Properties effects chain flexibility

Optical and electro-optical behavior of side-chain liquid crystalline polymers are described 350-351>. The effect of flexible siloxane spacers on the phase properties and electric field effects were determined. Rheological properties of siloxane containing liquid crystalline side-chain polymers were studied as a function of shear rate and temperature 352). The effect of cooling rate on the alignment of a siloxane based side-chain liquid crystalline copolymer was investigated 353). It was shown that the dielectric relaxation behavior of the polymers varied in a systematic manner with the rate at which the material was cooled from its isotropic phase. 

Chain flexibility also effects the ability of a polymer to crystallize. Excessive flexibility in a polymer chain as in polysiloxanes and natural rubber leads to an inability of the chains to pack. The chain conformations required for packing cannot be maintained because of the high flexibility of the chains. The flexibility in the cases of the polysiloxanes and natural rubber is due to the bulky Si—O and rxv-olelin groups, respectively. Such polymers remain as almost completely amorphous materials, which, however, show the important property of elastic behavior. 

The conclusion was reached that the mechanical properties of glass-reinforced unsaturated polyester are influenced by the chemical structure of the spacer groups in the methacrylate functional silane. Effective factors include hydro-phobicity, reactivity of the double bond, chain flexibility of the backbone, and adsorption behavior. 

In random copolymers chain flexibility and crystallinity can be quite different from those in either of the component /zomopolymers. In consequence, the copolymer may well present an entirely new set of physical properties. On the other hand, the different chain segments in block or graft copolymers often segregate into effectively separate phases, when the properties of the composite resemble those of a mixture of the individual homopolymers. 

Only a smaU number of researchers have attempted to interpret the experiments data on the Kerr effect from the standpoint of theories based on a rotational isomer medianism of chain flexibility and tensor additivity of the polarizability of chain bonds > These attempts did not yield good agreement between theory and experimental data. This may result from both the unreliability of the data and the inadequacy of some suggestions used in the theory (additivity of optical properties of vSence bonds, character of the internal field etc.). 

PET is useful polymer used for fiber, film, and plastic containers such as carbonated beverage bottles. Recently, the recycling of polymers such as PET after use is attracting the attention of many researchers aware of environmental problems and wishing to find ways to save earth resources. Previous studies showed that unsaturated polyester resins can be economically prepared from recycled PET and the resins may be useful for resin concretes (1 4). However, there is little information on the molecular features of the UPE resins. Thus, we synthesized various UPE resins from PET. Especially, the PET content, chain flexibility and degree of unsaturation of the resins were systematically varied and the effects of those variables on the mechanical properties of the cured resins and polymer mortars made therefrom were studied. 

Polymer properties are directly dependent on both the Inherent shape of the polymer and on its treatment. Contributions of polymer shape to polymer properties are often complex and interrelated, but can be broadly divided into terms dealing with chain flexibility, chain regularity, interchain forces, and steric effects. 

Measurement of low-temperature flexibility was significantly advanced by the method of Clash and Berg. This assessment of torsional modulus was adopted as an ASTM procedure (41). By its use, it can be shown that plasticizing with linear molecular structures enhances the low-temperature flex most efficiently (i.e., lower plasticizer concentration has a more pronounced effect) chain branching and ringed aromatic moieties show lower efficiency. Increasing any compatible plasticizer s concentration in the composition lowers the temperature at which brittleness develops. However, this formulation approach may sacrifice the optimum in other properties, such as tensile strength, modulus, or hand. 

In discussing the influence of steric features on mechanical properties, it is convenient to consider the side chains and the main chain separately. The effects of flexible side chains differ completely from those of stiff side chains. Long, flexible side chains reduce the glass transition temperature, while stiff side chains increase it. Long, flexible side chains increase the free volume and ease the steric hindrance from neighboring chains and as such facilitate the movement of the main chain. Figure 13.28 illustrates... 

The linkage between the enhancement of heat transfer at boiling of dilute polymer solutions and the elastic properties of the system is confirmed by the existence of the optimal concentration corresponding to (Figure 7.2.14). Similar optimal concentration was established in addition of polymers to water to suppress turbulence - the phenomenon that also owes its origin to elasticity of macromolecules. Therefore, it is possible to expect that the factors favoring the chain flexibility and increase in the molecular mass, should lead to strengthening of the effect. 

The simplicity of (2.25) is to be contrasted with the complexity of the exact P(R n) for realistic models of flexible chains for all R (and for small n). When dealing with the complicated problems of nonideal polymer solutions, etc., it is therefore customary to replace the real polymer chain by the so-called Kuhn effective random flight chain. An effective chain is one with N (in general different from n) links of size A5 such that N lS.s = L and (R ) is as given by (2.29). This substitution of a real chain by its equivalent chain is often a necessity so that we may separate errors in principle from errors arising from a poor mathematical approximation to the exact P(R n) when dealing with problems which are not exactly soluble. This equivalent chain therefore provides us with reasonable approximations to the properties of real polymer chains, provided the physical properties of interest do not depend heavily upon those chain configurations with i > L or upon chain properties over small distances for which the real chain is stiff. 

The net effect of external plasticization is to increase chain flexibility and, hence, affect the polymer s properties as shown in Table 12-1. A particularly important property change is an increase in impact strength. 

Measurements have been made of the size of the polymer coil in miscible blends, ° using neutron scattering. Some have observed expanded coils and others contracted coils. It has been suggested that this should depend on whether the polymer is glassy or rubbery, i.e., the chain flexibility. The results are not consistent but a definitive set of experiments remains to be done. Studies on PVC show the dominant effect that the small crystalline part of this polymer can play in scattering from its blends. The crystalline regions do not mix with the other polymer and this could greatly affect the properties of PVC blends. 

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