HTNR

Since the same grade of HTNR was used for all the synthesis, the soft segment transition is not expected to vary from sample to sample.

Beyond this value the hard segment formation suitable for proper chain extension with the HTNR may not be accomplished due to the presence of large excess of isocyanate in the reaction mixture.

All the insoluble samples were subjected to etching studies using toluene and THF successively in order to separate the unreacted reactants, viz., HTNR and the polyurethane oligomers and also to separate the low molecular weight block copolymers.

For the purpose of comparison, the IR spectra of HTNR and PU-10 were also given in Fig.

In the case of HTNR, the absorption band in the region 3600-3400 [cm.sup.-1] is the stretching vibration of OH group.

Figure 1 shows the IR spectra of (a) HTNR, (b) isocyanate endcapped HTNR, (c) polyurethane oligomer prepared from TDI and propylene glycol and (d) the block copolymer.

This value is very close to that observed for the parent HTNR, viz., -68 [degrees] C.