DBDI based PUs blends

Two PUs systems were obtained with MDI or DBDI, with the following structures  

When MDI was used in the polymer synthesis, irrespective of the synthesis route it obtained homogeneous soluble polymers inseparable in fractions, by selective dissolution in DMF. Certainly, the sequence of ordering on the macromolecular chain differs from a PU synthesis route to another. As mentioned, the reaction rate between phenyl isocyanate (FI) and chain extender, ethylene glycol (EG) was found by us to be 4 times higher than the reaction between FI and PEA when measured separately, and 11.6 higher respectively if they are in a mixture (EG + PEA) (synergetic effect) [45,89]. 

In parallel, the kinetic-statistically determined incipient reaction of DBDI with the MD, although rare, leaded to soluble oligomers with a good solubility, with sufficiently long SS so to maintain the so-obtained polymer in solution till the end of the process. 

The crystallinity of the copolymer resulted in suspension (separated by centrifugation), was evidenced with the aid of X-ray measurements. The X-ray diagram of the so-obtained insoluble copolymer was similar to the pure homopolymer -ED-DBDI [59], The similitude was as closer as the n number in the schemes from above was higher. 

Replacing the DMF solvent with l-Methyl-2-pyrrolidinone (NMP), the situation returned to the normal behaviour similar to the MDI based PUs reaction in solution. In this case the interaction between oligomer-solvent was always higher than the interaction between oligomer-oligomer (polymer-polymer), and it obtained only a single type of soluble copolymer [257]. 

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