Intramolecular Screening Effects in Polymer Mixtures. 1. Hydrogen-Bonded Polymer Blends

Abstract

Spectroscopic evidence is presented to indicate that local screening effects are important in polymer mixtures. Essentially, a polymer segment has a locally higher concentration of like segments because of this factor. A simple modification to existing theories is presented to account for this local screening.

Strong Screening Effect of Polyhedral Oligomeric Silsesquioxanes (POSS) Nanoparticles on Hydrogen Bonded Polymer Blends

“…The value of γ of 0.65 for the phenolic/PMMA-POSS blend was lower than that for the dendrimer-like polyester blend (γ = 0.8) [19], but higher than that for the linear chain blend system (γ = 0.3) [23], suggesting that the chain structure of PMMA-POSS is somewhere between those of dendrimer-like and linear chain structures [25]. When POSS moieties are located only at the chain ends of PMMA polymers, the amount of POSS in a sample would be extremely low and the screening effect should be minimal.…”

“…We rationalize this phenomenon in terms of the so-called "screening effect." The value of the intramolecular screening parameter (γ) for a linear chain structure blend (e.g., PVPh/PMMA) is approximately 0.3, whereas that of a dendrimer-like polyester blend (e.g., PVPh/dendrimer-like polyester) is approximately 0.8 [19,23]. From a previous study [25], we reported that a value of γ of 0.65 for a phenolic/PMMA-POSS block copolymer blend in which the POSS nanoparticles were positioned at the chain end of the PMMA polymer.…”

“…Serman et al [11] used DSC to study the phase behavior of PVPh blended with PMMA, finding them to be miscible; they determined the inter-association equilibrium constant (K A ) for the interactions of the OH groups of PVPh with the C=O groups of PMMA to be 37.4. Painter and Coleman proposed [19][20][21] that "intramolecular screening and functional group accessibility" can have significant effects on the number of hydrogen-bonded functional groups. They used FTIR spectroscopy to measure the fraction of hydrogen-bonded C=O groups present in miscible blends of PVPh/PMMA as functions of the composition and temperature and compared their results with those of analogous PVPh-co-PMMA copolymers and polymer solutions of PVPh and ethyl isobutyrate (EIB) [22].…”

“…Painter and Coleman found that there were significant differences in the equilibrium fractions of intermolecular hydrogen-bonded C=O groups that formed under otherwise identical concentrations and temperatures [22]. They introduced an intramolecular screening parameter (γ), defined as the fraction of same-chain contacts originating from polymer chain self-bending, primarily through local, but also through long-range, connectivity effects [19][20][21]. Painter and Coleman also examined the screening effect for a hyperbranched, dendrimer-like polyester in the presence of low-molecular-weight PVPh as a model compound.…”

“…Painter and Coleman also examined the screening effect for a hyperbranched, dendrimer-like polyester in the presence of low-molecular-weight PVPh as a model compound. The values of γ for a linear chain structure blend (e.g., PVPh/PMMA) is approximately 0.3; for a dendrimer-like polyester blend (e.g., PVPh/dendrimer-like polyester) it is approximately 0.8 [19,23]. Scheme 1.…”