Hard segments 88-series adhesives

C)8 Pa as compared to 10 Pa) over the temperature range between hard and soft segment glass transitions. Table IV lists the transition temperatures for 87- and 88-series adhesives. 

As in the case of 73-series adhesives, degradation of 87 and 88-series polyurethanes was bimodal (Fig. 9). These adhesives were somewhat more stable than the 73-series (compare Fig. 6 with Fig. 9). Volatilization began at about 250°C. Assuming that the hard segments degrade first, this implies that the polyurea hard segments of 87- and 88-series polymers have better thermal stability than the polyurethane hard segments of the 73-series adhesives. 

There are several ways of changing the properties of segmented polyurethane copolymers. In this study, the chemical structure of the hard segments was changed to adjust the modulus of the adhesive. Further fine tuning is possible by varying the concentration of the different blocks. For example, the 87-series adhesives have a lower modulus than the 88-series adhesives because their hard segment concentration is lower. Studies of concentration effects (16) have shown that much wider variation of modulus is possible tTian was achieved here. 

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