Many formulation and nanotechnology requirements for polymeric
materials include well-defined molecular characteristics (molar
mass, composition, architecture, etc.) Objective
To create new combinatorial library fabrication techniques
that enable integration of these variables into existing NCMC
and Polymers Division measurements
Polymer Formulation on Chip.
Our goal is to demonstrate that polymer synthesis can be an
integral part of the factory on a chip.
Experimental
Our experimental approach involves manipulation of microfluidic
devices and environments to synthesize libraries of polymers,
either as confined, continuous gradients or discrete samples.
We provide three examples of this strategy here
1. Continuous flow reactors
can be constructed on chip for rapidly changing reaction
conditions and preparing microgram quantities of well-defined
polymer in solution.
2. Microchannel confined
surface initiated polymerization (µSIP). Elastomeric
microchannels are used to confine fluids and trap reagent
gradients at an initiator-functionalized surface to control
the type of surface grafted polymer produced locally.
3. Discrete, monodisperse
droplets of organic media can be formed, polymerized and
characterized for preparation of discrete colloidal arrays.
Results
1. Controlled Radical Polymerization (CRP) Chip
SEC traces for different flow rates (correlated to conversion)
for ATRP of 2-hydroxypropyl methacrylate (HPMA) inside
a microchannel reactor.
Semi-logarithmic plot of conversion versus time showing
near linear apparent rate constant of propagation (kapp)
similar to literature results for batch atom transfer
radical polymerization (ATRP) of HPMA.
Block Copolymer Synthesis
A range of molecular weights can be grafted from
the same macroinitiator by varying the initial stoichiometry
and flow rates. The figure shows various molecular
weights of HPMA grown from a PEO macroinitiator in
the same experiment.
Matyjaszewski’s traditional
kinetic model…. (J. Am. Chem. Soc. 1997)
Kinetic modeling of ATRP
Using a 3-channel chip (schematic, upper right),
rapid changes in stoichiometry can be obtained while
maintaining a constant flow rate (time). Very rapid
scanning of kinetic parameter space is possible and
can be fit (lower right) to the classical model for
ATRP, restructured for the different perspective observed
in the chip.
…. restructured for the
CRP Chip
Contributors:
Tao Wu, Chang Xu, Zuzanna T. Cygan, Ying Mei, Kathryn L.
Beers* and Eric J. Amis
Combinatorial Methods Group
Polymers Division
Materials Science and Engineering Laboratory
