Synthesis and UCST‐type phase behavior of OEGylated poly(γ‐benzyl‐l‐glutamate) in organic media

A series of OEGylated poly(γ‐benzyl‐l ‐glutamate) with different oligo‐ethylene‐glycol side‐chain length, molecular weight (MW = 8.4 × 10³ to 13.5 × 10⁴) and narrow molecular weight distribution (PDI = 1.12–1.19) can be readily prepared from triethylamine initiated ring‐opening polymerization of OEGylated γ‐benzyl‐l ‐glutamic acid based N‐carboxyanhydride. FTIR analysis revealed that the polymers adopted α‐helical conformation in the solid‐state. While they showed poor solubility in water, they exhibited a reversible upper critical solution temperature (UCST)‐type phase behavior in various alcoholic organic solvents (i.e., methanol, ethanol, 1‐propanol, 1‐butanol, 1‐pentanol, and isopropanol). Variable‐temperature UV–vis analysis revealed that the UCST‐type transition temperatures (T_pts) of the resulting polymers were highly dependent on the type of solvent, polymer concentration, side‐ and main‐chain length. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1348‐1356     

Synthesis and thermoresponsive properties of OEGylated polypeptide with a LCST at body temperature in water and with a UCST in alcohol or ethanol/water solvent mixture

Thermoresponsive polypeptides bearing oligo(ethylene glycol) (OEG) pendants (i.e., P1‐OEG_x and P2‐OEG_x, x = 3, 7) were synthesized by copper‐mediated 1,3‐dipolar cycloaddition with high grafting efficiency (≥97%) between side‐chain “clickable” polypeptides, namely poly(γ‐4‐(propargoxycarbonyl)benzyl‐l ‐glutamate) (P1) or poly(γ‐4‐(4‐propargoxyphenoxycarbonyl)benzyl‐l ‐glutamate) (P2) and azido functionalized OEG (N₃‐OEG_x). P1 and P2 with similar degree of polymerization (DP = 35 or 37) were prepared from triethylamine initiated ring‐opening polymerization of respective N‐carboxyanhydrides. P1‐OEG_x (x = 3, 7) and P2‐OEG₇ showed reversible UCST‐type phase transitions in various alcoholic solvents (e.g., ethanol, propanol, n‐butanol, and n‐pentanol). P2‐OEG₃ also showed reversible UCST‐type phase transitions in ethanol/water solvent mixtures at the weight percentage of ethanol no less than 50 wt %. P1‐OEG₇ and P2‐OEG₇ showed reversible LCST‐type phase transitions in aqueous solutions. Variable‐temperature UV–vis spectroscopy revealed that the LCST‐type phase transition temperature (T_pt) of P2‐OEG₇ with benzoic acid phenyl ester linkages was at around body temperature and it was barely changed with the variation of polymer concentration, yet it showed noticeable dependence on the nature of salt (i.e., NaCl, NaBr, NaI, or KCl) and salt concentration in the range of 0–300 mM. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 163–173     

Synthesis,Characterization, and thermoresponsive properties of Helical Polypeptides Derivatized from Poly(γ−4‐(3‐chloropropoxycarbonyl)benzyl‐L‐glutamate)

A series of side‐chain‐functionalized α‐helical polypeptides, i.e., poly(γ‐4‐(3‐chloropropoxycarbonyl)benzyl‐_L‐glutamate) (6) have been prepared from n‐butylamine initiated ring‐opening polymerization (ROP) of γ‐4‐(3‐chloropropoxycarbonyl)benzyl‐_L‐glutamic acid‐based N‐carboxyanhydride. Polypeptides bearing oligo‐ethylene‐glycol (OEG) groups or 1‐butylimidazolium salts were prepared from 6 via copper‐mediated [2+3] alkyne‐azide 1,3‐dipolar cycloaddition or nuleophilic substitution, respectively. CD and FTIR analysis revealed that the polymers adopt α‐helical conformations both in solution and the solid state. Polymers bearing OEG (m = 3) side‐chains showed reversible LCST‐type phase transition behaviors in water while polymers bearing 1‐butylimidazolium and I^? counter‐anions exhibited reversible UCST‐type transitions in water. Variable‐temperature UV‐vis analysis revealed that the phase transition temperatures (T_pts) were dependent on the main‐chain length and polymeric concentration. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2469–2480     

Synthesis and UCST‐type phase behaviors of OEGylated random copolypeptides in alcoholic solvents

A series of OEGylated random copolypeptides with similar main‐chain lengths and different oligo(ethylene glycol) (OEG) molar content and chain lengths were prepared from triethylamine initiated ring‐opening polymerization (ROP) of OEGylated γ‐benzyl‐_L‐glutamic acid based N‐carboxyanhydride (OEG_mBLG–NCA, m = 2, 3) and γ‐benzyl‐_L‐glutamic acid based N‐carboxyanhydride (BLG–NCA). ¹H NMR analysis verified copolypeptides structures and determined the OEG molar content (x). FTIR analysis further confirmed the molecular structures, indicated α‐helical conformations of copolypeptides in the solid‐state, and revealed H‐bonding interactions between OEG pendants and alcoholic solvents. The copolypeptides exhibited a reversible upper critical solution temperature (UCST)‐type phase behavior in various alcoholic solvents (i.e., methanol, ethanol, 1‐propanol, 1‐butanol, and 1‐pentanol) depending on the x values and OEG side‐chain lengths (m). Variable‐temperature UV–vis analysis revealed that the UCST‐type transition temperatures (T_pts) of the copolypeptides in alcohols decreased as x or m value increased or as polymer concentration decreased. T_pts of copolypeptides with high x values (x ≥ 0.50) increased as the number of methylene of the alcoholic solvent increased from 3 (i.e., 1‐propanol) to 5 (i.e., 1‐pentanol). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3444–3453     

Revisiting the crystallization of poly(2‐alkyl‐2‐oxazoline)s

Poly(2‐alkyl‐2‐oxazoline)s (PAOx) exhibit different crystallization behavior depending on the length of the alkyl side chain. PAOx having methyl, ethyl, or propyl side chains do not show any bulk crystallization. Crystallization in the heating cycle, that is, cold crystallization, is observed for PAOx with butyl and pentyl side chains. For PAOx with longer alkyl side chains crystallization occurs in the cooling cycle. The different crystallization behavior is attributed to the different polymer chain mobility in line with the glass transition temperature (T_g) dependency on alkyl side chain length. The decrease in chain mobility with decreasing alkyl side chain length hinders the relaxation of the polymer backbone to the thermodynamic equilibrium crystalline structure. Double melting behavior is observed for PButOx and PiPropOx which is explained by the melt‐recrystallization mechanism. Isothermal crystallization experiments of PButOx between 60 and 90 °C and PiPropOx between 90 and 150 °C show that PAOx can crystallize in bulk when enough time is given. The decrease of T_g and the corresponding increase in chain mobility at T > T_g with increasing alkyl side chain length can be attributed to an increasing distance between the polymer backbones and thus decreasing average strength of amide dipole interactions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 721–729     

Studies on the Solvation Dynamics of Coumarin 153 in 1‐Ethyl‐3‐Methylimidazolium Alkylsulfate Ionic Liquids: Dependence on Alkyl Chain Length

Steady‐state and time‐resolved fluorescence behavior of coumarin 153 (C153) is investigated in a series of 1‐ethyl‐3‐methylimidazolium alkylsulfate ([C₂mim][C_nOSO₃]) ionic liquids differing only in the length of the linear alkyl chain (n=4, 6, and 8) in the anion. The aim of the present study is to understand the role of alkyl chain length in solute rotation and solvation dynamics of C153 in these ionic liquids. The blueshift observed in the steady‐state absorption and emission maxima of C153 on going from the C₄OSO₃ to the C₈OSO₃ system indicates increasing nonpolar character of the microenvironment of the solute with increasing length of the alkyl side chain of the anion of the ionic liquids. The average solvation time is also found to increase on changing the substituent from butyl to octyl, and this is attributed to the increase in the bulk viscosity of the ILs. A steady blueshift of the time‐zero maximum of the fluorescence spectrum with increasing alkyl chain length also indicates that the probe molecule experiences a less polar environment in the early part of the dynamics. Rotational dynamics of C153 are also analyzed by using the Stokes–Einstein–Debye (SED), Gierer–Wirtz (GW), and Dote–Kivelson–Schwartz (DKS) theories. Analyses of the results seem to suggest decoupling of the rotational motion of the probe from solvent viscosity.     

Water‐Soluble Thermoresponsive α‐Helical Polypeptide with an Upper Critical Solution Temperature: Synthesis,Characterization, and Thermoresponsive Phase Transition Behaviors

Water‐soluble polypeptides bearing 1‐alkylimidazolium (methyl or n‐butyl) and various counter‐anions (i.e., Cl⁻, I⁻ or BF₄⁻) are prepared by ring‐opening polymerization of γ‐4‐chloromethylbenzyl‐_l‐glutamate‐based N‐carboxyanhydride ( 3 ), post‐polymerization of poly(γ‐4‐chloromethylbenzyl‐_l‐glutamate) ( 4 ), and ion‐exchange reaction. Circular dichroism (CD) analysis reveals that the resulting polypeptides adopt an α‐helical conformation in water with a fractional helicity in the range of 30%–56% at 20 °C and exhibit good conformational stability against temperature variations. The polypeptides exhibit lower critical solution temperature (LCST)‐type or upper critical solution temperature (UCST)‐type transitions in organic solvents or in water. The UCST‐type transition temperature (T_pt) in water is independent on the molecular weight, yet it decreases upon addition of NaCl and increases upon addition of NaI or NaBF₄, suggesting a mainly electrostatic interaction mechanism.

     

Organic gels prepared from side‐chain liquid crystalline polymers without the spacer

A series of side‐chain liquid crystal polymers (SCLCPs) without the spacer, named poly[ω‐(4′‐n‐alkyl oxybiphenyl‐4‐oxy)methacrylate (PMBiCm, m = 1, 2, 4, 6, 8, 10, 12, 14, 16, and 18), have been synthesized. The novel polymer organogels were prepared by introducing PMBiCm into common organic solvents. Solubility and gel properties of polymer organogelators differ widely according to the nature of the solvents. In aromatic solvents, PMBiCm completely dissolved in solvent due to good compatibility between biphenyl mesogen group and aromatic solvents. Poly[ω‐(4′‐n‐alkyl oxybiphenyl‐4‐oxy)methacrylate were still insoluble in polar solvents such as acetone, ethanol, DMF, ethylene glycol, and n‐butanol. This behavior resulted from mismatch of solubility parameter between PMBiCm and solvent. Considering the factors of solvent, we have systematically studied 3 organic solvents with different polarities (butyl acetate, n‐butyl amine, and n‐heptane). It is found that the length of the alkoxy tail chain of the SCLCPs has significant influence on gelability and gel thermal stability. In further studies discussed by UV‐Vis spectroscopy, the results revealed that the π‐π stacking interaction of the biphenyl mesogens might be the key factor for guiding the self‐assembly processes and the polymer gel formation. This work is useful to comprehending physical mechanism of polymer organogels. Meanwhile, those expand SCLCPs to a wide range of applications.     

Polymer BHJ solar cell performance tuning by C60 fullerene derivative alkyl side‐chain length

A systematic study on the influence of the alkyl side‐chain length of C₆₀ based fullerene derivatives in polymer solar cells based on an anthracene‐containing poly(p‐phenylene‐ethynylene)‐alt‐poly(p‐phenylene‐vinylene) (PPE‐PPV) copolymer (AnE‐PV) is reported. It is shown that the alkyl side‐chain length of the fullerene derivative strongly correlates with the individual photovoltaic parameters. The most pronounced dependence on the side‐chain length is found for the fill factor, spanning the range between 50–72%, which dominantly controls in combination with the short‐circuit current the power conversion efficiency. The maximum performance of 4.8% was found for an ethyl terminated side‐chain, whereas larger alkyl groups resulted in a gradually decreasing power conversion efficiency. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

1,2‐Diaza‐3‐silacyclopent‐5‐ene – Synthese und Reaktionen

1,2‐Diaza‐3‐silacyclopent‐5‐ene – Synthesis and Reactions The dilithium salt of bis(tert‐butyl‐trimethylsilylmethylen)ketazine ( 1 ) forms an imine‐enamine salt. 1 reacts with halosilanes in a molar ratio of 1:1 to give 1,2‐diaza‐3‐silacyclopent‐5‐enes. Me₃SiCH=CCMe₃ [N(SiR,R′)‐N=C‐C]HSiMe₃ ( 2 ‐ 7 ). ( 2 : R,R′ = Cl; 3 : R = CH₃, R′ = Ph; 4 : R = F, R′ = CMe₃; 5 : R = F, R′ = Ph; 6 : R = F, R′ = N(SiMe₃)₂; 7 : R = F, R′ = N(CMe₃)SiMe₃). In the reaction of 1 with tetrafluorosilane the spirocyclus 8 is isolated. The five‐membered ring compounds 2 ‐ 7 and compound 9 substituted on the silicon‐fluoro‐ and (tert‐butyltrimethylsilyl) are acid at the C(4)‐atom and therefore can be lithiated. Experiments to prepare lithium salts of 4 with MeLi, n‐BuLi and PhLi gave LiF and the substitution‐products 10 ‐ 12 . 9 forms a lithium salt which reacts with ClSiMe₃ to give LiCl and the SiMe₃ ring system ( 13 ) substituted at the C(4)‐atom. The ring compounds 3 ‐ 7 and 10 ‐ 12 form isomers, the formation is discussed. Results of the crystal structure and analyses of 8 , 10 , 12 , and 13 are presented.     

A new thermo‐responsive block copolymer with tunable upper critical solution temperature and lower critical solution temperature in the alcohol/water mixture

The multi‐thermo‐responsive block copolymer of poly[2‐(2‐methoxyethoxy)ethyl methacrylate]‐block‐poly[N‐(4‐vinylbenzyl)‐N,N‐diethylamine] (PMEO₂MA‐b‐PVEA) displaying phase transition at both the lower critical solution temperature (LCST) and the upper critical solution temperature (UCST) in the alcohol/water mixture is synthesized by reversible addition‐fragmentation chain transfer polymerization. The poly[2‐(2‐methoxyethoxy)ethyl methacrylate] (PMEO₂MA) block exhibits the UCST phase transition in alcohol and the LCST phase transition in water, while the poly[N‐(4‐vinylbenzyl)‐N,N‐diethylamine] (PVEA) block shows the UCST phase transition in isopropanol and the LCST phase transition in the alcohol/water mixture. Both the polymer molecular weight and the co‐solvent/nonsolvent exert great influence on the LCST or UCST of the block copolymer. By adjusting the solvent character including the water content and the temperature, the block copolymer undergoes multiphase transition at LCST or UCST, and various block copolymer morphologies including inverted micelles, core‐corona micelles, and corona‐collapsed micelles are prepared. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4399–4412     

Recombination of Lophyl Radicals in Pyrrolidinium‐Based Ionic Liquids

The recombination of photolytically generated lophyl radicals has been investigated by UV/Vis spectroscopy in 1‐alkyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imides (NTf₂) in comparison with 1‐butyl‐3‐methylimidazolium NTf₂, dimethyl sulfoxide, and triacetin. The 1‐alkyl‐1‐methylpyrrolidinium‐based ionic liquids contain an alkyl substituent varying between butyl and decyl groups. Optically pure ionic liquids are used in these studies. Temperature‐dependent investigation of lophyl radical recombination shows an increase in the radical recombination rate with increasing temperature in each solvent, which is caused by decreasing viscosity with increasing temperature. Furthermore, the viscosity of the 1‐alkyl‐1‐methylpyrrolidinium NTf₂ increases nearly linearly within the row of these ionic liquids. In contrast, the recombination of the photolytically generated lophyl radicals is significantly faster in the ionic liquids than in the traditional organic solvents under investigation. Moreover, the recombination rate increases with the length of the alkyl chain bound at the cation of the ionic liquid at a given temperature. This may be caused by an increase in the extent of lophyl radical recombination within the solvent cage. Solvent cage effects dominate in the case of lophyl radical recombination in ionic liquids bearing a long alkyl chain or if the temperature is near the melting temperature of the ionic liquid. The positive value of the activation entropy supports this hypothesis. The results obtained are important for discussion of bimolecular radical reactions in ionic liquids.     

Polymer Structure‐Guided Self‐Assisted Preparation of Poly(ester‐thioether)‐Based Hollow Porous Microspheres and Hierarchically Interconnected Microcages for Drug Release

Porous polymer microspheres (PPMs) have been widely applied in various biomedical fields. Herein, the self‐assisted preparation of poly(ester‐thioether)‐based porous microspheres and hierarchical microcages, whose pore sizes can be controlled by varying the polymer structures, is reported. Poly(ester‐thioether)s with alkyl side chains (carbon atom numbers were 2, 4, and 8) can generate hollow porous microspheres; the longer alkyl chain length, the larger pore size of microspheres. The allyl‐modified poly(ester‐thioether) (PHBDT‐g‐C₃) can form highly open, hierarchically interconnected microcages. A formation mechanism of these PPMs is proposed; the hydrophobic side chains‐mediated stabilization of oil droplets dictate the droplet aggregation and following solvent evaporation, which is the key to the formation of PPMs. The hierarchically interconnected microcages of PHBDT‐g‐C₃ are due to the partially crosslinking of polymers. Pore sizes of PPMs can be further tuned by a simple mixing strategy of poly(ester‐thioether)s with different pore‐forming abilities. The potential application of these PPMs as H₂O₂‐responsive vehicles for delivery of hydrophobic (Nile Red) and hydrophilic (doxorubicin hydrochloride) cargos is also investigated. The microspheres with larger pore sizes show faster in vitro drug release. The poly(ester‐thioether)‐based polymer microspheres can open a new avenue for the design of PPMs and provide a H₂O₂‐responsive drug delivery platform.     

Reaction of Ketene Dithioacetals with Pyrazolylcarbohydrazide： Synthesis and Biological Activities of Ethyl 5-Amino-1-（5＇-methyl-1 ＇-t-butyl-4＇-pyrazolyl）carbonyl-3-methylthio-1 H-pyrazole-4-carboxylate

The title compound, C16H23N5O3S, ethyl 5-amino-1-(5‘-methyl-1‘-t-butyl-4‘-pyrazolyl)carbonyl-3-methylthio-1H-pyrazole-4-carboxylate (5) has been synthesized by the treatment of ethyl 2-cyano-3,3-dimethylthioacrylate with 1-t-butyl-5-methyl-4-hydrazinocarbonylpyrazole (4) in refluxed ethanol. The possible mechanism of the above reaction was also discussed. The results of biological test show that the title compound has fungicidal and plant growth regulation activities.     

Self‐Assembly of Imidazolium‐Based Surfactants in Magnetic Room‐Temperature Ionic Liquids: Binary Mixtures

The phase behaviour of binary mixtures of ionic surfactants (1‐alkyl‐3‐imidazolium chloride, C_nmimCl with n=14, 16 and 18) and imidazolium‐based ionic liquids (1‐alkyl‐3‐methylimidazolium tetrachloroferrate, C_nmimFeCl₄, with n=2 and 4) over a broad temperature range and the complete range of compositions is described. By using many complementary methods including differential scanning calorimetry (DSC), polarised microscopy, small‐angle neutron and X‐ray scattering (SANS/SAXS), and surface tension, the ability of this model system to support self‐assembly is described quantitatively and this behaviour is compared with common water systems. The existence of micelles swollen by the solvent can be deduced from SANS experiments and represent a possible model for aggregates, which has barely been considered for ionic‐liquid systems until now, and can be ascribed to the rather low solvophobicity of the surfactants. Our investigation shows that, in general, C_nmimCl is a rather weak amphiphile in these ionic liquids. The amphiphilic strength increases systematically with the length of the alkyl chain, as seen from the phase behaviour, the critical micelle concentration, and also the level of definition of the aggregates formed.     

Cationic ring‐opening polymerization of novel 1,3‐dehydroadamantanes with various alkyl substituents: Synthesis of thermally stable poly(1,3‐adamantane)s

Cationic ring‐opening polymerizations of 5‐alkyl‐ or 5,7‐dialkyl‐1,3‐dehydroadamantanes, such as 5‐hexyl‐ ( 4 ), 5‐octyl‐ ( 5 ), 5‐butyl‐7‐isobutyl‐ ( 6 ), 5‐ethyl‐7‐hexyl‐ ( 7 ), and 5‐butyl‐7‐hexyl‐1,3‐dehydroadamantane ( 8 ), were carried out with super Brønsted acids, such as trifluoromethanesulfonic acid or trifluoromethanesulfonimide in CH₂Cl₂ or n‐heptane. The ring‐opening polymerizations of inverted carbon–carbon bonds in 4–8 proceeded to afford corresponding poly(1,3‐adamantane)s in good to quantitative yields. Poly( 4–8 )s possessing alkyl substituents were soluble in 1,2‐dichlorobenzene, although a nonsubstituted poly(1,3‐adamantane) was not soluble in any organic solvent. In particular, poly( 8 ) exhibited the highest molecular weight at around 7500 g mol^?1 and showed excellent solubility in common organic solvents, such as THF, CHCl₃, benzene, and hexane. The resulting poly( 4–8 )s containing adamantane‐1,3‐diyl linkages showed good thermal stability, and 10% weight loss temperatures (T₁₀) were observed over 400 °C. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4111–4124     

Synthesis of a variety of star‐shaped polybenzamides via chain‐growth condensation polymerization with tetrafunctional porphyrin initiator

A variety of well‐defined tetra‐armed star‐shaped poly(N‐substituted p‐benzamide)s, including block poly(p‐benzamide)s with different N‐substituents, and poly(N‐substituted m‐benzamide)s, were synthesized by using porphyrin‐cored tetra‐functional initiator 2 under optimized polymerization conditions. The initiator 2 allowed discrimination of the target star polymer from concomitantly formed linear polymer by‐products by means of GPC with UV detection, and the polymerization conditions were easily optimized for selective synthesis of the star polybenzamides. Star‐shaped poly(p‐benzamide) with tri(ethylene glycol) monomethyl ether (TEG) side chain was selectively obtained by polymerization of phenyl 4‐{2‐[2‐(2‐methoxyethoxy)ethoxy]ethylamino}benzoate ( 1b ′) with 2 at ?10 °C in the case of [ 1b ′]₀/[ 2 ]₀ = 40 and at 0 °C in the case of [ 1b ′]₀/[ 2 ]₀ = 80. Star‐shaped poly(p‐benzamide) with 4‐(octyloxy)benzyl (OOB) substituent was obtained only when methyl 4‐[4‐(octyloxy)benzylamino]benzoate ( 1c ) was polymerized at 25 °C at [ 1c ]₀/[ 2 ]₀ = 20. On the other hand, star‐shaped poly(m‐benzamide)s with N‐butyl, N‐octyl, and N‐TEG side chains were able to be synthesized by polymerization of the corresponding meta‐substituted aminobenzoic acid alkyl ester monomers 3 at 0 °C until the ratio of [ 3 ]₀/[ 2 ]₀ reached 80. However, star‐shaped poly(m‐benzamide)s with the OOB group were contaminated with linear polymer even when the feed ratio of the monomer 3d to 2 was 20. The UV–visible spectrum of an aqueous solution of star‐shaped poly(p‐benzamide) with TEG side chain indicated that the hydrophobic porphyrin core was aggregated. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Order in amorphous di‐n‐alkyl itaconate polymers,copolymers, and blends

The presence of a main‐chain correlation distance (d_II) in the poly(di‐n‐alkyl itaconate)s was confirmed with small‐angle X‐ray scattering/wide‐angle X‐ray scattering measurements taken over the temperature range of 293–478 K. Data for a series of alkyl acrylate polymers were also obtained for comparison. The intensity of the itaconate d_II peak was significant and indicated a greater level of nanophase formation than in analogous systems. In the lower members of the series, nanophase formation appeared to be further enhanced in the temperature range above the glass‐transition temperature (T_g). This was ascribed to the rapidly increasing main‐chain mobility in this region. Macroscopically phase‐separated itaconate blends displayed the individual d_II nanospacings of each homopolymer component. Copolymers, on the other hand, showed more interesting behavior. Poly(methyl‐co‐di‐n‐butyl itaconate) followed an average behavior in which the d_II spacing and T_g changed progressively with the comonomer content. In contrast, the side‐chain pairing in poly(methyl‐co‐di‐n‐octyl itaconate) generated d_II spacings characteristic of separate methyl and octyl nanodomains. The observation of the dioctyl nanodomains, along with the dioctyl side‐chain lower T_g relaxation event, confirmed the concept of independent side‐chain‐domain relaxation in these polymers. The temperature behavior of the poly(methyl‐co‐di‐n‐octyl itaconate) small‐angle X‐ray scattering profiles and scattering correlation lengths indicated that the two nanodomains were not completely structurally independent. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4000–4016, 2004     

Design of Weak‐Donor Alkyl‐Functionalized Push–Pull Pyrene Dyes Exhibiting Enhanced Fluorescence Quantum Yields and Unique On/Off Switching Properties

We designed, synthesized, and evaluated environmentally responsive solvatochromic fluorescent dyes by incorporating weak push–pull moieties. The quantum yields of the push (alkyl)–pull (formyl) pyrene dyes were dramatically enhanced by the introduction of alkyl groups into formylpyrene (1‐formylpyrene: Φ_F=0.10; 3,6,8‐tri‐n‐butyl‐1‐formylpyrene: Φ_F=0.90; in MeOH). The new dyes exhibited unique sensitivity to solvent polarity and hydrogen‐bond donor ability, and specific fluorescence turn‐on/off properties (e.g., 3,6,8‐tri‐n‐butyl‐1‐formylpyrene: Φ_F=0.004, 0.80, 0.37, and 0.90 in hexane, chloroform, DMSO, and MeOH, respectively). Here, the alkyl groups act as weak donors to suppress intersystem crossing by destabilizing the HOMOs of 1‐formylpyrene while maintaining weak intramolecular charge‐transfer properties. By using alkyl groups as weak donors, environmentally responsive, and in particular, pH‐responsive fluorescent materials may be developed in the future.     

Ring opening polymerization of α‐amino acid N‐carboxyanhydrides catalyzed by rare earth catalysts: Polymerization characteristics and mechanism

Five rare earth complexes are first introduced to catalyze ring opening polymerizations (ROPs) of γ‐benzyl‐L ‐glutamate N‐carboxyanhydride (BLG NCA) and L ‐alanine NCA (ALA NCA) including rare earth isopropoxide (RE(OiPr)₃), rare earth tris(2,6‐di‐tert‐butyl‐4‐methylphenolate) (RE(OAr)₃), rare earth tris(borohydride) (RE(BH₄)₃(THF)₃), rare earth tris[bis(trimethylsilyl)amide] (RE(NTMS)₃), and rare earth trifluoromethanesulfonate. The first four catalysts exhibit high activities in ROPs producing polypeptides with quantitative yields (>90%) and moderate molecular weight (MW) distributions ranging from 1.2 to 1.6. In RE(BH₄)₃(THF)₃ and RE(NTMS)₃ catalytic systems, MWs of the produced polypeptides can be controlled by feeding ratios of monomer to catalyst, which is in contrast to the systems of RE(OiPr)₃ and RE(OAr)₃ with little controllability over the MWs. End groups of the polypeptides are analyzed by MALDI‐TOF MS and polymerization mechanisms are proposed accordingly. With ligands of significant steric hindrance in RE(OiPr)₃ and RE(OAr)₃, deprotonation of 3‐NH of NCA is the only initiation mode producing a N‐rare earth metallated NCA ( i ) responsible for further chain growth, resulting in α‐carboxylic‐ω‐aminotelechelic polypeptides after termination. In the case of RE(BH₄)₃(THF)₃ with small ligands, another initiation mode at 5‐CO position of NCA takes place simultaneously, resulting in α‐hydroxyl‐ω‐aminotelechelic polypeptides. In RE(NTMS)₃ system, the protonated ligand hexamethyldisilazane (HMDS) initiates the polymerization and produces α‐amide‐ω‐aminotelechelic polypeptides. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012