No abstract

Noncovalent chemistry may offer diversity in the functions and applications for artificial polymers by allowing various ordered−disordered phase transitions in a precisely controlled manner. To verify this notion from a fundamental perspective, we examined an achiral poly(phenylacetylene) derivative with an αhelical structure as a helical-spring polymer for revealing phase changes through control of intramolecular hydrogen bonding with the chiral solvent and temperature. When an amine capable of hydrogen bonding was used as the chiral solvent, either an irreversible helix−helix or a reversible helix−coil phase change occurred in an optically dissymmetric manner according to the amount of the chiral solvent added and ambient temperature. Considering the hydrogen-bonding strength values of the solvent mixture and the thermodynamic parameters, we could predict if the optical-dissymmetry phase changes would occur and, if so, how they occur. Our results were similar to those see for the denaturation of proteins, induced by solvent and temperature, based on helix−coil phase transition.

Conjugated polyelectrolytes (CPEs) are emerging as promising materials in the sensor field because they enable high-sensitivity detection of various substances in aqueous media. However, most CPE-based sensors have serious problems in real-world application because the sensor system is operated only when the CPE is dissolved in aqueous media. Here, the fabrication and performance of a water-swellable (WS) CPE-based sensor driven in the solid state are demonstrated. The WS CPE films are prepared by immersing a water-soluble CPE film in cationic surfactants of different alkyl chain lengths in a chloroform solution. The prepared film exhibits rapid, limited water swellability despite the absence of chemical crosslinking. The water swellability of the film enables the highly sensitive and selective detection of Cu 2+ in water. The fluorescence quenching constant and the detection limit of the film are 7.24 × 10 6 L mol −1 and 4.38 nM (0.278 ppb), respectively. Moreover, the film is reusable via a facile treatment. Furthermore, various fluorescent patterns introduced by different surfactants are successfully fabricated by a simple stamping method. By integrating the patterns, Cu 2+ detection in a wide concentration range (nM−mM) can be achieved.

Polyamideimides were prepared via consecutive high-temperature polycondensation imidization and amidation. The acid byproduct generated during amidation was removed using propylene oxide as a reactive additive, avoiding cumbersome purification. All of the varnishes had appropriate viscosities for film casting: 2300–6300 cP at 15 wt % concentration in a mixed solvent of γ-butyrolactone and N,N-dimethylacetamide. The solubility parameters of the obtained polymers were around 24.0 MPa1/2, close to that of N,N-dimethylacetamide; the densities and fractional free volumes of the polymer films were determined to be approximately 1.39 g/cm3 and 0.22, respectively. The polymer films were quite tough with an elastic modulus of up to 6.5 GPa and a tensile strength of up to 200 MPa, and their glass transition temperature reached 366 °C. A colorless and transparent film with a transmittance of 84.8% at 440 nm and a low yellow index of 1.77 was obtained by adding a bluing agent.

Polyamideimides and polyimides are prepared based on chemical imidization using aromatic diamine, diacid anhydride, and diacid chloride as monomers, with the precursor polyamic acid remaining in part, to produce mechanically unique films through convection drying. The resulting films are colorless and transparent and exhibit unidirectional fracture behavior. These films do not break when bent in the direction of the air contact surface but easily break when bent in the opposite direction. A cross‐sectional electron microscope image of the broken film shows that the film consists of a double layer. After examining both sides of the film through various spectroscopic and gel permeation chromatography analyses, it is found that the residual polyamic acid undergoes both hydrolytic and thermal decomposition, exclusively on the air contact surface. Later, the polymer film is laminated with two sheets of glass through UV curing of commercial acryl resin. Because of the unidirectional fracture characteristics of the film, the laminated glass does not completely break when subjected to bending toward the air contact surface but easily breaks (without fragments) in the opposite direction, indicating its potential application in safety glasses suitable for emergency escapes.