Ring‐Opening Copolymerization of 2‐Aryl‐1‐methylenecyclopropanes with Carbon Monoxide Initiated by Pd–bpy Complexes

[PdCl(Me)(bpy)] and a mixture of the complex with cocatalysts; NaBARF (BARF = [B{C₆H₃(CF₃)₂‐3,5}₄]^?), NaBF₄, AgBARF, AgBF₄, and AgOTf, catalyze the copolymerization of 2‐phenyl‐1‐methylenecyclopropane with carbon monoxide to produce a new polyketone accompanied by ring opening of the monomer. ¹H and ¹³C{¹H} NMR spectra indicate that the polymers have two isomeric repeating units in which the phenyl substituents occupy different positions. The molecular weights of the polyketones formed by the reactions with a [Pd]/[cocatalyst]/[2‐phenyl‐1‐methyleneyclopropane] ratio of 1:3:70 are in the range of M _n = 13 100–86 000. The polymer obtained by the reaction promoted by [PdCl(Me)(bpy)]/MBARF, where M = Ag or Na, shows a narrow molecular weight distribution, M _w/M _n = 1.44 and 1.59, respectively. The catalysis is effective also for the ring‐opening copolymerization of 2‐aryl‐1‐methylenecyclopropanes bearing Me and F substituents on the phenyl ring. Isotope‐labeled experiments revealed the mechanism of the polymerization, which involves a 1,2‐insertion of the monomer into the Pd–acyl bond to produce a cyclopropylmethyl palladium intermediate, and subsequent β‐alkyl elimination to give the Pd–alkyl complex.

     

Radical Copolymerization of N‐Vinylformamide with Methylvinylketone: An Approach to Iminium/Imine Ring Containing Polymers

The free radical copolymerization of N‐vinylformamide (NVF) with methylvinylketone in water and the subsequent alkaline or acidic hydrolysis produce iminium structures containing polymers. It can be concluded from the copolymerization parameters (r_{N ‐vinylformamide} = 0.02, r _{methylvinylketone} = 0.50) that alternating copolymers are formed which contain few amounts with statistically arranged monomer sequences. The acidic hydrolysis of the copolymer results in a water‐soluble polymer bearing five‐membered iminium rings along the polymer chain. A water‐insoluble polymer is generated under alkaline conditions also containing five‐membered imine rings. The formation of the iminium ring polymer is attributed to the fact that generated free amino groups derived from NVF immediately react with the keto groups in the vicinity. The molecular structures of the obtained polymers are characterized by ¹H‐NMR, ¹³C‐NMR, and IR spectroscopy. The assignment of the signals in the novel polymers are confirmed by model compounds.     

First Poly(2‐oxazoline)s with Pendant Amino Groups

Summary: A new 2‐oxazoline monomer with a Boc protected amino function, 2‐[N‐Boc‐5‐aminopentyl]‐2‐oxazoline; ( Boc ‐ AmOx ), was synthesized from commercially available compounds. With an initiator salt system (N‐methyl‐2‐methyl‐2‐oxazolinium triflate; MeOxOTf ), the monomer could be converted via living cationic ring‐opening polymerization to well‐defined homopolymers with narrow molar mass distributions and targeted polymer chain length. After a quantitative deprotection, poly(2‐oxazoline)s with pendant amino functions were obtained. In order to vary the polymer functional group density and solubility of the polymer, copolymerization with different monomer ratios of Boc ‐ AmOx and 2‐ethyl‐2‐oxazoline ( EtOx ) was performed. Ex‐situ NMR spectroscopy studies verified the randomness of the cationic copolymerization. The accessibility of the pendant amino side functions was confirmed in polymer analog thiourea formation with different isothiocyanates, such as benzyl isothiocyanate ( BzNCS ), or a fluorescence dye, tetramethyl rhodamine isothiocyanate ( TRITC ). A cross‐linking reaction with a bifunctional isothiocyanate ( Ph(NCS)₂ ) resulted in poly(2‐oxazoline) hydrogels.

     

Vinylic Polymerization of Norbornene by Late Transition Metal‐Based Catalysis

The polymerization of norbornene with two new families of late transition metal‐based catalysts derived from: (i) Ni and Pd complexes bearing bulky diammine ligands, with the general formula [ArN=C(R)—C(R)=NAr]MeX₂ and (ii) Fe and Co complexes bearing bulky arylimine ligands with the general formula [(2, 6‐ArN=C(Me))₂C₅H₃N]MX₂ is reported. New Co‐based complexes have been tested as well. A prevailingly vinylic, amorphous polymer was obtained with all the catalysts tested, whose solubility in organic solvents is substantially dependent on the molecular weight. Polymerization activity greatly varies from one catalyst to another and depends rather on the metal than on the ligand. Solvent polarity and temperature greatly affect the polymerization yields. Besides a dramatic reduction of molecular weights, the addition of small amounts of 1‐hexene produces a noticeable increase in the catalytic activity. NMR analysis shows that in all cases a certain percentage of ROMP polymer is present and that, in general, the variations in polymerization conditions, which produce an increase in activity, simultaneously affect a reduction of the ROMP percentage.     

Ring‐Opening Polymerization of ε‐Caprolactone by Phosphorane Iminato and Cyclopentadienyl Complexes of Rare Earth Elements

Rare earth element complexes with triphenyl phosphorane iminato ligands such as [La₂(NPPh₃)₄(μ‐NPPh₃)₂(μ‐THF)] and [Yb(NPPh₃)₃]₂ initiate the polymerization of ε‐caprolactone to give high molecular weight poly(ε‐caprolactone) with moderate polydispersity. The reactivity of these complexes is higher as compared to complexes with three cyclopentadienyl ligands with corresponding metal centers. The initiation mechanism for the polymerization of ε‐caprolactone by [La₂(NPPh₃)₄(μ‐NPPh₃)₂(μ‐THF)] is discussed based on the end groups of low molecular weight polycaprolactones. Living chain ends of poly(ε‐caprolactone) were proved by block copolymerization of ε‐caprolactone and δ‐valerolactone. The mixed complex [Cp₃Dy₂(NPPh₃)₃] has been successfully applied for ROP of CL. A significant increase in molecular weight of ROP has been observed with decrease of reaction temperature.     

Chain‐Growth Polycondensation in Solid‐Liquid Phase with Ammonium Salts for Well‐Defined Polyesters

Polycondensation of a potassium 4‐bromomethylbenzoate derivative dispersed in organic solvent was carried out with tetrabutylammonium iodide as a phase transfer catalyst (PTC) and a reactive benzyl bromide as an initiator to yield polyesters having a defined molecular weight and a narrow molecular weight distribution (M̄_w/M̄_n < 1.3). Polymerization involves the transfer of monomer to organic solvent layer with the PTC and the reaction of monomer with the initiator and the polymer end benzyl bromide moiety in a chain polymerization manner, as evidenced by polymerization behavior; increase of the molecular weight in proportion to monomer conversion and equal amount of the initiator unit and the end group in polymer irrespective of monomer conversion. Furthermore, the molecular weight increased in proportion to feed ratio ([monomer]₀/[initiator]₀), and the polydispersity index M̄_w/M̄_n stayed less than 1.3 over the whole range of feed ratio.     

Syndiospecific Living Block Copolymerization of Styrenic Monomers Containing Functional Groups,and Preparation of Syndiotactic Poly{(4‐hydroxystyrene)‐block‐[(4‐methylstyrene)‐co‐(4‐hydroxystyrene)]}

At –25°C, the sequential block copolymerizations of 4‐(tert‐butyldimethylsilyloxy)styrene (TBDMSS) and 4‐methylstyrene (4MS) were investigated by using a syndiospecific living polymerization catalyst system composed of (trimethyl)pentamethylcyclopentadienyltitanium (Cp*TiMe₃), trioctylaluminum (AlOct₃) and tris(pentafluorophenyl)borane (B(C₆F₅)₃). The number‐average molecular weight (M̄_n) of the poly(TBDMSS)s increased linearly with increasing the polymer yield up to almost 100 wt.‐% consumption of TBDMSS used as 1^st monomer. The M̄_n value of the polymer after the second monomer (4MS) addition continued to increase proportionally to the polymer yield. The molecular weight distributions (MWDs) of the polymers remained constant at around 1.05–1.18 over the entire course of block copolymerization. It was concluded that the block copolymerizations of TBDMSS and 4MS with the Cp*TiMe₃ /B(C₆F₅)₃ /AlOct₃ catalytic system proceeded with a high block efficiency. The ¹³C NMR analysis clarified that the block copolymers obtained in this work had highly syndiotactic structure. By the deprotection reaction of silyl group with conc. hydrochloric acid (HCl), syndiotactic poly{(4‐hydroxystyrene)‐block‐[(4‐methylstyrene)‐co‐(4‐hydroxystyrene)]} (poly[HOST‐b‐(4MS‐co‐HOST)]) was successfully prepared.     

Polyacetylenes with Ferrocenophane Pendant Groups: Synthesis by Rh‐Complex‐Catalyzed Polyaddition,Characterization and Properties

The Rh(I)‐complex‐catalyzed polymerization of N‐(4‐propynyloxyphenyl)‐2‐aza‐[3]‐ferrocenophane ( 1 ) and of N‐(4‐pentynyloxyphenyl)‐2‐aza‐[3]‐ferrocenophane ( 2 ) gives the corresponding polyacetylenes with ferrocenophane pendant groups; compounds 3 and 4 , respectively. Polymers 3 and 4 are soluble in organic solvents such as tetrahydrofuran and CHCl₃ , although polymer 3 contains a small portion of an insoluble fraction. The molecular weights of polymers 3 (soluble part) and 4 are determined to be M̄_n = 10 000 and M̄_w = 14 000, and M̄_n = 5 100 and M̄_w = 9 300, respectively. The copolymerization of 1 and 4‐ethynyltoluene yields copolymers containing the two monomer units in various ratios depending on the ratio of the monomers used in the polymerization. Molecular weights of the copolymers range from M̄_n = 8 800 and M̄_w = 13 200 to M̄_n = 23 800 and M̄_w = 36 900, and increase with a decreasing content of monomer units derived from 1 . The thermal decomposition temperature is also influenced linearly over a wide range by the monomer unit ratios. All these polymers are characterized by NMR and UV spectroscopies as well as by elemental analyses. The polymers undergo two electrochemical oxidations: quasi‐reversible oxidation of the Fe and irreversible oxidation of the nitrogen‐containing part of the ferrocenophane unit.     

Controlled Synthesis and Ti—O Bond Stability of Star‐Shaped Biodegradable Polyesters via Titanate‐Initiated ROP of Cyclic Esters at Ambient Temperature

Four‐arm star‐shaped PCL polymers are synthesized using iPT as initiator for the controlled ROP of CL at 25–40 °C. The number‐average molecular weights of the star‐shaped Ti(O‐PCL)₄ with narrow molecular weight distributions are proportional to the molar ratios of monomer to initiator. The four‐branch star‐shaped structures of Ti(OPCL)₄ are confirmed through polymer hydrolysis monitoring by GPC, which indicates that the stability of the Ti—O bond in the core of the star‐shaped polymer chain increases with the increase of polymer molecular weights. The star‐shaped Ti(O‐PCL)₄ can act as a macroinitiator for successive block copolymerization with d,l ‐Lactide in bulk at 60 °C.     

Polymerization of lactides and lactones, 12. Synthesis of poly[(glycolic acid)‐alt‐(L‐glutamic acid)] and poly{(lactic acid)‐co‐[(glycolic acid)‐alt‐(L‐glutamic acid)]}

Glutamic acid/glycolic acid‐based biodegradable polymers have been prepared by ring‐opening polymerization of (3S)‐3‐[(benzylcarbonyl)ethylene] morpholine‐2,5‐dione, and the copolymerization of the morpholine‐2,5‐dione derivative and lactide. The homopolymerization and copolymerization were carried out in bulk at 140°C with SnOct₂ as a catalyst to give the corresponding protected poly(Glc‐alt‐Glu) and protected poly[LA‐co‐(Glc‐alt‐Glu)], respectively. After removal of the protective group by catalytic hydrogenation with Pd/C (5%) as a catalyst, poly(Glc‐alt‐Glu) and poly[LA‐co‐(Glc‐alt‐Glu)] showed excellent hydrophilicity.     

Multi‐arm star block copolymers based on ε‐caprolactone with hyperbranched polyglycerol core

Multi‐arm star block copolymers based on ε‐caprolactone have been prepared by a core‐first approach using propoxylated hyperbranched polyglycerol P(G₅₂PO₃) as a polyfunctional initiator. Various monomer/initiator ratios were employed in the Sn‐catalyzed polymerization in order to vary the length of the caprolactone arms (DP_n(arm) = 10 to 50). The molecular weights of the block copolymers were in good aggreement with the calculated values. Careful NMR analysis revealed that the monomer/initiator ratio not only controls the arm length, but also influences the degree of functionalization. Poly(ε‐CL) stars with 52 arms and absolute molecular weights between 69 200 and 360 400 g/mol have been prepared. SEC measurements showed that the narrow polydispersity of the core molecule (M_w/M_n = 1.24) could be maintained upon block copolymerization. The resulting star polymers exhibited polydispersities between 1.21 and 1.33.     

Addition Polymers of Strained Cyclic Olefins – Transition Metal Catalysed Polymerisations of the Cyclobutene Derivative Bicyclo[3.2.0]hept‐6‐ene

Bicyclo[3.2.0]hept‐6‐ene was converted into the corresponding addition polymer poly(6,7‐bicyclo[3.2.0]heptylene) with the aid of early and late transition metal based olefin polymerisation catalysts. Moderate to very good yields (42–99%) of polymer were obtained with [Pd(NCEt)₄][BF₄]₂, [(η³‐allyl)Pd(solv)₂][SbF₆], [(2,9‐dimethyl‐1,10‐phenanthroline)Pd(CH₃)(NC(CH₂)₆CH₃)][SbF₆], and Cp₂ZrCl₂/MAO, using monomer to transition metal ratios between 50/1 and 250/1. Reaction occurs at the olefin π‐bond, and the four‐membered ring of the monomer is retained during polymerisation which differs from ring‐opening olefin metathesis polymerisation in which the four‐membered ring is opened. The nearly exclusively saturated structure of the polymer was confirmed by ¹H and ¹³C NMR spectroscopy. It is proposed that the polymers consist of repeating units that are predominantly cis‐exo‐enchained. GPC analysis of the soluble polymers prepared with [Pd(NCEt)₄][BF₄]₂ showed that the molecular mass values (GPC) were in the range of 3 700 to 22 600.

     

Radical Copolymerization Behavior of 2,2‐Dimethyl‐5‐methylene‐1,3‐dioxolan‐4‐one with Common Monomers

Radical copolymerization of 2,2‐dimethyl‐1,3‐dioxolan‐4‐one (DMDO) consisting of a hybrid structure of acrylate and vinyl ether moieties with styrene, methyl methacrylate, and vinyl acetate was examined. The radical copolymerization was carried out without a solvent or in chlorobenzene in the presence of 3 mol‐% of 2,2′‐azoisobutyronitrile at 60°C for 20 h to obtain the copolymers with number‐average molecular weights of 1 400‐700 000 in 27–86% yields. No ring‐opening occurred but vinyl polymerization of DMDO selectively proceeded in the copolymerization. The monomer reactivity ratios were evaluated as r₁ = 6.42, r₂ = 0.08 (M₁, DMDO; M₂, styrene) by the Fineman‐Ross method. The Alfrey‐Price Q‐ and e‐values of DMDO were calculated as 5.97 and –0.13, respectively. Ab initio molecular orbital calculations were carried out to compare the reactivity of DMDO with methyl α‐methoxyacrylate and vinyl ether.     

Novel Controlled Polymerization of Cyclo‐olefins,Dienes, and Trienes by Utilizing Reaction Properties of Late Transition Metals

Pd complexes with diimine ligands promote polymerization of cyclopentenes, 1,6‐dienes, and 1,6,11‐trienes to afford polymers having 1,2‐ or 1,3‐five‐membered ring in every repeating unit. The Pd complexes with C₂ symmetrical structure catalyze the polymerization reactions to produce polymers with high stereoselectivity. Some of the obtained polymers show characteristic properties such as thermoreversible gelation and liquid crystal formation. Ni complexes bring about the cyclopolymerization of the dienes to afford polymers containing five‐ and/or six‐membered rings in controlled stereochemistry.

     

Homo‐ and Copolymerization of Strained Cyclic Olefins with New Palladium(II) Complexes Bearing Ethylene‐Bridged Heterodonor Ligands

Amorphous and high molar mass polymers of norbornene and phenylnorbornene (endo/exo ratio of 80/20) were prepared by the use of new dicationic palladium(II) single‐component catalysts of the general type [Pd(L∩L)(NCCH₃)₂](BF₄)₂. [(L∩L) = 2‐(diphenylarsino)‐1‐(methylthio)ethane (S∩As, 1 ) ( 4 ), 2‐(diphenylphosphino)‐1‐methylthio)ethane (S∩P, 2 ) ( 5 ), 1, 2‐bis(diphenylphosphino)ethane (P∩P, 3 ) ( 6 ). With increasing the trans influence of the donor atom in the ligands (P > As > S) the polymerization activity of the catalysts towards polymerization of norbornene increases instantly. Both the molecular weight and the thermal behavior of the polymer can be tailored using ethene as chain transfer agent. Catalyst 4 is also active towards the alternating copolymerization of carbon monoxide and norbornene. The isolated copolymer is highly soluble in toluene, THF and chlorinated solvents. The DSC measurement of the norbornene‐carbon monoxide copolymer showed a melting temperature (T_m) of 241°C (ΔH_f = 47.3 J/g) and a glass transition temperature (T_g) of 161°C which is about 170°C lower compared to the homopolynorbornene (T_g ≅ 330°C).     

Excellent Control of Perylene Diimide End Group in Polyfluorene via Suzuki Catalyst Transfer Polymerization

Six aryl Pd(II) bromide complexes based on perylene diimide derivative (Ar) and phosphine mixed‐ligands are successfully synthesized by directly oxidative addition of Ar–Br to the Pd(0) precursor. These complexes with the general formulas ArPdBr(PCy₃)₂ (PCy₃ = tricyclohexylphosphine; Pd1–Pd3 ) and [ArPdBr(TXP‐2,4)]₂ (TXP‐2,4 = tri‐2,4‐xylylphosphine; Pd4–Pd6 ) are stable and can be handled in air at room temperature. By employing the Pd(II) complexes as initiators, Suzuki catalyst transfer polymerization (SCTP) of AB‐type fluorene monomer is investigated for preparing polyfluorenes (PFs) with the defined end group. Complexes Pd4–Pd6 with auxiliary TXP‐2,4 ligand can initiate polymerization of AB‐type fluorene monomer at room temperature, while higher polymerization temperature is required for Pd1–Pd3 with alkyl phosphine PCy₃. The obtained polymers are analyzed by matrix‐assisted laser desorption ionization‐time‐of‐flight mass spectrometry, which confirms that the Ar group is appended to the terminus of the polymer chain. Moreover, PFs prepared by Pd4–Pd6 ‐catalyzed SCTP bear precisely the Ar group on one chain end and 4‐tert‐butylphenyl end‐capping group on the opposite end, which indicates that Pd4–Pd6 with the bulky TXP‐2,4 exhibit better catalytic performance in SCTP. Photoluminescence spectra of the obtained polymers show a dual or a blue emission resulting from the difference of the molecular weight.

     

Synthesis and Polymerization of Fused‐Ring Thienodipyrrole Monomers

The synthesis and polymerization of fused‐ring 1,7‐didodecyl‐1,7‐dihydrothieno[3,2‐b:4,5‐b′]dipyrrole monomer are reported. The FeCl₃‐mediated oxidative polymerization and Stille coupling polymerization of the thienodipyrrole monomer were employed to generate homopolymers and an alternating copolymer with thiophene. The synthesized polymers have molecular weights ranging from 1600 to 6500 g mol^?1 and display the absorption maxima at ≈355 nm.     

Homogeneous metallocene/MAO‐catalyzed polymerizations of polar norbornene derivatives: copolymerizations using ethene,and terpolymerizations using ethene and norbornene

Terpolymerizations of norbornene derivatives containing different functional substituents were carried out with ethene and norbornene using the homogeneous catalyst system iPr[CpInd]ZrCl₂/MAO. The norbornene derivatives 5‐norbornene‐2‐methanol and 5‐norbornene‐2‐carboxylic acid were prereacted with triisobutylaluminium to prevent the deactivation of the catalyst. ¹³C NMR studies revealed the composition of the polymer. The incorporation rate was 5–12 mol‐% at a content of 50 mol‐% of the norbornene derivative in the monomer feedstock. IR‐GPC coupled experiments confirmed the homogeneous composition of the polymer. In addition, we investigated the ethene copolymerization and the ethene/norbornene terpolymerization using the trialkylsilyl protected norbornene derivates such as 5‐norbornene‐2‐methyleneoxytriethylsilane and 5‐norbornene‐2‐methyleneoxy‐tert‐butyldimethylsilane. These norbornene derivatives reveal an incorporation rate of 5–6 mol‐% in the polymer at a content of 20 mol‐% in the monomer feedstock.     

Thermally Stable and Well‐Defined Pentadiene‐Derived Copolymers Prepared by Anionic Alternating Copolymerization and Subsequent Controlled Postmodification

Thermally stable and well‐defined hydrocarbon polymers prepared via anionic alternating copolymerization of 1,3‐pentadiene (P monomer: trans (TP) and cis (CP) mixture) and styrene derivatives (S monomer: styrene (St) and 1,1‐diphenylethylene (DPE)) and subsequent hydrogenation and cationic cyclization modifications are reported. The TP/S/CP terpolymerization reveals that an incorporation of S‐alt‐CP sequence into the alternating chain is more favorable, while the S‐alt‐TP insertion is also possible especially under high temperature owing to their competitive energy barriers and thermodynamic properties. Then the resultant copolymers with equimolar amount of the two monomers and predominant linear units are intramolecularly cyclized with CF₃SO₃H, or hydrogenated with p‐toluenesulfonyl hydrazide, to afford soluble and thermally stable hydrocarbon polymers with controlled Mns and narrow ?_Ms. The T_g of cylized polymer increases dramatically (ΔT_g > 100 °C) on cyclization between the adjacent C?C bond in the P structure and the aromatic ring of S unit through the intramolecular Friedel–Crafts alkylation. On the other hand, the T_g of hydrogenated product slightly decreases (ΔT_g ≈ 10 °C) after 98% hydrogenation due to the increasing flexibility of the saturated main‐chain, while the Td increases about 60 °C due to the loss of C?C bonds under oxygen atmosphere.     

Ethylene and propylene polymerizations with the MgCl2‐supported tris(acetylacetonato)chromium‐diethylaluminium chloride catalyst system

Highly isotactic poly(propylene) with T_m = 169.5°C and [mmmm] > 99% in high selectivity (I.I. > 99.9%) was prepared with the catalyst system Cr(acac)₃/MgCl₂‐DEAC. ¹³C NMR analysis of low molecular weight isotactic polypropylene indicates that the propylene monomer was inserted in the polymer‐metal bond via 1,2‐addition selectively. Polymerization activities and isospecificity of the catalyst markedly increase with decreasing Cr content in the catalyst. In ethylene homopolymerization, the Cr(acac)₃/MgCl₂ catalyst showed almost constant activity for 3 h and produced high molecular weight polyethylene with narrow molar mass distribution.