Particle size dependence polymer molecular weight

The properties of PTFE are dependent on the type of polymer and the method of processing. The polymer may differ in particle size and/or molecular weight. The partiele size will influence ease of processing and the quantity of voids in the finished product whilst the moleeular weight will influenee crystallinity and... 

Effect of PVA Molecular Weight on Adsorbed Layer Thickness. Figure 4 shows the variation of reduced viscosity with volume fraction for the bare and PVA-covered 190nm-size PS latex particles. For the bare particles, nre(j/ is independent of and the value of the Einstein coefficient is ca. 3.0. For the covered particles, rired/ t increases linearly with tp. Table IV gives the adsorbed layer thicknesses calculated from the differences in the intercepts for the bare and covered particles and determined by photon correlation spectroscopy, as well as the root-mean-square radii of gyration of the free polymer coil in solution. The agreement of the adsorbed layer thicknesses determined by two independent methods is remarkable. The increase in adsorbed layer thickness follows the same dependence on molecular weight as the adsorption density, i.e., for the fully hydrolyzed PVA s and... 

Emulsion polymerization refers to a unique process employed for some radical chain polymerizations. It involves the polymerization of monomers in the form of emulsions (i.e., colloidal dispersions). The process bears a superficial resemblance to suspension polymerization (Sec. 3-13c) but is quite different in mechanism and reaction characteristics. Emulsion polymerization differs from suspension polymerization in the type and smaller size of the particles in which polymerization occurs, in the kind of initiator employed, and in the dependence of polymer molecular weight on reaction parameters. 

Figure 1. Critical hydroxyethyt)cellulose concentration for latex particles flocculation, Dependence of both polymer molecular weight and latex median particle size on thickener concentration is illustrated. Reproduced with permission from reference 5. Copyright 1984 Academic Press.)...

A gas foaming/particulate leaching process can be employed to fabricate interconnected open pore structures of PLGA for controlled release of DNA [113,199]. This process employs carbon dioxide to process a mixture of polymer and porogen, in order to fuse adjacent polymer particles into an interconnected structure. The DNA can be lyophilized with the microspheres [113] or encapsulated within the microspheres [200,201]. Lyophilization of DNA with the microspheres can provide large quantities of incorporated DNA, with relatively rapid release kinetics. Incorporation of DNA into the microspheres provides for a more sustained release relative to the lyophilization method [200], with the release kinetics dependent on the polymer molecular weight and microsphere size [201]. DNA can be incorporated into polymer microspheres using several approaches [201-205]. Subcutaneous implantation of scaffolds results in transfected cells observed within the scaffold... 

In concluding this section, we note parenthetically that the particle size and molecular weight dependencies elaborated above follow immediately from the over-simplified viewpoint that the polymer chains and the particles compete for space. The higher is the polymer molecular weight and the larger are the particles, the more intense is that competition for space. 

Non-Newtonian fluids exhibit complex flow behavior, typically because they contain additives such as polymers or particles that alter the response of the fluid. Unlike Newtonian fluids, which have constant viscosity (resistance to flow), the viscosity of a non-Newtonian fluid is not constant. The viscosity depends oti the shear rate and the amount of strain accumulated, as well as the nature of the additives, including the concentration of additives, the polymer molecular weight, and the particle size. In addition, flexible polymers stretch in a flow, leading to an elastic response. Development of microfluidic devices has centered on miniaturizing assays to analyze the biological, physical, and chemical properties of DNA, proteins, and biopolymers in solution, as well as suspensimis of cells and bioparticles. Since the analysis is typically performed in the... 

HIPS microstructure depends on the process variables used in the polymerization. There are many publications reporting experimental evidence of the effect of the process variables on polymer microstructure [7-16], For example, Soto et al. [15] analyzed the effects of the initiator type, temperature and stirring rate on the particle morphology and molecular weights of the free PS. Heuristic knowledge available indicates that the particle size depends on the ratio between the solution viscosities of the PBD- and PS-rich phases the agitation rate and the interface tension between the two phases. The interface tension in turn depends on the grafting efficiency. 

The parameters of the first (initial) SMP level do not depend on polymer conccuitration when r > 3g/dl. If c < 3g/dl, the size of SMPs decretwes, and, at a certain concentration C( (0.5... 0.8 g/dl in accordance with polymer molecular weight), the particles dissolve. There are no SMPs in solution when c < q (Klenin et al., 1973c, I97dbc). 

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]... 

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