Lecture handout including QS - Department of Materials Science ...

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BH20 Course B: Materials for Devices BH20 A few examples of common polymers with different side-groups: Monomer Polyvinylchloride (PVC) Polypropylene Polystyrene The side-groups (Cl, or CH 3 , or C 6 H 5 in the above examples) may be arranged in different ways along the chain, which defines the molecule’s configuration, or tacticity. Considering the chain in the all trans conformation … ... in the isotactic arrangement, the side-group is always on the same side: …. the syndiotactic arrangement has the side-group on alternate sides: … and the side-groups distributed randomly corresponds to an atactic arrangement:
BH21 Course B: Materials for Devices BH21 Polyvinylidene fluoride (PVDF) e.g. all trans conformation: The resultant charge imbalance, across the molecule, leads to technologically important electronic properties (to be discussed later in the course). Polymer Microstructure and Properties Linear chain polymers typically form a network of entangled chains. At relatively high temperatures, or in a dilute solution, conformational changes mean that the chains can flex and coil, and slide around each other. As the temperature is lowered there is less thermal activation and, as the polymer contracts, less space for the chains to move around in, so that these processes are restricted and the polymer becomes more and more viscous. Large side-groups, side branches and cross links between chains can reduce mobility further. Small molecules can be added to a polymer to space out the chains and increase mobility. These small molecule additives are called plasticizers. A rubber is a cross-linked network: the chain segments between cross-links are free to twist and flex by conformational changes (rubbery-ness!), but they cannot slide past each other to give permanent shape changes.
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Lecture handout including QS - Department of Materials Science ...

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