Evidence of ionic aggregates in some ampholytic polymers by transmission electron microscopy
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J. Cardoso, O. Manero, and V. M. Monroy Instituto de Investigaciones en Materiales, Universidad National Autonoma de Mexico, Apdo. Postal 70-360, 04510 Mexico, D. F. (Received 9 November 1988; accepted 13 October 1989)
Transmission electron microscopy observations were conducted on some zwitterionic polymers. Our observations were concentrated on the morphology of the solid state of poly (4-vinyl pyridine-sulfopropyl betaines), with different degrees of quaternization. Among the morphological features, a microstructure arising from aggregated regions in the range of 50 to 200 A is observed. Quite striking is the fact that this structure is absent in the micrographs for the base polymer, indicating that the aggregates are due to the interactions of the ion pairs of the polyzwitterions, as in the ionomer case. It is also found that the density of the aggregates increases when we increase the zwitterionic content of the copolymers.
I. INTRODUCTION
There has been an increasing interest in recent years in polyampholytes (i.e., macromolecules which possess both negative and positive moieties).1 Among the whole variety of polyampholytes, the poly(sulfobetaines) have been the subject of some studies related to their synthesis,2"4 solution,5"8 membrane,6 and solid-state properties.9"11 More recently, results on the association behavior both in dilute solution12 and the melt,13 as well as a theoretical work on the zwitterionic head-head interactions of polymers containing sulfobetaine end groups14 were reported. The polyzwitterions (the charges of opposite sign are linked covalently) of the sulfobetaine type are easily obtained by reacting a sultone ring with an aromatic or aliphatic amine, as illustrated by the synthesis of (l-(3-sulfonatopropyl) pyridiniom-4-yl) ethylene,4 as shown schematically in Fig. 1. These sulfobetaine monomers can be polymerized by free-radical polymerization to yield homo-4 and copolymers.4'59 To our knowledge, there has been no report in the literature on the study of these polymers
by Transmission Electron Microscopy (TEM). It is the purpose of this article to report our first results on the study of the morphology of some ampholytic polymers of various zwitterionic contents by TEM. II. EXPERIMENTAL DETAILS A. Polymer preparation and chemical characterization
The copolymers under study have the structure depicted in Fig. 2, with X = mole percent of the zwitterionic units. In our case, the copolymers were obtained by reacting poly (4-vinyl pyridine), P4VP, with 1,3 propane sultone to yield materials with different degrees of quaternization, X, here denominated as P4VP-SB. The copolymers were characterized by FT-IR, JH-NMR, DSC, TGA, and elemental analysis. These results have been reported elsewhere.15 -f CH--CH
CH2)3
so; X = mole FIG. 1. The reaction of a sultone ring with an amine, to yield (l-(3-sulfonatopropyl) pyridiniom-4-yl). 654
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J. Mater. Res., Vol. 5, No. 3, Mar 1990
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percent of zwitterionic units.
FIG. 2. The zwitterionic po
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