Magic-angle carbon-13 nuclear magnetic resonance study of the compatibility of solid polymeric blends

Abstract

A theoretical analysis of coupled relaxation processes has been used in the quantitative interpretation of carbon-resolved, proton TI, data obtained at 15.1 MHz for a variety of solid blends of poly(pheny1ene oxide) and polystyrene. This analysis permits an estimate of spin-diffusion rates between different chemical species. These rates are strongly dependent on spatial proximity and hence are applicable to the determination of the homogeneity of the blends. Proton Tl,'s in the blends are nearly but not quite averaged to a single value by spin diffusion, indicating extensive intermixing of poly(pheny1ene oxide) and polystyrene chains. The proton TI, experiments are sensitive enough to distinguish between identically prepared blends made from poly(pheny1ene oxide) and either atactic or isotactic polystyrenes. While the bulk of both types of blends is an intimate mixture of polymer chains, there are also some small regions in the atactic polystyrene blend where the polystyrene is not uniformly dispersed.

Structural characterization of silk-polyurethane composite material for biomaterials using solid-state NMR

“…The estimated domain sizes are satisfactorily small enough for 1 H spin diffusion to affect T 1 H but not sufficient to have an identical T 1 H decay for both components. 22,23 The r value of 24 nm for the SF/PU ¼ 1:1 composite is smaller than those of the 1:10 and 1:2 composite materials. This estimation indicates that SF and PU are partially in close proximity, particularly in the SF/PU ¼ 1:1 composite, indicating there is a portion of the molecules that contact each other through an intermolecular interaction, such as through hydrogen bonding.…”

“…The observed T 1 H curves were successfully fitted using the assumption of the two-spin system with the insufficient 1 H spin NMR analysis of silk-polyurethane composite material Y Nakazawa et al diffusion rate k. 22,26 The two proton magnetizations M A (t) and M B (t), which are indirectly observed from 13 C signals, are expected as follows: 22,23 d dt…”

“…Furthermore, because PU has hard and soft segmental regions, the intrinsic calorimetric transition will be difficult to detect, particularly for PU in blends towing to its diluted concentration. Therefore, we employed 1 H spin-lattice relaxation time (T 1 H ) to detect the domain size, [22][23][24][25] which is effective in detecting the domain size on a level of several 10 nm increments from T 1 H even for the current PU/SF composite case. H values of pure SF and pure PU were 1.059 and 0.467 s, respectively.…”

“…Thus, the observed decay curves are typical in the case of the existence of the effective 1 H spin diffusion. 22,23 The 1 H spin-diffusion affects 1 H spin-lattice relaxation times (T 1 H and T 1r H ) and causes them to be non-exponential depending on both the proton densities in a system and its diffusive path length, which is the domain size of components. Therefore, if SF and PU in these composite materials are in completely separate states, the observed T 1 decays of SF and PU in SF/PU composites were the same as those of pure ones.…”

“…The maximum diffusive path length (r) is calculated using the spin-diffusion rate k. [22][23][24][25] The maximum diffusive path length for three dimensions is obtained by the typical solution of the diffusion equation as r ¼ ffiffiffiffiffiffiffiffiffiffi 6D/k p . We employed the average value (700 nm 2 s À1 ) of the typical diffusion coefficient D range of 500-1000 nm 2 s À1 to estimate the domain size.…”