Effects of controlling the molecular weight of poly(vinyl alcohol) via cobalt mediated radical polymerization on printability and degradation behavior of poly(vinyl alcohol) scaffolds

Cobalt-mediated radical polymerization (CMRP) is the best technique to obtain polyvinyl acetate (PVAc) and PVAc derivatives such as poly(vinyl alcohol) (PVA). Therefore, controlled synthesis of PVA via CMRP of vinyl acetate (VAc) can be a helpful technique to address the limitations related to the poor printability and rapid degradation rate of pure PVA for biomedical applications. In this research, PVAc was synthesized under controlled conditions using CMRP of VAc. The polymerization was performed with different initiator ratios at different temperatures using cobalt(II) acetylacetonate (Co(acac)₂) as the controlling agent and benzoyl peroxide (BPO) as the initiator. Also, N,N-dimethylformamide (DMF) was used as the ligand. The increase in the initiator ratio and temperature led to an accelerated polymerization process. For instance, the polymerization finished after 110 and 80 min for 0.75 and 1 initiator ratio, respectively. It is important to highlight that each experiment was repeated at three distinct time intervals after obtaining maximum viscosity of the polymerization system. The conversion rate of monomer to polymer and ln[M]₀/[M] ratio increased over time, demonstrating the controllability of the polymerization. The Co(acac)₂ complex successfully acted as the controlling agent in the polymerization process. Homopolymerization of VAc was then optimized, and optimum PVAc samples were successfully hydrolyzed to PVA homopolymers, which was confirmed by proton nuclear magnetic resonance (¹H NMR) analysis. PVA homopolymers were synthesized with controlled molecular weight (M_n), which was illustrated by gel permeation chromatography (GPC) test. Furthermore, the polymers showed suitable printability using fused deposition modeling (FDM) technique. According to the scanning electron microscopy (SEM) analysis, pore size in PVA scaffolds increased with an increase in M_n. The swelling ratio after 24 h decreased from 97.413% to 84.215% by increasing the M_n from 8840 to 12,266. Also, the degradation ratio after 28 days decreased from 85.113% to 74.118% for the same M_n. This phenomenon was attributed to the higher chain entanglements in higher M_n. Therefore, the swelling capacity and the degradation of the PVA scaffolds were successfully controlled by controlling the M_n. Hence, using CMRP method, pure PVA scaffolds can be obtained and widely used in biomedical applications such as tissue engineering and drug delivery as they are controllably degradable and biocompatible.

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