Sanjib Banerjee

Photoinduced Smart, Self-Healing Polymer Sealant for Photovoltaics

Polyisobutylene (PIB)-based polymer networks potentially useful as smart coatings for photovoltaic devices have been developed. Low molecular weight coumarin functional triarm star PIB was synthesized via a single step SN2 reaction of bromoallyl functional triarm star PIB with 4-methylumbelliferone or umbelliferone in the presence of sodium hydride. Quantitative end functionality was confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. UVA (λmax = 365 nm) induced reversible photodimerization of the coumarin moieties resulted in cross-linked elastomeric films exhibiting self-healing behavior. The extent of photodimerization/photoscission was monitored by UV-vis spectroscopy. The low oxygen (1.9 × 10(-16) mol m m(-2) s(-1) Pa(-1)) and moisture (46 × 10(-16) mol m m(-2) s(-1) Pa(-1)) permeability of the cross-linked polymer films suggest excellent barrier properties of the cross-linked polymer films. The self-healing process was studied by atomic force microscopy (AFM). For this, mechanical cuts were introduced in the cross-linked PIB films through micromachining with an AFM tip and the rate of healing induced by UV, sunlight, or both was followed by taking AFM images of the film at different time intervals during the repair process.

Surface confined atom transfer radical polymerization: access to custom library of polymer-based hybrid materials for speciality applications

A significant advance has been achieved in the techniques for growing polymers from a surface via atom transfer radical polymerization (ATRP). In this review, we highlight recent advances and developments in the field of surface-confined atom transfer radical polymerization (SC-ATRP) with a brief overview of the fundamentals of ATRP. Some exciting current and forthcoming applications of the materials made by SC-ATRP are presented. We conclude with an outline of the future directions in the applications of SC-ATRP towards the design of advanced functional materials with designed performances for many high-value future applications.

In situ prepared mesoporous silica nanosphere supported palladium(II) 2-aminopyridine complex catalyst for Suzuki–Miyaura cross-coupling reaction in water

We report the synthesis and catalytic activities of a mesoporous silica nanosphere supported palladiumII 2-aminopyridine complex (Pd-AMP-MSN). First, chloroalkyl functionalized mesoporous silica nanospheres (Cl-MSN) is prepared by an in situ co-condensation reaction of tetraethyl orthosilicate (TEOS) with ((chloromethyl)phenylethyl)trimethoxysilane (CMPE-TMS) using cetyltrimethylammonium bromide (CTAB) as the structure directing agent. The reaction of Cl-MSN with 2-aminopyridine followed by complexation with palladium acetate produces the catalyst Pd-AMP-MSN. FTIR spectroscopic analysis confirms the presence of 2-aminopyridine functionality inside the mesopores of the Pd-AMP-MSN. Nitrogen adsorption–desorption and X-ray diffraction analyses reveal mesoporous structures of the Pd-AMP-MSN catalyst with a specific surface area of 372 m2 g−1, a pore volume of 0.172 cm3 g−1 and a narrow pore size distribution (D ∼ 1.92 nm). FESEM and HRTEM results indeed show the formation of nanospheres with mesoporous structures. This catalytic system exhibits excellent activity in Suzuki–Miyaura cross-coupling reactions of aryl iodides, aryl bromides and also aryl chlorides with phenylboronic acids in water medium with high yields. This Pd-AMP-MSN catalyst could be quantitatively recovered by simple filtration and is found to be highly active without any significant loss of its catalytic activity in eight consecutive runs.

Towards new strategies for the synthesis of functional vinylidene fluoride-based copolymers with tunable wettability

Synthesis of poly(vinylidene fluoride)-based functional polymers with tunable wettability was achieved via radical copolymerizations of vinylidene fluoride (VDF) with tert-butyl 2-trifluoromethacrylate (MAF-TBE) followed by hydrolysis of the tert-butyl ester groups. Radical copolymerizations of VDF with 2-trifluoromethyl acrylic acid (MAF) and MAF-TBE were investigated under various experimental conditions: initiators, temperatures, and solvents. The polymerizations using peroxide initiators led to good yield (≥57%), while azo initiators did not lead to any polymerization. The compositions and microstructures of all the obtained copolymers were determined by 1H and 19F NMR spectroscopies. The very low yield (23%) achieved in radical copolymerization of VDF with MAF in water was attributed to the regioselective nucleophilic addition of water onto MAF, yielding a potential fluorosurfactant, 3-hydroxy-2-(trifluoromethyl)propanoic acid in good yield (85%). In contrast, no reaction was observed between MAF-TBE and water, even in the presence of ammonium perfluorooctanoate as a (fluorinated) surfactant. The poly(VDF-co-MAF-TBE) copolymer was shown to be easily hydrolyzed under mild conditions to prepare –COOH-functionalized PVDF copolymers, without any dehydrofluorination of VDF units. The wettabilities of these copolymers were studied by water contact angle (WCA) measurement. Compared to the poly(VDF-co-MAFTBE) copolymers (WCA = 102°), the –COOH functionalized PVDF copolymer exhibits a lower WCA (57°). This work paves the way for the synthesis of PVDF-based functional copolymers with tunable wettability for potential applications in the preparation of membranes for water purification, coatings or oil recovery systems.

Specific Counterion Repercussions on the Thermal, pH-Response, and Electrochemical Properties of Side-Chain Leucine Based Chiral Polyelectrolytes

Effects of counterions of side chain amino acid based polyelectrolytes (PEs) on the solubility in aqueous medium, pH responsiveness, thermal properties, and ionic conductivities have been appraised. Deprotection of the tert-butyl carbamate (Boc) group from poly(Boc-l-leucine methacryloyloxyethyl ester) [P(Boc-l-Leu-HEMA)] was carried out to produce PE with trifluoroacetate as an associative counteranion (1a). PEs with bis(trifluoromethylsulfonyl)imide and hexafluorophosphate counteranion were prepared through anion exchange reactions of 1a. Protonation of the neutralized polymer (2) obtained from 1a, followed by anion exchange, leads to the production of miscellaneous PEs bearing different counteranions, such as tetrafluoroborate, trifluoromethanesulfonate, chloride, and nitrate. Differential scanning calorimetry traces of the PEs reveal that the comparatively larger and weakly coordinated counteranions require less thermal energy to dissociate, and thus, the glass transition temperature (Tg) of the PEs fall off with an increase in the size of the counteranion. A remarkable conductivity of 2.1 mS/cm was obtained in deionized water when Cl(-) acted as the counteranion. Steric and electronic factors of the counteranion induce a change of transition pH in different PEs, although the chiroptical nature was retained, as confirmed by circular dichroism spectroscopy.

Amino-acid-based zwitterionic polymer and its Cu(II)-induced aggregation into nanostructures: a template for CuS and CuO nanoparticles.

A convenient and water-based approach is described for the synthesis of an l-lysine-based zwitterionic polymer, poly(ε-l-lysinyl acrylamide) (PLAM), without using protecting group chemistry, chromatographic purifications, and organic solvents as the reaction media. PLAM contains both amine and carboxylic acid groups in each repeating unit, which can either be protonated or deprotonated just by altering the pH of the solution to obtain overall positive or negative charge. PLAM is tested for its applicability as a zwitterionic polymeric buffer in water. Cu(II) ion-induced aggregation of PLAM as a function of solution pH is studied. Spherical nanogel aggregates are formed at pH 9.5 due to aggregation of PLAM through its complexation with Cu(II) ion. Spherical aggregates appear to dissociate via breaking of the complexation at a pH < 5.5 resulting in molecular dissolution of PLAM. This aggregation process is pH reversible. The Cu(II)-PLAM aggregates are used as a template for fabrication of CuO and CuS nanoparticles.

Organometallic‐Mediated Alternating Radical Copolymerization of tert‐Butyl‐2‐Trifluoromethacrylate with Vinyl Acetate and Synthesis of Block Copolymers Thereof

Organometallic-mediated radical polymerization (OMRP) has given access to well-defined poly(vinyl acetate-alt-tert-butyl-2-trifluoromethacrylate)-b-poly(vinyl acetate) and poly(VAc-alt-MAF-TBE) copolymers composed of two electronically distinct monomers: vinyl acetate (VAc, donor, D) and tert-butyl-2-trifluoromethacrylate (MAF-TBE, acceptor, A), with low dispersity (≤1.24) and molar masses up to 57 000 g mol-1 . These copolymers have a precise 1:1 alternating structure over a wide range of comonomer feed compositions. The reactivity ratios are determined as rVAc = 0.01 ± 0.01 and rMAF-TBE = 0 at 40 °C. Remarkably, from a feed containing >50% molar VAc content, poly(VAc-alt-MAF-TBE)-b-PVAc block copolymers are produced via a one-pot synthesis. Such diblock copolymers exhibit two glass transition temperatures attributed to the alternating and homopolymer sequences. The OMRP of this fluorine-containing alternating monomer system may provide access to a wide range of new polymer materials.

Polymerization of isobutylene catalyzed by EtAlCl2/bis(2-chloroethyl) ether complex in steel vessels

When synthesis of highly reactive polyisobutylene (HR PIB) via cationic polymerization of isobutylene (IB) using ethylaluminum dichloride·bis(2-chloroethyl) ether (EADC·CEE) complex were carried out in metal reactors made of 316 stainless steel (SS), PIB olefin with up to 20% lower exo-olefin content were obtained compared to that obtained in glass reactors (up to 90%). In an effort to investigate this reduction in exo-olefin selectivity in SS reactors, we have studied the polymerization of IB using EADC·CEE complex in SS (minimum of 10.5% chromium content by mass), carbon steel (CS) (0% chromium content by mass), monel alloy 400 (M400) (0% chromium content by mass) and glass reactors. The latter was examined in the presence and absence of SS balls. Mechanistic studies using ATR-FTIR and 1H NMR spectroscopy suggest that this decrease in exo-olefin selectivity is due to a side reaction of EADC with Cr2O3 involving the loss of the ethyl group from EADC and decomplexation of the EADC·CEE complex which hinders the selective abstraction of the β-proton from the growing chain end. In the absence of chromium (CS and M400 reactors), the exo-olefin content is virtually identical to that obtained in glass reactors. Therefore, CS and M400 reactors are suitable to produce HR PIB with high exo-olefin content.

Ultrasound-Induced In Situ Formation of Coordination Organogels from Isobutyric Acids and Zinc Oxide Nanoparticles

The discovery of ultrasound-induced in-situ formation of coordination organogels using various isobutyric acids (such as isobutyric acid or 2-methylisobutyric acid or 2-bromoisobutyric acid) and zinc oxide nanoparticles was described. FTIR and XRD results suggest that ultrasound irradiation triggers the quick dissolution of zinc oxide nanoparticles by isobutyric acids, resulting in the in-situ formation of zinc isobutyrate complexes that undergoes fast sonocrystallization into gel fibers. FESEM results clearly demonstrate the formation of well-defined networks of fibers with several micrometers in length, but the average diameter of the fiber ranges from 30 to 65 nm, depending upon the nature of the isobutyric acids used. A combination of single-crystal structure analysis and powder XRD result was used to envisage the molecular packing present in the gel state. This is probably a very rare case of ultrasound-induced organogelation where metal oxide NPs are used as the precursor.

A stimuli-responsive methionine-based zwitterionic methacryloyl sulfonium sulfonate monomer and the corresponding antifouling polymer with tunable thermosensitivity

This report describes the design and synthesis of a zwitterionic [Boc-L-methionine-(2-methacryloylethyl)]sulfoniopropanesulfonate (METMASPS) monomer derived from methionine followed by its subsequent RAFT polymerization in water to produce a zwitterionic polymer (PMETMASPS). The aqueous METMASPS monomer solution exhibits transparent to turbid and turbid to transparent transitions near to its isoelectric point (5.75) upon switching the pH from anything below 4.8 to 4.8–6.8 and from 4.8–6.8 to above 6.8. Furthermore, in the pH range of 4.8–6.8, this turbid suspension transforms into a transparent solution showing a clear upper critical solution temperature (UCST)-type phase transition. However, the zwitterionic polymer is soluble in water at any pH value ranging from 1 to 12, but its transparent aqueous solution turns into a turbid solution exhibiting a soluble–insoluble phase transition upon addition of different kosmotropic anions such as SO42−, Ct3−, H2PO4− and Ac− of the Hofmeister series. This colloidal turbid suspension containing anion becomes transparent showing a distinct UCST-type phase transition upon heating. The cloud point (Tcp) is tunable with respect to the molecular weight of the polymer and the concentration of ions as well as solution pH. Finally, the antifouling property of the as-synthesized zwitterionic PMETMASPS is studied against resistance towards a model protein, bovine serum albumin (BSA) through the monitoring of anti-aggregating behaviour via DLS and is compared with that of poly(ethylene glycol) (PEG).