Hard segments sequence lengths

Number Average and Weight Average Hard Segment Sequence Lengths at Separation As a Function of Soft Segment Content. 

Although short-segment sequences are expected to be the most compatible, the 1/2/1 random copolymer with an average hard-block-sequence length of only two units does exhibit a phase-separated morphology—as reflected for the as-reacted sample in hard-segment crystal-... 

Figure 8. Effect of soft segment content on point of phase separation during polyurethane polymerization as indicated by discontinuity in DSC reaction profile. Dotted line shows theoretical prediction assuming separation at constant number-average sequence length (1.3) of hard segments ("see text).

This NMR analysis is particularly useful as the block TMPS-DMS copolymers exhibit a wide range of properties depending upon the composition and average sequence lengths of the soft dimethylsiloxane segments and the hard crystalline silphenylene blocks. 

Previous publications [136, 137] reviewed models proposed for HS achieved with the diisocyanate MDI and extended with BDO. A detailed morphological analysis [137] of a series of such materials showed that the hard microdomain structure was in qualitative agreement with the model proposed by Koberstein and Stein [136], This model was based on the partial solubilization of short HS into the soft microphase. HS shorter than the critical length for microphase separation were presumed to remain within the soft microphase while longer segments aggregated into lamellar hard microdomains of thickness proportional to the critical sequence... 

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