Small Angle X-ray Scattering Study of PS Conformation in Tetrahydrofuran Solvent with Gas Anti-solve

Chinese Chemical Letters Vol. 11, No.12, pp. 1093-1094, 20001093Small Angle X-ray Scattering Study of PS Conformation inTetrahydrofuran Solvent with Gas Anti solventDan LI, Zhi Min LIU', Guan Ying YANG', Qing HUO-, Bu Xing HAN1*,Yi LIU', Zhong Hua WU', Bao Zhong DONG1 Center for molecular sciences, Instute of chemistry, Chinese Academy of Science,Beijing 1000802 Chemical Engineering College, Beijing Union University, Beijing 1000233 Institute of High Energy Physics, Chinese Academy of Science, Beijing 100039Abstract: Small angle X-ray scattering (SAXS) was used to study the effect of dissolved CO2 onthe conformation of polystyrene (PS) in PS/tetrahydrofuran(THF) solution at 308.15 K and atpressures up to 3 MPa. The cloud pressure and the expansion curve of the solution were alsodetermined. The dependence of the conformation on pressure was discussed.Keywords: Small angle X-ray scattering, polystyrene, THF, CO2, conformation.Compressed gases or supercritical fluids (SCFs) are highly soluble in some liquidsolvents, and thus reduces the solvent strength of the liquids'. As a result, precipitation ofthe dissolved solutes occurs, which is called as gas anti-solvent (GAS) process. Recently,this new technique has been used to produce fine particles of different compounds, suchas polymers?. Effect of the dissolved gases on the conformation of polymer molecules isa very interesting topic. In this work, we report the first application of small angle X-rayscattering (SAXS) to study the conformation of a polymer in the solution with a GAS.The average molecular weight of the PS was 7.8x10* with a narrow molecularweight distribution (Mw/Mn=1.1), which was kindly supplied by Polymer Laboratory ofInstitute of Chemistry, Chinese Academy of Sciences. The concentration of PS in CO2-free PS/THF solution was in the range from 6.74x10+ to 8.36x10*g/cm3. SAXSexperiments were carried out at Beamline 4B9A at Beijing Synchrotron RadiationFacility. A high pressure, temperature- controlled sample cell with two diamond windowswas used. Its structure was similar to that of our UV sample cell'.The temperature of the cell was controlled at 308.15 K. A known amount ofPS/THF solution was introduced into the sample cell. CO2 was then charged and mixedwith the liquid solution under controlled pressure. Scattering measurement wasperformed. The scattering curve of the CO/THF solution without PS was alsodetermined at the same condition, which was used as background in the data treatment.Using the procedure reported', the radii of gyration 12 were obtained from theSAXS data, which reflect the conformation of polymer chains. Figure 1 shows thedependence of 12 on pressure and the volume expansion (Ve=A VV: V is the中国煤化工YHCNMH G ..1094DanLI et al.volume of gas-free solution, O V is the volume change caused by the dissolved CO2 ) ofthe solution caused by anti-solvent.Figure 1 Dependence of 12 on pressure and volume expansion150F0.61250.5100 -F0.3二号0.2750.1-0.05(0005101520253.0 3.5P, MPaIt is well known that the larger the I/, the more expanded the polymer is inthe solution. It can be seen from Figure 1 that 12 decreases with increasingpressure, or volume expansion. It indicates that the PS chain experience shrinking in thecourse of adding anti-solvent CO2. THF is a good solvent for PS and the coil expandeddue to prevailing intersegmental repulsion. After adding CO2, the solvent power of THFis reduced and PS chain shrunk due to prevailing intersegmental attraction. In addition, 12 is more sensitive to pressure at the higher pressure.AcknowledgmentsThis work was supported by the National Basic Research Project-Macromolecular CondensedState and the National Natural Science Foundation of China (29633020, 29725308)ReferencesC. s. Tan, W. w. Chang, Ind. Eng. Chem. Res, 1998, 37, 1821.L. Benedetti, A. Bertucco, P. Pallado, Biotechnol. Bioeng., 1997, 53, 23.J. Lu, B. X. Han, H. K. Yan, Phys. Chem. Chem. Phys., 1999, I, 449.4. 0.Glatter, O. Kratky,“Small Angle X-ray Scattering", Academic Press, London, 1982.Received 15 May 2000中国煤化工MHCNMH G.