0

2 104

4 104

6 104

8 104

1 105

1.2 105

0 0.01 0.02 0.03 0.04 0.05 0.06

Initiator Concentration vs. Theoretical Molecular Weight

Theoretical Mn

Initiator Concentration (M)

ARGET ATRP of PMMA with Targeted Molecular WeightDerek 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 Process1

Cu(II)Br2Cu(I)BrEnd 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 WorkAfter 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

𝑝𝑃𝑖−1• 𝑀 − 𝑘𝑝 𝑃𝑖

• 𝑀 + 𝑘𝑎 𝑃𝑖𝑋 𝐶 − 𝑘𝑑𝑎 𝑃𝑖• 𝐶𝑋 − 𝑘𝑡

𝑗

𝑃𝑖• 𝑃𝑗• − 𝑘𝑡𝑟 𝑃𝑖

•

𝑑 𝑃𝑖𝑋

𝑑𝑡= −𝑘𝑎 𝑃𝑖𝑋 𝐶 + 𝑘𝑑𝑎 𝑃𝑖

• [𝐶𝑋]

𝑑 𝑃𝑖𝑑𝑡=𝑘𝑡𝑐2

𝑗=0

𝑖

𝑃𝑗• 𝑃𝑖−𝑗• + 𝑘𝑡𝑑

𝑗

𝑃𝑖• 𝑃𝑗• − 𝑘

𝑡𝑟𝑃𝑖•

200;2;0.007;0.07;0.07

ARGET ATRP RatioATRP 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 MExperimental 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 FlaskA 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 WeightTo 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 3Trial 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.

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2

2.1

0 1 104

2 104

3 104

4 104

5 104

6 104

7 104

8 104

Polydispersity vs. Actual Molecular Weight

Polydispersity

Molecular Weight (kg/mol)

0

2 104

4 104

6 104

8 104

1 105

1.2 105

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.