Synthesis of L-Valine-based polyester materials

L-valine-based polyester materials are a class of biomaterials with promising application prospects. The following is an introduction to their synthesis methods and research on biodegradable properties:

I. Synthesis Methods

Interfacial polymerization: L-valine can be used to prepare polyesteramides with isosorbide, dicarboxylic acid acyl chloride, etc., through a two-step interfacial polymerization process. Relevant monomers are first dissolved in two immiscible solvents, and the polymerization reaction occurs at the interface to form L-valine-based polyester materials. The resulting polymers generally have good thermal stability, with a glass transition temperature (Tg) ranging from 115.9°C to 182.6°C.

Metal catalyst-catalyzed polymerization: A valine-acetylene adduct, such as 4-ethynylbenzoyl-L-valine methyl ester, can be prepared first. Then, with (Rh(nbd)Cl)₂ as the catalyst, the adduct undergoes polymerization to form the corresponding polyester. This polyester can be further hydrolyzed to obtain its "polybasic acid" analog, poly(4-ethynylbenzoyl-L-valine).

Polycondensation reaction: Similar to the synthesis of polylactic acid-amino acid copolymers, L-valine and monomers such as lactide can be placed in a reaction tube, purged with inert gas, and stirred under vacuum in an oil bath for polycondensation to prepare L-valine-based polyester materials. After the reaction, pure polymers can be obtained through operations such as reprecipitation.

II. Research on Biodegradable Properties

Degradation mechanism: The degradation of L-valine-based polyester materials mainly occurs through hydrolysis and enzymatic hydrolysis. The ester bonds in the materials are susceptible to attack by water, undergoing hydrolysis reactions that break polymer chains and reduce molecular weight. Meanwhile, esterases in the body can specifically recognize and act on ester bonds, accelerating the degradation process.

Factors affecting degradation: The structure of the polymer significantly influences its degradation performance. For example, L-valine-based polyesters containing hydrophobic side groups or rigid dicarboxylic acid groups hinder the penetration of degradation media into the polymer interior, resulting in a slower degradation rate. Adjusting the hydrophilicity of main chain or side chain groups can alter the degradation rate. In addition, the type and concentration of enzymes also affect the degradation rate; for instance, L-valine-based polyesterurea materials degrade faster under proteases than under lipases.

Degradation products and safety: The degradation of L-valine-based polyester materials typically produces amino acids such as L-valine, as well as small molecules like corresponding alcohols and acids. These products generally cause no environmental pollution, are non-toxic to cells, and induce low cellular inflammatory responses, thus exhibiting good safety in biomedical applications.

Evaluation of degradation performance: The degradation degree can be evaluated by determining changes in the number-average molecular weight, weight-average molecular weight, and polydispersity index of the material during degradation using size exclusion chromatography (SEC). Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) can also be used to study changes in the thermal properties of the material before and after degradation, thereby indirectly understanding its degradation status.