Current Position: Product Stewardship Professional, Celanese
Undergraduate Institution: University of Delaware

Ph.D. Thesis Research:

Block copolymers are polymers that contain long contiguous blocks of two or more dissimilar repeating units covalently bonded together. Because the polymer chains are tethered to each other, macroscopic phase separation cannot occur. Instead, interactions between the blocks lead to separation into ordered structures on the nanoscale. Incorporating crystallinity into one of the blocks increases the complexity of the phase behavior, and also enables potentially precise control over the crystal thickness and resulting material properties as a direct result of the microphase separation and block interactions. The goal of my project is to use block copolymer architecture to direct crystallization and precisely tune crystal thickness within the block copolymer structure.

We use living ring opening metathesis polymerization (ROMP) to synthesize our well-defined block copolymers. ROMP and subsequent hydrogenation provides all the basic building blocks necessary to tune polymer structure and properties. The blocks we use include: hydrogenated polynorbornene (hPN), a highly crystalline block; hydrogenated polyalkylnorbornenes (hPaN), rubbery amorphous blocks with low glass transition temperatures [1]; and hydrogenated polymethyltetracyclododecenes (hPMTD), a glassy amorphous polymer with high glass transition temperatures. Hydrogenated polynorbornene shows a rotationally disordered polymorph below its melting point that should enable rapid crystal thickening, which would be of considerable interest for our block copolymers [2].

In particular, we plan to investigate hPN-based lamellar structures both crystallized from homogeneous melts and confined within a glassy matrix. The structures crystallized from the homogeneous melt should show equilibrium crystal thickness tunable through the crystalline and amorphous block lengths [3]. Here we will synthesize hPN-hPaN-hPN triblock copolymers, which should show thermoplastic elastomer behavior that could rival that of current amorphous-based thermoplastic elastomers. The confinement of crystallization within a glassy matrix changes the orientation of the crystallites as they stack perpendicularly with respect to the amorphous region rather than parallel for crystallization from homogeneous melts [4, 5]. The constraint of an equilibrium crystal thickness is also removed. We will synthesize glassy-crystalline hPMTD-hPN diblocks and elucidate the features that dictate the crystal thickness and melting point. The characterization of the morphology and orientation of our semicrystalline block copolymers will be investigated primarily through small- and wide-angle x-ray scattering.

[1] Hatjopoulos, J.D. and R.A. Register, Macromolecules, 38, 10320-10322 (2005).

[2] Lee, L.-B.W. and R.A. Register, Macromolecules 38, 1216-1222 (2005).

[3] Lee, L.-B.W. and R.A. Register, Macromolecules 37, 7278-7284 (2004).

[4] Douzinas, K. C. and R. E. Cohen, Macromolecules 25, 5030-5035 (1992).

[5] Loo, Y.-L. and R.A. Register, “Crystallization Within Block Copolymer Mesophases”, Chapter 6 in Developments in Block Copolymer Science and Technology, I.W. Hamley, ed. (New York: Wiley, 2004), 213-243.