Preparation of block copolymers by ring-opening polymerization of cycloalkenes initiated by a tungstencyclopentylidene complex

The possibility of making block copolymers at room temperature from the monomer pairs 2a,b/1, 4/1, 5/1 and 5/3 (1 = norbornene = bicyclo[2.2.1]hept-2-ene; 2a,b = anti- and syn-7-methylbicyclo[2.2.1]hept-2-ene; 4 = methyl endo-bicyclo[2.2.1]hept-5-ene-2-carboxylate; 5 = endo-bicyclo[2.2.1]hept-5-ene-2-carbonitrile; 3 = 1,5-cyclooctadiene) was explored using as initiator of metathesis polymerization in CD₂Cl₂. The reactions of successive small amounts of the monomers with the catalyst were first followed by ¹H NMR to determine the rate of the reaction and the stability of the metal-carbene propagating species. AB and ABA type block copolymers were prepared on this basis and analysed by GPC. An increase in molecular weight after each addition was observed in most cases. Secondary metathesis reactions of double bonds in the polymer chains appear to be significant only for blocks formed from 3 .     

Controlled carbocationic polymerizations of bicyclo[2,2,1]hepta-2,5-diene with AlCl3 in the presence of electron pair donor components

The cationic isomerization polymerization of bicyclo[2.2.1]hepta-2,5-diene (norbornadiene) was investigated. The synthesis of gel-free poly(3,5-tricyclo[2.2.1.0^2,6]heptylene) was achieved at a reaction temperature of 0°C. These polymerizations were initiated by AlCl₃ in the presence of the weakly donating additives nitrobenzene or nitromethane. NMR spectra show that the polymer contains a small fraction (between 2 and 4 mol-%) of branched structures in addition to a small amount of 5,7-linked bicyclic olefin units (approximately 2%). A reaction mechanism involving non-classical carbocation intermediates is proposed in order to account for the 5,7-enchainment of the bicycloheptenylene units, which contrasts with earlier studies on cationic norbornadiene polymerizations. Further, pentamethylbenzene was utilized as a chain transfer reagent in order to adjust the number average molecular weight M _n to values below 2500.     

Synthesis of amphiphilic star-shaped and graft copolymers based on polystyrene and poly(ethylene oxide)

Amphiphilic block macromonomers possessing a central unsaturation were synthesized by condensation of polystyrene half-ester of maleic acid {α-[2-(3-carboxyacryloyloxy)ethyl]-ω-sec-butylpoly[1-phenylethylene]} with poly(ethylene glycol) monoether or polystyrene-block-poly(ethylene oxide). In the radical monomer cis-trans-isomerization homopolymerization of the diblock macromonomers, four-to eight-armed amphiphilic star-shaped copolymers were obtained. Radical copolymerization of the diblock macromonomers with styrene led to graft copolymers with low degree of grafting. The triblock macromonomers proved to be unable to polymerize.     

Vinylic polymerization of bicyclo[2.2.1]hept-2-ene by Co(II)-catalysis

The vinylic polymerization of bicyclo[2.2.1]hept-2-ene (norbornene) with Co(II) compounds, such as Co(II) stearate, substituted bis(1,3-diketo)cobalt(II), Co(dppe)Cl₂, and the metallocene [η⁵-(C₅Me₅)Co-η²-Cl]₂, in chlorobenzene activated with methylaluminoxane (MAO) is reported. MAO^* synthesized by the hydrolysis of trimethylaluminium in chlorobenzene instead of toluene increases the catalytical activity strongly, and a turn over of 2.7 tons of poly(2,3-bicyclo[2.2.1]hept-2-ene) per mol cobalt per hour was achieved. The polymers obtained are amorphous (WAXS). They show weight-average molecular weights up to M̄_w = 1.5 · 10⁶ and are soluble in chlorobenzene, 1,2-dichlorobenzene, cyclohexane, and decahydronaphthalene.     

Anionic living polymerization of β-propiolactone initiated with crowned potassium methacrylate: Macromonomers and their copolymers with butyl acrylate

The polymerization of β-propiolactone (βPL) with crowned K⁺ counterion has been shown previously to be a living process. This behaviour was used to prepare macromonomers of poly(βPL) with the methacryloyl reactive group. Poly(βPL) is known to be a crystalline polymer; thus, copolymers of poly(βPL) macromonomers with butyl acrylate gave graft copolymers with properties stemming from this ability. Selected mechanical properties of the copolymers are close to those of acrylic rubbers reinforced with fillers.     

Versatile,Highly Controlled Synthesis of Hybrid (Meth)acrylate–Polyester–Carbonates and their Exploitation in Tandem Post‐Polymerization–Functionalization

The use of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) as a mild catalyst for the ring‐opening polymerization (ROP) of the pharma‐friendly and biodegradable monomer lactide and a functionalizable tert‐butyloxycarbonyl (BOC)‐protected cyclic carbonate is explored. Successful and controlled ROP is demonstrated when employing a series of labile‐ester (bis)(meth)acrylate initiators to produce macromonomers suitable for a range of post‐polymerization modifications. Importantly, the use of DBU ensured retention of the BOC group of the carbonate monomer during the polymerization, thus facilitating the production of highly functionalizable hybrid materials unobtainable using the more reactive triazabicyclodecene (TBD). Subsequently, a variety of short homo‐ and copolymers are synthesized with good control over material properties and final polymer composition. Successful attainment of these short copolymers confirm that DBU can overcome the previously observed limitations of TBD related to its kinetic competition between ROP and transesterification side‐reactions under these reaction conditions. Furthermore, the fidelity of the hydroxyl and (meth)acrylic end groups are maintained as confirmed by a series of secondary tandem reactions. The macromonomers are also utilized in reversible addition?fragmentation chain‐transfer polymerization (RAFT) polymerization for the production of amphiphilic block or random copolymers with a hydrophilic comonomer, poly(ethyleneglycol)methacrylate. The amphiphilic copolymers produced via the tandem RAFT reaction demonstrate the ability to self‐assemble into monodisperse nanoparticles in aqueous environments.     

Synthesis and copolymerization of macromonomers based on 2-nonyl- and 2-phenyl-2-oxazoline

Several macromonomers were prepared by cationic ring-opening polymerization of 2-nonyl- and 2-phenyl-2-oxazoline using different techniques of functionalization. Introduction of the unsaturated functional group directly via a suitable termination agent proved to be superior to the use of a phenol-functionalized initiator and to the introduction of hydroxyl end groups via hydrolysis of the reactive cationic chain end and subsequent esterification with methacryloyl chloride. The macromonomers were characterized by spectroscopic techniques as well as GPC. One of the 4-vinylbenzyl-terminated macromonomers was copolymerized with MMA in different ratios. The copolymerization parameter r₁ was determined to be 0.75. The resulting graft copolymers were characterized regarding number of grafts per chain, molar mass, and glass transition temperature.     

The Synthesis of Liquid Crystalline Copolymers with Block Copolymer Grafts

The synthesis of novel copolymers consisting of a side‐group liquid crystalline backbone and poly(tetrahydrofuran)‐poly(methyl methacrylate) block copolymer grafts was realized by using cationic‐to‐free‐radical transformation reactions. Firstly, photoactive poly(tetrahydrofuran) macroinimers were prepared by cationic polymerization of tetrahydrofuran and subsequent termination with 2‐picoline N‐oxide. Secondly, the macroinimers and acrylate monomers containing different spaced cyanobiphenyl mesogenic groups were copolymerized to yield the respective graft copolymers. Eventually, these were used for indirect photochemical polymerization of methyl methacrylate by UV irradiation in the presence of anthracene as a photosensitizer leading to the final copolymers with block copolymer grafts. The liquid crystalline, semicrystalline, and amorphous blocks were micro‐phase separated in the graft copolymers.     

Thermotropic liquid-crystalline aromatic polyester-graft-poly(2,6-dimethyl-1,4-phenylene oxide) copolymers

Dicarboxy-terminated poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) macromonomers were prepared and subjected to the preparation of tailor-made aromatic thermotropic liquid-crystalline (LC) polyester-graft-PPO copolymers. The macromonomers were obtained by hydrolysis of dimethyl carboxylate-terminated PPO macromonomers without cleavage of the PPO chains, which were derived from PPO oligomers with a terminal phenolic OH-group and a bromo derivative of isophthalate. The tailor-made aromatic thermotropic LC graft copolymers were prepared by direct polycondensation from the dicarboxy-terminated macromonomers, p-hydroxybenzoic acid, aromatic dicarboxylic acids and diphenols at definite mole ratios in pyridine in the presence of diphenyl chlorophosphate as a condensation reagent. The polyester-graft-PPO copolymers are thermally stable up to 280–300°C and show a thermotropic LC nematic phase in spite of introduction of PPO grafts on the polyester backbones.     

Proton‐Conducting Poly(phenylene oxide)–Poly(vinyl benzyl phosphonic acid) Block Copolymers via Atom Transfer Radical Polymerization

Block copolymers containing poly(phenylene oxide) (PPO) and poly(vinyl benzyl phosphonic acid) segments are synthesized via atom transfer radical polymerization (ATRP). Monofunctional PPO blocks are converted into ATRP active macroinitiators, which are then used to polymerize a diethyl p‐vinylbenzyl phosphonate monomer in order to obtain phosphonated block copolymers bearing pendent phosphonic ester groups. Poly(phenylene oxide‐b‐vinyl benzyl phosphonic ester) block copolymers are hydrolyzed to corresponding acid derivatives to investigate their proton conductivity. The effect of the relative humidity (RH) is investigated. The proton conductivity at 50% RH and one bar of vapor pressure approaches 0.01 S cm^?1.     

The 13C NMR spectra of poly(1-pentenylene) and poly(1,3-cyclopentylenevinylene)

¹³C NMR spectra were obtained for polymers made by ring-opening polymerization of cyclopentene and bicyclo[2.2.1]hept-2-ene respectively. The fraction of cis double bonds could be determined with much greater precision from ¹³C NMR spectra than from IR spectra and varied from 0,66 to 0,31 for the samples of poly(1-pentenylene), ( 2 ), and from 1,0 to 0,14 for the samples of poly(1,3-cyclopentylenevinylene), ( 4 ). This is the first time an all-cis polymer of 4 has been reported. The spectra of 2 showed a cis (upfield) and trans (downfield) peak for each of ?CH and α-CH₂, but only one peak for β-CH₂. The spectra of 4 showed multiple fine structure, the main splittings corresponding to a cis (upfield) and trans (downfield) peak for α-CH, and a reverse line order for the other three carbons; subsidiary splittings were observed for all but the olefinic carbons, interpreted in terms of sensitivity of the chemical shifts to the cis/trans structure at the next nearest double bond. A complete interpretation of the line orders in 4 is given in terms of steric compression effects. The possibility that ring tacticity accounts for some of the fine structure cannot be entirely discounted. The stereochemistry of 4 is discussed in relation to the four possible modes of addition of monomer to a carbene chain carrier during polymerization.     

Copolymerization of 5-norbornen-2-yl acetate with cycloalkenes by the metathesis catalyst WCl6/(CH3)4Sn

Ring-opening metathesis copolymerization of 5-norbornen-2-yl

1 System. name: bicyclo[2.2.1]hept-5-en-2-yl.

acetate (NBEAc; 80% endo) with cyclooctene (COE) and norbornene

2 System. name: bicyclo[2.2.1]hept-2-ene.

(NBE) was studied using WCl₆/(CH₃)₄Sn as catalytic system. The copolymerization parameters (r₁ = r₂ = 1 for the NBEAc/NBE system and r₁ = 1/r₂ = 132 for the NBEAc/COE system) show that the reactivity of the monomers is not affected by the presence of an ester substituent but that it depends on the structure of the hydrocarbon cycle. Thus the well known inhibition effect of the ester group may be concluded not to lie in the propagation step of the catalytic cycle.     

Polymethacrylate graft copolymers with a liquid-crystalline component

This paper reports on the synthesis and characterization of graft copolymers built up by amorphous poly(methyl methacrylate) grafts and a side-chain liquid-crystalline backbone. The interest was focussed on the copolymerization behaviour of the liquid-crystalline monomers and styryl-terminated methyl methacrylate macromonomers. The radical polymerization of the liquid-crystalline monomers depends on the liquid-crystalline monomer concentration and on the amount and length of the grafts (macromonomers). The liquid-crystalline backbone is the longer the higher the concentration of the mesogenic monomers itself and the smaller the molecular weight of the macromonomers. Variation of the amounts of grafts yielded a maximum length of the liquid-crystalline backbone at approximately 4 mol-% (for a molecular weight of 7800 of the graft).     

Anionic synthesis of well‐defined,poly[(styrene)‐block‐(propylene oxide)] block copolymers

Well‐defined, narrow molecular weight distribution (M_w/M_n ≤ 1.1) poly[(styrene)‐block‐(propylene oxide)] block copolymers with relatively high molecular weight poly(propylene oxide) blocks [e. g. M_n (PPO) = 10 000–12 000 g/mol] have been prepared by anionic polymerization. The polystyrene block (M_n = 5 000; M_w/M_n = 1.1) was prepared by alkyllithium‐initiated polymerization of styrene followed by chain‐end functionalization with ethylene oxide and protonation with acidic methanol. The resulting ω‐hydroxyl‐functionalized polystyrene was converted to the corresponding alkali metal salts with alkali metals (Na/K alloy, Rb, Cs) and then used to initiate block polymerization of propylene oxide in tetrahydrofuran. The effects of crown ethers (18‐crown‐6 and dicyclohexano‐24‐crown‐8) and added dimethylsulfoxide were investigated. Chain transfer to the monomer resulted in significant amounts of poly(propylene oxide) formation (50%); however, the diblock molecular weight distributions were narrow. The highest molecular weight poly(propylene oxide) blocks (12 200 g/mol) were obtained in tetrahydrofuran with cesium as counterion without additives.     

Synthesis of Multifunctionalized Graft‐Type Polyolefin‐Based Elastomers with a High Utility Temperature

A novel polyolefin‐based elastomer of polyolefin‐graft‐poly(t‐butylstyrene) is synthesized from styrene moieties via graft‐from anionic living polymerization. The afforded elastomer comprises a soft poly(ethylene‐t‐1‐hexene‐t‐divinylbenzene) segment and a hard poly(t‐butylstyrene) [P(t‐BS)] segment. The polymerization proceeds via complete lithiation of the pendent styrene groups (polyolefin elastomer) and subsequent graft anionic polymerization of 4‐tert‐butylstyrene (2000–10 000 g mol⁻¹). The graft‐from living anionic polymerization controls the grafting size with excellent efficiency by increasing the monomer concentration. To introduce functional groups into the polymer chain‐end, vinyl isoprene units are introduced into the polyolefin‐graft‐poly(t‐butylstyrene) anion to form polyolefin‐graft‐[poly(t‐butylstyrene)‐block‐polyisoprene] via living block copolymerization. Subsequent graft chain‐end multicarboxyl functionalization via thiol‐ene “click” reactions introduces carboxyl groups into the [P(t‐BS)] graft chain‐end. The water contact angle of this multicarboxyl functionalized product exhibits a sharper decrement, which affects its hydrophilicity significantly. This process produces a novel, well‐defined functionalized graft‐type polyolefin‐based elastomer with a high utility temperature and excellent mechanical properties.     

Macromonomers of acrylates by group transfer polymerization

Bifunctional initiators for group transfer polymerization (GTP) were prepared, substituted by a vinyl, 2-propyl, isoprenyl (2-methylene-3-butenyl) or 4-vinylphenyl group at the ketene acetal C?C double bond. All initiators initiated GTP of methyl methacrylate in tetrahydrofuran with tris(piperdino)sulfonium bifluoride or tetrabutylammonium cyanide as catalysts to yield macromonomers with low polydispersities. It is recommended to perform GTP as the first step, since the silyl groups of the initiators give side reactions with active species of other polymerization systems. Macromonomers from isoprenyl - or 4-vinylphenyl-substituted initiators could be radically copolymerized with styrene to yield graft copolymers. The copolymerization of acrylic macromonomers derived from the other two initiators has yet to be established.     

Functionalized initiators for group transfer and metal-free anionic polymerization for the synthesis of macromonomers: overview and new results

Vinylphenyloxy- and allyloxy-substituted silyl ketene acetals are presented as new functionalized initiators for group transfer polymerization (GTP). All initiators initiated GTP of butyl acrylate in tetrahydrofuran with tetrabutylammonium cyanide as catalyst to yield butyl acrylate macromonomers with number-average molecular weights somewhat lower than those calculated for an ideal living polymerization and with polydispersities of about 1,8–2,6. For the metal-free anionic polymerization, functionalized initiators were obtained introducing allyloxy and vinylbenzyl groups into tetrabutylammonium diethyl malonate. Both compounds initiated a very rapid polymerization of butyl acrylate in tetrahydrofuran with high monomer conversion. The number-average molecular weights of the macromonomers, produced in a semi-batch procedure, reached nearly theoretical values, the polydispersities were about 1,2. In all macromonomers the functionality with respect to terminal vinyl and allyl groups was near one, so that they can be used with other monomers to form graft copolymers, e. g., in a free-radical polymerization.     

Living coordination polymerization of end‐allenyloxy poly(ethylene glycol) macromonomer by a π‐allylnickel catalyst

The living coordination polymerization of end‐allenyloxy poly(ethylene oxide)s ( 2A – 2C ) was carried out by [(η³‐allyl)NiOCOCF₃]₂ ( 1 ) in the presence of PPh₃ to produce narrowly dispersed polyallenes bearing poly(ethylene oxide) side chains. For instance, the polymerization of 2B (M_n = 590, [ 2 ]/[ 1 ] = 100) proceeded smoothly to give a polymer (M_n = 39 800, M_w/M_n = 1.13) in high yield. The molecular weight of poly( 2 ) could be controlled by the ratio of 2 to 1 and by the molecular weight of 2 . The block copolymers of 2B with various alkoxyallenes ( 3A – 3C ) or with 1‐phenylethyl isonitrile ( 3D ) were also obtained by the two‐stage copolymerization process (i. e., the polymerization of 2 , followed by that of 3A – 3D ). The resulting block copolymers were found to serve as polymeric surfactants in the polymer blend systems of PSt and PMMA.     

Blockcopolymere aus 2-Isopropenylnaphthalin und Hexamethylcyclotrisiloxan, 7

Anionic polymerization of 2-isopropenylnaphthalene (2-IPN), with butyllithium in THF at ?78°C was terminated with ethylene oxide and the resulting terminal alkoxide was used to initiate the polymerization of hexamethylcyclotrisiloxane (D₃) at +40°C. This led to the formation of AB-block copolymers which were coupled to ABBA-block copolymers by addition of dichlorodimethylsilane. ABBA-blockcopolymers were obtained with contents of polymethylsiloxane (poly(DMS)) between 77 and 84% of weight and block molecular weights between 1 700 and 27 000 (poly(2-IPN)) and 13 000 and 240 000 (poly(DMS)). Phase separation in polymer films casted from different solvents was studied by electron microscopy and by DSC measurements. The block copolymers behave as elastomers in the temperature range from ?40 to +190°C. Above 290°C depolymerization of poly(2-IPN) starts.     

Reactions of macro-ions resulting in the formation of block and graft copolymers. Grafting of polymers with aromatic groups

Grafting of poly(oxytetramethylene) (polytetrahydrofuran) chains containing living oxonium end groups onto polymers containing aromatic rings was investigated. The rate of grafting was found to be slow, but under favourable conditions several moles of polytetrahydrofuran can be grafted to one mole of polystryrene. Macrocations may also be grafted to the surface of in-soluble polymers dispersed in a solution of grafting ions. This was proved by grafting living polytetrahydrofuran onto poly(phenylene oxide) or random poly(1-butene-co-styrene). Macro-cations can be prepared from an anionic living polymer via transformation of the growing centers. Thus, poly(dimethylsiloxane), whose original anionic centers were transformated into cationic ones, was grafted to polystyrene. Exchange reactions were found to take place in the living system on polytetrahydrofuran or poly(dimethylsiloxane) grafts, thus influencing their length. The graft copolymers are strong surfactants. Separation from their mixture with homo-polymers by a repeated extraction of homopolymers with a solvent is difficult and sometimes impossible.