Polymerization kinetics of polyacrylamide gels II. Effect of temperature

TLDR: In this article, it is suggested that polymerization at 0-4°C should be abandoned, since it leads to unhomogeneous and unreproducible pore size matrices.

Abstract: The temperature at which polyacrylamide gels are polymerized strongly affects the structure and physical properties of this matrix. The suggested temperature of 0–4 °C has been found to produce highly turbid, highly porous and unelastic gels. At temperature of 25 °C of higher, the gels became progressively transparent, less porous and more elastic. This phenomenon is strongly pronounced in N,N′-methylenebisacrylamide (Bis) gels and progressively decreases for N,N′-(1,2-dihydroxyethylene)bisacrylamide (DHEBA) and N,N′-bisacrylylcystamine (BAC) gels. It has been attributed to the formation of hydrogen bonds among cross-linker molecules, which are presumably stabilized by low temperature and progressively broken at higher temperatures. The most extensively H-bonded compounds seem to be Bis molecules, since they can form four H-bonds/molecule, followed by DHEBA (in which inter-molecular H-bonds have to compete with intra-molecular H-bonds) and finally by BAC, which is sparingly H-bonded at 2 °C, and fully uncomplexed at 30°C. It is suggested that polymerization at 0–4°C should be abandoned, since it leads to unhomogeneous and unreproducible pore size matrices. Since H-bonds in Bis molecules are fully disrupted only at 60°C (a temperature unsuitable for gel polymerization, since it produces short chains and unelastic matrices), it is also suggested that the use of Bis should be discontinued in favour of better cross-links, such as DHEBA. In all cases, best polymerization conditions are obtained at 25–30°C. For all three cross-linkers, homogeneous gels are obtained in presence of 8 M urea or in pure formamide as solvent, since both agents fully disrupt H-bonds.