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
π ππβ’
ππ‘= βπ
πππβ1β’ π β ππ ππ
β’ π + ππ πππ πΆ β πππ ππβ’ πΆπ β ππ‘
π
ππβ’ ππβ’ β ππ‘π ππ
β’
π πππ
ππ‘= βππ πππ πΆ + πππ ππ
β’ [πΆπ]
π ππππ‘=ππ‘π2
π=0
π
ππβ’ ππβπβ’ + ππ‘π
π
ππβ’ ππβ’ β π
π‘πππβ’
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.
Experimentsβ’ Four separate trials of varying target
molecular weights, based on differing initiator concentration
β’ Monomer: MMAβ’ Solvent: Anisoleβ’ Initiator: Ethyl Ξ±-bromoisobutyrateβ’ Ligand: Me6TRENβ’ 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.
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