Topic 1

Question 1

What is a polymer?

Answer 1

A chain of small molecules (monomers) linked together

Question 2

How do we make polymers?

Answer 2

Growth of polymer chain = propagation. For covalent polymers, polymerisation involves a transition from weak intermolecular interactions to strong intramolecular bonding

Question 3

What are the mechanisms of polymerisation?

Answer 3

Step growth and chain growth

Question 4

Describe the main features of step growth polymerisation

Answer 4

Condensation mechanism; growing chains combine with one another as well as with individual monomers.; polymer named after the functional group in the backbone

Question 5

Describe the main features of chain growth polymerisation

Answer 5

Addition mechanism; addition of single monomers to an active polymer chain end; polymer named poly(monomer)

Question 6

Describe the process of step growth polymer synthesis

Answer 6

All monomers are equally reactive; monomers react in pairs to form dimers; dimers grow simultaneously, forming many chains with different lengths; polymerisation stops when no more monomers are available to react

Question 7

Describe living polymer synthesis

Answer 7

Unique type of addition mechanism; still chain growth but no termination, enables molecular weight control i.e. control over the number of monomer units added to an initiator by using a capping agent (caps active chain end so very controlled addition of momomers). Monomer + initiator (+ capping agent) –> polymer

Question 8

Describe the process of chain growth polymer synthesis

Answer 8

Monomer + initiator –> polymer

Question 9

What is DP?

Answer 9

Degree of polymerisation

Question 10

What is row?

Answer 10

Conversion (between 0 and 1); 1 = full conversion/monomer consumption; 0 = no conversion/no polymer formed

Question 11

What is MW?

Answer 11

Molecular weight (Mn and Mw)

Question 12

What is DM?

Answer 12

Polydispersity index (Mw/Mn; always greater than 1 as Mw > Mn)

Question 13

What is Mn?

Answer 13

Number average molecular weight

Question 14

What is Mw?

Answer 14

Weight average molecular weight

Question 15

True or false - small molecules possess a well-defined molecular weight that can be defined as a population of molecules of identical mass.

Answer 15

True. For a given small molecule, every molecule in a sample will have the same mass (ignoring variations in isotope)

Question 16

True or false - natural polymers such as DNA and proteins possess a well-defined molecular weight that can be defined as a population of molecules of identical mass.

Answer 16

True. DNA and proteins are what is known as sequence-defined polymers - they have a known sequence and number of monomers. For example, green fluorescent protein is a poly(peptide) that is precisely 238 amino acids long. All molecules in a sample are therefore the same mass (ignoring variations in isotope)

Question 17

True or false - synthetic polymers such as polystyrene possess a well-defined molecular weight that can be defined as a population of molecules of identical mass.

Answer 17

False. Synthetic polymers - even those made by controlled polymerisation techniques - consist of a mixture of chains of different lengths and therefore different masses

Question 18

True or false - the size of a polymer in solution is related to its molecular weight.

Answer 18

True. As polymers get larger the volume they occupy in solution changes. Usually, the heavier a polymer chain, the bigger its size in solution

Question 19

What is the radius of gyration (Rg)?

Answer 19

RMS distance of a chain segment from the centre of mass of the molecule. Root mean square (Rrms) end to end distance. Polymer is assumed to have free rotation about the bond with no restrictions.

Question 20

What is GPC?

Answer 20

Gel permeation chromatography

Question 21

What is SEC?

Answer 21

Size exclusion chromatography

Question 22

What is the principle of GPC/SEC?

Answer 22

A polymer solution is washed down a chromatographic column packed with porous particles. Separation is based on size in solution; size exclusion or restricted diffusion principle; no interaction between the media surface and the sample; polymer size in solution is dependent on solvent and temperature

Question 23

What is a GPC system composed of?

Answer 23

Solvent supply (mobile phase) –> solvent delivery system (ensure a constant flow) –> injector (where sample is inserted) –> column(s) (different columns for different MW ranges) –> detector (measures difference in refractive index of sample coming out c.f. just solvent) –> data system (analysis)

Question 24

Describe peak integration in GPC

Answer 24

The sample peak when integrated can be assumed to be a histogram consisting of a number of individual ‘slices’

Question 25

How are GPC columns calibrated using narrow standards?

Answer 25

Chromatograph a series of well characterised, narrow polydispersity polymer standards; plot peak retention time (RT) vs peak log molecular weight (logM); fit the data using a mathematical function; the calibration curve will be characteristic of the GPC column set used

Question 26

True or false - two polymer samples of different chemistry but possessing exactly the same molecular weight distributions will always elute the same during an SEC experiment.

Answer 26

False - the chemistry of a polymer affects its size in solution, and therefore when it elutes during an SEC experiment. As a result, polymers with exactly the same molecular weight distribution but differing chemistry will almost always elute differently.