Characterization of microstructures and reaction mechanisms of Tröger's base polymers of intrinsic microporosity.

Rationale: Tröger's base polymers of intrinsic microporosity (PIMs) are receiving increasing attention for applications such as polymer molecular sieve membranes. Development of novel membrane materials requires microstructure analysis in order to overcome processing and applications challenges. This study aims to address these challenges and overcome some of the solubility/aggregation issues that hinder the analysis of these materials.

Methods: A combination of matrix-assisted laser desorption/ionization mass spectrometry and collision-induced dissociation was used to examine the reaction products of unfunctionalized Tröger's base PIMs.

Results: Enhanced data mining, using ultrahigh-resolution mass spectrometry and statistical analysis, yielded a wealth of information on the molecular mass, chemical connectivity, and end groups of species generated during synthesis. Modifications of interest include N-methyl, N-methanimine, N-formyl, and N-methylol end-capping moieties, as well as incomplete backbone methanodiazocine rings with missing bridging methylene linkages. Most importantly, a general fragmentation mechanism, supported by computational modeling, was developed to assist in the rapid identification of main-chain and end-group modifications in Tröger's base PIMs.

Conclusions: Unfunctionalized Tröger's base polymers were selected as a model system, to thoroughly study their end-group modification chemistry. This model system could then be used to gain insights into complex hydroxy-functional PIM materials.