The principles of RAFT polymerization were applied to the polymerization of N-isopropylacrylamide (NIPAAm), which was carried out in the presence of the dithiocarbamates benzyl 1-pyrrolecarbodithioate and cumyl 1-pyrrolecarbodithioate, respectively, as chain transfer agents in 1,4-dioxane at 60 °C. A kinetic investigation using in situ FT-NIR spectroscopy shows very long induction periods which depend on the nature and concentration of the chain transfer agent. The resulting polymers have polydispersity indices M w/Mn < 1.3 and have been investigated by MALDI-TOF mass spectrometry, GPC, NMR, and UV spectroscopy. The expected end group signals for chain transfer agent (CTA) and initiator could be identified together with fragmentation of the dithioester end group under MALDI conditions. The number-average molecular weights obtained by MALDI-TOF MS are significantly lower than those obtained by GPC with polystyrene calibration. With the use of the abovementioned dithiocarbamates, new thiocarbonylthio compounds have been applied in the RAFT polymerization of N-isopropylacrylamide.

Summary: We report the synthesis of star‐shaped poly(acrylic acid) (PAA), with 5, 8, and 21 arms, by atom transfer radical polymerization of tert‐butyl acrylate. We employ the core‐first approach using glucose‐, saccharose‐ and cyclodextrin‐based initiators. Subsequent acidic treatment of poly(tert‐butyl acrylate) (PtBA) leads to star‐shaped poly(acrylic acid) (PAA). Alkaline cleavage of the arms enabled us to determine the initiation site efficiency. The PAA stars and arms were esterified to poly(methyl acrylate) (PMA). Molecular weight determination by means of GPC/viscosity, MALDI‐TOF MS and NMR end‐group determination showed that the initiation site efficiency is close to unity. Results from potentiometric titration of PAA arms and stars show that the apparent pKa values increase with increasing arm number, which is a direct result of increasing segment density. Osmometry measurements of aqueous solutions of the PAA stars result in osmotic coefficients between 0.05 and 0.38, indicating that most of the counterions are confined within the star. The confinement increases with arm number.

The reaction order with respect to TiCl4 was investigated in the living polymerization of isobutylene (IB) initiated by 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl4 in hexane/methyl chloride (Hx/MeCl) 60/40 v/v cosolvents at -80 °C. It was found that the reaction is more complex than previously believed. The TiCl4 order was found to be closer to 1 at [TMPCl]0 > [TiCl4]0, and closer to 2 when [TMPCl]0 < [TiCl4]0. Kinetic complexity is demonstrated by the fraction order in TiCl4, and the rate-acceleration found when [TMPCl]0 . [TiCl4]0. A comprehensive mechanistic scheme to explain the kinetic behavior of living IB polymerizations is proposed. Further, a new fiber optic mid-IR monitoring method for more convenient kinetic investigations is demonstrated.

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.

Silsesquioxanes-based nanoparticles synthesized by hydrolytic condensation of a functionalized precursor, N,N-di(2,3-dihydroxypropyl)(aminopropyl)triethoxysilane, (HOCH2CH(OH)CH2)2NCH2CH2CH2Si(OCH2CH3)3, were characterized using MALDI-TOF MS, NMR, elemental analysis, FT-IR, transmission electron microscopy (TEM), and scanning force microscopy (SFM). MALDI-TOF MS analysis indicated that the product consists of many species having 12−18 Si atoms with different numbers of intramolecular cyclizations, and Si−O−C bonds are formed through the reaction of SiOH (or SiOEt) groups with the hydroxyl functionalities of an organic moiety bonded to a Si atom. The species having high number of intermolecular cyclization (f ≥ 0.5 at 10 ≥ n ≥ 7) were predominantly detected, suggesting that the product mainly consists of complete and incomplete cagelike structures. The chemical composition of the product was consistent with that calculated from the structure, (R−SiO1.5) n , indicating that the nanoparticles belong to a family of silsesquioxanes characterized by a ratio of 1.5 between the silicon and oxygen atoms. Reasonable NMR and FT-IR spectra were observed, corresponding to the structure assuming that majority of the alkyl chain attached on a Si atom was intact during the hydrolytic condensation. The resulting particles have relatively narrow size distribution with average particle diameter less than 3.0 nm, as confirmed by TEM and SFM.

Randomly branched (arborescent) cationic polyelectrolytes were synthesized by self-condensing vinyl copolymerization (SCVCP) of a methacrylic AB* inimer, 2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM), with (diethylamino)ethyl methacrylate (DEAEMA) via atom transfer radical polymerization (ATRP), followed by quaternization. Homopolymerization of DEAEMA with the CuBr/hexamethyltriethylenetetramine (HMTETA) catalyst system gave a linear polymer having controlled molecular weights and narrow molecular weight distribution, which were evaluated by conventional GPC, GPC−viscosity, and MALDI−TOF mass spectrometry. The catalyst system could be applied to self-condensing vinyl polymerization (homo-SCVP) of BIEM in bulk and in solution to provide hyperbranched architectures, as confirmed by 1H and 13C NMR and GPC−viscosity measurements. SCVCP with CuBr/HMTETA in solution gave a series of tertiary amine methacrylate-based branched polymers, in which the molecular weights, the composition of the DEAEMA segment, and the branched structure can be adjusted by an appropriate choice of the comonomer composition, γ. Quaternization reaction of the branched poly(DEAEMA)s with methyl iodide led to water-soluble cationic polyelectrolytes with branched structures.

No abstract

A new synthetic route for the synthesis of polyisobutylene (PIB) stars and PIB-poly-(methacrylate) block copolymers was developed by combining living carbocationic and anionic polymerizations. Rapid and quantitative monoaddition of thiophene to living PIB chains has been observed in conjunction with TiCl 4 as Lewis acid in n-hexane/CH2Cl2 60/40 v/v at -78 °C leading to the formation of 2-polyisobutylenyl-thiophene (PIB-T). PIB-T was quantitatively metalated with n-butyllithium in THF at -40 °C. 1 H NMR spectroscopic and GC studies of the corresponding model compound, 2-(1,1,3,3tetramethylbutyl)thiophene, clearly verified quantitative metalation. The resulting stable macrocarbanion (PIB-T -,Li + ) was used to initiate living anionic polymerization of tert-butyl methacrylate (tBMA) yielding PIB-b-PtBMA block copolymers with high blocking efficiency. PIB stars were prepared via the coupling reaction of the stable macrocarbanion with SiCl4 as a coupling agent. Characterization of these block copolymers and PIB stars was carried out by size exclusion chromatography (SEC), liquid adsorption chromatography at critical conditions (LACCC), and NMR spectroscopy.