Effect of chain extender length and molecular architecture on phase separation and rheological properties of ether-based polyurethanes

Different types of chain extenders in the synthesis of polyurethanes affect its structural, mechanical, and rheological properties. Effects of chain extender length, functionality, and molar ratio of the reactants on different properties of polyurethane elastomers based on poly (oxytetramethylene)glycol as the soft segment and toluene diisocyanate as the hard segment were investigated. Polyurethane samples were synthesized using different chain extenders including glycerol as the trifunctional and 1,2-propanediol, 1,4-butanediol, and 1,6-hexanediol as the bi-functional hydroxyl-containing chemicals. Fourier-transform infrared spectroscopy, X-ray diffraction, rheomechanical analysis, dynamic mechanical thermal analysis, differential scanning calorimetry, and stress–strain analysis were used for characterization of the products. By phase separation of the hard and soft segments, two different glass transition temperatures were observed. Increasing phase separation and degree of hydrogen bonding between the chain extender and diisocynates in the hard segments were resulted in higher mechanical properties. With increasing the amount of hard segment, a higher polymer toughness is determined due to higher degree of hydrogen bonding.