Structural characteristics of biodegradable water-based polyurethanes

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Biodegradation primarily depends on the size and structure of the polymer molecules, the types of microorganisms, and environmental factors, among which the molecular structure and composition of the material are the decisive influencing factors. Under normal circumstances, aliphatic ester bonds > peptide bonds > carbamates > aliphatic ether bonds > methylene groups. Furthermore, polymer materials with high molecular weight, regular molecular arrangement, and high hydrophobicity are less susceptible to microbial erosion and growth, as well as being less prone to biodegradation. Polyurethanes are polymers whose backbone contains repeated urethane segments. The main chain of polyurethanes is typically composed of block segments consisting of soft segments with a glass transition temperature below room temperature, and rigid segments with a glass transition temperature above room temperature. The soft segments are made up of oligomeric polyols such as polyesters and polyethers, while the rigid segments are formed from diisocyanates and low-molecular-weight chain extenders such as diamines and diols. Due to the strong polarity of the hard segments and the large attractive forces between them, the hard segments and soft segments have a thermodynamic tendency to separate spontaneously. Therefore, the rigid segments tend to aggregate together, forming numerous microdomains that are distributed within the soft segment phase, resulting in a microphase-separated structure. The microphase surface structure of polyurethane is very similar to that of biofilms, granting it good biocompatibility. The chain structure of polyurethane determines its degree of biodegradability. During the synthesis of polyurethanes, it is possible to design them by selecting different blocks and adjusting the ratio between the soft and hard segments, thereby producing polyurethanes with various chemical structures (such as linear, branched, or cross-linked), mechanical properties (rigid or flexible), and thermal properties to meet different application requirements.