A convenient synthesis of a porphyrin cross-linked polymer,its application as a size selective heterogeneous catalyst and a comparison with a porphyrin-cored hyperbranched polymer

This paper describes how the polymeric structure and environment surrounding supported catalysts can be used to affect the product outcome from a reaction. As well as reporting a size/shape selectivity, we also describe a significant effect on product distribution. Specifically, how the polymeric environment can favour or disfavour particular products. As such, these results illustrate how it may be possible to target more or less of a specific compound (from a possible mix) by careful choice of the polymer architecture surrounding a catalyst.     

Adsorption behavior of water soluble polymers with lower critical solution temperature

The adsorption behavior of hydroxylpropyl cellulose (HPC), ethyl hydroxylethyl cellulose (EHEC) and poly-vinylalcohol (PVA) polymers, which have a lower critical solution temperature (LCST), have been studied in comparison with the behavior of hydroxylethyl cellulose (HEC) with no LCST. The saturated amount of adsorption (A _s ) for the polymers with LCST depended significantly on the adsorption temperature and theA _s , e. g., for HPC obtained at the LCST, the amount was 1.5 times as large as the value at room temperature. The highA _s values obtained at the LCST were maintained over a long period at room temperature, and the dense adsorption layer formed on the latex particles at the LCST showed a strong protective action against flocculation. Furthermore, the effect of the surface nature of the adsorbent on the polymer adsorption at the LCST has been investigated using six kinds of synthetic latices with different surface natures. It was found that the hydrophobic interaction between the polymer and the adsorbent plays an important role in inducing the adsorption, and the trend of increasing the hydrophilic character of the latex surface prevents the formation of the adsorption layer of the polymer.     

Using Soluble Polymers to Enforce Catalyst‐Phase‐Selective Solubility and as Antileaching Agents to Facilitate Homogeneous Catalysis

The enforced phase‐selective solubility of polyisobutylene (PIB)‐bound Rh^II catalysts in biphasic heptane/acetonitrile mixtures can be used not only to recycle these catalysts but also to minimize bimolecular reactions with ethyl diazoacetate. When cyclopropanation and O? H insertion reactions are carried out with PIB‐bound Rh^II catalysts either with or without addition of an unfunctionalized hydrocarbon polymer cosolvent, dimer by‐product formation is suppressed even without slow syringe pump addition of the ethyl diazoacetate. This suppression of by‐product formation is shown to be due to increased phase segregation of the soluble polymer‐bound catalyst and the ethyl diazoacetate reactant. These studies also reveal that added hydrocarbon polymer cosolvents can function as antileaching agents, decreasing the already small amount of a soluble polymer‐bound species that leaches into a polar phase in a biphasic mixture during a liquid/liquid separation step.     

液/液两相催化新进展--温控非水液/液两相催化

温控非水液/液两相催化,是指一类由两种或多种液态有机物组成的催化反应体系,其特点是体系的相态变化可通过温度来调控,即体系在高温时相互混溶呈均相,低温不溶分成两相,催化剂和产物分别处于两相,从而为解决均相催化剂分离难的问题开拓了一个新方向,是液/液两相催化研究领域最引人注目的进展之一.首次以"温控"为主线将氟两相催化作为温控液/液两相催化的一个特定类型纳入"温控非水液/液两相催化"范畴,并与其它通过温度来调控的有机液/液两相和作者提出的温控相分离催化串在一起作一较为详细的评述.     

An amphiphilic polymer for the synthesis of diverse polymer libraries exemplified using conjugates with lower critical solution temperatures that span water's liquid state

The discovery of new polymer functions is intrinsically tied to the synthesis of diverse structures. Herein we report the synthesis of a new polymer library precursor, poly[N-(12-carboxyl-3,6,9-trioxado) methacrylamide] (pCTMAAm), that is functionalizable with hydrophilic or hydrophobic ligands in both protic and aprotic solvents. The polymer is made through RAFT polymerization with narrow dispersities. Carboxylic acid groups terminate the pCTMAAm side chains, which allows conjugation of both hydrophobic and hydrophilic groups. As a demonstration, three very different ligands, agmantine (cation), galactosamine (polyol) and hexylamine (hydrophobic), were conjugated to pCTMAAm using DMTTM as a condensing agent with greater than 80% conjugation efficiency. To demonstrate the potential utility of the amphiphilic polymer, a polymer library containing side chains with a series of alkanes and varying degrees of substitution was synthesized showing lower critical solution temperature (LCST) profiles that span a temperature range of 7 °C to above 90 °C in water. Multivariate linear regression analysis of the polymer library was used to understand how polymer composition correlates to LCST, using molecular weight, alkane length and degree of substitution as continuous variables. The outcome showed that alkane length has the greatest influence on LCST and that LCST can be estimated using these material composition inputs.     

Control of the conjugation length and solubility in electroluminescent polymers

A new type of cyclolinear polymer, poly(phenylene vinylene‐alt‐cyclotriphosphazene), was synthesized through Heck‐type coupling reactions to produce π‐conjugated macromolecules with excellent solubility and precise electronic control of the band‐gap energy. This synthesis method is capable of producing well‐defined alternating polymers. The method is highly adaptable and can be readily used for other chromophore systems. The resulting polymers were also capable of accommodating a wide variety of substituents on the cyclophosphazene rings with minimal effect on the electronic properties. The band gap and electron affinities of the polymer were varied through the manipulation of the π‐conjugated unit located between the insulating phosphazene rings. Each chromophore matched the intended conjugation length consistently throughout the macromolecules. The polymers were good film formers because of the chosen substituents on the phosphazene rings. The absorbance of the polymers indicated minimal spectral shift from the monomer absorbance. This suggested an effective insulation of each chromophore unit from its neighbors by the phosphazene rings. Solution photoluminescence efficiencies were found to be up to 44.1%. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 69–76, 2006     

Pickering Interfacial Catalysis for Biphasic Systems: From Emulsion Design to Green Reactions

Pickering emulsions are surfactant‐free dispersions of two immiscible fluids that are kinetically stabilized by colloidal particles. For ecological reasons, these systems have undergone a resurgence of interest to mitigate the use of synthetic surfactants and solvents. Moreover, the use of colloidal particles as stabilizers provides emulsions with original properties compared to surfactant‐stabilized emulsions, microemulsions, and micellar systems. Despite these specific advantages, the application of Pickering emulsions to catalysis has been rarely explored. This Minireview describes very recent examples of hybrid and composite amphiphilic materials for the design of interfacial catalysts in Pickering emulsions with special emphasis on their assets and challenges for industrially relevant biphasic reactions in fine chemistry, biofuel upgrading, and depollution.     

Aqueous solution behavior of new thermoassociative polymers

A new kind of water-soluble polymer was obtained by grafting side chains, characterized by a phase separation on heating (Lower Critical Solution Temperature LCST), on a hydrosoluble backbone. For semidilute solutions, the side chains associate as the temperature exceeds a critical temperature (T _ass), which is close to their LCST. Microdomains are formed which act like physical crosslinking units between the main chains, and an increase in the aqueous solution viscosity is observed. Systems based on 2-Acrylamido-2-methyl propane sulfonic acid (AMPS) backbone and polyethylene oxide (PEO) side chains were developed. Their rheological behavior in both dilute and semi-dilute states was studied by varying differents parameters such as polymer and salt concentrations, grafting ratio, etc. Fluorescence measurements indicate the formation of hydrophobic microdomains on heating, in agreement with the thickening properties of the solutions.     

Preparation of thermoresponsive polymers bearing amino acid diamide derivatives via RAFT polymerization

We report here the synthesis of well‐defined homopolymer bearing amino acid diamide, poly(N‐acryloyl‐L ‐valine N′‐methylamide), via reversible addition fragmentation chain transfer (RAFT) polymerization using alkynyl‐functionalized 2‐dodecylsulfanylthiocarbonylsulfanyl‐2‐methyl‐propionic acid propargyl alcohol ester as chain transfer agent (CTA) and 2,2′‐azobis(isobutyronitrile) as initiator. The effects of a variety of parameters, such as temperature and solvent, on RAFT polymerization were examined to determine the optimal control of the polymerization. The controlled nature of RAFT polymerization was evidenced by the controllable molecular weight and low‐molecular‐weight polydispersity index (M_w/M_n) of resulting homopolymers and further demonstrated to have retained end‐group functionality by the fact of the successful formation of block copolymers from further RAFT polymerization by using the resultant polymer as macro‐CTA, as well as from “click” chemistry. Thermoresponsive property of the prepared polymer was evaluated in terms of the lower critical solution temperature in aqueous solution by measuring the transmittance variation at 500 nm from UV/vis spectroscopy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3573–3586, 2010     

Reversible Thermal Switching of Aqueous Dispersibility of Multiwalled Carbon Nanotubes

Easily reversible aqueous dispersion/precipitation of multiwalled carbon nanotubes (MWNTs) has been demonstrated using small‐molecule non‐ionic pyrene‐based surfactants, which exhibit lower critical solution temperature (LCST) phase behaviour. The MWNTs are dispersed by means of non‐covalent interactions. The dispersibility can be switched “off” (i.e., MWNTs precipitated) upon heating and switched “on” (i.e., MWNTs re‐dispersed) upon cooling and merely swirling the sample at room temperature, that is, under very mild conditions. This effect is also observed under high ionic strength conditions with NaCl in the aqueous phase.     

Liquid-liquid equilibria and theta temperatures in homopolymer-solvent solutions from a perturbed hard-sphere-chain equation of state

The perturbed hard-sphere-chain (PHSC) equation of state is used to calculate liquid-liquid equilibria of binary nonpolar solvent/homopolymer systems exhibiting both an upper critical solution temperature (UCST) and a lower critical solution temperature (LCST). Systems studied include polyisobutylene, polyethylene, and polystyrene solutions. Equation-of-state parameters of homopolymers are obtained by regressing the pressure-volume-temperature data of polymer melts. In polymer solutions, however, theory overestimates the equation-of-state effect which causes the LCST at elevated temperature. To correct the overestimated equation-of-state effect, an empirical adjustable parameter is introduced into the perturbation term of the PHSC equation of state. An entropy parameter is also introduced into the Helmholtz energy of the mixture to correlate quantitatively the dependence of critical temperatures on polymer molecular weight. For systems exhibiting a LCST, two adjustable parameters are required to obtain quantitative agreement of theoretical critical temperatures with experiment as a function of polymer molecular weight. For systems exhibiting both an UCST and a LCST, three adjustable parameters may be necessary. The need for so many empirical binary parameters is probably due to the oversimplified perturbation term which is based on the mean-field assumption. © 1996 John Wiley & Sons, Inc.     

Thermo‐Responsive Solid‐Phase Extraction Using Poly(methyl vinyl ether)–Containing Segmented Polymer Networks

Segmented polymer networks containing poly(methyl vinyl ether) (PMVE) segments were prepared by free‐radical‐initiated copolymerization of PMVE‐α,ω‐dimethacrylate with styrene or 2‐hydroxyethyl methacrylate (HEMA). These networks were evaluated as thermo‐responsive solid‐phase extraction materials. Suspension‐derived polymer networks consisting of 80% of PMVE and 20% of HEMA adsorb toluene from an aqueous solution at 40°C and release the adsorbed toluene quantitatively at 20°C.     

A pressure and temperature study on solubility and micelle formation of sodium perfluorodecanoate in aqueous solution

Both the critical solution temperature (CST, or the Krafft temperature) and the critical solution pressure (CSP, or the Tanaka pressure) were determined for sodium perfluorodecanoate (NaPFDe) in water, and the result shows that the Krafft temperature is raised with the increase in the Tanaka pressure. A thermodynamic analysis has been made on the data for the critical micellization concentration (cmc) and of the solubility at various temperatures and pressures. The estimated change in the partial molal volume, resulting from micelle formation from the singly dispersed state and from the hydrated solid state, was found to be conspicuously higher for NaPFDe compared to hydrocarbon surfactants. This has been ascribed to the more pronounced role of carbon chain-water interactions and water structure effects of the fluorocarbon surfactants.     

Use of an isotactic‐propylene/hexene copolymer as a new,versatile, soluble support

The use of isotactic‐poly(propylene‐co‐hexene) (iPPH) as new polymeric scaffold for synthesis as well as a phase‐selective, soluble polymer support for homogeneous catalysis is described. It was possible to functionalize olefin‐terminated iPPH using standard organic transformations. Each derivative could be isolated and purified using typical precipitations into a minimum amount of polar solvent, negating the need for wasteful work up and chromatographic procedures. Furthermore, it was demonstrated that an iPPH‐supported DMAP could serve as a recoverable, recyclable catalyst. Published 2013. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 600–605     

Synthesis and Characterization of a Novel Thermo‐Sensitive Copolymer of N‐Isopropylacrylamide and Dibenzo‐18‐crown‐6‐diacrylamide

Summary: A series of novel, thermo‐sensitive copolymers with different molar ratios of N‐isopropylacrylamide (NIPAM) and hydrophobic cis‐dibenzo‐18‐crown‐6‐diacrylamide (cis‐DBCAm) were prepared via free‐radical copolymerization. cis‐DBCAm with polymerizable end groups was successfully synthesized by reacting the corresponding amino crown ether with acryloyl chloride. The copolymers were characterized by FT‐IR and elemental analysis, and the thermo‐sensitivities of the copolymers were evaluated by measuring their lower critical solution temperatures (LCSTs) in the absence or presence of various metal ions. The results indicated that incorporation of cis‐DBCAm lowered LCSTs, and that the LCSTs of the copolymers decreased with the increase in cis‐DBCAm content in the copolymers. When the cavities of the crown ether units captured either K⁺ or Cs⁺ ions, the LCST of the respective copolymer–metal ion complex was further decreased, whereas the capture of Na⁺ or Li⁺ ions did not have a significant influence on the LCSTs of the copolymers.

Incorporation of cis‐DBCAm into PNIPAM resulted in a lower LCST. The LCST was decreased more when the cavities of the crown ether units captured K⁺ ions.     

Synthesis of silica‐supported rhodium carbene complex as efficient catalyst for the addition of phenylboronic acid to aldehydes

Silica‐supported catalytically active functional materials, such as the rhodium(I) carbene complex with 1‐(triethoxysilylpropyl)‐3‐(2,4,6‐trimethylbenzyl)imidazolidine‐2‐ylidine (L), were prepared using the sol–gel method. The complex ( 1 ; COD = 1,5‐cyclooctadiene) RhCl(COD)[1‐(triethoxysilylpropyl)‐3‐(2,4,6‐trimethylbenzyl)imidazolidin‐2‐ylidine] was characterized by conventional spectroscopic methods and elemental analyses and the silica‐supported functional material RhCl(COD)(L) were tested for the catalytic addition of phenylboronic acid to aldehydes. Copyright © 2005 John Wiley & Sons, Ltd.     

Spherically Symmetric Solvent is Sufficient to Explain the LCST Mechanism in Polymer Solutions

The mechanism of the lower critical solution temperature (LCST) in thermoresponsive polymer solutions has been studied by means of a coarse‐grained single polymer chain simulation and a theoretical approach. The simulation model includes solvent explicitly and thus accounts for solvent interactions and entropy directly. The theoretical model consists of a single chain polymer in an implicit solvent where the effect of solvent is included through the intrapolymer solvophobic potential proposed by Kolomeisky and Widom. The results of this study indicate that the LCST behavior is determined by the competition between the mean energy difference between the bulk and bound solvent, and the entropy loss due to the bound solvent. At low temperatures, solvent molecules are bound to the polymer and the solvophobicity of the polymer is screened, resulting in a coiled state. At high temperatures the entropy loss due to bound solvent offsets the energy gain due to binding which causes the solvent molecules to unbind, leading to the collapse of the polymer chain to a globular state. Furthermore, the coarse‐grained nature of these models indicates that mean interaction energies are sufficient to explain LCST in comparison to specific solvent structural arrangements.

     

Poly(ether tert‐amine): A novel family of multiresponsive polymer

A novel multiresponsive poly(ether tert‐amine) (PEA) was synthesized by nucleophilic addition/ring‐opening reaction of commercial poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), and di‐epoxy and di‐amine monomer. The process of synthesis was very simple and green in ethanol as reactive media. These PEAs exhibit sharp response to temperature, pH, and ionic strength, with adjustable and sharp phase transitions in the range of 27–100 °C. The lower critical solution temperature (LCST) of PEA's aqueous solution presents a linear relationship to the PEO content (y = 35.7 + x), indicating well‐tunable LCST. The concentration of PEA has no obvious effect on LCST. Therefore, PEA will be potential in applications of drug delivery, separation, and biotechnology. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1292–1297, 2009     

Recent approaches for clickable poly(2-oxazoline)-based functional stimuli-responsive polymers and related applications

Abstract

Poly(2-oxazoline)s (POxs) are well-known thermo-responsive polymers that exhibit reversible hydrophilic–hydrophobic phase transitions at the lower critical solution temperature (LCST). Using living cationic ring-opening polymerisation, various functional groups can be introduced into POxs. Several clickable POxs with propargyl or azide end groups have been designed and subsequently reacted with various functional groups to prepare multifunctional POxs that respond to stimuli such as temperature, pH, chemicals and light. In this article, we briefly review recent approaches for clickable POx-based functional stimuli-responsive polymers and related applications.