Understanding rapid pseudo-solid state step-growth polymerization in micro-layers leading to ultra-high molecular weight polymers with unusual molecular structures

University Of Maryland, College Park, College Park MD

Investigators

Abstract

1033071 Choi This research will investigate the pseudo-solid state step-growth polymerization in the confined reaction space of an amorphous polymer micro-layer where high to ultra-high molecular weight (MW) polymers are rapidly produced. Pseudo-solid state polymerization (p-SSP) has the ability to produce ultra-high MW polymers in short reaction times. The extraordinary high MWs and the exceptional properties of the final polymer can only be compared with condensation polymers produced via ring opening polymerization, but p-SSP is more economically feasible and environmentally friendly. This polymerization technique consists of formulating a low MW amorphous polymer precursor with catalyst into a confined reaction space of a polymer micro-layer, and carrying out the polymerization at reduced pressures and at temperatures close to but below the polymer melting point. Preliminary experimental results indicate that the reaction proceeds more than 20 times faster than conventional solid state polymerizations in semi-crystalline particles, and polymer MWs and polydispersities notably exceed the theoretical limits of the classical step-growth polymerization theory. At moderate reaction times, insoluble/infusible structures coexist with soluble structures, and the final polymer exhibits excellent optical clarity. The presence of branched structures has been confirmed by 13C-NMR and 1H-NMR, and the rheological characterization of the polymer. The relatively high mobility of polymer chains in the amorphous state, the efficient removal of polycondensation byproduct from the micron-sized reaction space, the radical-induced branching reactions via thermal decomposition of the residual casting solvent or via scission reactions, Fries rearrangement, interchange reactions, and high reactivities are hypothesized to be mainly responsible for the fast and unusual increase of the polymer MWs and the formation of insoluble polymer. Three model systems have been investigated: bisphenol-A polycarbonate, poly(L-lactic acid), and a copolymer of polycarbonate and poly(dimethylsiloxane). It is expected that the technique can be applied to many other condensation systems, suggesting that p-SSP can have a broad impact on step-growth polymerization technology. Through experimental and theoretical studies, this project will develop fundamental understandings of the chemical and physical phenomena that govern the p-SSPs process. The Intellectual Merit: The goal is to develop new quantitative understandings of the chemical and physical phenomena that drive the kinetics of p-SSP to unusual reaction behaviors through experimentation and theoretical modeling. P-SSP is different from melt and conventional solid-state polymerizations, and its kinetics deviates from the traditional approaches. Integration of comprehensive experimentation and mathematical modeling will provide a systematic way to produce tailor-made condensation polymers for a variety of special applications where high or ultra-high MWs, solvent resistance, and thermal resistance are required. The Broader Impacts of the Proposed Study: P-SSP is a method to produce ultra-high MW condensation polymers in short reaction times. This research will provide fundamental data and knowledge for the development of an advanced polymerization process technology, especially for large-scale mass production, as well as new polymer properties. For instance, the synthesis of insoluble and infusible structures for traditionally soluble polymers can inspire a variety of novel applications. The research results are expected to be applicable to many other condensation polymerizations. The results of the research will be presented at relevant scientific and engineering fields. Undergraduate students at all levels, regardless of ethnic background and gender, will be strongly encouraged to participate in the proposed project as semester research or summer internship programs. Academically talented high school students will also be invited to a summer research experience program through University of Maryland's Women In Engineering (WIE) program. The participating students at different levels will be encouraged to develop innovative applications and test the ideas as the research progresses.