The Semicrystalline State

Can this building principle be transferred to polymers At first, one cannot see any reason why it should not be employed for polymers in the same way, in case we have sharp fractions. For a polymer with uniform molar mass, the same type of crystal, composed of extended straight chains with the end-groups assembled in planar interfaces, could be formed in principle and it would again represent the equilibrium state with the lowest free energy. How- 

In the previous chapter, we discussed liquid polymer systems. These exist in specific states selected by the laws of equilibrium thermodynamics. The rules that control structure formation during crystallization are different and this is an important point Structure formation is here governed by kinet-ical criteria rather than by equilibrium thermodynamics. What does this mean Indeed, here we encounter a new criterion The structure that develops at a given temperature is that with the maximum rate of development rather than that with the lowest free energy. As a consequence, treatment of 

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The present discussion of physical structure and properties is intended to serve merely as a basis for appraising the characteristics of various polymers here surveyed. The nature of the semicrystalline state in polymers and its influence on their physical properties will be dealt with in greater detail in a later chapter. 

As has been emphasized previously (IJ), the level of crystallinity is not the major determinant of the linewidth in the semicrystalline state. Rather the supermolecular structure or morphology is a major factor in governing the magnitude of the linewidth. Structural factors and crystallization conditions under which low density (branched) polyethylene forms... 

The fluidity of membranes primarily depends on their lipid composition and on temperature. At a specific transition temperature, membranes pass from a semicrystalline state to a more fluid state. The double bonds in the alkyl chains of unsaturated acyl residues in the membrane lipids disturb the semicrystalline state. The higher the proportion of unsaturated lipids present, therefore, the lower the transition temperature. The cholesterol content also influences membrane fluidity. While cholesterol increases the fluidity of semicrystalline, closely-packed membranes, it stabilizes fluid membranes that contain a high proportion of unsaturated lipids. 

Estimate the solubility and the heat of solution (sorption) of oxygen in poly(ethylene terephthalate) (PETP), both in the quenched amorphous glassy state and in the semicrystalline state (xc = 0.45). 

The first effect implies that the difference in order between the semicrystalline state and the mesophase is smaller than the difference between the mesophase and the isotropic melt. This indicates that the mesophases involved are highly otdered and the high values of the enthalpies and entropies may also be taken as another indication supporting this assumption. The photomicrograph in Figure 6 clearly shows that the mesophase is highly ordered. The mosaic domain is characterized by a uniform... 

The second effect, the well-known odd-even dependence, may be explained in terms of different degrees of order for polymers having odd or even numbers of methylene units in the spacer. The overall order in the semicrystalline state and in the mesophase is larger in the even-numbered samples than in the odd-numbered. 

In many publications the electron density difference is addressed as Ap (r) = p (r) — (p (r))y. Exercise Compute the average electron density (p)y of a sample from pure poly(ethylene terephtha-late) (PET) with a mass density of 1.38 g/cm. The chemical formula of PET is C10H8O4. Because PET is most probably in the semicrystalline state, it makes sense to stress that the computed electron density is a volume average ()y. 

Another use of Raman spectroscopy for quantitative analysis is the determination of percent crystallinity in polymers. Both the frequency and intensity of peaks can shift on going from the amorphous to the semicrystalline state for polymers. The percent crystallinity can be calculated with the help of chemometrics software. 

PBT is one of the faster crystallizing polymers. The high crystallization rate is a consequence of the considerable mobility that is provided by the butylene imit in the chain. Pure PBT has a crystalhnity in the range of 30-40%. The enthalpy of fusion, AHf°, of the 100% crystalline PBT is 142 J/g. The melting temperature, T, is about 225°C. The crystallization temperatirre, T, is approximately 180°C. The glass transition temperature, T, of the semicrystalline state is about 40 C. ... 

Crist B (2013) Chapter 3 structure of polycrystalline aggregates. In Piorkowska E, Rutledge G (eds) Handbook of polymer crystallization. Wiley, Hoboken de Rosa C, Auriemma F (2013) Crystals and crystallinity in polymers diffraction analysis of ordered and disordered crystals. Wiley, Hoboken Dettenmaier M, Fischer EW, Stamm M (1980) Calculation of small-angle neutrrai scattering by macromolecules in the semicrystalline state. Colloid Polym Sci 258(3) 343-349 Donald AM, Windle AH, Hanna S (2006) Liquid crystal polymers, 2nd edn. Cambridge University Press, Cambridge... 

Further cooling of the smectic phase may lead to crystallization or perhaps to the formation of a smectic glass. The semicrystalline state of the rigid-rod polymers is different from that of the flexible-chain polymers described in Chapter 7. The low segmental flexibility of the former prevents chain folding and the crystals should be of the fringed micelle type. 

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