e-Polymers 2006, no. 054 http://www.e-polymers.org ISSN 1618-7229 Synthesis and some Mechanical Properties of Polysulfobetaine – Polyacrylamide Double Networks George Georgiev, 1* Konstantina Dyankova, 1 Elena Vassileva, 1 Klaus Friedrich 2 1 Faculty of Chemistry, University of Sofia, 1 J. Bourchier Ave., 1164 Sofia, Bulgaria; e-mail: georgs@chem.uni-sofia.bg 2 Institute for Composite Materials, University of Kaiserslautern, 58 Erwin-Schrödinger Ave., 67663 Kaiserslautern, Germany; e-mail: klaus.friedrich@ivw.uni-kl.de (Received: 4 February, 2006; published: 20 August, 2006) Abstract: Double polymer networks (DNs) with poly(N-(3-sulfopropyl)-N- methacroyloxyethyl-N,N-dimethylammonium betaine) component as a high density cross-linking agent were synthesized by thermoinitiated cross-linking polymerization. Good mechanical properties of the produced DNs were established. These, in combination with an excellent biocompatibility of polyzwitterions, open a possibility for wide biomedical applications of these materials. It is also shown that the mechanical properties could be controlled by the factors (cross-linking agent and monomer concentrations, temperature and time for the cross-linking polymerization, order of single network formation) influencing the junction point densities of the two single networks and on the microphase separation taking place during the formation of the second single network. Specific dipole-dipole interaction between polyzwitterion monomer units as a reason for this separation is a distinct peculiarity of poly(N-(3-sulfopropyl)-N-methacroyloxyethyl-N,N- dimethylammoniumbetaine)/poly(acrylamide) double networks in comparison to poly(2-acrylamido-2-methylpropanesulfonic-acid)/poly(acrylamide) ones. Introduction Double polymer networks (DN) are special types of interpenetrating networks (IPN), which consist of single networks (SN) strongly differing in their cross-linking density and in the length and the stiffness of their intercross-linking segments (Mott et al. [1], Gong et al., [2]). The network with a high degree of cross-linking (HDSN) plays the role of a composite filler, imparting hardness and strength to the DN, while the low density network (LDSN) represents an isotropic polymer matrix. Their advantage is the possibility to change (within a wide range) their physical and mechanical properties as a function of specific guiding parameters, such as the monomer ratio, the initiator and cross-linking agent nature and concentration, the cross-linking time and temperature, the order of performance of the two polymerizations, the nature and thermodynamic compatibility of the two SN and the degree of swelling of the first SN in the solution of the monomer of the second one (Gong et al. [2]). Recently, it was established that the hydrogels of DN of poly(2-acrylamido-2-methylpropanesulfonic- acid) (PAMPS) and poly(acrylamide) (PAAm) have very high elastic and shear modulus values at definite concentration ratios of the two monomers and the 1