Molecular weight effects on the miscibility behavior of dextran and maltodextrin with poly(vinylpyrrolidone).
OBJECTIVE
To characterize and interpret the miscibility of dextran and maltodextrin with poly(vinylpyrrolidone) (DEX-PVP) as a function of polymer molecular weights.


METHODS
Blend miscibility was studied using 4 different molecular weight (MW) grades of DEX combined with 5 MW grades of PVP, over a broad compositional range. Miscibility was evaluated by inspection of glass transition events measured by differential scanning calorimetry (DSC). Fourier transform mid-infrared spectroscopy (FTIR), combined with curve fitting, was performed to characterize the extent of hydrogen bonding. The observed miscibility behavior was further interpreted in terms of mixing thermodynamics.


RESULTS
Miscibility of the blends ranged from fully miscible to completely immiscible with multiple partially miscible systems observed. Increasing polymer molecular weight decreased miscibility. For the lowest DEX grade, hydrogen bonding was independent of PVP MW, as expected since all systems were completely miscible. Higher molecular weights of DEX resulted in reduced intermolecular hydrogen bonding and decreased miscibility, increasingly so for higher MW PVP grades. Evaluation of the mixing thermodynamics supported these findings.


CONCLUSIONS
With higher combined molecular weights of DEX-PVP blends, phase behavior evolves from completely miscible to virtually immiscible. Concurrently, DEX-PVP hydrogen bonding decreases. From a thermodynamic perspective, the combinatorial mixing entropy was observed to decrease as the molecular weight of the polymers increased, providing a reduced counterbalance to the unfavorable mixing enthalpy thought to accompany this polymer combination.
Department of Industrial and Physical Pharmacy, College of Pharmacy, Purdue University, 575 Stadium Mall Drive, West Lafayette, Indiana 47907, USA.
Bernard
B
Van Eerdenbrugh
Lynne S
LS
Taylor
D002152:Calorimetry, Differential Scanning / Q000379:methods; D003911:Dextrans / Q000737:chemistry*; D006860:Hydrogen Bonding; D008970:Molecular Weight; D011134:Polysaccharides / Q000737:chemistry*; D011145:Polyvinyls / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D013816:Thermodynamics
D003911:Dextrans; D011134:Polysaccharides; D011145:Polyvinyls; C008315:maltodextrin