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Molecular dynamics simulations (MD) were carried out to model the miscibility behavior of blends of poly(p-dioxanone) (PPDO) with poly(vinylphenol) (PVPh). The Hildebrand solubility parameters of the pure polymers and the Flory-Huggins interaction parameters of the blends at different compositions were computed. Negative interaction parameters were found across the whole range of compositions, suggesting the miscibility of the system, in agreement with the experimental results. The interaction parameter obtained from melting point depression studies was also found to be in good agreement with the value computed from the simulations. The repeat unit of PPDO contains one ether and one ester group, and both can act as hydrogen bond acceptors. The radial distribution functions (RDFs) between those groups and the hydroxyl groups of PVPh were computed to investigate the competence between the acceptor groups for the specific interactions. The RDFs indicate that interassociation occurs mainly with the ester groups, which is detrimental to the ether groups. This result was also corroborated by the analysis of the hydroxyl stretching region of the blends using Fourier transform infrared spectroscopy (FTIR). The good overall agreement found between the simulated and the experimental data reveals the importance of the molecular modeling techniques in the analysis of the miscibility behavior of polymer blends.

A miscibility and phase behavior study was conducted on poly(ethylene glycol) (PEG)/poly(L-lactide-e-caprolactone) (PLA-co-CL) blends. A single glass transition evolution was determined by differential scanning calorimetry initially suggesting a miscible system; however, the unusual T g bias and subsequent morphological study conducted by polarized light optical microscopy (PLOM) and atomic force microscopy (AFM) evidenced a phase separated system for the whole range of blend compositions. PEG spherulites were found in all blends except for the PEG/PLA-co-CL 20/80 composition, with no interference of the comonomer in the melting point of PEG (T m 5 64 C) and only a small one in crystallinity fraction (X c 5 80% vs. 70%). However, a clear continuous decrease in PEG spherulites growth rate (G) with increasing PLA-co-CL content was determined in the blends isothermally crystallized at 37 C, G being 37 mm/min for the neat PEG and 12 mm/min for the 20 wt % PLA-co-CL blend. The kinetics interference in crystal growth rate of PEG suggests a diluting effect of the PLA-co-CL in the blends; further, PLOM and AFM provided unequivocal evidence of the interfering effect of PLA-co-CL on PEG crystal morphology, demonstrating imperfect crystallization in blends with interfibrillar location of the diluting amorphous component. Significantly, AFM images provided also evidence of amorphous phase separation between PEG and PLA-co-CL. A true T g vs. composition diagram is proposed on the basis of the AFM analysis for phase separated PEG/PLA-co-CL blends revealing the existence of a second PLA-co-CL rich phase. According to the partial miscibility established by AFM analysis, PEG and PLA-co-CL rich phases, depending on blend composition, contain respectively an amount of the minority component leading to a system presenting, for every composition, two T g 's that are different of those of pure components.