Solvents for PMMA

Because we wanted to suppress the effects of thermodynamic quality of the eluent toward the polymer probes, we therefore looked for liquids that would be thermodynamically good solvents for PMMA. At the same time, one solvent should promote polymer adsorption whereas the others should promote desorption. 

Figure 4.8 shows the fluorescence anisotropy decay curves for PMMA brushes with various graft densities swollen in benzene and acetonitrile. Benzene and acetonitrile are good and 0 solvents for PMMA. As clearly shown in this figure. 

Polymer Matrix Effects. In order to approximate the environment experienced by the arylcarbamate moieties in coatings based on aromatic diisocyanates, we chose to study the photochemistry of alkyl N-arylcarbamates in polymethacrylate (PMMA) and polypropyl-methacrylate (PPMA) films. First, however, 2a and 3a were irradiated in ethyl propionate (a model solvent for PMMA and PPMA) to determine the effect of the solvent polarity (dielectric) on the photolysis of the carbamates. Upon excitation at 280 nm, where the solvent absorbance was negligible, is 0.006 for 2a and 0j) is 0.005 for 3a. These values are significantly smaller... 

PMMA) film is quenched by permeation of methyl ethyl ketone (MEK), a good solvent for PMMA. A steady-state MEK concentration profile has been estimated from quenching data with existing sorption and light scattering data. The profile contains all the features of Case II diffusion the Fickian precursor, the solvent front, and the plateau region. However, the solvent front is not so steep as those observed in systems where penetrant diffusion is much slower. 

PMMA chain. This shows that the local density of the units near the junction increases. The influence of the increase in the Icwal density of units on the mobility of the junction becomes more pronounced as the thermo namic strength of the solvent for PMMA decreases and as the molecular weight of the polymer chain increases (Table 17). 

Fig. 15 Normalized diffusion coefficients D(q 0)/Do as functions of the volume fraction for PMMA-grafted silica particles DP 150 open square) and DP 760 (open circle) in CCL4 (good solvent for PMMA) at 2(FC [208]. The different crossover concentrations in the dynamics are indicated by solid and vertical arrows. The inset shows in magnification the area bounded by the rectangle around a normalized diffusion coefficient value of 1 in the main plot, using the same colors and symbols (solid ) for the two systems. Lines are drawn to guide the eye...

For a given sample, the tacticity was found to be identical in the two solvents. For PMMA, the chemical shifts of the a-methyl protons are most sensitive to poljnner configuration. Therefore, triad tacticity information was obtained by integration of the a-methyl resonances. All polymer configurations are expressed in terms of triad tacticities. 

Fig. 10. LC methods based on CEEC represented on chromatograms of PMMA eluted in different modes from silica gel column. Detector ELSD. The figure is constructed according to data published by Berek [57]. THE and toluene are thermodynamically good solvents for PMMA, herefore LC LCS is not possible in this system...

Materials. PMMA (Polysciences, MW=60,000, Mw/Mn=1.10), PS (Aldrich, MW=44,000, Mw/Mn=1.10), and PET (Aldrich) films were prepared by spin coating (2000 rpm) 0.25 wt % polymer/solvent solutions onto silicon (100) wafers, which had a native oxide layer. Toluene was used as the solvent for PMMA and PS, and 2-chlorophenol was used for PET. Films were annealed at 100°C under vacuum ( 0.01 torr) for 2 hours and allowed to cool under vacuum. Experiments were performed within days of film coating, and 1 day or less after annealing. Film thicknesses were measured using ellipsometry (Sopra) and found to be approximately 21, 12, and 20 nm ( 5nm), for PMMA, PET, and PS, respectively. Film surfaces were homogeneous with rms roughnesses < 1 nm. 

The sapphire surface was highly polished to make the surface roughness as small as possible (<30 A rms), in order to minimize the possibility of stray light excitation of the bulk solution. Toluene was chosen not only because it is a good solvent for PMMA but also, and more importantly, because its refractive index is very close to that of PMMA (1.494 compared to 1.492). Under such conditions of optical matching, it is reasonable to assume that the refractive index of the solution is independent of the polymer concentration. This simplifies considerably the data analysis. 

The Hansen radius of solubility of PMMA is equal to 3.1 (cal cm ). Are benzene and methanol good solvents for PMMA Discuss briefly the results. 

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