Polymerization of Polyacrylamide-Gels

 

The pore diameter of the gel can be controlled in a reproducibly and exact way by the concentration of acrylamide ( T ) and the degree of crosslinking ( C ).

 

T [%] =      (a+b)x 100 / V

C [%] =     b x 100 / (a + b)

        a      [Acrylamide] in g

        b      [Methylenbisacrylamide] in g

        V      Volume in ml.

 

If: C is constant and T increases

 

-->Pore diameter decreases

 

If: T is constant and C increases

 

--> Pore diameter is a parabolic function of [c]

--> At large and small values of C the pore diameter is big

--> Pore size minimum is at about C = 4%.

--> Gels with C > 5 % are brittle and hydrophobic.

 

Additional to methylenbisacrylamide a wide variety of crosslinking agents can be used. N,N'-Bisacryloylcystamine is a reversible crosslinker which can be split using a strong reducing agent.

 

Polymerization needs an inert atmosphere (N₂, Ar,..) due to the fact that the chain length of the polymer is severely decreased by oxygen as a radical scavenger.

 

Polymerization should proceed at T > 20 °C to ensure proper timing and a low content of monomers and oligomers.