A novel approach to study self-nucleation in semicrystalline polymers is presented. Self-nucleation, i.e., the peculiar increase of recrystallization kinetics associated with a range of melting temperatures above or below the melting point, is investigated in parallel with differential scanning calorimetry (DSC) and rheological measurements, for a series of metallocene propene/ethylene random copolymers of varying comonomer content. DSC experiments revealed the exact temperature region where self-nucleation effects are detected in the various samples, while with dynamic viscoelastic results the obedience to the time−temperature superposition principle (TTS) is tested, for both self-nucleated and homogeneous melts. Self-nucleated melts do not obey to the TTS principle, contrary to fully isotropic copolymer melts. Such rheological thermocomplexity constitutes the first physical experimental evidence of the presence of melt heterogeneities, which act as self-nuclei when the melt is cooled and recrystallizes. The degree of thermorheological complexity of the different copolymers is quantified and correlated with the original crystalline content of the copolymer.

Melt memory effects on polymer crystallization are commonly reported in the literature, even when they are not completely understood. In particular, the exact nature of the melt heterogeneities that cause an enhanced nucleation (i.e., the “self-nuclei”) is unknown. This is partly due to sensitivity limitations of the experimental techniques employed to study melt memory. In this work, the melt memory effect of semicrystalline polymers is studied for the first time by dielectric measurements. Polycaprolactones of two different molecular weights have been investigated. Isotropic or self-nucleated melt states are obtained, at a given experimental temperature, by cooling from the isotropic melt or heating from the semicrystalline solid, respectively. A detectable decrease in electrical permittivity is obtained for a self-nucleated melt, consistent with the presence of molecular dipoles with restricted mobility in the case of samples displaying crystalline memory. The volume fraction of repeating units involved in the formation of self-nuclei is estimated to be lower than 0.4%. The relative difference in dielectric permittivity between self-nucleated and isotropic melt state shows excellent correlation with rheological measurements that detect an increase in Newtonian viscosity and with the enhancement of nucleation density, measured by DSC. Each of these measured parameters showed a different sensitivity to the presence of self-nuclei, which is linked both to their nature and to the features of the specific measurements. It is suggested that the relatively strong memory effect displayed by PCL, which can be evidenced by different techniques, is related to the presence of weak intermolecular hydrogen-bonding interactions.

A new family of supramolecular ionic polymers is synthesized by a simple method using (di-/tri-)carboxylic acids and (di-/tri-)alkyl amines. These polymers are formed by carboxylate and ammonium molecules that are weakly bonded together by a combination of ionic and hydrogen bonds, becoming solid at room temperature. The supramolecular ionic polymers show a sharp rheological transition from a viscoelastic gel to a viscous liquid between 30 and 80 °C. This sharp viscosity decrease is responsible for an unprecedented jump in ionic conductivity of four orders of magnitude in that temperature range. As a potential application, this chemistry can be used to develop polymeric materials with self-healing properties, since it combines properties from supramolecular polymers and ionomers into the same material.