Enhancement of the properties of polymer blends by hydrogen bonding and transesterification

The importance of polymer rigidity on the extent of intermolecular hydrogen bonding in the blends of copolymers of 4-vinylphenol and styrene (PS-co-PVPh) and polyethers has been studied utilizing FT-IR spectroscopy. A series of polyethers containing mesogens with different rigidity including a liquid crystalline poly ether (LCP) are synthesized using phase transfer polyesterification and blended with PS-co-PVPh. The extent of intermolecular hydrogen bonding between the hydroxyl group ofPS-co-PVPh and the ethereal oxygen is correlated to the rigidity of polyethers. The results of this study indicate that extent of intermolecular hydrogen bonding in blends increases as the flexibility of polyethers increases, causing a shift in the frequency of the hydrogen bonded hydroxyl band towards lower frequency. The rigidity of the polyethers inhibits the formation of intermolecular hydrogen bonds, however this effect is not dramatic. It must be recognized that the LCP utilized in this study can not be considered as a rod-like LCP, as it contains flexible aliphatic spacers. Therefore, the result shows that the rigidity of LCP does not dramatically affect the formation of intermolecular hydrogen bonds is only applicable to non-rodlike LCP. The data also show that a lower concentration of the polyether in the blends induces better mixing and higher extent of intermolecular hydrogen bonding due to better dispersion of polyether in PS-co-PVPh. This suggests that a one-phase system may exist in the region of the phase diagram of the blends that are rich in PS-co-PVPh. The result also shows that the extent of intermolecular hydrogen bonding between PSco-PVPh and polyethers decreases at the higher temperatures. The concept of functional group accessibility of hydroxyl groups for intermolecular hydrogen bonding is also examined in these blends. The amount of intermolecular hydrogen bonds increases with an increase in spacing between the hydroxyl groups. The transesterification Reaction between poly(carbonate) (PC) and thermoplastic liquid crystalline poly (hydroxy benzoate)-poly(ethylene terephthalate) (PHB-PET) and its consequences on the blend morphology and mechanical properties of the blend has also been investigated. The transesterification reaction between PC and PHB-PET upon annealing at 260 °C is characterized and quantified by 13C NMR spectroscopy, showing peaks at 120.9 ppm, 148.3 ppm, and 165.9 ppm corresponding to bisphenol-A terephthalate and bisphenol-A oxybenzoate diads, respectively. These peaks are the result of the initial formation of block copolymer and eventual formation of random copolymer at the interface as the mole fraction of corresponding diads increases. Polarized optical microscopy and tensile measurements reveal that there is a direct correlation between the loss of liquid crystallinity character and mechanical properties of the blend to the extent of transesterification reaction. The results of this study indicate a trade-off between the loss of liquid crystallinity of the blend and its strength resulting from transesterification upon annealing

High contrast solid-state electrochromic devices from substituted 3,4-propylenedioxythiophenes using the dual conjugated polymer approach

Solid-state electrochromic windows from 3,4-propylenedioxythiophene (ProDOT) derivatives using dual polymer electrochromic architecture were fabricated and their electro-optical characteristics were recorded. DibenzylProDOT (DiBz-ProDOT) and biphenylmethyloxymethyl ProDOT (BPMOM-ProDOT) were used as cathodically coloring polymers, whereas bis(2-(3,4-ethylenedioxy)thienyl)-N-methyl carbazole (BEDOT-NMCz) was used as their complementary anodically coloring polymer. Straightforward assembly of the devices was designed by means of using a UV photo-curable gel. These devices exhibited response speeds of approximately 1 s with photopic contrasts as high as 52% for the complete device, and were found to exhibit good stability under open circuit conditions. Convenience of reporting photopic values to characterize electrochromic devices compared to reporting contrasts at a single wavelength is remarked.© Elsevie