Phosphonium ionenes from well-defined step-growth polymerization: thermal and melt rheological properties

• Published in: Polymer chemistry Vol. 4; no. 12; pp. 3582 - 3590
• Main Authors: Hemp, Sean T., Zhang, Musan, Tamami, Mana, Long, Timothy E.
• Format: Journal Article
• Language: English
• Published: 01.01.2013
• Subjects: Cations; Charge density; Condensation polymerization; Ionenes; Melts; Molecular weight; Phosphines; Stability
• ISSN: 1759-9954; 1759-9962
• DOI: 10.1039/c3py00365e

Step-growth polymerization of ditertiary phosphines with dibromoalkanes enabled the synthesis of novel phosphonium ionenes. In situFTIR spectroscopy monitored the increase in absorbance as a function of time at 1116 cm super(-1), which corresponded to the polymeric P super(+)-Ph stretch. Aqueous size-exclusion chromatography (SEC) provided absolute molecular weights and confirmed expected molecular weight growth for difunctional, step-growth polymerization. Phosphonium ionenes exhibited improved thermal and base stability compared to ammonium ionenes, which was attributed to the propensity of the ammonium cation towards Hofmann elimination. Melt rheology examined phosphonium ionene viscous flow and the influence of charge density on melt viscosity as a function of shear rate and temperature. Time-temperature superposition (TTS) resulted in both master curves and pseudomaster curves depending on phosphonium ionene composition. Two primary relaxations occurred: (1) onset of long-range segmental motion at T sub(g), and (2) relaxation attributed to electrostatic interactions. Higher charge densities shifted these two relaxations to longer time scales and increased flow activation energies. Phosphonium ionenes also readily bound pDNA effectively ( plus or minus ratios of 1), and base stability suggested applications in energy generation.