Small-angle neutron scattering characterization of polyhydroxyalkanoates and their BioPEGylated hybrids in solution.

ABSTRACT

Small-angle neutron scattering was used to probe the molecular conformation of various polyhydroxyalkanoates (PHAs) and their bioPEGylated counterparts (PHA- b-PEG). Analysis of neutron scattering profiles of these polymers dissolved in deuterated chloroform at various concentrations from dilute (approximately 0.1% w/v) to semidilute (approximately 7% w/v) showed the two distinct regimes and established overlap concentrations around 4-9 mg mL(-1). Scattering profiles were similar for all polymers investigated; power laws of approximately Q(-1.66) at high Q demonstrated that chloroform behaves as a good solvent for PHAs and suggests that under conditions synonymous with processing the solvated chains were swollen rather than in Gaussian conformation as previously reported. A gradual change to Guinier knees was followed by slopes of Q(-3) suggesting the presence of supramolecular structures at larger length scales. These observations in both the dilute and semidilute concentrations have not been previously reported. Zimm analysis of the data provided gyration radii and absolute molecular weights consistent with trends established using light scattering but showed some variation in their second virial coefficients. While natural-synthetic hybrids of PHA- b-PEG can self-assemble into microporous films, they showed no noticeable differences in chain conformation when in solution, the fabricating medium. This suggests that some form of entropic inducement is required.