Tri-block copolymers with mono-disperse crystallizable diamide segments: Synthesis, analysis and rheological properties

Tri-block copolymers with polyether mid-segments and mono-disperse amide end segments were synthesized, analyzed and some properties studied. The end segment was an aromatic diamide (diaramide, TΦB). The polyether mid-segment was a difunctional poly(tetramethylene oxide) (PTMO, 1000 and 2900 g/mol). In order to increase the soft segment (SS) length, PTMOs were extended with terephthalic groups. The length of the mid-soft segment was varied from 1000 to 20,000 and thereby the concentration of the hard end segment changed from 22 to 3 wt.%. The molecular weight of the tri-block copolymers was determined by NMR and inherent viscosity measurements. The crystallinity of the hard segment was studied by IR and DSC measurements. Temperature modulated IR was carried out to explore the change in crystallinity with temperature. The morphology was investigated by AFM analysis and the thermo-mechanical properties by DMA, whereas the melt rheological behaviour was analyzed by a plate-plate method. The results of the tri-block copolymer were compared with those of a similar multi-block copolymer. The glass transition of the soft phase was low and the melting temperature of the diamide end blocks was high. The crystallinity of the hard end segments in the tri-block was found to be very high (>95%) and remained high until melting. The AFM picture showed crystalline ribbons with a high aspect ratio. Also the modulus at room temperature was relatively high, particularly at low contents of hard end segment. The melt rheological behaviour of a low molecular weight tri-block copolymer revealed a low melt viscosity at high shear rates, and a high viscosity at low shear rates. Moreover, a gelling of the melt was observed with decreasing frequency and this was probably due to agglomeration of the end segments.