Precision Ionomers: Synthesis and Thermal/Mechanical Characterization

Abstract

Six perfectly regioregular polyethylene (PE)-based ionomers containing 1-methylimidazolium bromide groups on exactly every 9th, 15th, or 21st carbon (precision ionomers) and two regiorandom analogues have been synthesized and characterized via dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). Because these materials were synthesized by a postpolymerization functionalization route, their number-average molecular weights (Mns) and polydispersity indices (PDIs) could be accurately calculated based on measurements of the preionized polymers; Mns range from 36 to 53 kDa with PDIs all close to 2. Thermal gravimetric analysis (TGA) indicates stability up 250 °C, and DSC measurements indicate that crystallinity is a function of the polymer backbone spacer length. Tms range from ∼80 to 106 °C, with longer spacer lengths inducing semicrystallinity. DSC measured glass transition temperatures (Tgs) range from −1.6 to 26.8 °C and appear to be dependent on both spacer length and crystallinity. DMA data loosely mirror the DSC results, but with transitions occurring at lower temperatures that we attribute to differences in the thermal history and/or the different heating ramp rates used.