1. Polymer and Nanoparticle Fabrication
Polymer Folding via Intramolecular Cross-linking by Atom Transfer Radical Coupling (ATRC)
Cashman F. Mark, Hanlon M. Ashley, Dickinson M. Jessica, and Erik B. Berda. Department of Chemistry, University of New Hampshire.
Introduction
Polymer and Nanoparticle Fabrication
Work in Progress
Work to elucidate what influences the efficiency of single-chain nanoparticle (SCNP) collapse via ATRC was undertaken. Three MMA copolymers of varying pendant functionality and percent monomer incorporation were synthesized via RAFT polymerization as to utilize it’s living-control capabilities to achieve precise molecular weight control. SCNP formation of these polymer candidates was facilitated via copper-initiated Atom-Transfer Radical-Coupling (ATRC), by which the pendant halide moieties underwent radical-initiated, intra-chain, bi-termination, causing each polymer chain to radicalize and collapse upon the loss of bromide. The following collapse results were analyzed to elucidate information about the primary contributing factors in ATRC mediated SCNP fabrication.
Figure 5: Synthetic scheme for synthesis of MeBrEMA monomer and polymer
Work currently in progress is to improve the experimental procedure for the synthesis of the MeBrEMA monomer. To do this, the column separation must be improved in order to efficiently isolate the monomer from undesired byproducts. Once sufficient supply of purified co-monomer is obtained, the finicky RAFT synthesis can be smoothed out. Further RAFT syntheses on co-monomer MeBrEMA and Me2BrEMA will be performed with the goal of yielding proper molecular weight (20,000 g/mol) polymers of 10% or 20% co-monomer incorporation, which can then be collapsed and results compared to those already gathered from the PhBrEMA collapses.
Figure 2: Synthetic schemes and NMR results of parent polymer syntheses (Me2BrEMA and PhBrEMA syntheses exhibited success through NMR analysis).
Scheme 1: General scheme for polymer syntheses of the three co-monomers with MMA, then corresponding polymer to SCNP collapse.
Future Work
Monomer Syntheses
NP1.2
NP1.3
To further understand exactly what factors contribute to the intra-chain collapse, how much, and why, further iterations of each copolymer with various percent monomer incorporation, various molecular weight, various pendant functionalities, various-sized spacer unit incorporation should be fabricated and quantitative kinetic studies via monitored GPC collapses should be performed.
Acknowledgements
The author would like to graciously thank the Army Research Office for support through award W911NF , and NIST for support through award 70NANB15H060 as well as Dr. Erik Berda, and Ashley M Hanlon sharing their time and expertise.
Sample  Mn Mw
PDI
Rh(v)n
[n]n
a-value
% Incorp.
P1.2
2.274×104 
2.319×104 
1.02 
4.383 
23.537 
0.512
~10%
NP1.2
5.182×104
5.252×104 
1.014 
3.819 
6.917
1.301 
Sample  Mn Mw
PDI
Rh(v)n
[n]n
a-value
% Incorp.
P1.3
1.073×104
1.097×104
1.022 
3.212 
19.649 
0.992 
~50%
NP1.3
1.002×104
1.110×104
1.108  --
References
1. Lyon, C. K.; Prasher, A.; Hanlon, A. M.; Tuten, B. T.; Tooley, C. A.; Frank, P. G.; Berda, E. B. Polym. Chem. 2015, 6,
2. Das, A.; Theato, P. Activated Ester Containing Polymers: Opportunities and Challenges for the Design of Functional Macromolecules. Chemical Reviews 2015.
Figure 1: Synthetic schemes for synthesis of co-monomer units: MeBrEMA, ME2BrEMA, and PhBrEMA.
Figure 3: : ARTC, intra-chain cross-linking results of 1.2p to 1.2np
Figure 4: ARTC, intra-chain cross-linking results of 1.3p to 1.3np