Acta Physico-Chimica Sinica

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Cross-Linkable Yet Biodegradable Polymer Films

Shuai Chen1,2, Jianglei Qin3,4, Jianzhong Du1,2   

  1. 1 Department of Orthopedics, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai 200072, China;
    2 Department of Polymeric Materials, School of Materials Science and Engineering, Tongji University, Shanghai 201804, China;
    3 College of Chemistry and Environmental Science, Hebei University, Baoding 071002, Hebei Province, China;
    4 State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China
  • Received:2020-06-11 Revised:2020-07-27 Accepted:2020-07-27 Published:2020-07-31
  • Supported by:
    The project was supported by the Natural Science Foundation of Hebei Province, China (B2018201140), State Key Laboratory of Organic-Inorganic Composites, China (oic-202001005), the National Science Fund for Distinguished Young Scholars, China (21925505), and the National Natural Science Foundation of China (21674081).

Abstract: Polymer films are widely used as biomaterials, electronic devices, food packaging materials and gas separation membranes. In practice, cross-linking is an effective method to enhance their stability and increase the strength of these films. However, conventional cross-linked polymer films cannot degrade under mild conditions. Herein, we fabricated two cross-linkable, yet biodegradable, polymer films of ~0.2 mm via solution casting using cinnamate-grafted polycaprolactones, namely:a poly((α-(cinnamoyloxymethyl)-1,2,3-triazol) caprolactone) (PCTCL133) homopolymer and a poly(caprolactone-stat-CTCL) (P(CL156-stat-CTCL28)) copolymer. The successful syntheses of the polymers were confirmed via proton nuclear magnetic resonance (1H NMR) spectroscopy, size exclusion chromatography (SEC), and Fourier transform infrared (FT-IR) spectroscopy. The PCTCL homopolymer appeared as a transparent film, owing to its side groups that impede its crystallinity; in contrast, the copolymer film appeared translucent, owing to its PCL segments that are easily crystallized. The cinnamate groups facilitated the cross-linking of the polymer films when irradiated by ultraviolet (UV) light; this is indicated by its insoluble character in tetrahydrofuran, which is a good solvent for both polymers. SEC analysis indicated that a fraction of the P(CL156-stat-CTCL28) film remained un-cross-linked after irradiation, owing to its crystalline structure. In contrast, UV irradiation caused the PCTCL homopolymer film to become homogeneously cross-linked, which exhibited a cross-linking density of 49% after 2 h as indicated by the 1H NMR results. Thermogravimetric analysis (TGA) indicated that cross-linking of the PCTCL films caused a minimal change in thermal stability. Both the cross-linked polymer films were able to degrade upon the addition of a modest amount of concentrated hydrochloric acid, as confirmed by SEC and 1H NMR. However, the degradation rate significantly decreased after cross-linking, thereby indicating its tunable character that can be altered by varying the cross-linking density. In addition, the rate of degradation can be adjusted upon varying the fraction of cross-linked PCTCL groups in the copolymer. In principle, treating the polymer films with sufficient amounts of acid could form degradation products with molecular weights less than 300 g·mol-1. To further explore the mechanical properties of such materials, we investigated the correlation between the initial concentration used for solution casting and the Young's modulus of the film by employing molecular dynamics simulations. These results indicate that tougher films are prepared when using more concentrated polymer solutions, owing to a higher degree of chain entanglement. In summary, the prepared films with tunable degradability are promising materials for biomedical applications. In principle, this platform could be utilized in hydrogels and coating materials for a broad scope of applications.

Key words: Polymer film, Polycaprolactone, Photocross-linking, Degradability, Solution casting


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