Polylactides with one or more carboxyl groups at one chain end were synthesized by cationic polymerization according to activated monomer mechanism and by application of “thiol-yne” click chemistry for subsequent functionalization. End groups of such obtained polylactides were converted into ionic groups by neutralization of polymer solutions with metal oxides, mainly calcium oxide, and the aggregation of individual stereoisomers as well as that of the mixture of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) was investigated. The extent and progress of the aggregation was followed by viscosity measurements, and aggregated polymers in the solid state were examined by SEM and DSC. Solution viscosity increase was observed upon the aggregation of individual PLA stereoisomers, whereas PLA stereocomplex precipitation occurred in the case of the aggregation of PLLA/PDLA/metal oxide mixture.

Crystallization-controlled structure and thermal properties of biobased poly(ethylene 2,5-furandicarboxylate) (PEF) were studied. The cold-crystallization temperature controlled the structure and thermal properties of the biobased PEF. The melting was complex and evidenced the presence of a significant fraction of less-stable crystals with a low melting temperature that linearly increased with T_c, which formed already during the early stages of crystallization, together with those melting at a higher temperature. Low T_c resulted in the α’-phase formation, less crystallinity, and greater content of the rigid amorphous phase. At high T_c, the α-phase formed, higher crystallinity developed, the rigid amorphous phase content was lower, and the melting temperature of the less-stable crystals was higher; however, slight polymer degradation could have occurred. The applied thermal treatment altered the thermal behavior of PEF by shifting the melting of the less stable crystals to a significantly higher temperature. SEM examination revealed a spherulitic morphology. A lamellar order was evidenced with an average long period and small average lamella thickness, the latter about 3–3.5 nm, only slightly increasing with T_c.