PSI - Issue 17

Michał Kwietniewski et al. / Procedia Structural Integrity 17 (2019) 154 – 161 Michał Kwietniewski / Structural Integrity Procedia 00 (2019) 000 – 000

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3. Spatial structure and its influence on the properties of polymers

Depending on the physical structure of the chain, polymers are divided into linear, branched and cross-linked ones. An example of polymers which chains have a linear structure is polystyrene and poly (vinyl chloride), their chains do not have branches, while side groups may exist. Branched polymers are homopolymers, e.g. low-density polyethylene as well as graft copolymers, in turn an example of crosslinked polymers are thermosetting polymers which chains are connected by crosslinks to form a lattice. The type of construction of polymer chains is illustrated in Fig. 4. a

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Fig. 4. Polymer chain structure: (a) linear; (b) branched; (c) cross-linked one; Garcia (2014).

Linear or branched polymer chains depicted schematically in Fig. 4 are rarely in straight form and most often take on a globular, lamellar or rectal shape. Conformational forms of the polymer chain are illustrated Fig. 5.

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Fig. 5. Formation of polymer main chain: (a) globular form (ball); (b) lamellar form (folded); (c) rectal form (zigzag plane); Garcia (2014).

Linear or branched polymer chains depicted schematically in Fig. 4 are rarely in straight form and most often take on a globular, lamellar or rectal shape. Conformational forms of the polymer chain are illustrated Fig. 5. Polymers are composed of macromolecule chains containing repeating units – so called "mers". Polyethylene (PE) is an example of a polymer. A molecule (mer) of C2H4 ethylene and a poly (macroparticle) of polytylene (C2H4)n were shown in Fig. 6. In addition to pure polymers (consisting of one type of mers), in practice combinations of various polymer chains are often used, as are alloys in metals. Examples of "polymer alloys" are copolymers, e.g. ABS (which chains consist of durable but brittle acrylonitrile A and styrene S molecules, with grafted branches of elastic butadiene B, making the material less brittle (Fig. 7). Atoms and molecules are linked in strong polymer chains by strong covalent bonds, but the van der Waals' weak physical bonds act between the chains, allowing the chains to move easily relative to each other under load - hence the good deformability of linear-structured polymers. Chains can also be linked to each other by strong covalent