Solvent quality as reflected in concentration‐ and temperature‐dependent Flory–Huggins interaction parameters

Flory–Huggins interaction parameters (χ) between poly(dimethylsiloxane) (weight‐average molecular weight = 152 kg/mol) and various solvents (methyl ethyl ketone, toluene and n‐octane) were determined as a function of composition and temperature with vapor‐pressure measurements. These data, complemented by independent information for dilute and very concentrated solutions, serve as the basis for a discussion of solvent quality via different theoretical relations. Regardless of polymer concentration, the χ values fall from methyl ethyl ketone via toluene to n‐octane, the ketone being the worst solvent and the hydrocarbon being the best solvent. The variation of χ with composition and temperature is complex. Within the range of moderate polymer concentrations, the influences of composition decrease with increasing solvent quality. Additional effects become noticeable at the ends of the composition scale. The enthalpy parts (χ_H) and entropy parts (χ_S) of the Flory–Huggins interaction parameter, obtained from χ(T), vary considerably with composition and change their sign in some cases; these constituents of the Flory–Huggins interaction parameter do not permit a direct assessment of solvent quality. A clear‐cut picture is, however, regained with a comparison of the interdependence of χ_S and χ_H. The elimination of explicit concentration influences re‐establishes the order in the solvent quality setup via χ. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 651–662, 2001     

Poly(acrylonitrile) ultrafiltration membranes. I. Polymer‐salt‐solvent interactions

Fourier transform infrared spectroscopy was used to study the interactions among LiCl, ZnCl₂, and AlCl₃ with N,N‐dimethylformamide (DMF) and poly(acrylonitrile) (PAN). It was observed that all three salts complex with DMF as well as PAN. The strength of the cation interaction with the >C?O oxygen of DMF was found to be higher than that with the ? CN group of PAN. The >C?O stretching frequency of DMF with ZnCl₂ was red shifted, indicating stronger complex formation compared with other two cations. With the addition of salt, the salt–DMF pseudo solvent was found to become a θ solvent for PAN compared with neat DMF. This change in PAN solvation power was primarily the result of DMF–salt complexation. As a result of the complexation, Mark‐Houwink constant a, was found to reduce from 0.75 (for pure DMF) to ～0.6 for DMF–salt solvents, indicating decreased PAN chain expansion. Comparison of intrinsic viscosity [η] values indicated that addition of salts to PAN–DMF solutions resulted in: (i) decrease in the DMF solvation power, which causes less expanded polymer coils, and (ii) increased interpolymer chain entanglements via salt‐promoted chain association. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2061–2073, 2005     

Thermodynamic interactions in rubbery polymer/gas systems

The Flory–Huggins interaction parameters χ for 23 gases (He, Ne, Ar, Kr, Xe, H₂, N₂, O₂, N₂O, CO₂, CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈, 1,3-C₄H₆, four C₄H₈'s, n-C₄H₁₀, iso-C₄H₁₀, and n-C₅H₁₂) in five rubbery polymers (1,2-polybutadiene (PB), poly(ethylene-co-vinyl acetate)) (EVAc), polyethylene (PE), polypropylene (PP), and poly(dimethyl siloxane) (PDMS) were determined from either literature data on Henry's law coefficient and partial molar volume or those on sorptive dilation for each polymer/gas system. Values of χ for the gases increased in the order of PDMS < PP ≡ PB < EVAc ≡ PE. Among the gases except He and H₂ whose χ values are not reliable, Ne and Xe have respectively the highest and the lowest values of χ for the polyolefins. The χ values of the hydrocarbons were compared together with previously reported χ values of n-alkanes C₃-C₁₀. The dependencies of χ upon concentration and temperature were discussed on the basis of the literature data. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1049–1053, 1997     

Intramolecular screening effects in nondilute polymer solutions: An equation‐of‐state approach

In a previous article, we presented a simple modification of the traditional Flory–Huggins theory that took intramolecular screening effects (or same chain contacts) into account. In this article, we present a natural extension of that work, in which free‐volume effects are also explained with an equation‐of‐state model. The predictions of the interaction parameter, χ, for several polymer–solvent systems are presented, over the entire concentration range, in θ solvents and good solvents. A geometric mean assumption is applied to the calculation of an exchange energy interaction term. The predictions of χ are successful to various degrees when internal pressures are used, whereas the use of solubility parameters in most cases produces fairly good agreement with experimental results. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2911–2922, 2003     

Pressure dependence of the second virial coefficient of dilute polystyrene solutions

The pressure derivatives of the second virial coefficients [dA₂/dP; 0.1 ≤ P (MPa) ≤ 35.0] for dilute polystyrene (PS) solutions in good, θ, and poor solvents were measured with static light scattering. The solvent quality improved (dA₂/dP > 0) in the good and poor solvents that we investigated (toluene, chloroform; and methylcyclohexane) but deteriorated (dA₂/dP < 0) in θ solvents (cyclohexane and 50‐50 cis,trans‐decalin). The effects of temperature [22 < T (°C) < 45] and molecular weight [25 × 10³ < weight‐average molecular weight (amu mol^?1) < 900 × 10³] on dA₂/dP for PS/cyclohexane solutions were examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3070–3076, 2003     

Synthesis and photoisomerization of poly(1‐methylpropargyl ester)s carrying azobenzene moieties

Optically active 1‐methylpropargyl esters bearing azobenzene groups, namely, (S)‐(?)‐3‐methyl‐3‐{4‐[4‐(n‐butyloxy)phenylazophenyl]carbonyl}oxy‐1‐propyne ( 1 ), (S)‐(?)‐3‐methyl‐3‐{4‐[4‐(n‐hexyloxy)phenylazophenyl]carbonyl}oxy‐1‐propyne ( 2 ), and (S)‐(?)‐3‐methyl‐3‐{4‐[4‐(n‐octyloxy)phenylazophenyl]carbonyl}oxy‐1‐propyne ( 3 ) were synthesized and polymerized with Rh⁺(nbd)[η⁶‐C₆H₅B^?(C₆H₅)₃] (nbd, norbornadiene) as a catalyst to afford the corresponding poly(1‐methyloropargyl ester)s with moderate molecular weights (M_n = 24,000–31,300) in good yields (79–84%). Polymers were soluble in common organic solvents including toluene, CHCl₃, CH₂Cl₂, THF, and DMSO, whereas insoluble in diethyl ether, n‐hexane, and methanol. Large optical rotations and strong CD signals demonstrated that all the polymers take a helical structure with a predominantly one‐handed screw sense. The helical structure of the polymers changed with the addition of MeOH and heat. The trans‐azobenzene of the polymer side chains isomerized into cis on UV irradiation, which was accompanied with drastic helical conformational changes of the polymer backbone. The cis‐azobenzene moiety reisomerized into trans on visible‐light irradiation, which induced the recovery of chiral geometry of azobenzene moieties in the side chain. Conformational analysis revealed that the polymers form a tightly twisted right‐handed helical structure with a dihedral angle of 70° at the single bond of the main chain. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4749–4761, 2009     

Chain transfer to solvent in the radical polymerization of N‐isopropylacrylamide

Chain transfer to solvent has been investigated in the conventional radical polymerization and nitroxide‐mediated radical polymerization (NMP) of N‐isopropylacrylamide (NIPAM) in N,N‐dimethylformamide (DMF) at 120 °C. The extent of chain transfer to DMF can significantly impact the maximum attainable molecular weight in both systems. Based on a theoretical treatment, it has been shown that the same value of chain transfer to solvent constant, C_tr,S, in DMF at 120 °C (within experimental error) can account for experimental molecular weight data for both conventional radical polymerization and NMP under conditions where chain transfer to solvent is a significant end‐forming event. In NMP (and other controlled/living radical polymerization systems), chain transfer to solvent is manifested as the number‐average molecular weight (M_n) going through a maximum value with increasing monomer conversion. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Solubilization of C60 by micellization with a thermoresponsive block copolymer in water: Characterization,singlet oxygen generation,and DNA photocleavage

Water‐soluble diblock copolymer, poly(N‐isopropylacrylamide)‐block‐poly(N‐vinyl‐2‐pyrroridone) (PNIPAM_m‐b‐PNVP_n), was found to associate with fullerene (C₆₀), and thus C₆₀ can be solubilized in water. The 63C₆₀/PNIPAM_m‐b‐PNVP_n micelle formed a core‐shell micelle‐like aggregate comprising a C₆₀/PNVP hydrophobic core and a thermoresponsive PNIPAM shell. The C₆₀‐containing polymer micelle formation and its thermoresponsive behavior were characterized using light scattering and ¹H NMR techniques. The hydrodynamic radius (R_h) of the C₆₀‐bound polymer micelle increased with increasing temperature, which was ascribed to the hydrophobic association between dehydrated PNIPAM shells above lower critical solution temperature (LCST). ¹H NMR data suggest that the motion of the PNIPAM block is restricted above LCST due to the dehydration of the PNIPAM shell in water. The generation of singlet oxygen by photosensitization by the C₆₀‐bound polymer micelle was confirmed from photooxidation of 9,10‐anthracenedipropionic acid. Furthermore, DNA was found to be cleaved by visible light irradiation in the presence of the C₆₀‐bound polymer micelle. Therefore, there may be a hope for a pharmaceutical application of the C₆₀‐bound polymer micelle to cancer photodynamic therapy. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Quantification of ATRP initiator density on polymer latex particles by fluorescence labeling technique using copper‐catalyzed azide‐alkyne cycloaddition

We developed a novel fluorescence labeling technique for quantification of surface densities of atom transfer radical polymerization (ATRP) initiators on polymer particles. The cationic P(St‐CPEM‐C₄DMAEMA) and anionic P(St‐CPEM) polymer latex particles carrying ATRP‐initiating chlorine groups were prepared by emulsifier‐free emulsion polymerization of styrene (St), 2‐(2‐chloropropionyloxy)ethyl methacrylate (CPEM), and N‐n‐butyl‐N,N‐dimethyl‐N‐(2‐methacryloyloxy)ethylammonium bromide (C₄DMAEMA). ATRP initiators on the surface of polymer particles were converted into azide groups by sodium azide, followed by fluorescent labeling with 5‐(N,N‐dimethylamino)‐N′‐(prop‐2‐yn‐1‐yl)naphthalene‐1‐sulfonamide (Dansyl‐alkyne) by copper‐catalyzed azide‐alkyne cycloaddition (CuAAC). The reaction time required for both azidation of ATRP‐initiating groups and successive fluorescence labeling of azide groups with Dansyl‐alkyne by CuAAC were investigated in detail by FTIR and fluorescence spectral measurement, respectively. The ATRP initiator densities on the cationic P(St‐CPEM‐C₄DMAEMA) and anionic P(St‐CPEM) particle surfaces were estimated to be 0.21 and 0.15 molecules nm^?2, respectively, which gave close agreement with values previously determined by a conductometric titration method. The fluorescence labeling through click chemistry proposed herein is a versatile technique to quantify the surface ATRP initiator density both on anionic and cationic polymer particles. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4042–4051     

The effect of polymer side chains on vapor sorption in polyacrylate and polymethacrylate solutions

The segment fraction Ψ₁ activity coefficients, a₁/Ψ₁, of solvents have been determined by the piezoelectric sorption method for 0.1 ≤ Ψ₁ ≤ 0.5 in binary solutions of chlorinated methanes [carbon tetrachloride (CCl₄), chloroform (CHCl₃), and dichloromethane (CH₂Cl₂)] with aromatic hydrocarbons (benzene and toluene) in poly(methyl methacrylate), poly(methyl acrylate), poly(ethyl methacrylate), and poly(n-butyl acrylate) at 23.5°C. The present results for toluene in PMMA agree with previously published values obtained by gas-liquid chromatography. For CCl₄ and the aromatic hydrocarbons, the polymer–solvent interaction parameter χ is positive and constant, while for the polar solvents (CHCl₃ and CH₂Cl₂), χ is negative and increases with increasing Ψ₁. The effect of the polymer side chains on vapor sorption in nonpolar and polar solvent systems is discussed in terms of the χ parameter.     

Fluorine‐containing vinyl ether polymers: Living cationic polymerization in fluorinated solvents as new media and unique solubility characteristics in organic solvents

Living cationic polymerization of fluorine‐containing vinyl ethers [CH₂?CH? O? C₂H₄? O? C₃H₆? C_nF_2n+1: 5FVE (n = 2), 13FVE (n = 6)] was investigated in various solvents with a CH₃CH(OiBu)OCOCH₃/Et_1.5AlCl_1.5 initiating system in the presence of an added base. 5FVE was polymerized quantitatively in toluene at 0 °C, and the obtained polymers had predetermined molecular weights with narrow molecular weight distributions (M_w/M_n < 1.1). On the other hand, for the polymerization of 13FVE, the product polymers precipitated due to their extremely poor solubility in nonfluorinated organic solvents. Therefore, fluorinated solvents such as hydrochlorofluorocarbons, hydrofluorocarbons, hydrofluoroethers, or α,α,α‐trifluorotoluene, as‐yet uninvestigated for cationic polymerization, were employed. In these solvents, living polymerization was achieved even with 13FVE, yielding well‐defined polymers (M_w/M_n < 1.1, by size exclusion chromatography using a fluorinated solvent as an eluent). The solvents were also shown to be good for living polymerization of isobutyl vinyl ether. The obtained fluorine‐containing polymers underwent temperature‐responsive solubility transitions in organic solvents. Poly(5FVE) showed sensitive upper critical solution temperature (UCST)‐type phase separation behavior in toluene. Copolymers of 13FVE and isobutyl vinyl ether showed UCST‐type phase separation in common organic solvents with different polarities depending on their composition, while a homopolymer of 13FVE was insoluble in all nonfluorinated organic solvents. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and helical conformation of poly(N‐propargylamides) carrying L‐aspartic acid in the side chain

Aspartic acid‐based novel poly(N‐propargylamides), i.e., poly[N‐(α‐tert‐butoxycarbonyl)‐L ‐aspartic acid β‐benzyl ester N′‐propargylamide] [poly( 1 )] and poly[N‐(α‐tert‐butoxycarbonyl)‐L ‐aspartic acid α‐benzyl ester N′‐propargylamide] [poly( 2 )] with moderate molecular weights were synthesized by the polymerization of the corresponding monomers 1 and 2 catalyzed with (nbd)Rh⁺[η⁶‐C₆H₅B^?(C₆H₅)₃] in CHCl₃ at 30 °C for 2 h in high yields. The chiroptical studies revealed that poly( 1 ) took a helical structure in DMF, while poly( 2 ) did not in DMF but did in CH₂Cl₂, CHCl₃, and toluene. The helicity of poly( 1 ) and poly( 2 ) could be tuned by temperature and solvents. Poly( 2 ) underwent solvent‐driven switch of helical sense, accompanying the change of the tightness. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5168–5176, 2005     

Synthesis and miscibility studies of [60]fullerenated poly(2‐hydroxyethyl methacrylate)

[60]Fullerenated poly(2‐hydroxyethyl methacrylate)s containing 0.6–3.0 wt % C₆₀ were synthesized. These polymers are soluble in methanol and N,N‐dimethylformamide (DMF). [60]Fullerenated poly(2‐hydroxyethyl methacrylate)s with higher C₆₀ contents are only sparingly soluble in DMF and virtually insoluble in other organic solvents. A loading of 1.2 wt % C₆₀ in poly(2‐hydroxyethyl methacrylate) does not greatly affect its miscibility with poly(N‐vinyl‐2‐pyrrolidone), poly(1‐vinylimidazole), and poly(4‐vinylpyridine). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1157–1166, 2002     

Scaling and structural properties of a polymer in a simple solvent: A study based on integral equations

We present a statistical mechanical theory for polymer–solvent systems based on integral equations derived from the polymer Kirkwood hierarchy. Integral equations for pair monomer–monomer, monomer–solvent, and solvent–solvent correlation functions yield polymer–solvent distribution, chain conformation in three dimensions, and scaling properties associated with polymer swell and collapse in athermal, good, and poor solvents. Variation of polymer properties with solvent density and solvent quality is evaluated for chains having up to 100 bonds. In good solvents, the scaling exponent v has a constant value of about 0.61 at different solvent densities computed. For the athermal solvent case, the gyration radius and scaling exponent decrease with solvent density. In a poor solvent, the chain size scales as N^v with the value of the exponent being about 0.3, compared with the mean field value of ⅓. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 3025–3033, 1998     

Asymmetric radical polymerization and copolymerization of N‐(1‐phenyldibenzosuberyl)methacrylamide and its derivative leading to optically active helical polymers

N‐(1‐Phenyldibenzosuberyl)methacrylamide (PDBSMAM) and its derivative N‐[(4‐butylphenyl)dibenzosuberyl]methacrylamide (BuPDBSMAM) were synthesized and polymerized in the presence of (+)‐ and (?)‐menthols at different temperatures. The tacticity of the polymers was estimated to be nearly 100% isotactic from the ¹H NMR spectra of polymethacrylamides derived in D₂SO₄. Poly(PDBSMAM) was not soluble in the common organic solvents, and its circular dichroism spectrum in the solid state was similar to that of the optically active poly(1‐phenyldibenzosuberyl methacrylate) (poly(PDBSMA)) with a prevailing one‐handed helicity, indicating that the poly(PDBSMAM) also has a similar helicity. Poly(BuPDBSMAM) was optically active and soluble in THF and chloroform. Its optical activity was much higher than that of the poly[N‐(triphenylmethayl)methacrylamide], suggesting that one‐handed helicity may be more efficiently induced on the poly(BuPDBSMAM). The copolymerization of BuPDBSMAM with a small amount of optically active N‐[(R)‐(+)‐1‐(1‐naphthyl)ethyl]methacrylamide, particularly in the presence of (?)‐menthol, produced a polymer with a high optical activity. The prevailing helicity may also be efficiently induced. The chiroptical properties of the obtained polymers were studied in detail. The chiral recognition by the polymers was also evaluated. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1304–1315, 2007     

Fluorous solvent‐soluble imaging materials containing anthracene moieties

Highly fluorinated photoresist polymers that can undergo photodimerization reactions were designed using an anthracene‐based monomer. Through the random radical copolymerizations of 6‐(anthracen‐9‐yl)hexyl methacrylate ( AHMA ) and semiperfluorodecyl methacrylate ( FDMA ) with four different compositions, polymers with M_n = 20,000–27,000 (M_w/M_n = 2.0–2.9) were prepared in benzotrifluoride. The polymers, in particular fluorous solvent‐soluble imaging material‐2 ( FSIM‐2 ), showed sufficient solubility in fluorous solvents, including hydrofluoroethers, but were rendered insoluble by UV exposure (365 nm). This photochemical solubility change was evaluated quantitatively by a quartz crystal microbalance technique, along with tracing the chemical reaction by UV–vis spectroscopy. Finally, FSIM‐2 and fluorous solvents were applied to the photolithographic patterning of organic light‐emitting diode pixels. In the patterning protocol involving the lift‐off of resist films in fluorous solvents, FSIM‐2 was recognized as a promising photoreactive material when compared with a reference polymer P(FDMA‐MAMA) , which necessitates acidolysis reactions for lithographic imaging. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1252–1259     

A polymer–solvent system with two homogeneous double critical points: Polystyrene (PS)/(n-heptane + methylcyclohexane)

Liquid–liquid (LL) critical demixing loci have been experimentally determined in the (T,P) projection for some polystyrene/solvent systems with nonspecific interaction for (∼ 270 K < T < ∼ 500 K) and (0 MPa < P < 200 MPa). A lower homogeneous double critical pressure and lower homogeneous double critical temperature have been located for a solution of PS (M_w = 2.0 × 10⁶) dissolved in an n-heptane/methylcyclohexane mixture [PS/n-C₇H₁₆/CH₃C₆H₁₁//0.029/0.194/0.777 (wt. fractions)]. That solution forms the first example of a polymer/solvent with nonspecific interaction that exhibits two double critical points. A symmetrical representation of the LL critical loci in the (P,T) plane is developed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2747–2753, 1999     

Interpretation of the polyelectrolyte and antipolyelectrolyte effects of poly(N‐vinylimidazole‐co‐sodium styrenesulfonate) hydrogels

Hydrogels of N‐vinylimidazole (VI) and sodium styrenesulfonate (SSS) were synthesized in aqueous solution by radical crosslinking copolymerization with N,N′‐methylene‐bis(acrylamide) as crosslinker. Swelling in several saline solutions was measured for hydrogel samples synthesized with different comonomer concentrations (C_T = 10, 25, or 40%) and with SSS mole fractions covering a broad range (f_SSS = 0–0.7), while the crosslinker ratio was 2 wt % in all cases. The degree of swelling in aqueous solution with a specific ionic strength (μ), plotted versus the SSS composition of the feed, shows a minimum for any set of samples synthesized with a fixed C_T. The dependence of swelling on μ shows both polyelectrolyte (f_SSS beyond the minimum) and antipolyelectrolyte behaviors (in the low f_SSS limit). It was found that the nonGaussian factor of the crosslinking density and the polymer‐solvent interaction parameter increase with f_SSS for any C_T. Moreover, in the low f_SSS limit, the osmotic swelling pressure is governed not only by the ionic contribution, but also by the polymer‐solvent mixing and, the concentration of mobile counterions inside the gel is not proportional to the net fixed charge but to the addition of cationic and anionic side groups, what discards the formation of ionic pairs. The antipolyelectrolyte effect is interpreted as due to the increasing protonation of VI as μ goes up. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1683–1693, 2007     

A series of two‐dimensional lanthanide coordination polymers: synthesis,structures, magnetism and selective luminescence detection for heavy metal ions and toxic solvents

A series of two‐dimensional (2D) coordination polymers (CPs), namely poly[[bis(μ‐acetato)diaqua(μ₆‐biphenyl‐3,3′,5,5′‐tetracarboxylato)bis(N,N‐dimethylacetamide)digadolinium(III)] N,N‐dimethylacetamide monosolvate], {[Gd₂(C₁₆H₆O₈)(C₂H₃O₂)₂(C₄H₉NO)₂(H₂O)₂]·C₄H₉NO}_n ( CP1 ), poly[[bis(μ‐acetato)diaqua(μ₆‐biphenyl‐3,3′,5,5′‐tetracarboxylato)bis(N,N‐dimethylacetamide)didysprosium(III)] N,N‐dimethylacetamide monosolvate], {[Dy₂(C₁₆H₆O₈)(C₂H₃O₂)₂(C₄H₉NO)₂(H₂O)₂]·C₄H₉NO}_n ( CP2 ), poly[bis(μ‐acetato)diaqua(μ₆‐biphenyl‐3,3′,5,5′‐tetracarboxylato)bis(N,N‐dimethylacetamide)dineodymium(III)], [Nd₂(C₁₆H₆O₈)(C₂H₃O₂)₂(C₄H₉NO)₂(H₂O)₂]_n ( CP3 ), poly[bis(μ‐acetato)diaqua(μ₆‐biphenyl‐3,3′,5,5′‐tetracarboxylato)bis(N,N‐dimethylacetamide)disamarium(III)], [Sm₂(C₁₆H₆O₈)(C₂H₃O₂)₂(C₄H₉NO)₂(H₂O)₂]_n ( CP4 ), has been synthesized from rigid biphenyl‐3,3′,5,5′‐tetracarboxylic acid under solvothermal conditions. Their structures have been determined by single‐crystal X‐ray diffraction analyses, elemental analyses, IR spectra, powder X‐ray diffraction and thermogravimetric analyses, and CP1 – CP4 crystallize in the monoclinic space group P2₁/n. CP1 – CP4 are isomorphous and feature similar 2D double layers, which are further extended via interlayer hydrogen‐bonding interactions into a three‐dimensional (3D) supramolecular structure. Hydrogen‐bonding interactions between N,N‐dimethylacetamide molecules and carboxylate O atoms strengthen the packing of the layers. The organic ligands interconnect with metal ions to generate 2D layered structures with a (4,4)‐connected net having {4⁴.6²} topology. CP1 has been investigated for its magnetic properties and magnetic susceptibility measurements were carried out in the range 2.0–300 K. The results of the magnetic measurements show weak antiferromagnetic coupling between the Gd^III ions in CP1 . Moreover, the strong luminescence of CP2 and CP4 can be selectively quenched by the Fe³⁺ ion and toxic solvents (e.g. acetone).     

Topological polymer chemistry by electrostatic self‐assembly

Recent developments in topological polymer chemistry are outlined. First, nonlinear polymer topologies are systematically classified on the basis of topological considerations of constitutional isomerism in a series of alkanes (C_nH_2n+2), monocycloalkanes (C_nH_2n), and polycycloalkanes (C_nH_2n?2, C_nH_2n?4, etc.). Various pairs of topological isomers are identified in randomly coiled, flexible polymer molecules with cyclic and branched structures. An electro‐ static self‐assembly and covalent fixation strategy has subsequently been developed for the efficient synthesis of a variety of topologically unique polymers, including monocyclic and polycyclic polymers, topological isomers, and topological block copolymers. In this process, new telechelics with moderately strained cyclic onium salt groups carrying multifunctional carboxylate counteranions have been designed as key polymeric precursors. Further extensions of topological polymer chem‐ istry have been achieved by the use of cyclic telechelics (kyklo‐telechelics) and cyclic macromonomers, obtainable also by means of the electrostatic self‐assembly and covalent fixation process. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2905–2917, 2003