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

Step-growth polymerization

Answer

Ring-opening metathesis polymerization

Answer

Cationic coordination polymerization

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

50

Answer

5,000

Answer

50,000

Question 3

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

Accepted Answer

Đ = Mw / Mn

Answer

Đ = Mn / Mw

Answer

Đ = Mz / Mw

Answer

Đ = Mn / Mz

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

It acts as a free-radical initiator

Answer

It provides a cationic active center for ionic polymerization

Answer

It opens strained ring monomers via metathesis

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

Nuclear magnetic resonance (NMR) spectroscopy

Answer

Differential scanning calorimetry (DSC)

Answer

Thermogravimetric analysis (TGA)

Question 6

What is the glass transition temperature (Tg) of a polymer?

Accepted Answer

The temperature above which amorphous regions transition from a glassy to a rubbery state

Answer

The temperature at which the polymer crystallizes from the melt

Answer

The melting point of crystalline polymer domains

Answer

The temperature at which thermal degradation begins

Question 7

In living anionic polymerization of styrene using n-BuLi as initiator, why is the dispersity typically very low (Đ ≈ 1.05)?

Accepted Answer

There are no termination or chain-transfer reactions, so all chains grow at the same rate

Answer

Termination reactions are very fast, limiting chain length

Answer

The ionic mechanism inherently produces only oligomers

Answer

Chain transfer to monomer dominates, creating uniform chain lengths