Thermodynamics of poly(ethylene oxide)-poly(methyl methacrylate) blends: prediction of miscibility based on the corresponding-states theory

Effects on the Properties after Addition of Lithium Salt in Poly(ethylene oxide)/Poly(methyl acrylate) Blends

The studies of phase behavior, dielectric relaxation, and other properties of poly(ethylene oxide) (PEO)/poly(methyl acrylate) (PMA) blends with the addition of lithium perchlorate (LiClO₄) were done for different blend compositions. Samples were prepared by a solution casting technique. The binary PEO/PMA blends exhibit a single and compositional-dependent glass transition temperature (T_g), which is also true for ternary mixtures of PEO/PMA/LiClO₄ when PEO was in excess with low content of salt. These may indicate miscibility of the constituents for the molten systems and amorphous domains of the systems at room temperature from the macroscopic point of view. Subsequently, the morphology of PEO/PMA blends with or without salt are correlated to the phase behavior of the systems. Phase morphology and molecular interaction of polymer chains by salt ions of the systems may rule the dielectric or electric relaxation at room temperature, which was estimated using electrochemical impedance spectroscopy (EIS). The frequency-dependent impedance spectra are of interest for the elucidation of polarization and relaxation of the charged entities for the systems. Relaxation can be noted only when a sufficient amount of salt is added into the systems.

Microscopic Chain Motion in Polymer Nanocomposites with Dynamically Asymmetric Interphases

Dynamics of the interphase region between matrix and bound polymers on nanoparticles is important to understand the macroscopic rheological properties of nanocomposites. Here, we present neutron scattering investigations on nanocomposites with dynamically asymmetric interphases formed by a high-glass transition temperature polymer, poly(methyl methacrylate), adsorbed on nanoparticles and a low-glass transition temperature miscible matrix, poly(ethylene oxide). By taking advantage of selective isotope labeling of the chains, we studied the role of interfacial polymer on segmental and collective dynamics of the matrix chains from subnanoseconds to 100 nanoseconds. Our results show that the Rouse relaxation remains unchanged in a weakly attractive composite system while the dynamics significantly slows down in a strongly attractive composite. More importantly, the chains disentangle with a remarkable increase of the reptation tube size when the bound polymer is vitreous. The glassy and rubbery states of the bound polymer as temperature changes underpin the macroscopic stiffening of nanocomposites.

Reversible Thermal Stiffening in Polymer Nanocomposites

Miscible polymer blends with different glass transition temperatures (Tg) are known to create confined interphases between glassy and mobile chains. Here, we show that nanoparticles adsorbed with a high-Tg polymer, poly(methyl methacrylate), and dispersed in a low-Tg matrix polymer, poly(ethylene oxide), exhibit a liquid-to-solid transition at temperatures above Tg's of both polymers. The mechanical adaptivity of nanocomposites to temperature underlies the existence of dynamically asymmetric bound layers on nanoparticles and more importantly reveals their impact on macroscopic mechanical response of composites. The unusual reversible stiffening behavior sets these materials apart from conventional polymer composites that soften upon heating. The presented stiffening mechanism in polymer nanocomposites can be used in applications for flexible electronics or mechanically induced actuators responding to environmental changes like temperature or magnetic fields.

Phase stability and dynamics of entangled polymer-nanoparticle composites

Nanoparticle-polymer composites, or polymer-nanoparticle composites (PNCs), exhibit unusual mechanical and dynamical features when the particle size approaches the random coil dimensions of the host polymer. Here, we harness favourable enthalpic interactions between particle-tethered and free, host polymer chains to create model PNCs, in which spherical nanoparticles are uniformly dispersed in high molecular weight entangled polymers. Investigation of the mechanical properties of these model PNCs reveals that the nanoparticles have profound effects on the host polymer motions on all timescales. On short timescales, nanoparticles slow-down local dynamics of the host polymer segments and lower the glass transition temperature. On intermediate timescales, where polymer chain motion is typically constrained by entanglements with surrounding molecules, nanoparticles provide additional constraints, which lead to an early onset of entangled polymer dynamics. Finally, on long timescales, nanoparticles produce an apparent speeding up of relaxation of their polymer host.

Leakage of enteric (Eudragit L)-coated dosage forms in simulated gastric juice in the presence of poly(ethylene glycol)

Poly(methacrylic acid) (PMAA) and related copolymers strongly interact with poly(ethylene glycol) (PEG) in acidic fluids. Due to the in vitro experiments presented in this paper, there is a clear indication for a drug-drug interaction in vivo between PEG solutions, e.g., commercially available laxatives, and dosage forms with PMAA-based enteric-coatings (Eudragit L). In these studies, enteric-coated tablets did not fulfil the pharmacopoeias' criteria of the disintegration test if PEGs were present in the simulated gastric juice. Drug substances which are known to be unstable in acidic media or which can cause gastric irritation were released from their enteric-coated dosage forms in acidic PEG media (pH 1). Various drug dosage forms, single and multiple unit systems, were tested. They show higher and faster drug release in the presence of PEG. To get insight into the mechanism of the interaction, experiments and theoretical calculations were performed which reveal that PEGs with high molecular weight show stronger interactions with PMAA coatings indicating a contribution of hydrophobic interactions to the occurring intermolecular forces. Hydrogen bonds can be build between each monomeric unit of PEG and the acidic sequences of the copolymer.