Comparative studies on short-chain and long-chain crosslinking in polyurethane networks

Isocyanate terminated prepolymers were synthesises using poly(tetramethylene oxide) glycol of molecular weight 1 000 (PTMG 1000) and poly(propylene oxide) glycol of molecular weight 1 000 (PPG 1000 ) with tolylene-2,4-diisocyanate (TDI). The prepolymers were chain extended with N,N-bis(2-hydroxyethyl)isonicotinamide to form polyurethanes containing pyridine moieties. These polyurethanes were converted to cationomers by crosslinking with (a) 1,4-dibromobutane to form short-chain crosslinked polymers (SCCPs) and (b) bromine-terminated prepolymers to form long-chain crosslinked polymers (LCCPs). The cationomers were characterised by Fourier transform infrared spectroscopy, thermal and mechanical analysis. FTIR spectral results of SCCPs and LCCPs confirmed the quaternisation of heterocyclic nitrogen leading to crosslinking. Dynamic mechanical analysis showed better damping properties for LCCPs than SCCPs. The stress-strain mesurements showed higher elongation and lower tensile strength for LCCPs.