Search

Graphical abstract:

Stereocomplexation of enantiomeric poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) endows the Polylactide (PLA) with outstanding heat resistance and durability. However, PLA with exclusive stereo-complexation (sc-PLA) is difficult to achieve. Both stereo-complexation PLA and homo-crystallization PLA (hc-PLA) often formed together when PLLA and PDLA blended. In this research, a new strategy was proposed to prepare the PLA with exclusive stereo-complexation (without homo-crystallization) by Pickering emulsion approach, where regenerated cellulose (RC) was used to stabilize the PLLA/PDLA blends and form RC/sc-PLA microsphere. The DSC result shows that the PLA composites prepared in this method presents single melt peak around 220 °C, which is the characteristics of sc-PLA. Most important, this 0.5%RC/sc-PLA possesses excellent melt stability. It does not divide into stereo-complexation and homo-crystallization during the 3 heating cycles. The results indicate that Pickering emulsion approach firstly provide the limited space to limit the diffusion of macromolecular chains and fully combine PLLA and PDLA chains and form complete RC/sc-PLA microspheres. Then the microspheres were hot pressed into films and homogeneous distribution of RC as heterogeneous nucleation agent provides nucleation sites. The intermolecular hydrogen bonding between RC and PLA improves crystallization property and stabilizes the stereo-complexation. This study provides a strategy to prepare the PLA materials with exclusive stereo-complexed crystal and excellent melt stability, which determines the heat resistance and repeated processing.

Novel amphiphilic conetworks (APCNs) with uniform channel size were synthesized through end-cross-linking of well-defined amphiphilic triblock copolymers via atom transfer radical polymerization (ATRP). A new ditelechelic polydimethylsiloxane macroinitiator was synthesized to initiate the polymerization of N,N-dimethylacrylamide. The resulting triblock copolymers show well-defined molecular weight with narrow polydisperisty, which are telechelic modified by allylamine and fully cross-linked with polyhydrosiloxanes through hydrosilylation. Transmission electron microscopy shows that the APCN has the behavior of microphase separation with small channel size and uniform phase domain. The resulting APCNs with idealized microstructure exhibit a combination of excellent properties, i.e., superhigh mechanical strength (4 ± 1 MPa) and elongation ratio (175 ± 25%), outstanding oxygen permeability (350 ± 150 barrers), a high water uptake property, and excellent biocompatibility, indicating that in this way, “near perfect” networks are obtained. These results are better than those reported in the literature, suggesting a promising semipermeable barrier for islet encapsulation in relative biomaterial fields.

In this research, stereocomplex poly(lactide acid) (scPLA) microsphere with complete sc-PLA crystal was prepared from poly(L-lactide acid) (PLLA) and poly(D-lactide acid) (PDLA) with different molecular weight using common dimethylacetamide solvent. Size of the scPLA microsphere is closely associated with the molecular weight, which determines the number of crystal nuclei and the mobility of macromolecules chains. Its morphology presented wrinkle surface and porous structure due to the formation of spherocrystal. This scPLA microsphere is an effective heterogeneous nucleating agent to increase the stereocomplex of PLLA/PDLA solution blend. The results of DSC showed that the degree of stereocomplex increased from 49.44% to 91.63% when the content of scPLA microsphere was 7%. The research provides a simple method for producing complete scPLA microspheres, which are expected as renewable additives in PLA-based composites and delivery carriers in biomedical fields.