Synthesis and spectroscopic study of phenylene-(poly)ethynylenes substituted by amino or amino/cyano groups at terminal(s): electronic effect of cyano group on charge-transfer excitation of acetylenic π-systems

To gain insight into substituent electronic effect on charge-transfer excitation of acetylenic π-systems, phenylene-(poly)ethynylenes substituted by Ph₂N or Ph₂N/cyano groups were synthesized by combination of Sonogashira coupling and double elimination protocol of β-substituted sulfones. These substituted phenyleneethynylenes showed large molar absorption coefficients ?, and emitted strong fluorescence upon UV light irradiation. Phenylene-(poly)ethynylenes, which involve butadiyne or hexatriyne motifs, emitted fluorescence in remarkably lower fluorescence quantum yields Φ_F as their polyethynylene motifs -(CC)_n- expanded. The drastic decrease of fluorescence quantum yields Φ_F were explained in terms of increasing nonradiative reaction rate constants k_nr, which had been determined by the corresponding fluorescence quantum yields Φ_F and lifetime values τ. The emission underwent a large bathochromic shift in polar solvents because the charge-separated excited state is more stabilized than the ground state. Comparison of slope values ρ in Lippert/Mataga plot for the Ph₂N and Ph₂N/cyano-substituted phenylene-(poly)ethynylenes revealed that the latter underwent large change of dipole moments upon photo-excitation although highly expanded acetylenic π-systems with cyano group did little.     

Synthesis and conformation of poly(L-azetidine-2-carboxylic acid-L-proline) and poly([L-proline]3-L-azetidine-2-carboxylic acid)

The synthesis, characterization, and conformational assessment of poL y(L -Aze-L -Pro) and poly[(L -Pro)₃-L -Aze] are reported. The polymers were prepared by using the pentachlorophenol active ester as the polymerizable tetrapeptide derivatives. The copolymer, poly(L -Aze-L -Pro), assumes a Form II helix in polar solvents, and is converted into a form I-like helix at a critical solvent composition of ethanol to trifluoroethanol. The CD spectrum of this Form I-like conformation of poly(L -Aze-L -Pro) is similar to that of poly(trans-5-isopropyl-L -proline), indicating that the rigid four-membered ring at the alternating position can lock in the structure by a mechanism similar to that of a bulky substituent at the trans-5-position of proline. The helix conformation of this copolymer was unfolded in a 0.2M CaCl₂ aqueous solution. In contrast to poly(L -Aze-L -Pro), the copolymer of poly[(L -Pro)₃-L -Aze] contains both cis and trans peptide bond geometry when dissolved in a 90:10 ETOH-H₂O mixture. The conversion of the mixed conformation of poly[(L -Pro)₃-L -Aze)] into a polyproline Form II-like structure occurred in highly polar solvent environments such as water.     

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.     

Novel amphiphilic network polymers consisting of nonpolar,short primary polymer chains and polar,long crosslink units: Influence of characteristic dangling chains on swelling behavior of resulting amphiphilic gels

Novel amphiphilic network polymers consisting of nonpolar, short primary polymer chains and polar, long crosslink units were prepared, and the swelling behavior of resulting amphiphilic gels is discussed by focusing on the influence of characteristic dangling chains; that is, benzyl methacrylate (BzMA) was copolymerized with tricosaethylene glycol dimethacrylate [CH₂?C(CH₃)CO(OCH₂CH₂)₂₃OCOC(CH₃)?CH₂, PEGDMA‐23] in the presence of lauryl mercaptan as a chain‐transfer agent because BzMA forms nonpolar, short primary polymer chains and PEGDMA‐23 as a crosslinker contains a polar, long poly(oxyethylene) unit. The enhanced incorporation of dangling chains into the network polymer was brought by shortening the primary polymer chain length, and copolymerization with methoxytricosaethylene glycol methacrylate, a mono‐ene counterpart of PEGDMA‐23, enforced the incorporation of flexible dangling poly(oxyethylene) chains into the network polymer, although the former dangling chains as terminal parts of primary poly(BzMA) chains were rather rigid. Then, the influence of characteristic dangling chains on the swelling behavior of amphiphilic gels was examined in mixed solvents consisting of nonpolar t‐butylbenzene and polar methanol. The profiles of the solvent‐component dependencies of the swelling ratios were characteristic of amphiphilic gels. The introduction of dangling poly(oxyethylene) chains led not only to an increased swelling ratio but also to sharpened swelling behavior of amphiphilic gels. The swelling response of amphiphilic gels was checked by changing the external solvent polarity. The dangling chains with freely mobile end segments influenced the swelling response of gels. The amphiphilic gels with less entangled, collapsed crosslink units exhibited faster swelling response than the ones with more entangled, collapsed primary polymer chains. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2192–2201, 2004     

Quasiliving Carbocationic Polymerization. VIII. Quasiliving Polymerization of Methyl Vinyl Ether and Its Blocking from Quasiliving Poly(isobutyl Vinyl Ether) Dication

Quasiliving carbocationic polymerization of methyl vinyl ether (MVE) was achieved with the p-dicumyl chloride (p-DCC)/AgSbF₆ initiator system by the slow and continuous monomer-addition (quasiliving) technique. A polar solvent (CH₂Cl₂) and a low reaction temperature (-70°C) were optimum for the quasiliving MVE polymerization. Under these conditions, the number-average molecular weight (M _n) of poly(MVE) increased linearly with the cumulative weight of added monomer (W_MVE), and linear M _n versus W_MVE plots passed through the origin. M _n's were inversely proportional to the initial initiator (p-DCC) concentration. Reactions in a nonpolar solvent (toluene) at -70°C or in a polar solvent (CH₂Cl₂) at ?30°C resulted in deviations from these quasiliving characteristics. Block polymerization of MVE from quasiliving poly(isobutyl vinyl ether) dications by the quasiliving technique (p-DCC/AgSbF₆ initiator, CH₂Cl₂ solvent,(-70°C) led to novel isobutyl vinyl ether (IBVE)-MVE block polymers in high yield (>93 wt%) and at high blocking efficiency. The block polymers, most likely poly(MVE-b-IBVE-b-MVE), having M _n = 10,900–14,000 [M _n(center block) = 6,200–9,0001, were soluble in n-heptane and insoluble in water, and gave hazy homogeneous solutions when dissolved in methanol at room temperature.     

Solvent effect on the radical polymerization of di-n-butyl itaconate

Solvent effect on the polymerization of di-n-butyl itaconate (DBI) with dimethyl azobisisobutyrate (MAIB) was investigated at 50 and 61°C. The solvents used were found to affect significantly the polymerization. The polymerization rate (R_p) and the molecular weight of the resulting polymer are lower in more polar solvents. The initiation rate (R_i) by MAIB, however, shows a trend of being rather higher in polar solvents. The stationary state concentration of propagating poly(DBI) radical was determined by ESR in seven solvents. The rate constants of propagation (k_p) and termination (k_t) were evaluated by using R_p, R_i, and the polymer radical concentration observed. The k_p value decreases fairly with increasing polarity of the solvent used, whereas k_t is not so influenced by the solvents. The solvent effect on k_p is explained in terms of a difference in the environment around the terminal radical center of the growing chain. Copolymerization of DBI with styrene (St) was also examined in three solvents with different physical properties. The poly(DBI) radical shows a lower reactivity toward St in a more polar solvent.     

Stereoregularity of poly(vinyl ether)

α-Methylvinyl isobutyl and methyl ethers were polymerized cationically and the structure of the polymers was studied by NMR. Poly(α-methylvinyl methyl ether) polymerized with iodine or ferric chloride as catalyst was found to be almost atactic, whereas poly(α-methylvinyl isobutyl ether) polymerized in toluene with BF₃OEt₂ or AlEt₂Cl as catalyst was found to be isotactic. In both cases, the addition of polar solvent resulted in the increase of syndiotactic structure as is the case with polymerization of alkyl vinyl ether. tert-Butyl vinyl ether was polymerized, and the polymer was converted into poly(vinyl acetate), the structure of which was studied by NMR. A nearly linear relationship between the optical density ratio D₇₂₂/D₇₃₆ in poly(tert-butyl vinyl ether) and the isotacticity of the converted poly(vinyl acetate) was observed.     

Synthesis of star poly(1,3‐cyclohexadiene): Grafting reaction of poly(1,3‐cyclohexadienyl)lithium onto C60

The grafting reaction of poly(1,3‐cyclohexadienyl)lithium onto fullerene‐C₆₀ (C₆₀) was strongly affected by the nucleophilicity of poly(1,3‐cyclohexadiene) (PCHD) carbanions and the polymer chain microstructure, and progressed via step‐by‐step reactions. A star‐shaped PCHD, having a maximum of four arms, was obtained from poly(1,3‐cyclohexadienyl)lithium composed of all 1,4‐cyclohexadiene (1,4‐CHD) units. The rate of the grafting reaction was accelerated by the addition of amine. The grafting density of PCHD arms onto C₆₀ decreased with an increase in the molar ratio of 1,2‐cyclohexadiene (1,2‐CHD) units. The electron‐transfer reaction from PCHD carbanions to C₆₀ did not occur in either a nonpolar solvent or a polar solvent. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3282–3293, 2008.     

Synthesis and properties of poly(phenylacetylenes) having two polar groups or one cyclic polar group on the phenyl ring

Phenylacetylene (PA) derivatives having two polar groups (ester, 2a – d ; amide, 4) or one cyclic polar group (imide, 5a – c ) were polymerized using (nbd)Rh⁺[(η⁶‐C₆H₅)B^?(C₆H₅)₃] catalyst to afford high molecular weight polymers (～1 × 10⁶ – 4 × 10⁶). The hydrolysis of ester‐containing poly(PA), poly( 2a) , provided poly(3,4‐dicarboxyPA) [poly ( 3 )], which could not be obtained directly by the polymerization of the corresponding monomer. The solubility properties of the present polymers were different from those of poly(PA) having no polar group; that is, poly( 2a )–poly( 2d ) dissolved in ethyl acetate and poly( 4 ) dissolved in N,N‐dimethylformamide, while poly(PA) was insoluble in such solvents. Ester‐group‐containing polymers [poly( 2a )–poly( 2d )] afforded free‐standing membranes by casting from THF solutions. The membrane of poly( 2a ) showed high carbon dioxide permselectivity against nitrogen (PCO₂/PN₂ = 62). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5943–5953, 2006     

IONIC CONDUCTIVITY OF POLY(β-ALKOXYCARBONYLETHYLMETHYLSILOXANE)-LiClO4 CROSSLINKED FILMS

Poly (β-carboxyethylmethylsiloxane)-LiClO_4 and poly (β-alkoxylethylmethylsiloxane)-LiClO_4 crosslinked fllms have been prepared. The ionic conductivity of the films depends on the polymer species, concentration of lithium perchlorate, temperature and content of crosslinking agent. The effect of high polar organic solvent 1, 4-butyrolactone on the ionic conductivity and mechanical properties of poly (β-carhoxyethylmethylsiloxane )-LiClO_4 system was also investignied.     

Grafting by in situ coupling of epoxy groups of a living copolymer with an anionic living polymer

A tetrahydrofuran (THF) solution of the living random copolymer of methyl methacrylate (MMA) and glycidyl methacrylate (GMA) was prepared by the living anionic copolymerization of the two monomers, using 1,1‐diphenylhexyllithium (DPHLi) as initiator, in the presence of LiCl ([LiCl]/[DPHLi]₀ = 3), at −50°C. The copolymer thus obtained has a controlled composition and molecular weight and a narrow molecular weight distribution. By introduction of an anionic living polystyrene (poly(St)) or anionic living polyisoprene (poly(Is)) solution into the above system at −30°C, a coupling reaction took place and a graft copolymer with a polar backbone and nonpolar side chains was produced. The solvent used in the preparation of the living poly(St) or poly(Is) affects the coupling reaction. When benzene was the solvent, a graft copolymer of high purity, controlled graft number and molecular weight, and narrow molecular weight distribution (M_w/M_n = 1.11–1.21) was obtained. In the coupling reaction, the living poly(St) reacted only with the epoxy groups and not with the carbonyls of the backbone polymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 105–112, 1999     

Structure and supramolecular structures of star-shaped fullerene-containing heteroarm polymers in deuterotoluene

Self-organization of star-shaped polymers containing six PS arms and six polar polymer arms on a common C₆₀ branching center is studied by means of small-angle neutron scattering in deuterotoluene. The results are compared with the corresponding characteristics of six-arm star-shaped fullerene-containing PSs. It is shown that the incorporation of additional polar arms into a six-arm macromolecule leads to its compression due to an increase in the degree of coiling of polar chains in the nonpolar solvent. In solution, heteroarm stars give rise to supramolecular structures in the form of clusters whose dimensions and density depend on the nature of the polar arms. Stars containing PS and poly(2-vinylpyridine) arms are weakly associated, and the mean number of particles in an associate is ∼1.3. Hybrid polymers containing PS and poly(tert-butyl methacrylate) arms demonstrate capability for mutual penetration that favors the appearance of large structures that have a diameter of ∼50 nm and that include up to 12 macromolecules. Hybrid stars containing PS and diblock copolymer (poly(2-vinylpyridine)-poly(tert-butyl methacrylate)) arms exhibit moderate self-organization that manifests itself in the formation of chain associates built from four macromolecules.     

The propagating species in living cationic polymerization: Living nature and steric structure of polymers

This paper discusses the nature of the living growing species in cationic polymerization from the viewpoint of the steric structure of poly(isobutyl vinyl ether) [poly(IBVE)]. At −78 °C, living polymerization was induced with the HCl-IBVE adduct (1)/ZnCl₂ system in a EtNO₂/CH₂Cl₂ mixture, whereas similar systems with EtAlCl₂ led to conventional cationic polymerization. In this polar medium, both systems gave polymers with very similar and low isotacticity (meso ≈ 56%), indicating that the propagating reaction is mediated by free ions. Thus, regardless of solvent polarity, or involvement of free ions or ion pairs, living cationic polymerization requires a suitably nucleophilic counteranion. As model reactions of the growing species, 1/ZnCl₂ and 1/EtAlCl₂ were directly analyzed by ¹H NMR spectroscopy.     

The influence of carbon dioxide cosolvent on solubility in poly(ethylene glycol)

Supercritical carbon dioxide (CO₂) and poly(ethylene glycol) (PEG) can be utilized as an environmentally friendly biphasic solvent system for catalysis reactions and subsequent product separation. To efficiently implement this technology, it is important to understand how solutes partition between these phases as well as how dissolved CO₂ in PEG affects the solvent properties. The work presented here explores the influence of CO₂ on the solubility of four different solutes in PEG. The transferable potentials for phase equilibria-united atom force field and configurational-bias Monte Carlo molecular simulation were employed to determine the solubilities of ethylbenzene, 1-octene, 1-pentanol, and 2-pentanone at 323.15 K and 15?MPa in PEG-600 using an ideal vapor phase with a Poynting-corrected vapor pressure. The effect of CO₂ concentration within the PEG phase was determined by varying the amount from no CO₂ to the saturation limit. The results indicate that while there is preferential solvation of CO₂ around the solutes, solubility of non-polar solutes is unchanged whereas there is a modest increase for polar solutes as the concentration of CO₂ increases. Increased solubility is analyzed in terms of both modified solvent structure and direct solute–CO₂ interactions.     

Photooxygenations par transfert d'electron sensibilisees par le dicyano-9,10 anthracene. Role du solvant et formation d'oxygene singulet.

Photooxygenation of naphtalenic compounds sensitized by electron acceptors like 9,10 dicyanoanthracene (DCA) is shown to proceed by two distinct ways depending on the solvent polarity. In a polar solvent superoxide ion (O₂^-.) as well as singlet oxygen (¹O₂★) are involved while in a non polar solvent only singlet oxygen is produced.     

Synthesis and Helical Structures of Poly(ω‐alkynamide)s Having Chiral Side Chains: Effect of Solvent on Their Screw‐Sense Inversion

New ω‐alkynamides, (S)‐HC?CCH₂CONHCH₂CH(CH₃)CH₂CH₃ ( 1 ) and (S)‐HC?CCH₂CH₂CONHCH(CH₃)CH₂CH₂CH₂CH₂CH₃ ( 2 ) were synthesized and polymerized with a rhodium catalyst in CHCl₃ to obtain cis‐stereoregular poly(ω‐alkynamide)s (poly( 1 ) and poly( 2 )). Polarimetric, CD, and IR spectroscopic studies revealed that in solution the polymers adopted predominantly one‐handed helical structures stabilized by intramolecular hydrogen bonds between the pendent amide groups. This behavior was similar to that of the corresponding poly(N‐alkynylamide) counterparts (poly( 3 ) and poly( 4 )) reported previously, whereas the helical senses were opposite to each other. The helical structures of the poly(ω‐alkynamide)s were stable upon heating similar to those of the poly(N‐alkynylamide)s, but the solvent response was completely different. An increase in MeOH content in CHCl₃/MeOH resulted in inversion of the predominant screw‐sense for poly( 1 ) and poly( 2 ). Conversely, poly( 3 ) was transformed into a random coil, and poly( 4 ) maintained the predominant screw‐sense irrespective of MeOH content. The solvent dependence of predominant screw‐sense for poly( 1 ) and poly( 2 ) was reasonably explained by molecular orbital studies using the conductor‐like screening model (COSMO).     

Solvent‐Dependent Structure of Iridium Dihydride Complexes: Different Geometries at Low and High Dielectricity of the Medium

The hydride iridium pincer complex [(PCyP)IrH₂] (PCyP=cis‐1,3‐bis[(di‐tert‐butylphosphino)methyl]cyclohexane, 1 ) reveals remarkably solvent‐dependent hydride chemical shifts, isotope chemical shifts, J_HD and T₁(min), with r_HH increasing upon moving to more polar medium. The only known example of such behaviour (complex [(POCOP)IrH₂], POCOP=2,6‐(tBu₂PO)₂C₆H₃) was explained by the coordination of a polar solvent molecule to the iridium (J. Am. Chem. Soc. 2006 , 128, 17114). Based on the existence of an agostic bond between α‐C?H and iridium in 1 in all solvents, we argue that the coordination of solvent can be rejected. DFT calculations revealed that the structures of 1 and [(POCOP)IrH₂] depend on the dielectric permittivity of the medium and these compounds adopt trigonal‐bipyramidal geometries in non‐polar media and square‐pyramidal geometries in polar media.     

Solubility of vinylidene fluoride polymers in supercritical CO2 and halogenated solvents

The cloud‐point behaviors of poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride‐co‐22 mol % hexafluoropropylene) (VDF–HFP₂₂) are reported at temperatures up to 250 °C and pressures up to 3000 bar in supercritical CO₂, CHF₃, CH₂F₂, CHClF₂, CClF₃, CH₃CHF₂, CH₂FCF₃, CHF₂CF₃, and CH₃CClF₂. The molecular weight of PVDF has a smaller effect on the cloud point than the solvent quality. Cloud‐point pressures for both fluoropolymers decrease as the solvent polarizability, polar moment per molar volume, and density increases. However, it is extremely difficult to dissolve either fluoropolymer in CClF₃, which has a large polarizability and a small dipole moment. CO₂ is an effective solvent because it complexes with the C F dipole at low temperatures where energetic interactions fix the phase behavior. In addition, polymer architecture has a strong impact on the cloud‐point pressure. VDF–HFP₂₂ has lower cloud‐point pressures than PVDF in all solvents because it has a larger free volume that promotes facile interactions between the solvent and the polymer segments. Cloud‐point data are also reported for amorphous poly(tetrafluoroethylene‐co‐x mol % 2,2‐bistrifluoromethyl‐4,5‐difluoro‐1,3‐dioxole) (TFE–PDD_x ; x = 65 and 85) in CO₂. These data provide an interesting comparison to the PVDF–CO₂ and VDF–HFP₂₂–CO₂ systems because TFE–PDD₆₅ and TFE–PDD₈₇ have very high glass‐transition temperatures of 160 and 240 °C, respectively. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2832–2840, 2000     

Pyrene functional poly(vinyl alcohol) by “click” chemistry

Side‐chain pyrene functional poly(vinyl alcohol) (PVA) was synthesized by using “click chemistry” strategy. First, partial tosylation of PVA with p‐toluene sulfonyl chloride were performed. The resulting PVA‐Ts polymer was then quantitatively converted into poly(vinyl alcohol)‐azide (PVA‐N₃) in the presence of NaN₃/DMF at 60 °C. Propargyl pyrene was prepared independently as a photoactive click component. Finally, azido functionalized PVA was coupled to propargyl pyrene with high efficiency by click chemistry. Incorporation of pyrene functionality in the resulting polymer was confirmed by spectral analysis. It is also shown that pyrene functionalized PVA (PVA‐Py) exhibited characteristic fluorescence properties and improved solubility in highly polar solvents such as water, DMSO, and DMF as well as less polar solvent such as THF compared with pristine PVA. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1317–1326, 2009     

Synthesis and properties of carbamate‐ and amine‐containing poly(phenylacetylenes)

The 3‐ and 4‐aminophenylacetylenes protected by t‐butoxycarbonyl (t‐Boc) and 9‐fluorenylmethoxycarbonyl (Fmoc) groups ( 3a – 6a ) were synthesized and polymerized using [(nbd)RhCl]₂ ( 1 ) and [(nbd)Rh⁺‐η⁶‐PhB^?Ph₃] ( 2 ) catalysts. The t‐Boc‐containing polymers [poly( 3a ) and poly( 4a )] were obtained in high yield (82–91%). Among the Fmoc‐protected monomers, the para‐derivative polymerized well [poly( 6a ); yield = 85–94%], whereas its meta‐substituted analogue did not afford high molecular weight polymer in good yield [poly( 5a ); yield = 10–15%]. The use of KN(SiMe₃)₂ as a cocatalyst in conjunction with 1 led to a dramatic increase in the molecular weight of the polymers. The acid‐ and base‐catalyzed removal of the t‐Boc and the Fmoc groups, respectively, generated primary amine‐containing polymers [poly( 3b )–poly( 6b )] which cannot be obtained directly by the polymerization of the corresponding monomers. The solubility characteristics of the polymers bearing protected amino groups were quite different from those of the unprotected ones, the former being soluble in polar solvents, whereas the latter displayed poor solubility even in polar protic or highly polar aprotic solvents. The attempts to accomplish the free‐standing membrane fabrication by solution casting were successful only for poly( 3a ), and an augmentation in the gas permeability and CO₂/N₂ permselectivity was discerned in comparison with the unsubstituted poly(phenylacetylene) and poly(m‐t‐butyldimethylsiloxyphenylacetylene). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1853–1863, 2009