Colloid & Polymer Science Colloid & Polymer Sei. 261,224-230 (1983) Structural organization of polar-group-containing polymers in the molten state V. Busico, P. Cernicchiaro, A. Scopa, and M. Vacatello Istituto Chimico dell' Universit~t, Naples (Italy) Abstract: Model compounds in which flexible polymethylenic sequences of variable length alternate with -NH2-ZnX 2- groups were characterized both in the crystalline and in the molten state, in order to evaluate the effect of regularly distributed dipoles on the melting behavior of linear flexible chains. Microphase segregation of the polar groups was observed resulting in the formation of smectic meso,hases or of smectic-like fluids. Possible analogies with the structural organization of me' ,en dipole-containing polymers and ionomers are briefly discussed. Key words: Smectogenic polymers, smectic mesophases, dipole-containing polymers. Introduction Rigid groups with high axial ratios connected by flexible junctions are a common structural feature of mesophasic polymers [1]. Liquid crystalline order in such systems, as first evidenced by Flory [2], is due to the fact that the free energy of packing of the rigid parts reaches a minimum, mainly for steric reasons, when these are aligned along a common direction, this effect prevailing over the resulting loss of disorienta- tion entropy. On the other hand, intermolecular interactions alone are able to stabilize mesomorphic states for low molecular weight compounds, even in the absence of rod-like mesogenic groups. Examples are the anhy- drous soaps [3-6] and several other systems consti- tuted by polymethylenic molecules with an ionic end group [7-9]. Liquid crystallinity in these systems results from the tendency of the ionic parts to segregate in layers up to temperatures well above the onset of conformational disorder of the hydrocarbon parts [7, 8]. Ion clustering is likewise observed in ion- containing polymers (ionomers) [10-12]. The presence of polar (rather than ionic) groups along a (flexible) polymeric chain might be able to induce similar behaviors. In order to check for this possibility, we syn- thesized model compounds in which totally flexible polymethylenic sequences alternate with -NHa-ZnX2- groups. These were chosen in order not to perturb the geometry of the chain to a great extent, and because the presence of heavy atoms makes the X- ray diffraction patterns more readily interpretable. We wish to report here the results of a characteriza- tion of these systems, and to discuss briefly such results also in relation to the available information on dipole-containing polymers and ionomers. Experimental Compounds ~ H2N(CH2)mNHzZnX2 ~ (short notation CmX) with X = CI, Br; m = 6, 7..... 12 were synthesized reacting at room temperature equimolar amounts of ZnX 2 and of the ce, t0- diaminoalkanes in absolute ethanol. The products precipitate istant- ly as white microcrystalline powders, practically insoluble in all the common use solvents unable to complexate Zn. The precipitates were filtered, washed twice with ethanol and dried under vacuum, The purivy of the products was checked by elemental analysis, All the compounds were characterized with differential scanning calorimetric (DSC), variable temperature X-ray diffractometric and IR spectrophotometric techniques. The DSC curves were registered between 270 and 600 K with a PERKIN ELMER DSC-2 calorimeter, in nitrogen flow, at the scanning rate of 10 K/rain. The temperature scale was calibrated with pure reference compounds. A sample of Indium (A/~ = 28.4 J/g) was used as a standard for the enthalpic measurements, :Variable temperature X-ray photographs (temperature control + 2 K) were taken with a flat camera at a fixed distance from the powdered samples, sealed in Lindemann 0.5 mm capillaries, Ni- filtered CuKa radiation (3, = 1.5418 A) was used throughout the measurement. All the patterns were subjected to microdensitomet- ric reading. Attempts to obtain single crystals suitable for diffractometric studies were unsuccessful. IR spectra were registered at room temperature with a PERKIN ELMER 684 spectrometer, the samples pressed in KBr pellets. 0 561