RESUMO
Polylactide (PLA), a main biodegradable and biobased candidate for the replacement of petrochemical polymers, is stiff and brittle at room conditions. It is therefore of high interest to formulate new PLA-based materials suitable for applications demanding flexibility and toughness. In this work, novel blends of PLA with polyhedral oligomeric silsesquioxanes (POSS) grafted with longer (P1) and shorter (P2) arms of ethylene glycol derivatives were prepared and studied. It was hypothesized that, owing to their architecture with the central POSS cage grafted with arms, miscibility and stability of the blends could be improved. Indeed, PLA/P1 blends were homogeneous despite P1 relatively high Mw of 9,500 g mol-1. The blend with 20 wt% of P1, having Tg at 16 °C, was transparent and flexible, elastomer-like material with excellent drawability. The blend remained homogeneous and retained its good drawability as well as flexibility during 6 months of aging at room temperature: a 2 % secant modulus of elasticity well below 100 MPa, a low yield stress below 2 MPa, and and a large strain at break of 8 (800 %). Contary to that, PLA/P2 blends were only partially miscible. Nevertheless, owing to the liquid state of the dispersed phase, the blend with 15 wt% of P2 was transparent and ductile, with Tg at 49 °C, a relatively high yield strength of 29 MPa, and a large strain at break of 2.3 (230 %). The toughening mechanism involved the initiation of crazes and facilitation of their propagation by the liquid inclusions via the local plasticization effect.
RESUMO
Benzoxaboroles possessing aryl substituents in the oxaborole ring were synthesized, and their structures were determined by single-crystal X-ray diffraction. Structures in the solid state are centrosymmetric dimers with two intermolecular hydrogen bonds. These compounds were investigated using a combination of the spectroscopic and the computational approach, comparing their properties with the unsubstituted compound. Investigated compounds were characterized by (1)H, (13)C, and (11)B NMR spectroscopy in solution. Assignment of (1)H and (13)C signals was made on the basis of HSQC and HMBC spectra. The molecular structure of 1,3-dihydro-1-hydroxy-3-phenyl-2,1-benzoxaborole was calculated by the density functional (B3LYP) method with the extended 6-311++G(d,p) basis set. The calculated geometrical parameters were compared with experimental X-ray data, and the differences between experimental and calculated values were found to be of the order of experiment standard deviation, confirming a good description by this level of theory. The harmonic frequencies, potential energy distribution (PED), and IR intensities of this compound and its deuterated analogue were calculated with the B3LYP method. The assignment of the experimental spectra was made on the basis of the calculated PED. The consequence of dimer formation is the splitting of the vibrational modes into symmetric and antisymmetric vibrations. The structure modification resulting from the hydrogen bonded dimers formation is presented.
