Search results for "Methyl methacrylate"

Accidental Contamination of Substrates and Polymer Films by Organic Quantum Emitters.

2019

[Image: see text] We report the observation of ubiquitous contamination of dielectric substrates and poly(methyl methacrylate) matrices by organic molecules with optical transitions in the visible spectral range. Contamination sites of individual solvent-related fluorophores in thin films of poly(methyl methacrylate) constitute fluorescence hotspots with quantum emission statistics and quantum yields approaching 30% at cryogenic temperatures. Our findings not only resolve prevalent puzzles in the assignment of spectral features to various nanoemitters on bare dielectric substrates or in polymer matrices but also identify the means for the simple and cost-efficient realization of single-phot…

MCM-41 and related materials as media for controlled polymerization processes

1994

The synthesis of mesoporous MCM-41 type materials based on transition metal oxides and the polymerization of several monomers within MCM-41 is presented with the aim to specifically investigate the effects of the interface and confinement on host-guest interactions. In addition to standard MCM-41, material based on transition metal oxides is obtained although template removal has been unsuccessful for such compounds until now. In situ polymerization of styrene, methyl methacrylate and vinyl acetate is possible within the mesopore system. The properties of some of the encapsulated polymers differ markedly with those obtained in the bulk.

Cyclodextrins in polymer synthesis: Free radical polymerization of methylated β-cyclodextrin complexes of methyl methacrylate and styrene, controlled…

2000

Methylated β-cyclodextrin (me-β-CD) was used to complex the hydrophobic monomers methyl methacrylate (1) or styrene (2) yielding the water-soluble 1 : 1-host/guest complexes methyl methacrylate/me-β-CD (1 a) and styrene/me-β-CD (2 a), respectively. In addition, the hydrophobic chain-transfer agent dodecanethiol (3) was complexed by two equivalents of me-β-CD yielding the water-soluble dodecanethiol/me-β-CD (3 a). The included monomers were polymerized in water by a free-radical mechanism in the presence of 3 a as the chain-transfer agent. The chain-transfer constants were determined. In order to evaluate these results, the chain-transfer constants of 3 were also determined in the case of th…

Polymer and Dye Probe Diffusion in Poly(methyl methacrylate) below the Glass Transition Studied by Forced Rayleigh Scattering

1999

By dissolving tracer quantities of 9,10-phenanthrenequinone (PQ) in poly(methyl methacrylate) (PMMA) it was possible to study by forced Rayleigh scattering (FRS) the tracer diffusion of the unbleached PQ as well as the photoproduct which is covalently bound to the PMMA molecules. The PMMA samples with molecular weights, Mw, of 103−105 were intermittently annealed at 80 °C for diffusion times of up to one year. From the results we conclude that polymer chain diffusion may be possible at temperatures more than 20 K below the glass transition temperature Tg, but further experiments are necessary, in particular, since we cannot exclude that our results are due to yet unexplained long time aging…

Metal-free anionic polymerization of methyl methacrylate in tetrahydrofuran using bis(triphenylphosphoranilydene)ammonium (PNP+) as counterion

2000

Bis(triphenylphosphoranilydene)ammonium (PNP + ) triphenylmethanide (Ph 3 C - ) is a new metal-free initiator for the living polymerization of methyl methacrylate (MMA). The kinetics of the polymerization strongly depend on the metal counterion the initiator precursor. When the initiator is made from the metathesis reaction of Ph 3 CK and PNPCl, the polymerization follows first-order kinetics up to 0°C with half-lives below 0.1 s. The propagation rate constants are much higher than those obtained with tetraphenylphosphonium (TPP + ) cations, indicating a smaller fraction of dormant ylides. When the initiator is synthesized from Ph 3 CLi, polymerization proceeds much slower and molecular wei…

Hetero-Telechelic Dye-Labeled Polymer for Nanoparticle Decoration

2009

The synthesis of poly(methyl methacrylate) (PMMA) exhibiting one fluorescent dye (Texas Red) and one methyl disulfide end group is described. It is shown that the latter end group enabled the exchange of both oleic amine on gold nanoparticles (AuNP) and of oleic acid on CdSe/ZnS quantum dots (QD), allowing for a phase transfer of both types of nanoparticles (NP) from hexane into dimethylformamide due to the solubility provided by the PMMA chains. For AuNP, a fluorescence quenching of the dye was found due to fluorescence resonance energy transfer (FRET) from the dye to the AuNP, while QDs caused a fluorescence enhancement by FRET from the QD to the attached dyes. Due to the hetero-telecheli…

Versatile ω-end group functionalization of RAFT polymers using functional methane thiosulfonates

2009

Five different polymers, poly[methyl methacrylate] (PMMA), poly[lauryl methacrylate] (PLMA), poly[diethylene glycol methacrylate] (PDEGMA), poly[N-iso-propylacrylamide] (PNIPA), and poly[styrene] (PS) prepared by the RAFT process and thus terminated with dithioesters were aminolyzed in the presence of S-3-butynyl methane thiosulfonate (MTS), which was synthesized in two steps. Analysis of the polymers by 2D NMR, UV–vis absorbance, and gel permeation chromatogra-phy revealed them to quantitatively carry acetylene end groups connected with disul-fide bridges, indicating that functional MTS reagents can be employed for end group functionalization of RAFT polymers. This versatile method is of ad…

Anionic polymerization of methyl methacrylate using tetrakis[tris(dimethylamino)phosphoranylidenamino] phosphonium (P5+) as counterion in tetrahydrof…

2000

A novel metal-free initiator, i.e. the salt of the tetrakis[tris(dimethylamino)phosphoranylidenamino]phosphonium (P5+) cation with the 1,1-diphenylhexyl (DPH–) anion was prepared by cation metathesis. It initiates a very fast and controlled anionic polymerization of methyl methacrylate in THF. Kinetic investigations between –20 and +20°C using a flow tube reactor provide nearly linear first-order time-conversion plots with half-lives below 0.1 s, a linear dependence of the number-average degree of polymerization, and rather narrow molecular weight distributions (Mw/Mn ≈ 1.2). 13C NMR measurements on a model of the active chain end (the P5+ salt of ethyl isobutyrate) in THF-d8 show 15 and 25…

Anionic Polymerization of Alkyl (Meth)acrylates Using Metal-Free Initiators:  Effect of Ion Pairing on Initiation Equilibria

1999

Metal-free anionic polymerizations of alkyl (meth)acrylates using tetrabutylammonium salts of diethylphenylmalonate, fluorene, and 9-ethylfluorene as initiators were performed in THF at 30 °C. A poor control of molecular weights, inconsistent initiator efficiencies, and broad or bimodal molecular weight distributions were obtained. The effect of counterion nature was studied from the polymerization of methyl methacrylate using the 1,1-diphenylhexyl anion with tetrabutylammonium, tetramethyldiethylguanidinium, and lithium as counterions under otherwise identical conditions. Metal-free initiators resulted in incomplete initiation which is attributed to the fact that the initiation is an equil…

1982