PURE COMPONENT ANALYSIS OF CHAIN-LENGTH DISTRIBUTIONS FROM SOLID-STATE POLYMERIZATION OF FORMALDEHYDE

Infrared spectra of oligomers formed during solid-state polymerization of formaldehyde at 77 K and subsequent warm-up to 150 K have been analyzed with the use of Simple Interactive Self-Modeling Multivariate Analysis (SIMPLISMA). Two pure spectral components, corresponding roughly to ''short''- and ''long''-chain oligomers, were extracted from the data along with their associated infrared spectra. The cutoff length that separates the two types of oligomers has been determined to be about 20 monomer units. This value is calculated within the context of a statistical model of solid-state polymerization in which chain length distributions are governed largely by spatial and orientational disorder of molecules in lattice sites adjacent to the growing end of each polymer chain. The cutoff length is observed to be essentially constant during thermal annealing cycles in which chain growth takes place, lending support to the validity of the model.