Structure and dynamics of poly(carbosilane) dendrimers as revealed by pulsed field gradient NMR technique

Abstract

The self-diffusion of poly(carbosilane) dendrimer macromolecules solutions in the highconcentration region starting from the polymer block was investigated by pulsed fietd gradient nuclear magnetic resonance techniques. A restrietion of diffusion was observed for the concentration region of 50-95 wt% of dendrimer in tetrachloride CC14 solutions. This phenomenon has been explained by the formation of solutions at a thermodynamical nonequilibrium. A theoretical approach on the basis of thermodynamics and statistical mechanics was developed. lntroductionThe unique physical-chemical properties of dendrimers stimulate wide theoretical and experimental investigations of these polymers. There are a lot of papers devoted to the dendrimer spatial structure and dynamics of the molecular motion.Pulsed field gradient nuclear magnetic resonance (PFG NMR) became the method of choice, among other physical techniques, to characterize the dendrimer structural and translational mobility [1][2][3][4][5][6][7][8][9]. This technique gives the opportunity to measure directly molecular self-diffusion coefficients in dendrimer solutions starting from the polymer in block (the dendrimer itself).The main part of investigations were carried out for a relatively Iow dendrimer concentration (less than 60 wt%). The dendrimer self-diffusion may be characterized by a single self-diffusion coefficient dependent on the concentration [3][4][5][6][7][8][9]. In this case, the dendrimer solutions are homogeneous systems without any macromo[ecular associations and the self-diffusion coefficient is determined by the translational motion of separate macromolecules.

Cellulose-Based Absorbent Production from Bacterial Cellulose and Acrylic Acid: Synthesis and Performance

“…The network structure of the superabsorbent composite is important to its water absorbency, and a large number of studies paid attention to the detection of the network structure of superabsorbent composites [35,43]. Solid state NMR spectroscopy has been widely used to investigate the composition of the composite network structure, and this technology can detect the substance’s structure accurately [44,45]. The results of NMR showed that there exist signals in the range of 110 to 60 ppm both in the original sample and the composite, and these signals included four characteristic peaks belonging to the six carbon atoms of cellulose, indicated at 105.28 (C1′), 83.56 89.24 (C4′), 72.22 76.13 (C2′, 3′, 5′), and 65.57 (C6′) ppm (original samples) 105.28 (C1′), 84.54 89.24 (C4′), 71.83 74.56 (C2′, 3′, 5′), and 65.37 (C6′) ppm (polymerization products), respectively [46,47,48,49], and this confirmed that the essence of this composite was cellulose.…”

PFG-NMR Studies of Linear and Dendritic Polymers

“…[12] In this report we employ PFG-NMR to measure the diffusion coefficients of commercially available PAMAM dendritic polymers and narrow molecular weight distribution polystyrenes, and combine the results with our previous data to analyze the molecular weight dependence of the hydrodynamic radius for low molecular weight linear and dendritic polymers. While there have been numerous papers published on the PFG-NMR of linear polymers and dendritic polymers, [13,14,15,16] there have been few reports that have directly compared results on both molecular architectures.…”