R. Dhamodharan

Controlled Growth of PMMA Brushes on Silicon Surfaces at Room Temperature

The atom-transfer radical polymerization of methyl methacrylate at room temperature starting from monolayers of initiators, which are covalently anchored to silicon substrates, is described. The control of layer thickness and molecular weight, a constant graft density, and a narrow molecular weight distribution of the polymers produced provide evidence for a controlled surface-initiated polymerization, and dense surface-attached polymer brushes on the SiO 2 surfaces are obtained under mild reaction conditions.

Polymer Brushes via ATRP: Role of Activator and Deactivator in the Surface‐Initiated ATRP of Styrene on Planar Substrates

The role of activator and deactivator species in the surface-initiated atom-transfer radical polymerization of styrene using CuBr/CuBr 2 /pentamethyl-diethylenetriamine as a model system is described. The influence of initially added deactivator with respect to the degree of controlling the layer growth and thickness is studieed. Variation of the activator concentration results in changes of the kinetics as wells as brush thicknesses consistent with the well-known rate laws of ATRP. System used for the generation of polymer brushes via ATRP.

Grafting of Poly(methyl methacrylate) Brushes from Magnetite Nanoparticles Using a Phosphonic Acid Based Initiator by Ambient Temperature Atom Transfer Radical Polymerization (ATATRP)

Poly(methyl methacrylate) in the brush form is grown from the surface of magnetite nanoparticles by ambient temperature atom transfer radical polymerization (ATATRP) using a phosphonic acid based initiator. The surface initiator was prepared by the reaction of ethylene glycol with 2-bromoisobutyrl bromide, followed by the reaction with phosphorus oxychloride and hydrolysis. This initiator is anchored to magnetite nanoparticles via physisorption. The ATATRP of methyl methacrylate was carried out in the presence of CuBr/PMDETA complex, without a sacrificial initiator, and the grafting density is found to be as high as 0.90 molecules/nm2. The organic–inorganic hybrid material thus prepared shows exceptional stability in organic solvents unlike unfunctionalized magnetite nanoparticles which tend to flocculate. The polymer brushes of various number average molecular weights were prepared and the molecular weight was determined using size exclusion chromatography, after degrafting the polymer from the magnetite core. Thermogravimetric analysis, X-ray photoelectron spectra and diffused reflection FT-IR were used to confirm the grafting reaction.

Synthesis of Polymer Grafted Magnetite Nanoparticle with the Highest Grafting Density via Controlled Radical Polymerization

The surface-initiated ATRP of benzyl methacrylate, methyl methacrylate, and styrene from magnetite nanoparticle is investigated, without the use of sacrificial (free) initiator in solution. It is observed that the grafting density obtained is related to the polymerization kinetics, being higher for faster polymerizing monomer. The grafting density was found to be nearly 2 chains/nm2for the rapidly polymerizing benzyl methacrylate. In contrast, for the less rapidly polymerizing styrene, the grafting density was found to be nearly 0.7 chain/nm2. It is hypothesized that this could be due to the relative rates of surface-initiated polymerization versus conformational mobility of polymer chains anchored by one end to the surface. An amphiphilic diblock polymer based on 2-hydroxylethyl methacrylate is synthesized from the polystyrene monolayer. The homopolymer and block copolymer grafted MNs form stable dispersions in various solvents. In order to evaluate molecular weight of the polymer that was grafted on to the surface of the nanoparticles, it was degrafted suitably and subjected to gel permeation chromatography analysis. Thermogravimetric analysis, transmission electron microscopy, and Fourier transform infrared spectroscopy were used to confirm the grafting reaction.

A practical route for the preparation of poly(4‐hydroxystyrene), a useful photoresist material

The synthesis and characterization of poly(4-hydroxystyrene) (PHS) and poly(4-vinylphenol) (PVPh) by the polymer modification route are reported. Polystyrene prepared by free-radical and anionic polymerization was acetylated quantitatively to poly(4-acetylstyrene) (ACPS) with acetyl chloride and anhydrous aluminum trichloride in carbon disulfide. The acetylation worked equally well in a mixture of 1,2-dichloroethane (DCE) and nitrobenzene containing largely DCE. The extent of the acetylation was estimated by 1 H NMR. The oxidation of ACPS was carried out with various oxidizing agents and reaction conditions. The peracetic acid oxidation in chloroform resulted in quantitative oxidation to poly(4-acetoxystyrene) (APS) as estimated by 1 H NMR spectroscopy. The treatment of APS with hydrazine hydrate in dioxane resulted in the formation of PVPh. Deacetylation occurred with equal versatility in a mixture of aqueous sodium hydroxide and tetrahydrofuran. All the polymers were characterized via gel permeation chromatography, IR, UV, 1 H NMR, and 13 C NMR spectroscopic techniques. This is the first report on the synthesis of ACPS, APS, and PHS of reasonably narrow molecular weight distributions or otherwise by the polymer modification route.

Rational design of phenothiazine (PTz) and ethylenedioxythiophene (EDOT) based donor–acceptor compounds with a molecular aggregation breaker for solid state emission in red and NIR regions

Two novel donor–acceptor (A–π–D–π–A) fluorophores based on phenothiazine (PTz) and ethylenedioxythiophene (EDOT) have been synthesized. Interestingly, an unusual π-stacking induced planarization of the crystal structure was observed for the PTz ring in the dialdehyde. The solid fluorophores exhibited emission in red (600 nm) and near infrared (NIR; 739 nm) regions with quantum yields of 8.9% and 0.9%, respectively. High quantum yields were obtained for the fluorophore doped polystyrene films.

Synthesis and Morphological Study of Thick Benzyl Methacrylate–Styrene Diblock Copolymer Brushes

We demonstrate, for the first time, the synthesis of model poly(benzyl methacrylate) [P(BnMA)] brushes of very high thickness (>300 nm) on silicon wafer. P(BnMA) brush is also synthesized from the surface of silica nanoparticles, from a covalently anchored initiator monolayer, using ambient temperature ATRP. The kinetic studies and block copolymerization from the surface anchored P(BnMA)-Br macroinitiator showed that the polymerization was controlled in nature. AFM, ellipsometry, and water contact angle were used for the characterization of the polymer brush. The grafting density of the P(BnMA) brush, formed by immersion in a dilute monomer solution, was relatively less (∼11% less) in comparison to that obtained by immersion in neat monomer under similar conditions. The P(BnMA)-Br macroinitiator brushes were used to synthesize P(BnMA-b-S) diblock copolymer brushes by the ATRP of styrene at 95 °C. The P(BnMA-b-S) brushes showed stimulus response to a selective solvent and various nanopatterns were observed according to the composition of the block copolymer.

A solvent‐free method for the synthesis of block copolymers with fluorinated pendant groups by a hydrosilylation reaction

A solvent-free method for the hydrosilylation of pendant double bonds in block copolymers is reported in this article. An anionically prepared block copolymer, poly(styrene-b-1,2-butadiene), was heated with 1H,1H,2H,2H-perfluorooctyldimethylhydrosilane in the presence of a nonacidic platinum catalyst for 24–26 h to obtain a quantitatively hydrosilylated block copolymer. Gel permeation chromatography, IR, and thermogravimetric analysis were used to characterize the block copolymers obtained.

A NOVEL AND SIMPLE METHOD OF PREPARATION OF POLY(STYRENE-B-2-VINYLPYRIDINE) BLOCK COPOLYMER OF NARROW MOLECULAR WEIGHT DISTRIBUTION: LIVING ANIONIC POLYMERIZATION FOLLOWED BY MECHANISM TRANSFER TO CONTROLLED/“LIVING” RADICAL POLYMERIZATION (ATRP)

A novel and simple method of preparation of a block copolymer of styrene and 2-vinylpyridine with narrow molecular weight distribution is reported. The novelty lies in the transformation of the polymerization mechanism from living anionic to controlled/“living” radical polymerization (ATRP). Thus, anionic polymerization of styrene is carried out in benzene using sec-butyllithium as the initiator followed by termination with ethylene oxide to prepare hydroxy-terminated polystyrene (PS-OH). PS-OH is converted to chloride-terminated polystyrene (PS-Cl) by a displacement reaction involving thionyl chloride and pyridine in benzene. PS-Cl is used to initiate the heterogeneous ATRP of 2-vinylpyridine in p-xylene with CuCl/2,2′-bipyridine system. The polymers synthesized are characterized by gel permeation chromatography (GPC), thin layer chromatography (TLC), IR and proton NMR spectroscopies.

Tetrakis(trialkylsilylethynylphenyl)ethenes: mechanofluorochromism arising from steric considerations with an unusual crystal structure

Mechanofluorochromism (MFC) arising from extended partial planarization of a conjugated molecular framework through the transfer of mechanical stress by terminal bulky groups is demonstrated. Thus the tetrakis(triisopropylsilyl-4-ethynylphenyl)ethene [TPE-(TIPS)4] luminophore, synthesized for the first time, is shown to exhibit MFC when the threshold pressure exceeds about 1.3 MPa. An analogous luminophore, tetra(trimethylsilyl-4-ethynylphenyl)ethene [TPE-(TMS)4], with smaller bulky groups at the periphery of TPE, synthesized for comparative studies, was also observed to exhibit MFC. MFC is observed under visible and UV light excitation. The color change is reversed upon annealing or under solvent fumigation conditions. The luminophores show high quantum yields in the solid state ranging from 60 to 74%. Very interestingly, TPE-(TMS)4 exhibited quite an unusual crystal structure, where no intermolecular interactions attributed to mechanofluorochromism are observed. The solid state optical absorption and CP-MAS 13C NMR measurements strongly suggested that the mechanism of MFC could have originated from partial planarization of the molecule upon grinding/shearing, facilitated by the bulky peripheral/terminal groups. These high solid state emitting luminophores with MFC properties could find applications in the areas of solid state lighting and sensors. The synthetic design, in principle, should enable MFC as a function of pressure (through variation in steric handle) and temperature (through electronic and conformational handles). The novel and rational synthetic design, in principle, should enable MFC in a family of organic molecules as a function of pressure and temperature.