**4. Conclusions**

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 their shear-induced crystallization was examined. The polymers were sheared at 170 ◦C and 150 ◦C at 5/s, 10/s and 20/s for 20 s, 10 s, and 5 s, respectively, and next cooled at 10 or 30 ◦C/min. The shear flow induced crystallization of the PLLAs during cooling at 30 ◦C/min and enhanced the crystallization at 10 ◦C/min, which was reflected in an increase of crystallization peak temperature, Tc, and crystallinity, χc. The flow-induced orientation of crystals was evidenced by 2D-WAXS and 2D-SAXS, although dependent on shearing conditions and molecular characteristics of the polymers. The lamellae stack perpendicular to the flow direction, suggestive of fibrillar nucleation, were observed by SEM, although spherulites were found between them, especially in PLLAs with Mw close to 120 kg/mol.

The results showed the crucial role of shearing temperature, Ts, and cooling rate, v, as the lower Ts increases the relaxation times of macromolecules and loweres the energy barrier for nucleation, whereas the slower cooling enabled a longer time for crystallization before too low temperature was reached. The shear-induced crystallization was also strongly influenced by molar mass of PLLA, as can be expected, but it was also affected by macromolecular architecture. It was well reflected in χc of PLLAs with Mw close to 120 kg/mol sheared at 150 ◦C and cooled at 30 ◦C/min. The effect of shear was the weakest on L121, stronger on 6S120, and the strongest on 4S123,despite the higher Mz of L121. During cooling at 10 ◦C/min, Tc and ΔHmc values of all PLLAs with Mw near 120 kg/mol were similar. However, this evidenced the stronger shear-induced nucleation in both star PLLAs than in L121, because the crystal growth in them was slower than in L121 [24]. The effect of molecular architecture on shear-induced crystallization during cooling at 10 ◦C/min was clearly seen in an increase of Tc and ΔHmc in respect to the corresponding values for the control specimens, with similar thermal history but not subjected to shearing. The stronger effect of shear on 6S120 and 4S123 as compared to that on L121 undoubtedly resulted from the star architecture of macromolecules, which hindered the relaxation of the stretched macromolecular chain network. On the contrary, the shear-induced crystallization in 6S245 and L240 was similar, and even somewhat stronger in the latter. This can be understood taking into account that in the flow-induced crystallization of polymers, a high molar mass tail of molar mass distribution plays a crucial role, due to long relaxation times. Mz of L240, 414 kg/mol, exceeded that of 6S245, 294 kg/mol, evidencing the higher content of larger macromolecules, which at Mw of 240–245 kg/mol compensated the effect of star architecture on the shear-induced crystallization. Moreover, due to its higher molar mass, the number of branching points in 6S245 was smaller than in 6S120, which reduced their effect on macromolecular mobility.

**Supplementary Materials:** The following are available online. Figure S1: Increase of crystallization peak temperature, Tc−Tcq, of PLLAs during cooling at 10 ◦C/min, caused by shearing at 170 and 150 ◦C, versus shear rate, .*γ*. Tcq denotes the crystallization peak temperature of control specimens during cooling at 10 ◦C/min. Figure S2, 2D-WAXS pattern of PLLA L339 sheared at 170 ◦C at 5/s for 20 s and next cooled at 10 ◦C/min, with arrows indicating characteristic reflections.

**Author Contributions:** Conceptualization, J.B. and E.P.; methodology, J.B., A.M.; validation, J.B., E.P. and G.L.; formal analysis, J.B.; investigation, J.B.; writing—original draft preparation, J.B., E.P.; writing—review and editing, J.B., E.P.; visualization, J.B.; supervision, E.P.; funding acquisition, G.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by the National Science Centre (Narodowe Centrum Nauki), Poland, gran<sup>t</sup> No. 2013/09/B/ST5/03619, and statutory funds of CMMS PAS.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Acknowledgments:** The work was supported by the National Science Centre (Narodowe Centrum Nauki), Poland, gran<sup>t</sup> No. 2013/09/B/ST5/03619 and statutory funds of CMMS PAS.

**Conflicts of Interest:** The authors declare no conflict of interest.

**Sample Availability:** Samples of the compounds are not available from the authors.
