Novel Substituted Epoxide Initiators for the Carbocationic Polymerization of Isobutylene

This article presents the first detailed account of the discovery that substituted epoxides can initiate the carbocationic polymerization of isobutylene. α-Methylstyrene epoxide (MSE), 2,4,4-trimethyl-pentyl-epoxide-1,2 (TMPO-1), 2,4,4-trimethyl-pentyl-epoxide-2,3 (TMPO-2), and hexaepoxi squalene (HES) initiated isobutylene polymerization in conjunction with TiCl4. MSE, TMPO-2, and HES initiated living polymerizations. A competitive reaction mechanism is proposed for the initiation and propagation. According to the proposed mechanism, initiator efficiency is defined by the competition between the SN1 and SN2 reaction paths. A controlled initiation with external epoxides such as MSE should yield a primary hydroxyl head group and a tert-chloride end-group. The presence of tert-chloride end-groups was verified by NMR spectroscopy, whereas the presence of primary hydroxyl groups was implied by model experiments. Multiple initiation by HES was verified by diphenyl ethylene end-capping and NMR analysis; the resulting star polymer had an average of 5.2 arms per molecule. A detailed investigation of the reaction mechanism and the characterization of the polymers are in progress. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 444–452, 200

Fluorescence correlation spectroscopy of single dye-labeled polymers in organic solvents

We discuss the use of fluorescence correlation spectroscopy (FCS) to study the diffusion of single dye-labeled polymer chains in organic solvents. Monodisperse batches of polystyrenes labeled with a single Rhodamine B molecule have been synthesized via anionic polymerization of styrene and ethylene oxide end-capping followed by a polymer analogous coupling reaction. MALDI-ToF mass spectrometry is used to characterize the resulting material. A commercial FCS system has been modified to permit FCS measurements in volatile organic solvents. FCS was used to determine the molecular weight dependence of the diffusion coefficient of 10 nM solutions of end-labeled polystyrenes in toluene. The data are utilized to establish a calibration procedure for FCS measurements in organic solvents

Interleukin-16 stimulates the expression and production of pro-inflammatory cytokines by human monocytes

Interleukin-16 (IL-16) acts as a chemoattractant for CD4+ cells, as a modulator of T-cell activation, and plays a key role in asthma. This report describes the cytokine-inducing effects of IL-16 on total peripheral blood mononuclear cells (PBMC) and PBMC subpopulations. While CD4+ T lymphocytes did not secrete cytokines in response to rhIL-16, CD14+ CD4+ monocytes and maturing macrophages secrete IL-1β, IL-6, IL-15 and tumour necrosis factor-α (TNF-α) upon rhIL-16 stimulation. The mRNA species for these four cytokines were detected as early as 4 hr post-stimulation, with protein being secreted by 24 hr. Secretion of IL-1β and IL-6 by total PBMC was dose dependent, with maximal secretion being observed using 50 ng/ml rhIL-16. However, for IL-15 or TNF-α maximal secretion by total PBMC occurred with all concentrations between 5 ng/ml to 500 ng/ml rhIL-16. Purified monocytes/macrophages secreted maximal concentrations of all four cytokines in the presence of 500 ng/ml rhIL-16, except for monocytes where maximal secretion of IL-15 was, interestingly, observed with only 50 ng/ml rhIL-16. The use of higher concentrations of rhIL-16 (1000 ng/ml) inhibited secretion of all four cytokines. While these IL-16-induced cytokines are likely to be involved in the immune system's response to antigen, the data suggest that IL-16 may play a key role in initiating and/or sustaining an inflammatory response