Electron microscopy investigations of polyester‐polyurethane elastomers stained with ruthenium tetroxide

Microphase separation of as‐reacted polyester‐polyurethane samples based on α‐hydro‐ω‐hydroxypoly(oxyethyleneoxyadipoyl)/4,4′‐methylenedi(phenyl isocyanate)/1,4‐butanediol/2‐ethyl‐2‐hydroxymethyl‐1,3‐propanediol (mole ratio 1:3,2:1,9:0,1) was studied using transmission electron microscopy. A new staining technique was applied which uses ruthenium tetroxide vapour for the treatment of the polymer. Ruthenium tetroxide reacts preferably with the hard‐segment‐rich microdomains of the polyester‐polyurethane. Therefore, a well‐contrasted pattern is formed by staining which reflects the microdomain structure of the polymer. The hard‐segment‐rich microdomains have irregular, mostly globular shape, and their sizes range from about 2 to 8 nm.