Mechanical properties molecular weight

Phthalazinone, 355 synthesis of, 356 Phthalic anhydride, 101 Phthalic anhydride-glycerol reaction, 19 Physical properties. See also Barrier properties Dielectric properties Mechanical properties Molecular weight Optical properties Structure-property relationships Thermal properties of aliphatic polyesters, 40-44 of aromatic-aliphatic polyesters, 44-47 of aromatic polyesters, 47-53 of aromatic polymers, 273-274 of epoxy-phenol networks, 413-416 molecular weight and, 3 of PBT, PEN, and PTT, 44-46 of polyester-ether thermoplastic elastomers, 54 of polyesters, 32-60 of polyimides, 273-287 of polymers, 3... 

The following material properties are used as input parameters in one or more of the correlations discussed in this chapter for the mechanical properties molecular weight M, length... 

Also, the high molecular weight poly(anhydride)s are melt processable under inert atmospheric conditions at temperatures greater than 200°C. The high molecular weight poly(anhydride)s are also stable to Cobalt irradiation without loss of mechanical properties, molecular weight, or changes in chemical structure. 

Poly[(trifluoroethoxy) (octafluoropentoxy) (X)phosphazene] (X — cross-link site) PFAP(II), undergoes a loss in molecular weight at elevated temperatures (135°-200°C) that is detrimental to mechanical properties. The mechanism of molecular weight loss was found to be random chain scission at weak links in the PFAP(II) chain. These weak links are postulated to be phosphazane moieties which would be attacked by water, acids, and POH to produce PN chain scission. 

Monomer composition (mol%) Thermal properties Molecular weight Mechanical properties Reference... 

Macromolecules are very diverse in composition and function and they occur in many fields of chemistry and biochemistry. The usual applications of synthetic polymers mainly deal with their physical properties molecular weight, conformations, van des Waals interactions... which don t require detailed knowledge of the electronic structure and can be approached by classical computational force fields which are at the basis of what one usually calls molecular mechanics. Nevertheless, one may be interested in the chemical reactivity of some region of the polymer, such as structural defects, and a quantum computation may be the only way to get the reliable chemical information. The other, very important class of macromolecules contains the innumerable biomacromolecules polypeptides, enzymes, nucleic acids. The understanding of their role in life usually requires the knowledge of the electronic structure and often the reactivity of at least well defined parts of the large system they constitute. This knowledge can only be reached by means of quantum chemical computations. 

It is no surprise then that nucleic acid synthesized in vitro according to this mechanism has the same base composition, the same physical properties (molecular weight), and even the same biologic activity (as a transformation factor) as the primer nucleic acid. The polymerase is not species specific primer nucleic acids of different species origin are multiplied indiscriminately by the enzyme from E. coU. 

Before we can explore how reactor conditions can be chosen, we require some measure of reactor performance. For polymerization reactors, the most important measure of performance is the distribution of molecular weights in the polymer product. The distribution of molecular weights dictates the mechanical properties of the polymer. For other types of reactors, three important parameters are used to describe their performance ... 

Most properties of linear polymers are controlled by two different factors. The chemical constitution of tire monomers detennines tire interaction strengtli between tire chains, tire interactions of tire polymer witli host molecules or witli interfaces. The monomer stmcture also detennines tire possible local confonnations of tire polymer chain. This relationship between the molecular stmcture and any interaction witli surrounding molecules is similar to tliat found for low-molecular-weight compounds. The second important parameter tliat controls polymer properties is tire molecular weight. Contrary to tire situation for low-molecular-weight compounds, it plays a fimdamental role in polymer behaviour. It detennines tire slow-mode dynamics and tire viscosity of polymers in solutions and in tire melt. These properties are of utmost importance in polymer rheology and condition tlieir processability. The mechanical properties, solubility and miscibility of different polymers also depend on tlieir molecular weights. 

The function/( C) may have a very simple form, as is the case for the calculation of the molecular weight from the relative atomic masses. In most cases, however,/( Cj will be very complicated when it comes to describe the structure by quantum mechanical means and the property may be derived directly from the wavefunction for example, the dipole moment may be obtained by applying the dipole operator. 

Equation (2.61) predicts a 3.5-power dependence of viscosity on molecular weight, amazingly close to the observed 3.4-power dependence. In this respect the model is a success. Unfortunately, there are other mechanical properties of highly entangled molecules in which the agreement between the Bueche theory and experiment are less satisfactory. Since we have not established the basis for these other criteria, we shall not go into specific details. It is informative to recognize that Eq. (2.61) contains many of the same factors as Eq. (2.56), the Debye expression for viscosity, which we symbolize t . If we factor the Bueche expression so as to separate the Debye terms, we obtain... 

The isothermal curves of mechanical properties in Chap. 3 are actually master curves constructed on the basis of the principles described here. Note that the manipulations are formally similar to the superpositioning of isotherms for crystallization in Fig. 4.8b, except that the objective here is to connect rather than superimpose the segments. Figure 4.17 shows a set of stress relaxation moduli measured on polystyrene of molecular weight 1.83 X 10 . These moduli were measured over a relatively narrow range of readily accessible times and over the range of temperatures shown in Fig. 4.17. We shall leave as an assignment the construction of a master curve from these data (Problem 10). 

It has been hypothesized that cross-linked polymers would have better mechanical properties if interchain bridges were located at the ends rather than the center of chains. To test this, low molecular weight polyesters were synthesizedf... 

To a large extent, the properties of acryUc ester polymers depend on the nature of the alcohol radical and the molecular weight of the polymer. As is typical of polymeric systems, the mechanical properties of acryUc polymers improve as molecular weight is increased however, beyond a critical molecular weight, which often is about 100,000 to 200,000 for amorphous polymers, the improvement is slight and levels off asymptotically. 

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