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Abstract Untethered octaisobutyl- polyhedral oligomeric silsesquioxane (POSS) molecularly dispersed into low-density polyethylene (LDPE) induced entanglement dilation and dynamics acceleration, reduced the melt viscosity and acted as nano-plugs thus reducing O 2 transmission. POSS nanoparticles were melt mixed with LDPE using a twin-screw extruder and adding up to 10 wt% POSS. High-resolution transmission electron microscopy (HRTEM) demonstrated excellent dispersion of POSS into LDPE, at a single POSS unit at low concentrations. The dynamics was probed by shear rheometry constructing master curves at T ref = 190 °C using the time-temperature superposition (TTS) principle. In the low concentration range (c POSS <5 wt%) the terminal (liquid-like) regime showed that POSS nanoparticles induced accelerated dynamics, decreasing the terminal relaxation time τ t. This translated into an anomalous, non-Einstein, reduction of viscosity. Increasing concentration to c∼10 wt% POSS formed clusters of ca. 10 units, the terminal relaxation time increased and the melt exhibited higher viscosity than the neat LDPE, as predicted for particulate filled suspensions. Therefore, at low concentrations the size of POSS (ca. 1.5 nm), smaller than entanglement mesh size of polyethylene (tube diameter d t = 3.28 nm), would drive chain disentanglement and be responsible for the dilution effect. At higher concentrations POSS aggregated and therefore increased the viscosity of the nanocomposite, a behavior akin to Einstein's prediction. Strikingly, the intercalation of POSS into the entangled molecular mesh reduced oxygen transmission, suggesting that POSS acted as nano-plugs by filling the voids in the entangled mesh. Graphical abstract Image 1 Highlights • Untethered POSS dispersed at a single unit in LDPE. • POSS induced chain disentanglement and viscosity reduction in LDPE. • POSS acted as nano-plug reducing O 2 transmission in LDPE. [ABSTRACT FROM AUTHOR]

Abstract A multi-scale analysis, at the μm → nm → Å-scale on the influence of thermal treatment on the microstructure of the thermotropic polymer based on 60 mol% (1,4)-hydroxybenzoic acid (B), 5 mol% (2,6)-hydroxynaphthoic acid (N), 17.5 mol% terephthalic acid (T) and 17.5 mol% biphenol (BP) -named COTBP- was carried out. Extruded tapes 30 μm thick were heat treated at 300 °C for up to 300 min. Wide-angle X-ray scattering of as-extruded tapes revealed high macromolecular alignment. Small-angle X-ray scattering exhibited diamond-shaped diffuse scattering along the equatorial axis and, strikingly, meridional scattering revealed long-range order of ca. 43.9 nm periodicity. Heat treatment reduced surface roughness, increased the birefringence, and sharpened the meridional and main interchain reflections indicating an increase of crystallinity, molecular register and alignment. On the other hand, SAXS intensity decreased in 2θ and became azimuthally narrower evidencing lateral compression of scattering features. The width of scattering objects decreased from 8.7 to 6.6 nm, whereas their length increased from 20.9 to 22.8 nm, and the misorientation angle B ϕ decreased from 2.1° to 0.5°. Because heat treatment was carried out without applied tension, the results also revealed a self-reinforcing effect. The structural re-organization correlated with significant increase of thermal properties, i.e. the changes relative to as-extruded tape of degradation and melting temperatures were ΔT dec ∼20 K, ΔT s→ñ 75 K, and the change of Young's modulus was ΔE ∼50 GPa. Graphical abstract Image 1 Highlights • Thermotropic random copolyester exhibits non-periodic layer crystals. • Plate-like crystals are spatially correlated. • Thermal treatment increased of melting transition (>70 K) and Young's modulus (>250%). • Thermal treatment revealed a self-reinforcing effect. [ABSTRACT FROM AUTHOR]