Aspects of acid-base interactions and use of inverse gas chromatography

Spectroscopic characterization of molecular interdiffusion at a poly(vinyl pyrrolidone)/vinyl ester interface

A novel experimental approach involving fluorescence nonradiative energy transfer (NRET) is employed to study the Fickian diffusion of small molecules in rubbery polymer films near the glass transition. A theoretical formalism has been developed which directly relates the small molecule translational diffusion coefficient, &#x1d49f;, to changes in the energy transfer efficiency, E. Values of &#x1d49f; as low as 5 × 10-16 cm2/s have been measured. In this approach, two thin polymer films are sandwiched together, one labeled with either NRET donor or acceptor chromophores and the second doped with the complementary chromophore. Upon annealing for a time t, dopant chromophore diffusion occurs in which E is proportional to (&#x1d49f;t)1/2/w, where w is the donor film thickness. Values of &#x1d49f; for pyrene, N-(2-hydroxyethyl)-N-ethyl-4-(tricyanovinyl)aniline (TC1), bis(phenylethynylanthracene) (BPEA), and decacyclene in poly(isobutyl methacrylate) (PiBMA) and for BPEA in poly(ethyl methacrylate) (PEMA) have been measured over temperatures...

https://blogs.uakron.edu/dhinojwala/files/2013/10/DeDD-1996.pdf

Small molecule probe diffusion in thin polymer films near the glass transition: A novel approach using fluorescence nonradiative energy transfer

The molecular-level cause of the gel effect in free radical polymerization, associated with a decrease in the termination rate parameter with increasing conversion, is studied by experimental and modeling approaches. The predictive Vrentas−Duda free volume theory serves as a basis for modeling as it handles quantitatively the temperature and polymer concentration dependencies of monomer diffusion. The polymer concentration (c) dependencies of various diffusional processes fit an expression of the form [Dm(c)/Dm(0)]ξx,m, where Dm is the monomer diffusion coefficient and ξx,m expresses the power-law dependence of the diffusional process of interest (x) relative to that of monomer (m). Relevant values of ξx,m vary from ∼ 0.8 for segmental mobility, to ∼1−2 or 3 for oligomeric diffusion, to ∼ 3.0−3.5 for unentangled polymer diffusion, and to ∼ 9.5−10 for entangled polymer diffusion. If the very high conversion regime, where issues unrelated to the origin of the gel effect add unnecessary complications, is avo...

Modeling Insight into the Diffusion-Limited Cause of the Gel Effect in Free Radical Polymerization

The free-volume theory for solvent self-diffusion coefficients in polymer−solvent systems is modified to include a more general analysis of the effects of solvent size. The predictions of the theory are compared with self-diffusion data for a diverse set of solvents and four polymers, polystyrene, poly(vinyl acetate), poly(methyl methacrylate), and poly(p-methylstyrene). The new prediction of size effects is based on the consideration of the asymmetry of solvent molecules.

Effect of Solvent Size on Solvent Self-Diffusion in Polymer−Solvent Systems

Capillary column inverse gas chromatography (CCIGC) has been used for the measurement of diffusion coefficients in polymer-solvent systems at conditions approaching on a solvent diffusion in two polymers, poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc, measuremnets of diffusion coeffiients were made at temperatures ranging from T g to 70 K above T g . Over 30 solvents were evaluated: alkanes, alkenes, aromatic hydrocarbons, and aliphatic esters.

Dominique Arnould

Papers

Size effects on solvent diffusion in polymers