Particulate ionomer films prepared from dispersions of crosslinked polymer colloids: a structure-property study.
Polymers with properties that are governed by ionic interactions in discrete regions are termed ionomers. This work presents a comprehensive study of polymer films prepared from dispersions of crosslinked poly(butadiene/methacrylic acid) (poly(Bd/MAA)) particles in water. We showed recently [O. Pinprayoon, R. Groves, B.R. Saunders, J. Colloid Interface Sci. 321 (2008) 315-322] that poly(Bd/MAA) particles could be considered to have a core-shell structure with a MAA-rich shell. The poly(Bd/MAA) dispersions used here contained added ZnO particles which provided a source of Zn(2+). The films were investigated using AFM, FTIR, small-angle X-ray scattering (SAXS), dynamic mechanical thermal analysis (DMTA) and tensile stress vs. strain measurements. The films showed differences and similarities to conventional ionomers which are discussed. The FTIR data revealed that the Zn(2+) ions formed ionic crosslinks with the carboxylate groups (RCOO(-)). Mechanical property studies were conducted using DMTA and stress vs. strain measurements. The DMTA data revealed evidence of two main phases in the systems: a poly(Bd)-rich phase and a poly(MAA)-rich phase. A third phase was also found; which was ascribed to an interphase between the particle core and shell. The SAXS data showed that the films were composed of distinct poly(Bd/MAA) particles, implying that only partial coalescence occurred across the particle interfaces during formation of these particulate ionomer films. Ionic crosslinking of the particles was suggested to occur in the interfacial region (knit regions). The SAXS data also showed scattering from Zn(2+)(RCOO(-)) ionic-aggregates. These ionic aggregates had an average separation of 2.9 nm, which is much smaller than that for conventional ionomers. Interestingly, the concentration of these aggregates passed through a maximum and decreased as the degree of neutralisation of the MAA groups approached 100%. A conceptual model for the structure of these unconventional ionomers is discussed.
Pinprayoon
Orawan
O
Polymer Science and Technology Group, School of Materials, The University of Manchester, Grosvenor Street, M1 7HS, UK.
Saiani
Alberto
A
Groves
Robert
R
Saunders
Brian R
BR