Polydispersity Values Research Articles

Polyoxazoline: Chemistry, Properties, and Applications in Drug Delivery

Polyoxazoline polymers with methyl (PMOZ), ethyl (PEOZ), and propyl (PPOZ) side chains were prepared by the living cationic polymerization method and purified by ion-exchange chromatography. The following properties of polyoxazoline (POZ) were measured: apparent hydrodynamic radius by aqueous size-exclusion chromatography, relative lipophilicity by reverse-phase chromatography, and viscosity by cone-plate viscometry. The PEOZ polymers of different molecular weights were first functionalized and then conjugated to model biomolecules such as bovine serum albumin, catalase, ribonuclease, uricase, and insulin. The conjugates of catalase, uricase, and ribonuclease were tested for in vitro activity using substrate-specific reaction methods. The conjugates of insulin were tested for glucose lowering activity by injection to naïve Sprague-Dawley rats. The conjugates of BSA were injected into New Zealand white rabbits and serum samples were collected periodically and tested for antibodies to BSA. The safety of POZ was also determined by acute and chronic dosing to rats. The results showed that linear polymers of POZ with molecular weights of 1 to 40 kDa can easily be made with polydispersity values below 1.10. Chromatography results showed that PMOZ and PEOZ have a hydrodynamic volume slightly lower than PEG; PEOZ is more lipophilic than PMOZ and PEG; and PEOZ is significantly less viscous than PEG especially at the higher molecular weights. When PEOZ was attached to the enzymes catalase, ribonuclease, and uricase, the in vitro activity of the resultant bioconjugates depended on the extent of protein modification. POZ conjugates of insulin lowered blood glucose levels for a period of 8 h when compared to 2 h for insulin alone. PEOZ, like PEG, was also able to successfully attenuate the immunogenic properties of BSA. The POZ polymers (10 and 20 kDa) are safe when administered intravenously to rats, and the maximum tolerated dose (MTD) was greater than 2 g/kg. Blood counts, serum chemistry, organ weights, and the histopathology of key organs were normal. These results conclude that POZ has the desired drug delivery properties for a new biopolymer.

Ambient temperature rapid ATRP of methyl acrylate, methyl methacrylate and styrene in polar solvents with mixed transition metal catalyst system

Ambient temperature atom transfer radical polymerization (ATRP) of methyl acrylate (MA), methyl methacrylate (MMA) and styrene (Sty) in the presence of polar solvents (dimethyl sulfoxide: DMSO, dimethylformamide: DMF and acetonitrile: MeCN) with a mixed transition metal catalyst system (Fe(0) as initial activator and CuBr 2/Me 6TREN complex as deactivator) provides a rapid synthesis of polymers with very low polydispersity (PDI) values and predetermined molecular weights. The polymethylacrylate (PMA) prepared using this novel approach contains the Br-terminated chain ends (functionality ∼100%) and can be successfully used for block copolymer synthesis (as demonstrated on the chain extension experiment performed using the PMA–Br macroinitiator). The key elementary reactions involved in this novel ATRP system and some preliminary mechanistic aspects of the process are also discussed.

Determining Nanoparticle Size in Real Time by Small-Angle X-ray Scattering in a Microscale Flow System

Precise in situ measurements are becoming more important as we seek to identify and harness the unique properties of novel nanomaterials, yet key challenges remain in determining structures with current analytical approaches. We report here an in situ multitechnique approach that permits the real-time measurement of the sizes of nanoparticles in flowing solutions. A series of ligand-stabilized Au nanoparticle standards (dCORE = 0.8−5 nm) was analyzed by simultaneous small-angle X-ray scattering (SAXS) and UV−vis spectroscopy in a microscale flow system. A specially designed observation cell provided access to both measurements at an identical location in the flow system and allowed for the correlation of SAXS and TEM analyses. Comparison of flow-based UV−vis data to those obtained ex situ provided a bridge between in situ SAXS and ex situ TEM measurements. Average core size from both techniques matched closely for each sample, while polydispersity values from SAXS measurements were smaller than those from TEM. By correlating in situ and ex situ measurements for well-defined nanoparticle standards, these experiments form the basis of a powerful approach to assess nanoparticle core size within flowing microscale systems.

Synthesis and characterization of soluble aromatic–aliphatic polyamide

AbstractA soluble polyamide was synthesized from aromatic and aliphatic monomers by condensing 4‐aminophenyl sulfone with sebacoyl chloride in dimethylacetamide (DMAc) at low temperature under inert atmosphere. A stoichiometric amount of triethylamine was added to precipitate the HCl produced during the polymerization reaction. The precipitates were isolated, yielding a clear neat polyamide solution. Thin and transparent film achieved from the polymer resin was characterized for FTIR, NMR, gel permeation chromatography (GPC), thermogravimetry, differential scanning calorimetry, water absorption, and mechanical measurements. The dried film was found to be soluble in DMAc, DMSO, and DMF. The film‐forming property of polyamide is being exploited for the preparation of the nanocomposites. Spectroscopic analyses confirmed the formation of polyamide. The values of Mn, Mw, and polydispersity as determined by GPC were found to be 9,779, 20,280 g/mol and 2.07 with RI detector whereas 10,133, 20,865 g/mol and 2.06 with UV detector, respectively. The thermally stable polyamide exhibited tensile strength (18.86 MPa), glass transition temperature (72.34°C), and water absorption (16.1%). These studies further verified the related physical properties of the polyamide. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:300–308, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20197

Synthesis of ω‐amino‐α‐phenylcarbonate alkanes and their polymerization to [n]‐polyurethanes

AbstractAliphatic [n]‐polyurethanes have recently been synthesized from ω‐isocyanato‐α‐alkanols or, more traditionally, by cationic ring‐opening polymerization of cyclourethanes or by the Bu2Sn(OMe)2‐promoted polycondensation of ω‐hydroxy‐α‐O‐phenylurethane alkanes. For the latter procedures, the conditions employed do not seem to be suitable for highly functionalized monomers. In contrast, the polymerization of ω‐amino‐α‐phenylcarbonate alkanes is expected to occur under milder conditions. ω‐Amino‐α‐phenylcarbonate alkanes have been synthesized from 6‐aminohexanol (1) and 3‐aminopropanol (6). The procedure involves the N‐Boc protection of the amino group, followed by activation of the alcohol. Removal of the N‐Boc affords the corresponding ω‐amino‐1‐O‐phenyloxycarbonyloxyalkane hydrochlorides. Other oligomeric comonomers between 1 and 6 have been prepared. The polymerization of these precursors takes place in the absence of metal catalysts to afford the corresponding linear and regioregular [n]‐polyurethanes. The procedure described is useful for the preparation of stable ω‐amino‐α‐phenylcarbonate alkane derivatives, which possess varied chain lengths between the terminal functions. These monomers yield [n]‐polyurethanes having various structures starting from just two aminoalkanols. The polyurethanes were obtained in high yields, with reasonable molecular weight and polydispersity values, and they were characterized spectroscopically and thermally. These studies reveal constitutionally uniform structures that are free of carbonate or urea linkages. Copyright © 2010 Society of Chemical Industry

Fucose-containing exopolysaccharide produced by the newly isolated Enterobacter strain A47 DSM 23139

Enterobacter strain A47 (DSM 23139) was found to produce a fucose-containing exopolysaccharide (EPS). The EPS is composed of fucose, galactose, glucose, pyruvate, succinate and acetate in the molar ratios 1.6:1.3:1.1:1.2:0.7:1.5. It is a high molecular weight (5.8 × 10 6) homogeneous biopolymer, as indicated by the low polydispersity value (1.3). The steady shear flow properties of the EPS aqueous solutions are similar to guar gum and fucogel, and its viscoelastic properties indicate the formation of viscous aqueous solutions with entangled polymer chains. Additionally, the EPS has demonstrated good flocculating and emulsion stabilizing capacities, comparable to some commercially available products. These functional properties make the fucose-containing EPS a good alternative to many synthetic polymers, as well as other natural polysaccharides, in several applications in the food, pharmaceutical, cosmetic, textile, paper and petroleum industries.

The kinetic evidence for the formation of multiple active species in a bis(phenoxy-imine) zirconium dichloride/MAO catalyst during ethylene polymerization

The effects of polymerization time and temperature on the molecular weight and molecular weight distribution of polyethylene, produced over homogeneous catalyst bis[N-(3-tert-butyl salicylidene)anilinato]zirconium(IV) dichloride tBu-L2ZrCl2/MAO have been studied. The data on the number of active centers (CP) and propagation rate constants (kP) at different polymerization time have been obtained as well. It was found that at a short polymerization time two types of active centers, producing low molecular weight PE (Mw = (4–10) × 103 g mol−1) are formed. The number of these centers was estimated to be 11% of total zirconium complex and their reactivity is very high (the kP value was found to be 54 × 103 L mol−1 s−1 at 35 °C). High initial activity of the catalyst fell with the increase in polymerization time, whereas the polydispersity values of the resulting PE increase due to formation of new centers, producing high molecular weight PE (Mw = (30–1300) × 103 g mol−1). It was found that the decrease in activity is caused by reducing the initial active centers number and lower reactivity of the new-formed centers (kP = 17 × 103 L mol−1 s−1).

Vibrational dynamics and boson peak in a supercooled polydisperse liquid

Vibrational density of states (VDOS) in a supercooled polydisperse liquid is computed by diagonalizing the Hessian matrix evaluated at the potential energy minima for systems with different values of polydispersity. An increase in polydispersity leads to an increase in the relative population of localized high-frequency modes. At low frequencies, the density of states shows an excess compared to the Debye squared-frequency law, which has been identified with the boson peak. The height of the boson peak increases with polydispersity and shows a rather narrow sensitivity to changes in temperature. While the modes comprising the boson peak appear to be largely delocalized, there is a sharp drop in the participation ratio of the modes that exist just below the boson peak indicative of the quasilocalized nature of the low-frequency vibrations. Study of the difference spectrum at two different polydispersity reveals that the increase in the height of boson peak is due to a population shift from modes with frequencies above the maximum in the VDOS to that below the maximum, indicating an increase in the fraction of the unstable modes in the system. The latter is further supported by the facilitation of the observed dynamics by polydispersity. Since the strength of the liquid increases with polydispersity, the present result provides an evidence that the intensity of boson peak correlates positively with the strength of the liquid, as observed earlier in many experimental systems.

충진제 개질을 통한 에폭시복합체의 성능개선

In this study, the performance improvement of epoxy resin system had been tried by the improvement of particle size distribution and globularization of filler using polymerization method. From the results of particle size distribution measurement, the polydispersity value of reformed filler was 1.04 and that of silica flour before reformation was 2.6, it could be confirmed that the particle size uniformity of reformed filler had been improved greatly and the shape of particle was globular. Compatibility between monomer and silica was improved remarkably with the silanization pretreatment of silica flour. From the results of degree of crosslinking test, it could be confirmed that the binding structure of reformed filler was 3-dimensional net structure. And it could be also confirmed that the fluidness was improved at the casting of epoxy resin with reformed filler. From the above results, it could be concluded that the reformation of filler with the improvement of particle size distribution and globularization was very successful method to improve the performance of cast epoxy resin system.

Optimization of 5-fluorouracil solid-lipid nanoparticles: a preliminary study to treat colon cancer

Solid lipid nanoparticle (SLNs) formulae were utilized for the release of 5-flurouracil (5-FU) inside the colonic medium for local treatment of colon cancer. SLNs were prepared by double emulsion-solvent evaporation technique (w/o/w) using triglyceride esters, Dynasan™ 114 or Dynasan™ 118 along with soyalecithin as the lipid parts. Different formulation parameters; including type of Dynasan, soyalicithin:Dynasan ratio, drug:total lipid ratio, and polyvinyl alcohol (PVA) concentration were studied with respect to particle size and drug entrapment efficiency. Results showed that formula 8 (F8) with composition of 20% 5-FU, 27% Dynasan™ 114, and 53% soyalithicin andformula 14 (20% 5-FU, 27% Dynasan™ 118, and 53% soyalithicin), which were stabilized by 0.5% PVA, as well as F10 with similar composition as F8 but stabilized by 2% PVA were considered the optimum formulae as they combined small particle size and relatively high encapsulation efficiencies. F8 had a particle size of 402.5 nm ± 34.5 with a polydispersity value of 0.005 and an encapsulation efficiency of 51%, F10 had a 617.3 ± 54.3 nm particle size with 0.005 polydispersity value and 49.1% encapsulation efficiency, whereas formula F14 showed a particle size of 343 nm ± 29 with 0.005 polydispersity, and an encapsulation efficiency of 59.09%. DSC and FTIR results suggested the existence of the lipids in the solid crystalline state. Incomplete biphasic prolonged release profile of the drug from both formulae was observed in phosphate buffer pH 6.8 as well as simulated colonic medium containing rat caecal contents. A burst release with magnitudes of 26% and 28.8% cumulative drug released were noticed in the first hour samples incubated in phosphate buffer pH 6.8 for both F8 and F14, respectively, followed by a slow release profile reaching 50% and 52% after 48 hours.

High fidelity vinyl terminated polymers by combining RAFT and cobalt catalytic chain transfer (CCT) polymerization methods

In this work, we combine reversible addition fragmentation transfer polymerization (RAFT) with cobalt catalytic chain transfer (CCT) to obtain omega-unsaturated polymers with relatively low polydispersity values.

Single electron transfer‐living radical polymerization of methyl methacrylate in fluoroalcohol: Dual control over molecular weight and tacticity

AbstractThe Cu(0)‐mediated single electron transfer‐living radical polymerization (SET‐LRP) of methyl methacrylate (MMA) using ethyl 2‐bromoisobutyrate (EBiB) as an initiator with Cu(0)/N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine as a catalyst system in 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) was studied. The polymerization showed some living features: the measured number‐average molecular weight (Mn,GPC) increased with monomer conversion and produced polymers with relatively low polydispersities. The increase of HFIP concentration improved the controllability over the polymerization with increased initiation efficiency and lowered polydispersity values. 1H NMR, MALDI‐TOF‐MS spectra, and chain extension reaction confirmed that the resultant polymer was end‐capped by EBiB species, and the polymer can be reactivated for chain extension. In contrast, in the cases of dimethyl sulfoxide or N,N‐dimethylformamide as reaction solvent, the polymerizations were uncontrolled. The different effects of the solvents on the polymerization indicated that the mechanism of SET‐LRP differed from that of atom transfer radical polymerization. Moreover, HFIP also facilitated the polymerization with control over stereoregularity of the polymers. Higher concentration of HFIP and lower reaction temperature produced higher syndiotactic ratio. The syndiotactic ratio can be reached to about 0.77 at 1/1.5 (v/v) of MMA/HFIP at −18 °C. In conclusion, using HFIP as SET‐LRP solvent, the dual control over the molecular weight and tacticity of PMMA was realized. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6316–6327, 2009

Heterobimetallic aluminium and zinc complex with N-arylanilido-imine ligand: Synthesis, structure and catalytic property for ring-opening polymerization of ε-caprolactone

Treatment of a N-arylanilido-imine ligand [ ortho-C 6H 4(NHAr)CH N] 2CH 2CH 2 (Ar = 2,6-Me 2C 6H 3) ( LH 2) with one equiv. of AlMe 3 affords a monometallic complex [C 6H 4(NHAr)–CH N)]CH 2CH 2(C 6H 4(NAr)CH NAlMe 2) ( 1). The monometallic complex 1 reacts with one equiv. of ZnEt 2 to give a heterobimetallic complex [C 6H 4(NAr)–CH NZnEt]CH 2CH 2[C 6H 4(NAr)–CH NAlMe 2] ( 2). Both complexes were characterized by 1H and 13C NMR spectroscopy and elemental analyses, and the molecular structures of 1 and 2 were determined by X-ray diffraction analysis. The complexes 1 and 2 both are efficient catalysts for ring-opening polymerization of ε-caprolactone in the presence of benzyl alcohol yielding polymers with narrow polydispersity values and complex 2 initiates the polymerization in a controllable manner.

Microbial Transformation of Dissolved Leaf Litter Organic Matter and Its Effects on Selected Organic Matter Operational Descriptors

Changes in selected spectroscopic and chromatographic characteristics of water-soluble organic matter (WSOM) extracted from leaf litter and its ability to bind pyrene were monitored throughout 14 day microbial incubation experiments. To provide additional insight into the microbial transformation of the WSOM, incubation experiments were similarly conducted with controlled-composition mixtures of glucose and dissolved humic substances (HS) that were base extracted from the same leaf litter source. Microbial transformation increased the specific ultraviolet absorbance and number-average molecular weight of residual WSOM while polydispersity values decreased. Fluorescence measurements revealed loss of protein-like fluorescence and enhancement of fulvic- and humic-like fluorescence in residual WSOM. Overall, the incubation results suggest that nonaromatic and smaller sized carbon structures were being degraded while the microbial activity produced humic-like aromatic components in solution. Together, these changes resulted in enhanced pyrene binding by the altered WSOM. Consistent findings resulted from mixtures of glucose and the leaf litter HS. Changes in measured operational descriptors were more pronounced for mixtures containing a higher percentage of glucose, suggesting that utilization of labile constituents may be necessary for formation of unknown structures associated with high pyrene binding capabilities. Simple mass balance, end member mixing models often failed to predict changes in pyrene binding brought about by microbial transformation, suggesting that microbial utilization of labile constituents is not the predominant process governing the enhanced pyrene binding.

Highly active and stereospecific polymerizations of 1,3-butadiene by using bis(benzimidazolyl)amine ligands derived Co(II) complexes in combination with ethylaluminum sesquichloride

A family of cobalt(II) complexes supported on tridentate dibenzimidazolyl ligands having a general formula: [N(CH3)(CH2)2(Bm–R)2]CoCl2 (where Bm=benzimidazolyl, R=H; –Me; –Bz), have been prepared by the condensation of o-phenylene diamine with methyliminodiacetic acid. The Co(II) complexes exhibited high activities for the polymerization of 1,3-butadiene, on activation with ethylaluminum sesquichloride (EASC), to yield predominantly cis-1,4 microstructure. The polymers are characterized by high molecular weight with polydispersity values between 2.35 and 3.37. The ligand modification shows remarkable influence on polymerization activity. The stereospecificity of the catalysts is consistent for a wide range of reaction conditions, except temperature. The electronic influence of ligand structure towards metal center is investigated by using cyclic voltammetric analysis and the generation of cationic active centers is identified via UV–vis spectroscopic analysis of the catalyst system.

Characterization and evaluation of supported rac‐dimethylsilylenebis(indenyl)zirconium dichloride on ethylene polymerization

Abstractrac‐Dimethylsilylenebis(indenyl)zirconium dichloride was grafted onto commercial methyl aluminoxane modified silica (SMAO) at different loadings (0.1–1.5 wt % Zr/SMAO). Supported catalysts were evaluated in ethylene polymerization with isoprenylaluminum as a cocatalyst. The characterization of two supported catalysts bearing 0.3 and 0.8 wt % Zr/SiO2 by extended X‐ray absorption fine structure indicated that the number and the intensity of the peaks beyond the coordination shell, associated with the next nearest neighbors, depended on the Zr concentration. For the catalyst with a higher Zr content, only one peak (2.8 Å) was observed. The catalyst with 0.3 wt % Zr/SMAO presented two small peaks at 2.8 and 3.8 Å. Polymers produced with the supported catalysts presented lower crystallinity and higher molar mass and polydispersity values in comparison to that produced by the homogeneous one. Gel permeation chromatogram deconvolution suggested the presence of four catalyst sites for the supported systems. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Latent cationic palladium(II) phosphine carboxylate complexes for norbornene polymerization

AbstractThe catalytic efficacy of trans‐[(R3P)2Pd(O2CR′)(LB)][B(C6F5)4] (1) (LB = Lewis base) and [(R3P)2Pd(κ2‐O,O‐O2CR′)][B(C6F5)4] (2) for mass polymerization of 5‐n‐butyl‐2‐norbornene (Butyl‐NB) was investigated. The nature of PR3 and LB in 1 and 2 are the most critical components influencing catalytic activity/latency for the mass polymerization of Butyl‐NB. Further, it was shown that 1 is in general more latent than 2 in mass polymerization of Butyl‐NB. 5‐n‐Decyl‐2‐norbornene (Decyl‐NB) was subjected to solution polymerization in toluene at 63(±3) °C in the presence of several of the aforementioned palladium complexes as catalysts and the polymers obtained were characterized by gel permeation chromatography. Cationic trans‐[(R3P)2PdMe(MeCN)][B(C6F5)4] [R = Cy (3a), and iPr (3b)] and trans‐[(R3P)2PdH (MeCN)][B(C6F5)4] [R = Cy (4a), and iPr (4b)], possible products from thermolysis of trans‐[(R3P)2Pd(O2CMe)(MeCN)][B(C6F5)4] [R = Cy (1a) and iPr (1g)], as well as trans‐[(R3P)2Pd(η3‐C3H5)][B(C6F5)4] [R = Cy (5a), and iPr (5b)], were also examined as catalysts for solution polymerization of Decyl‐NB. A maximum activity of 5360 kg/(molPd h) of 2a was achieved at a Decyl‐NB/Pd: 26,700 ratio which is slightly better than that achieved with 5a [activity: 5030 kg/(molPd h)] but far less compared with 4a [activity: 6110 kg/(molPd h)]. Polydispersity values indicate a single highly homogeneous character of the active catalyst species. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 103–110, 2009

Synthesis of Novel Polyamide-Hyperbranched Polymers via Self Condensing Atom Transfer Radical Polymerization

Novel inimer was synthesized from p-amino phenol via successive preparative methods by using both bromoisobutyrylbromide and acryloyl chloride. The new inimer was well characterized via Infrared Spectra (IR) and 1H nuclear magnetic resonance (NMR). New hyperbranched polyamide (H1) was prepared via Atom Transfer Radical Polymerization (ATRP). Several reaction conditions (ligands, solvents, temperatures, etc.) were studied. However, the N,N,N′,N″,-pentamethyldiethylenetriamine (PMDETA)/CuBr catalytic system showed good results in toluene at 100°C. Three arm star methylmethacrylate (MMA) homopolymers reacted with (H1) in different percentages to form copolymers with low polydispersity values, especially at 1:115 for poly MMA:H1. The formed polymers were characterized via Gel Permeation Chromatography (GPC), 1HNMR, thermal analyses, and Transmission Electron Microscopy (TEM).

Characterization of the molecular mass distribution of pullulans by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry using 2,5‐dihydroxybenzoic acid butylamine (DHBB) as liquid matrix

The performances of several matrices were investigated for the accurate determination of the molecular mass distributions of pullulans by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The ionic liquid matrix (ILM) 2,5-dihydroxybenzoic acid butylamine (DHBB) gave better and more reliable results than the crystalline matrices 2,5-dihydroxybenzoic acid (DHB) and 2,4,6-trihydroxyacetophenone (THAP). With the ILM it was possible to obtain spectra of pullulans up to more than 100 kDa, the highest molar mass reported thus far. Owing to the known advantages of liquid matrices providing better spot-to-spot reproducibility, an almost noise-free spectrum and constant baselines were obtained when working under optimized conditions. In particular, the extent of in-source fragmentation occurring with this group of fragile polymers was considerably and decisively reduced. Thus, a more reliable representation of the true oligomer and polymer distributions is experimentally attainable, especially for distributions with small polydispersity values. The maximum error in the measured distribution associated with fragmentation was estimated by model calculations describing the changes in the polymer distribution upon different probabilities of fragmentation events. These simulation results indicated that the data obtained by MALDI-TOFMS using the liquid DHBB matrix were of high reliability. In particular, the average value of the distributions, M(w), and the polydispersity were obtained with predicted uncertainties of between 3 and 15% depending on the width of the distribution and the mass of the polymers.

Synthesis, characterization and applications in ethylene polymerization of asymmetric ansa-titanocene complexes. Molecular structure of [Ti{Me 2Si(η 5-C 5Me 4)(η 5-C 5H 3iPr)}Cl 2

The ansa-titanocene complexes, [Ti{Me 2Si(η 5-C 5Me 4)(η 5-C 5H 3R)}Cl 2] (R = Me ( 5), iPr ( 6), tBu ( 7), SiMe 3 ( 8)), were obtained from the reaction of Li 2{Me 2Si(C 5Me 4)(C 5H 3R)} (R = Me ( 1), iPr ( 2), tBu ( 3), SiMe 3 ( 4)) with [TiCl 4(THF) 2], respectively. Compounds 5– 8 have been tested as catalysts in the polymerization of ethylene and compared with the ansa-titanocene complexes [Ti{Me 2Si(η 5-C 5H 4) 2}Cl 2] and [Ti{Me 2Si(η 5-C 5Me 4)(η 5-C 5H 4)}Cl 2]. The resulting polyethylene showed molecular weights of about 200 000 g mol −1 and polydispersity values of approximately 3. In addition, the molecular structure of 6 has been determined by single crystal X-ray diffraction studies.