Abstract Segmented polyurethanes based on poly(l-lactide)diol - PLLA, poly(ethylene-glycol) - PEG, poly(trimethylene-carbonate)diol - PTMC and hexamethylene diisocyanate were synthesized by a two-step polyaddition. Polyurethanes with variable compositions and molar mass were semi-crystalline and presented PLLA or PLLA + PEG crystalline phases and a heterogeneous amorphous phase. Sequential crystallization of PLLA and PEG resulted in a confined PEG crystallization into the PLLA crystalline phase. The random distribution of the segments in the polymer chains and the partial miscibility of the segments in the amorphous phase strongly influenced the morphology of the crystalline phase, and the kinetics of the crystallization. Morphology changed from not well-defined spherulites with Maltese cross to ring banded spherulites and axialites as the PLLA mass fraction decreased. PLLA nucleation and crystal growth rates varied with crystallization temperature similarly to homopolymers, presenting a bell-shaped curve, and the temperature for the maximum growth rate dependent on the polyurethanes composition.

The high cost of sensitivity commercial calorimeters may represent an obstacle for many calorimetric research groups. This work describes the construction and calibration of a batch differential heat conduction calorimeter with sample cells volumes of about 400 μL. The calorimeter was built using two small high sensibility square Peltier thermoelectric sensors and the total cost was estimated to be about US$ 500. The calorimeter was used to study the excess enthalpy of solution of binary mixtures of liquids, as a function of composition, for the following binary systems of solvents: water + 1,4-dioxane or + dimethylsulfoxide at 298,2 ± 0,5 K.

Usually, the concepts of the Sol-Gel technique are not applied in experimental chemistry courses. This work presents a feasible experiment for chemistry instruction, which involves the synthesis of luminescent materials - Zn2SiO4, with and without Mn2+ as a dopant - by the Sol-Gel technique. The obtained materials were analyzed by scanning electron microscopy, X-Ray diffraction, IR spectroscopy and luminescence measures by UV-vis spectroscopy. The results allow the students to confirm the luminescent properties of the zinc orthosilicate luminophores as well as the structural features expected from literature data.