Small-angle X-ray scattering by dilute solution of bisphenol A polycarbonate during adding antisolvent CO2

Small-angle X-ray scattering (SAXS) was used to investigate the dimension, shape, and microstructure of bisphenol A polycarbonate (PC) of narrow distr ibution in tetrahydrofuran (THF) in the course of adding gaseous antisolven t CO2 at 308.15 K and at pressures up to 2 MPa. The weight-average molecula r weights (M-w) of the polymer samples were 1.4 x 10(4), 1.8 x 10(4), 2.4 x 10(4), and 2.9 x 10(4), and the concentration of the polymer in the soluti on ranged from 1.2 x 10(-3) to 9.1 x 10(-3) g/cm(3). The second virial coef ficient A(2) and the radius of gyration (R-g(2))(1/2) = R-g were found to d ecrease with the increasing of the antisolvent pressure. The M-w of the PC chain was scaled to the R-g of the polymer chain as M-w proportional to R-g (dR) (dR = 2.17, 2.38, 2.56, 2.74, and 2.95) for different antisolvent CO2 pressures (P = 0, 0.5, 1, 1.5, and 2 MPa), suggesting that the PC chain has a fractal structure in the presence antisolvent CO2. Self-similar structur e behavior was also observed with a detailed analysis of the particle scatt ering factor P(q) (angular dependence of the scattered light), and the frac tal dimensions d(f) at 0, 0.5, 1.0, 1.5, and 2 MPa are 2.14, 2.35, 2.53, 2. 70, and 2.92, respectively. All of these revealed a large effect of antisol vent pressure or the solubility of CO2 in the solution on PC structure. Inc rease of fractal dimension (d(R) or d(f)) from 2.17 to 2.95 indicates that the polymer chain changes from a swollen coil to a rather dense globule in the course of adding antisolvent CO2.