Synthesis and aqueous phase behavior of thermoresponsive biodegradable poly(D,L‐3‐methylglycolide)‐block‐poly(ethylene glycol)‐block‐poly(D,L‐3‐methylglycolide) triblock copolymers

Novel biodegradable thermosensitive triblock copolymers of poly(D ,L ‐3‐methylglycolide)‐block‐poly(ethylene glycol)‐block‐poly(D ,L ‐3‐methylglycolide) (PMG‐PEG‐PMG) have been synthesized. Ring‐opening polymerization of D ,L ‐3‐methyl‐glycolide (MG) initiated with poly(ethylene glycol) (PEG) and Ca[N(SiMe₃)₂]₂(THF)₂ provided triblock copolymers with alternating lactyl/glycolyl sequences of controlled molecular weight, low polydispersity index and uniform chain structure. At relatively low temperatures (≈ 10 °C) these copolymers formed clear solutions in water up to high concentrations (50 wt.‐%). Depending on molecular mass ratios of PMG and PEG blocks, a sol‐gel transition or an increase in viscosity without gel formation was observed upon increasing the temperature of the aqueous solutions. The temperature‐induced gelation was ascertained by rheology and dynamic differential scanning calorimetry (DDSC).

Phase diagram of PMG‐PEG‐PMG 1 400‐1 450‐1 400 in an aqueous solution.     

Facile Synthesis of Aqueous‐dispersible Nano‐PEDOT:PSS‐co‐MA Core/Shell Colloids Through Spray Emulsion Polymerization

This paper describes a novel spray emulsion polymerization technique for the preparation of aqueous‐dispersible nanoscale core/shell poly(3,4‐ethylenedioxythiophene) (n‐PEDOT) colloids doped with poly[(4‐styrenesulfonic acid)‐co‐(maleic acid)] (PSS‐co‐MA). Scanning electron microscopy and transmission electron microscopy images revealed that these n‐PEDOT:PSS‐co‐MA colloids possessed sharp core/shell morphologies. X‐ray diffraction and Raman spectroscopy measurements revealed semi‐crystalline morphologies and quinoid‐dominated structures for these n‐PEDOT:PSS‐co‐MA colloids. The conductivities of n‐PEDOT and n‐PEDOT:PSS‐co‐MA pellets were ca. 3.2 and 0.29 S · cm^?1, respectively, suggesting that PSS‐co‐MA acted as a shell that blocked the hopping of charges from the n‐PEDOT core to neighboring latexes. The work functions of pristine n‐PEDOT and n‐PEDOT:PSS‐co‐MA, measured using photoelectron spectroscopy, were ca. 4.7 and 5.05 eV, respectively; thus, they are close to that of indium tin oxide. The PSS‐co‐MA used in this study featured two different types of interactive functional groups, which acted as oxidative sites, dopants, and core/shell stabilizers during polymerization.

     

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).     

Unique morphology of amorphous polystyrene synthesised by nickel bis(acetyl acetonate)/methylaluminoxane

Polystyrene synthesised at room temperature by nickel bis(acetyl acetonate)/methylaluminoxane is globally atactic and amorphous in solid state. Unexpectedly, the amorphous polystyrene displays, in addition to normal amorphous scattering, a Bragg X‐ray diffraction at 2θ = 14°. This sharp reflection has been related to the presence of individual isotactic polystyrene sequences, as shown by ¹³C NMR. The isotactic sequences are long enough so that they are likely to form 3₁ helices, but not necessarily significantly laterally ordered and crystalline in solid state.

WAXD diagrams of (1) polystyrene synthesised by Ni(acac)₂/MAO; (2) poly(styrene‐co‐norbornene), styrene content 28.4 mol‐%; (3) poly(styrene‐co‐norbornene), styrene content 9.5 mol‐%; (4) polynorbornene.     

Photoinitiated Cationic Polymerization of Substituted Vinylcyclopropanes

Summary: The photoinitiated cationic polymerization of 1‐cyclopropyl‐l‐phenyl‐ethylene, 1‐cyclopropyl‐l‐(p‐methoxyphenyl)ethylene and 1‐cyclopropyl‐l‐(p‐fluorophenyl)ethylene at ambient temperatures in bulk and in solution was investigated using (η⁵‐2,4‐cyclopentadiene‐l‐yl)[l,2,3,4,5,6‐η] (l‐(methylethyl) benzene)iron(I) hexafluorophosphate (Irgacure 261, I‐1 ) and ditolyliodonium hexafluorophosphate ( I‐2 ). In contrast to our results in the polymerization of 2‐cyclopropyl‐4‐methylene‐l,3‐dioxolanes, partial ring‐opening of the cyclopropane ring could be detected. A volume shrinkage of about 11% was found.

     

Accessing Chain Length Dependent Termination Rate Coefficients of Methyl Methacrylate (MMA) via the Reversible Addition Fragmentation Chain Transfer (RAFT) Process

Summary: The RAFT‐CLD‐T methodology is demonstrated to be not only applicable to 1‐substituted monomers such as styrene and acrylates, but also to 1,1‐disubstituted monomers such as MMA. The chain length of the terminating macromolecules is controlled by CPDB in MMA bulk free radical polymerization at 80 °C. The evolution of the chain length dependent termination rate coefficient, k, was constructed in a step‐wise fashion, since the MMA/CPDB system displays hybrid behavior (between conventional and living free radical polymerization) resulting in initial high molecular weight polymers formed at low RAFT agent concentrations. The obtained CLD of k_t in MMA polymerizations is compatible with the composite model for chain length dependent termination. For the initial chain‐length regime, up to a degree of polymerization of 100, k_t decreases with α (in the expression k = k · i^−α) being close to 0.65 at 80 °C. At chain lengths exceeding 100, the decrease is less pronounced (affording an α of 0.15 at 80 °C). However, the data are best represented by a continuously decreasing non‐linear functionality implying a chain length dependent α.

     

Macrocyclic and Acyclic Bis(2,5‐diphenyl‐1,3,4‐oxadiazole)s with Electron‐Transporting and Hole‐Blocking Ability in Organic Electroluminescent Devices

Summary: Two types of bis(2,5‐diphenyl‐1,3,4‐oxadiazole)s, macrocyclic and acyclic, were prepared and evaluated as electron‐transporting and hole‐blocking materials in phosphorescent EL devices. Maximum efficiencies of η_ext = 10.4% at J = 0.11 mA · cm⁻² for the macrocycle and η_ext = 14.1% at J = 3.01 mA · cm⁻² for the acycle were observed. X‐ray crystallographic analysis and DSC measurements revealed a strong intermolecular interaction between the macrocycles and weaker intermolecular interactions between the acycles. The EL characteristics depend on the intermolecular interactions.

The two types of bis(2,5‐diphenyl‐1,3,4‐oxadiazole)s used in the study.     

Synthesis of Monodisperse Polymer Microspheres with Mercapto Groups and Their Application as a Stabilizer for Gold Metallic Colloid

Summary: Monodisperse polymer microspheres with functional mercapto groups on the surface were prepared from poly[(ethylene glycol dimethacrylate)‐co‐(2‐hydroxyethyl methacrylate)], poly(EGDMA‐co‐HEMA), microspheres successively through esterification of the active hydroxyl groups with acryloyl chloride to introduce carbon‐carbon double bonds and then the addition reaction of hydrogen sulfide to the double bond at pH 10–11. All of the polymer microspheres were characterized by scanning electron microscopy (SEM) and FT‐IR spectra. The mercapto‐functionalized polymer microspheres were utilized as a stabilizer for gold metallic colloids through coordination of the mercapto group on the polymer with gold metallic nanoparticles, which were prepared by the reduction of gold chloride trihydrate with sodium borohydride as the reductant. The size and morphology of the gold on the microspheres were determined to be of narrow dispersity (in the range 4–8 nm) by transmission electron microscopy (TEM).

Preparation of mercapto‐modified polymer microspheres and their application as a stabilizer for gold metallic colloids.     

Control of the radical polymerization by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl and its sodium salt

The control of the radical polymerization of styrene by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl is reported here in bulk at 90 °C, 120 °C and in miniemulsion. Similarly, the control by its sodium complex is reported in bulk at 90 °C.

M _n vs. conversion for 3 , 3Na , and TEMPO.     

Synthesis and Characterization of Water Soluble Saccharide Functionalized Polysiloxanes and Their Use as Polymer Surfactants for the Stabilization of Polycaprolactone Nanoparticles

Summary: Monosaccharide functionalized polysiloxanes bearing either terminal or pendant mannose moieties have been obtained starting from the allyloxyethyl glycoside and appropriate H‐containing siloxane compounds, via hydrosilylation reactions. The starting modified monosaccharide was reacted as trimethylsilyl protected derivative and a convenient method for deprotection of the hydroxyl groups was found in order to avoid the degradation of the polysiloxane chains. The reaction products were characterized by IR and NMR spectroscopy. The water solubility of these functionalized polysiloxanes was investigated and critical micelle concentration values were found to be in the range 10⁻⁴–10⁻⁵ M . Some of the water soluble compounds were used as non ionic surfactants for the elaboration of poly(ε‐caprolactone) nanoparticles by nanoprecipitation, and particle sizes of less than 200 nm were observed.

     

Swelling and Mechanical Properties of a Temperature‐Sensitive Dextran Hydrogel and its Bioseparation Applications

Summary: A series of temperature‐sensitive dextran hydrogels (poly(NIPA‐co‐GMA‐Dex)) were synthesized by the copolymerization of glycidyl methacrylate‐derivatized dextran (GMA‐Dex) and N‐isopropylacrylamide (NIPA) in aqueous solution. Their swelling and mechanical properties and bioseparation behaviors were studied. It is found that poly(NIPA‐co‐GMA‐Dex) hydrogels simultaneously exhibit much better swelling and mechanical properties. The interactions between poly(NIPA‐co‐GMA‐Dex) hydrogels and sodium dodecylsulfate (SDS), Rutin, and DL ‐α‐alanine were different because of their different hydrophobic nature, polarity, and molecular structure, and obviously depend on the temperature: the mechanism is discussed. In addition, using poly(NIPA‐co‐GMA‐Dex) hydrogels as the absorbents, gel‐extraction separation experiments of dextran and BSA solutions showed that the separation ability of poly(NIPA‐co‐GMA‐Dex) hydrogels obviously increased upon reaching the LCST.

Temperature dependence of the swelling ratio of the PNIPA (▪) and poly(NIPA‐co‐GMA‐Dex) hydrogels (r = 0.2(•), 0.4 (▴), 0.5 (▾), 0.6(♦), 0.8 (+)).     

Synthesis and copolymerization of vinylidene fluoride (VDF) with Trifluorovinyl Monomers, 11

The radical telomerization of vinylidene fluoride with 1‐chloro‐1,2‐dibromotrifluoroethane is presented. This dibrominated transfer agent was produced readily from the addition of bromine to chlorotrifluoroethylene in high yields. Four different ways of initiation (thermal, photochemical, or in the presence of redox catalysts or radical initiators) were used in order to obtain optimized yields and degrees of telomerization. Interestingly, the thermal process carried out at 210 °C led to fair to good yields in contrast to photochemically induced reaction or that catalyzed by redox systems (this latter reaction produced the monoadduct only). When radical initiators were used, tert‐butyl peroxypivalate was the most efficient one, despite the lower reaction temperature. ¹H and ¹⁹F NMR spectra enabled the microstructure of VDF telomers to be described and to determine the cumulative average degrees of telomerization (DP _n). Similarly, gas chromatography, able to detect even the ninth‐order adduct, was also useful to assess the DP _n. The kinetics of telomerization of this reaction allowed the determination of the first three order transfer constants ( ) and led to = 1.3 at 75 °C.

     

Propene Polymerisation with rac‐[Me2Si(2‐Me‐4‐(α‐naphthyl)‐1‐Ind)2]ZrCl2 as a Highly Active Catalyst: Influence of Monomer Concentration,Polymerisation Temperature and a Heterogenising Support

Propene was polymerised at high temperatures (up to 90 °C) using rac‐[Me₂Si(2‐Me‐4‐(α‐naphthyl)‐1‐Ind)₂]ZrCl₂/MAO as the catalytic system. The increasing deactivation reaction rate of the catalyst for polymerisations above 60 °C was less for a silica supported catalyst compared with the homogeneous one. The isotacticity of polypropene decreases from 99 to 96%. Also the morphology changes with different temperatures.

Increasing of the thermal stability for the rac‐[Me₂Si(2‐Me‐4‐(α‐naphthyl)‐1‐Ind)₂]ZrCl₂/MAO/SiO₂ with respect of the rac‐[Me₂Si(2‐Me‐4‐(α‐naphthyl)‐1‐Ind)₂]ZrCl₂/MAO system.     

The Rapid Chain Extension of Anthracene‐Functional Polyesters by the Diels‐Alder Reaction with Bismaleimides

Summary: The chain extension of anthracene end‐capped oligoesters by reaction with bismaleimides constitutes a rapid route to high molecular weight polyesters. Polytransesterification of bis(2‐hydroxyethyl) terephthalate in the presence of a small amount of 2‐hydroxyethyl 2‐anthracenecarboxylate provides low molecular weight anthracene‐terminated macromers with anthracene end group functionality (f_AN) of 1.66–1.85. These are subject to rapid chain extension with di(4‐maleimidophenyl)methane by Diels‐Alder cycloadditions resulting in consumption of the anthracene and maleimide end groups to generate polymers with > 2.0 × 10⁴ g · mol⁻¹. Thus, generation of the polymeric structure is achieved rapidly by addition reactions rather than sluggish transesterification reactions in which a condensate must be removed from the viscous polymer melt.

Chain extension of low‐molecular weight 2‐anthracenecarboxylate terminated oligoesters.     

Novel Brush Copolymers via Controlled Radical Polymerization

Summary: A combination of reversible addition‐fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) techniques were applied for the synthesis of novel polymer brushes by using the “grafting from” approach or a combination of “grafting through” and “grafting from” methods. The procedure included the following steps: (1) Synthesis of 2‐(2‐bromoisobutyryloxy)ethyl methacrylate (BIEM), (2a) RAFT homopolymerization of BIEM to obtain PBIEM as the polymer backbone. (2b) RAFT copolymerization of BIEM and PEO macromonomer (PEOMA, = 450 g · mol^?1, = 9) to obtain a more hydrophilic polymer backbone. Well‐controlled copolymers containing almost 25 mol‐% of PEOMA were obtained, and (3) ATRP homopolymerization of methyl acrylate (MA) and copolymerization of MA with 1‐octene using both PBIEM homopolymer and poly(BIEM‐co‐PEOMA) as polyinitiators resulted in brushes with densely grafted homopolymer and copolymer side chains, respectively. Well‐controlled copolymer side chains containing 15 mol‐% of 1‐octene were obtained. Relatively narrow molar mass distributions (MMD) were obtained for the ATRP experiments. The formation of the side chains was monitored using size exclusion chromatography (SEC) and NMR spectroscopy. The copolymer composition in the side chain was confirmed using ¹H NMR spectroscopy. Contact angle measurements indicated that for the brush polymers, containing 1‐octene in the side chain, there was a decrease in the surface energy, as compared with the brush polymers containing only the homopolymer of MA in the side chain.

Tapping‐mode SFM images for the poly(BIEM)‐graft‐poly(MA‐co‐octene) brush polymer, dip coated from dilute THF solution on mica.     

Nanoscale Analysis of Polymer Interfaces by Energy‐Filtering Transmission Electron Microscopy

Summary: Energy‐filtering transmission electron microscopy (EFTEM) was employed for the analysis of polymer‐polymer interfaces. To attain imaging and spectral analyses with a spatial resolution of 10 nm, problems arising in the EFTEM analysis for polymer specimens were investigated. Interfaces in poly(methyl methacrylate)/polystyrene‐co‐polyacrylonitrile random copolymer (PMMA/SAN) bilayer films annealed at different temperatures were analyzed by means of elemental mapping and Image‐EELS on EFTEM and the effect of the annealing temperature on the interfacial structures was also investigated.

     

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.     

Photoinduced Polymerization of Thiophene Using Iodonium Salt

Summary: Thiophene was polymerized by means of UV irradiation using diphenyliodonium hexafluorophosphate as a photoinitiator. An initiation mechanism involving electron transfer from photochemically generated onium radical cations to thiophene was proposed. N‐Ethoxy‐2‐methylpyridinium hexafluorophosphate and triphenylsulfonium hexafluorophosphate were also found to be effective in facilitating the polymerization of thiophene. Polymerization is accompanied with the film formation on the surface of the reaction tube. The photochemically obtained polymers were characterized by FT‐IR, DSC, and SEM analyses and compared with those obtained by oxidative and electrochemical means. Electrical conductivities of the samples were measured by four‐probe technique.

Photograph of the polymerization mixture containing thiophene and iodonium salt in CH₂Cl₂ before (a), after 5 min of irradiation (b), and dried film (c).     

The Formation of a Stable,Helical Conformation in Poly(N‐propargylamides) through Synergic Effects among their Pendent Groups

Copolymerization reactions of two N‐propargylamides [ 1 : HC?CCH₂NHCO(CH₂)₅CH₃, 2 : (HC?CCH₂NHCOC(CH₃)₃] were carried out with different monomer feed ratios. Compared with the two corresponding homopolymers, the series of resulting copolymers poly( 1 ‐co‐ 2 ) had a higher helix content. They also performed very differently in conformational transitions, either from random coil to helix or from helix to random coil, mainly depending on the composition of the copolymers. Synergic effects among the pendent groups played a significant role in the copolymer main chains adopting stable helices.

     

Synthesis and Optical Properties of a Copolymer of Tetrafluoro‐ and Dialkoxy‐Substituted Poly(p‐phenylenevinylene) with a High Percentage of Fluorinated Units

A copolymer of 2,3,5,6‐tetrafluoro‐1,4‐phenylenevinylene and 2,5‐dioctyloxy‐1,4‐phenylenevinylene [co(TFPV‐DOPV)], containing more than 60% of tetrafluorophenylenevinylene monomeric units, was synthesized by the Stille cross‐coupling reaction. Its linear and nonlinear optical properties were investigated. Linear absorption and photoluminescence measurements performed on thin films and solution indicate interchain migration upon excitation. The Z‐scan technique was used to evaluate the third‐order nonlinear susceptibility at λ = 1064 nm. A very high refractive nonlinearity (n₂ = (?10 ± 2) × 10^?12 cm² · W^?1) was measured with a value one order of magnitude larger than that of the corresponding dialkoxy‐substituted homopolymer.