Soft segment activation energy

Hard- and Soft-Segment Polymers. The structure of the diisocyanate component has a significant influence on dynamic mechanical properties of both hard- and soft-segment polymers. Both 2,4- and 2,6-TDI/ BD a relaxations occur at about the same temperature and have a comparable activation energy. However, the symmetrical structure of... 

The rate constants k obtained for thermally differently treated polyurethanes are represented in the Arrhenius plot. Fig. lO. The apparent energy of activation E for the thermal cis-trans isomerization, as determined from the slopes in Fig. lO, is about 80 kj/mol (k ) in polymers with completely amorphous soft phase, a similar figure as found in solution in samples with partially crystallized soft segments, values of about 60 kJ/mol (k ) and 19 kj/mol (k.) are found for the two simultaneous first order processes (line 2 and 3, Fig. lO). The occuring of these two apparent energies of activation, which are similar to the energies required for rotational (crankshaft (15) ) and translational (3)... 

The apparent activation energies ( ACT) of the dynamic mechanical transitions can be calculated from the temperature at the maximum in the loss modulus T(G"max) as a function of frequency. A typical Arrhenius plot (see Fig. 2) of the apparent activation energy of the soft segment glass transition for 73 series polymers yields E/ ct values of approximately 75 + 5 kcal/mole (314 kJ/mole) over a frequency range of 2 decades. 

Figure 2. The apparent activation energy of the soft segment glass transition for Halthane 73-15 is determined from the slope of a plot of In f vs. 1 /T(G"max).

Block copol3nners form a new class of molecular composite materials by the phase separation of incompatible hard and soft segments which form their macro-molecular structure. Thermoplastic elastomers where the soft segments form the continuous phase have been extensively investigated by means of an adsorption-interdiffusion (A-I) model for the interfacial phase which bonds the hard and soft phases. The molecular structure and rheological activity of the interfacial phase in thermoplastic elastomer block copolymers is shown to play a dominant role in nonlinear viscoelastic response, mechanical hysteresis and energy absorption. Creation of elastomeric microphases in epoxy structural adhesives has been recently identified with in situ block copol3nnerization between carboxy terminated nitrile (CTBN) rubber and the diepoxide. 

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