Synthesis and association of poly(N,N‐dimethylacrylamide) copolymers with perfluorocarbon pendent groups connected through polyethylene‐glycol tethers

The synthesis is reported of copolymers of N,N‐dimethylacrylamide (DMA) and methacrylates containing 2,2′‐dihydroperfluorodecanoyl (RF) groups separated from the methacrylate by long polyethylene glycol (PEG) tether groups (between 1000 and 14,000 Da). At concentrations of between 1 and 8 wt % the copolymers with macromonomer contents of 1 mol % or less give gels in organic solvents such as dioxane, THF, or methanol, as well as in water. Given the low molecular weights, this indicates very efficient association of very low numbers of RF groups. Association and gel formation is enormously enhanced in the presence of longer PEG tethers. This is consistent with smaller poly(N,N,‐dimethylacrylamide) (PDMA) intermolecular excluded volume effects that are mediated by the longer PEG tethers and possibly by the incompatibility of PEG and PDMA that may lead to the formation of PEG microdomains. This increases the local concentrations of the RF groups in the PEO domains that are not diluted by the PDMA chains, as would be the case in the absence of PEG tethers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 360–373, 2004     

Mechanism of coupling reactions of polystyryllithium with dihalomethanes

We report here an in‐depth analysis of the reaction mechanisms involved in the formation of polymer dimers formed by the coupling of polystyryllithium (PSLi) with dichloromethane (DCM), dibromomethane (DBM), and diiodomethane (DIM) in tetrahydrofuran at ?78 °C. The DBM‐mediated reactions give a high degree of coupling but generate 1,2‐diphenyl linkages in addition to the expected 1,3‐diphenyl linkages and small amounts of β‐substituted styrenic end groups that are detectable by fluorescence measurements. This is consistent with the formation of bromobenzyl end groups by lithium–bromine exchange and PSLi‐mediated elimination. The formation of α‐substituted styrenic end groups by conventional displacement and elimination is also possible. Although reactions of PSLi with DCM show no coupling at all, DIM is a much better coupling agent than DBM, significantly suppressing side reactions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1081–1091, 2002     

Synthesis and characterization of macrocyclic vinyl aromatic polymers

The synthesis and characterization by size exclusion chromatography, liquid chromatography, NMR, matrix‐assisted laser desorption/ionization, thermal analysis, and other techniques of well‐defined and narrow molecular weight distribution macrocyclic polystyrene (PS), poly(2‐vinylpyridine), poly(α‐methylstyrene), poly (2‐vinyl‐naphthalene) (P2VN), and poly(9,9‐dimethyl‐2‐vinylfluorene) (PDMVF) containing a single 1,4‐benzylidene, methylidene, or 9,10‐anthracenylidene unit are reviewed. The absorption and emission spectroscopy of PS, P2VN, and PDMVF is also discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2139–2155, 2006     

Synthesis of macrocyclic polystyrene-polydimethylsiloxane block copolymers

A series of macrocyclic polystyrene (PS)-polydimethylsiloxane (PDMS) block copolymers and similar block copolymers was synthesized by sequential polymerization of styrene and hexamethyl cyclotrisiloxane (D₃) initiated by a difunctional anionic initiator in THF at −78° followed by coupling with Cl₂SiMe₂ in very dilute (10⁻⁵ – 10⁻⁶ M) solutions. Total molecular weights ranged from about 2–85 × 10³. The formation of monodisperse macrocyclic block copolymers was indicated by the lower (15–30%) hydrodynamic volume of the rings compared to that of the linear block copolymers. Carbon-13 and ²⁹Si NMR likewise supported the absence of linear polymer in the macrocyclic block copolymer. The behavior of second virial coefficient A₂ of the rings and the linears versus temperature was examined by static light scattering in cyclohexane. Below 20° the A₂ for the linear polymer goes negative while that for the cycle remains positive. Dynamic light scattering (DLS) as a function of temperature also reflects that the cyclic polymers remain well solvated even down to 12°C. The DLS autocorrelation functions for the linear triblock however demonstrate the onset of aggregation and phase separation as the temperature is reduced below 20°C.     

1,4‐Dilithio‐1,1,4,4‐tetraphenylbutane in diethyl ether: An effective initiator for the living anionic polymerization of dienes

The anionic polymerization of butadiene initiated with 1,4‐dilithio‐1,1,4,4‐tetraphenylbutane (LiTPB) in diethyl ether (DEE) gives polybutadiene (PBD) with high 1,2 content (>70%), narrow polydispersities (1.04 < M_w/M_n < 1.20), and predicted molecular weights. In THF, this polymerization does not work very well. After removal of DEE and addition of THF, the PBD dianion is end capped quantitatively by addition of 1,1‐diphenylethylene (DPE) to give the diphenylalkyl end capped PBD dianion. Subsequent addition of methyl methacrylate at low temperatures results in the formation of well‐defined PMMA‐b‐PBD‐b‐PMMA triblock copolymers. The results are accounted for by taking into account the effects of Li ion solvation on the BD initiation and end capping of the PBD anion by DPE. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2198–2206, 2009     

Synthesis and hydrophobic association of poly(N,N‐dimethylacrylamide) end‐functionalized with perfluorocarbon and hydrocarbon groups

Polydimethylacrylamides (PDMAs) end‐functionalized with hydrophobic groups were synthesized by the reaction of cesium salts of one‐ or two‐ended living PDMA anion with octadecanoyl and perfluorooctanoyl chlorides and with α‐phenylacrylate monomers containing an octadecyl group attached via oligooxyethylene spacers to the acrylate functionality. Size exclusion chromatography or NMR studies indicated that the end functionalizations were nearly quantitative. Reduced viscosity measurements were consistent with predominantly dimeric association of the perfluorooctanoyl‐end‐functionalized PDMAs. The association of the two‐ended, perfluorooctanoyl‐ and octadecanoyl‐functionalized polymers was more extensive and consistent with pairwise association. Furthermore, the presence of oligoethylene oxide spacers between the octadecyl and α‐phenylacrylate groups greatly enhanced the hydrophobic association of bis(octadecyl)‐end‐functionalized PDMA. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1403–1418, 2001     

Reactions of polystyryllithiums and model lithium carbanions with 9,10‐bis(halomethyl)anthracenes

The direct and nearly quantitative incorporation of 9,10‐anthracenylidene (AN) chromophores into polystyrene occurred via the reaction of polystyryllithium (PSLi) with 9,10‐bis(chloromethyl)anthracene (BCMA) at ?78 °C in tetrahydrofuran (THF)/ hexane containing between 30 and 40 vol % hexane. Although the reaction of PSLi and BCMA or 9,10‐bis(bromomethyl)anthracene (BBMA) in THF at ?78 °C gave nearly quantitative coupling, typically only 30–50% AN incorporation was observed, as determined by ultraviolet–visible spectrometry. Model coupling reactions of 3,3‐dimethyl‐1,1‐diphenyl‐1‐lithiobutane, (1,1,2,2‐tetramethyl)propylcyclopentadienyllithium, 9‐methylfluorenyllithium, and triphenylmethyllithium with BCMA or BBMA at ?78 °C in THF in nearly all cases gave several AN‐containing coupling products. This was consistent with lithium–halogen exchange leading to the linking of multiple AN groups. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3121–3129, 2001     

Phosphorescence quenching by conjugated polymers

Energy transfer between phosphors and conjugated polymers was investigated using a fluorene trimer (F3) as a model conjugated material. The phosphors studied were bis-cyclometalated iridium complexes (FP, PPY, BT, PQ, and BTP), with triplet energies of 2.6, 2.4, 2.2, 2.1, and 2.0 eV, respectively (based on phosphorescence spectra). Stern-Volmer analysis of luminescent quenching shows that energy transfer from either FP or PPY to F3 is an exothermic process with Stern-Volmer quenching constants (kqSV) of near 109 M-1 s-1 while energy transfer from BT, PQ, and BTP is endothermic (kqSV = 107-106 M-1 s-1). On the the basis of above results, the triplet energy of F3 is estimated to be less than 2.3 eV (530 nm). This study suggests that conjugated polymers, which typically have lower T1 energies than F3, should also quench phosphorescent emission in thin films and organic light-emitting diodes (OLEDs) incorporating these and related phosphorescent dopants.