The overall crystallization and crystal melting of one low‐molecular mass poly(ethylene oxide) (PEO) fraction (MW 3000) have been investigated by differential scanning calorimetry (DSC) and in situ small‐angle x‐ray scattering (SAXS). The salient new results indicate that initial transient crystals with nonintegral folding (NIF) chain lengths form over a wide range of crystallization temperatures. This NIF structure subsequently transforms into crystal forms with integral folding (IF). The PEO IF crystals consist of the extended chain (n = 0) crystal and the once‐folded chain (n = 1) crystal, while the NIF has an intermediate fold length. The NIF → IF transformation occurs either by lamellar thickening or thinning. The NIF crystal is less stable than the IF(n = 1) crystal, but its growth is more rapid. Crystallization of the PEO (MW 3000) fraction is thus recognized as a compromise between the direction of the thermodynamic driving force and the kinetic pathway. Some potential consequences of these observations are also addressed.

Differential scanning calorimetry (DSC) and in situ small‐angle x‐ray scattering (SAXS) indicate that in an α ω‐methoxy‐poly(ethylene oxide) (MPEO) fraction (MW 3000) a transient nonintegral folding (NIF) crystal initially forms during crystallization throughout a wide range of crystallization temperatures. Subsequent transformations of the NIF to IF (integral folding) crystals at low temperatures occur mainly through isothermal thickening or thinning via perfection processes or, at higher temperatures, through primary crystal formation. The NIF crystal is thermodynamically the least stable state among the crystal forms, but its growth is the most rapid. The overall crystallization and crystal melting of this MPEO fraction reveal that the NIF crystal and the NIF → IF crystal transformations are common to low‐molecular mass PEO fractions without regard to the end group. Nevertheless, diffusion coefficient and viscosity measurements provide clear evidence of an end‐group effect in PEO and MPEO fractions. The difference in the overall crystallization and isothermal thickening and thinning kinetics of low‐molecular mass PEO and MPEO fractions can lead to further understanding of end‐group effects.

SYNOPSISThe crystallization of the monotropic liquid crystal forming polyether, poly-n-nonyl-4 4'biphenyl-2-chloroethane, was investigated using DSC calorimetry and polarizing optical microscopy. The principal theme was the nature of crystallization from the nematic liquid crystalline state, which in the monotropic system could be directly compared with the more familiar crystallization from the isotropic melt using one and the same compound. Novel, polarizing optical structures were observed that combine features of both the usual LCPs (fine "grains") and those of the conventional crystallizeable polymers (spherulites) with differing degrees of prominence of each according to crystallization conditions. The considerations of such structural observations, combined with the calorimetric results and the newly gained information on the kinetics of the crystallization process, reveal an acceleration of the overall crystallization rate at the stage where liquid crystal formation sets in as assessed by calorimetry but not as registered with the polarizing microscope, leading to wider issues regarding the conception of "amorphous crystalline ratio" and its extension to the liquid crystal state. Beyond polymers, the new findings lead to the more general considerations on metastable phases, specifically to their emergence and competition with the phases of ultimate stability. In this respect the present study on a monotropic LCP provides a n illustrative example of a more general treatment presented previously. 0 1995

Poly[(1,7‐dihydrobenzo[1,2‐d:4,5‐d′] diimidazole‐2,6‐diyl)‐2‐(2‐sulfo)‐p‐phenylene], a conjugated rigid‐rod polymer, was derivatized with pendants of propane‐sulfonated ionomers. The derivatized rigid‐rod polymer was soluble in aprotic solvents as well as in water for isotropic solutions that were processed into isotropic films. Direct‐current electrical conductivity σ of the films was measured using the four‐probe technique. Room‐temperature σ as high as 2.9 × 10−4S/cm was achieved on pristine isotropic films without using dopants. When the rigid‐rod polymer concentration exceeded 25 wt %, the isotropic solution could be transformed into a liquid‐crystalline solution that allowed deformations to be applied to produce anisotropic films. Significant increase in σ was obtained in a sheared film along both the parallel direction (∥) and the transverse direction (⊥) with a σ∥/σ⊥ = 5. Additionally, enhanced σ was realized in films heat‐treated at about 100°C, in the derivatized polymer with higher molecular weight from dialysis, and in substituting the sulfonated ion Na+ by H+ in the pendants of the polymers. Constant‐voltage measurements were applied to the polymers to monitor the σ stability for ascertaining the nature of the conductivity. No electronic contribution in σ was detected. Instead, a monotonically decreasing σ was consistently observed indicative of ionic conductivity. © 1993 John Wiley & Sons, Inc.

Quantitative thermal analysis of a family of semicrystalline polyimides containing from one to three ethylene glycol spacer units has been conducted. Special emphasis has been placed upon the changes in the thermodynamic properties resulting from the successive additions of ethylene glycol units. The solid and liquid heat capacities were measured in the temperature range 230–640 K. The solid heat capacities were also calculated from the vibration spectra of the polymers. An in‐depth description of the glass transitions, the heat capacity increases at the glass transition temperatures, and the widths of the glass transitions is provided. Three parts of the heat of fusion have been identified: Wc (H), that contributed from the high melting peak; wc (L), that contributed from the low melting peak; and wc (C), that developed during cooling after isothermal crystallization. The metastability, sequence of crystallization, and rate of reorganization of the low and high melting peaks have been investigated by stepwise crystallization and by analysis using different heating rates after isothermal crystallization. A rigid amorphous fraction is needed to explain the failure of the two‐phase (crystallinity) model.