Synthesis and characterisation of soluble block copolymers from NR and TDI based polyurethanes

Soluble block copolymers from toluene diisocyanate (TDI), with chain extender diols, viz., propylene glycol (PG), 1,4-butane diol (1,4-BDO) and 1,3-butane diol (1,3-BDO), were synthesised for the first time by solution polymerisation. Maintaining low hard segment content and keeping optimum NCO/OH ratio, formation of linear, flexible elastomers is achieved. They were characterised by spectral, thermal, microscopic and stress-strain analysis. The dilute solution properties of these block copolymers dissolved in tetrahydrofuran (THF) are studied by viscometry and gel permeation chromatography (GPC). IR and NMR spectral data support the notion that a chemical reaction leads to block copolymerisation. Differential scanning calorimetric (DSC) analysis showed a soft segment glass transition temperature around -58 degrees C and a hard segment glass transition temperature between 75 and 70 degrees C for these samples. This observation and two-stage thermal decomposition of the samples in thermogravimetric analysis (TGA) clearly indicate that the block copolymers are completely phase-segregated systems. SEM indicates the amorphous heterophase morphology of the samples.