Effect of Polymer Molecular Weight

FIGURE 10.11. In stericaUy stabilized systems, a given adsorbed polymer molecule wiU be associated with one particle (a). In systems containing a low polymer concentration and/or very high-molecular-weight polymer, molecules can become adsorbed to two or more particles leading to bridging flocculation (b). 

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Lin, TH Phillies, GDI, Prohe Diffusion in Polyacrylic Acid Water—Effect of Polymer Molecular Weight, Journal of Colloid and Interface Science 100, 82, 1984. 

Wang, Y. and Dubin, RL., Capillary modification by non-covalent polycation adsorption effects of polymer molecular weight and adsorption ionic strength, Anal. Chem. 71, 3463, 1999. 

Effect of Polymer Molecular Weight on Membrane Formation... 

K. Ciftci, A. A. Hincal, and H. S. Kas, Microspheres of 5-fluorou-racil using poly(DL-lactic acid), effect of polymer molecular weight... 

Huang M, Fong C-W, Khor E et al (2005) Transfection efficiency of chitosan vectors effect of polymer molecular weight and degree of deacetylation. J Control Release 106(3) 391—406... 

McCrystal, C.B. Ford, J.L. Rajabi-Siahboomi, A.R. Water distribution within cellulose ethers using differential scanning calorimetry. 1. Effect of polymer molecular weight and drug addition. J. Pharm. Sci. 1999, 88, 792-796. 

Rowe, R.C. Forse, S.F. The effect of polymer molecular weight on the incidence of film cracking and splitting... 

Santhiya, D. et al., Effect of polymer molecular weight on the adsorption of polyacrylic acid at the alumina-water interface, Colloids Sutf. A, 133. 157. 1998. 

The effects of polymer molecular weight on the rate and extent of adsorption on carbon black at equilibrium is fundamentally no different from other polymeric adsorbate-adsorbent systems (95). When microporosity is present in carbon black, the adsorption is governed by the external surface area (96), but with very high molecular weight polymers adsorption is also limited by the inability of the molecular coils to penetrate the internal void space of the primary structure aggregates (95). 

Figure 4. Effect of polymer molecular weight on clarification of clay suspensions.

Park K, Kim JH et al (2007) Effect of polymer molecular weight on the tumor targeting characteristics of self-assembled glycol chitosan nanoparticles. J Control Release 122 305-314... 

Jalil R, Nixon JR. Microencapsulation using poly(DL-lactic acid), ni Effect of polymer molecular weight on the release kinetics. Journal of Microencapsulation. July-September 1990 7(3) 357-374. PubMed PMID 2384838. 

The reptation idea could account for the effect of polymer molecular weight and solvent concentration on the dissolution rate. However the key concentration identified in this approach [57,59] is one at the surface. This implies independence of the solvent concentration history. This may not be true as the disentanglement of polymer chains does not commence till the local solvent concentration is greater than a critical value at which the local glass transition temperature is lowered below the experimental temperature so that the glassy polymer changes into a gel. Also, all of the efforts discussed so far failed to take into account the effect of the viscoelastic properties of the polymer on the dissolution mechanism. 

Dissolution experiments were conducted on the PEG-water system by investigating the effect of polymer molecular weight on the gel layer thickness. Experiments were conducted with PEG samples of molecular weight 10,000,20,000 and 35,000. All the experiments were conducted at 21 C. Figure 13 shows the position of the normalized gel layer thickness as a function of time for various polymer molecular weights during PEG dissolution in deionized water. The positions were normalized with respect to the initial position, which is the initial radius of the disk (6.5 mm). It is instructive to note that since PEG is rubbery at 21 C, the whole section essentially represents the gel layer. 

Ferretti, R., Zhang, J. and Buffle, J. (1997). Kinetics of hematite aggregation by polyacrylic acid effect of polymer molecular weights. Colloids Surf. A, 121, 203-215. 

The effect of polymer molecular weight on the viscosity when added at T < is shown in Figure 5. The viscosities were measured at a shear rate of 100 s and T = 25 C. The viscosity ratio is the viscosity of the dispersion plus polymer to the viscosity of the dispersion. The viscosity of the lamellar dispersion is reduced by the addition of the nonionic polymers of all molecular weights and the ranking of effectiveness (i.e., 20K > PVA = 3350 > 600) is consistent with the expected osmotic pressure due to the second virial coefficient of the polymers. At an equal molar concentration the second virial coefficient and the osmotic pressure due to the concentration gradient increases with molecular weight. 

Mittal G, Sahana DK, Bhardwaj V et al (2007) Estradiol loaded PLGA nanoparticles for oral administration effect of polymer molecular weight and copolymCT cranpositirai on release behavior in vitro and in vivo. J Control Release 119 77-85... 

Colloidal copper, prepared by borohydride reduction of copper(II) salts in the presence of protective polymers and with particle sizes of 5.0-15.0 nm (depending on preparation details), is an active catalyst for the hydration of unsaturated nitriles to their corresponding unsaturated amides with 100% selectivity. [53, 268] The copper particle size was unaffected by the catalytic process. The catidyst performance was optimized in a detailed study of the effects of polymer molecular weight, polymer/metal ratio, and the chemical constitution of the polymer. [268, 269]... 

Figure 3. Effect of polymer molecular weight on the release of myoglobin from ATRIGEL formulations C>, inherent viscosity 0.05 ri inherent viscosity 0.33. The polymer used was 45% PLA. Formulation solvent was NMP, and the protein load was 10%. Cumulative release profiles were generated in PBS, pH 7.4.

Yaszemski, M.J., Mikos, A.G., Payne, R.G. and Hayes, W.C. (1994) Biodegradable Polymer Composites for Temporary Replacement of Trabecular Bone The Effect of Polymer Molecular Weight on Composite Strength and Modulus, In Biomatetials for Drug and Cell Delivery, Mikos. A.G., Murphy R., Bernstein H., Peppas N..V., eds., 331, Pittsburgh Materials Research Society) 251-256. 

The EOS predictions of Sanchez and Lacombe are shown in Figure 2.5 for PMMA at 25°C at infinite molecular weight. The Sanchez and Lacombe (SL) EOS allows for the effect of polymer molecular weight in the EOS. The characteristic temperature values in Table 2.4 for the same set of polymers as indicated before for SL, EOS, are a lot lower compared to other EOS values. The proximity of the characteristic temperatures of polymers to operating temperatures in the molding and other polymer processing operations may indicate that this model may be a better representation of polymer PVT behavior compared with other models. 

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