States of Order in Polymers

Optical isomerism is possible whenever the substituents X contain centers of asymmetry polymers obtained fi om pure enantiomeric monomers are optically active. However, the specific rotation of the polymers is in general clearly different from that of the monomers. Optical isomerism is also possible when asymmetrically substituted carbon atoms are placed in the main chain (see Example 3.25a) (Fig. 1.6). 

The above considerations concerning structural isomerism and stereoisomerism are not restricted to homopolymers but can occur in copolymers as well. Here, moreover, structural isomerism can have its origin additionally in different distributions of two (or more) types of constitutional repeating units within the polymer chain. 

For the nomenclature of copolymers it is commOTi either to use the full name, for example statistic copolymer of styrene and butadiene , or to use the abbreviations recommended by lUPAC. Some cases are listed in Table 1.1. 

Aside from chemical composition and chain length the properties of macromolecu-lar substances are substantially determined by the conformation and configuration of the individual macromolecules. Isolated macromolecules do not take up a 

Polymers can exist as liquids, as elastomers or as solids but can be transferred into the gaseous state only tmder very special conditions as are realized in, for example, MALDI mass spectrometry. This is because their molecular weight is so high that thermal degradation sets in before they start to evaporate. Only a few polymers are technically applied in the liquid state (silicon oils, specialty rubbers) but most polymers are applied either as elastomers, or as rigid amorphous or semicrystalline solids. 

Statistic copolymer Poly(A-stot-B) e.g., Poly(styrene-stflf-butadiene) 

Graft copolymer Poly (A)-graft- Poly( B) e.g.,Poly(styrene)-gr j/f-Poly(butadiene) 

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The processes of ordering in polymer systems consisting of linear polymers are related, at least on one level of supermolecular organization, to the development of a predominant localization of macromolecules (or their parts) along some directions the orientation axes, i.e. to the transition of the system into the oriented state. The most simple and most widely spread type of polymer orientation is the uniaxial orientation, i.e. the one-dimensional orientation in the direction of the axes of macromolecules. 

The blend of poly(bisphenol A carbonate)-(poly(caprolactone) PC-PCL is particularly unusual in that both polymers are capable of crystallization and FT-IR has been used to study the state of order in these blends as a function of the method of preparation 254,255). In this case, PCL is a macromolecular plasticizer for PC. The PCL becomes progressively less crystalline as the concentration of PC increases. PC is amorphous if the blend is cast from methylene chloride but semicrystalline if cast from tetrahydrofuran. When PC in the pure form is exposed to acetone, it will not crystallize, but in the blend, exposure of acetone causes the PC to crystallize which emphasizes the additional mobility of the PC in the blend. 

Polypyrrole containing tetrasulphonated metallophtha-locyanines (PPy-MPcTs) has been intensively studied by Saunders and co-workers. The state of order in complexes with M = Cu, Co, Fe and Ni is comparable to that of PPy-pTS, but conductivity is lower and less environmentally stable [243,244]. A polymer synthesized from /V-methylpyrrole (PNMePy-CoPcTs) is clearly less ordered than the polymers from plain pyrrole. This is a likely result of the twisted character of the chain, as discussed earlier. The x-ray pattern of PNMePy-CoPcTs appears to have considerable contributions from aggregates of counteranions. For the... 

Despite of the unsolved problem of the colour changes the absorption behaviour of the polymer can be used to deduce information on the state of order in lipid layer structures and on phase transitions in those structures. This has recently been demonstrated studying the morphology of mixed multilayers... 

The effect of the chemical ermstitution of the crosslinker oti the local topology of the network is the second new feature to be considered. If the crosslinker molecule is flexible it can behave like an isotropic solvent. In that case, essentially only the phase transition and phase transformatiOTi temperatures of the LC phase are affected [90]. If, however, the chemical constitution resembles that of a mesogen of the constituent polymer backbone, the history of the crosslinking process becomes important. Under these conditions the crossUnker adopts the state of order in which the final crosslink process of the network occurs and thus determines the local topology of the crosslink [120,121]. The mechanical properties and the reorientational behavior are considerably modified for networks with the same chemical constitution but crosslinked either in the isotropic or in the liquid crystalline state [122-124]. Other important aspects of the local topology at the crosslink concern the phase transformation behavior [125] as well as the positional ordering in smectic systems [126]. 

Crystallinity Crystallinity bands are often assigned for polymer molecules in conjunction with the parameters of other techniques, such as density and x-ray diffraction. They describe the state of order in an investigated polymer molecule. In the spectmm of poly(vinyl alcohol), for example, the absorption band at 1141 cm is assigned to the crystallinity of the molecule. The degree of crystallinity is measured by the intensity of the band at 1141 cm which matches the density of the molecule. Figure 17.24 shows this phenomenon. 

The advantages of the vibrational methods are that they are nondestructive, fast, and easy to use, and that remote measurement can be achieved through use of optic-fiber technology. Vibrational spectroscopic techniques provide methods of determining the chemical structure of a polymer and have the advantage that the methods are applicable to all polymers regardless of the phase or state of order in the system. The complete analysis of any type or shape of a polymer sample, from raw material via intermediate to final product, is possible on an as it is basis in the majority of cases. 

After having considered the structural behavior of single chains we turn now to the collective properties of polymers in bulk phases and discuss in this chapter liquid states of order. Liquid polymers are in thermal equilibrium, so that statistical thermodynamics can be applied. At first view one might think that theoretical analysis presents a formidable problem since each polymer may interact with many other chains. This multitude of interactions of course can create a complex situation, however, cases also exist, where conditions allow for a facilitated treatment. Important representatives for simpler behavior are melts and liquid polymer mixtures, and the basic reason is easy to see As here each monomer encounters, on average, the same surroundings, the chain as a whole experiences in summary a mean field , thus fulfilling the requirements for an application of a well established theoretical scheme, the mean-field treatment . We shall deal with this approach in the second part of this chapter, when discussing the properties of polymer mixtures. 

One field of materials science for which FT-IR imaging has proved extraordinarily important, from both scientific and practical aspects, is that of polymer analysis and polymer physics. In order to illustrate the broad range of applicability of these disciplines with a special focus on polymer blends, some selected applications will be discussed in detail these range from phase separation and characterization of the state of order in biopolymer blends, to the use of polarized radiation to produce thickness and anisotropy images of inhomogeneously deformed polymer films. 

One further application of FT-IR imaging spectroscopy is its combination with DSC. As well as allowing the detection of phase separation in polymer blends (as described above), information on the state of order in blend films also becomes... 

A number of new surface analysis techniques have also become available with the advent of high-brightness synchrotron x-ray sources. Grazing incidence x-ray diffraction methods now allow one to elucidate the state of order in the 5 nanometers just below polymer surfaces, while near-edge absorption of polarized soft x-rays can interrogate the orientation of molecular segments of polymers at surfaces. 

In another study Milehev and Landau [27] investigated in detail the transition from a disordered state of a polydisperse polymer melt to an ordered (liquid erystalline) state, whieh oeeurs in systems of GM when the ehains are eonsidered as semiflexible. It turns out that in two dimensions this order-disorder transition is a eontinuous seeond-order transformation whereas in 3d the simulational results show a diseontinuous first-order transformation. Comprehensive finite-size analysis [27] has established... 

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