MChem Master of Chemistry Polymer Chemistry

Question 1

Which mechanism describes the polymerization of styrene initiated by a free radical?

Accepted Answer

Chain-growth (addition) polymerization

Answer

Styrene undergoes chain-growth (addition) polymerization via a free-radical mechanism, where monomers add sequentially to a growing radical chain end.

Question 2

What is the degree of polymerization (DP) of a polymer sample with a number-average molecular weight (Mn) of 50,000 g/mol and a monomer molecular weight of 100 g/mol?

Accepted Answer

500

Answer

DP = Mn / M0 = 50,000 / 100 = 500, giving the average number of repeat units per chain.

Question 3

Which of the following best defines the dispersity (Đ) of a polymer sample?

Accepted Answer

Đ = Mw / Mn

Answer

Dispersity Đ = Mw/Mn (weight-average over number-average molecular weight), and a value of 1 indicates a perfectly monodisperse sample.

Question 4

In Ziegler-Natta polymerization of ethylene, what is the primary role of the titanium catalyst?

Accepted Answer

It acts as a coordination site that controls monomer insertion stereospecifically

Answer

The titanium center in Ziegler-Natta catalysts coordinates the monomer and controls the stereochemistry of insertion, enabling isotactic or syndiotactic polymer production.

Question 5

Which technique is most commonly used to determine the molecular weight distribution of a polymer?

Accepted Answer

Gel permeation chromatography (GPC/SEC)

Answer

Gel permeation chromatography (size exclusion chromatography) separates polymer chains by hydrodynamic volume, allowing determination of Mn, Mw, and dispersity.

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Polymer Chemistry