On the Crystal Structure of Isotactic cis‐1,4‐Poly(1,3‐pentadiene)

Summary: A comparison between the crystal structure of isotactic cis‐1,4‐poly(1,3‐pentadiene) previously predicted by molecular mechanics calculations and that successively determined by other authors by experimental data is reported. The agreement between the two structures is very good as far as the space group, the unit cell parameters and the conformation of the polymer chain are concerned. The mode of packing of the chains proposed in the experimental crystal structure is very similar to that found as relative minimum in the previous energy calculations. The coexistence, in different amounts, of these two modes of packing is suggested by the analysis of the simulated X‐ray spectra and by the results of new energy calculations.

A mode of packing of chains of isotactic cis‐1,4‐poly(1,3‐pentadiene).     

Synthesis and Characterization of Long‐Chain‐Branched Polyolefins with Metallocene Catalysts: Copolymerization of Ethylene with Poly(ethylene‐co‐propylene) Macromonomer

Poly(ethylene‐co‐propylene) macromonomer (EPM) was synthesized in a high‐temperature continuous stirred tank reactor (CSTR) with [C₅Me₄(SiMe₂N^tBu)]TiMe₂ (CGC‐Ti) as the catalyst system. PE samples with EPM long chain branching (LCB) were produced by semi‐batch copolymerization of ethylene and EPM with CGC‐Ti. The LCB frequencies were up to 21.8 EPM side chains per PE backbone. The effects of temperature and ethylene pressure on the degree of EPM grafting and catalyst activity were examined.

Incorporation of EPM into a growing PE chain forming an LCB polymer.     

Electropolymerizable Terthiophene S,S‐Dioxide‐Fullerene Diels‐Alder Adduct for Donor/Acceptor Double‐Cable Polymers

The preparation of a novel fullerene‐thiophene derivative by Diels‐Alder addition of terthiophene S,S‐dioxide was demonstrated. Extrusion of SO₂ from the adduct is an effective process that yields a stable cyclohexadiene‐1,4‐bisthiophene–C₆₀ adduct in good isolable yield. The product has been accurately characterized and opens the way to synthesize new C₆₀ derivatives “via” Diels‐Alder methodology without the possibility of cycloreversion. Electrochemical and spectroscopic properties of this macromolecule were studied and supported by theoretical calculations to interpret its electronic structure. The first approach to the electropolymerization of this macromonomer produces donor‐acceptor molecular wires providing a new and versatile way to fullerene‐based double cable polymers.

     

Stereoselective Complex Formation between Polybutadiene and Cyclodextrins in Bulk

Polybutadienes (PBs) are found to form inclusion complexes with cyclodextrins (CDs) stereoselectively to give crystalline compounds in bulk. These complexes have been isolated and characterized by means of ¹H NMR and ¹³C CP/MAS NMR spectroscopy, and X‐ray diffraction. Although α‐CD did not form inclusion complexes with any kinds of PBs in aqueous solutions, α‐CD did form inclusion complexes with PBs having 1,4‐cis‐ and 1,4‐trans‐butadiene units in bulk by heating at 100 °C. On the other hand, PB having 79% of a 1,2‐structure did not form inclusion complexes with α‐CD. The yield of the inclusion complexes increases with an increase in the content of the 1,4‐cis‐structure of PB and decreases with the molecular weights of the PBs.

     

Photoinduced Fusion of Micro‐Vesicles Self‐Assembled from Azobenzene‐Containing Amphiphilic Diblock Copolymers

Poly(N‐isopropylacrylamide)‐block‐poly{6‐[4‐(4‐methylphenyl‐azo) phenoxy] hexylacrylate} (PNIPAM‐b‐PAzoM) was synthesized by successive reversible addition‐fragmentation chain transfer (RAFT) polymerization. In H₂O/THF mixture, amphiphilic PNIPAM‐b‐PAzoM self‐assembles into giant micro‐vesicles. Upon irradiation of light at 365 nm, fusion of the vesicles was observed directly under an optical microscope. The real‐time fusion process is presented and the derivation is preliminarily due to the perturbation by the photoinduced trans‐to‐cis isomerization of azobenzene units in the vesicles.

     

η3‐Benzyl‐Nickel‐Diimine Complex: Synthesis and Catalytic Properties in Ethylene Polymerization

The oxidative addition of benzyl chloride to Ni(cod)₂ in the presence of 1,4‐bis(2,6‐diisopropylphenyl)acenaphthenediimine followed by chloride abstraction affords [(η³‐CH₂C₆H₅)Ni(α‐diimine)][PF₆] (α‐diimine = 1,4‐bis(2,6‐diisopropylphenyl)acenaphthenediimine) in 70% yield. The complex is active in ethylene polymerization in the presence of methylaluminoxane and under mild reaction conditions. The polyethylenes obtained are highly branched, have very low densities, do not show T_m or measurable crystallinity and have molecular weights ranging from 80 × 10³ to 290 × 10³ g · mol⁻¹.

     

Mixed Aluminum‐Magnesium‐Rare Earth Allyl Catalysts for Controlled Isoprene Polymerization: Modulation of Stereocontrol

Summary: The performances of readily available Ln(allyl)₂Cl(MgCl₂)₂ · (THF)₄ precursors (Ln = Nd, 1 ; Y, 2 ; La, 3 ), in combination with alkyl aluminum activators [MAO, AlMe₃, AlEt₃, Al(iBu)₃], have been studied in isoprene polymerization. The catalyst combination 1 /MAO (1:30) shows a high activity (average TOFs up to ca. 5 × 10⁴ mol (Ip) · mol (Nd)⁻¹ · h⁻¹ at 20 °C) and produces polyisoprene in a controlled fashion with up to 98.5% cis content, number‐average molecular weights in reasonable agreement with calculated values, and relatively narrow polydispersities index ( = 1.20–1.70). The yttrium precursor 2 affords systems with much lower activity and degree of control, but enables the formation of either 1,4‐cis‐enriched (75%) or 1,4‐trans‐enriched (91%) polyisoprenes, simply replacing the MAO activator by AlEt₃ or Al(iBu)₃, respectively.

Formation of 1,4‐cis‐ or 1,4‐trans‐enriched polyisoprenes upon activation with MAO.     

Silyl‐Terminated Ethylene‐co‐Norbornene Copolymers by Organotitanium‐Based Catalysts

Ethylene (E) and norbornene (N) were copolymerized in the presence of PhSiH₃ as chain‐transfer agent with [Ti(η⁵:η¹‐C₅Me₄SiMe₂NBu^t)(η¹‐Me)₂] precatalyst combined with [Ph₃C][B(C₆F₅)₄]. The silane was introduced at chain‐ends of E‐co‐N copolymers with concomitant reinitiation of the growing polymer chain. The concentrations of the silane and polymer molecular weight are inversely correlated. The characteristic signals of  SiH₂Ph chain‐ends were observed by ¹H NMR. The Si heteroatom is predominantly adjacent to ethylene units in E‐co‐N copolymers with high N content.

     

Novel C60‐Anchored Two‐Armed Poly(tert‐butyl acrylate): Synthesis and Characterization

Summary: A multistep synthetic procedure for preparing novel C₆₀‐anchored two‐armed poly(tert‐butyl acrylate) was developed. First, two‐armed poly(tert‐butyl acrylate) bearing a malonate ester core with well‐controlled molecular weight was synthesized through atom transfer radical polymerization. The effective Bingel reaction between C₆₀ and the well‐defined polymer was then carried out to yield C₆₀‐anchored polymer. GPC, ¹H NMR, and UV‐vis spectroscopy indicated that the C₆₀‐anchored polymer was a monosubstituted and ‘closed’ 6,6‐ring‐bridged methanofullerene derivative.

Schematic of a novel C₆₀‐anchored two‐armed polymer.     

A Soluble High Molecular Weight Copolymer of Benzo[1,2‐b:4,5‐b′]dithiophene and Benzoxadiazole for Efficient Organic Photovoltaics

The synthesis and characterization of a soluble high molecular weight copolymer based on 4,8‐bis(1‐pentylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene and 2,1,3‐benzoxadiazole is presented. High efficiency organic photovoltaic (OPV) devices comprised of this polymer and phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) were fabricated by additive processing with 1‐chloronapthalene (CN). When the active layer is cast from pristine chlorobenzene (CB), power conversion efficiencies (PCEs) average 1.41%. Our best condition—using 2% chloronapthalene as a solvent additive in CB—results in an average PCE of 5.65%, with a champion efficiency of 6.05%.

     

Synthesis,Characterization, and Mechanism of Polymerization of Poly(but‐2‐ene sulfide)

Summary: The effect of structural factors on polymer formation versus cyclization is reported. The reaction of sodium sulfide with either 1,4‐dibromobut‐2‐ene 1 or 1,4‐dibromobutane 2 has been carried out in presence of a phase transfer catalyst and it was observed that the former yields polymer, whereas the latter gives cyclic and linear products. Interestingly, trans/cis isomerization takes place during the polymer formation from 1 and a plausible mechanism has also been discussed.

The reaction mechanism for unsaturated compound 1 and saturated compound 2 is discussed here.     

Preparation of a Polyethylene Latex by Catalytic Hydrogenation of a Polybuta‐1,4‐diene‐Based Dispersion

Summary: Fully linear polyethylene‐based latexes have been prepared by the hydrogenation of polybuta‐1,4‐diene dispersions. The latter were synthesized via dispersion ring‐opening metathesis polymerization of cycloocta‐1,5‐diene, and hydrogenated using RuCl₂(PPh₃)₃ as catalyst, without any further treatment. A high hydrogenation efficiency was achieved as demonstrated by different techniques including DSC, and ¹H NMR and FT‐IR spectroscopy. The hydrogenation process could be carried out without detrimental effect on particle size and colloidal stability as evidenced by optical microscopy and light scattering analysis.

Optical microscopy photograph of a polybutadiene‐based dispersion after hydrogenation. No change in size is observed.     

Ultimately Specific 1,4‐cis Polymerization of 1,3‐Butadiene with a Novel Gadolinium Catalyst

Novel complexes [(C₅Me₅)₂Ln][B(C₆F₅)₄] (Ln = Pr, Nd, or Gd) were prepared, which in combination with ⁱBu₃Al efficiently induce highly 1,4‐cis‐specific polymerization of butadiene. The activity of the Gd complex/ⁱBu₃Al system is high enough to exhibit good catalytic activity even at low temperature. Polymerization at −78 °C gave polybutadiene with nearly perfect 1,4‐cis microstructure (>99.9%) with sharp molecular weight distribution (M _w/M _n = 1.45) and in reasonable yield.

ORTEP drawing of 2b . Selected bond distances (Å): Pr‐F1 = 2.549(2), Pr‐F19 = 2.625(2).     

Cyclopolymerization of Nonconjugated Dienes with a Tridentate Phenoxyamine Hafnium Complex Supported by an sp3‐C Donor: Isotactic Enchainment and Diastereoselective cis‐Ring Closure

Cyclopolymerization of nonconjugated dienes produces poly(methylene‐1,3‐cycloalkanes) and provides a pathway to a number of stereochemically complex polymers. Activation of a diastereomeric mixture of a six‐membered metallacycle complex (rac‐ 1 ) in the presence of 1,5‐hexadiene produced poly(methylene‐1,3‐cyclopentane) (PMCP) with >98% cyclization of the diene monomer. The catalyst was found to cyclopolymerize 1,5‐hexadiene with relatively high activity. The microstructure of the PMCP furnished by rac‐ 1 was found to contain a high proportion of cis‐cyclopentane rings (σ = 0.70–0.74) and a relatively high isotactic content (α = 0.93–0.96). These are the first cis‐enriched isotactic cyclopolymers of 1,5‐hexadiene. Cyclopolymerization of 1,6‐heptadiene with rac‐ 1 /B(C₆F₅)₃ produced poly(methylene‐1,3‐cyclohexane) containing 97% cis‐isotactic rings. This is the first report of this highly isotactic and diastereomerically‐pure microstructure.

     

Multi‐Morphological Complex Aggregates Formed from Amphiphilic Poly(ethylene oxide)‐block‐Polydimethylsiloxane‐block‐Poly(ethylene oxide) Triblock Copolymers

Summary: Amphiphilic triblock copolymers (PEO_x‐b‐PDMS_y‐b‐PEO_x) with different block lengths were synthesized and multi‐morphological complex crew‐cut, star‐like, and short‐chain aggregates were prepared by self‐assembly of the given copolymers. The morphologies and dimensions of the aggregates can be well controlled by variation of the preparation conditions. TEM, SEM, FFR‐TEM, and LLS studies show the resulting morphologies range from LCMs, unilamellar or multilayer vesicles, LCVs, porous spheres to nanorods.

TEM images of the vesicles formed from PEO‐b‐PDMS‐b‐PEO.     

Linear‐Hyperbranched Amphiphilic AB Diblock Copolymers Based on Polystyrene and Hyperbranched Polyglycerol

Summary: A convenient three‐step strategy has been developed for the preparation of well‐defined amphiphilic, linear‐hyperbranched block copolymers by hypergrafting. The synthetic procedure is based on a combination of carbanionic polymerization with the alkoxide‐based, controlled ring‐opening multibranching polymerization of glycidol. A linear AB diblock copolymer polystyrene‐block‐polybutadiene (PS‐b‐PB) with narrow polydispersity was obtained by anionic copolymerization. Subsequent hydroxylation by hydroboration led to PS₅₀₈‐b‐(PB‐OH)₅₆, used as macroinitiator for the polymerization of glycidol under slow monomer addition conditions.

Structure of the linear‐hyperbranched amphiphilic AB diblock copolymer PS₅₀₈‐b‐(PB₅₆‐hg‐PG_x) and an AFM micrograph of its micellar core–shell structure observed after solution casting.     

Preparation and Properties of New Soluble π‐Conjugated Polymers Containing a Fumaronitrile Unit in the Main Chain

Summary: A class of new, soluble, π‐conjugated polymers containing a fumaronitrile unit in the main chain were synthesized by the reaction between di(4‐bromophenyl)fumaronitrile and bis(2,2‐dimethylpropane‐1,3‐diyl)‐1,4‐dialkoxyphenylene‐2,5‐diborate employing palladium catalysts. All the polymers were photoluminescent and electrochemically active.

The new soluble π‐conjugated polymers 1a – d with photoluminescence and electrochemical activity synthesized here.     

Redox‐Responsive Hydrogel System Using the Molecular Recognition of β‐Cyclodextrin

Summary: We have successfully constructed a redox‐responsible hydrogel system by combination of β‐cyclodextrin (β‐CD), dodecyl‐modified poly(acrylic acid) [p(AA/C₁₂)], and a redox‐responsive guest, ferrocenecarboxylic acid (FCA). In the reduced state of FCA, the ternary mixture exhibited a gel‐like behavior, whereas, in its oxidized state, the mixture exhibited a sol behavior.

Conceptual illustration for the redox‐responsive hydrogel system.     

Single‐Chain‐Particles of Poly(N‐isopropylacrylamide)

Spherical single‐chain‐particles of poly(N‐isopropylacrylamide) were prepared in aqueous solution above the lower critical solution temperature upon the addition of sodium dodecyl sulfate. The size of the single‐chain‐particles was investigated by means of transmission electron microscopy and viscosity measurements of the corresponding solutions, indicating the absence of inter‐chain entanglements among the single‐chain‐particles.

Schematic of the preparation of PNIPAM single‐chain‐globules in solution.     

Copolymerization of Ethylene with Sterically Hindered 3,3‐Dimethyl‐1‐Butene Using a Chain‐Walking Pd‐Diimine Catalyst

In this Communication, the copolymerization of ethylene with a sterically hindered α‐olefin comonomer, γ‐trisubstituted 3,3‐dimethyl‐1‐butene (DMB), using a chain‐walking Pd‐diimine catalyst, [(ArNC(Me) (Me)CNAr)Pd(CH₃)(NCMe)]SbF₆ (Ar2,6‐(iPr)₂C₆H₃) ( 1 ) is reported. In spite of its high steric bulkiness in the close proximity of the double bond, appreciable DMB incorporations (up to 3 mol‐%) are successfully achieved in the copolymers. The chain microstructure of the copolymers is elucidated, and the effect of DMB incorporation on polymer topology and thermal properties are examined. This work thus demonstrates the high capability of the Pd‐diimine catalyst in incorporating sterically encumbered α‐olefins.