RAFT and Other Processes Ryan Gunckel 4/19/2012 Mentor 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!