Degree of polymerization Molecular weight

Antimicrobial activity of chitosan depends on type of chitosan, degree of polymerization, molecular weight, pH and solvent -Chitosan nanoparticles could exhibit superior antimicrobial effect against various micro-organism than chitosan itself -The unique character of chitosan nanoparticles for their positive charge and small particle size is responsible for their potential antibacterial activity and acceptable biocompatibility... 

Mass Spectrometry. An alternative to using GPC with viscometry and li t scattering detection for the determination of low molecular wei t polymer distributions is mass spectrometry. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDITOFMS) can give fast, accurate information about the degree of polymerization (molecular weight stribution). 

Kakimoto et al. 43h have reported the preparation of hyperbranched engineering plastic, poly(phenylene sulfide)(PPS) dendrimers via the polymerization of methyl 3,5-bis-(phenylthio)-phenyl sulfoxide. The degree of polymerization and weight average molecular weight were determined to be 80 and 25,700 amu, respectively T% values were determined to increase (102 to 124 °C) proportionately relative to molecular weight. 

Two preparations of cytochrome b from beef heart mitochondria have been reported which resemble our preparation with regard to degree of purity. Molecular weights of 28,000 and 22,400 were calculated on the basis of the specific heme contents. As these preparations were obtained in highly polymeric states, a possible quaternary structure for cytochrome b was not considered. Cytochrome b preparations from cells with proteins selectively labeled as described above (so as to allow their attribution to one of the two protein-synthesizing systems) have not yet been described by other authors. 

Figure C2.1.3. Schematic dependence of tire molecular weight of a polymer as a function of tire degree of monomer conversion for different polymerization reactions.

The second category of polymerization reactions does not involve a chain reaction and is divided into two groups poly addition and poly condensation [4]. In botli reactions, tire growth of a polymer chains proceeds by reactions between molecules of all degrees of polymerization. In polycondensations a low-molecular-weight product L is eliminated, while polyadditions occur witliout elimination ... 

In homopolymers all tire constituents (monomers) are identical, and hence tire interactions between tire monomers and between tire monomers and tire solvent have the same functional fonn. To describe tire shapes of a homopolymer (in the limit of large molecular weight) it is sufficient to model tire chain as a sequence of connected beads. Such a model can be used to describe tire shapes tliat a chain can adopt in various solvent conditions. A measure of shape is tire dimension of tire chain as a function of the degree of polymerization, N. If N is large tlien tire precise chemical details do not affect tire way tire size scales witli N [10]. In such a description a homopolymer is characterized in tenns of a single parameter tliat essentially characterizes tire effective interaction between tire beads, which is obtained by integrating over tire solvent coordinates. 

The degree of polymerization of a polymer is simply the number of repeat units in a molecule. The degree of polymerization n is given by the ratio of the molecular weight of the polymer to the molecular weight of the repeat unit ... 

We began this section with an inquiry into how to define the size of a polymer molecule. In addition to the molecular weight or the degree of polymerization, some linear dimension which characterizes the molecule could also be used for this purpose. For purposes of orientation, let us again consider a hydrocarbon molecule stretched out to its full length but without any bond distortion. There are several features to note about this situation ... 

Note that the average weight per repeat unit could be used to evaluate the overall degree of polymerization of this terpolymer. For example, if the molecular weight were 43,000, the corresponding degree of polymerization would be... 

The high molecular weight of a polymer is one of the most immediate consequences of the chain structure of these molecules. As indicated in Sec. 1.2, it is also the basis for describing the size of the polymer molecule, either directly or through the degree of polymerization. Most methods for the determination... 

As should be expected, both (fg ) and r show the same dependence on the degree of polymerization or molecular weight. Since the radius of gyration can be determined experimentally through the measurement of viscosity or light scattering, it is through this quantity that we shall approach the evaluation of 1. 

It should be noted that a log-log plot condenses the data considerably and that the transition between a first-power and a 3.4-power dependence occurs over a modest range rather than at a precise cutoff. Nevertheless, the transition is read from the intersection of two lines and is identified as occurring at a degree of polymerization or molecular weight designated n, or, respectively. 

The next step in the development of a model is to postulate a perfect network. By definition, a perfect network has no free chain ends. An actual network will contain dangling ends, but it is easier to begin with the perfect case and subsequently correct it to a more realistic picture. We define v as the number of subchains contained in this perfect network, a subchain being the portion of chain between the crosslink points. The molecular weight and degree of polymerization of the chain between crosslinks are defined to be Mj, and n, respectively. Note that these same symbols were used in the last chapter with different definitions. 

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