Waterborne polyurethane ionomers: structure–property relationships of elastomeric polyurethane ureas and polyurethane ionomers

Two groups of water-borne polyurethane ionomers were synthesised using well known methods of synthesis in order to determine the type of elastomers that may be obtained from each method. To begin with, the conventional methods of synthesis for water-borne polyurethane dispersions (WPUDs) in which the process of chain extension occurs in the presence of water was evaluated. This method is restricted to the use of diamines as chain extenders. It was demonstrated that the use of diamines, whether they are primary such as ethylene diamine, or tertiary such as NN’-dimethyl ethylene diamine lead to the formation of polyurethane-urea ionomers that are known for their higher modulus, strength, and lower elongation at break (EAB). The copoly(urethane–urea) ionomers indicated a decreased rate of stress relaxation (RSR). The alternative method of synthesis evaluated was the bulk method of synthesis in which the chain extension process takes place in the bulk. This method allowed the use of diols as chain extenders and resulted in softer elastomers. The polyurethane ionomers obtained by the bulk method of synthesis indicated a high rate of stress relaxation, and, a rapid reduction of load immediately after the application due to their weaker inter-segmental hydrogen bonding interaction. [Continues.]