Synthetic polymers; plastics, liquid crystals, nanomaterials: Practice Questions

A chemical plant is designed to manufacture long, continuous sections of plastic gutters and window frames. Which fabrication process is most appropriate for this type of production?

In the chemical modification of natural rubber via vulcanisation, sulfur is reacted with the polymer chains. What is the nature of the reaction that occurs at the site of the double bonds to create the cross-links?

Polymethyl methacrylate (PMMA) is a thermoplastic often used as a substitute for glass. Which of the following structural characteristics accounts for its high transparency?

Consider a bulk cube of a material with a side length of \(1 \text{ cm}\) and a collection of nanocubes of the same material, each with a side length of \(10 \text{ nm}\). By what factor is the surface area to volume ratio \((A/V)\) of a nanocube greater than that of the bulk cube?

Polylactide (PLA) is a popular polymeric biomaterial. Which of the following statements regarding the synthesis and properties of PLA is correct?

Liquid-crystalline behavior is often observed in molecules with a rigid, rod-like core. Suggest how the presence of a polar functional group at one end of such a molecule influences the formation of liquid crystal phases.

Gold nanoparticles can exhibit colors such as red or purple, which differ significantly from the yellow appearance of bulk gold. Suggest a reason for this phenomenon in terms of the interaction between light and matter at the nanoscale.

Explain why organic molecules that exhibit liquid crystalline properties typically possess a rigid, rod-like structural core and specify how this shape affects their behavior in the liquid state.

Polypropene (Polypropylene) is a major synthetic thermoplastic used in packaging and textiles.
(a) Draw the structural formula of the monomer required to produce polypropene.
(b) Write the chemical equation for the addition polymerisation of this monomer, showing the repeating unit and using (n) monomers.

Polyethylene (PE) is commercially produced as Low-Density Polyethylene (LDPE) and High-Density Polyethylene (HDPE).
(a) Describe the difference in the molecular structure, specifically referring to chain branching, between LDPE and HDPE.
(b) Explain why LDPE is less rigid and has a lower density and melting point than HDPE, referring to the packing efficiency and intermolecular forces between the polymer chains.
(c) Explain why the melting of a synthetic polymer like PE typically occurs over a wide temperature range rather than at a single sharp melting point.