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.

     

Synthesis and Optical Properties of a New Series of Side‐Chain Poly(amic acid)s With p‐π Conjugation

Summary: After the condensation polymerization of benzoguanamine (BGA) and pyromellitic dianhydride (PMDA) under microwave irradiation, the resulting p‐π conjugate poly(amic acid) was grafted via the azo coupling reaction. The obtained side‐chain polymers were further grafted with TDI‐aliphatic alcohol derivatives and TDI‐aniline derivatives. The third‐order NLO coefficient and response time of PAA and graft polymers were measured by degenerated four wave mixing (DFWM) technique and their fluorescent properties were also investigated. All of the graft polymers have larger NLO coefficients and film‐formability than PAA. Their fluorescent properties were also changed by the different electronic effect of the side‐chains. The influences of the introduction of side‐chains, the side‐chain length and the electronic effect of the substituting groups on the azobenzol side‐chain to both optical properties of the polymers by varying the conjugation degree were investigated.

     

Synthesis and Characterization of Block Copolymers of ε‐Caprolactone and DL‐Lactide Initiated by Ethylene Glycol or Poly(ethylene glycol)

Biodegradable copolymers were prepared by ring‐opening polymerization of sequentially added ε‐caprolactone and DL ‐lactide in the presence of ethylene glycol or poly(ethylene glycol), using zinc metal as catalyst. Polymerization was performed in bulk and yielded block copolymers with predetermined PEG/PCL/PLA segments. The obtained polymers were characterized by ¹H NMR, SEC, IR, DSC, TGA, and X‐ray diffraction. Data showed that the copolymers preserved the excellent thermal behavior inherent to PCL. The crystallinity of PLA‐containing copolymers was reduced with respect to PCL homopolymer. The presence of both hydrophilic PEG and fast degrading PLA blocks should improve the biocompatibility and biodegradability of the materials, which are of interest for applications as substrate in drug delivery or as scaffolding in tissue engineering.

Block copolymerization of ε‐caprolactone and DL ‐lactide initiated by dihydroxyl PEG.     

Photocurable Shape‐Memory Copolymers of ε‐Caprolactone and L‐Lactide

Biodegradable and photocurable block copolymers of ε‐caprolactone and L ‐lactide were synthesized by polycondensation of PLLA diol ( = 10 000 g · mol^?1), PCL diol ( = 10 000 g · mol^?1), and a chain extender bearing a coumarin group. The effect of copolymer composition on the thermal and mechanical properties of the photocured copolymers was studied by means of DSC and cyclic tensile tests. An increase in Young's modulus and a decrease in the tensile strain with increasing PLLA content was observed for the block copolymers. Block copolymers with high PCL content showed good to excellent shape‐memory properties. Random copolymers exhibited R_f and R_r values above 90% at 45 °C for an extremely large tensile strain of 1 000%.

     

X‐Ray Diffraction Studies on the Phase‐Transformational Behavior of a Smectic Liquid‐Crystalline Elastomer Composed of Chiral Mesogens

Structural changes through successive phase transformations of a chiral smectic liquid‐crystalline elastomer are investigated by X‐ray scattering technique. In uniaxially deformed elastomers, the smectic layer seemingly tilts even in the SmA phase, in which an in‐plane chevron structure formed in the tilted smectic phase. On the basis of an analysis of the layer reflection peaks, the layer correlation length in the tilted smectic phases is shorter than that in the non‐tilted SmA phase, though smectic layers in the tilted smectic phases are better ordered than those in SmA.

Experimental arrangement for X‐ray measurements of the uniaxially deformed elastomer in the tilted smectic phase at room temperature.     

Synthesis and self‐assembly of polymers containing dicarboximide groups by living ring‐opening metathesis polymerization

Polymers with narrow molecular weight distributions and controlled architectures were generated by living ring‐opening metathesis polymerization of exo‐7‐oxabicyclo[2.2.1]hept‐5‐ene‐2,3‐dicarboximide. The dicarboximide units have been previously shown to exhibit biological activity, can selectively bind to the nucleic acid base adenine by hydrogen‐bonding, and are readily functionalizable. Block copolymers containing these moieties were generated, and underwent self‐assembly into nanoscale spherical aggregates, with surface localized molecular recognition motifs.

     

Synthesis of Di‐block Copolymers Containing Regioregular Poly(3‐hexylthiophene) and Poly(tetrahydrofuran) by a Combination of Grignard Metathesis and Cationic Polymerizations

Poly(3‐hexylthiophene)‐block‐poly(tetrahydrofuran) was synthesized by cationic ring‐opening polymerization of tetrahydrofuran (THF) using a poly(3‐hexylthiophene) macroinitiator. Poly(3‐hexylthiophene) macroinitiator used for the ring‐opening polymerization of THF was synthesized by reacting the hydroxypropyl end‐group with trifluoromethanesulfonic anhydride in the presence of 2,6‐di‐tert‐butylpyridine. ¹H NMR spectroscopy and SEC data confirmed the formation of the di‐block copolymers. Field‐effect mobility of poly(3‐hexylthiophene)‐block‐poly(tetrahydrofuran) was measured in a thin‐film transistor configuration and was found to be 0.009 cm² · V^?1 · s^?1.

     

Block Copolymers from Organomodified Siloxane‐Containing Macroinitiators by Atom Transfer Radical Polymerization

Alternating copolymers of 1,3‐diisopropenylbenzene and 1,1,3,3‐tetramethyldisiloxane were synthesized by hydrosilylation–polyaddition. These linear copolymers were functionalized at both ends with 2‐bromoisobutyryl or benzyl chloride moieties. Subsequently, the obtained organomodified siloxane‐containing macroinitiators were successfully used for the preparation of ABA‐type block copolymers by atom transfer radical polymerization (ATRP) of styrene and tert‐butyl acrylate. The high chain‐end functionality of the macroinitiators was confirmed by ¹H NMR analysis of the macroinitiators and GPC measurements of the obtained ABA‐type block copolymers. The macroinitiator peaks disappeared in GPC traces after ATRP, and the obtained block copolymers showed a significantly narrower molecular‐weight distribution than the macroinitiators.

Synthesis of ABA‐type block copolymers by means of ATRP using organomodified siloxane‐containing, benzyl chloride functionalized macroinitiators.     

Synthesis of Polyphenylene Ether Derivatives: Estimation of Their Dielectric Constants

A series of poly(2‐alkyl‐6‐phenylphenylene ether)s were prepared by the oxidative polymerization of 2‐alkyl‐6‐phenylphenols. Their dielectric constants were approximately 2.5, whereas it was found that the phenyl group at the 6‐position clearly increased the Q factor of the polymer compared with poly(2,6‐dimethylphenylene ether), PPE. These values were qualitatively predicted from the polarizability and the molar volume calculated by the theoretical analysis of the unit structure at the HF/6‐31G* level.

     

Self‐Assembly of Carbon Nanotubes Modified by Amphiphilic Block Polymers in Selective Solvent

Block copolymers of polystyrene and poly(tert‐butyl methyacrylate) were prepared by ATRP. Halogen atoms at the chain ends were transformed into azide groups to obtain  N₃ terminated block copolymers, which were connected to the surface of multi‐walled carbon nanotubes (MWNTs) by reacting  N₃ with MWNT's surface. Amphiphilic diblock copolymer modified MWNTs were obtained after PtBMA blocks were hydrolyzed to polymethyacrylic acid (PMAA). Results showed that the amphiphilic diblock copolymer was grafted onto MWNTs by covalent bonds. TEM showed that they formed self‐assembly structures by hydrophilic/hydrophobic interaction in good solvents. As the block length of PMAA increased, the self‐assembly structures of amphiphilic MWNTs became increasingly ordered and uniform.

     

pH‐dependence of the swelling capacity of poly(N‐vinylimidazole) hydrogels

The swelling capacity (S) of poly(N‐vinylimidazole) (PVI) hydrogels in aqueous acid solutions was measured as a function of the pH, the nature of the acid, and the polymer network structure. In acid solutions, imidazole groups become protonated and the swelling capacity increases to reach a maximum corresponding to a degree of protonation equivalent to the Manning limit charge density. The variable controlling the degree of protonation, and therefore the swelling capacity, is the mass of dry polymer immersed in a given volume of solution, which was called the gel effective concentration. Divalent counteranions reduce significantly S with respect to the same ionic strength and degree of protonation, obtained with monovalent anions, while non‐complexant divalent cations have no specific influence on the PVI swelling capacity. Results were discussed in terms of the effective charge density caused by counterion condensation on protonated PVI, the non‐covalent crosslink density caused by ionic interactions with divalent anions, and the non‐Gaussian character of chains between crosslinks.

Swelling capacity of two PVI samples in aqueous solutions of HCl with two different gel effective concentrations: 10⁻² M and 2.7 × 10⁻² M .     

Synthesis of poly(fluorenevinylene‐co‐phenylenevinylene) by suzuki coupling

Suzuki coupling modified by adding Ag₂O instead of the Na₂CO₃ used in the original reaction protocol, was used as a synthetic tool for the synthesis of a copolymer in which 9,9‐dialkylfluorene moieties were coupled to unsubstituted poly(p‐phenylenevinylene) (PPV) units. The possibility of performing the polymerisations at moderate temperatures appears to be an advantage related to the use of Ag₂O. The copolymer shows a M _w of 21 000 and M _w/M _n = 2.1 and is suitable for the construction of electroluminescent devices. Monolayer organic light‐emitting diodes (OLEDs) have been built which emit greenish light.

Synthesis of poly(fluorenevinylene‐co‐phenylenevinylene).     

Janus Micelle Formation Induced by Protonation/Deprotonation of Poly(2‐vinylpyridine)‐block‐Poly(ethylene oxide) Diblock Copolymers

A novel approach to amphiphilic polymeric Janus micelles based on the protonation/deprotonation process of poly(2‐vinylpyridine)‐block‐poly(ethylene oxide) (P2VP‐b‐PEO) diblock copolymers in THF is presented. It is found that addition of HCl to the micelles solution of P2VP‐b‐PEO copolymers leads to the formation of vesicles. Subsequently mixing a small amount of hydrazine monohydrate with the vesicle solution can induce the dissociation and reorganization of the vesicles into Janus micelles. When HCl is replaced by HAuCl₄ precursors, composite Janus particles containing gold in P2VP blocks are obtained.

     

Synthesis of Telechelic Oligomers via Atom Transfer Radical Polymerization, 3

Summary: ATRP of butyl α‐fluoroacrylate (FABu) was carried out at 90 °C using methyl 2‐bromoisobutyrate (2‐MBiB) as initiator and the homogeneous catalyst CuBr/1,1,4,7,10,10‐hexamethyltriethylenetetramine (HMTETA). Telechelic oligomers were obtained by coupling the bromo terminated polymers in the presence of Cu⁽⁰⁾ and 2,2′‐bipyridyl ligand. The ¹H and ¹⁹F NMR, SEC and MALDI TOF analyses show that the poly(FABu) chains recombination was the main reaction (80% yield). About 20% of disproportionation reaction also occurs in the process, whereas transfer reactions can be neglected.

Compounds produced by recombination, disproportionation and transfer during the coupling reaction of poly(FABu) oligomers.     

Modification of Oligomeric Cyanate Ester Polymer Properties with Multi‐Walled Carbon Nanotube‐Containing Particles

The properties of an oligomeric cyanate ester polymer were modified by the addition of 0.01–3 wt.‐% multi‐walled carbon nanotube (MWNT) containing particles. The dynamic mechanical behavior and thermal properties of the cyanate ester/MWNT nanocomposites were evaluated. The storage modulus, G′, of the nanocomposite with 1 wt.‐% MWNT particles was nearly 60 and 600% higher than the neat polymer at 100 and 200 °C, respectively. The glass transition temperature of the nanocomposite was also raised by 30 °C and its thermal stability in air and nitrogen was increased by 58 and 25 °C, respectively. The property improvements are attributed to reinforcement of the cyanate ester as a result of good nanotube dispersion and effective polymer‐MWNT interaction.

     

Novel Light Emitting Diode Using Organic Electroluminescence Microcapsules

Novel light emitting diodes (LEDs) were prepared using electroluminescence (EL) material/polymer microcapsules (ELC). N‐vinylcarbazole as a hole‐transporting component and methyl methacrylate (MMA) were copolymerized for producing the seed particles using dispersion polymerization. An oxadiazole derivative, synthesized as a electron‐transporting component, and tris(8‐hydroxyquinolinato) aluminium(III) (Alq₃) were incorporated into the polymer particles by using the solute co‐diffusion method (SCM). The LEDs for the EL characterization were fabricated in a thin sandwich configuration: Al anode/ELC/ITO cathode. The surface imaging of the LED prepared using ELC was performed by atomic force microscopy (AFM). The EL characteristics of the ELC were investigated by UV, photoelectron and luminescence spectroscopy, and the current‐voltage and the light‐voltage characteristics for the LED were determined.

Encapsulation procedure using solute co‐diffusion method (SCM).     

Formation of Inorganic/Organic Nanocomposites by Nitroxide‐Mediated Polymerization in Bulk Using a Bimolecular System

Summary: A series of organic‐inorganic nanoparticles were synthesized by nitroxide‐mediated polymerization (NMP) of butyl acrylate initiated by a self‐assembled monolayer of an azo initiator. The azo initiator was immobilized on silica particles in the presence of a stable nitroxide radical, SG1 (an acyclic β‐phosphonylated nitroxide, N‐tert‐butyl‐N‐(1‐diethylphosphono‐2,2‐dimethyl)propyl nitroxide). After preliminary qualitative characterization by X‐ray spectroscopy (XPS) and Fourier‐transform infrared (FTIR) measurements, the nanoparticles were studied by thermogravimetric analysis (TGA) to determine the polymer grafting density and to permit a comparison with corresponding values of the initiator monolayer. It was demonstrated that the grafting from polymerization exhibits a controlled character with a low polydispersity ( < 1.2) in a large range of molecular weights of the grafted chains (from 4 000 up to 145 000 g · mol^?1) under the conditions when the stable radical SG1, acting as chain growth moderator tethered to the inorganic core, was used.

     

Grafting of Polystyrene onto Poly(butyl acrylate) and Polystyrene Backbones Using Functionalized Methacrylates

Summary: Grafting of terminal epoxide‐functionalized polystyrene onto poly[styrene‐co‐(2‐hydroxyethyl methacrylate)] or poly[(butyl acrylate)‐co‐(2‐hydroxyethyl methacrylate)] backbones was carried out by coupling reactions catalyzed by boron trifluoride. The functionalized backbones were prepared by free radical copolymerization of 2‐hydroxyethyl methacrylate (HEMA) with styrene or butyl acrylate. For the synthesis of terminal functionalized polymer chains a side reaction of the TEMPO‐mediated free radical polymerization of methacrylates could be used successfully to convert TEMPO‐terminated polymers into terminal epoxide‐functionalized polymers by the use of glycidyl methacrylate. The number of epoxide units attached to the backbone was directly related to the TEMPO concentration during the disproportionation reaction. Taking P(S‐co‐HEMA) as well as P(BuA‐co‐HEMA) backbones in coupling reactions with different epoxy‐functionalized polystyrenes in the presence of boron trifluoride, graft polymers with up to 7 and 37 side chains per backbone were produced.

Molecular weight distribution curves of a linking experiment between P(BuA‐co‐HEMA) backbones and epoxide‐functionalized polystyrene side chains.     

Blue Light Emission from a Fluorene‐Carbazole‐Fluorene Trimer Incorporated as the Side Chain into a Polynorbornene

Summary: A well defined blue electroluminescent fluorene‐carbazol‐fluorene trimer 3,6‐bis‐(9,9‐dihexyl‐9H‐fluoren‐3‐yl)‐9‐alkyl‐9H‐carbazole was synthesized using a Suzuki type cross coupling reaction as the key step. A way to attach this chromophore to a norbornene was developed and the resulting electroactive monomer was polymerised using the “3^rd generation Grubbs catalyst” (N,N‐bis(mesityl) 4,5‐dihydroimidazol‐2‐ylidene)(3‐bromo‐pyridine)₂(Cl)₂Ru?CHPh), yielding an amorphous polymer with a narrow molecular weight distribution, which was used to build a light‐emitting diode exhibiting electroluminescence peaking at 410 nm.

Incorporation of the fluorene‐carbazol‐fluorene trimer as the emissive layer in an ITO/PEDOT:PSS/emitter/Ca/Al light emitting device.     

Thermal Properties and SSA Fractionation of Metallocene Ethylene‐Oct‐1‐ene Copolymers with High Comonomer Content Cross‐linked by Dicumyl Peroxide or β‐Radiation

Two metallocene ethylene‐oct‐1‐ene copolymers, differing in comonomer content and in molecular weight, were cross‐linked either by dicumyl peroxide or β‐radiation. The effect of high comonomer content on the crystalline morphology, once the materials were cross‐linked, was analyzed by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The gel content was determined in boiling xylene, and the cross‐linking process was monitored by FT‐IR spectroscopy. Two endotherms were distinguished: the first one was associated to the primary crystallization, and the second one to the shorter sequences that are excluded from the primary crystallization. The successive self‐nucleation annealing (SSA) technique has revealed that as the comonomer content increases the crystal size distribution is more homogeneous, and therefore, the melting and crystallization behaviour is reversible, because of its fringed‐micellar morphology. In spite of their crystalline morphology with very low crystallites, DCP cross‐linked samples displayed a considerable decrease in crystallinity and in crystal size, whereas β‐irradiated samples showed no significant decline in crystal size. Slight changes in crystallinity were detected and attributed to the heat generation that every irradiation process involves and affects smaller crystallites preferentially. DMA analysis has confirmed DSC results on crystalline size and crystallinity variations induced by both cross‐linking processes. By means of FT‐IR spectroscopy, it was detected that a high comonomer content induces oxidation during cross‐linking. Moreover, β‐irradiation samples exhibited a lower degree of oxidation than DCP cross‐linked samples.

The heating scan of DCP cross‐linked EG8411 after being submitted to successive self‐nucleation annealing.