Thermoresponsive Molecular Brushes with a Rigid-Chain Aromatic Polyester Backbone and Poly-2-alkyl-2-oxazoline Side Chains

A new polycondensation aromatic rigid-chain polyester macroinitiator was synthesized and used to graft linear poly-2-ethyl-2-oxazoline as well as poly-2-isopropyl-2-oxazoline by cationic polymerization. The prepared copolymers and the macroinitiator were characterized by NMR, GPC, AFM, turbidimetry, static, and dynamic light scattering. The molar masses of the polyester main chain and the grafted copolymers with poly-2-ethyl-2-oxazoline and poly-2-isopropyl-2-oxazoline side chains were 26,500, 208,000, and 67,900, respectively. The molar masses of the side chains of poly-2-ethyl-2-oxazoline and poly-2-isopropyl-2-oxazoline and their grafting densities were 7400 and 3400 and 0.53 and 0.27, respectively. In chloroform, the copolymers conformation can be considered as a cylinder wormlike chain, the diameter of which depends on the side chain length. In water at low temperatures, the macromolecules of the poly-2-ethyl-2-oxazoline copolymer assume a wormlike conformation because their backbones are well shielded by side chains, whereas the copolymer with short side chains and low grafting density strongly aggregates, which was visualized by AFM. The phase separation temperatures of the copolymers were lower than those of linear analogs of the side chains and decreased with the concentration for both samples. The LCST were estimated to be around 45 °C for the poly-2-ethyl-2-oxazoline graft copolymer, and below 20 °C for the poly-2-isopropyl-2-oxazoline graft copolymer.

Poly(3,4-ethylenedioxythiophene) Electrosynthesis in the Presence of Mixtures of Flexible-Chain and Rigid-Chain Polyelectrolytes

The electrochemical synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) was first carried out in the presence of mixtures of flexible-chain and rigid-chain polyacids and their Na-salts. Earlier on with the example of polyaniline, we have shown the non-additive effect of the rigid-chain component of polyacid mixtures on the electrodeposition of polyaniline films, their morphology and spectroelectrochemical properties. In this study, we confirmed the non-additive effect and showed that such mixed PEDOT–polyelectrolyte films possess unique morphology, spectroelectrochemical and ammonia sensing properties. The electrosynthesis was carried out in potential cycling, galvanostatic and potentiostatic regimes and monitored by in situ UV–Vis spectroscopy. UV–Vis spectroelectrochemistry of the obtained PEDOT–polyelectrolyte films revealed the dominating influence of the rigid-chain polyacid on the electronic structure of the mixed complexes. The mixed PEDOT–polyacid films demonstrated the best ammonia sensing performance (in the range of 5 to 25 ppm) as compared to the films of individual PEDOT–polyelectrolyte films.

Thermal Properties of Poly(3-(2′-Ethyl)Hexylthiophene): Study with a Real-Time Combination of Synchrotron X-Ray Scattering and Ultrafast Chip Calorimetry

Here we report on reorganization on heating of a perspective organic semiconductor poly(3-(2′-ethyl)hexylthiophene) (P3EHT). P3EHT is an analogue of a well-known poly(3-hexylthiophene) (P3HT), which has comparable optoelectronic properties and the advantage of a lower processing temperature. The processes of structural reorganization during heating of P3EHT have been explored with a combination of synchrotron X-ray scattering and ultrafast chip calorimetry. The signature of reorganization has been identified from an increase of d-spacing of 100 peak of the P3EHT unit cell. It was observed that reorganization operates during heating of P3EHT at conventional rates of a DSC experiment (i.e., at 10 deg/min), whereas it is largely suppressed at a heating rate of 100 deg/s. Despite the absence of reorganization at high heating rates the calorimetric curves exhibit pronounced double melting, which corroborates the model of the negative pressure building up during crystallization of semi-rigid chain polymers.