New Poly(oxyethylene) Derivatives from Diels–Alder Reactions of 3‐[Methoxypoly(oxyethylene)]methylene Furan

Summary: A new poly(ethylene glycol) derivative, 3‐[methoxypoly(oxyethylene)]methylene furan, I , was prepared from the reaction of 3‐furanmethanol with the mesylate of methoxypoly(oxyethylene) in tetrahydrofuran. The degree of end‐group conversion, as determined by NMR spectroscopy, was 100%. The Diels–Alder reactions of I with N‐phenylmaleimide, N‐glycinylmaleimide, maleic anhydride, N,N′‐hexamethylene bismaleimide, and diethyl acetylenedicarboxylate resulted in the corresponding adducts. For the adduct derived from I and N‐phenylmaleimide, its thermal reversible character was confirmed by applying a retro‐Diels–Alder reaction in the presence of a large excess of 2‐methylfuran, which restored the initial polymer I quantitatively. The adduct obtained from I and N‐glycinylmaleimide was converted into its succinimidyl ester and its hydrolysis rate in phosphate buffer (pH = 8) was determined. The reactivity of the adduct derived from I and N,N′‐hexamethylene bismaleimide with benzyl mercaptan was also investigated.

     

Photoactive Azobenzene Polymers Containing Carbazole Chromophores

Summary: Polymeric systems containing side‐chain photoactive chromophores were prepared by free‐radical copolymerization of N‐vinylcarbazole with 4‐methacryloyloxyazobenzene and 4‐methacryloyloxy‐4′‐cyanoazobenzene. The resulting materials were characterized by size exclusion chromatography, TGA and DSC thermal analysis, FT‐IR, ¹H NMR, UV‐vis, and fluorescence spectroscopy and photoisomerization experiments. In all cases, the copolymer composition was almost independent of the feed composition, in agreement with the strong tendency of the investigated monomers to alternating copolymerization. Spectroscopic and thermal data clearly highlighted the occurrence of charge‐transfer electronic interactions between electron‐rich carbazole rings and electron‐poor azobenzene chromophores. These interactions facilitate the trans‐cis photoisomerization of azobenzene side‐chains.

Aromatic proton NMR spectra of different poly(MCA‐co‐NVK) samples.     

Spectroelectrochemical and Photovoltaic Characterization of a Solution‐Processable n‐and‐p Type Dopable Pyrrole‐Bearing Conjugated Polymer

D‐A‐D‐type polymers are of high interest in the field of photovoltaics and electrochromism. In this study we report the synthesis and electrochemical properties of PPyBT along with its photophysical properties and photovoltaic performance. PPyBT is soluble in common organic solvents and both n‐ and p‐type dopable, which is a desired property for conjugated polymers. During electrochemistry studies, the onset potentials of the polymer were determined as +0.2 V for oxidation and ?1.4 V for reduction. Using these values, HOMO and LUMO energy levels were calculated. The photovoltaic properties of PPyBT were also studied. PL studies showed that there is a charge transfer between PPyBT (donor) and PCBM (acceptor).

     

Back‐Biting Termination in Methyl Methacrylate/tert‐Butyl Acrylate Anionic Block Copolymerization

The product of spontaneous termination formed after addition of one or two t‐BuA units onto living PMMA chains in the MMA/t‐BuA block copolymerization was isolated and characterized by SEC, UV, FT‐IR, Raman and NMR spectroscopy. It appears as a low‐molecular‐weight peak in SEC eluograms of the copolymers, absorbing at 260 nm; its retention time corresponds to that of the PMMA block. In its FT‐IR and Raman spectra, new bands appeared corresponding to the C?C and C?O vibrations of a conjugated and H‐bonded ester group of the enol form of the cyclic oxoester composed of MMA and t‐BuA units. Experimental support of a back‐biting reaction at the link between PMMA and Pt‐BuA blocks is presented.

     

The Role of Intermolecular Hydrogen Bonding on Thermal Properties of Maleimide–Isobutene Alternating Copolymers with Polar Groups

Thermally stable copolymers with an alternating repeating structure, poly(RMI‐alt‐IB)s, were synthesized by radical copolymerization of N‐substituted maleimides containing a polar group with isobutene. The onset temperature of decomposition was higher than 300 °C and the glass‐transition temperature increased by the introduction of hydroxy and carboxy groups. IR spectroscopic analysis revealed the role of intermolecular hydrogen bonding on the thermal stability of the copolymers. It was also revealed that the amount of water absorbed into poly(RMI‐alt‐IB)s with a hydroxymethyl substituent was as high as 270% of the weight of the used polymer, while the introduction of a carboxy group resulted in lower water absorption properties.

     

Preparation of Crosslinked Poly(2‐bromoethyl methacrylate) Microspheres and Decoration of Their Surfaces with Functional Polymer Brushes

Synthesis and crosslinking copolymerization of 2‐bromoethylmethacrylate in aqueous suspension is described for preparing bromoalkyl‐functional microbeads (125–420 µm). Highly transparent microspheres with a density of accessible bromoethyl groups of 1.55 mmol · g^?1 were prepared in the suspension, stabilized with poly(N‐vinyl pyrrolidone), by using methyl methacrylate as diluting co‐monomer and ethylene glycol dimethacrylate as crosslinker. Bromoalkyl groups on the microparticles were employed as initiation sites for either surface‐initiated ATRP of glycidyl methacrylate or ring‐opening polymerization of 2‐methyl‐2‐oxazoline to generate epoxy‐ and N‐acetylethyleneimine‐functional hairy grafts, tethered to the particle surfaces with hydrolytically stable linkages.

     

One‐Pot Synthesis of Hyperbranched Polyethylenes Tethered with Pendant Acryloyl Functionalities by Chain Walking Copolymerizations

Chain walking copolymerization of ethylene with 1,4‐butanediol diacrylate at elevated concentrations for the synthesis of low‐viscosity hyperbranched polyethylenes tethered with a controllable amount of acryloyl functionality is reported. At concentrations much higher than the critical gelation concentrations, the diacrylate comonomer is copolymerized predominantly following the mono‐insertion pattern. A range of hyperbranched polyethylenes tethered with acryloyl functionality (1.3–4.8 mol‐%) and having low melt viscosity (ca. 25 Pa · s at 25 °C) and low glass transition temperature (T_g = ?69 °C) has been synthesized. This unique method is specific to the Pd‐diimine‐catalyzed chain‐walking copolymerization 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.     

Synthesis and Optical Properties of π‐Conjugated Polymers Composed of Benzo[1,2‐b:4,5‐b′]dithiophene and Thiophenes Bearing Electron‐Deficient Ethenyl Groups in the Side Chains

π‐Conjugated polymers composed of dialkoxybenzo[1,2‐b:4,5‐b′]dithiophene and thiophenes bearing cyano‐alkoxycarbonylethenyl [? CH?C(CO₂R)CN] and bis(alkoxycarbonyl)ethenyl groups [? CH?C(CO₂R)₂] were prepared. The optical properties of the obtained polymers were investigated by UV‐vis and photoluminescence spectroscopy to demonstrate that the absorption maxima of the polymers were tunable by varying the substituent of thiophene unit. The photoluminescence wavelengths and intensities of the polymer in solution were significantly dependent on the polymer side chain. The HOMO energy level of the polymer was lowered by up to ?5.51 eV by introducing electron‐deficient cyano groups. Polymer solar cells based on the new polymers were fabricated to achieve a PCE of 1.90%.

     

Synthesis and characterization of [PEG400‐alt‐DEOS]/(δ‐MgCl2)0.2597 complex

An alternating copolymer with the formula α‐hydro‐ω‐oligo(oxyethylene)hydroxy poly[oligo(oxyethylene)oxydimethylsilylene] and a molecular weight of 9 860 was synthesized. Doping of this polymer with the extremely anhydrous salt δ‐MgCl₂ resulted in a new magnesium complex with the formula poly[PEG400‐alt‐DEOS]/(MgCl₂)_0.2597. The structural hypothesis for the polymer was proposed on the basis of elemental analyses and molecular weight. Detailed ¹H, ¹³C and ²⁹Si NMR spectral investigations fully confirmed the structure of poly[PEG400‐alt‐DEOS]. Mid‐infrared FT‐IR studies of the polymer showed that it presents 1) a sufficient number of terminal hydroxyl groups to confer a substantial degree of dissolution and salt‐dissociation in the polymer complex; and 2) polyether fragments in a conformational geometry close to trans–gauche–trans. The conductivity against temperature plot for this very amorphous magnesium polymer complex demonstrated that the material conducts ionically by means of two types of charge‐migration mechanisms.

¹³C NMR spectrum of poly[PEG400‐alt‐DEOS] in CDCl₃.     

Can the First Addition of Alkyl Radicals Play a Role in the Fate of NMP?

Values of k_d for the C? ON bond homolysis were measured for alkoxyamines based on imidazoline and imidazole nitroxides. They were analyzed in terms of polar/stabilization, steric, and entropic effects. k_d decreased with increasing electron‐withdrawing capacities of the groups attached to the nitroxide, but increasing with both the bulkiness of the group attached to the nitroxide and the presence of substituents on the ring. With three alkoxyamines, it was shown that the fate of the NMP of styrene depended on the type of initiating alkyl radical: successful for initiating 1‐phenylethyl radicals and unsuccessful for initiating p‐nitrophenyloxycarbonyl‐2‐prop‐2‐yl radicals.

     

Synthesis and Characterization of Alternating and Random Copolymer Brushes

Alternating free‐radical copolymerization of vinylbenzyl‐ and methacryloyl‐terminated macromonomers in the presence of Lewis acid was applied to the synthesis of prototype copolymer brushes composed of polystyrene/poly(ethylene oxide) (PS/PEO) alternating structure. Random copolymer brushes were also prepared by radical copolymerization of both macromonomers in the absence of Lewis acid. It was found from dilute solution properties that both copolymer brushes composed of short aspect ratio formed an ellipsoid‐like single molecule in solution. To discuss the intramolecular phase separation of PS/PEO brushes in solution, we determined the radius of gyration (R_g) and cross‐sectional radius of gyration (R_g,c) of copolymer brushes by small‐angle X‐ray scattering (SAXS) using Guinier's plots in DMF and styrene. We used styrene as a solvent to cancel each other out with the electron density of PS side chains. We made also clear the effect of branching topology on polymer crystallinity to be examined by comparing the copolymer brushes with corresponding linear PEO or PEO‐block‐PS block copolymer.

     

Thermosetting Maleimide/Isobutene Alternating Copolymer as a New Class of Transparent Materials

We synthesized an alternating copolymer of N‐allylmaleimide (AMI) and isobutene (IB) [poly(AMI‐alt‐IB)] as a new class of thermosetting polymers by the free radical copolymerization process. The reactivity of the maleimide group of the AMI monomer was evaluated to be 10³ times higher than that of the N‐allyl group based on the results for the ternary copolymerization system composed of N‐methylmaleimide (MMI), N‐allylphthalimide (AP), and IB. The maleimide moiety exclusively participated in the propagation during the copolymerization of AMI with IB, resulting in the formation of the soluble poly(AMI‐alt‐IB). The copolymer included an alternating repeating structure consisting of maleimide and IB units in the main chain and the unreacted allyl group in the side chain. The onset temperature of the decomposition for poly(AMI‐alt‐IB) was over 400 °C in a nitrogen stream. The transparent cast film of poly(AMI‐alt‐IB) was readily cured upon heating without any catalyst.

     

The Development of Stereoerrors During the Homo‐ and Copolymerization of Propylene Using C2‐Symmetric Metallocene Catalysts – A Cautionary Note

Summary: A recent paper described the development of atactic sequences during the copolymerization of propylene and 1‐pentene using the C₂‐symmetric metallocene catalyst rac‐dimethylsilyl‐bis(2‐methylbenz(e)indenyl) zirconium dichloride. We have found similar stereoerrors, and showed that atactic material could in fact be extracted from the material, indicating that the catalyst in question had probably isomerized in solution, leading to a mixture of isotactic and atactic polymers.

     

Synthesis and Properties of a New Poly(arylene ethynylene) Containing 1,3,5‐Triazine Units

Summary: A new photoluminescent poly(arylene ethynylene) containing 1,3,5‐triazine units was prepared by polycondensation between 2,4‐diphenyl‐6‐N,N‐bis(4‐bromophenyl)amino‐1,3,5‐triazine and 1,4‐didodecyloxy‐2,5‐diethynylbenzene using Pd(PPh₃)₄ and CuI as the catalysts in the presence of triethylamine. The polymer showed good solubility in common organic solvents and had a number average molecular weight, , of 3 400, and a weight average molecular weight, , of 8 100. In toluene the polymer exhibited an intrinsic viscosity [η] of 0.11 dL · g^?1 at 30 °C. The polymer showed photoluminescence (PL) with emission peaks at 479 nm in CHCl₃ and at 509 nm in the solid state; quantum yield of the PL in CHCl₃ was 21%. Electrochemical reduction (or n‐doping) of the polymer started at about ?2.05 V versus Ag/AgNO₃ and gave a peak at ?2.30 V versus Ag/AgNO₃.

The 1,2,3‐triazine unit‐containing poly(arylene ethynylene) (PATZ) polymer synthesized and investigated here.     

Diels–Alder Cycloaddition‐Cycloreversion: A Powerful Combo in Materials Design

Reactive polymers are increasingly becoming materials of wide interest because they offer solutions to challenges in biomolecular immobilization, drug‐delivery and enzyme modifications. The Diels–Alder (DA) cycloaddition and the retro Diels–Alder (rDA) cycloreversion reaction in combination enables synthesis of maleimide based reactive polymeric materials. Also, the DA cycloaddition offer a reagent‐free ‘click’ reaction to construct various macromolecular architectures. Furthermore, the thermally reversible nature of the DA adducts makes them attractive building blocks for the design of thermoreversible materials. A discussion of some of the author's own research work in this area is presented in this article within the context of recent reports in polymer chemistry employing this reaction combo.

     

Blue‐Green Light Emitting Poly(phenylenevinylene) Derivatives as Candidates for Polymer LEDs: Synthesis and Characterization

Summary: Alkoxy substituted derivatives of poly‐ and oligo[(m‐phenylenevinylene)‐alt‐(p‐phenylenevinylene)] were synthesized via the Wittig ( P1 , OPV1 , OPV2 ) and the Wittig‐Horner ( P2 , OPV3 , OPV4 ) condensation routes. The polymers were characterized by ¹³C NMR, ¹H NMR, FT‐IR spectroscopy and GPC. ¹H NMR was a convenient tool to distinguish between the cis and trans double bonds in the compounds. Poly[(4‐decyloxy‐1,3‐phenylenevinylene)‐alt‐(1,4‐phenylenevinylene)] ( P1 ) contained cis and trans double bonds in significant amounts, the vinylene configuration of poly[(4‐decyloxy‐1,3‐phenylenevinylene)‐alt‐(2,5‐dipentyloxy‐1,4‐phenylenevinylene)] ( P2 ) was nearly exclusively trans. Model compounds ( OPV1–4 ) were also synthesized to support the structural and optical characterization. UV‐vis absorption, photoluminescence (PL) and cyclic voltammetry measurements have been performed to investigate the influence of the positions and the number of substituents on electronic levels. The polymers exhibited an intensive solid‐state emission in the blue‐green ( P1 ) and the green ( P2 ) region of the spectrum. Light emitting diodes have been fabricated consisting of ITO, PEDOT:PSS, P2 and Ca/Al. They exhibited high luminance of 100 cd · m^?2 at 5.9 V and low onset voltages (4.3 V) for the electroluminescence (EL).

Schematic representation of a light emitting diode fabricated by use of an alkoxy substituted derivative of poly[(m‐phenylenevinylene)‐alt‐(p‐phenylenevinylene)] ( P2 ).     

Design,Synthesis, and Characterization of Crosslinkable Doped NLO Materials Based on Polyurethanes Containing Spindle‐Type Chromophores

Spindle‐type chromophore molecules have been successfully designed and synthesized. Furthermore, a new series of main‐chain second‐order nonlinear PUs with spindle‐type chromophore molecules have been prepared. These PU offered good processability; thus thin films of optical‐quality could be easily prepared from their solutions. The molecular structural characterization of the resulting PU was achieved by ¹H NMR and FTIR spectroscopy and elemental analysis. TGA measurement of the PU showed that they had good thermal stability with decomposition temperature higher than 250 °C. The nonlinear electro‐optic coefficient of the PU‐2/poly(MMA‐co‐GMA) doped film was measured up to 32 pm · V^?1 by Teng‐Man technique after poling and crosslinking.

     

Thermally Reversible Cross‐Linked Polyamides with High Toughness and Self‐Repairing Ability from Maleimide‐ and Furan‐Functionalized Aromatic Polyamides

Polyamides having various amounts of maleimide (PA‐MI) and furan (PA‐F) pendent groups, respectively, as well as their cross‐linked polymers (PA‐MI/PA‐F) were prepared. PA‐MI/PA‐F cross‐linked polymers showed thermally reversible cross‐linking behavior via Diels‐Alder (DA) and retro‐DA reactions. Cross‐linked PA‐MI/PA‐F films exhibited enhanced toughness and mechanical properties compared to PA‐MI and PA‐F precursors. Moreover, PA‐MI/PA‐F films also showed thermal self‐repairing behavior, which was observed in the micrographs and instron tests.

     

Peculiar Catalytic Behavior of Poly(vinylidene fluoride) for Cationic Polymerization

Summary: A cationic polymerization of isobutylene, isobutyl vinyl ether, ethyl vinyl ether, vinylcarbazole and α‐methylstyrene was induced by mixing with poly(vinylidene fluoride) (PVDF) powder. The polymerization was an exothermic reaction and gave a high yield. An electron was abstracted from the monomer by PVDF. By the abstraction of the electron, the monomer was converted to a cation radical which induced polymerization. The generation of the cation radicals of the vinyl ethers was confirmed by an ESR spin trapping method, although the cation radicals could be coupled immediately. The resulting polymer was isolated from PVDF (not grafted) and characterized by size exclusion chromatography, IR, UV‐Vis and NMR spectroscopy. The copolymerization of vinyl ethers or vinyl ether/vinylcarbazole was carried out successfully to obtain their random copolymer. PVDF is regarded as a reusable catalyst for cationic polymerizations.

Reaction mechanism of the cationic polymerization of iBVE.