Chinese Acad Sci, Inst Chem, Ctr Mol Sci, Beijing 100080, Peoples R China
; Beijing Union Univ, Chem Engn Coll, Beijing 100032, Peoples R China
; Chinese Acad Sci, Inst High Energy Phys, Beijing 100039, Peoples R China
Small-angle X-ray scattering (SAXS) was used to investigate the dimension, shape, and microstructure of bisphenol A polycarbonate (PC) of narrow distribution in tetrahydrofuran (THF) in the course of adding gaseous antisolvent CO(2) at 308.15 K and at pressures up to 2 MPa. The weight-average molecular 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 solution ranged from 1.2 x 10(-3) to 9.1 x 10(-3) g/cm(3). The second virial coefficient A(2) and the radius of gyration (R(g)(2))(1/2) = R(g) were found to decrease 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 CO(2) pressures (P = 0, 0.5, 1, 1.5, and 2 MPa), suggesting that the PC chain has a fractal structure in the presence antisolvent CO(2). Self-similar structure behavior was also observed with a detailed analysis of the particle scattering factor P(q) (angular dependence of the scattered light), and the fractal 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 antisolvent pressure or the solubility of CO(2) in the solution on PC structure. Increase 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 CO(2).