Significant Polymer Properties

Because of the capacity to tailor select polymer properties by varying the ratio of two or more components, copolymers have found significant commercial appHcation in several product areas. In fiber-spinning, ie, with copolymers such as nylon-6 in nylon-6,6 or the reverse, where the second component is present in low (<10%) concentration, as well as in other comonomers with nylon-6,6 or nylon-6, the copolymers are often used to control the effect of sphemUtes by decreasing their number and probably their size and the rate of crystallization (190). At higher ratios, the semicrystalline polyamides become optically clear, amorphous polymers which find appHcations in packaging and barrier resins markets (191). 

According to the concepts, given in the paper [7], a significant difference between the values of yield stress of equiconcentrated dispersions of mono- and polydisperse polymers and the effect of molecular weight of monodisperse polymers on the value of yield stress is connected with the specific adsorption on the surface of filler particles of shorter molecules, so that for polydisperse polymers (irrespective of their average molecular weight) this is the layer of the same molecules. At the same time, upon a transition to a number of monodisperse polymers, properties of the adsorption layer become different. 

A Comparison of Polyiminocarbonates and Polycarbonates The Effect of the NH Group on Polymer Properties. The replacement of the carbonyl oxygen by an NH group presents the only molecular difference between polyiminocarbonates and polycarbonates. In spite of the overall structural similarity between these two types of polymers, we found very significant differences between their respective material properties. In general, polyiminocarbonates and polycarbonates tend to complement each other in several aspects. 

In conclusion f-block element-based catalysts represent a significant improvement in the synthesis of polydienes, both from the pont of view of the process and that of the polymer properties. 

Incorporation Into a co- or terpolymer of a d1ol containing monomer such as solketal acrylate (SA, H, a comonomer readily hydrolyzed by aqueous add to a diol) likewise Increases crosslinking (Scheme 4). Such polymers exhibit Improved dry, wet and solvent resistance (Table V). Alternatively, half of the ABDA comonomer can be substituted with SA, without significantly degrading properties vs the Initial ABDA only sample. 

While both the Bicerano and van Krevelen systems model a significant number of polymer properties, most QSPR studies have focused on only a small number of key properties (which is mainly correlated to the availability of data for model development). 

The isomeric polysaccharides amylose (a component of starch) and cellulose also show the significance of stereoisomerism on polymer properties. Cellulose and amylose have the structures shown in Fig. 8-8. (Amylopectin, the other component of starch, has the same structure as amylose except that it is branched at carbon 6.) Both are polymers of glucose in which the... 

One problem encountered in the field is the apparent irre-producibility of the results of different workers, even those in the same laboratory. This is particularly the case with molar mass distribution and steric triad composition. The explanation of these apparent inconsistencies comes with the realization that the mechanisms are eneidic and the polymer properties are primarily determined by independent active centres of different reactivities and stereospecificities whose relative proportions are set at the initiation step, which is completed in the first seconds of the polymerization. The irreproducibilities arise from irreproducibilities in the initiation step which had not been thought relevant. Ando, Chfljd and Nishioka (12) noted that these rapid exothermic reactions tend to rise very significantly above bath temperature (we have confirmed this effect) and allowed for this in considering the stereochemistry of the propagation reaction. However our results show that the influence on the initiation reactions can have a more far-reaching effect. 

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