Chain segment organization

Figure 5. Scheme of primary chain structure of segmented polyurethane elastomers and chain segment organization. 

Noncrystalline domains in fibers are not stmctureless, but the stmctural organization of the polymer chains or chain segments is difficult to evaluate, just as it is difficult to evaluate the stmcture of Hquids. No direct methods are available, but various combinations of physicochemical methods such as x-ray diffraction, birefringence, density, mechanical response, and thermal behavior, have been used to deduce physical quantities that can be used to describe the stmcture of the noncrystalline domains. Among these quantities are the amorphous orientation function and the amorphous density, which can be related to some of the important physical properties of fibers. 

Re-organization of amorphous chain segments adjacent to crystallite surfaces leads to crystallite thickening. These segments align themselves to form additional crystalline unit cells that increase the c dimensions of the crystallites. 

In the broadest terms, the rate of polymer crystallization is increased by factors that increase the free energy difference between the amorphous and crystalline states and factors that favor the re-organization of amorphous chain segments. The factors that influence the crystallization rate fall into two categories molecular characteristics and external conditions. Molecular... 

While the lamellar structures present in spherulites are similar to those present in polymer single crystals, the folding of chains in spherulites is less organized. Further, the structures that exist between these lamellar structures are generally occupied by amorphous structures including atactic chain segments, low molecular weight chains, and impurities. 

The resulting star-like macromers with CTA were solid materials with distinct crystallinity, even at 20 and 40% HPL (Fig. 6). This suggests that even short CTA chains (i.e., DP 12) have the ability to organize into a crystalline lattice, thereby serving as pseudo-crosslinks. Depending on the chemical nature, and the molecular weight, multiphase materials result with variable mechanical properties. Above Tm of the chain segment,... 

The intention of this brief survey has been to demonstrate that besides the "classical" aspects of isotropic polymer solutions and the amorphous or partially crystalline state of polymers, a broad variety of anisotropic structures exist, which can be induced by definable primary structures of the macromolecules. Rigid rod-like macromolecules give rise to nematic or smectic organization, while amphiphilic monomer units or amphiphilic and incompatible chain segments cause ordered micellar-like aggregation in solution or bulk. The outstanding features of these systems are determined by their super-molecular structure rather than by the chemistry of the macromolecules. The anisotropic phase structures or ordered incompatible microphases offer new properties and aspects for application. 

To summarize, it must be assumed that amorphous PC does not exhibit strong intermolecular spatial and orientational correlations between chain segments. This result is consistent with the fact that PC chains are highly entangled (see Sect. 4.2). It is believed that, up to the present time, insufficient experimental evidence has been provided to prove the existence of some sort of molecular organization in glassy poly-... 

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