X-ray studies on the morphology of zwitterionic polymers
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O. Manero Instituto de Investigaciones en Materiales, UNAM. A.P. 70-360, Coyoacdn 04510, Mexico, D.F., Mexico (Received 27 September 1993; accepted 12 April 1995)
Wide Angle X-ray Scattering (WAXS) and Small Angle X-ray Scattering (SAXS) were applied to elucidate the microstructure and morphology of two zwitterionic copolymers. The first system is a sulfobetaine derivative of poly(4-vinyl pyridine) with an ionic content of 10% (10% of the degree of quaternization). The copolymer is almost amorphous, with a small degree of crystallinity (10%). The second copolymer is a N-oxide derivative of the poly(N,N dimethyl aminoethyl methacrylate) highly crystalline (90%). The latter forms superstructures of globular shape with crystalline domains of coordinated polymer-salt systems. X-ray data are in accordance with those published by Castano et al. [J. Mater. Res. 5, 654 (1990)]. These authors reported TEM micrographs of zwitterionic systems, where clusters with grainy appearance were observed within the length of scale range found in this work. Models for the morphology of these copolymers are proposed for each use.
I. INTRODUCTION Some of the most interesting properties exhibited in the solid state by zwitterionic polymers are related to their morphology. For example, the onset of ionic conductivity and the melting of the crystalline phase occur simultaneously as temperature is increased.1 Similarly, an interesting effect in the ionic conductivity is observed due to pressure-induced structural changes in the morphology of specific samples.2 The formation of clusters and domains in these polymers controls extensively their thermal properties,3 and the appearance of aggregated states profoundly affects their solution properties. In this regard, viscoelasticity is also observed at moderate polymer concentrations.4 In a previous study,5 transmission electron microscopy (TEM) showed the presence of ionic aggregates of poly(vinyl pyridines sulfobetaines) in the solid state. The morphology of the samples was related to their ionic content and showed larger clusters than those observed in ionomers. McKnight et al.6 proposed a model for the ionomer clustering that assumes the presence of coreshell structures, with a core of ion pairs surrounded by a shell of hydrocarbon chains of about 7 nm in diameter. In the zwitterionic case, on the other hand, a loosely packed grainy structure was observed by TEM at low ionic contents in the sulfobetaine copolymers. In this previous work, the size of the grains was 10 nm, although this could be larger due to the aggregation of the grainy structure on the edges of regions of high polymer concentration. In this regard, the present investigation aims to provide additional evidence on 2106 http://journals.cambridge.org
J. Mater. Res., Vol. 10, No. 8, Aug 1995 Downloaded: 01 Apr 2015
the microstructure and morphology of two zwitterionic moieties, one of them being highly crystalline. Wide (WAXS) and small (SAXS) angle x-ray scattering were used to provide information on the spatial arrangement o
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