*Article* **Shear-Induced Crystallization of Star and Linear Poly(L-lactide)s**

**Joanna Bojda \*, Ewa Piorkowska, Grzegorz Lapienis and Adam Michalski**

> Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Lodz, Poland; epiorkow@cbmm.lodz.pl (E.P.); lapienis@cbmm.lodz.pl (G.L.); michadam@cbmm.lodz.pl (A.M.)

**\*** Correspondence: jbojda@cbmm.lodz.pl

**Abstract:** The influence of macromolecular architecture on shear-induced crystallization of poly(Llactide) (PLLA) was studied. To this aim, three star PLLAs, 6-arm with Mw of 120 and 245 kg/mol, 4-arm with Mw of 123 kg/mol, and three linear PLLAs with Mw of 121, 240 and 339 kg/mol, were synthesized and examined. The PLLAs were sheared at 170 and 150 ◦C, at 5/s, 10/s and 20/s for 20 s, 10 s and 5 s, respectively, and then cooled at 10 or 30 ◦C/min. Shear-induced crystallization during cooling was followed by a light depolarization method, whereas the crystallized specimens were examined by DSC, 2D-WAXS, 2D-SAXS and SEM. The effect of shear depended on the shearing conditions, cooling rate and polymer molar mass but it was also affected by the macromolecular architecture. The shear-induced crystallization of linear PLLA with Mw of 240 kg/mol was more intense than that of the 6-arm polymer with similar Mw, most possibly due to its higher Mz. However, the influence of shear on the crystallization of the star polymers with Mw close to 120 kg/mol was stronger than on that of their linear analog. This was reflected in higher crystallization temperature, as well as crystallinity achieved during cooling.

**Keywords:** poly(L-lactide); star poly(L-lactide); shear-induced crystallization; crystallinity; fibrillar nuclei
