Thermotropic liquid‐crystalline polymers containing five‐membered heterocyclic groups. X. Relationships between structures of semirigid polyesters based on three disubstituted 2,5‐diphenyl‐1,3,4‐thiadiazoles and thermotropic liquid‐crystalline and optical properties

Thermotropic liquid‐crystalline (LC) semirigid polyesters based on three terphenyl analogues of 1,3,4‐thiadiazole (2,5‐diphenyl‐1,3,4‐thiadiazole)s (DPTD) linking undecamethyleneoxy chain at different substituted positions were synthesized from three disubstituted (4,4′‐, 3,4′‐, and 3,3′‐) dioxydiundecanols of DPTD and four diesters, and the relationships between polymer structures and LC and optical properties were investigated. DSC measurements, texture observations, and wide‐angle X‐ray analyses revealed that the polymers composed of DPTD moiety having a more linear molecular structure and 1,4‐phenylene unit or short aliphatic chain tend to exhibit LC smectic C and/or A phases. The following observations were made: (1) the emergence of smectic C and/or A phases in all the polymers on the basis of 4,4′‐disubstituted DPTD, (2) formation of enantiotropic smectic C and/or A phases in the polymers containing a 1,4‐phenylene unit in the main chain, (3) formation of a more stable smectic C phase in the polymers having a short aliphatic [(CH₂)₄] chain, and (4) a decrease of the mesomorphic property of the polyesters in the order of 4,4′‐DPTD > 3,4′‐DPTD > 3,3′‐DPTD. Solution and solid‐state ultraviolet–visible and photoluminescent spectra indicated that all the polyesters display maximum absorbances and blue emissions arising from the DPTD moiety, whose peak maxima were shifted to lower wavelengths in the order of 4,4′‐DPTD > 3,4′‐DPTD > 3,3′‐DPTD as well as the aforementioned LC property. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2676–2687, 2003     

On the correlation of surface charge and energy in non‐thermal plasma‐treated polyethylene

Non‐thermal non‐equilibrium oxidative air 40‐kHz frequency, 13.56‐MHz radiofrequency and 2.46‐GHz microwave discharge plasma treatment were used for modifying low‐density polyethylene foils. The untreated and treated samples were chemically characterised by X‐ray photoelectron spectroscopy. In order to estimate the extent of the plasma sources at distinct treatment times, surface charge and energy were determined by zeta potential (ζ) and surface tension measurements. In addition, the isoelectric points (IEPs) of the studied samples were ascertained, and surface property variations were appraised by ageing time. The overall outcome indicated that ζ‐potential and surface energy progressively changed after each treatment, as well as the influences of ageing on surface features, the IEP shifting to lower pH values and how all of these changes are associated with the new surface chemistry. This contribution seeks to shed light on topics related to polymer science and plasma‐based strategies for surface modification. Copyright © 2014 John Wiley & Sons, Ltd.     

Simultaneous wide‐angle X‐ray diffraction and differential scanning calorimetry analysis of the melting and recrystallization behavior of polyethylene and isotactic polypropylene containing cyclopentane units in the main chain

The melting and crystallization behavior of polyethylene and isotactic polypropylene containing 1,2‐ or 1,3‐disubstituted cyclopentane units in the main chain has been studied with simultaneous wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry. For the ethylene‐based copolymers, the position of a reflection peak in the WAXD patterns shifts to a low angle with the increasing acquired temperature. The temperature dependence on the axial length of the crystal lattice is more marked in the copolymers forming orthorhombic crystals (containing 1,2‐cyclopentane or 5.6 mol % 1,3‐cyclopentane units) than in those forming hexagonal crystals (containing 8.1 mol % 1,3‐cyclopentane units). For the isotactic propylene‐based copolymers, the position of the reflection peaks in the WAXD patterns is independent of the acquired temperature. The proportion of the γ form in the copolymer containing the 1,2‐cyclopentane units is higher than that in the copolymers containing the 1,3‐cyclopentane units. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1457–1465, 2004     

Morphology of homogeneous copolymers of ethylene and 1‐octene. II. Structural changes on annealing

Based on DSC evidence, annealing of ethylene‐1‐octene copolymers results in a gradually increasing thermal stability of the original, metastable, crystals. SAXS and WAXD were used to monitor the structural changes involved after isothermal annealing for a fixed time at step‐wise higher temperatures. A series of samples that differ in molar mass and comonomer content, ranging from 0 to 11.8 mol % 1‐octene, were cooled at two extreme rates from 150°C, i.e., a quenching into liquid nitrogen and a controlled cooling at 0.1°C per minute to room temperature. The crystallinities of the quenched linear polyethylenes (LPEs), being included in this study as reference materials, and of the quenched copolymer with a 1‐octene content of 2.1 mol % are always found to be lower than the crystallinities of the slowly cooled samples. On the other hand, higher crystallinities can be found for the quenched copolymers with a higher comonomer content compared to the slowly cooled specimens. A sequence of cocrystallization and recrystallization events is proposed to explain this contraintuitive, but reproducible experimental fact. This reasoning can also account for the steeper increase of the amorphous layer thickness of the latter slowly cooled copolymers compared to the quenched samples. All copolymers show a very moderate increase of the lamellar thickness after each heating step. Besides additional crystallization and recrystallization, lateral growth of the crystals and an increase of the crystallite density can account for the gradual increase of the thermal stability of copolymer crystals during prolonged annealing. The morphological effects observed for the LPEs confirm earlier findings. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 83–100, 1999