October 15
@
4:00 PM
–
5:00 PM
Nathaniel Lynd
McKetta Department of Chemical Engineering
The University of Texas-Austin
Austin, TX
Understanding Multicomponent Polymerization in the 21st Century
Copolymerization is the incorporation of more than one type of repeat unit into a single polymer backbone. Many plastics used by society are copolymers, whose properties are determined by composition and sequence of different repeat units. We understand the sequencing through experimentally determined reactivity ratios defined by ratios of the propagation rate constants. The copolymer-equation has formed the basis for interpreting copolymerization statistics and reactivity since it was introduced in 1944 by Mayo, Lewis and Wall. While advances in our ability to measure copolymer composition have advanced substantially over the subsequent decades, the underlying conceptual model and methods of using it have changed little.
In this talk, I will answer three questions:
- Of all the methods of determining reactivity ratios, how does one select the right model?
- How can we use this new understanding to characterize new materials and determine the structure of complex copolymers such as degradable poly(orthoester-co-ether)s or graft architectures derived from monomers with very different steric demand?
- How do we move beyond the copolymer-equation to understand copolymerizations that cannot even be practically represented mathematically?
An important example is degradable poly(lactide-co-glycolide) (PLGA) that is produced using a reversible copolymerization subject to simultaneous transesterification. PLGA is a degradable/sustainable material and an important component in many pharmaceutical applications. To understand PLGA structure and polymers like it, we have developed new methods of extracting reaction parameters from experimental data based on numerical and probabilistic stochastic kinetic models.