End Group Analysis of Polyisobutylene Succinic Anhydride (PIBSA) Carried Out with Pyrene Excimer Fluorescence

A procedure is established to determine the molar fraction (fdoubly) of doubly-maleated polyisobutylene (PIBSA2) in a PIBSA sample mainly constituted of mono-maleated polyisobutylene (PIBSA1), where the succinic anhydride (SA) groups are located at the end of the PIB chain. To this end, a PIBSA sample was labeled with 1-pyrenemethylamine (PyMA) to generate PIB-PySI, where the 1-pyrenemethyl group was linked to the PIB chain via a succinimide group. Depending on the procedure applied to purify the PIB-PySI samples, different regions of the molecular weight distribution (MWD) representing the PIBSA samples could be isolated and characterized by a combination of GPC, FTIR, and UV–vis absorption analysis to yield its MWD, number of isobutylene units per succinic anhydride (NIB/NSA), and pyrene content (λPy, in μmol of pyrene per gram of sample). These analyses were consistent with the expected size and chemical composition of the different PIB-PySI samples. fdoubly was calculated from the molar fraction (fagg) of pyrene labels attached onto the PIBSA2 species. fagg was determined through the global model free analysis (MFA) of the fluorescence decays of the pyrene monomer and excimer acquired for solutions of the PIB-PySI samples in THF. The different fractions of the MWD of the PIBSA sample yielded similar fdoubly values across the MWD, implying an even distribution of PIBSA2 species across a PIBSA MWD. The constancy of fdoubly across the MWD enabled the determination of the number average molecular weight (Mn) of the PIB-PySI samples from λPy. An analysis combining the GPC traces obtained with a differential refractive index and UV–vis absorption detector yielded the MWD of the original PIBSA sample. These experiments demonstrated that the proposed PEF-based methodology can be applied to characterize the SA end groups of PIBSA samples and could be further extended to characterize the end groups of other end-functionalized polymers.