A Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry Study of the Imidization of Vapor-Deposited ODA−PMDA Poly(amic acid)

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.

All-aromatic polyetherimide and polyamide-imide thin films deposited by the infrared laser ablation

The thermo-oxidative stability and molecular weight were determined for polyimide and polyamide-imide thin films, deposited by resonant infrared laser ablation (RIR-LA). RIR-LA films were deposited at various wavelengths and compared with the traditional solution-cast films using thermogravimetric analysis. The RIR-LA films showed slightly lower oxidation temperatures, but the initial weight loss temperatures were greater. Since molecular weight is directly correlated with the physical and mechanical properties of the polymer, multiangle laser light scattering was employed to ascertain the weight-average molecular weight of the polymers before and after LA. The RIR-LA films exhibited slightly reduced weight-average molecular weight. This degradation has three possible sources: bond scission during LA, reduced solvent transfer leading to lower chain extension and hydrolysis caused by the presence of atmospheric water.

Interpretation of Reversible Addition−Fragmentation Chain-Transfer Polymerization Mechanism by MALDI-TOF-MS

Several polystyrene polymers were prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization of styrene, using two different RAFT agent-initiator systems, and then further characterized by NMR and SEC as well as MALDI-TOF-MS techniques. The data indicate that most of the polymer chains are terminated by the active groups (Ph-C(=S)-S-) derived from RAFT agents, and few of the polymer chains bear initiator fragments at one end. Most importantly, the structures arising from the intermediate RAFT radicals and their cross-termination adducts were detected. Also, the MALDI-TOF-MS analysis shows that the combination termination between two macromolecular radicals is minor, and the amount of dead chains is quite low. Thus, narrow molecular weight distribution is obtained. This analysis confirms the operation of the Rizzardo mechanism including the Monteiro intermediate radical termination model for the RAFT polymerization.

A MALDI-TOF MS Study of Oligomeric Poly(m-phenyleneisophthalamide)

MALDI-TOF MS was used to study the end-group distribution of a series of poly(m-phenyleneisophthalamide) oligomers which were synthesized using various mole percent ratios of diamine to diacid chloride (90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80, and 10:90) to clarify results obtained in previous work published in this journal. Oligomers synthesized with excess diamine or excess diacid chloride were found to contain abundances of amine or carboxylate end groups, respectively, as expected. Oligomers synthesized with equal molar ratios of reactants produced cyclic species which were also found in a previous publication as an oligomer in commercially produced, high molecular mass Nomex.