The synthesis and structural analysis of a library containing 13 taper- and conical-shaped self-assembling dendrons, 16 dendritic monomers, and their corresponding polymers is reported. Fifteen of these polymers exhibit a well-defined cylindrical shape produced by the self-assembly of their dendritic side groups that self-organizes in a hexagonal columnar two-dimensional liquid crystalline lattice. The retrosynthetic analysis of this lattice by X-ray diffraction (XRD) showed that the diameter (60 to 41 Å) and the number of repeat units forming the cylinder cross-section (7 to 1.9) of these polymers are determined by the structure of their dendritic side groups. This demonstrates that, in the hexagonal columnar lattice, the conformation (from helical to fully extended) and the stiffness of the polymer backbone penetrating through the center of the cylinder are controlled in a systematic and predictive way by the structure of the side groups. Dynamic and static light-scattering experiments have demonstrated the same trend for the stiffness of these polymers in solution (Kuhn segment length from 200 to 1032 Å). Single chains and monolayers of these polymers were visualized and quantitatively analyzed by scanning force microscopy (SFM) on a graphite surface to provide the first comparative study of the conformation, stiffness, and contour length in solution (by light scattering), in the disordered solid state on a flat substrate (by SFM), and in the hexagonal columnar lattice (by XRD). The elaboration of this library of visualizable cylindrical macromolecules with controlled chain conformation and stiffness accesses the elucidation of many fundamental problems of the field of polymer science at the molecular level and the design of multifunctional nanoscale systems based on single polymer chains.

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Positron annihilation lifetime measurements are reported for four monodisperse polystyrenes with molar mass M = 4,000, 9,200, 25,000, and 400,000. The temperature dependences of orthopositronium (o‐Ps) lifetime (τ3) and intensity (I3) were measured from 5°C to Tg + 30°C for each sample. From these data, the free volume hole size, 〈vf(τ3)〉, and fractional free volume hps=CI3〈vf(τ3)〉 were calculated. The temperature dependences of τ3, 〈vf(τ3)〉 and hps show a discrete change in slope at an effective glass transition temperature, Tg,ps, which is measurably below the conventional bulk Tg. This suggests that τ3 is sensitive to large holes which retain their liquid‐like mobility in the glassy state. Good agreement was found for T > hg,ps between hps and the theoretical free volume fraction hth deduced from experimental P‐V‐T data for polystyrene using the statistical mechanical theory of Simha and Somcynsky. Below Tg,ps, deviations between hps and hth are observed, hps falling increasingly below hth as temperature decreases. Whereas hps and hth depend strongly on M in the melt, each essentially independent of M in the glass. A free volume quantity, computed from the bulk volume, which is in good numerical agreement with the Simha‐Somcynsky h‐function in the melt, gives improved agreement with hps in the glassy state. © 1994 John Wiley & Sons, Inc.