Poly(3-n-butylthiophene) (P3BT) samples with different average molecular weights and headto-tail regioregularity were crystallized in the form II crystal polymorph either from solution or by annealing with CS 2 vapors. With a combined approach, making also use of literature electron diffraction data, we show that form II is well described by a limit-ordered monoclinic model in space group P2 1 /c with lattice parameters a = 10.76(1) A ˚, b = 7.77(1) A ˚(chain axis), c = 9.44(1) A ˚, and β = 64.66°, yielding a calculated density of 1.29 g/cm 3 in qualitative agreement with proposals by Winokur et al. for the form II structures of regioregular poly(3-octylthiophene) and poly(3-dodecylthiophene) (P3DDT). Our structural model was refined by Rietveld analysis and has been confirmed by molecular mechanics (MM) and molecular dynamics (MD) calculations adopting a thiophene-specific force field developed in our group. Consistent with its higher density and with thermal data, form II shows lower potential energy than the form I 0 crystalline polymorph of P3BT. Both the main-chain and the side-chain conformations closely correspond to those found in form I 0 polymorph. The form II P3BT refined structural model presents an antidirectional looser stacking and tightly interdigitated layering, different from those observed in the form I family of poly(3-alkythiophenes) (P3ATs) and crystallite dimension of 20-30 A ˚along the chain axis. This feature and the lamellar structure implied by the spherulitic morphology are consistent with substantial chain-folding for high molecular weight samples. Oriented X-ray diffraction patterns from thin films of form II P3BT are explained assuming that the stacking axis c, corresponding to the radial, fast growth direction of the bidimensional form II spherulites, is preferentially in the plane of the film, while the layer axis a and the chain axis b approach random orientation around c, at variance with recent literature suggestions. The small crystal dimensions along the chain axis, the looser stacking, the relevance of chain folding and the spherulitic morphology implying film discontinuity suggest that the form II structural family of P3AT's are less viable than the form I polymorphs for molecular electronics applications.

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An easy synthetic procedure for soluble poly[3‐(4‐alcoxyphenyl)thiophene]s is reported. The polymers present a high regioregularity degree as determined by both UV–vis spectra and 1H and 13C NMR analysis. Furthermore, X‐ray powder diffraction analysis performed on films of the polymers suggests a π‐stacked packing structure of the macromolecules. Electrical characterization was performed on one of the synthesized polythiophenes on both undoped and doped (with FeCl3 or iodine) films. The conductivity and charge‐carrier mobility were assessed by current–voltage and field effect measurements. Well‐structured polymer films were obtained simply via spin coating from chloroform solutions and without the need of further processing, unlike other regioregular polythiophenes reported in the literature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1758–1770, 2007

The synthesis and a preliminary structural characterization of syndiotactic poly(m-methylstyrene) are reported. A complex polymorphic behavior has been revealed. Three different polymorphic forms and two clathrate structures, characterized by the inclusion of guest molecules in the crystalline lattice, have been found. The conditions for the obtaining of the various polymorphic forms, in unoriented and. oriented fiber samples, are described. Form I, obtained by crystallization from the melt or from the amorphous phase, is characterized by chains in the s(2/1)2 helical conformation. The same helical conformation has been found in the clathrate structures containing molecules of o-dichlorobenzene or benzene. Form II can be obtained by crystallization from solutions of solvents which do not form clathrate structure or by removing the guest molecules from the clathrate forms. Form III, obtained in oriented fibers by stretching amorphous films, is a mesomorphic modification characterized by chains in the trans-planar conformation with a high degree of disorder in the lateral packing of the chains. Annealing treatments or solvent-induced crystallization of the oriented mesomorphic form allow the obtaining of oriented fibers in some of the polymorphic forms. The differences and analogies with the polymorphic behavior of syndiotactic poystyrene and poy(p-methylstyrene) are outlined

Models for the crystal structure of alternating isotactic ethylene−norbornene copolymers (ENCs) are presented. Oriented fibers of ENCs samples have been obtained, and the corresponding X-ray fiber diffraction pattern has been reported. A value of the chain axis periodicity of 8.9 Å has been evaluated. A geometrical analysis and conformational energy calculations have shown that both isotactic and syndiotactic ENC chains assume nearly extended conformations having 2-fold helical s(2/1)m and glide plane t cm symmetries, respectively. Both conformations account for the experimental chain axis periodicity of 8.9 Å. The crystal structure is mainly defined by the packing of the quasi-spherical norbornene units. The barycenters of the norbornene units are arranged on a face-centered crystalline lattice, producing a short-range three-dimensional positional order. Different kinds of structural disorder are present in the structure. A short-range order in the average positioning of the norbornene rings is maintained, while disorder in the positioning of the carbon atoms of the ethylene units is present. The ethylene units may assume different positions along a and b axes of the unit cell and connect with equal probability a given norbornene unit with any of its next neighbors, producing orientational disorder of the polymer chains as well as of the spherical norbornene units. The amount and the kind of disorder depend on the microstructure of the chains and on the condition of crystallization. The structure may be described by limit disordered models of packing, in unit cells having a = b = 9.4 Å and c = 8.9 Å or a = 9.3 Å, b = 9.5 Å, and c = 8.9 Å. and statistical orthorhombic or tetragonal space groups Bmcm or I4/mmm. The partial threedimensional order, guided by the ordered positioning of the ball-like norbornene units, is obtained even though the polymers are configurationally disordered, provided that they have a regular alternation of the comonomeric units.