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Solid supported catalysts such as amines are in high demand for the chemical fixation of CO2 into commodity chemicals.

Double hydrophilic ABA-type amphiphilic polyurethane (PU)-based poly(N-vinylpyrrolidone) (PNVP)-b-PU-b-PNVP and poly(N-isopropylacrylamide) (PNIPAM)-b-PU-b-PNIPAM triblock copolymers have successfu...

The review reports an aqueous solution behavior of commercially available and easy-to-use polymers, i.e., Pluronics®- and PNIPAM-based block copolymers. Both the polymers are stimuli responsive in nature. The present review covers the different aspects of aggregation behavior of Pluronics®- and PNIPAM-based block copolymeric micelles. Here, a comparison of physical properties such as EO–PO block, CP, CMC and CMT is made. Such physical parameters can be modulated with ease by the presence of external stimuli, viz. electrolytes, organic additives such as alcohols, phenols, amides and acids, different types of surfactants and water-soluble polymers, and also by modification of end groups of Pluronics®. But in this review, our main focus is to study the addition of salts and non-electrolytes on the aggregation behavior of Pluronics®. With the help of above parameters, users can get idea about the stability, partition coefficient, solubilization capacity, etc. In analogy with Pluronics®, PNIPAM is also a thermo-responsive polymer with ~ 32 °C lower critical solution temperature (LCST). However, the LCST is independent of the degree of polymerization, i.e., molecular weight of homopolymer. However, the LCST can be tuned in the presence of external stimulus. PNIPAM-based di-block copolymers form various morphologies in different environments. An inverted morphology by double-hydrophilic-block copolymers is also possible. According to US and British Pharmacopoeia, some of the Pluronics® and PNIPAM are recognized as pharmaceutical excipients. Therefore, they have been extensively used for various pharmaceutical formulations. The other applications of these polymers are tissue engineering, bioseparation devices, active membranes, biosensors, rheological modifier, lithium batteries, etc.

Pluronics® and Tetronics® are used in industry for solubilizing various kinds of hydrophobic compounds since decades. In present study, moderately hydrophobic linear and star block copolymer viz. Pluronic® P104 and Tetronic® T1304 are employed for the solubilization of four polycyclic aromatic hydrocarbons (PAHs) viz. naphthalene (Np), anthracene (An), phenanthrene (Ph) and pyrene (Py). The aggregation behaviour of these block copolymers in an aqueous media has been investigated by cloud point (CP), viscometry, dynamic light scattering (DLS), and small angle neutron scattering (SANS) techniques. The aqueous solubilities of these PAHs are quite poor, hence their extractions from contaminated areas are difficult. Cloud point of block copolymers linearly decreases as a function of PAHs concentration and strongly depends on the structure of PAHs. The aqueous solutions of both block copolymers are Newtonian fluid. The solubilization of PAHs in these copolymeric micelles leads to increase in the viscosity of solution suggesting the growth of micelles. The effect of concentration and temperature on the size and shapes of micelles were evaluated from DLS and SANS studies. The study provides an alternative method for the remediation of PAHs using inexpensive commercially available block copolymers.

A nanohybrid has been synthesized by incorporating organically modified layered silicate in a poly(vinylidene fluoride) (PVDF) matrix. Molecular-level phenomena have been explored after exposing PVDF and its nanohybrid to an electron beam of varying doses. The electron beam interacts with polymer chains and thereby generates different free radicals, the number of which is quite high in nanohybrid as compared to pure PVDF. The stability of free radicals has been confirmed through density functional theory energy minimization, predicting stable β-phase free radicals in the nanohybrid. Quantitative analyses of chain scission, crosslinking and double bond formation are reported and compared after irradiation for both PVDF and its nanohybrid using UV-visible and Fourier transform infrared spectroscopies, sol–gel analyses and gel permeation chromatography, revealing both chain scission and crosslinking phenomena in irradiated PVDF and its nanohybrid, but at higher dose (>90 Mrad) crosslinking dominates in the nanohybrid due to more free radicals and proximity of radical chains on top of templated system in the nanohybrid as compared to pure PVDF. The enhanced crosslinking alters the nanostructure causing disappearance of the peak at 2θ ≈ 3°. Moreover, the electron beam induces significant piezoelectric β-phase in the nanohybrid against only α-phase in pure PVDF at a similar dose and raises the possibility for the use of electron-irradiated nanohybrid as an electromechanical device. β-Phase formation is also supported through solid-state NMR, scanning electron microscopy and differential scanning calorimetry studies. The thermal properties in terms of heat of fusion and degradation temperature have been verified indicating steady decrease of melting point and heat of fusion for pure PVDF while considerably less effect is observed for the nanohybrid. The combined effect of chain scission and crosslinking makes both PVDF and its nanohybrid brittle, but with greater stiffness with respect to unirradiated specimens. © 2014 Society of Chemical Industry

Well-defined linear dihydrophilic amphiphilic ABA-type triblock copolymers of e-caprolactone (CL) and N-isopropylacrylamide (NIPAAm) have successfully been synthesized with a high yield by combining the ring opening polymerization (ROP) and xanthate-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization methods. The resulted block copolymer shows the formation of micelles in water as supported by light scattering. The critical micelle concentration (cmc) value of the micelle increases with the increase in the chain length of the poly (N-isopropylacrylamide) (PNIPAAm) block. Cloud point of the block copolymers decreases with the decrease in the PNIPAAm chain length. The TGA analysis shows a one-step degradation and a lower thermal stability of the triblock copolymer than the PNIPAAm. The DSC analysis of the triblock copolymer shows the lowering of glass transition temperature (T g), and melting temperature (T m) peaks possibly due to the partial miscibility of the poly (e-caprolactone) (PCL) block with the amorphous PNIPAAm block through the interaction of ester groups of PCL with the amide groups of PNIPAAm. The XRD pattern of the triblock copolymer shows a broad peak due to the suppression of the crystallization of PCL block owing to the mixing of PNIPAAm block with the PCL block.

Well-defined amphiphilic poly( d , l -lactide)- b -poly( N -vinylpyrrolidone) (PDLLA- b -PNVP) block copolymers were successfully prepared using ring-opening polymerization (ROP) and xanthate-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization. Synthesized PDLLA- b -PNVP block copolymers were characterized by 1 H NMR spectroscopy and GPC. Spherical micelles of ∼30.2 nm diameter were formed from the aqueous solution of amphiphilic diblock copolymer PDLLA 42 - b -PNVP 63 as revealed by TEM and supported by 1 H NMR and light scattering. The critical micelle concentration value of the block copolymers, determined by fluorescence spectroscopy using pyrene as probe, increased with the increase in the chain length of PNVP block. The average hydrodynamic radius ( R h ) of the micelles remained almost constant above the cmc value over the angles of scattering measurement. Thermal properties of these block copolymers were studied by TGA, DTA and DSC. Crystalline properties of these block copolymers were studied by WXRD.

Two new alkyne-terminated xanthate reversible addition-fragmentation chain-transfer (RAFT) agents: (S)-2-(Propynyl propionate)-(O-ethyl xanthate) (X3) and (S)-2-(Propynyl isobutyrate)-(O-ethyl xanthate) (X4) were synthesized and characterized and used for the controlled radical polymerization of N-vinylpyrrolidone (NVP). X3 showed better chain transfer ability in the polymerization at 60°C. Molecular weight of the resulted polymer increased linearly with the increase in monomer loading. Kinetics study with X3 showed the pseudo-first order kinetics up to 67% monomer conversion. Molecular weight (Mn) of the resulting polymer increased linearly with the increase in the monomer conversion up to around 67%. With the increase in the monomer conversion, polydispersity of the corresponding poly(NVP)s initially decreased from 1.34 to 1.32 and then increased gradually to 1.58. Chain-end analysis of the resulting polymer by 1H-NMR and FTIR showed clearly that polymerization started with radical forming out of xanthate RAFT agent. Living nature of the polymerization was also confirmed from the successful homo-chain extension experiment and the hetero-chain extension experiment involving synthesis of poly(NVP)-b-polystyrene amphiphilic diblock copolymer. Formed alkyne-terminated poly(NVP) also allowed easy conjugation to azide-terminated polystyrene by click chemistry to prepare well-defined poly(NVP)-b-polystyrene block copolymers. Resulting polymers were characterized by GPC, 1H-NMR, FTIR, and thermal study. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

S)-2-(Ethyl propionate)-(O-ethyl xanthate) (X1) and the newly syn- thesized (S)-2-(ethyl isobutyrate)-(O-ethyl xanthate) (X2) were used as the revers- ible addition-fragmentation chain transfer (RAFT) agents for the radical polymerization of N-vinylpyrrolidone (NVP). The former showed the better chain transfer ability in the polymerization at 60 C. Kinetics study with X1 shows the psuedo-first order kinetics upto 45% monomer conversion. Molecular weight (Mn) of the resulted polymer increases linearly with increase in the monomer conversion upto around 45%. Polydispersity of the corresponding poly(NVP)s increase grad- ually from 1.2 to 1.9 with increase in the monomer conversion. Chain-end analysis of the resulted polymer by 1 H NMR shows clearly that polymerization started with radical forming out of xanthate mediator. Living nature of the polymerization was confirmed from the successful homo chain extension experiment and also the het- ero-chain extension experiment involving synthesis of poly(NVP)-b-polystyrene amphiphilic diblock copolymer.

Poly(N-isopropylacrylamide) (PNIPAM) hydrogels were simply prepared by free radical polymerization in different methanol–water mixture. A scanning electron microscopy study revealed that the freeze-dried hydrogels were macroporous. The swelling ratios in water at 20°C of the resulting hydrogels followed the order: X0.43>X0.21>X0.76 ≈ X0.57>X0.31>X0.13>X0.06>X0, where Xm denotes a gel prepared in a methanol–water mixture with m mole fraction of methanol (xm). Below the lower critical solution temperature, the swelling ratio values of all of the hydrogels gradually decreased with the increase in the temperature. The complete collapse of the PNIPAM chain of all the gels occurred at about 38°C, whereas the same was observed at about 35°C for the conventional gel prepared in water. The swelling ratio values of all the PNIPAM gels in the methanol–water mixtures with different xm values at 20°C passed through a minimum in the cononsolvency zone. The deswelling rates of the hydrogels decreased in the following order: X0.43> X0.31> X0.21> X0.57> X0.76 ≈ X0.13> X0.06> X0. The reswelling rates of these hydrogels decreased in the following order: X0> X0.31> X0.06 ≈ X0.13 > X0.76> X0.57> X0.21> X0.43. The release rates of the Tramadol Hydrochloride drug at 37°C from the drug-loaded hydrogels were almost same for all of the hydrogels. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Well-defined amphiphilic poly(e-caprolactone)-b-poly(N-vinylpyrrolidone) (PCL-b-PNVP) block copolymers were successfully prepared via the combination of ring-opening polymerization (ROP) and xanthate-mediated reversible addition−fragmentation chain transfer (RAFT) polymerization. Well-defined poly(e-caprolactone) (PCL−OH) was synthesized by ROP in bulk at 110 °C using benzyl alcohol as initiator and stannous octate [Sn(Oct)2] as catalyst . The −OH end group was then converted into its corresponding xanthate (PCL−X) via the conversion to its corresponding bromide (PCL−Br). These are verified by 1H NMR spectroscopy. PCL-b-PNVP block copolymers were synthesized via RAFT polymerization in tetrahydrofuran (THF) at 80 °C using PCL−X as macro-chain transfer agent and characterized by 1H NMR spectroscopy and gel permeation chromatography (GPC). The amphiphilic diblock copolymer PCL63-b-PNVP90 forms spherical micelles of ∼34 nm diameter in water as shown by transmission electron microscopy (TEM), supported by 1H N...

Poly(N-isopropylacrylamide) (PNIPAM) hydrogels were prepared by free-radical polymerization in different ethanol–water mixtures. A scanning electron microscopy study revealed that the resulting hydrogels were macroporous. The swelling ratios of the resultant hydrogels in water at 20°C followed this order: X0.34 ≈ X0.68 > X0.48 > X0.09 > X0.04 > X0, where Xa denotes a gel prepared in an ethanol–water solvent mixture with an ethanol molar fraction of a. Below the lower critical solution temperature, the swelling ratio values of all of the hydrogels gradually decreased with increasing temperature. The complete collapse of the PNIPAM chain of all of these gels occurred at about 38°C, whereas the same was observed at about 35°C for the conventional gel prepared in water. The swelling ratio values of all of the PNIPAM gels with different molar fractions of ethanol at 20°C passed through a minimum in the cononsolvency zone. The deswelling rates of the hydrogels decreased in the following order: X0.34 > X0.48 > X0.68 > X 0.09 > X0.04 > X0. The reswelling rates of these hydrogels decreased in the following order: X0 > X0.04 ≈ X0.48 > X0.09 ≈ X0.68 > X 0.34. The freeze-drying process decreased the swelling ratios but increased the deswelling and reswelling properties of the PNIPAM gels. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

(S)-2-(Ethyl propionate)-(O-ethyl xanthate) (X1) and the newly synthesized (S)-2-(ethyl isobutyrate)-(O-ethyl xanthate) (X2) were used as the reversible addition-fragmentation chain transfer (RAFT) agents for the radical polymerization of N-vinylpyrrolidone (NVP). The former showed the better chain transfer ability in the polymerization at 60 °C. Kinetics study with X1 shows the psuedo-first order kinetics upto 45% monomer conversion. Molecular weight (M n) of the resulted polymer increases linearly with increase in the monomer conversion upto around 45%. Polydispersity of the corresponding poly(NVP)s increase gradually from 1.2 to 1.9 with increase in the monomer conversion. Chain-end analysis of the resulted polymer by 1H NMR shows clearly that polymerization started with radical forming out of xanthate mediator. Living nature of the polymerization was confirmed from the successful homo chain extension experiment and also the hetero-chain extension experiment involving synthesis of poly(NVP)-b-polystyrene amphiphilic diblock copolymer.

A series of high molecular weight poly(N-isopropylacrylamide) (PNIPAM)s with low polydispersity (Mn = 7.0 × 104 to 10.2× 104 g mol–1, PDI = 1.23–1.35) having different isotacticity [meso diad (m) =...

Novel amphiphilic ABA-type poly(D-gluconamidoethyl methacrylate)-b-polyurethane-b-poly(D-gluconamidoethyl methacrylate) (PGAMA-b-PU-b-PGAMA) tri-block copolymers were successfully synthesized via the combination of the step-growth and copper-catalyzed atom transfer radical polymerization (ATRP). Dihydroxy polyurethane (HO-PU-OH) was synthesized by the step-growth polymerization of hexamethylene diisocyanate with poly(tetramethylene glycol). PGAMA-b-PU-b-PGAMA block copolymers were synthesized via copper-catalyzed ATRP of GAMA in N, N-dimethyl formamide at 20°C in the presence of 2, 2′-bipyridyl using Br-PU-Br as macroinitiator and characterized by 1H-NMR spectroscopy and GPC. The resulting block copolymer forms spherical micelles in water as observed in TEM study, and also supported by 1H NMR spectroscopy and light scattering. Miceller size increases with increase in hydrophilic PGAMA chain length as revealed by DLS study. The critical micellar concentration values of the resulting block copolymers increased with the increase of the chain length of the PGAMA block. Thermal properties of these block copolymers were studied by thermo-gravimetric analysis, and differential scanning calorimetric study. Spherical Ag-nanoparticles were successfully synthesized using these block copolymers as stabilizer. The dimension of Ag nanoparticle was tailored by altering the chain length of the hydrophilic block of the copolymer. A mechanism has been proposed for the formation of stable and regulated Ag nanoparticle using various chain length of hydrophilic PGAMA block of the tri-block copolymer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013