Poly(N,N‐dimethylacrylamide)‐block‐Poly(L‐lysine) Hybrid Block Copolymers: Synthesis and Aqueous Solution Characterization

Four poly(N,N‐dimethylacrylamide)‐block‐poly(L ‐lysine) (PDMAM‐block‐PLL) hybrid diblock copolymers and two PLL homo‐polypeptides are prepared via ROP of ε‐trifluoroacetyl‐L ‐lysine N‐carboxyanhydride initiated by primary amino‐terminated PDMAM and n‐hexylamine respectively. The PLL blocks render the copolymers a multi‐responsive behavior in aqueous solution due to their conformational transitions from random coil to α‐helix with increasing pH, and from α‐helix to β‐sheet upon heating. The random coil‐to‐α‐helix transition is found to depend on the PLL length: the longer the peptide segment, the more readily the transition occurred. The same trend was observed for the α‐helix‐to‐β‐sheet transition, which was found to be inhibited for short polypeptides unless conjugated with the PDMAM block.

     

Thermo‐Responsive and Emulsifying Properties of Poly(N‐vinylcaprolactam) Based Graft Copolymers

Thermo‐responsive graft copolymers have been synthesized based on a poly(N‐vinylcaprolactam) (PVCL) backbone and either hydrophilic poly(ethylene oxide) (PEO) or hydrophobic poly(tetrahydrofuran) (PTHF) side chains. The phase separation behavior of the graft polymers in water was studied by transmittance measurements and compared to that of the corresponding swollen segmented polymer networks and aqueous solutions of both polymers. The influence of the concentration and length of the grafts on the cloud point temperature (T_CP) has been demonstrated. PVCL‐g‐PTHF copolymers have been synthesized by using the macromonomer technique, i.e. the radical copolymerization of VCL with a PTHF macromonomer. A special feature of these amphiphilic graft copolymers is their ability to stabilize aqueous emulsions below the T_CP and to suddenly break them above the T_CP. PVCL‐g‐PEO copolymers were prepared by a grafting onto method. First, succinimide groups were introduced in the backbone, to which amino terminated PEO chains were grafted in the second step. This leads to di‐hydrophilic copolymers that become amphiphilic after heating their aqueous solutions above the T_CP.

     

Supplemental Activator and Reducing Agent Atom Transfer Radical Polymerization of 2‐Hydroxyethyl Acrylate from High Molar Mass Poly(ethylene oxide) Macroinitiator in Dilute Solution

Triple hydrophilic asymmetric poly(2‐hydroxyethyl acrylate)‐b‐poly(ethylene oxide)‐b‐poly(2‐hydroxyethyl acrylate) (PHEA‐b‐PEO‐b‐PHEA) triblock copolymers are obtained by copper(0) catalyzed reversible deactivation radical polymerization (RDRP). Copper wire catalyzed polymerization of HEA from large PEO (M_n = 35 000 g mol^?1) macroinitiator in dimethylsulfoxide or in water fails to reach high monomer conversion in a controlled manner contrary to what is previously published with a shorter PEO macroinitiator. Catalysis by nascent Cu(0) particles generated by disproportionating CuBr in water allows rapid polymerization and high monomer conversion with a rather good control of both dispersity and HEA block length. Model disproportionation experiment shows that HEA influences the disproportionation/comproportionation equilibrium. Larger quantities of HEA lead to higher apparent rate constants and less disproportionation of CuBr which is in agreement with the supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) mechanism and not with the single electron transfer–living radical polymerization (SET‐LRP) mechanism.

     

Thermoresponsive Poly(2‐Oxazoline) Molecular Brushes by Living Ionic Polymerization: Modulation of the Cloud Point by Random and Block Copolymer Pendant Chains

Molecular brushes (MBs) of poly(2‐oxazoline)s were prepared by living anionic polymerization of 2‐isopropenyl‐2‐oxazoline to form the backbone and living cationic ring‐opening polymerization of 2‐n‐propyl‐2‐oxazoline and 2‐methyl‐2‐oxazoline to form random and block copolymers. Their aqueous solutions displayed a distinct thermoresponsive behavior as a function of the side‐chain composition and sequence. The cloud point (CP) of MBs with random copolymer side chains is a linear function of the hydrophilic monomer content and can be modulated in a wide range. For MBs with block copolymer side chains, it was found that the block sequence had a strong and surprising effect on the CP. While MBs with a distal hydrophobic block had a CP at 70 °C, MBs with hydrophilic outer blocks already precipitated at 32 °C.     

Preparation of a Siloxane Acrylic Functional Siloxane Colloid for UV‐Curable Organic‐Inorganic Hybrid Films

Summary: A new siloxane colloid was developed, for the use in UV‐curable inorganic‐organic hybrid films. The UV‐crosslinkable silica‐colloids were prepared from vinyltrimethoxysilane (VTMS) via a sol‐gel method. The structure of silica‐colloids was characterized using ¹H NMR, ²⁹Si NMR, FT‐IR, and matrix‐assisted laser desorption/ionization (MALDI‐TOF) mass spectrometry (MS). The particle size of the siloxane colloid was evaluated using atomic force microscopy (AFM) and small angle light scattering (SALS). Organic phase was based on an acrylated polyester which was synthesized using 1,4‐cyclohexane dimethanol (1,4‐CHDM), neopentyl glycol (NPG), 1,6‐hexanediol (1,6‐HD), maleic anhydride (MA), adipic acid (ADA), and acrylic acid (AA). The acrylated polyester was characterized by gel‐permeation chromatography (GPC) and acid titration. A photo‐initiator was added to the formulation and the UV‐crosslinking reaction of hybrid film was monitored via photo‐differential scanning calorimetry (Photo‐DSC) and real‐time infrared spectroscopy (RT‐IR). The effect of the concentration of VTMS colloids, UV‐light intensity, and exposure time on the polymerization rate was investigated and compared with an inorganic‐organic hybrid film based on TEOS oligomers. Photo‐DSC and RT‐IR results indicated that VTMS colloids can greatly increase free radical polymerization rate and the VTMS colloids functioned effectively as cross‐linker and reactive diluent. AFM and small angle light scattering (SALS) data showed that the silica‐colloids were well dispersed in the organic phase.

     

One‐Pot Formation of ZnO‐graft‐Poly(d,l‐Lactide) Hybrid Systems via Microwave‐Assisted Polymerization of d,l‐Lactide in the Presence of ZnO Nanoparticles

The surface modification of inorganic nanoparticles by polymer grafting is generally required for obtaining well dispersed polymer‐based (bio)nanocomposites, and the in situ polymerization of corresponding monomers is considered to be a versatile approach to this purpose. In this work, the microwave‐assisted ring‐opening polymerization of d ,l ‐lactide in the presence of zinc oxide (ZnO) nanoparticles affords an original and straightforward method for generating ZnO‐graft‐poly(d ,l ‐lactide) hybrid systems. The influence of ZnO particle size and concentration on polymerization kinetics and molar masses of free poly(d ,l ‐lactide) (PLA) chains is analyzed. Several physico‐chemical techniques, including proton nuclear magnetic resonance (¹H NMR), Fourier‐transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and thermogravimetric analysis, are used to characterize intermediates and/or reaction products. Taking into account the kinetic and spectroscopic investigation, competitive chemical pathways based on grafting from and grafting onto reactions are proposed for the one‐pot formation of PLA‐grafted ZnO nanoparticles.

     

Formation of Thermoresponsive Gold Nanoparticle/PNIPAAm Hybrids by Surface‐Initiated,Atom Transfer Radical Polymerization in Aqueous Media

Summary: We investigated the formation of thermoresponsive gold nanoparticle/poly(N‐isopropylacrylamide) (AuNP/PNIPAAm) core/shell hybrid structures by surface‐initiated, atom transfer radical polymerization (SI‐ATRP) in aqueous media and the effect of cross‐linking on the thermoresponsiveness of the AuNP/PNIPAAm hybrids. The disulfide containing an ATRP initiator was attached onto AuNPs and the monomer, NIPAAm, was polymerized from the surface of AuNPs in the absence or presence of a cross‐linker, ethylene diacrylate, in aqueous media at room temperature. The resulting brush‐type and cross‐linked AuNP/PNIPAAm hybrids were characterized by Fourier‐transform infrared spectroscopy, transmission electron microscopy, and variable temperature dynamic light scattering.

     

The Effect of NaCl on the Conformational Behavior of Acenaphthylene Labeled Poly(N,N‐diethylacrylamide) in Dilute Aqueous Solution

Summary: The effect of salts on the conformational behavior of acenaphthylene labeled poly(N,N‐diethylacrylamide) (PDEA/ACE) has been investigated in dilute aqueous solution using UV‐vis and fluorescence spectroscopy. It is demonstrated here that the effectiveness of various salts in changing the lower critical solution temperature (T_LCS) of the PDEA/ACE solution followed the Hoffmeister series. The addition of NaCl linearly lowered the T_LCS. In dilute aqueous solution, the PDEA/ACE adopted a loose coil conformation below its T_LCS. The PDEA/ACE adopted a compact globule conformation above the temperature at which the coil to globule transition (CGT) was completed. A fluorescence anisotropy investigation suggested that a molten globule conformation existed during the CGT of the PDEA/ACE solution. In all of the above three conformations, the PDEA/ACE was more compact in the presence of NaCl than in the absence of any salt.

Temperature and NaCl concentration dependence of fluorescence anisotropy of a PDEA/ACE solution. Inset: thermodynamically stable states of PDEA/ACE.     

Thermo‐ and pH‐Sensitivities of Thiosemicarbazone‐Incorporated,Fluorescent and Amphiphilic Poly(N‐isopropylacrylamide)

Summary: Novel hydrophobic comonomer (p‐methacrylamido)acetophenone thiosemicarbazone was synthesized and polymerized with N‐isopropylacrylamide to get a series of amphiphilic copolymers. The self‐aggregation behavior and thermo‐sensitive character of the (co)polymers were confirmed by TEM observation, fluorescence spectra, and cloud point measurement. Fluorescence emission of copolymer was significantly strengthened or switched off at an excitation wavelength of 320 nm upon the addition of acid or base, respectively. Thermo‐sensitivity, pH‐sensitivity, and pharmacologically versatile thiosemicarbazone groups were integrated into these novel fluorescent and amphiphilic copolymers, which will develop the novel applications of amphiphilic copolymer and environment‐responsive materials.

Fluorescence intensity at 393 nm of polymer 2 in water at 18 °C excited at 320 nm upon addition of acid and base.     

Novel Soluble N‐Phenyl‐Carbazole‐Containing PPVs for Light‐Emitting Devices: Synthesis,Electrochemical, Optical,and Electroluminescent Properties

Summary: Novel PPV derivatives (PCA8‐PV and PCA8‐MEHPV) containing N‐phenyl‐carbazole units on the backbone were successfully synthesized by the Wittig polycondensation of 3,6‐bisformyl‐N‐(4‐octyloxy‐phenyl)carbazole with the corresponding tributyl phosphonium salts in good yields. The newly formed and dominant trans vinylene double bonds were confirmed by FT‐IR and NMR spectroscopy. The polymers (with of 6 289 for PCA8‐PV and 7 387 for PCA8‐MEHPV) were soluble in common organic solvents and displayed high thermal stability (T_gs are 110.7 °C for PCA8‐PV and 92.2 °C for PCA8‐MEHPV, respectively) because of the incorporation of the N‐phenyl‐carbazole units. Cyclic voltammetry investigations (onsets: 0.8 V for PCA8‐PV and 0.7 V for PCA8‐MEHPV) suggested that the polymers possess enhanced hole injection/transport properties, which can be also attributed to the N‐phenyl‐carbazole units on the backbone. Both the single‐layer and the double‐layer light‐emitting diodes (LEDs) that used the polymers as the active layer emitted a greenish‐blue or bluish‐green light (the maximum emissions located 494 nm for PCA8‐PV and 507 nm for PCA8‐MEHPV, respectively). Compared with those of the single‐layer devices, the emission efficiencies of the double‐layer devices, in which an electron‐transporting layer (Alq₃) was added, were enhanced by a factor of 10, implying that the better hole‐electron balance is achieved because of the incorporation of the electron‐transporting layer.

The N‐phenyl‐carbazole‐containing polymers synthesized.     

Temperature and pH Dual‐Responsive Behavior of Dendritic Poly(N‐isopropylacrylamide) with a Polyoligomeric Silsesquioxane Core and Poly(2‐hydroxyethyl methacrylate) Shell

Novel temperature and pH dual‐responsive dendritic polyoligomeric silsesquioxane (POSS)–poly(N‐isopropylacrylamide) (PNIPAm)–poly(2‐hydroxyethyl methacrylate) (PHEMA) copolymers are prepared via atom transfer radical polymerization and click reactions. The cloud points (T_c) decrease with decreasing pH from 10.0 to 5.0 due to the weakened inter‐molecular interactions and enhanced intra‐molecular hydrogen bonding, whereas the T_c exhibits a small increase from pH 5.0 to 4.0 because of the better solvation of PHEMA at highly acidic conditions. The above findings are corroborated by the different sizes of aggregates observed by dynamic light scattering. The encapsulation of a fluorescent dye and stimulated release by temperature and pH changes are also demonstrated.     

A Poly(vinyl alcohol)‐graft‐Copolyester: Synthesis of a Novel Graft Copolymer Containing Adamantane Moieties as Guest for Cyclodextrin

A novel graft copolymer is synthesized from commercially available poly(vinyl alcohol) using ring‐opening polymerization. For the polymerization reaction of novel brush‐like poly(vinyl alcohol)‐graft‐poly(?‐caprolactone‐co‐(3‐/7‐(prop‐2‐ynyl)oxepan‐2‐one) 5 Sn(Oct)₂ is used as a catalyst. The formation of the graft copolymer is confirmed by ¹H NMR, ¹³C NMR, and Fourier transform infrared (FTIR) spectroscopy. Furthermore, the modification of the novel synthesized graft copolymer via a “click” reaction to implement adamantane groups is described. The success of the “click” reaction is proven by ¹H NMR spectroscopy and visualized by decomplexation of cyclodextrin with included phenolphthalein.

     

The Dependence of the Cloud Point,Clearing Point,and Hysteresis of Poly(N‐isopropylacrylamide) on Experimental Conditions: The Need for Standardization of Thermoresponsive Transition Determinations

Inappropriately, the critical solution temperature (CST) of lower CST(LCST)‐ or upper CST(UCST)‐type thermoresponsive polymers, measured by one, individual set of conditions, is considered almost exclusively as the LCST or UCST, respectively. These are correctly the minimum or maximum, respectively, of the full phase diagrams. Because the dynamic phase transition depends on the conditions, and no standardized or widely accepted process exists for CST determination, systematic investigations are carried out with the most widely investigated poly(N‐isopropylacrylamide) (PNIPAAm) to unveil the effect of data evaluation, measurement conditions on the transmittance–temperature curves, cloud point (T _CP), clearing point (T _CL), and heating–cooling hysteresis. The unusual dependence of the fundamental hysteresis parameters, i.e., width of hysteresis (X _H) and extent of transmittance recovery (Y _H), on a broad range of conditions is revealed for the first time. On the basis of the findings, the inflection point of transmittance(absorbance)–temperature curves as T _CP and T _CL, 0.1 wt% solution, 0.2 °C min⁻¹ heating/cooling steps with 5 min equilibration between the gradual change of temperature, 488 nm wavelength to obtain data comparable to light scattering at this wavelength, and determination of X _H and Y _H are proposed as standard set of conditions.

     

Synthesis and Characterization of a Red‐Emitting Copolymer Containing 5,8‐Quinoline Units

A novel nitrogen‐containing electroluminescent copolymer, PQV‐alt‐MOPPV has been designed and synthesized by Wittig‐Horner polymerization. Structure, thermal stability, and optical and electrochemical properties of the resulting copolymer were characterized by FT‐IR, ¹H NMR, elemental analysis, GPC, DSC, TGA, UV‐vis, PL, EL, and CV. The copolymer possesses excellent solubility in common organic solvents and good thermal stability. The absorption maxima of the copolymer in solution and a thin film are 490 and 516 nm, and the photoluminescence maxima in solution and thin film are 571 and 629 nm, respectively. The PLED (ITO/PEDOT: PSS (40 nm)/PQV‐alt‐MOPPV (80 nm)/Ca (30 nm)/Al (150 nm) shows a very pure red light emission with maximum peaks around 618 nm.

     

Novel Castor Oil‐Derived Block Copolymers as Promising Candidates for Biological Applications: Biorelevant and Biocompatible

The castor oil‐derived fatty acid (thioether‐containing ω‐hydroxyacid) is obtained using the UV‐catalyzed thiol‐Michael addition and is used for the first time as a monomer, for the development of biorelevant copolymers based on ε‐caprolactone, methoxy‐poly(ethylene glycol), and poly(ethylene glycol). Proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, and size exclusion chromatography, confirm the successful synthesis of diblock and triblock copolymers with very narrow molecular weight distributions. X‐ray diffractometry, polarizing light microscopy, and differential scanning calorimetry, suggest that crystallization of the crystalline block chains is restricted within the microphase‐separated morphology and that it is strongly affected by the competition between the two semicrystalline blocks. Moreover, thermogravimetric analysis reveals that the thermal properties of the copolymers are intermediate between those of their parent homopolymers. Regardless of their block composition, the biorelevant copolyesters do not exhibit apparent cytotoxicity, according to the (3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide) (MTT) and fluorescence microscopy assays.     

Synthesis and Characterization of PNIPAm Core Cross‐Linked Star Polymers and Their Functionalization with Cyclodextrin

Poly(N‐isopropylacrylamide) (PNIPAm) core cross‐linked star (CCS) polymers (s‐(PNIPAm)_n) are synthesized by arm‐first ATRP method. The related synthesis conditions are investigated and optimized. By varying cross‐linker N,N‐methylenebisacrylamide (BIS) concentration, PNIPAm CCS polymers with about 47, 86, and 211 arms are synthesized. Then, under ATRP condition, the “living” sites at the core of s‐(PNIPAm)_n reacting with a monovinyl β‐cyclodextrin (β‐CD) monomer afford β‐CD functionalized s‐(PNIPAm)_n (CDF‐SPNIPAm). The structures of the star polymers are characterized. The results indicate that in CDF‐SPNIPAm, the ratio of β‐CD units to PNIPAm arm numbers could be up to 0.6:1. The fluorescence spectra of star polymer/ANS (8‐­anilino‐1‐naphthalenesulfonic acid ammonium salt hydrate) systems prove that the β‐CD moieties of CDF‐SPNIPAm are available for including guest molecules. By using pH‐sensitive adamantyl (Ada)‐terminated poly(4‐vinylpyridine) (Ada‐P4VP) (synthesized by ATRP strategy) as a model guest macromolecule, the host–guest complexation between β‐CD units of CDF‐SPNIPAm and adamantyl groups of Ada‐P4VP is confirmed via 2D NOESY ¹H NMR and DLS measurements. The results indicate that the presence of the Ada‐P4VP arms provides temperature‐responsive star polymers with pH sensitivity. Therefore, the β‐CD‐functionalized star PNIPAm could provide host macromolecular platform for constructing novel miktoarm star polymers.

     

Synthesis,Self‐Assembly,and Properties of Homoarm and Heteroarm Star‐Shaped Inorganic–Organic Hybrid Polymers with a POSS Core

Novel homoarm and heteroarm star‐shaped inorganic–organic hybrid polymers with a polyhedral oligomeric silsesquioxane (POSS) core are prepared via click chemistry of azide POSS [POSS‐(N₃)₈], alkynyl poly(L ‐lactide) (PLLA), and alkynyl poly(ethylene oxide) (PEO). The melting and crystallization behaviors of the polymers can be adjusted by altering the PLLA to PEO ratio. The hybrid polymers reveal unique crystalline morphology due to the influence of the star‐shaped structure and the mutual influence of PLLA and PEO. The hybrid polymers show different thermostabilities, owing to the different compositions of the polymers. The hydrophilicity can be adjusted by alternating the composition of the PLLA and PEO segments. In addition, the sizes of the polymer micelles change with the change of the ratio of PLLA and PEO arms in the hybrid polymers.

     

Controlled Synthesis and Characterization of Poly[ethylene‐block‐(L,L‐lactide)]s by Combining Catalytic Ethylene Oligomerization with “Coordination‐Insertion” Ring‐Opening Polymerization

Model poly[ethylene‐block‐(L ,L ‐lactide)] (PE‐block‐PLA) block copolymers were successfully synthesized by combining metallocene catalyzed ethylene oligomerization with ring‐opening polymerization (ROP) of L ,L ‐lactide (LA). Hydroxy‐terminated polyethylene (PE‐OH) macroinitiator was prepared by means of ethylene oligomerization on rac‐dimethyl‐silylen‐bis(2‐methyl‐benz[e]indenyl)‐zirconium(IV)‐dichloride/methylaluminoxane (rac‐MBI/MAO) in presence of diethyl zinc as a chain transfer agent, and subsequent in situ oxidation with synthetic air. Poly[ethylene‐block‐(L ,L ‐lactide)] block copolymers were obtained via ring‐opening polymerization of LA initiated by PE‐OH in toluene at 100 °C mediated by tin octoate. The formation of block copolymers was confirmed by ¹H NMR spectroscopy, fractionation experiments, thermal behavior, and morphological characterization using AFM and light microscopy techniques.