Structure and phase transitions in poly(diethylsiloxane)

Abstract

The structure changes accompanying phase transitions in poly(diethylsiloxane) (PDES) have been studied by WAXS and SAXS techniques using oriented and isotropic samples. PDES may exist in two low‐temperature modifications (the monoclinic α1‐form and presumably the “tetragonal” β1‐form) and two high‐temperature modifications (the monoclinic α2‐form and the “tetragonal” β2‐form). In linear PDES the crystal ‐ crystal transitions α1–α2 and β1–β2 occur near 214 and 206 K, respectively. At higher temperatures α2 (280 K) and β2 (290 K) forms transform into the mesomorphic phase αm that gradually melts at 280–300 K giving an amorphous phase. According to x‐ray and density data, αm phase is also characterized by monoclinic structure slightly different from hexagonal packing.

The thermal properties of polysiloxanes poly(dimethyl siloxane) and poly(diethyl siloxane)

“…Its nature is still not fully understood, but may be caused by a temperature-dependent fraction of rigid chain segments caused by intramolecular steric hindrance [12]. Additional DSC results were reported by Lee [14] and Papkov [15,16]. While Lee had provided no interpretation of the results, Papkov proposed that two crystal polymorphs exist at low temperature (0~1, ill)" At high temperature these become ~2 and r2 polymorphs (condis crystals in our nomenclature).…”

“…In order to arrive at a recommended set of data for the transition parameters, the results of K6gler et al [11] and Papkov et al [15,16] were critically reviewed and compared with the results obtained from our laboratory [10]. The data are listed in Table 1.…”

Structural characterization of poly(diethylsiloxane) in the crystalline, liquid crystalline and isotropic phases by solid‐state 17O NMR spectroscopy and ab initio MO calculations

“…A 1.16 g quantity of 17 O-enriched PDES (1.12 ð 10 2 mol) with a cloudy gum was acquired after the ethanol was removed by drying at 110°C for 12 h. 17 O-enriched PDES was the same as that of the nonunlabeled PDES reported previously. 5,11,16,18 From the DSC diagram, the 17 O-enriched PDES forms a low-temperaturě 1 crystalline phase at temperatures below 70°C, a hightemperatureˇ2 crystalline phase at temperatures of 60 to 0°C, a mesomorphic phase at temperatures of 10-25°C (actually the biphasic system consisting of the liquid crystalline and isotropic regions) and an isotropic phase at >40°C.…”

“…(SAXS), 16 Raman spectroscopy, 13 pulse 1 H NMR 19,20 and solid-state 2 H, 13 C and 29 Si NMR. 7 -12,21 In our recent paper, 26 the diffusional behavior of PDES in the biphasic form consisting of the liquid crystalline and isotropic regions was documented by means of high-field-gradient 1 H spectroscopy and 13 C NMR.…”

Block copolymers and networks from polybutadiene and polydiethylsiloxane

“…A regular pattern of PDES cylinders in a PB matrix was observed, with cylinder diameters round 20 nm. Taking the length of two monomer units in an extended siloxane chain as 4.88 Å [17] yields a value of ca. 72 nm for the length of an extended PDES chain with a number average molecular weight of ca.…”