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

An alternating copolymer has a perfectly regular sequence of two different monomers (ABABAB), which arises when the reactivity ratios r1 and r2 are both close to zero.

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

Vulcanization introduces polysulfide (C-S-S-C) cross-links between polyisoprene chains via reaction with elemental sulfur, converting the linear rubber into an elastic three-dimensional network.

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

At equilibrium swelling, the elastic restoring force of the stretched cross-linked network exactly balances the thermodynamic driving force (free energy of mixing) for solvent absorption.

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

Polyurethanes are identified by the N-H stretch (~3300 cm⁻¹) from the urethane linkage and the C=O carbonyl stretch (~1700-1730 cm⁻¹) of the carbamate group.

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

Reptation theory (de Gennes) describes how an entangled polymer chain diffuses by wriggling along its own contour through a 'tube' formed by surrounding entanglements, like a snake (reptile) moving.

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Polymer Chemistry 3