Direct Measurement of the Enthalpy of Mixing in Miscible Blends of Poly(dl-lactide) with Poly(vinylphenol)

Abstract

Blends of poly(DL-lactide) (PDLLA) with poly(vinylphenol) (PVPh), obtained by solventcasting and solution/precipitation, have been studied by DSC and FTIR. DSC results obtained in the first heating scan suggest that as-prepared blends are phase separated in nearly pure components. In addition, the initial FTIR spectra of the as-precipitated blends show no sign of specific interactions, which is also consistent with the phase separation. In solution/precipitation blends, the first calorimetric scan shows an exothermic peak attributed to the enthalpy of mixing. To our knowledge, this is the first polymer blend system for which this thermodynamic parameter has been possible to directly measure. The exothermic peak occurs at temperatures just below the T g of PVPh. The consecutive DSC scans show a single Tg for the whole composition range, indicating complete miscibility. The interaction energy density (B) has been calculated and shows a strong dependence on composition. The decrease in B (in terms of absolute value) as the content of PVPh decreases is related to the higher energy consumed to break its strong autoassociation. Phase separation into the neat polymers for the as-prepared blends is attributed to accessibility issues between interacting groups, including steric shielding, group spacing, and chain stiffness, aggravated by blending temperatures below the corresponding T gs. At high temperatures thermal motion increases chain mobility, allowing the development of an intimately mixed single-phase blend. On the other hand, phase separation is observed in solution-cast blends with high PVPh content, certainly due to the ∆χ effect, resulting in macroscopic domains that prevent obtaining a homogeneous blend at high temperatures in the absence of a shearing mechanism. Interaction development during heating has been followed by FTIR. Both the hydroxyl and carbonyl stretching regions indicate hydrogen bonding between OH groups of PVPh and CdO groups of PDLLA, suggesting weaker interactions than in other PVPh/polyester systems.

Compatibilization through Specific Interactions and Dynamic Fragility in Poly(D,L‐lactide)/Polystyrene Blends

“…[2] Only a few counterparts have been reported to give miscible blends with PLAs: poly(3-hydroxybutyrate) (PHB), [3,4] poly(methyl methacrylate) (PMMA), [5,6] poly(methylacrylate) (PMA), [5] poly(vinyl acetate) (PVAc), [7][8][9][10] poly(ethylene oxide) (PEO) [11][12][13][14] , and poly(hydroxystyrene) (PHS), also known as poly(vinylphenol) (PVPh). [15,16] From all of them, only the last one is a hydrogen-bonding counterpart for PLA.…”

“…[15] However, miscibility could only be achieved in blends prepared following a particular thermal conditioning after solution/precipitation in the THF/hexane pair. As obtained mixtures were found phase-separated at the molecular level as confirmed in the initial DSC scan, carried out in specifically mild thermal conditions (heating rate 20 8C Á min À1 , final temperature 200 8C) to avoid any polymer degradation reaction (the occurrence of these undesired side reactions was also discarded using DSC and NMR).…”

Kinetic Analysis on Effect of Poly(4-vinyl phenol) on Complex-Forming Blends of Poly(L-lactide) and Poly(D-lactide)

“…20,21 Moreover, blends of amorphous poly(D,L-lactide) (PDLLA) with amorphous PVPh by solvent casting are phase separated in blends with high PVPh contents. 22 It was of interest to investigate effects of a miscible polymer on the stereocomplexation behavior of PLLA and PDLA in a blend system. Poly(4-vinyl phenol) (PVPh), with a hydroxyl group at the pendant phenyl ring, is capable of interacting with proton-accepting functional groups with both PLLA and PDLA.…”

Miscibility Criterion in Polymer Blends and its Determination

“…Blends in which hydrogen bonding interactions exist between the components offer ideal systems for FTIR investigations [187][188][189][190]. For example, IR spectroscopy has provided the main proof for the presence of a strong interactions between poly(4 hydroxystyrene), P4HS, and the carbonyl groups of polyacrylates [194], polymetha crylates [195][196][197], polyesters [198], and polylactides [199], as well as with the ether groups of polyethers [200]. The H-bond interaction clearly affects the hydroxyl region of the IR spectra (3100-3700 cm 1 ) and three distinct contributions are usually observed due to free, intra-and inter-associated O H vibrations [196].…”