## 1 Introduction  
Biomedical polyurethane devices, because of their excellent mechanical flexibility, chemical resistance, and good biocompatibility [1; 2; 3; 4], have been deeply investigated and widely used in the medical fields of both engineering and countless biomedical consumer products such as artificial hearts, catheters, injectable gels, pacemaker leads, and biodegradable scaffolds [5; 6; 7; 8; 9]. Most polyurethanes are multiblock co-polymers commonly consisting of hard and soft segments. For these types of materials, the various thermal and mechanical properties are determined by these alternating segments, repeating units of urethane linkages made by the reaction of an isocyanate with hydroxyl in polyurethanes, and especially the strong intermolecular forces of the hard domains [10; 11]. In order to cater to specific property requirements, a large number of different polyurethanes were synthesized from the reaction between diisocyanate, microdiols, and the chain extender [12; 13; 14]. The elastic deformability of elastomers is of great importance for all kinds of polyurethane. Their available properties are directly related to the two phase microphase separation morphology caused by their unique structure of alternating hard and soft segments [15]. Investigators have devoted themselves to this field for at least fifty years, and have made great strides in understanding their excellent properties, attributed to their synthetic methods and chemical structures [16; 17].  
The mechanical properties are influenced by the type of diisocyanate, microdiols, the chain extender, and especially the urethane linkages of the hard segments [18; 19; 20; 21]. The material will be broken when the local strength is more than the limited strength giving rise to the rupture of the local molecular chains. For the hard segment, the polyfunctional isocyanate can be divided into aliphatic, aromatic, polycyclic, or cycloaliphatic. 1,6-hexamethylene diisocyanate (HDI) is a kind of aliphatic diisocyanate, replacing aromatic ones which may release toxic components like 4,4\({}^{\prime}\)-methylenediphenyl diisocyanate (MDI) and toluene diisocyanates (TDI) after degradation [22; 23; 24]. For many medical devices, where excellent histocompatibility and blood compatibility of the materials are seriously required, the widely used poly(1,6-hexanediol)carbonate microdiol (PCDL) based polyurethane exhibit excellent biostable elastic properties after exposure to oxidative, hydrolytic, and other biological solutions [25; 26; 27]. However, little attention has been paid to the comprehensive investigation of the relationship between the content of the hard segment and mechanical properties, particularly the phase-separated microstructure, crystallization behavior, surface performance, and biocompatibility.  
In this work, biomedical polyurethane materials with various contents of the hard segment were synthesized through the melting pre-polymer method using PCDL (\(Mw\) = 2000 Da) as soft segments, and using 1,6-hexamethylene diisocyanate (HDI) and 1,4-butanediol (BDO) as the hard segments. In the present study, the physical and chemical properties of the polyurethanes were studied by FTIR, differential scanning calorimeter (DSC), gel permeation chromatography (GPC), and mechanical tests, and the maximum tensile elongation was about 500%. We have concluded that with the increment of different contents of the hard segment (less than 35%), the degree of microphase separation increased while the mechanical behavior of the prepared poly(carbonate-urethane) elastomers slightly decreased. Finally, hemolytic tests and the MTT assay were carried out using adult rabbit blood and L929 fibroblast cells to assess hemocompatibility and cellular viability in vitro, indicating a good biocompatibility of the fabricated membranes.