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Transparent thermoplastic polyurethanes based on aliphatic diisocyanates and polycarbonate diol
2016
Segmented thermoplastic polyurethanes (PUs) were synthetized using polycarbonate diol as soft segment with a molar mass of 500 and as a hard segment 1,5-pentanediol with a combination of isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI). Differential scanning calorimetry, differential mechanical analysis, Fourier transform infrared-attenuated total reflection spectroscopy, haze, transmittance, hardness, tensile properties and retention of tensile properties tests were employed to characterize the different PUs. The results of this study show that IPDI/HDI relation has a significant impact on the phase mixing, crystallinity and therefore on the PU’s properties. The variati…
PLLA/PLA scaffolds prepared via Thermally Induced Phase Separation (TIPS): tuning of properties and biodegradability
2008
Foams for tissue engineering applications were prepared via thermally induced phase separation (TIPS). Poly-L-Lactic Acid (PLLA) and blends of PLLA with PLA in different proportions were used (100/0, 90/10, 75/25, 50/50, 0/100 PLLA/PLA wt/wt) starting from ternary systems where dioxane was the solvent and water the non-solvent. Morphology was evaluated by Scanning Electron Microscopy (average pore size and interconnection) and the void fraction was measured by means of Hg porosimetry. Foams apparent density was also evaluated (porosity ranges from 87% to 92%). Biodegradability was estimated in a body mimicking fluid. Results show that structure and morphology (in terms of average pore size …
Polyethylene glycol/clay nanotubes composites
2012
Nanocomposites of poly(ethylene) glycol (PEG) 20000 filled with clay nanotubes (HNTs) were prepared. The thermal properties obtained from thermogravimetry and differential scanning calorimetry were correlated to the morphology imaged by scanning electron microscopy. Low amounts of HNTs generate compact structure while large amounts of HNTs create craters and voids. The decrease of polymer degradation temperature in the presence of large amount of nanoclay (ca. 80 wt%) is a consequence of the morphology at the mesoscale range. The thermal opposite effect observed in the HNTs low regime (up to ca. 20 wt%) is due to the gas entrapment into the nanoparticles lumen. The quantitative analysis of …
Methylcellulose-Based Edible Films and Coatings: 2. Mechanical and Thermal Properties as a Function of Plasticizer Content
1997
Several edible films based on methylcellulose and polyethylene glycol 400 (PEG400) were prepared and stored until equilibration at different relative humidities. Tensile stress−strain curves show very different behaviors as a function of PEG400 and relative humidity. Tensile strength strongly depends on relative humidity and then on water content, more than on PEG400 content. On the contrary, elongation is dependent both on water and PEG400. These differences correspond to the glass transition of the polymer, which affects the elongation more than the tensile strength. However, from DSC measurements, it appears that the PEG400 has no or a very low compatibility with the methylcellulose matr…
Blends from redox active liquid crystal ionomers and amorphous ionomers
1994
Abstract Biphasic blends (mixtures) of liquid crystal ionomers (prepared from ferrocene containing liquid crystal polymers by a redox reaction) and partially sulfonated polystyrene combine the constituent properties in a way, which is dependent on the measuring method. Polarizing microscopy shows homogenous textures similar to the pure liquid crystal polymer. Mechanical measurements show however the elastomeric behaviour of sulfonated polystyrene. The phase separated structure of these blends is proved by differential scanning calorimetry measurements.
Functional Group Distribution and Gradient Structure Resulting from the Living Anionic Copolymerization of Styrene and para-But-3-enyl Styrene
2014
The functional group distribution along the polymer backbone resulting from the living anionic copolymerization of styrene (S) and para-but-3-enyl styrene (pBuS) was investigated in cyclohexane at room temperature. A variety of copolymers with different comonomer contents x(S) = 0–0.84 have been synthesized with molecular weight dispersities Mw/Mn ≤1.12. All polymers have been characterized in detail by 1H NMR spectroscopy, size exclusion chromatography (SEC), and differential scanning calorimetry (DSC). A detailed understanding of the monomer sequence distribution during the copolymerization was achieved by real-time 1H NMR spectroscopy. This technique permits us to determine the changing …
Hyperbranched-linear-hyperbranched ABA-type block copolymers based on poly(ethylene oxide) and polyglycerol
2009
BACKGROUND: Until recently, hyperbranched polymers were thought to be ill-defined materials that were not useful as building blocks for well-defined complex polymer architectures. It is a current challenge to develop strategies that offer rapid access to well-defined hyperbranched block copolymers. RESULTS: A convenient three-step protocol for the synthesis of double-hydrophilic hyperbranched–linear–hyperbranched ABA-type triblock copolymers based on poly(ethylene oxide) (PEO) and hyperbranched polyglycerol (hbPG) is presented. The Bola-type polymers exhibiting an aliphatic polyether structure were prepared from a linear (lin) linPG-b-PEO-b-linPG precursor triblock. The materials exhibit lo…
Hydrogen-Bonded Aggregates of Oligoaramide−Poly(ethylene glycol) Block Copolymers
2010
Rod−coil copolymers with an oligomeric rod aggregate on a nanometer length scale, which is important for many applications like e.g. organic photovoltaics. However, this aggregation behavior and the driving forces such as hydrogen bonding and π−π interactions, as well as the role of side groups, are not yet fully understood. Here, we investigated these noncovalent interactions in oligo(p-benzamide)−poly(ethylene glycol) (OPBA−PEG) copolymers using solid-state NMR supported by wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and polarization optical microscopy (POM). It was found that longer OPBAs form layered β-sheet-like aggregates and that these are stabilized …
Transmission of mechanical energy through polymeric liquid crystals and their blends
1988
Molecular composites, also called polymeric liquid crystals (PLC), are contrasted with the traditional composites; the name heterogeneous composites is proposed for the latter. Advantages of blending PLCs with ordinary engineering polymers are discussed. Results reported for blends of poly(ethylene terepthalate) (PET) with a PLC containing sequences of PET and p-hydroxybenzoic acid (PHB) include thermophysical properties, melt rheology, mechanical properties of solid blends, and scanning electron microscopy of fracture surfaces. A model called the island model was developed to explain the results: One assumes that the lines of force as well as propagating cracks tend to concentrate in the p…
Sorption of n-hexane in amorphous polystyrene
2014
Sorption properties of pure n-hexane vapor in amorphous polystyrene (PS) were studied at 298 K by thermogravimetry under controlled vapor pressure. Two sorption-desorption cycles were performed by varying the relative pressure between 0 and 0.91. Mixing of PS with n-hexane resulted in a strong plasticization, which was evidenced by quite significant depression in the glass transition temperature of the polymer as shown by differential scanning calorimetry. Maximum quantity of n-hexane sorbed in the PS at 298 K and at a pressure close to saturation was about 12.4 wt %. The thermogravimetry yielded an isotherm with a strong hysteresis loop, explanation of which was hypothesized with the help …