Hard segment content effect

Figure 3. Small-angle x-ray scattering intensity curves demonstrating the effect of soft-segment molecular weight for three polycaprolactone polyurethanes (MDI/BD) of approximately equal hard-segment content. (A) 57% by wt, FCL 2000-178 (S) (B) 53% by wt FCL 830-123 (S) and (C) 61% by wt, FCL 830-134 (S).

Figure 9. Effect of hard-segment content on storage modulus and loss tangent of compression-molded FTMO/FTMT-segmented copolymers...

The increase in the 8-relaxation temperature for 2,6-T-lP samples with increasing hard-segment content is caused by extreme broadening of the relaxation maximum attributable to increasing hard block crystallinity. These effects are similar to changes in dynamic mechanical and... 

Effects of Phase Segregation on Modulus. The magnitude of the modulus between as and h for 2,4-T-2P or 8 for 2,6-TDI block polyurethanes was found to highly depend upon hard-segment content. The presence of a plateau region in modulus-temperature plots has been attributed to phase segregation in block copolymers (27). The hard... 

Table III. Effect of Hard Segment Content and Diol Structure on Transition Properties...

These improved properties may be related to 1) increased hydrogen bonding due to the increased polyester diol content, 2) increased hard segment content, and 3) evidence of crystallinity in the hard segment domain. All effects result in a higher modulus material. The structure-property relationships of these formulations in terms of their crystalline morphology are discussed in another paper. ... 

The 8000-MW, ultra-low monol PPG is used particularly in the development of soft, plasticiser-free elastomers [16, 17]. The nse of this high MW, low polydispersity polyol allows for the preparation of low viscosity prepolymers with low isocyanate contents. Initial evalnations of these very soft elastomers showed lower than expected physical properties. The lower properties can be attributed to the very low hard-segment content of these polymers. The lack of hard segment (physical crosslinks) can be compensated for by the incorporation of low levels of chemical crosslinks (triol) [18]. This is accomplished by the addition of a 6000-MW, ultra-low monol triol (Acclaim Polyol 6300) into the polymer matrix. Table 9.7 shows the triol effect on prepolymer viscosities, elastomer processability and physical properties. It shonld be noted that very low levels of crosslinking are needed to improve the elastomer properties. 

Effect of increasing the hard segment content on the compression properties... 

The effect of temperature on the properties of analogous PPDI and CHDI elastomers is shown in Table 5.17 and Fig. 5.11. Influence of the diisocyanate content on hardness is shown in Table 5.18 which reveals a consistently increasing hardness as the hard segment content of the PU increases. 

Figure 14 Effect of hard segment content on mechanical properties.

Several studies have been conducted on biostable polyurethanes to elucidate the effects of hard segment chemistry on polyurethane degradation rate. Tang et al. [104,105] observed the effects of hard segment chemistry and hard segment content... 

---