Systematic Modification of the Glass Transition Temperature of Ion-Pair Comonomer Based Polyelectrolytes and Ionomers by Copolymerization with a Chemically Similar Cationic Monomer.

Guodong Deng,Timothy D Schoch,Kevin A Cavicchi

doi:10.3390/gels7020045

Abstract

Ion-pair comonomers (IPCs) where both the anion and cation contain polymerizable functional groups offer a route to prepare polyampholyte, ion-containing polymers. Polymerizing vinyl functional groups by free-radical polymerization produces bridging ion-pairs that act as non-covalent crosslinks between backbone segments. In particular the homopolymerization of the IPC vinyl benzyl tri-n-octylphosphonium styrene sulfonate produces a stiff, glassy polymer with a glass transition temperature (Tg) of 191 °C, while copolymerization with a non-ionic acrylate produces microphase separates ionomers with ion-rich and ion-poor domains. This work investigates the tuning of the Tg of the polyelectrolyte or ion-rich domains of the ionomers by copolymerizing with vinyl benzyl tri-n-octylphosphonium p-toluene sulfonic acid. This chemically similar repeat unit with pendant rather than bridging ion-pairs lowers the Tg compared to the polyelectrolyte or ionomer containing only the IPC segments. Rheological measurements were used to characterize the thermomechanical behavior and Tg of different copolymers. The Tg variation in the polyelectrolyte vs. weight fraction IPC could be fit with either the Gordon–Taylor or Couchman–Karasz equation. Copolymerization of IPC with a chemically similar cationic monomer offers a viable route to systematically vary the Tg of the resulting polymers useful for tailoring the material properties in applications such as elastomers or shape memory polymers.

Highlights

Ion-containing polymers have long attracted attention due to the physical properties associated with the ionsand their interactions with other chemical species.Of particular interest is the ready ability to manipulate the glass transition temperature (Tg ) of ion-containing polymers by manipulating the strength and connectivity of the ionic interactions
Scheme 1a depicts the synthetic routes for the preparation of polyelectrolytes through the copolymerization of the ionpair comonomer VBTOP-SS and cationic monomer VBTOP-TS with different feed ratios using reversible addition-fragmentation chain transfer (RAFT) polymerization
°C), a gravimetric yield of over 94% was observed, which indicates almost complete incorporation of the ionic monomer into the polymer. These polyelectrolyte polymers were systematically named as PIPC-cationic monomer (CM)-y-z, where y and z are the mol fraction of VBTOP-SS

Summary

Introduction

Ion-containing polymers have long attracted attention due to the physical properties associated with the ions (e.g., conductivity [1], glass transition [2], and dynamic bonding [3])and their interactions with other chemical species (i.e., solvent [4], salts [5], and non-ionic repeat units [6]).Of particular interest is the ready ability to manipulate the glass transition temperature (Tg ) of ion-containing polymers by manipulating the strength and connectivity of the ionic interactions. Ionic groups offer the flexibility to tune Tg through mild reaction and processing conditions, such as choice of the initial ions (e.g., ammonium vs phosphonium [7], zwitterion formation [8]), ion-exchange [9,10,11], polyelectrolyte complexation [12,13], and plasticizing with salt and water [5,14,15,16,17] These plasticizers are especially attractive as benign additives to temper or aid in the processing of polyelectrolyte complexes [18,19]. It has recently been shown that the Tg is related to the ratio of water molecules surrounding an intrinsic ion pair (nH2O /nintrinsic ion pairs ) as 1/Tg ~ ln(nH2O /nintrinsic ion pairs )

Methods

Results

Conclusion