Polymer Networks for Enrichment of Calcium Ions

Abstract

In this study, solvogels containing (2-((2-(ethoxycarbonyl)prop-2-en-1-yl)oxy)-ethyl) phosphonic acid (ECPA) and N,N′-diethyl-1,3-bis-(acrylamido)propane (BNEAA) as the crosslinker are synthesized by UV induced crosslinking photopolymerization in various solvents. The polymerization of the ECPA monomer is monitored by the conversion of double bonds with in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The morphology of the networks is characterized by in situ photorheology, solid state NMR spectroscopy, and scanning electron microscopy (SEM) of the dried gels. It is demonstrated that the storage modulus is not only determined by the crosslinker content in the gel, but also by the solvent used for preparation. The networks turn out to be porous structures with G′ being governed by a rigid, phase-separated polymer phase rather than by entropic elasticity. The external and internal pKa values of the poly(ECPA-co-BNEAA) gels were determined by titration with a specially designed method and compared to the calculated values. The polymer-immobilized phosphonic acid groups in the hydrogels induce buffering behavior into the system without using a dissolved buffer. The calcium accumulation in the gels is studied by means of a double diffusion cell filled with calcium ion-containing solutions. The successful accumulation of hydroxyapatite within the gels is shown by a combination of SEM, energy-dispersive X-ray spectroscopy (EDX) and wide-angle X-ray scattering (WAXS).

Design, Synthesis and Characterization of Vitrimers with Low Topology Freezing Transition Temperature

“…We detect and thus "count" protons in the sample, which allows for an objective quan- Microphase separation in our vitrimeric systems is further confirmed by the joint analysis of free-induction decay (FID) and MSE-refocused FIDs at different temperatures (Figure 5). We detect and thus "count" protons in the sample, which allows for an objective quantification of phases with different mobility [41,42]. Note that these experiments were done at room temperature and above; thus, we focus on the range above the different melting transitions seen in DSC.…”

“…This sample is thus more homogeneous and closer to the "equilibrated vitrimer" shown in Figure 1 To shed more light into the cross-linked network structure, we have applied MQ NMR. The experiment provides two different data sets, the reference and the double-quantum (DQ) intensity measured as a function of pulse sequence duration (DQ evolution time), subject to further processing [42,44,45] (Figure 6). In the first step, shown in the insets, a "tail" with long T 2 relaxation time is identified.…”

“…Proton low resolution NMR experiments were performed on a Bruker minispec mq20 low-field NMR spectrometers according to the previous published procedures [39][40][41][42]. Phase distinction in static proton NMR is based on the effect of molecular motion (mostly segmental rotations) on the spectral linewidth, or, as done here, without Fourier transform in the time domain on the directly detected free-induction decay (FID).…”

“…We further used a suitable refocusing pulse sequence, termed magic-sandwich echo (MSE), in order to overcome the receiver dead-time problem [43]. Secondly, we applied multiple-quantum (MQ) NMR for characterization of the network structure [42,44,45].…”