Polyamines and Polysulfides

Cationic polymerization of both cyclic amines and sulfides is combined in this section because of the similarities in their polymerization. This similarity is due to the high nucleophilicities of monomers that belong to these groups, the high stability of the active centers and the relatively higher basicity of heteroatoms in the polymer units than in the corresponding monomers. This combination of features leads to very similar synthetic methods used for polymer preparations. 

There are two different ways of preparing the simplest polyamine, polyethylen-imine. The first method leads to a commercial polymer. The parent monomer (aziri-dine) is used and the resulting polymer is highly branched due to pronounced chain transfer. The second method, leading to linear polyethylenimine, requires the preparation of polyoxazoline intermediate and is discussed in the next section. 

Synthetic aspects as well as the mechanisms of polymerization of these monomers were reviewed by Goethals 1,2,3,4), who largely contributed to these fields. 

The synthesis of polyamines can occur only by cationic polymerization. Anionic polymerization is not possible because the positive charge on the a-C atoms in the monomer is too low to be susceptible to attack by anions. On the contrary, theC—N = bond in the ammonium cation is sufficiently reactive to break when the carbon atom is attacked by a highly nucleophilic monomer. 

Cationic polymerization of cyclic amines proceeds usually with a high activation energy and often requires relatively high temperatures, even for the strained four-membered rings, e.g. for 1,3,3-trimethylazetidine AH = 73 kJ mol-1, kp = 1.4 xl0 4mor1 -1-s 1 at 78 °C 5). 

---