Molecular weight dispersion effect

Fig. 22. The effect of solvent composition on the molecular weight ( ), conversion (O), and molecular weight dispersity ( ) of PaMeSt prepared using the HSi(CH3)2CH2CH2

The effect of changing solvent composition (polarity) on molecular weight dispersity is noteworthy. Mw/Mn is quite low (1.69) in the experiment carried out by the use of 100% CH2C12 and it increases monotonically with increasing n-C6H14 content. It is very difficult to interpret these data at this time. 

It was suggested in a previous publication (9) that flocculation at the UCFT can be ascribed to the free volume dissimilarity between the polymer stabilizing the particle and the low molecular weight dispersion medium. Incorporating this idea in a quantitative way into the theory of steric stabilization allowed for a qualitative interpretation of the experimental data. This idea is further extended to include the effect of pressure on the critical flocculation conditions. 

The Effect of Experimental Conditions on Molecular Weights and Molecular Weight Dispersities GPC Studies... 

Figure 15.5 Effect of molecular weight dispersity ( )) (formerly known as polydispersity) using schematic Gibbs triangle diagrams for polymer-solvent system, generation of cloud point curve and shadow curve in temperature-composition diagram.

The experimental estimate of 37.5 nm for p may be compared with the predictions of the rotational isomeric state model using the result for C of Yathindra and Rao mentioned above, for which p lies in the range 13 to 22 nm. The difference is small enough to be attributed to error in experimental light scattering, the effects of residual intermolecular association, the effects of molecular weight dispersity, or solvation effects, which are neglected in the theoretical estimate of p. 

To see the effect of dipole—dipole forces, we compare the boiling points of two compounds of similar molecular weight acetonitrile (CH3CN, MW 41 amu, bp 355 K) and propane (CH3CH2CH3, MW 44 amu, bp 231 K). Acetonitrile is a polar molecule, with a dipole moment of 3.9 D, so dipole—dipole forces are present. However, propane is essentially nonpolar, which means that dipole—dipole forces are absent. Because acetonitrile and propane have similar molecular weights, dispersion forces are similar for these two molecules. Therefore, the higher boiling point of acetonitrile can be attributed to dipole-dipole forces. 

Photoacid diffusion behavior in t-BOC-blocked chemically amplified positive DUV resists under various conditions was studied. Based on the experimental results, it was confirmed that only one mechanism dominated the acid diffusion in the resist film, and two diffusion paths, i.e., the remaining solvent in the resist film and hydrophilic OH sites of base phenolic resin, existed. Moreover, the effects of molecular weight dispersion, acid structure, and additional base component on both acid-diffusion behavior and lithographic performance were revealed. Finally, the acid diffusion behavior in the resist film was clarified and the acid diffusion length that affected the resist performance could be controlled. 

It has been reported that for dilute solutions of PPSQ values of determined by electric birefringence studies are in good agreement33 with the relation tr 2M[n]rt/RT expected for a rigid coil. With the estimate for Tr, we find that Tc/tr is equal to 0.04 and 0.1 for the data on samples A-2 and A-2 shown in Fig. 12. Thus, Tq is smaller, and less dependent on molecular weight than t r for a rigid coil. The dependence of Tq snd M is not yet understood. It could reflect, for example, the effects of molecular weight dispersity, a few uncyclized repeat units, restricted torsional chain motions, or the cooperative nature of motion in a concentrated solution. 

The theoretical treatments of Ajg discussed here were motivated by the question of the effects of molecular weight dispersion on measured second virial coefficients. Once Ajf Mjy Mj ) is available it is obvious in principle how to obtain A 2 or. 4 2 for any desired form of distribution. Detailed calculations using the hard-spherelike interaction model with the familiar Schulz-Zimm distribution indicate that the ratio of virial coefficients increase wi out limit with the... 

The most commonly used scale inhibitors are low molecular weight acrylate polymers and organophosphoms compounds (phosphonates). Both classes of materials function as threshold inhibitors however, the polymeric materials are more effective dispersants. Selection of a scale control agent depends on the precipitating species and its degree of supersaturation. The most effective scale control programs use both a precipitation inhibitor and a dispersant. In some cases this can be achieved with a single component (eg, polymers used to inhibit calcium phosphate at near neutral pH). 

The most effective and widely used dispersants are low molecular weight anionic polymers. Dispersion technology has advanced to the point at which polymers are designed for specific classes of foulants or for a broad spectmm of materials. Acrylate-based polymers are widely used as dispersants. They have advanced from simple homopolymers of acryflc acid to more advanced copolymers and terpolymers. The performance characteristics of the acrylate polymers are a function of their molecular weight and stmcture, along with the types of monomeric units incorporated into the polymer backbone. 

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