Probing miscibility and intermolecular interactions in solid polymer blends using the nuclear Overhauser effect

Abstract

We discuss a new strategy for probing polymer-polymer miscibility and detecting specific intermolecular interactions in polymer blends by exploiting nuclear Overhauser effects (NOE) in 13C magicangle spinning (MAS) NMR spectra of solid blends. In the comparison of deuterated polystyrene (PS)/ poly(viny1 methyl ether) (PVME) blends cast from toluene versus chloroform, steady-state equilibrium NOE enhancements of the PS signals were observed for the toluene-cast films but not for the chloroform-cast films. Since cross-relaxation of the PS carbons may occur only through dipolar interactions with PVME protons (which have an inverse sixth power dependence on the internuclear distances), this demonstrates molecular level miscibility for the blends cast from toluene only. Below Tg, methyl group rotation about the C3 axis is the only motion fast enough to stimulate dipolar cross-relaxation in the blend. Additional information concerning the molecular structure of the blend was obtained from the NOE growth rates for each type of carbon nucleus in the blend. The cross-relaxation rate constants for the PS aromatic ring carbons were several times greater than that of the PS main-chain carbons. This implies that the phenyl ring is much closer to the methyl group of PVME than to the main-chain carbons of PS. These results suggest that there exists a specific intermolecular interaction between the PS phenyl ring and the PVME methyl group in the solid state. Such an interaction has previously been suggested for polymer blend solutions. IntroductionPolymer blends, mixtures, and composites are commercially important materials, and the increased interest in these materials is reflected by the variety of methods that have been developed to study polymer-polymer interfaces, to probe polymer miscibility, and to detect specific intermolecular interactions. Magnetic resonance methods have played an important role in evaluating the length scale of polymer mixing and for characterizing the intramolecular interactions. The 'H spin diffusion measured via the T1 and T1, relaxation times are frequently used to establish the length scale over which the blend is homogeneously m i~e d .~J A single averaged value for the lH 2' 1, is observed if the two constituents in a polymer

WIM/WISE NMR Studies of Chain Dynamics in Solid Polymers and Blends

“…This could be interpreted either as evidence for microphase separation or evidence that the component polymers have different dynamics in the miscible blend. Following these initial studies, several NMR experiments, including intermolecular cross polarization (19), NOE methods (20), and 2D multipulse exchange NMR (21), have shown that there are close contacts between the two chains. Other studies have shown that the blend contains heterogeneities on a length scale estimated to be 0.6 -3.5 nm (4,22).…”

Material Design and Manufacture of a New Thermoplastic Polyester Elastomer

“…Nemoto et al 2 calculated the diffusion coefficient and reported interaction between PS and PVME based on NMR analysis, 3,4 suggesting that the phenyl ring is much closer to the methyl group of PVME than to the main chain carbons of PS.…”

Investigation of Chain Dynamics in Poly(n‐alkyl methacrylate)s by Solid‐State NMR: Comparison with Poly(n‐alkyl acrylate)s

“…[5][6][7][8] We recently developed a new solid-state NMR method to quantify chain dynamics in polymers with weak dynamic contrast: the NOE experiment with dipolar filter. [9] The principle of nuclear Overhauser effect (NOE) had been previously used differently in other solid-state NMR experiments to study miscibility in polymer blends [10][11][12] and chain dynamics in polymer melts, [13][14][15] or to differentiate chain length of branches in polyethylene. [16] The comparatively simple NOE experiment with dipolar filter is a combination of a conventional exchange experiment [4] with a dipolar filter, which selects according 28,160).…”