Synthesis of polyethylene and polypropylene containing fluorene units in the side chain

Copolymerizations of ethylene or propylene and allyl monomers containing 9‐fluorenyl group, diallyl‐di‐9‐fluorenylsilane (DAFS), 9,9‐diallylfluorene (DAF), and 9‐allylfluorene (AF), were investigated with various zirconocene catalysts using methylaluminoxane as a cocatalyst. The bridged zirconocene catalysts, especially a syndioselective catalyst, showed a higher reactivity for all the comonomers than the nonbridged catalysts. DAFS was mainly incorporated into the polymer chain via cyclization insertion, whereas DAF was copolymerized via both 1,2‐ and cyclization insertions. Cyclization selectivity, ratio of cyclized insertion unit, of DAF in the copolymerization with propylene was higher than that in the copolymerization with ethylene. Copolymerization with AF yielded low‐molecular weight copolymer because of frequent chain transfer reaction. Optical properties of the propylene based‐copolymers were investigated by UV‐vis and photoluminescence spectroscopy, and absorption‐ and emission‐derived from fluorenyl groups were detected in the copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3542–3552, 2010     

Hydrogen effects in propylene polymerization reactions with titanium‐based Ziegler–Natta catalysts. I. Chemical mechanism of catalyst activation

The hydrogen activation effect in propylene polymerization reactions with Ti‐based Ziegler–Natta catalysts is usually explained by hydrogenolysis of dormant active centers formed after secondary insertion of a propylene molecule into the growing polymer chain. This article proposes a different mechanism for the hydrogen activation effect due to hydrogenolysis of the Ti? iso‐C₃H₇ group. This group can be formed in two reactions: (1) after secondary propylene insertion into the Ti? H bond (which is generated after β‐hydrogen elimination in the growing polymer chain or after chain transfer with hydrogen), and (2) in the chain transfer with propylene if a propylene molecule is coordinated to the Ti atom in the secondary orientation. The Ti? CH(CH₃)₂ species is relatively stable, possibly because of the β‐agostic interaction between the H atom of one of its CH₃ groups and the Ti atom. The validity of this mechanism was demonstrated in a gas chromatography study of oligomers formed in ethylene/α‐olefin copolymerization reactions with δ‐TiCl₃/AlEt₃ and TiCl₄/dibutyl phthalate/MgCl₂–AlEt₃ catalysts. A quantitative analysis of gas chromatography data for ethylene/propylene co‐oligomers showed that the probability of secondary propylene insertion into the Ti? H bond was only 3–4 times lower than the probability of primary insertion. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1353–1365, 2002     

Copolymerization of ethylene with cyclopentene or 2‐butene with half titanocenes‐based catalysts

Half titanocenes (CpCH₂CH₂O)TiCl₂ (1), (CpCH₂CH₂OCH₃)TiCl₃ (2), and CpTiCl₃ (3), activated by methylaluminoxane (MAO) were tested in copolymerization of ethylene with internal olefins such as cyclopentene. All the catalysts were able to give incorporation of cyclopentene in polyethylene matrix. ¹³C NMR analysis of obtained copolymers showed that the catalytic systems have low regiospecificity. In fact, in ethylene–cyclopentene copolymers, cyclic olefin inserts with both 1,2 and 1,3‐enchainment. X‐ray powder diffraction analysis of these copolymers confirmed that 1,2 inserted cyclopentene units are excluded from crystalline phase, whereas 1,3‐cyclopentene units are included, giving rise to expansion of unit cell of crystalline polyethylene. Titanium‐based catalysts were investigated also in the copolymerization of ethylene with E and Z‐2‐butene. Only complex (1) was able to give copolymers and ¹³C NMR analysis of products showed 2‐3, 1‐3, and 1‐2 insertion of 2‐butene. Differential scanning calorimetry analysis displayed that ethylene–cyclopentene, as well as ethylene‐2‐butene, copolymers are crystalline and their melting point decreases by increasing the comonomer content. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4725–4733, 2008     

Isomeric effect of the Et(H4Ind)2Zr(CH3)2 catalyst on the copolymerization of ethylene and styrene: A computational study

A density functional theory (B3LYP) computational study of the ethylene–styrene copolymerization process using meso‐Et(H₄Ind)₂Zr(CH₃)₂ as the catalyst is presented. The monomer insertion barriers in meso species are evaluated and compared with previously obtained barriers in rac diastereoisomers. Differences related to ethylene homopolymerization and ethylene–styrene copolymerization activities as well as styrene incorporation into the copolymer are found between the meso and rac diastereoisomers. Nevertheless, a migratory insertion mechanism seems to hold for both diastereoisomeric species. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4752–4761, 2006     

Alternating copolymerization of propylene oxide with carbon monoxide catalyzed by Co complex and Co/Ru complexes

Co₂(CO)₈ catalyzes the ring‐opening copolymerization of propylene oxide with CO to afford the polyester in the presence of various amine cocatalysts. The ¹H and ¹³C{¹H} NMR spectra of the polyester, obtained by the Co₂(CO)₈–3‐hydroxypyridine catalyst, show the following structure ? [CH₂? CH(CH₃)? O? CO]_n? . The Co₂(CO)₈–phenol catalyst gives the polyester, which contains the partial structural unit formed through the ring‐opening copolymerization of tetrahydrofuran with CO. The bidentate amines, such as bipyridine and N,N,N′,N′‐tetramethylethylenediamine, enhance the Co complex‐catalyzed copolymerization, which produces the polyester with a regulated structure. Acylcobalt complexes, (RCO)Co(CO)_n (R = Me or CH₂Ph), prepared in situ, do not catalyze the copolymerization even in the presence of pyridine. This suggests that the chain growth involves the intermolecular nucleophilic addition of the OH group of the intermediate complex to the acyl–cobalt bond, forming an ester bond rather than the insertion of propylene oxide into the acyl–cobalt bond. Co₂(CO)₈? Ru₃(CO)₁₂ mixtures also bring about the copolymerization of propylene oxide with CO. The molar ratio of Ru to Co affects the yield, molecular weight, and structure of the produced copolymer. The catalysis is ascribed to the Ru? Co mixed‐metal cluster formed in the reaction mixture. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4530–4537, 2002     

Cyclocopolymerization of 1,4‐pentadiene with ethene in the presence of group‐4 metallocenes

The behaviors of rac‐[CH₂(3‐tert‐butyl‐1‐indenyl)₂]ZrCl₂ ( 1 ) and Cp₂ZrCl₂ ( 2 ) activated by methylaluminoxane in ethene/1,4‐pentadiene copolymerization are compared. In the presence of 1 , inserted methylene‐1,3‐cyclobutane units, a large number of crosslinks, and a small number of methylene‐1,3‐cyclohexane units are obtained. Differently, a polyethene containing only 1,3‐cyclohexane rings is achieved with 2 as the catalytic precursor. Polymer microstructures are compared with those obtained with 1 and 2 in ethene/1,6‐heptadiene copolymerization, which leads only to polyethene containing cyclohexane rings. A tentative rationalization of the experimental data is reported. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5525–5532, 2006     

Asymmetric,regio‐ and stereo‐selective alternating copolymerization of CO2 and propylene oxide catalyzed by chiral chromium Salan complexes

Chiral chromium complexes of tetradentate N,N′‐disubstituted bis(aminophenoxide) (designated as Salan, a saturated version of Schiff‐base Salen ligand) in conjunction with an ionic quaternary ammonium salt can efficiently catalyze the copolymerization of CO₂ with racemic propylene oxide (rac‐PO) at mild conditions to selectively afford completely alternating poly(propylene carbonate) (PPC) with ～ 95% head‐to‐tail linkages and moderate enantioselectivity. These new catalyst systems predominantly exceed the previously much‐studied SalenCr(III) systems in catalytic activity, polymer enantioselectivity, and stereochemistry control. The chiral diamine backbone, sterically hindered substitute groups on the aromatic rings, and the presence of sp³‐hydridized amino donors and its N,N′‐disubstituted groups in chiral SalanCr(III) complexes all play significant roles in controlling polymer stereochemistry and enantioselectivity. Furthermore, a relationship between polycarbonate enantioselectivity and its head‐to‐tail linkages in relation to regioselective ring‐opening of the epoxide was also discussed on the basis of stereochemical studies of PPCs derived from the copolymerization of CO₂ with chiral PO at various conditions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6102–6113, 2008     

Alternating copolymerization of propylene oxide and carbon dioxide with highly efficient and selective (salen)Co(III) catalysts: Effect of ligand and cocatalyst variation

Synthetic routes to a series of new (salen)CoX (salen = N,N′-bis(salicylidene)-1,2-diaminoalkane; X = Br or pentafluorobenzoate (OBzF₅)) species are described. Several of these complexes are active for the copolymerization of propylene oxide (PO) and CO₂, yielding regioregular poly(propylene carbonate) (PPC) without the generation of propylene carbonate byproduct. Variation of the salen ligand, as well as the inclusion of organic-based ionic or Lewis basic cocatalysts, has dramatic effects on the resultant (salen) CoX catalytic activity. Highly active (R,R)-(salen- 1 )CoOBzF₅ (salen- 1 = N,N′-bis(3,5- di-tert-butylsalicylidene)-1,2-diaminocyclohexane) catalysts with [Ph₄P]Cl or [PPN]Y ([PPN] = bis(triphenylphosphine)iminium; Y = Cl or OBzF₅) cocatalysts exhibited turnover frequencies up to 720 h⁻¹ for rac-PO/CO₂ copolymerization, yielding PPC with greater than 90% head-to-tail connectivity. Additionally, the (R,R)-(salen- 1 )CoOBzF₅/[PPN]Cl catalyst system demonstrated a k_rel of 9.7 for the enchainment of (S)- over (R)-PO when the copolymerization was carried out at low temperatures. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5182–5191, 2006     

Copolymerization of propylene with 1,3‐butadiene using isospecific zirconocene catalysts

Poly(propylene‐ran‐1,3‐butadiene) was synthesized using isospecific zirconocene catalysts and converted to telechelic isotactic polypropylene by metathesis degradation with ethylene. The copolymers obtained with isospecific C₂‐symmetric zirconocene catalysts activated with modified methylaluminoxane (MMAO) had 1,4‐inserted butadiene units ( 1,4‐BD ) and 1,2‐inserted units ( 1,2‐BD ) in the isotactic polypropylene chain. The selectivity of butadiene towards 1,4‐BD incorporation was high up to 95% using rac‐dimethylsilylbis(1‐indenyl)zirconium dichloride (Cat‐A)/MMAO. The molar ratio of propylene to butadiene in the feed regulated the number‐average molecular weight (M_n) and the butadiene contents of the polymer produced. Metathesis degradations of the copolymer with ethylene were conducted with a WCI₆/SnMe₄/propyl acetate catalyst system. The ¹H NMR spectra before and after the degradation indicated that the polymers degraded by ethylene had vinyl groups at both chain ends in high selectivity. The analysis of the chain scission products clarified the chain end structures of the poly(propylene‐ran‐1,3‐butadiene). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5731–5740, 2007     

Ethene homopolymerization and copolymerization with 1‐hexene for all methyl‐substituted (RnC5H5−n)2ZrCL2/MAO catalytic systems: Effects of split methyl substitution

Ethene homopolymerization and copolymerization with 1‐hexene were catalyzed by methyl‐substituted cyclopentadienyl (Cp) zirconium dichlorides, (R_n C₅H_5−n)₂ZrCl₂ (R_n = H, Me, 1,2‐Me₂, 1,3‐Me₂, 1,2,3‐Me₃, 1,2,4‐Me₃, Me₄, or Me₅), and methylaluminoxane. The polymers were characterized with Fourier transform infrared, nuclear magnetic resonance, gel permeation chromatography, and differential scanning calorimetry techniques. Generally, an increasing number of methyl substituents on the Cp ligand results in lower 1‐hexene incorporation in the copolymer. The two catalysts with split methyl substitution (R_n = 1,3‐Me₂ and R_n = 1,2,4‐Me₃) show a higher comonomer response than their disubstituted and trisubstituted counterparts (R_n = 1,2‐Me₂ and R_n = 1,2,3‐Me₃). They even incorporate more 1‐hexene than R_n = H and R_n = Me. These findings are qualitatively in agreement with the results of a theoretical study based on density functional calculations. The presence of comonomer does not influence the termination reactions after the insertion of ethene. There is more frequent termination after each hexene insertion with increasing comonomer incorporation except for the two catalysts with split methyl substituents. The termination probability per inserted comonomer is highest for the less substituted catalysts. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3161–3172, 2000     

Propylene polymerization by C1‐symmetric {ONNO′}‐type salan zirconium complexes

The activities of C₁‐symmetric dibenzyl zirconium complexes of Salan ligands that bear a halo‐substituted phenolate ring and an alkyl‐substituted phenolate ring in propylene polymerization with methylaluminoxane as cocatalyst were studied. These {ONNO′}ZrBn₂‐type catalysts exhibited moderate‐to‐high activities and yielded polypropylene of low molecular weight. The degree of tacticity was found to depend on the steric bulk of the substituents on both phenolate rings and ranged from practically atactic to substantially isotactic (74–78% [mmmm] for polymerizations at room temperature by Lig⁵ZrBn₂). Hemi‐isotactic polypropylene was not obtained, despite the diastereotopicity of the two positions. The pattern of stereo errors was consistent with the enantiomorphic site control of propylene insertion typically observed for C₂‐symmetric catalysts and implied a facile site‐averaging mechanism. A regular 1,2‐insertion and a β‐H transfer to an incoming monomer correspond to the main propagation and termination processes, respectively. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Multicenter nature of titanium‐based Ziegler–Natta catalysts: Comparison of ethylene and propylene polymerization reactions

This article discusses the similarities and differences between active centers in propylene and ethylene polymerization reactions over the same Ti‐based catalysts. These correlations were examined by comparing the polymerization kinetics of both monomers over two different Ti‐based catalyst systems, δ‐TiCl₃‐AlEt₃ and TiCl₄/DBP/MgCl₂‐AlEt₃/PhSi(OEt)₃, by comparing the molecular weight distributions of respective polymers, in consecutive ethylene/propylene and propylene/ethylene homopolymerization reactions, and by examining the IR spectra of “impact‐resistant” polypropylene (a mixture of isotactic polypropylene and an ethylene/propylene copolymer). The results of these experiments indicated that Ti‐based catalysts contain two families of active centers. The centers of the first family, which are relatively unstable kinetically, are capable of polymerizing and copolymerizing all olefins. This family includes from four to six populations of centers that differ in their stereospecificity, average molecular weights of polymer molecules they produce, and in the values of reactivity ratios in olefin copolymerization reactions. The centers of the second family (two populations of centers) efficiently polymerize only ethylene. They do not homopolymerize α‐olefins and, if used in ethylene/α‐olefin copolymerization reactions, incorporate α‐olefin molecules very poorly. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1745–1758, 2003     

Synthesis and photophysical properties of polyethylene containing pyrenyl units in the side chain

Copolymerization of ethylene and diallyl‐bis(pyren‐1‐yl)‐silane (APyS) was investigated with zirconocene catalysts, rac‐ethylenebis(indenyl)zirconium dichloride ( 1 ) and diphenylmethylene(cyclopentadienyl)(9‐fluorenyl)zirconium dichloride ( 2 ), using methylaluminoxane as a cocatalyst. APyS was copolymerized via both 1,2‐insertion and cyclization insertion, and cyclization selectivity, ratio of cyclized insertion unit, of APyS in the copolymers obtained with Catalyst 1 was higher than that obtained with Catalyst 2 . Catalyst 2 showed a higher reactivity for APyS than Catalyst 1 . Photophysical properties of the copolymer were investigated by UV–vis and photoluminescence (PL) spectroscopy, and absorption and fluorescence derived from pyrenyl groups were detected in the copolymers. Chloroform solution of the copolymer showed emission derived from both monomer and eximer of pyrenyl units. Only the emission derived from eximer of pyrenyl units was observed in the cast film. The polarized PL spectrum of an oriented film showed anisotropy, and the polarization excitation parallel to the drawing direction showed high fluorescence intensity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Nonconjugated diene homopolymerization and copolymerization with ethylene catalyzed by α‐diimine Ni(II) complex/Et2AlCl

Four nonconjugated diene comonomers 1,9‐decadiene (19DD), 6‐ethylundeca‐1,10‐diene (EUD), 1,5‐cyclooctadiene (COD) and cinene (1‐methyl‐4‐(prop‐1‐en‐2‐yl) cyclohex‐1‐ene) (CE) were used in copolymerization with ethylene catalyzed by α‐diimine Ni(II) complex ([2,6‐(iPr)₂C₆H₃N = C(CH₃)?(CH₃)C = N2,6‐(iPr)₂C₆H₃)]NiBr₂ ( 1 )) activated by Et₂AlCl. These dienes showed quite distinct copolymerization behaviors. Ethylene‐19DD copolymerization formed highly branched polyethylene with cyclic units and pendent vinyls, and a large part of crosslinked polymer when the 19DD concentration was relatively high. Using EUD as comonomer lead to evidently reduced gel formation and increased content of pendent vinyl. COD can be incorporated in the copolymer with evidently lower catalyst efficiency than the ethylene homopolymerization, and CE behaves like an inert compound as it was not incorporated in the copolymer. Homopolymerization of 19DD with the same catalyst produced polymer containing both cyclic units and pendent vinyls. The cyclic units were formed by cyclopolymerization of the inserted 19DD after several steps of chain walking. Crosslinking through the pendent vinyl took place when the initial 19DD concentration was relatively high, forming large amount of gel in the product. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1900–1909     

Catalytic synthesis of styryl‐capped isotactic polypropylenes

Bis‐styrenic molecules, 1,4‐divinylbenzene (DVB) and 1,2‐bis(4‐vinylphenyl)ethane (BVPE), were successfully combined with hydrogen (H₂) to form consecutive chain transfer complexes in propylene polymerization mediated by an isospecific metallocene catalyst (i.e., rac‐dimethylsilylbis(2‐methyl‐4‐phenylindenyl)zirconium dichloride, I ) activated with methylaluminoxane (MAO), rendering a catalytic access to styryl‐capped isotactic polypropylenes (i‐PP). The chain transfer reaction took place in a unique way where prior to the ultimate chain transfer DVB/H₂ or BVPE/H₂ caused a copolymerization‐like reaction leading to the formation of main chain benzene rings. A preemptive polymer chain reinsertion was deduced after the consecutive actions of DVB/H₂ or BVPE/H₂, which gave the styryl‐terminated polymer chain alongside a metal‐hydride active species. It was confirmed that the chain reinsertion occurred in a regio‐irregular 1,2‐fashion, which contrasted with a normal 2,1‐insertion of styrene monomer and ensured subsequent continuous propylene insertions, directing the polymerization to repeated DVB or BVPE incorporations inside polymer chain. Only as a competitive reaction, the insertion of propylene into metal‐hydride site broke the chain propagation resumption process while completed the chain transfer process by releasing the styryl‐terminated polymer chain. BVPE was found with much higher chain transfer efficiency than DVB, which was attributed to its non‐conjugated structure with much divided styrene moieties resulting in higher polymerization reactivity but lower chain reinsertion tendency. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3709–3713, 2010     

DFT mechanistic study of the H2‐assisted chain transfer copolymerization of propylene and p‐methylstyrene catalyzed by zirconocene complex

DFT computations have been performed to investigate the mechanism of H₂‐assisted chain transfer strategy to functionalize polypropylene via Zr‐catalyzed copolymerization of propylene and p‐methylstyrene (pMS). The study unveils the following: (i) propylene prefers 1,2‐insertion over 2,1‐insertion both kinetically and thermodynamically, explaining the observed 1,2‐insertion regioselectivity for propylene insertion. (ii) The 2,1‐inserion of pMS is kinetically less favorable but thermodynamically more favorable than 1,2‐insertion. The observation of 2,1‐insertion pMS at the end of polymer chain is due to thermodynamic control and that the barrier difference between the two insertion modes become smaller as the chain length becomes longer. (iii) The pMS insertion results in much higher barriers for subsequent either propylene or pMS insertion, which causes deactivation of the catalytic system. (iv) Small H₂ can react with the deactivated [Zr]?pMS?PP_n facilely, which displace functionalized pMS?PP_n chain and regenerate [Zr]? H active catalyst to continue copolymerization. The effects of counterions are also discussed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 576–585     

Selective Insertion in Copolymerization of Ethylene and Styrene Catalyzed by Half‐Titanocene System Bearing Ketimide Ligand: A Theoretical Study

The copolymerization of ethylene and styrene can be efficiently carried out by using Cp*TiCl₂ (N = C^t Bu₂)/MAO (Cp*=η ⁵‐C₅Me₅ ) system, yielding the poly(ethylene‐co ‐styrene)s with isolated styrene units. In order to investigate the reasons for formation of the structure, the mechanism of copolymerization, especially the selective insertion of ethylene and styrene, is studied in detail by density functional theory (DFT ) method. At the initiation stage, insertion of ethylene is kinetically more favorable than insertion of styrene, and insertion of styrene kinetically and thermodynamically prefers 2,1‐insertion. That is different from the conventional half‐titanocene system, in which the 1,2‐insertion is favorable. At chain propagation stage, the computational results suggest that the continuous insertion of styrene is hard to occur at room temperature due to the high free energy barriers (28.90 and 35.04 kcal/mol for 1,2‐insertion, and 29.15 and 34.00 kcal/mol for 2,1‐insertion) and thermodynamically unfavorable factors in two different conditions. That is mainly attributed to the steric hindrance between the coming styrene and chain‐end styrene or ketimide ligand. The computational results are in good agreement with the experimental data.     

Kinetics and mechanism of metallocene‐catalyzed olefin polymerization: Comparison of ethylene,propylene homopolymerizations,and their copolymerization

A series of ethylene, propylene homopolymerizations, and ethylene/propylene copolymerization catalyzed with rac‐Et(Ind)₂ZrCl₂/modified methylaluminoxane (MMAO) were conducted under the same conditions for different duration ranging from 2.5 to 30 min, and quenched with 2‐thiophenecarbonyl chloride to label a 2‐thiophenecarbonyl on each propagation chain end. The change of active center ratio ([C^*]/[Zr]) with polymerization time in each polymerization system was determined. Changes of polymerization rate, molecular weight, isotacticity (for propylene homopolymerization) and copolymer composition with time were also studied. [C^*]/[Zr] strongly depended on type of monomer, with the propylene homopolymerization system presented much lower [C^*]/[Zr] (ca. 25%) than the ethylene homopolymerization and ethylene–propylene copolymerization systems. In the copolymerization system, [C^*]/[Zr] increased continuously in the reaction process until a maximum value of 98.7% was reached, which was much higher than the maximum [C^*]/[Zr] of ethylene homopolymerization (ca. 70%). The chain propagation rate constant (k_p) of propylene polymerization is very close to that of ethylene polymerization, but the propylene insertion rate constant is much smaller than the ethylene insertion rate constant in the copolymerization system, meaning that the active centers in the homopolymerization system are different from those in the copolymerization system. Ethylene insertion rate constant in the copolymerization system was much higher than that in the ethylene homopolymerization in the first 10 min of reaction. A mechanistic model was proposed to explain the observed activation of ethylene polymerization by propylene addition. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 867–875     

Heterograft copolymers of poly(ε‐caprolactone) prepared by combination of ATRA “grafting onto” and ATRP “grafting from” processes

This paper aims at reporting on the synthesis of a heterograft copolymer by combining the “grafting onto” process based on atom transfer radical addition (ATRA) and the “grafting from” process by atom transfer radical polymerization (ATRP). The statistical copolymerization of ε‐caprolactone (εCL) and α‐chloro‐ε‐caprolactone (αClεCL) was initiated by 2,2‐dibutyl‐2‐stanna‐1,3‐dioxepane (DSDOP), followed by ATRA of parts of the chlorinated units of poly(αClεCL‐co‐εCL) on the terminal double bond of α‐MeO,ω‐CH₂?CH? CH₂? CO₂‐poly(ethylene oxide) (PEO). The amphiphilic poly(εCL‐g‐EO) graft copolymer collected at this stage forms micelles as supported by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The unreacted pendant chloro groups of poly(εCL‐g‐EO) were used to initiate the ATRP of styrene with formation of copolymer with two populations of randomly distributed grafts, that is PEO and polystyrene. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6015–6024, 2006     

Insertion Homo‐ and Copolymerization of Diallyl Ether

The previously unresolved issue of polymerization of allyl monomers CH₂?CHCH₂X is overcome by a palladium‐catalyzed insertion polymerization of diallyl ether as a monomer. An enhanced 2,1‐insertion of diallyl ether as compared to mono‐allyl ether retards the formation of an unreactive five‐membered cyclic O‐chelate (after 1,2‐insertion) that otherwise hinders further polymerization, and also enhances incorporation in ethylene polymers (20.4 mol %). Cyclic ether repeat units are formed selectively (96 %–99 %) by an intramolecular insertion of the second allyl moiety of the monomer. These features even enable a homopolymerization to yield polymers (poly‐diallyl ether) with degrees of polymerization of DP_n≈44.