RAFT and Other ProcessesRyan Gunckel4/19/2012Mentor Program – Iowa State University

RAFT Overview Reversible Addition-Fragmentation chain

Transfer Often referred to as ‘living radical

polymerization’ because of its absence of a termination process.

Allows for easy control of the molecular weight and composition of the polymer produced.

RAFT Process During RAFT polymerization, a propagating

polymer is introduced to a thiocarbonylthio compound and two species are formed: a dormant chain and a new propagating chain.

This new radical reacts with a monomer to produce another propagating radical.

The two propagating radicals undergo rapid equilibrium along with the polymeric thiocarbonylthio compounds to produce chains in equilibrium.

RAFT Process (cont.) By controlling the amount of monomer,

thiocarbonylthio compounds, and radicals that react, the molecular weight and structure of the polymer produced can be easily controlled.

Very cost effective and does not require overly-hazardous materials or conditions in order to undergo the reaction.

Other Processes Aside from RAFT, there are other lab

procedures that I used throughout the Mentor Program, such as:

Cleaning Styrene/ Soybean Oil Degasing Styrene Using the ‘RotoVap’ machine NMR machine Initiator Crystalization

Cleaning Styrene/Soybean Oil Used to remove any

contaminants & water from the fluid.

When cleaning Styrene, filling the filter tube with alumina .

Soybean Oil, however, requires the alternation of alumina and inhibitor removal (hydroquinone).

Argon is pumped through to help speed the process.

RotoVap Used to remove a liquid

from a mixture of two liquids. Difference in boiling points.

In our case, the removal of THF from the soybean oil after it has been cleaned.

Condenses it back into liquid form using liquid nitrogen, and then lets it drip into the flask at the bottom.

Degasing Styrene Set up and maintained

the vacuum pump (using liquid nitrogen).

Used alteration of freezing and thawing under vacuum to remove any oxygen from the styrene

AIBN Azobisisobutyronitrile It decomposes into two 2-cyanoprop-2-yl

molecules (and nitrogen), that can each grow chains from their radicals.

Initiator Crystallization Simple process of dissolving the initiator

(AIBN) in ethanol (at 40 degrees Celsius) for 15 minutes and then cooling rapidly to form a crystalline structure of the initiator. The ethanol is then filtered out so that just the initiator is left.

The crystalized AIBN produced is then used in the RAFT polymerization process.

All Together… After the soybean oil/styrene has been

cleaned and RotoVap-ed, a pre-determined amount is dissolved in dioxane.

A pre-determined amount of AIBN (initiator) and CTA (radical) is also added.

The mixture is then heated and stirred for a given amount of time in order for the reaction to proceed and the desired molecular weight is reached.

All Together…(cont.) After the reaction is complete, a small sample is

evaluated by GPC to determine the molecular weight of certain blocks within the entire molecule.

Polymer is precipitated in Methanol and Water and vacuum oven dried.

The dried polymer is redissolved and the second monomer is added with initiator and allowed to react.

Repeat!

Results Diblocks and Triblocks were synthesized

with different molecular weights and different styrene/soy bean concentrations.

NMR Machine Uses magnetic field and the

spin states of the nucleus (when introduced to a magnetic field) to determine the molecular weight of the compound and its structure.

Can also be used to determine the molecular weight of different compounds.

Dissolved a miniscule amount of substance into chloroform and then inserted it into top of machine.

NMR (Continued) When observing the

graph output of the NMR machine, certain peaks (indicating presence of hydrogen molecules) are visible.

The integral of these peaks is equal to the molecular weight (as determined by a GPC machine) of a certain section of the molecule.

Thanks!I would like to thank Dr. Cochran for

giving me this opportunity to work for him and give me experience working in a lab. It has always been a dream of mine to go into research and discover new things and formulate new ideas. Also, I would like to personally thank Nacu for guiding me and showing me what it is like to work in a lab!