Extruded Saloplastic Polyelectrolyte Complexes

Biocompatible, nonporous and stoichiometric polyelectrolyte blends of both poly(styrene sulfonate), PSS, and poly(diallyldimethylammonium), PDADMA, were produced for the first time on a scale of ca. 300 g h-1 using a laboratory extruder. The oppositely charged polyelectrolytes form interpenetrating network held together by ionic crosslinking. Both salt doping and water plasticization weaken the network bonding, soften the blend and allow the extrusion at a lower temperature. Since Fourier Transform Infrared (FTIR) spectra of both extruded polyelectrolyte complexes (ExPECs) and polyelectrolyte multilayers (PEMUs) of sodium polystyrene sulfonate (PSS/PDADMA) are very similar and their equilibrium moduli converge at low salt doping, ExPECs are considered stoichiometric and almost as compact as PEMUs. Other proofs for stoichiometry of the blends are the nuclear magnetic resonance (NMR) measurements of PSS/PDADMA ratio and the thermal gravimetric analysis (TGA), which revealed almost no salt presence after water rinsing. Microscopic images of cross-sections for extruded fibers, tubes and tapes revealed a total pore volume of less than 10%. At physiological temperature and ionic strength, ExPECs rehydrate up to 40% by weight, maintain rigidity, and have a toughness of 3MJ m-3, comparable to that of tendon tissues. Next, differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) were applied to investigate the thermal transitions of ExPECs equilibrated at different salt doping levels. DSC showed a weak signal of 40 mW g-1 for samples in water and in salt, while DMTA exposed a significant change of dynamic modulus from 107 to 104 Pa. Such a change is regarded as a glass transition which is related empirically to frequency and salt doping by the equation: . Tg increases with the deformation rate and decreases with the salt doping, which breaks the ionic crosslinking and plasticizes the complex. Time/Temperature superposition master curves for ExPECs doped in different salt solutions were combined on one master curve; this explains a triple relation between time, temperature, and salt doping. The lack of detection of a strong calorimetric signal in DSC measurements reveals a weak enthalpic part in the transition. On the contrary, the Tg is sensitively detected by DMTA. Finally, a variety of composite ExPECs are presented in this work. For example, magnetic ExPECs were produced from a complex precipitated in the presence of biocompatible zwitterated iron oxide nanoparticles converted to ExPECs. The blend doping in ammonium carbonate converted it from compact ExPECs to porous 3D scaffold. The polymerization of polypyrrole and polyaniline on the surface of the ExPECs formed a conductive coating. Gold nanolayer was formed inside the ExPECs as well as on the outer surface.