Layered double hydroxides (LDHs) are a class of ionic lamellar compounds made up of positively charged brucite-like layers with an interlayer region containing charge compensating anions and solvation molecules. Delamination of LDHs is an interesting route for producing positively charged thin platelets with a thickness of a few atomic layers, which can be used as nanocomposites for polymers or as building units for making new designed organic-inorganic or inorganic-inorganic nanomaterials. The synthesis of nanosized LDH platelets can be generally classified into two approaches, bottom-up and top-down. It requires modification of the LDH interlamellar environment and then selection of an appropriate solvent system. In DDS intercalated LDHs, the aliphatic tails of the DDS- anions exhibit a high degree of interdigitation in order to maximize guest-guest dispersive interactions. Bellezza reported that the LDH colloids can also been obtained by employing a reverse microemulsion approach.

Recent advances in the synthesis and application of layered double hydroxide (LDH) nanosheets.

2.2.1. Polyisocyanates 6117 2.2.2. Polysilanes 6118 2.2.3. Polyacetylenes 6120 2.3. Foldamer-Based Helical Polymers 6124 2.3.1. Click Polymerization 6126 2.3.2. Ring-Closing Reaction 6126 2.4. Other Types of Helical Polymers 6127 2.4.1. π-Conjugated Helical Polymers 6127 2.4.2. Metallosupramolecular Helical Polymers 6128 2.5. Induced Helical Polymers 6130 2.5.1. Induced Helical Polyacetylenes 6130 2.5.2. Other Induced Helical Polymers and Oligomers 6132

Helical polymers: synthesis, structures, and functions

Synthetic helical polymers: conformation and function.

The effects of residues introduced during the transfer of chemical vapor deposited graphene from a Cu substrate to an insulating (SiO2) substrate on the physical and electrical of the transferred graphene are studied X-ray photoelectron spectroscopy and atomic force microscopy show that this residue can be substantially reduced by annealing in vacuum The impact of the removal of poly(methyl methacrylate) residue on the electrical properties of graphene field effect devices is demonstrated, including a nearly 2 × increase in average mobility from 1400 to 2700 cm2/Vs The electrical results are compared with graphene doping measurements by Raman spectroscopy

The effect of chemical residues on the physical and electrical properties of chemical vapor deposited graphene transferred to SiO2

Surface contamination by polymer residues has long been a critical problem in probing graphene’s intrinsic properties and in using graphene for unique applications in surface chemistry, biotechnology, and ultrahigh speed electronics. Poly(methyl methacrylate) (PMMA) is a macromolecule commonly used for graphene transfer and device processing, leaving a thin layer of residue to be empirically cleaned by annealing. Here we report on a systematic study of PMMA decomposition on graphene and of its impact on graphene’s intrinsic properties using transmission electron microscopy (TEM) in combination with Raman spectroscopy. TEM images revealed that the physisorbed PMMA proceeds in two steps of weight loss in annealing and cannot be removed entirely at a graphene susceptible temperature before breaking. Raman analysis shows a remarkable blue-shift of the 2D mode after annealing, implying an anneal-induced band structure modulation in graphene with defects. Calculations using density functional theory show that l...

Graphene Annealing: How Clean Can It Be?

Chromatographic resolution. 7. Useful chiral packing materials for high-performance liquid chromatographic resolution of enantiomers: phenylcarbamates of polysaccharides coated on silica gel

Polymerization of MMA with t-C4H9Li in toluene in the presence of trialkylaluminum(alkyl=methyl, ethyl, butyl, isobutyl, and octyl) was examined at various Al/Li ratios. Triethyl-, tributyl and trioctylaluminums worked quite effectively in the polymerization to give highly syndiotactic PMMA with narrow molecular weight distribution (MWD) at the Al/Li ratio of 3 and higher than 3. The highest syndiotacticity of 96% was attained with t-C4H9Li/(n-C8H17)3Al (1/3) at −93°C. The polymerization was initiated by t-C4H9 anion and proceeded in a living manner. The structure of the syndiotactic PMMA is chemically identical to that of isotactic PMMA prepared with t-C4H9MgBr. Consequently, highly isotactic and syndiotactic PMMAs with narrow MWD and with the same chemical structure from α-end to ω-end were obtained.

Highly syndiotactic poly(methyl methacrylate) with narrow molecular weight distribution formed by tert-butyllithium-trialkylaluminium in toluene

Highly isotactic living poly(methyl methacrylate) (PMMA) anion prepared with t-C4H9MgBr in toluene at −78°C reacted quantitatively with p-bromomethylstyrene (p-BMST) in the presence of hexamethylphosphoramide or 1,8-diazabicyclo[5.4.0]-undec-7-ene to give the PMMA macromonomer with narrow molecular weight distribution. Highly syndiotactic PMMA macromonomer was also prepared by the reaction of p-BMST and the living PMMA anion formed by t-C4H9Li-(n-C4H9),Al (Al/Li=3) initiation in the presence of tetramethylethylenediamine. Radical polymerization and copolymerization of these macromonomers were studied in some detail. The results showed the higher reactivity of the isotactic PMMA macromonomer than the syndiotactic one.

Preparation of highly isotactic and syndiotactic poly(methyl methacrylate) macromonomers having the same chemical structure and their polymerization

p- and m-Vinylbenzylmagnesium chlorides (VBzMgCl) were prepared in diethyl ether from the corresponding chloromethylstyrenes, and used as initiators in the polymerizations of MMA and styrene. PMMAs with a variety of tacticities were obtained in toluene and THF by these initiators, and highly syndiotactic (S>96%) PMMA of low polydispersity (Mw/Mn=1.19) could be prepared with m-VBzMgCl in THF at −110°C. It was found by the totally deuterated monomer technique that the polymer molecule thus obtained had one vinylbenzyl group at the beginning of the chain (α-end). The PMMAs could be used as macromers, which were polymerized and copolymerized with styrene by a radical initiator. p-VBzMgCl polymerized styrene in THF at 0°C, and the resulting polystyrene can also be used as a macromer. m-VBzMgCl and benzylmagnesium chloride did not give polystyrene. Spontaneous polymerizations of VBzMgCls to poly(Grignard reagent)s were also studied.

/pdf/studies-on-p-and-m-vinylbenzylmagnesium-chlorides-as-t8cxu41qid.pdf

Studies on p - and m -Vinylbenzylmagnesium Chlorides as Initiators and Monomers—Preparations of Macromers and Poly(Grignard reagent)

Gel permeation chromatography of. isotactic PMMA has been performed on a Chromatograph linked to a 500 MHz 1H NMR spectrometer. 1H NMR spectra of good resolution and high S/N ratio were collected over the entire Chromatographic peak. The Mn of the polymer sample can be directly determined by intensity measurements of the proton signals due to the endgroup and monomeric units, since the polymers used were prepared by the living polymerization initiated by t-C4H9MgBr. A good linear relation was obtained between the log(Mn) and elution time.

On-line GPC/NMR experiments using the isotactic poly(methyl methacrylate) with well-defined chemical structure

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