Solid amorphous polymers, lattice

Only recently have the lattice models been applied to solid amorphous and rubbery polymers (21-22). Table V contains a summary of the Interpretations of several solid polymers. In general, less extensive data are available on these systems. For PE ( ) and PIB ( ), the interpretation is based on carbon-lj Ti and NOE values. 

Wegner, however, established that radiation-induced solid-state polymerization of BCMO leads to a polymer morphology, which is incompatible with the so-called topochemical polymerization, i.e., a process in which monomer molecules are transformed into polymer without destruction of the crystal lattice 36). Electron microscopy, X-ray analysis and electron diffraction studies, have shown that polymerization starts at the edges and imperfections of the monomer crystals and that amorphous polymer is formed initially. Further transition from the amorphous state leads to the thermodynamically unstable monoclinic p-form. Density measurements indicate that the polymer is only 45-50% crystalline. The density of the amorphous poly-BCMO is 1.368 g/cm3 the density calculated for the crystalline polymer from crystallographic data of the p-form is 1.456 g/cm3. The density of the product of the radiation-induced solid-state polymerization is 1.41 g/cm3 36). 

A cluster model of pol5miers amorphous state structure allows introducing principally new treatment of structure defect (in the full sense of this term) for the indicated state [1,2], As it is known [3], real solids structure contains a considerable number of defects. The given concept is the basis of dislocations theory, widely applied for crystalline solids behavior description. Achieved in this field successes predetermine the attempts of authors number [4-11] to use the indicated concept in reference to amorphous polymers. Additionally used for crystalline lattices notions are often transposed to the structure of amorphous pol mers. As a rule, the basis for this transposition serves formal resemblance of stress - strain (a - ) curves for crystalline and amorphous solids. 

In the non-crystalline or amorphous solids (glasses and polymers) an arrangement of atoms in a lattice with a periodic order does not exist. 

The other class of motion only now being introduced into interpretive models is oscillatory motion. Anisotropic oscillatory motions of substituent groups have been considered by Chachaty (12) but not in conjunction with a lattice description of backbone motion. No attempt to develop a model based on oscillatory backbone rearrangements is known to these authors, and this avenue may be very important for the interpretation of concentrated solutions, rubbery or amorphous solids, and especially glassy polymers... 

The concept of polymer free volume is illustrated in Figure 2.22, which shows polymer specific volume (cm3/g) as a function of temperature. At high temperatures the polymer is in the rubbery state. Because the polymer chains do not pack perfectly, some unoccupied space—free volume—exists between the polymer chains. This free volume is over and above the space normally present between molecules in a crystal lattice free volume in a rubbery polymer results from its amorphous structure. Although this free volume is only a few percent of the total volume, it is sufficient to allow some rotation of segments of the polymer backbone at high temperatures. In this sense a rubbery polymer, although solid at the macroscopic level, has some of the characteristics of a liquid. As the temperature of the polymer decreases, the free volume also decreases. At the glass transition temperature, the free volume is reduced to a point at which the... 

Linear and branched polymers do not form crystalline solids because their long chains prevent efficient packing in a crystal lattice. Most polymer chains have crystalline regions and amorphous regions ... 

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