Crystalline polymer solids

The heterogeneity of the crystalline polymer solid is accentuated still more in the case of mechanical properties by the enormous mechanical anisotropy of the crystals and the large difference in the elastic moduli of the crystalline and amorphous components. With polyethylene, the elastic modulus of the crystals is 3452 or 2403 X 1010 dynes/cm2 in the chain direction (E ) and 4 X 1010 dynes/cm2 in the lateral direction (E ) (2, 3). The elastic modulus of the amorphous component (Ea) of polyethylene is 109-1010 dynes/cm2 (4). This is significantly less than Eu and Ebut at least 10 times the elastic modulus of a rubber that has about five monomers in the chain segments between the crosslinks. This is quite surprising since room temperature is far above the glass transition temperature of polyethylene (Tg is either —20°C or — 120°C), and therefore one would expect a fully developed rubbery... 

The complicated morphology of crystalline polymer solids and the coexistence of crystalline and amorphous phases make the stress and strain fields extremely nonhomogeneous and anisotropic. The actual local strain in the amorphous component is usually greater and that in the crystalline component is smaller than the macroscopic strain. In the composite structure, the crystal lamellae and taut tie molecules act as force transmitters, and the amorphous layers are the main contributors to the strain. Hence in a very rough approximation, the Lennard-Jones or Morse type force field between adjacent macro-molecular chain sections (6, 7) describes fairly well the initial reversible stress-strain relation of a spherulitic polymer solid almost up to the yield point, i.e. up to a true strain of about 10%. 

Wide-angle X-ray scattering (WAXS), SAXS, optical birefringence, IR dichroism and light scattering can be used for the detection and measurement of local and macroscopic orientation. One has mainly the following four cases of oriented crystalline polymer solid ... 

The amorphous component of the crystalline polymer solid contains beyond the amorphous component of single crystals, i.e. crystal defects (linear vacancies, kinks, and interstitials), chain folds and free chain ends, as new elements the rejected non-crystallisable impurities and tie molecules. The former concentrate on the outer boundaries of lamella stacks and spherulites, the latter in the amorphous layers separating the lamellae of the same stack. With the exception of impurities all other components of the amorphous phase are intimately connected with the crystals and cannot be physically separated from them or moved independently of them. 

Peterlin, A. (1975) Structural model of mechanical properties and failure of crystalline polymer solids with fibrous structure. Int. J. Fracture, 11, 761. 

Han and Pan (2009) compared degradation maps for amorphous (dashed lines) and semi-crystalline polymers (solid lines), which is reproduced in Figure 6.8. FuU details of the calculation can be found in the paper by Han and Pan (2009). It can be observed... 

Mesoscale simulations model a material as a collection of units, called beads. Each bead might represent a substructure, molecule, monomer, micelle, micro-crystalline domain, solid particle, or an arbitrary region of a fluid. Multiple beads might be connected, typically by a harmonic potential, in order to model a polymer. A simulation is then conducted in which there is an interaction potential between beads and sometimes dynamical equations of motion. This is very hard to do with extremely large molecular dynamics calculations because they would have to be very accurate to correctly reflect the small free energy differences between microstates. There are algorithms for determining an appropriate bead size from molecular dynamics and Monte Carlo simulations. 

Solid state materials have been studied by nuclear magnetic resonance methods over 30 years. In 1953 Wilson and Pake ) carried out a line shape analysis of a partially crystalline polymer. They noted a spectrum consisting of superimposed broad and narrow lines which they ascribed to rigid crystalline and amorphous material respectively. More recently several books and large articles have reviewed the tremendous developments in this field, particularly including those of McBrierty and Douglas 2) and the Faraday Symposium (1978)3) —on which this introduction is largely based. 

Smectic liquid crystalline polymer 51 Solid echo 32 ---spectra 37, 39... 

Kitamaru, R, Phase Structure of Polyethylene and Other Crystalline Polymers by Solid-State l3C/MNR.VoL 137, pp 41-102. 

In extraction from a polymer/additive solid matrix the rate-determining step in the extraction process is governed by the interaction of the solvent of sufficient dissolution power with the matrix and the removal of the analyte (cf. Section 3.4.1.3). There appears to exist a direct relationship between degree of swelling and efficiency of extraction. The amount of C02 absorbed depends on temperature, pressure and the polymer concerned. Crystalline polymers are-not surprisingly-plasticised less... 

The enthalpic change from the solid to the liquid-like phase of a semi-crystalline polymer can be obtained from DSC [16]. The mass-based degree of crystallinity (XI)SC) is calculated as the ratio of the heat of fusion of the sample (AH) and the value per mole of purely crystalline polymer (AHc). 

D.E. Axelson, Carbon—13 Solid State NMR of Crystalline Polymers, In R.A. Komoroski (Ed.), High Resolution NMR Spectroscopy of Synthetic Polymers in Bulk, VCH, E>eerfield Beach, Florida, USA, 1986. 

Figure 8. Solid-state polymerization of diacetylenes. A crystalline array of monomer units polymerizes through intermediate states to the final crystalline polymer chain.

Another example of solid-state polymerisation is polymerisation of diacetylene derivatives which results in the formation of highly crystalline polymer that also conducts electricity. 

The optical properties of bottles are a matter of crystallinity affected by nucle-ation, depending on the content and size of light-scattering polymer solids. The purity of the raw materials and the cleanness of the reactors are prerequisites for satisfactory quality. Bottle polymer should display as little contaminations as possible. The detection of impurities is carried out by the same methods as mentioned above. Thorough filtration of the polymer is therefore mandatory. It should... 

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