Investigation of the degradation mechanism of cross-linked polyethyleneimine by NMR spectroscopy

• Published in: Polymer degradation and stability Vol. 93; no. 2; pp. 476 - 482
• Main Authors: Peng, Min, Liu, Wei, Yang, Guang, Chen, Qun, Luo, Shufang, Zhao, Gang, Yu, Lei
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.02.2008; Elsevier Science
• Subjects: 1H NMR; Applied sciences; Chemical reactions and properties; Cross-linked polyethyleneimine; Degradation; Exact sciences and technology; Gene carrier; Monte Carlo simulation; Organic polymers; Physicochemistry of polymers; Degradation; 1H NMR; Cross-linked polyethyleneimine; Gene carrier; Monte Carlo simulation; Monte Carlo method; Computer simulation; Chemical stability; NMR spectrometry; Chemical degradation; Experimental study; Hydrolysis; Polyelectrolyte; Investigation method; Crosslinked polymer; Reaction mechanism; Proton; pH; Olefinimine polymer; Kinetics; Polyethylene imine
• ISSN: 0141-3910; 1873-2321
• DOI: 10.1016/j.polymdegradstab.2007.11.007

The degradation pathway of a cross-linked polyethyleneimine (c-PEI) suitable as a gene carrier was studied at different pH values by real-time 1H NMR and diffusion-weighted 1H NMR spectroscopy. The c-PEI was synthesized by cross-linking PEI segments with 2,4-pentanediol diacrylate (PDDA). The experimental results show that under basic, neutral and acidic conditions, the degradation of c-PEI occurs through hydrolysis of the ester moieties of the PDDA linkers. The degradation half-life of the polymer is 22, 48 and more than 720 h at pH 10.2, 7.4 and 4.6, respectively, showing that the degradation of c-PEI is highly pH sensitive. By using a modified version of diffusion-weighted 1H NMR experiment, the variation of the apparent molecular weight of c-PEI in the degradation process was monitored. Furthermore, a Monte Carlo simulation was applied to simulate the relation between the average molecular weight and the number of chain ends during the degradation process of a model system of c-PEI. By comparing the NMR results with those obtained from simulation, the mechanism of degradation under various pH conditions is discussed. The present work demonstrates that the combination of real-time 1H NMR, diffusion-weighted 1H NMR spectroscopy and Monte Carlo simulation is a useful strategy for characterizing the degradation process of degradable polymers.