An NMR Study on Solvent-Polymer Interactions

Abstract

<p> Approximately 80 percent of all synthetic polymers used are cross-linked polymers, unfortunately the characterization of cross-linked polymers has not kept up with their use. This study tries to help in the characterization of cross-linked polymer systems. More specifically the interactions of cross-linked polymer systems with solvents will be probed. Nuclear Magnetic Resonance (NMR) spectrometric techniques will be used to characterize solvent-polymer interactions.</p> <p> The cross-linked polymer system studied was the polymer ethylene glycol dimethacrylate (EGDMA) with methylmethacrylate (MMA). A splitting of the solvent signals was observed in the NMR spectrum which can be used to understand these solvent-polymer interactions. Several NMR parameters and swelling of the polymers were measured in order to understand these interactions. The chemical shift differences between the solvent types and the peak linewidths were measured. As the polymer becomes more highly cross-linked the chemical shift differences and the linewidths increases. This compactness can be monitored by measuring the degree of swelling of the polymer. In addition the possibility of an isotope effect was explored by monitored by placing the polymer in solvent mixture of CHCl3/JCDCl3 and varying the temperature. No isotope dependence was found to exist for chloroform over the temperature range analyzed. The degree of splitting and the occurrence of splitting was found to be dependent on the solvent system. In general, solvent splitting is present for solvents that are able to cause the polymer to swell appreciably. For 4.8 weight percent EGDMA in EGDMA/MMA polymer a splitting is usually observed for a solvent that is able to swell the polymer to twice its dry size. The association between the solvents and the polymers can be best explained by breaking the interactions into a number of components.</p> <p> The explanation is based on the presence of three interactions. A weak chemical interaction exists between the solvent and the polymer to account for the field dependent linewidths. A second chemical interaction that results is a binding between the solvent and the polymer and causes the solvent splitting to occur. The third interaction is a result of the increased rigidity and compactness of the polymer as the weight percent EGDMA in EGDMA/MMA polymer increases. Alternatively as the polymer becomes more compact the chemical shift difference between the two types of solvents increases.</p> <p> Ultimately, it is shown that NMR is a useful aid in understanding solvent-polymer interactions.</p>