2.1. Samples and preparation of films Four different sets of samples of 1 were investigated. The first set was the same oriented fiber which was described in Ref. [23] (Mw z 1.5 104). The fiber as-prepared could be studied only by XRD and Raman methods. In the XRD experiments, pieces of the fiber were mounted in a strictly parallel way either on a thin plate of fused quartz, or (to eliminate the contribution from quartz scattering) onto a metal ring holder. In the latter case, the pieces of the fiber were fixed in the manner of harp strings (Fig. 2) and arranged so as to align the X-ray source and the ring aperture.
The round fiber itself, ‘‘as is’’, could not be used for collecting UV data. Therefore we prepared a second set of samples from the fiber by carefully pressing it flat. This mechanical procedure, although mild, appeared to induce a change in the sample structure, leading to some disordering and to a slight redistribution in relative amounts of the polymer modifications present (see below).
The third set of samples correspond to thin films obtained by dissolving the same fiber in cyclohexane and subsequent film casting on a fused quartz or CsI plate. A special technique of uniform spreading of the polymer solution on the substrate surface has been developed, allowing us to obtain uniform polymer films of a given thickness. The latter varied from 3 to 0.3 mm, according to ellipsometric measurements.
The fourth set were films prepared in the same manner from a bulk, higher-molecular-weight (Mw z 3.5 105) sample synthesized according to Ref. [20]. The films were cast from a solution in hexane and relaxed for a week.
2.2. Measurements
Raman spectra were obtained using T64000 and LABRAM Jobin– Yvon laser Raman spectrometers with CCD detectors for the asprepared and flattened fiber samples as well as for the films.
Spectra Physics lasers 2022 and 124 were used for spectra excitation (Arþ 514.5 nm and He–Ne 632.8 nm lines, respectively). To control film uniformity, Raman micro-mapping of the film surface was performed using the microscope of a T64000 instrument equipped with a TV camera.
UV spectra for the flattened fiber and film samples were recorded with a computerized M-40 Carl Zeiss spectrophotometer.
Overlapping UV bands were resolved using a curve-fitting computer program assuming Gaussian and/or Lorentzian band shapes. Corrections for the background were made.
Temperature dependence of the Raman and UV spectra was measured in the interval from 80 to 190 C using specially constructed temperature cells.
XRD data were collected using an automated DRON-3 powder diffractometer in the reflection (Bragg-Brentano) focusing geometry (CuKa radiation, l ¼ 1.5418 Å; 20 kV/40 mA, graphite monochromator on the secondary beam, continuous scanning mode). In room temperature experiments, very long exposure times were used (scanning speed down to 1/32 deg./min). For variable-temperature X-ray measurements (in the range of 20– 60 C), the scanning speed was 0.5 deg./min; thus, one total scan took approximately 1.5 h. XRD experiments with heating of the ‘‘as-is’’ fiber close to the melting point of the polymer were possible only for the samples mounted on a quartz holder. To heat the samples, a controllable flow of heated air was used. Before