Stereocomplexation of enantiomeric star-shaped poly(lactide)s with a chromophore core

Herein, we aim to investigate the influence of the cooling rate from the melt on stereocomplex formation of equimolar blends of enantiomeric star-shaped poly(lactide)s with a dipyridamole core. As evidenced by differential scanning calorimetry, wide-angle X-ray scattering and Fourier-transform infrared spectroscopy, melt cooling of equimolar blends of star-shaped poly(l-lactide) (SSPLLA) and star-shaped poly(d-lactide) (SSPDLA) resulted in the non-crystalline state. A careful analysis of WAXS and FTIR data revealed that the slow-cooled sample (10 degrees C min(-1)) exhibited the amorphous phase and the fast-cooled sample (50 degrees C min(-1)) resulted in the mesophase. On subsequent heating, the slow-cooled sample remained in the amorphous phase, whereas the fast-cooled sample crystallized (cold crystallization) exclusively into the stereocomplex at similar to 90 degrees C. Aging of the slow-cooled sample at room temperature and subsequent heating led to the formation of the stereocomplex. Photoluminescence studies revealed that the cooling rate from the melt has a strong influence on core molecule (dipyridamole) aggregation and determines the geometry of interactions between the branches of SSPLLA and SSPDLA. In the slow-cooled sample, because of the longer residence time above the glass transition temperature, dipyridamole molecules form aggregated structures, whereas in the fast-cooled sample, dipyridamole molecules are distributed within the polymer matrix without much aggregation. Based on these results, we propose antiparallel chain packing in fast-cooled SSPLLA/SSPDLA blends because of the non-aggregation of dipyridamole core molecules and this geometry favored the exclusive formation of stereocomplex. On the other hand, due to the possible aggregation of dipyridamole molecules, the slow-cooled sample led to topological and geometric constraints where the interactions between SSPLLA and SSPDLA chains prevented the crystallization. The present findings could open new avenues for the design of a variety of macromolecular architectures for a better understanding of the stereocomplex formation mechanism of chiral polymers.

Automated summary

The cooling rate from the melt significantly influences the formation of stereocomplexes in equimolar blends of enantiomeric star-shaped poly(lactide)s with a dipyridamole core. Fast cooling leads to non-aggregated core molecules and antiparallel chain packing, favoring the formation of stereocomplexes, while slow cooling results in topological and geometric constraints due to possible core molecule aggregation, inhibiting crystallization of the poly(lactide) chains.