Abstract
There is a debate in the literature on whether or not polymer networks synthesized by reversible deactivation radical polymerization (RDRP) processes, such as reversible addition-fragmentation radical transfer (RAFT) copolymerization of vinyl/divinyl monomers, are less heterogeneous than those synthesized by conventional free radical copolymerization (FRP). In this contribution, the syntheses by FRP and RAFT of hydrogels based on 2-hydroxyethylene methacrylate (HEMA) and ethylene glycol dimethacrylate (EGDMA) in supercritical carbon dioxide (scCO2), using Krytox 157 FSL as the dispersing agent, and the properties of the materials produced, are compared. The materials were characterized by differential scanning calorimetry (DSC), swelling index (SI), infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Studies on ciprofloxacin loading and release rate from hydrogels were also carried out. The combined results show that the hydrogels synthesized by FRP and RAFT are significantly different, with apparently less heterogeneity present in the materials synthesized by RAFT copolymerization. A ratio of experimental (Mcexp) to theoretical (Mctheo) molecular weight between crosslinks was established as a quantitative tool to assess the degree of heterogeneity of a polymer network.
Highlights
One of the most challenging areas of polymer science and engineering is the synthesis, characterization and development of applications of polymer networks [1]
It is important to identify the region of a phase diagram where one is working
It is important to take into account the solubility in scCO2 of the components present in the reacting mixture, since it can drastically change during the startup of the reaction and even during the reaction itself, depending on temperature and, most importantly, pressure
Summary
One of the most challenging areas of polymer science and engineering is the synthesis, characterization and development of applications of polymer networks [1] (pp. 145–319). The reason for this is the difficulty in dissolving, processing or manipulating the polymer network after its synthesis. Many authors reported their way to analyze and handle these materials in their respective fields, trying to understand their behavior [1,2,3,4,5]. Polymer science is currently diversified into different fields. Other authors, including ourselves, have combined the use of RDRP with the utilization of supercritical fluids, mainly carbon dioxide, as a unique solvent in polymer synthesis [5,10,11,12,13,14]
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