Multicomponent amorphous polymers

Two terms for blends are commonly used in literature—miscible blend and compatible blend. The terminology recommended by Utracki (1) will be used in this article. By the miscible polymer blend, we mean a blend of two or more amorphous polymers homogeneous down to the molecular level and fulfilling the thermodynamic conditions for a miscible multicomponent system. An immiscible polymer blend is the blend that does not comply with the thermodynamic conditions of phase stability. The term compatible polymer blend indicates a commercially attractive polymer mixture that is visibly homogeneous, frequently with improved physical properties compared with the constituent polymers. 

For purposes of illustration, and for simplification, it will be assumed that the chemical reaction is restricted to the amorphous polymer phase, so that the crystalline phase remains pure. Furthermore, we shall assume that the composition of the amorphous phase is invariant with A even if the supernatant phase is multicomponent. Then... 

Properties of various amorphous polymers appear in Tables 1.4 and 1.5. For comparison, the properties of two commodity amorphous polymers, high-impact polystyrene (HIPS) and acrylonitrile/butadiene/ styrene (ABS), are included in Table 1.4. Since HIPS and ABS are multicomponent resins, their average property values are shown. Properties of the highly aromatic high-performance amorphous polymers... 

As demonstrated above, there is hardly any doubt regarding the existence of a linear relationship between Tg and the microhardness Hoi amorphous polymers characterized by dominating single, mostly C—C bonds in the main chain. This empirically derived analytical relationship (Eq. (13.8)) makes it possible to account quantitatively for the contribution of the soft component and/or phase to the overall microhardness of multicomponent and/or multiphase systems as demonstrated above. 

Bartos J (1996) Free volume microstmcture of amorphous polymers at glass transitirai temperatures from positron annihilation spectroscopy data. Colloid Polym Sci 274(1) 14—19 Blinov LM, Beresnev LA, Haase W (1995) Tilt angle, polarization and susceptibility and Landau expansion coefficients for multicomponent ferroelectric liquid crystal mixtures. Ferroelectrics 174 221-239... 

There are two possibilities first, nonuniform or multicomponent polymer materials. Internal stresses may appear due to differences in the properties of various parts of an article and the existence of phase boundaries. Second, uniform materials, which seem quite homogeneous, can be amorphous or polycrystalline.The physics of the development of residual stresses in such materials will be discussed in this section. 

The basic issue confronting the designer of polymer blend systems is how to guarantee good stress transfer between the components of the multicomponent system. Only in this way can the component s physical properties be efficiently used to give blends with the desired properties. One approach is to find blend systems that form miscible amorphous phases. In polyblends of this type, the various components have the thermodynamic potential for being mixed at the molecular level and the interactions between unlike components are quite strong. Since these systems form only one miscible amorphous phase, interphase stress transfer is not an issue and the physical properties of miscible blends approach and frequently exceed those expected for a random copolymer comprised of the same chemical constituents. 

Finally, it is worth mentioning that the linear relationship between H and Tg has been derived only from one-phase systems (amorphous homo- and copolymers. Table 3.2). However, it can be applied to explain the micromechanical behaviour of multicomponent or multiphase systems containing at least one liquid-like component or phase (see Chapter 5). Another peculiarity of the polymers listed in Table 3.2 is that their main chains comprise only single C-C, C-0 or C-N bonds... 

The interest in multicomponent materials, in the past, has led to many attempts to relate their mechanical behaviour to that of the constituent phases (Hull, 1981). Several theoretical developments have concentrated on the study of the elastic moduli of two-component systems (Arridge, 1975 Peterlin, 1973). Specifically, the application of composite theories to relationships between elastic modulus and microstructure applies for semicrystalline polymers exhibiting distinct crystalline and amorphous phases (Andrews, 1974). Furthermore, as discussed in Chapter 4, the elastic modulus has been shown to be correlated to microhardness for lamellar PE. In addition, H has been shown to be a property that describes a semicrystalline polymer as a composite material consisting of stiff (crystals) and soft, compliant elements. Application of this concept to lamellar PE involves, however, certain difficulties. This material has a microstructure that requires specific methods of analysis involving the calculation of the volume fraction of crystallized material, crystal shape and dimensions, etc. (Balta Calleja et al, 1981). 

Lignin is synthesised in plants from monomeric molecnles, whose functionality varies from two to four. Thus, both branched chain and the crosslinked structure may be formed. In plant tissue, the polymer chains of lignin are snrronnded by macromolecules of noncellulosic polysaccharides, with which they form an amorphous lignocarbohydrate matrix. The experimental methods that allow the stndy of the complex topology of macromolecules in a multicomponent solid composite are very limited. Therefore, most of the data are interpreted using theoretical methods developed from polymer chemistry. 

The significance of polymer blends has been an incentive for us to take also into consideration the advances in polymer blend preparation. The general characteristics of multicomponent polymeric systems included the formation and transitions of the complex structure in blends crystalline and amorphous components. Since the interactions between the blend components are of great importance the coupling agent activity and the modification of contacts between the components as well as general aspects of adhesion between polymers have been examined. 

For multicomponent systems, experiments with synthetic methods yield less information than with analytical methods, because the tie lines cannot be determined without additional experiments. A common synthetic method for polymer solutions is the (P-T-m ) experiment. An equilibrium cell is charged with a known amount of polymer, evacuated and thermostated to the measuring temperature. Then flie low-molecular mass components (gas, fluid, solvent) are added and the pressure inereases. These eomponents dissolve into the (amorphous or molten) polymer and the pressure in the equilibrium eell deereases. Therefore, this method is sometimes called pressure-decay method. Pressure and temperature are registered after equilibration. No samples are taken. The composition of the liquid phase is often obtained by weighing and using the material balance. The synthetic method is particularly suitable for measurements near critical states. Simultaneous determination of PVT data is possible. Details of experimental equipment can be found in the original papers compiled for this book and will not be presented here. 

Multiphase or multicomponent polymers can clearly be more complex structurally than single phase materials, for there is the distribution of the various phases to describe as well as their internal structure. Most polymer blends, block and graft copolymers and interpenetrating networks are multiphase systems. A major commercial set of multiphase polymer systems are the toughened, high impact or impact modified polymers. These are combinations of polymers with dispersed elastomer (rubber) particles in a continuous matrix. Most commonly the matrix is a glassy amorphous thermoplastic, but it can also be crystalline or a thermoset. The impact modified materials may be blends, block or graft copolymers or even all of these at once. 

Amorphous glassy polymers as natural nanocomposites puts forward to the foreground their study intercomponent interactions, that is, interactions nanoclusters - loosely packed matrix. This problem plays always one of the main roles at multiphase (multicomponent) systems consideration, since the indicated interactions or interfacial adhesion level defines to a great extent such systems properties [42]. Therefore, the authors of Ref. [43] studied the physical principles of intercomponent adhesion for natural nanocomposites on the example of PC. 

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