Interpenetrating polymer networks (IPN's) of polyurethane (PU) and polystyrene(PS) were synthesized by simultaneous polymerization in the presence of a common solvent. Polyurethane networks were prepared by reacting the polyurethane prepolymer based on 4,4'-diphenylmethane diisocyanate (MDI) and ploy(tetramethylene ether)glycol (PTMEG) with 1,4-butanediol (BD) and trimethylol propane (TMP) mixture (1:1 equivalent ratio) as the chain extending agent. Polystyrene networks were prepared by cross linking styrene monomer with divinyl benzene (DVB).
The effect of the presence of a common solvent in the reaction and the compositional variation on the rate of polymerization, the onset of phase separation and the morphology of products were investigated.
To select an appropriate common solvent, swelling experiment was conducted. From the solubility parameter values, 1,4-dioxane was selected as the common solvent for he IPN synthesis.
The conversion of PU at the onset of phase separation decreased with increasing the PS composition. The conversion of PS at the onset of phase separation in U50S50 IPN was relatively low compared with other compositions. The extent of reaction of both components at the onset of phase separation increased with increasing the amount of 1,4-dioxane in the reaction medium.
The morphology of final product was influenced by the extent of reaction at the onset of phase separation. In these IPN's, PS domains were observed since PU network was formed fist with faster rate of polymerization. The PS domain size decreased with increasing the PU composition. The PS domain size became more uniform and reduced in size with increasing the amount of 1,4-dioxane in the reaction medium.
The density, glass transition behavior, and thermal stability were also studied. The IPN's all showed slightly increased densities over the calculated densities. The glass transition behavior also showed an inward shift in glass transition temperatures (Tg's) with increasing the amount of 1,4-dioxane in the reaction medium indicating enhanced degree of interpenetration.
The IPN's synthesized in the presence of common solvent all showed increased thermal stability due to the higher degree of interpenetration.
Linear blends and semi IPN's were also synthesized in the presence of 1, 4-dioxane for comparison.
