The ligand effect in Ti‐mediated living radical styrene polymerizations initiated by epoxide radical ring opening. 2. Scorpionate and half‐sandwich LTiCl3 complexes

The ligand effect and the reaction conditions for the living radical polymerization of styrene initiated by epoxide radical ring opening was investigated in a series of piano‐stool, Ti(IV) scorpionate and, half‐sandwich metallocenes (LTiCl₃; L = Tp, Cp*, Ind and Cp, where Tp = hydrotris(pyrazol‐1‐ylborato), Cp* = pentamethylcyclopentadienyl, Ind = indenyl and Cp = cyclopentadienyl). The polymerization is mediated by the reversible termination of the growing chains with Ti(III) species derived from Zn reduction of parent Ti(IV) derivatives. A poor performance was observed for TpTiCl₃ because of probable over‐reduction. The strong electron donating effect of Cp* accounts for a strong C? Ti chain end bond and consequently, a living‐like process is observed only at T > 110 °C. However, both Ind and Cp ligands provide a linear dependence of M_n on conversion and narrow polydispersity over a wide range of experimental conditions. Investigation of the effect of temperature and reagent ratios generates an optimum for epoxide/CpTiCl₃/Zn = 1/2/4 at 70–90 °C. On the basis of a combination of steric and electronic properties, the ligands rank as Cp ≥ Ind ? Cp* ? Tp. This trend is different from coordination polymerization, and in conjunction with our previous results on Cp₂TiCl₂, further supports a radical mechanism. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6039–6047, 2005     

In situ‐generated Ru(III)‐mediated ATRP from the polymeric Ru(III) complex in the absence of activator generation agents

Past research has examined the atom transfer radical polymerization (ATRP) with high oxidation state metal complexes and without the need for any additives such as reducing agent or free radical initiator. To extend this research, half‐metallocene ruthenium(III) (Ru(III)) catalysts were used for the polymerization of methyl methacrylate (MMA) for the first time. These catalysts were generated in situ simply by mixing phosphorus‐containing ligand and pentamethylcyclopentadienyl (Cp*) Ru(III) polymer ((Cp*RuCl₂)_n). The complexes in their higher oxidation state such as Cp*RuCl₂(PPh₃) were air‐stable, highly active, and removable catalysts for the ATRPs of MMA with both precision control of molecular weight and narrow polydispersity index. The addition of ppm amount of metal catalyst contributed to the formation of very well‐defined homopolymers and copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Polymerization of vinyl chloride with half‐titanocene/methylaluminoxane catalysts

The polymerization of vinyl chloride (VC) with half‐titanocene /methylaluminoxane (MAO) catalysts is investigated. The polymerization of VC with the Cp*Ti(OCH₃)₃/MAO catalyst (Cp* = η⁵‐pentamethylcyclopentadienyl) afforded high‐molecular‐weight poly(vinyl chloride) (PVC) in good yields, although the polymerization proceeded at a slow rate. With the Cp*TiCl₃/MAO catalyst, the polymer was also obtained, but the polymer yield was lower than that with the Cp*Ti(OCH₃)₃/MAO catalyst. The polymerization of VC with the Cp*Ti(OCH₃)₃/MAO catalyst was influenced by the MAO/Ti mole ratio and reaction temperature, and the optimum was observed at the MAO/Ti mole ratio of about 10. The optimum reaction temperature of VC with the Cp*Ti(OCH₃)₃/MAO catalyst was around 20 °C. The stereoregularity of PVC obtained with the Cp*Ti(OCH₃)₃/MAO catalyst was different from that obtained with azobisisobutyronitrile, but highly stereoregular PVC could not be synthesized. From the elemental analyses, the ¹H and ¹³C NMR spectra of the polymers, and the analysis of the reduction product from PVC to polyethylene, the polymer obtained with Cp*Ti(OCH₃)₃/MAO catalyst consisted of only regular head‐to‐tail units without any anomalous structure, whereas the Cp*TiCl₃/MAO catalyst gave the PVC‐bearing anomalous units. The polymerization of VC with the Cp*Ti(OCH₃)₃/MAO catalyst did not inhibit even in the presence of radical inhibitors such as 2,2,6,6,‐tetrametylpiperidine‐1‐oxyl, indicating that the polymerization of VC did not proceed via a radical mechanism. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 248–256, 2003     

Control of molecular weight in polymerization of vinyl chloride with Cp*Ti(OPh)3/MAO catalyst

Polymerization of vinyl chloride (VC) with titanium complexes containing Ti‐OPh bond in combination with methylaluminoxane (MAO) catalysts was investigated. Among the titanium complexes examined, Cp*Ti(OPh)₃/MAO catalyst (Cp*; pentamethylcyclopentadienyl, Ph; C₆H₅) gave the highest activity for the polymerization of VC, but the polymerization rate was slow. From the kinetic study on the polymerization of VC with Cp*Ti(OPh)₃/MAO catalyst, the relationship between the M_n of the polymer and the polymer yields gave a straight line, and the line passed through the origin. The M_w/M_n values of the polymer gradually decrease as a function of polymer yields, but the M_w/M_n values were somewhat broad. This may be explained by a slow initiation in the polymerization of VC with Cp*Ti(OPh)₃/MAO catalyst. The results obtained in this study demonstrate that the molecular weight control of the polymers is possible in the polymerization of VC with the Cp*Ti(OPh)₃/MAO catalyst. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3872–3876, 2007     

Weak Ligand‐Field Effect from Ancillary Ligands on Enhancing Single‐Ion Magnet Performance

A series of bis‐pentamethylcyclopentadienyl‐supported Dy complexes containing different ancillary ligands were synthesized and characterized. Magnetic studies showed that 1 Dy [Cp*₂DyCl(THF)], 1 Dy’ [Cp*₂DyCl₂K(THF)]_n, 2 Dy [Cp*₂DyBr(THF)], 3 Dy [Cp*₂DyI(THF)] and 4 Dy [Cp*₂DyTp] (Tp=hydrotris(1‐pyrazolyl)borate) were single‐ion magnets (SIMs). The 1D dysprosium chain 1 Dy’ exhibited a hysteresis at up to 5 K. Furthermore, 3 Dy featured the highest energy barrier (419 cm^?1) among the complexes. The effects of ancillary ligands on single‐ion magnetic properties were studied by experimental, ab initio calculations and electrostatic analysis methods in detail. These results demonstrated that the QTM rate was strongly dependent on the ancillary ligands and that a weak equatorial ligand field could be beneficial for constructing Dy‐SIMs.     

Syndiospecific living polymerization of 4‐methylstyrene and styrene with (trimethyl)pentamethylcyclopentadienyltitanium/tris(pentafluorophenyl)borane/trioctylaluminum catalytic system

The polymerizations of styrene and 4‐methylstyrene (4MS) with a half‐metallocene type catalytic system composed of (trimethyl)pentamethylcyclopentadienyltitanium (Cp*TiMe₃), trioctylaluminum (AlOct₃), and tris(pentafluorophenyl)borane [B(C₆F₅)₃] were investigated at ?25 °C. The addition of AlOct₃ as a third component of the catalytic system is effective both to promote the syndiospecific polymerization and to inhibit the nonstereospecific polymerization at the low‐temperature region. The use of AlOct₃ was also effective to eliminate the chain transfer reaction to alkylaluminum. The number‐average molecular weights (M_n's) of poly(4MS) or polystyrene increased proportionally with increasing monomer conversion. The molecular weight distribution (MWD) of polymer stayed narrow [M_w/M_n = ～ 1.1 for poly(4MS) and M_w/M_n = ～ 1.5 for polystyrene]. It was thus concluded that the polymerizations of the styrenic monomers with Cp*TiMe₃/B(C₆F₅)₃/AlOct₃ catalytic system proceeded under living fashion at ?25 °C. The living random copolymerization behaviors of styrene and 4MS were also confirmed. The ¹³C NMR analysis clarified that each of the homopolymers and random copolymers obtained in this work had highly syndiotactic structure. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3692–3706, 2001     

High molecular weight atactic polypropene synthesized with (η5‐pentamethylcyclopentadienyl)tribenzyl titanium activated with MAO

The half‐titanocene (η⁵‐pentamethylcyclopentadienyl)tribenzyl titanium (Cp*TiBz₃) with methylaluminoxane (MAO) as the cocatalyst was employed to catalyze propene polymerization at ambient pressure. A novel atactic polypropene elastomer with a high molecular weight (M̄_w = 2 − 8 × 10⁵) was produced. The effects of the polymerization conditions on the catalytic activity and polymer molecular weight are discussed. ¹³C NMR analysis confirmed that the catalyst system Cp*TiBz₃/MAO produced atactic polypropenes, and the polymerization mechanism was in agreement with the Bernoullian process. The triad sequence distribution of the polymer was measured and found to be as follows: mm = 6.15%, mr = 40.87%, and rr = 52.98% (Bernoullian factor B = 1.03); this indicated that the insertion of propene with the catalyst system followed a chain‐end control model. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 411–415, 2000     

Unprecedented polymerization of epsilon-Caprolactone initiated by a single-site lanthanide borohydride complex, [Sm(eta-C5Me5)2(BH4)(thf)]: mechanistic insights

The monoborohydride lanthanide complex [Sm(Cp*)2(BH4)(thf)] (1a) (Cp* = eta-C5Me5), has been successfully used for the controlled ring-opening polymerization of epsilon-caprolactone (epsilon-CL). The organometallic samarium(III) initiator 1 a produces, in quantitative yields, alpha,omega-dihydroxytelechelic poly(epsilon-caprolactone) displaying relatively narrow polydispersity indices (<1.3) within a short period of time (30 min). The polymers have been characterized by 1H and 13C NMR, SEC, and MALDI-TOF MS analyses. Use of the single-site initiator 1 a allows a better understanding of the polymerization mechanism, in particular with the identification of the intermediate compound [Sm(Cp*)2(BH4)(epsilon-CL)] (1b). Indeed, one molecule of epsilon-CL initially displaces the coordinated THF in 1 a to give 1 b. Then, epsilon-CL opening (through cleavage of the cyclic ester oxygen-acyl bond) and insertion into the Sm--HBH3 bond followed by reduction of the carbonyl function by the BH3 end-group ligand, leads to the samarium alkoxyborane derivative [Sm(Cp*)2[O(CH2)6O(BH2)]] (2). This compound subsequently initiates the polymerization of epsilon-CL through a coordination-insertion mechanism. Finally, upon hydrolysis, alpha,omega-dihydroxypoly(epsilon-caprolactone), HO(CH2)5C(O)[O(CH2)5C(O)]nO(CH2)6OH (4) is recovered. The stereoelectronic contribution of the two Cp* ligands appears to slow down the polymerization and to limit transesterification reactions.     

The syndiospecific polymerization of styrene in the presence of fluorine‐containing half‐sandwich metallocenes

The syndiospecific polymerization of styrene was investigated with the fluorine‐containing half‐sandwich complexes η⁵‐pentamethylcyclopentadienyl titanium bis(trifluoroacetate) dimer, η⁵‐octahydrofluorenyl titanium tristrifluoro‐acetate, η⁵‐octahydrofluorenyl titanium dimethoxymonotrifluoroacetate, and η⁵‐octahydrofluorenyl titanium tris(pentafluorobenzoate) in comparison to known chloride and methoxide complexes in the presence of relatively low amounts of methylalumoxane and triisobutylaluminum. After the selection of effective reaction conditions for a solvent‐free polymerization, the following orders of decreasing polymerization activity of the titanium complexes can be observed: for pentamethylcyclopentadienyl compounds, Cp*Ti(OMe)₃ > [Cp*Ti(OCOCF₃)₂]₂O ≈ Cp*TiCl₃, and for octahydrofluorenyl compounds, [656]Ti(OMe)₃ > [656]Ti(OCOC₆F₅)₃ > [656]Ti(OCH₃)₂(OCOCF₃) > [656]Ti (OCOCF₃)₃. The [656]Ti complexes, showing the highest polymerization conversions at 70 °C and in comparison with the Cp* Ti compounds, turned out to be highly efficient catalysts for the syndiospecific styrene polymerization. The fluorine‐containing Cp* and [656]Ti complexes lead to much higher molecular weights than the chloride and methoxide compounds because of a reduction in chain‐limiting transfer reactions. The introduction of only one fluorine‐containing ligand into the coordination sphere of the metal compound is obviously sufficient for a significant increase in molecular weight. The active polymerization sites of the [656]Ti complexes with methylalumoxane and triisobutylaluminum are extremely stable during storage at room temperature in regard to their polymerization activity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2428–2439, 2000     

Borohydrido rare earth based coordinative chain transfer copolymerization: A convenient tool for tuning the microstructure of isoprene/styrene copolymers

A series of lanthanum and neodymium borohydrido complexes comprising the trisborohydrides Nd(BH₄)₃(THF)₃ ( 1a ) and La(BH₄)₃(THF)₃ ( 1b ) and the half‐lanthanidocenes Cp*Nd(BH₄)₂(THF)₂ ( 2a ) (Cp* = C₅Me₅) and Cp*La(BH₄)₂(THF)₂ ( 2b ) has been assessed for the chain transfer copolymerization of isoprene and styrene. A transmetalation process is occurring efficiently with the borohydride complexes in the presence of magnesium dialkyl. The transmetalation is accompanied by (i) a gradual decrease of the 1,4‐trans stereoselectivity of the reaction at the benefit of 3,4‐selectivity and (ii) an increase in the quantity of styrene inserted in the copolymer. This can be at least partially attributed to a magnesium induced co‐oligomerization of isoprene and styrene. By combining dialkylmagnesium and trialkylaluminum, a 1,4‐trans stereospecific reversible coordinative chain transfer copolymerization of isoprene and styrene is observed when the half‐lanthanocene 2b is used as precatalyst. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthese und Eigenschaften Pentamethylcyclopentadienyl-substituierter PPC- bzw. AsPC-Dreiring-Systeme

Synthesis and Properties of Pentamethylcyclopentadienylsubstituted PPC and AsPC three-membered Rings Via the reaction of bis-(pentamethylcyclopentadienyl)diphosphene [Cp*P?PCp*, 1 ] and 1-(pentamethylcyclopentadienyl)-2-(2,4,6-tri^tbutylphenyl)- diphosphene [Cp*P?PMes*, 2 ] with the diazomethanes N₂CHR [R = H, Si(CH₃)₃] the four new diphosphiranes Cp*PPCp*CHSi(CH₃)₃, 4a , Cp*PPMes*CHSi(CH₃)₃, 4b , Cp*PPCp*CH₂, 5a , Cp*PPMes*CH₂, 5b , are obtained. The formation of 4a results via a 2 + 3-cyclo-addition product, which could be proved by nmr spectroscopy. The reaction of As-(pentamenthylcyclopentadienyl)-P-(2,4,6-tri^tbutylphenyl) arsaphosphene [Cp*As?PMes*, 3 ] with diazomethane leads to 1-(pentamethylcyclopentadienyl)-2-(2,4,6-tri^tbutylphenyl)-1-arsa-2 -phosphacyclopropane [phospharsiran, Cp*AsPMes*CH₂, 6 ]. Analysis of the structures by nmr spectroscopy gives clear evidence for a trans-orientation of the substituents at the El? P bond (El = As, P) in all of the three membered ring systems. For the diphosphirane Cp*PPCp*CH₂ ( 5a ) a Cp*-phosphorus bond cleavage by thermolysis cannot be observed. From the reaction of compound 5a with Cr(CO)₅thf one obtains 1-(pentacarbonylchrom)-1,2-bis(pentamethylcyclopentadienyl)-1,2- diphosphacyclo-propane, 7 .     

Syndiospecific polymerization of styrene with Cp*TiCl((OCH(R)CH2)2NAr)/MMAO

A series of titanium complexes Cp*TiCl((OCH(R)CH₂)₂NAr) (Cp* = C₅Me₅, R = H, Ar = Phenyl ( 2a) ; R = H, Ar = 2,6‐dimethylphenyl ( 2b ); R = Me, Ar = Phenyl ( 2c )) was prepared by the reaction of corresponding N,N‐diethoxylaniline derivatives, with Cp*TiCl₃ in the presence of excessive triethylamine. All the titanium complexes display higher catalytic activities towards the syndiospecific polymerization of styrene in the presence of modified methylaluminoxane (MMAO) as a cocatalyst, and produce higher molecular weight polystyrenes with higher syndiotacticity and melting temperature than their mother complex Cp*TiCl₃. The catalyst activities and polymer yields as well as polymer properties are considerably affected by the steric and electronic effect of the tridentate ligands. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1562–1568, 2005     

Rare earths/main group metal alkyls catalytic systems for the 1,4‐trans stereoselective coordinative chain transfer polymerization of isoprene

A series of lanthanum and neodymium complexes comprising the half‐lanthanidocenes Cp*La(BH₄)₂(THF)₂ (Cp* = C₅Me₅) ( 1 ) and Cp*Nd(BH₄)₂(THF)₂ ( 2 ), the trisborohydrides La(BH₄)₃(THF)₃ ( 3 ) and Nd(BH₄)₃(THF)₃ ( 4 ), the trichlorides LaCl₃(THF)₃ ( 5 ) and NdCl₃(THF)₃ ( 6 ), the triisopropoxides La(OⁱPr)₃ ( 7 ) and Nd(OⁱPr)₃ ( 8 ), and the triaryloxide Nd(OC₆H₃‐^tBu₂‐2,6)₃ ( 9 ) has been assessed for the chain transfer polymerization of isoprene. A transmetalation process is occurring efficiently with the borohydride complexes in the presence of magnesium dialkyl. A gradual decrease of the 1,4‐trans stereoselectivity of the reaction is observed at the benefit of 3,4‐selectivity with increasing quantities of magnesium dialkyl. This can be at least partially attributed to the growth of 3,4 polyisoprene units onto the magnesium atom. By combining dialkylmagnesium and trialkylaluminum, a 1,4‐trans stereospecific reversible coordinative chain transfer polymerization of isoprene is reached using the half‐lanthanocene Cp*La(BH₄)₂(THF)₂. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

The influence of phenylsilane on the syndiotactic polymerization of styrene with η5‐pentamethylcyclopentadienyl titanium trifluoride

The syndiotactic polystyrene polymerization activity of a fluorinated half‐sandwich complex, η⁵‐pentamethylcyclopentadienyl titanium trifluoride (Cp*TiF₃), in the presence of relatively low amounts of methylalumoxane (MAO; MAO/Cp*TiF₃ molar ratio = 200/1) and triisobutylaluminum, is significantly increased by the addition of phenylsilane in molar ratios to Cp*TiF₃ ranging from about 300/1 to 600/1, if the phenylsilane is added to the monomer. Lower amounts of phenylsilane, such as a 100/1 molar ratio to Cp*TiF₃, lead to a reduced polymerization activity in comparison with styrene without phenylsilane. A prereaction of phenylsilane with the catalyst mixture shows a behavior that is strongly dependent on the storage time of the composition and the temperature. A storage time of about 16 h is sufficient to reduce the polymerization conversion to about half of the original value. The results are discussed on the basis of a chain‐transfer reaction with phenylsilane and several catalyst complexes of different stabilities and activities, including an alkylation product of phenylsilane. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3476–3485, 2000     

Cp*Me5P6C5: Ein neues Carbaphosphan mit einem Strukturelement aus dem Hittorfschen Phosphor

Cp*Me₅P₆C₅: A New Carbaphosphane with a Structure Unit of Hittorf-Phosphorus The thermolysis of 1,2,3-tris(pentamethylcyclopentadienyl)cyclotriphosphane [(Cp*P)₃, 1 ] or 2,3,4,6-Tetrakis(pentamethylcyclopentadienyl)bicyclo[3.1.0]hexaphosphane [Cp*₄P₆, 2 ] leads in addition to the known 3,4-bis(pentamethylcyclopentadienyl)tricyclo[3.1.0.0^{2, 6}]hexaphosphane [Cp*₂P₆, 3 ] to the pentacyclic carbaphosphanes 3,4,5,6,11-pentamethyl-endo-9-pentamethylcyclopentadienyl- 3,4,5,6,11-pentacarba-pentacyclo [6.1.1^1,8.1^3,6.0^2,70^10,11]-4-en-undecaphosphane and 3,4,5,6,11-pentamethyl-exo-9-pentamethylcyclopentadienyl-3,4,5,6,11-pentacarba-pentacyclo [6.1.1^1,8.1^3,6.0^2,70^10,11]-4-en-undecaphosphane [Cp*Me₅P₆C₅, 4a, 4b ]. Furthermore, other polyphosphanes are formed, like 1,2,3,4-tetrakis(pentamethylcyclopentadienyl)cyclotetraphosphane [(Cp*P)₄, 5 ] and 2,4-bis(pentamethylcyclopentadienyl)-tetraphosphabicyclo[1.1.0]butane [(Cp*P)₂P₂, 6 ]. The structure of 4a and 4b is determined by NMR-spectroscopy. The molecule contains a P₅C₃-cunean-unit, to which a C₂Me₂-brigde and a PCp*-brigde is bonded.     

β‐Diketiminate‐supported magnesium alkyl: synthesis,structure and application as co‐catalyst for polymerizations mediated by a lanthanum half‐sandwich complex

Mg(n‐Bu){η²‐HC[C(Me)NMes]₂} ( 2 ) (Mes = mesityl, 2,4,6‐Me₃C₆H₂), a new β‐diketiminate‐supported magnesium alkyl, has been synthesized and structurally characterized. The X‐ray analysis of the lanthanum half‐sandwich complex Cp*La(BH₄)₂(THF)₂ ( 1 ) (Cp* = pentamethylcyclopentadienyl; THF = tetrahydrofuran) is also reported. Complex 2 has been assessed as both alkylating agent and chain transfer agent for the lanthanum‐catalysed polymerization and coordinative chain transfer polymerization of isoprene and styrene using 1 as the pre‐catalyst. The results are compared with those for n‐butylethylmagnesium (BEM) which is traditionally used for this purpose. The 1,4‐trans stereospecific polymerization of isoprene shows a more controlled character using 2 versus BEM, and higher activities are observed for the chain transfer polymerization of styrene when 2 is used as chain transfer agent. The activity is in turn lower than that observed using BEM when 1 equiv. of magnesium compound is used for the polymerization of styrene. The combination of 1 , 2 and Al(i‐Bu)₃ leads finally to a 1,4‐trans stereoselective coordinative chain transfer polymerization of isoprene, in a similar way to BEM. Copyright © 2015 John Wiley & Sons, Ltd.     

Chain end analysis of bisphenol A polysulfone and its relation to molecular weight

The preparation of amine-terminated polysulfone by step polymerization of the monomers bisphenol A and dichlorodiphenyl sulfone in the presence of end-capping reagent 4-aminophenol was investigated. A persistent problem with end-capping strategy as applied to step polymerization is the presence of end groups other than those introduced by the end-capping reagent. These unintended end groups, which can persist in the polymer product even when 100% of the end-capping reagent has reacted, are associated with a proportionate decrease in polymer chain length. This situation renders quantitative analysis of a single type of end group invalid as a method for molecular weight determination. The presence of unintended end groups does not appear to correlate with a particular set of reaction conditions; unintended end groups were found to occur in polymerizations conducted under strong base conditions (NaOH), under weak base conditions (K₂CO₃), and with a wide range of monomer feed ratios. A scheme for unambiguous quantification of chain ends and molecular weight for end-capped polysulfone is described. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1309–1316, 1998     

Polymerization of MMA catalyzed by different novel mixed ligand lanthanocene{(Cp)(Cl) LnSchiff-base (THF)},(COT) -Ln(methoxyethylindenyl)(THF) /Al (i -Bu)_3 systems

This article deals that the rare earth metal complexes along with Al(i'-Bu),can catalyze the polymerization of methyl-methacrylate (MMA) into high molecular weight poly(MMA) along with narrow molecular weight distributions (MWD).A typical example was mentioned in the case of {Cp(Cl) Sm-Schiff-base(THF)} which expresses maximum (conv.% = 55.46 and Mn=354×103) efficiency along with narrow MWD (Mw/Mn<2) at 60℃.The resulting polymer was partially syndiotactic (>60%).The effect of the catalyst,temperature,catalyst/MMA molar ratio,catalyst/Al( i-Bu)3 molar ratio on the polymerization of MMA at 60℃ were also investigated.     

Sterically Less‐Hindered Half‐Titanocene(IV) Phenoxides: Ancillary‐Ligand Effect on Mono‐, Bis‐, and Tris(2‐Alkyl‐/arylphenoxy) Titanium(IV) Chloride Complexes

A series of mono‐, bis‐, and tris(phenoxy)–titanium(IV) chlorides of the type [Cp*Ti(2‐R? PhO)_nCl_3?n] (n=1–3; Cp*=pentamethylcyclopentadienyl) was prepared, in which R=Me, iPr, tBu, and Ph. The formation of each mono‐, bis‐, and tris(2‐alkyl‐/arylphenoxy) series was authenticated by structural studies on representative examples of the phenyl series including [Cp*Ti(2‐Ph? PhO)Cl₂] ( 1 PhCl2 ), [Cp*Ti(2‐Ph? PhO)₂Cl] ( 2 PhCl ), and [Cp*Ti(2‐Ph? PhO)₃] ( 3 Ph ). The metal‐coordination geometry of each compound is best described as pseudotetrahedral with the Cp* ring and the 2‐Ph? PhO and chloride ligands occupying three leg positions in a piano‐stool geometry. The mean Ti? O distances, observed with an increasing number of 2‐Ph? PhO groups, are 1.784(3), 1.802(4), and 1.799(3) Å for 1 PhCl2 , 2 PhCl , and 3 Ph , respectively. All four alkyl/aryl series with Me, iPr, tBu, and Ph substituents were tested for ethylene homopolymerization after activation with Ph₃C⁺[B(C₆F₅)₄]^? and modified methyaluminoxane (7% aluminum in isopar E; mMAO‐7) at 140 °C. The phenyl series showed much higher catalytic activity, which ranged from 43.2 and 65.4 kg (mmol of Ti?h)^?1, than the Me, iPr, and tBu series (19.2 and 36.6 kg (mmol of Ti?h)^?1). Among the phenyl series, the bis(phenoxide) complex of 2 PhCl showed the highest activity of 65.4 kg (mmol of Ti?h)^?1. Therefore, the catalyst precursors of the phenyl series were examined by treating them with a variety of alkylating reagents, such as trimethylaluminum (TMA), triisobutylaluminum (TIBA), and methylaluminoxane (MAO). In all cases, 2 PhCl produced the most catalytically active alkylated species, [Cp*Ti(2‐Ph? PhO)MeCl]. This enhancement was further supported by DFT calculations based on the simplified model with TMA.     

Synthesis of poly(vinyl ether) polyols with pendant oxyethylene chains and properties of hydrophilic,thermo‐responsive polyurethanes prepared therefrom

Hydroxy‐terminated telechelic poly(vinyl ether)s with pendant oxyethylene chains were synthesized by the reaction of the CH₃CH(OCOCH₃)? O[CH₂]₄O? CH(OCOCH₃)CH₃/Et_1.5AlCl_1.5/THF‐based bifunctional living cationic polymers of 2‐methoxyethyl vinyl ether (MOVE), 2‐ethoxyethyl vinyl ether (EOVE), and 2‐(2‐methoxyethoxy)ethyl vinyl ether (MOEOVE) with water and the subsequent reduction of the aldehyde polymer terminals with NaBH₄. The obtained poly(vinyl ether) polyols were reacted with an equimolar amount of toluene diisocyanates [a mixture of 2,4‐ (80%) and 2,6‐ (20%) isomers] to give water‐soluble polyurethanes. The aqueous solutions of these polyurethanes caused thermally induced precipitation at a particular temperature depending on the sort of the thermosensitive poly(vinyl ether) segments containing oxyethylene side chains. These polyurethanes also function as polymeric surfactants, lowered the surface tension of their aqueous solutions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1641–1648, 2010