The document describes an experiment using ARGET ATRP to synthesize PMMA of targeted molecular weights by varying the initiator concentration. Four trials were conducted but the actual molecular weights were lower than targeted and polydispersities were high. A kinetic model was created to predict molecular weight but did not closely match experimental results. Future work will use higher copper concentrations to reduce dead chains and improve polydispersity.

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Initiator Concentration vs. Theoretical Molecular Weight
Theoretical Mn
Initiator Concentration (M)
ARGET ATRP of PMMA with Targeted Molecular Weight
Derek Henry, Brandon Piercy, Mark Losego
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332
Technology: Activators ReGenerated by Electron Transfer Atom Transfer Radical Polymerization
(ARGET ATRP) is a form of controlled radical polymerization that allows for polymer growth to a
targeted molecular weight with low polydispersity and minimal contamination due to reactants.
Purpose: To construct a system capable of running ARGET ATRP and to write a computer script able
to model polymer growth and use them to synthesize PMMA of a predicted molecular weight.
The Polymerization Process
1
Cu(II)Br2Cu(I)Br
End Product:
n
2 3
The initiator reacts with
the copper to form a
radical.
The initiator reacts with
the monomer.
The chain propagates.
Conclusion and Future Work
After the first round of tests and GPC data, it is clear that PMMA
is being produced and that the computer model provides a rough
estimate of the molecular weight of the end product. High
polydispersity was caused by an excess of dead chains, which are
visible in the GPC data. In future experiments, higher
concentrations of copper will be used to speed up the reaction,
which reduces the amount of dead chains formed over time.
This will lower the polydispersity and close the gap between
targeted and actual molecular weight. Once that gap is closed,
synthesis of polystyrene will begin, followed by the synthesis of
block copolymers.
Data and Results
-4000
-2000
0
2000
4000
6000
8000
-5 0 5 10 15 20 25 30 35
GPC Results for 100K MN Trial
Time (min)
Asymmetric Curve
Solvent DataPMMA Data
𝑑 𝑃𝑖
•
𝑑𝑡
= −𝑘 𝑝
𝑃𝑖−1
•
𝑀 − 𝑘 𝑝 𝑃𝑖
•
𝑀 + 𝑘 𝑎 𝑃𝑖 𝑋 𝐶 − 𝑘 𝑑𝑎 𝑃𝑖
•
𝐶𝑋 − 𝑘 𝑡
𝑗
𝑃𝑖
•
𝑃𝑗
•
− 𝑘 𝑡𝑟 𝑃𝑖
•
𝑑 𝑃𝑖 𝑋
𝑑𝑡
= −𝑘 𝑎 𝑃𝑖 𝑋 𝐶 + 𝑘 𝑑𝑎 𝑃𝑖
•
[𝐶𝑋]
𝑑 𝑃𝑖
𝑑𝑡
=
𝑘 𝑡𝑐
2
𝑗=0
𝑖
𝑃𝑗
•
𝑃𝑖−𝑗
•
+ 𝑘 𝑡𝑑
𝑗
𝑃𝑖
•
𝑃𝑗
•
− 𝑘 𝑡𝑟
𝑃𝑖
•
200;2;0.007;0.07;0.07
ARGET ATRP Ratio
ATRP Reactions are standardized by a
single ratio or reactants, allowing easy
replication of experiments.
Controls
Molecular
Weight
Controls Polydispersity and
Rate of Reaction
The ratio is based on the known initial
concentration of the monomer. For these
experiments, [MMA]0 = 5 M
Experimental Procedure
The ARGET ATRP procedure runs in a
two-flask system attached to a schlenk
line. One flask is used to mix and degas
the reactants, which are transferred to
the other flask and heated for several
hours for the reaction to proceed.
Experiments
• Four separate trials of varying target
molecular weights, based on differing
initiator concentration
• Monomer: MMA
• Solvent: Anisole
• Initiator: Ethyl α-bromoisobutyrate
• Ligand: Me6TREN
• The same copper/ligand solution was
used for each trial
A 0.000385 M copper/ligand solution
was prepared to improve experiment
efficiency and reduce overall copper
concentration in reaction.
Schlenk Line
Mixing Flask with
bubbler
Reaction Flask
A reaction running in the oil
bath
Trial 4Trial 3
Trial 2Trial 1
Trials after solvent evaporation
Funding provided by:
A finished reaction
White color
means low
copper
contamination
Kinetic Model for Predicting Molecular Weight
To predict the molecular weight and polydispersity of the polymers, a
computer model was written in Wolfram Mathematica based on a previously
published differential system of kinetic equations:
The equations for a propagating radical chain, a dormant radical chain, and a dead chain.
Trial 1
Trial 2
Trial 3
Trial 4
Li et al. Macromolecular Reaction Engineering 5 467 (2011)
Polymer chains did
not reach theoretical
chain length in most
cases.
High polydispersity
varies wildly between
trials.
The asymmetric curve indicates a larger
proportion of smaller chains. This causes a
lower overall molecular weight and a higher
polydispersity.
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1.5
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1.8
1.9
2
2.1
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4
2 10
4
3 10
4
4 10
4
5 10
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6 10
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Polydispersity vs. Actual Molecular Weight
Polydispersity
Molecular Weight (kg/mol)
0
2 10
4
4 10
4
6 10
4
8 10
4
1 10
5
1.2 10
5
1 2 3 4
Theoretical vs. Actual Molecular Weight
Theoretical Mn
Actual Mn
Trial
The kinetic model was used
to calculate the different
molecular weights that
would be targeted for each
experiment, using the
initiator concentration as the
independent variable.