The role of acrylonitrile in controlling the structure and properties of nanostructured ionomer films

Abstract

Ionomers are polymers which contain ionic groups that are covalently bound to the main chain. The presence of a small percentage of ionic groups strongly affects the polymer's mechanical properties. Here, we examine a new family of nanostructured ionomer films prepared from core-shell polymer nanoparticles containing acrylonitrile (AN), 1,3-butadiene (Bd) and methacrylic acid (MAA). Three new AN-containing dispersions were investigated in this study. The core-shell nanoparticles contained a PBd core. The shells contained copolymerised Bd, AN and MAA, i.e., PBd-AN-MAA. Three types of crosslinking were present in these films: covalent crosslinks (from Bd); strong physical crosslinks (involving ionic bonding of RCOO(-) and Zn(2+)) and weaker physical crosslinks (from AN). We examined and compared the roles of AN and ionic crosslinking (from added Zn(2+)) on the structure and mechanical properties of the films. The FTIR spectroscopy data showed evidence for RCOOH-nitrile hydrogen bonding with tetrahedral geometry. DMTA studies showed that AN copolymerised within the PBd-AN-MAA phase uniformly. Tensile stress-strain data showed that inclusion of AN increased elasticity and toughness. Analysis showed that about 33 AN groups were required to provide an elastically-effective chain. However, only 1.5 to 2 ionically bonded RCOO(-) groups were required to generate an elastically-effective chain. By contrast to ionic bonding, AN inclusion increased the modulus without compromising ductility. Our results show that AN is an attractive, versatile, monomer for increasing the toughness of nanostructured ionomers and this should also be the case for other nanostructured polymer elastomers.

Tuning the modulus of nanostructured ionomer films of core–shell nanoparticles based on poly(n-butyl acrylate)

“…Furthermore, poly(n-butylacrylate) (PBA) has a T g of -49 o C 10 which is about 20 o C higher than the T g for PBd 8 . We hypothesised that increasing the T g of the nanoparticle phases would provide higher modulus nanostructured films with built-in modulus tuneability afforded by the AN and MAA groups.…”

“…Those core-shell nanoparticles were prepared using 1,3-butadiene (Bd), acrylonitrile (AN) and methacrylic acid (MAA). The proportions of AN and MAA and extents of neutralisation were shown to affect the modulus values 8,9 . Whilst those nanostructured ionomer films had good ductility, their modulus values were low.…”

“…The overwhelming majority of ionomer films studied to date have been prepared by casting films of linear polymers from organic solvent-based solutions 20 or using compounding 21 or compression molding 15,22 . However, there has been relatively little work reported for nanostructured ionomeric films prepared from aqueous dispersions 8,9 , which is an approach with obvious environmental benefits.…”

“…Whilst those nanostructured ionomer films had good ductility, their modulus values were low. Also, the use of Bd, which has a boiling point of -5 o C, restricted the versatility for nanoparticle preparation because a high pressure reactor was required 8 . In this study, we sought to overcome both the versatility and modulus deficiencies by investigating core-shell nanoparticles prepared using n-butyl acrylate (BA) in place of Bd.…”

“…However, elastomeric films constructed using core-shell nanoparticles containing COOH groups have received less attention. Our previous work introduced ductile nanostructured elastomeric films prepared by casting films from aqueous dispersions of low glass transition temperature (T g ) core-shell nanoparticles in the presence of ZnO 8,9 . The latter was used to neutralise the surface -COOH groups and introduced ionic inter-particle crosslinking.…”