Development of a high-pressure dynamic light scattering instrument to investigate the impact of solvent size on polymer conformational behavior in dilute solutions

A high-pressure dynamic light scattering (DLS) instrument is developed to study the impact of solvent size and polymer architecture on polymer conformational behavior as a function of pressure. Comparing macroscopic phase behavior results to hydrodynamic radii, R_H, results provides information on the characteristics of polymer-solvent interactions in the single-phase region. Instrument development and use are described in detail. Results are presented for a polystyrene (PS)-toluene system and several poly(ethylene-co-1-butene)-alkane systems.; The DLS instrument used in this thesis evolved from a two-cell design to a unicell design. The scattering cell is mounted on a goniometer, which rotates about the cell collecting data from each of the six scattering ports located around the cell body from 36° to 144°. All data presented in this thesis were collected using the unicell design.; DLS experiments are presented for four PS-toluene solutions at 25°C from pressures of 17 bar to 2,068 bar. The results are compared with existing literature values and validate the high-pressure capabilities of the DLS instrument. The R_H values of the PS coils do not change over the entire pressure range studied. The decrease in D ₀ with pressure is, therefore, entirely the result of an increase in solvent viscosity with pressure.; Novel results are presented for several poly(ethylene-co-1-butene)-alkane systems at 130°C and pressures to 2,068 bar in the single-phase region. Polyethylene-co-20.2 mol % 1-butene) (PEB-10) is studied using four alkane solvents. The R_H values of PEB-10 increase with pressure in ethane, propane, and n-butane. In n-pentane, however, the R_H values remain at the theta value over the entire pressure range studied. Polymer backbone branching is also studied by comparing DLS results for PEB-10 in ethane to polyethylene-co-94.2 mol % 1-butene) (PEB-47) in ethane. A qualitative comparison shows the R_H values for the more linear PEB-10 increasing more with pressure than the relatively branched PEB-47.