Structural characteristics of polyurethane

<font face=" The chemical structure of polyurethane is characterized by repeated urethane segments in its macromolecular backbone.

The main chain of the polyurethane macromolecule is composed of flexible segments with a glass transition temperature lower than room temperature（also known as soft link Paragraph or soft paragraph)and rigid segments with glass transition temperatures higher than room temperature（Also known as hard chain segment or hard segment ) made of blocks. Oligomer polyol(such as polyether, polyester, etc.）Constitute soft segment, isocyanate and small molecule chain extender(such as diols and diamines ）Constitute a hard link segment. In the molecular structure of polyurethane elastomer, soft segments account for a relatively large proportion, ranging from 50% to 90%, and hard segments account for 10% to 50%. Due to the strong polarity of the hard segments and the strong mutual attraction, the hard segments and the soft segments have a tendency to spontaneously separate thermodynamically, that is, they are incompatible. Therefore, hard chain segments tend to gather together to form many micro-domains(do-main, distributed in the soft segment phase. This phenomenon is called microphase separation. Microphase separation is a characteristic of the physical structure of polyurethane elastomers . The physical properties of polyurethane elastomer are not only related to the chemical structure, but also to the degree of micro-phase separation. This must be considered when analyzing the relationship between the physical properties and structure of polyurethane elastomer, and should be paid attention to in production practice.