MChem Master of Chemistry Polymer Chemistry 3

Question 1

Which type of copolymer has monomers arranged in a repeating sequence (e.g., ABABAB...)?

Accepted Answer

Alternating copolymer

Answer

Random copolymer

Answer

Block copolymer

Answer

Graft copolymer

Question 2

In cross-linked polymer networks such as vulcanized rubber, what is the primary chemical change introduced during vulcanization?

Accepted Answer

Formation of polysulfide cross-links between polyisoprene chains via sulfur

Answer

Addition of plasticizers to lower the glass transition temperature

Answer

Introduction of ester linkages between chain ends

Answer

Grafting of styrene onto the rubber backbone

Question 3

The swelling of a cross-linked polymer network in a solvent is described by the Flory-Rehner theory. What two competing factors determine the equilibrium swelling?

Accepted Answer

Elastic restoring force of the network and the thermodynamic drive for mixing with solvent

Answer

Chain crystallization and thermal expansion

Answer

Surface tension and osmotic pressure across a membrane

Answer

Enthalpy of mixing and chain scission rate

Question 4

Which spectroscopic feature in FTIR is most diagnostic for identifying a polyurethane?

Accepted Answer

A strong C=O stretch near 1730 cm⁻¹ and N-H stretch near 3300 cm⁻¹

Answer

A broad O-H stretch at 2500-3300 cm⁻¹ typical of carboxylic acids

Answer

A sharp C≡N stretch at 2200 cm⁻¹

Answer

A strong C-F stretch at 1100 cm⁻¹

Question 5

What phenomenon is described by reptation theory in polymer dynamics?

Accepted Answer

The snake-like diffusion of a polymer chain through entanglements in a melt or concentrated solution

Answer

The coil-to-globule transition of a polymer chain in poor solvent

Answer

The crystallization of semi-crystalline polymers from the melt

Answer

The phase separation of block copolymers into ordered microstructures

Question 6

Block copolymers such as polystyrene-b-polybutadiene can undergo microphase separation. Which factor primarily determines the equilibrium morphology (spheres, cylinders, lamellae)?

Accepted Answer

The volume fraction of each block and the Flory-Huggins interaction parameter χ

Answer

The total molecular weight of the copolymer only

Answer

The solvent polarity used during processing

Answer

The rate of cooling from the melt

Question 7

Which end-group analysis method is most appropriate for determining the number-average molecular weight of a low-molecular-weight polyester (Mn < 5,000 g/mol)?

Accepted Answer

¹H NMR end-group analysis

Answer

Dynamic light scattering (DLS)

Answer

Osmometry using a semi-permeable membrane

Answer

Gel permeation chromatography (GPC)