Homocrystal and stereocomplex formation behavior of polylactides with different branched structures

- Up to 14 folds decrease in crystallization t1/2 for branched compared to linear PLA.
- Increase in optimum crystallization temperature by increased chain branch content.
- Higher stereocomplex crystallinity for hyper branched PDLA due to higher nucleation.
- Different internal spherulite morphology for PLA homo and stereocomplex crystal.

Effect of chain architecture on homocrystallization and stereocomplex formation behavior of polylactide (PLA) in quiescent conditions was investigated by means of differential scanning calorimetry (DSC) and optical microscopy. Non-isothermal and isothermal crystallization of star shaped, comb like and hyper branched poly(L-lactides) (PLLAs) with similar molecular weights were studied and compared to a linear one. In dynamic mode, branched PLAs reached higher crystallinity and revealed much higher spherulite density as compared to linear PLA. Also blends of linear and branched PLA with different blending ratios revealed faster crystallization than neat linear PLA. Based on kinetics data obtained in isothermal crystallization experiments, much faster crystallization was achieved with a 4-14 fold decrease in crystallization half-time as a consequence of non-linear chain architecture. Crystallization upon cooling, reduced cold crystallization temperature, increased spherulite density and lower Avrami exponent values for branched PLAs in comparison to linear one suggest enhanced nucleation process as a result of a branched chain architecture. On the other hand, total crystallinity and growth rate were decreased by branching. Stereocomplex formation between linear PLLA and branched poly(D-lactides) (PDLAs) showed dependency of stereocomplex formation to branched architecture. Also, stereocomplex crystals nucleated PLA homocrystallization process while different internal morphology between stereocomplex and homocrystal spherulites was observed. These results confirm that chain architecture has a profound effect on the crystallization behavior of PLA.

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