Molecular Characterization of Semi-Fluorinated Copolymers with a Controlled Amount of Long-Chain Branching

Abstract

The molecular structure of various semi-fluorinated polymers derived from tetrafluoroethylene, hexafluoropropylene, and vinylidenefluoride is examined by different characterization methods in dilute solution. The polymer synthesis was tailored to set up samples with a straight linear topography as well as model polymers with a controlled amount of long chain branching. As anticipated from the reaction kinetics of the polymerization process, the absolute molar mass distributions of the linear samples as obtained by size exclusion chromatography coupled with multiangle light scattering are well described by a Schulz−Zimm distribution. With [η] ∼ M0.73 and 〈s2〉1/2 ∼ M0.53 in THF, scaling laws typical of coil dimensions of linear macromolecules in good solvents were observed. In the second set of samples, the presence of long-chain branching (LCB) becomes evident from a reduced radius of gyration in the high molar mass region. Solution viscometry on the polydisperse samples reveals a decreasing contraction factor gη = [η]br/[η]lin of the intrinsic viscosity (equivalent to g‘ as introduced by Zimm and Kilb) with increasing amount of branching agent utilized in the polymer synthesis. The branching parameter ε determined from gη together with the contraction factor of the radius of gyration gs = 〈s2〉br/〈s2〉lin is found to be increasing from 0.5 for M < 106 g/mol to about 1.3 at higher molar masses, which is indicative of a topography change from a starlike to a comblike polymer architecture.