ioan Druta a, Ecaterina Avram b,*, Vasile Cozan b a Faculty of Chemistry, ``Al.I. Cuza'' University, RO-6600 Jassy, Romania ``Petru Poni'' Institute of Macromolecular Chemistry, Aleea Gr. Ghica Voda, nr.41-A, RO-6600 Jassy, Romania

b

Received 16 June 1998; received in revised form 23 November 1998; accepted 26 January 1999

Abstract The amination reaction of linear chloromethylated polystyrene with N-phenacyl-4,4 '-bipyridinium bromide, N(4nitrophenacyl)-4,4 '-bipyridinium bromide and N(4-methoxyphenacyl)-4,4 '-bipyridinium bromide leads to the formation of crosslinked via a transquaternization reaction. # 1999 Elsevier Science Ltd. All rights reserved.

1. Introduction It is known that polymers with bipyridinium salt groups in the main chain are obtained by the Menshutkin reaction between dihaloalkanes or dihaloarylalkanes and 4,4 '-bipyridyl [1], or by interfacial polycondensation of N,N-bis(aminoalkyl)-4,4-bipyridinium with acid dichlorides [2±5]. Kamagawa et al. [6] and Okawara et al. [7] claimed that soluble polymers with bipyridinium salts as pendent groups have been prepared by the polymerization of vinylbipyridinium monomers and by the amination of chloromethylated polystyrene with dipyridylmonoamyl bromide [8]. However, we found that the polymers obtained by the latter method showed gel features and these preparations resulted in formation of crosslinked structures during the amination. This observation suggested us to study the amination reaction of linear chloromethylated polystyrene with N-phenacyl-4,4 '-bipyridinium bromide derivatives and to ®nd an experimental evi-

dence that the crosslink responsible for gelatin in these systems arise from a transquaternization reaction.

2. Materials and methods N-phenacyl-4,4 '-bipyridinium bromide derivatives used in the amination reaction of chloromethylated polystyrene have the following structures:

* Corresponding author. Fax: +40-32-211-299. 0014-3057/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 9 9 ) 0 0 0 4 2 - 7

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N-phenacyl-4,4 '-bipyridinium bromide (1a) N-(4-nitrophenacyl)-4,4 '-bipyridinium bromide (1b) N-(4-methoxyphenacyl)-4,4 '-bipyridinium bromide (1c) The monoquaternized derivatives of 4,4 '-bipyridyl were puri®ed by multiple recrystallization from diethy-

lether until the complete removal of the 4,4 '-bipyridyl traces. (1a): B:p: ˆ 197:58C, IR (KBr, cmÿ1) 3050 (nˆC±H ), 1690 (nCˆO ), 1637, 1598, 1540, 1493 (nCˆC ,nCˆN ). 1 HNMR (DMSO-d6, TMS) d: 9.216 (d, 2H, ortho

Scheme 1.

I. Druta et al. / European Polymer Journal 36 (2000) 221±224

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>N+<), 8.90±8.65 (m,4H, Ph-Ph), 8.175±7.65 (m, 5H, Ph, 2H, ortho >N), 6.55 (s, 2H, CH2). (1b): B:p: ˆ 1518C, IR (KBr, cmÿ1) 3040 (nˆC±H ), 1703 (nCˆO ), 1635, 1596, 1481 (nCˆC ,nˆN ), 1528, 1346 (nNO2 ). 1 H-NMR (DMSO-d6, TMS) d: 9.212 (d, 2H, ortho >N+<), 8.90±8.675 (m, 4H, Ph-Ph), 8.375 (m, 4H, Ph), 8.05 (d, 2H, ortho >N), 6.725 (s, 2H, CH2). (1c): B:p: ˆ 2708C, IR (KBr, cmÿ1) 3050 (nˆC±H ), 1666 (nCˆO ), 1250, 1035 (nO±C±O ), 1637, 1597, 1540, 1514, 1478 (nCˆC ,nCˆN ); 1 H-NMR (DMSO-d6, TMS) d: 9.425 (d, 2H, ortho >N+<), 8.950±8.675 (m, 4H, PhPh), 8.125±8.025 (m, 2H, ortho ±CO±O, 2H, ortho >N), 7.225 (d, 2H, ortho ±OCH3), 6.525 (s, 2H, CH2), 4.0 (s, 3H, ±OCH3). A chloromethylated polystyrene with a transformation degree DT ˆ 0:65 and viscometric average mol v ˆ 36,000 was used. ecular weight M The solvent N,N-dimethylformamide (DMF) was puri®ed by conventional methods. The amination reaction of chloromethylated polystyrene with 1a±1c was carried out at 508C, in N,Ndimethylformamide as solvent. The reaction product was precipitated into anhydrous diethylether, then was ®ltered and dried 24 h under vacuum over P2O5 at 208C. The unreacted low molecular weight compound was isolated by washing the quaternized polystyrene with methanol three to four times under stirring (the low molecular weight compounds are soluble in methanol). After puri®cation the polymers were dried in vacuum at 408C. The IR absorption spectra were obtained using KBr pellets on a SPECORD M 80 spectrophotometer and 1 H-NMR spectra were recorded on a BRUKER 80 AW spectrometer under standard measurement conditions.

periments, the dealkylated species 3a±3c appear and as a consequence one can postulate that a quaternization reaction between them and CH2Cl groups from another macromolecular chain also occurs to produce crosslink. A pronounced crosslinking of the reaction products takes place (in the case of 1b) due to the electron withdrawing e€ect of ±NO2 group in comparison with ±H or ±OCH3 groups. In order to support this supposition we studied the reaction between benzyl bromide and N(4-methoxyphenacyl)-4,4 '-bipyridinium bromide (1c). As the latter is less reactive, one can observe the reaction evolution in time. In Table 1 are presented the comparative values of the found protons number/theoretical protons number ratio determined by 1 H-NMR spectroscopy, for the reaction product obtained as a result of the benzyl bromide amination with 1c. The analysis of these data showed that the reaction takes place according to the Scheme 1B. Depending on the molar ratio between the two reagents the following structures are obtained: Mo (samples 1 and 2) and Di (sample 3). The use of a benzyl bromide/1c molar ratio of 1/1 lead to structure Mo. At a benzyl bromide/1c molar ratio of 2/1 a transquaternization reaction also takes place thus obtaining the Di structure (sample 3). In the sample 2 (2/1 molar ratio) one could expect the Di structure to be predominant but the reaction time is short, so in sample 2 exists only some traces of Di. The conclusion is supported by the greater number protons d +d ' and a (Table 1). From the IR spectra we calculated the absorbance for polymers 2a±2c, using a reported method [9]. The calculated absorbance (Ax ) is given by the Eq. (1).

3. Results and discussion

Ax ˆ log AC=AB

Initially, the reaction medium for the amination reactions of chloromethylated polystyrene with N-phenacyl-4,4 '-bipyridinium bromide derivatives (1a±1c) was a solution, but in time it turned to a gel. This ®nding indicates that crosslinking reactions of the polymers occurred, as a result of secondary reactions accompanying the main process of amination. These results suggest that during the amination reaction of chloromethylated polystyrene with N-phenacyl-4,4 '-bipyridinium bromide derivatives a nucleophilic attack of the bromide anion on the carbon atom of the methylenic group occurs as a consequence of the electron withdrawing e€ect of the carbonyl group and of the vicinity of bipyridinium quaternary nitrogen atoms (Scheme 1A). Assuming that, although 2a±2c are the main forms of our ex-

…1†

Table 1 Found protons number/theoretical protons number ratios for the benzyl bromide amination reaction with 1c

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Table 2 Ax =Aref ratios for polymers 2a±2c as a function of reaction time Wavelength (cmÿ1)

1710 1650 1550 1350 1280

Assignment

nCˆO n>N‡ < nNO2 asym. nNO2 sym. nCH2 Cl

tion is con®rmed by the increasing of the intensity for the absorption band at 1650 cmÿ1, assigned to the bipyridinium quaternary N atom.

Reaction time hours 50

72

100

150

References

1.45 1.48 2.30 1.82 0.70

0.81 1.85 1.60 1.64 0.56

0.88 1.94 1.64 1.58 0.46

0.64 2.07 1.40 1.41 0.35

[1] Factor A, Heinson GE. J Polym Sci, Polym Lett Ed 1971;9:289. [2] Simon MS, Moore PhT. J Polym Sci, Polym Chem Ed 1975;13:1. [3] Ageishi K, Endo T, Okawara M. J Polym Sci, Polym Chem Ed 1983;21:293. [4] Prasad BB. Bull Chem Soc Jpn 1989;62:1269. [5] Merz A, Reitmeier S. Angew Chem Int Ed Eng 1989;28:807. [6] Kamagawa H, Mizuno A, Todo Y, Nanasava M. J Polym Sci, Polym Chem Ed 1979;17:3149. [7] Okawara M, Hirose T, Kumiya N. J Polym Sci, Polym Chem Ed 1979;17:927. [8] Sato H, Tamamura T. J Appl Polym Sci 1979;24: 2075. [9] Rabek JF. Experimental methods in polymer chemistry. New York: Wiley, 1980 p. 241.

The 1610 cmÿ1 band was chosen as reference band (Aref). The Ax =Aref ratios as a function of reaction time are given in Table 2. As can be seen the absorption band intensity assigned to ±CH2Cl group (1270±1280 cmÿ1) decreases with the increase of the reaction time due to the consumption of these functional groups during the reaction. It is also noteworthy that the evolution of the reac-