Orientation of polymer chains

The parameters K1/ K2/ and K3 are defined by the refractive indices of the crystal and sample and by the incidence angle [32]. If the sample has uniaxial symmetry, only two polarized spectra are necessary to characterize the orientation. If the optical axis is along the plane of the sample, such as for stretched polymer films, only the two s-polarized spectra are needed to determine kz and kx. These are then used to calculate a dichroic ratio or a P2) value with Equation (25) (replacing absorbance with absorption index). In contrast, a uniaxial sample with its optical axis perpendicular to the crystal surface requires the acquisition of spectra with both p- and s-polarizations, but the Z- and X-axes are now equivalent. This approach was used, through dichroic ratio measurements, to monitor the orientation of polymer chains at various depths during the drying of latex [33]. This type of symmetry is often encountered in non-polymeric samples, for instance, in ultrathin films of lipids or self-assembled monolayers. 

The uniaxial orientation parameter related to the orientation of polymer chains gains particular importance, because it can also be determined by measurement of birefringence [250,252],... 

Even at their best, the models are able to predict only macroscopic properties of the films, yielding no information on microscopic parameters that may affect resist performance. It is highly probable that spin casting induces some structure or preferential chain orientation into the films, or causes secondary effects such as the aggregation observed by Law. These effects are barely addressed in the currently available literature. However, some earlier works (3.17-191 on solvent (static) cast films have investigated the molecular orientation of polymer chains as well as chain relaxation due to thermal annealing. 

Crystalline regions of polymers can be represented as combinations of folded chains forming lamellar structures. Amorphous regions are less ordered than crystalline regions. Additional orientation of polymer chains occurs. This results in increased strength in the order of the orientation. 

As it is seen from table 1 that the larger is the organomodified layered silieate content the higher are ultimate strength and initial modulus. It can be due to orientation of polymer chains in silicate layers. Percent elongation at break for all composites was equal to 4-8%. 

The type of carbosilane core and the length of siloxane arms play an important role in this process. For high siloxane arms the more flexible core (B) causes large (AH = 14 J/g for B-R-4 versus AH =34 J/g for R-4), but slightly less pronounced decrease of transition enthalpy than compact ones [A, C (AH =4J/g for C-R-4)] (Fig. 5). It implies easier orientation of polymer chains on heating. The opposite was found for lower polymers (AH =3 J/g for B-R-2 and AH =8 J/g for C-R-2). 

Also, the proportion of fibers in the skin (or shell) and those in the core depends on the rates of fiow." Low injection rates and low temperatures causes an expansion of the shell (skin) region These relationships also affect the orientation of polymer chains in filled and unfilled polymers during proc-essing Orientation of fiber in blow molding of bottles filled with fibers caused anisotropy of properties. Tensile strength was increased in the machine direction. At the same time, talc filled bottles had more uniform tensile properties than unfilled bottles. ... 

Because of the liquid crystalline nature of the melts in which the polymer chains are arranged in domains of parallel arrays, fibers are readily obtained with an appreciable degree of molecular orientation in the direction of the long fiber axis. This orientation of polymer chains leads to high tenacity and high modulus without a drawing step. 

In any anisotropic system, the depolarization factor may be used as a valuable source of information about the orientation of molecules, e. g. about the orientation of polymer chains in fibers or the orientation of adsorbed molecules on surfaces. 

Figures A.7 a - d depict isotropic polymer solutions in which there is no preferential orientation of polymer chains. However, as we have already mentioned, spontaneous ordering can occur in concentrated solutions of rigid i/d 1) polymers, and they become liquid crystalline (Figure 4.7...

B-1) Degree of orientation of polymer chains in crystalline and noncrystalline regions... 

Electrical conductivity of polyacetylene films depends on orientation of polymer chains. Figure 5 shows the relationship between relative electrical conductivity and dichroic ratio of polyacetylene films prepared by a mixture catalyst of Trihexyl aluminium and Tetradecyl titanate. Conductivity of fully stretched or oriented polyacetylene films showed twenty times higher than that of as-grown films. Conductivity of polyacetylene films, prepared by other catalysts systems of trialkyl aluminium and tetraalkyl titanate, showed similar relationship, although increment of the conductivity was lower. 

They observed that in injection-molded copolyesters containing 40-90 mol% of p-hydroxybenzoic acid (PHB), the linear thermal expansions were highly anisotropic. They also observed that the linear thermal expansion is zero along the flow but not across the flow. The anisotropy in linear thermal expansion is due to the orientation of polymer chains during molding. 

On the basis of the DSC data summarized in Table 8.3, the crystallization temperature (T ) of PLA fibers becomes lower than that of as-received PLA pellets. It is convincing that the crystallization process can be accelerated by the well-structured PLA molecular chains when tailored into the fiber-like form. By decreasing HMW PCL concentration from 15 to 9wt%/v, the glass transition temperature (T ) of PCL within PLA/PCL blends is reduced whereas the of PLA is hardly identified in that its point has overlapped the melting peak of PCL. The different thermal properties in terms of and melting temperature (T ) may be influenced by the variation of fiber diameters as well as electrospinning process for the orientation of polymer chains [32]. In comparison to HMW PCL with PLA in blends, LMW PCL gives rise to an evident increase in the of PLA, but a considerable decline in the of PCL. The solvent effect on thermal... 

FIGURE 1.22 Orientation of polymer chains during injection molding. 

Orientation of Polymer Chains. It is usually reported that the orientation of polymer chains has relatively small effect on the neutral and alkaline hydrolytic degradation of PLA, in contrast to the enzymatic... 

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