Comparison of Polymer Networks Synthesized by Conventional Free Radical and RAFT Copolymerization Processes in Supercritical Carbon Dioxide

Abstract

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 (scCO 2 ), 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 (Mc exp ) to theoretical (Mc theo ) molecular weight between crosslinks was established as a quantitative tool to assess the degree of heterogeneity of a polymer network.

Synthesis of metal organic framework (MOF-5) embedded cryogel composite and its application for the extraction and determination of cholesterol from milk samples

“…Characteristics peaks of MOF-5 were observed as; CH stretching vibration at 3150 cm -1 , asymmetric stretch of O2C-C6H4 at 1550 cm -1 , CC ring stretch at 1370 cm -1 , asymmetric OCO bending at 800 cm -1 and out-of-plane COO -CH bending at 748 cm -1 as reported by reference [20]. MOF-5/Cryogel composite vibration frequencies showed close match with a report on poly (HEMA) co-EGDMA by Perez-Salinas et al [21]. Wavenumber of 3420 cm -1 for OH from HEMA, 2990 cm -1 for CH from EGDMA and HEMA, 1717 cm -1 for C=O from EGDMA and HEMA structures, 1450 cm -1 from CH from EGDMA and HEMA, 1320 to 1300 cm -1 of C-O-ester from HEMA and EGDMA, 1170 cm -1 for C-O-carboxylic derivate confirms the presence of poly (HEMA) co-EGDMA on surface of composite.…”

Poly(vinyl alcohol) Membranes Cross‐linked with Maleic Anhydride and 2,5‐Furandicarboxylic Acid: Conventional Heating and Microwave Irradiation

“…Average molecular weight between cross‐links ( M c ), was calculated for PVA/MA CH 30% and PVA/MA MW 30% films. Table , resumes the results of the influence of cross‐linking reaction time.…”

Comparison of Thermoresponsive Hydrogels Synthesized by Conventional Free Radical and RAFT Polymerization

“…To be noted, the SR of G1R could be not evaluated because of the lack of gel consistency; we believe that this constitutes indirect evidence that non-defined chemical entanglement from side reactions (i.e., chain-chain crosslinking) contribute to the formation of gels by FRP; this explains the inability of RAFT to form gels at lower crosslinker feeds, simply because the reaction mechanism is more well-defined with a minimization of side-reactions [34] leading to better defined crosslinks overall and this is also corroborated by the difference between the SR of FRP and RAFT gels. RAFT polymerization allows for the incorporation of chemical crosslinks in a highly controlled manner, hence forming a well-defined hydrogel network [21,22,23,24,25,26]. Finally, after 24 h, the temperature was increased to 37 °C, and the SR of each gel instantly dropped to 1 due to the loss of PNIPAAm solubility in water above 32 °C.…”

“…This leads to a better understanding of structure-to-function properties and it also helps us to design intricate polymer structures of complex molecular topology. More particularly, RAFT polymerization [18,19,20] has been used to copolymerize (di-)vinyl monomers to form more homogeneous and structurally well-defined three-dimensional (3D) networks that are difficult, if not impossible, to obtain via the conventional FRP route [19,21]; these networks find numerous applications as swelling matrices, cell/drug encapsulants, separation technologies, self-healing materials, and responsive sensors and actuators. Recently, several groups reported on the macroscopic differences between RAFT and FRP-made polymer networks [21,22,23,24,25,26]; it is generally accepted that FRP networks tend to produce less well-defined polymer meshes with collapsed micro-domains, which in turn compromise the (de-)swelling or responsive properties of the bulk materials macroscopically.…”