# Synthesis of Shape-Memory Polyurethanes: Combined Experimental and Simulation Studies
## 1 Introduction  
With a worldwide production of nearly 25 Mt in 2021, polyurethanes (PURs) are the sixth most widely used polymers in the world and the global market for these polymers is going to grow in the next five years by 6.8% [1]. The high demand and popularity of PURs originate from their excellent physical and mechanical properties such as toughness, durability, elasticity, and abrasive resistance. They are used for the production of elastic and rigid foams, seals, high-performance coatings, and adhesives [2; 3; 4]. Due to excellent biocompatibility and biostability, PURs have also found application as biomedical materials [5; 6; 7; 8]. Conventional PURs are obtained from diisocyanates or polyisocyanates, polyols, and chain extenders. The desired properties of PURs are achievable by appropriate selectionof the reacting components, which makes them highly versatile materials. Applications of polyester diols as soft segments of PURs enable preparation of polymers of relatively good physical properties. However, they are susceptible to hydrolytic degradation of the ester linkages [9]. On the other hand, PURs based on polyether diols exhibit better hydrolytic resistance and are therefore favored in the applications where hydrolytic stability is expected. Unfortunately, the poly(ether-urethane)s are susceptible to oxidation processes. Both of mentioned disadvantages can be overcome by replacing polyester or polyether segments by hydrolytically and oxidatively stable polycarbonate ones [10; 11]. Synthesis of poly(carbonate-urethane)s (PCURs) requires appropriate soft segment precursors, oligocarbonate diols (OCDs). Aliphatic OCDs can be obtained by catalytic co-polymerization of oxiranes with carbon dioxide [12], ring-opening polymerization of six- and seven-membered cyclic carbonates [13], or in polycondensation processes using simple organic carbonates such as a linear dimethyl carbonate (DMC) or cyclic ethylene or propylene carbonates (EC or PC) and \(\alpha\),\(\omega\)-diols or \(\alpha\),\(\omega\)-diols mixtures. In the latter case, the use of DMC requires a two-step procedure leading to hydroxyl terminated oligomerols, while the use of EC or PC is a one-step reaction. Both methods allow OCDs of molar mass to be obtained in the range of 500 g \(\times\) mol\({}^{-1}\) to several thousand g \(\times\) mol\({}^{-1}\), depending on the type of \(\alpha\),\(\omega\)-diol used [14; 15]. The advantage of the OCD synthesis involving DMC is the lower reaction temperature, that is, the boiling point of DMC/methanol azeotrope, and the possibility of carrying out the reaction without the addition of organic solvents. Due to the direct or indirect use of carbon dioxide in their synthesis, OCDs are also considered to be environmentally friendly \"green starting materials\". Furthermore, PCURs, owing to their superior mechanical and biological properties, as well as being environmentally friendly starting materials, are favored as biopolymers for long-lasting implantation such as in the spine, as meniscus implants or as artificial heart elements [16; 17; 18]. What is more, the above-mentioned features of PCURs have also attracted attention in the field of shape-memory polymers (SMPs). Recently, we proposed the method of preparation of SMPs that involved the utilization of OCDs containing long hydrocarbon chains between the carbonate linkages. Obtained poly(carbonate-urea-urethane) networks (PCUUs) exhibited a high-strain shape-memory effect with excellent shape recovery and temporary shape fixation ratios [19; 20], as well as a superb reversible bidirectional shape-memory effect [21]. Segmented thermoplastic PURs have been investigated for many years [22; 23; 24; 25; 26]. In 1981, [PERSON] et al. detected early phase separation in PURs using light transmission and viscosity measurements [27]. [PERSON] et al. concluded that the improvement in microphase separation was related to the presence of urea hard segments, particularly when using symmetrical diisocyanates [28].