 Both types of segments are linked together by covalent links so that they actually form block-copolymers.The polarity of the hard pieces creates a strong attraction between them, which causes a high degree of aggregation and order in this phase, forming crystalline or pseudo crystalline areas located in a soft and flexible matrix.This so-called phase separation between both blocks can be more or less important, depending on the polarity and the molecular weight of the flexible chain, the production conditions, etc.