Weight Polypropylene Research Articles

Ligand Migration in the Reaction of Titanium Complexes with AlMe3

Five different titanium compounds cis-[Ti(η2-hbo)2(OEt)2]·0.5toluene (1), cis-[TiCl2(η2-thp)2] (2), [TiCl2(edbp)2] (3), [Ti2(μ-OMe)2(edbp)2(Me)2] (6), [Ti2(μ-OMe)2(edbp)2(OMe)2] (7) (Hhbo = 2-(2-hydroxyfenyl)benzoxazole, Hthp = tetrahydropyran-2-methanol, H2edbp = 2,2'-ethylidenebis(4,6-di-tert-butylphenol)), have been prepared and tested in combination with MAO as catalysts for propene polymerization and ethene and oct-1-ene copolymerization with the aim of gaining insight into the structure of the active species. Investigation of the 1/AlMe3 or 2/AlMe3 systems resulted in isolation of [Al(η2-hbo)2(Me)] (4) and [Al2(μ2-η2-thp)2(Me)4] (5) in high yields. This indicates that the trimethylaluminum contained in MAO abstracts ligands from 1 or 2, affecting thus the catalytic performance of the 1,2/MAO catalysts. In contrast, compound 3 reacted with MAO affording methylated product 6. Accordingly, the 3/MAO catalyst differed from the above ones, furnishing at 70 °C e.g., narrow molecular weight polypropylene (Mn = 454 000; Mw/Mn = 2.49; Tm = 158.2 °C).

Thermodynamic scaling of the viscosity of van der Waals, H-bonded, and ionic liquids

Viscosities eta and their temperature T and volume V dependences are reported for seven molecular liquids and polymers. In combination with literature viscosity data for five other liquids, we show that the superpositioning of relaxation times for various glass-forming materials when expressed as a function of TV(gamma), where the exponent gamma is a material constant, can be extended to the viscosity. The latter is usually measured to higher temperatures than the corresponding relaxation times, demonstrating the validity of the thermodynamic scaling throughout the supercooled and higher T regimes. The value of gamma for a given liquid principally reflects the magnitude of the intermolecular forces (e.g., steepness of the repulsive potential); thus, we find decreasing gamma in going from van der Waals fluids to ionic liquids. For some strongly H-bonded materials, such as low molecular weight polypropylene glycol and water, the superpositioning fails, due to the nontrivial change of chemical structure (degree of H bonding) with thermodynamic conditions.

Textile Analysis of Heavy Weight, Mid-Weight, and Light Weight Polypropylene Mesh in a Porcine Ventral Hernia Model

The purpose of this study was to assess the burst strength and stiffness of heavy weight (HW), mid-weight (MW), and light weight (LW) polypropylene mesh pre-implantation and 5 months post-implantation in a porcine ventral hernia model. HW (95 g/cm2), MW (45 g/cm2), and LW (28 g/cm2) polypropylene were tested as dry samples (n = 8/mesh) before implantation using a stamp strain machine. Three weeks after creating four hernia defects in each mini-pig (n = 18), the polypropylene meshes (8 x 10 cm; 24/mesh type) were implanted in the preperitoneal space, ensuring 2 cm overlap circumferentially. At 5 months, the mesh was harvested en bloc with the abdominal wall. Testing of burst strength and stiffness was repeated on the ex vivo specimens. After implantation in the pig for 5 months, the mean burst strength and stiffness of HW and MW meshes remains the same. LW mesh with an absorbable monofilament in its weave has significant reductions in mean burst strength (P = 0.01) and mean stiffness (P < 0.0001). The burst strength for all meshes tested was much higher than measured for the abdominal wall fascia alone. The degree of shrinkage of the various weight meshes did not differ. A reduction in mean burst strength and stiffness occurs after 5 months implantation of LW polypropylene mesh with an absorbable monofilament. All meshes exhibited burst strengths that were much greater than the burst strength of the abdominal wall fascia alone. After tissue incorporation, the LW polypropylene mesh maintains mean burst strength comparable to MW polypropylene mesh, while becoming less stiff than HW mesh. Long-term, this may contribute to more physiological abdominal wall compliance after LW polypropylene mesh implantation.

In situ Polypropylene Nanocomposites: Gas‐Phase Polymerization of Propylene in the Presence of Nanofillers using Nanosilica‐Supported‐Zirconocene Catalyst

This work concentrates on using the gas‐phase polymerization technique for the production of highly loaded nanocomposites. Filler loading levels near the vicinity of 40 wt% have been obtained using different nanofillers. Three different in situ Polypropylene (PP) nanocomposites, i.e., Cloisite‐20A filled polypropylene (CFPP), Kaolin filled polypropylene (KFPP) and nanosilica filled polypropylene (SFPP) have been prepared by gas‐phase polymerization. The catalyst used is Nanosilica‐Supported‐Zirconocene. The fillers used are Closite‐20A, Kaolin and nanosilica, respectively. These were pre‐treated with MAO (Methylaluminoxane) to inhibit their deactivating action on the catalyst because of the presence of either acidic or basic groups on their surfaces; in this way MAO acts as a co‐catalyst for the three polymerization reactions being discussed. Significantly higher molecular weight polypropylene was formed with nanosilica as the filler. The melting temperature and enthalpy is also observed to be comparatively higher in this case. However, in the case of other fillers, the molecular weights, as well as melting points, are comparatively lower. With the catalyst used, a mixture of crystalline and amorphous polypropylene was observed to form. Comparatively lesser amounts of crystalline polypropylene are also observed.

Thermal, Electrical and Mechanical Properties of Ultra-high Molecular Weight Polypropylene and Carbon Filler Composites

Isotactic ultra-high molecule weight polypropylene (UHMWPP) composites filled with multi-wall carbon nanotubes (MWNTs), vapor growth carbon fibers (VGCFs) and short carbon fibers (CFs) were prepared by gelation/crystallization from solutions, in which these aspect ratios of MWNTs, VGCFs and CFs chosen were 500–1000, 50–300 and 5–20, respectively. The thermal, electrical and mechanical properties of these composites were studied in terms of their aspect ratios of the three kinds of fillers. The admixture of the three kinds of carbon filler provided better improvement of thermal property in comparison with neat UHMWPP, and the effect was the most significant for the admixture of MWNTs with the highest average aspect ratio. The electrical conductivity by the admixture of carbon fillers was also sensitive to the aspect ratio. Namely, the electrical conductivity of undrawn UHMWPP-MWNT composite film was the highest, when the filler content of the composites was the same. The conductivities of UHMWPP-VGCF and UHMWPP-CF composites decreased drastically by elongation up to 5 times (λ=5), while the conductivity of UHMWPP-MWNT maintained ca. 10−3 S/cm at λ=5 but further elongation up to λ=20 caused a gradual decrease of the conductivity. Young’s modulus of the UHMWPP-VGCF composites was higher than that of neat UHMWPP films in undrawn and drawn states, while that of UHMWPP-MWNT composites became lower when the composite with 3 wt % MWNT content was elongated up to λ=20. These phenomena indicated that a number of entanglement points of MWNTs within the composite assure electric channels in drawn state but hamper the smooth orientation of UHMWPP chains.

Tension free open inguinal hernia repair using an innovative self gripping semi-resorbable mesh

Inguinal hernia repair according to Lichtenstein technique has become the most common procedure performed by general surgeons. Heavy weight polypropylene meshes have been reported to stimulate inflammatory reaction responsible for mesh shrinkage when scar tissue evolved. Additionally, some concerns remain regarding the relationship between chronic pain and mesh fixation technique. In order to reduce those drawbacks, we have developed a new mesh for anterior tension free inguinal hernia repair which exhibits self-gripping absorbable properties. 52 patients (69 hernias) were prospectivly operated with this mesh (SOFRADIM-France) made of low-weight isoelastic large pores knitted fabric which incorporated resorbable micro hooks that provides self gripping properties to the mesh during the first months post-implantation. The fixation of the mesh onto the tissues is significantly facilitated. The mesh is secured around the cord with a self gripping flap. After complete tissular ingrowth and resorption of the PLA hooks, the low-weight (40 g/m(2)) polypropylene mesh insures the long term wall reinforcement. Peroperativly, no complication was reported, the mesh was easy to handle and to fix. Discharge was obtained at Day 1. No perioperative complication occurred, return to daily activities was obtained at Day 5.5. At one month, no neurological pain or other complications were described. Based on the first results of this clinical study, this unique concept of low density self gripping mesh should allows an efficient treatment of inguinal hernia. It should reduce postoperative complications and the extent of required suture fixation, making the procedure more reproducible.

The interfacial conformation of polypropylene glycols and their foam properties

The foam behaviour of low molecular weight polypropylene glycols (PPG) was investigated as a function of concentration and molecular weight (190–2000 g mol −1). For each polypropylene glycol, foam stability increases with concentration and passes through a maximum, beyond which foamability is suppressed as the solubility limit of the glycol is exceeded and droplets of glycol form. Light scattering data as well as static and dynamic surface tension results provide the key information leading to these interpretations. A maximum in foamability was observed for the PPG molecules with increasing molecular weight (caused by a change in molecular conformation at the interface). This suppresses the Marangoni effect and leads to a decrease in foam stability.

Synthesis and Characterization of the New Alkyl Borates [RB(C6F5)3]- (R = CH2Me, CHMe2, CH2CMe3): Utilization of [Me3CCH2B(C6F5)3]- as a Weakly Coordinating Counteranion during Zirconocene-Induced Catalysis of Propylene Polymerization

Reactions of alkyllithium compounds RLi (R = Me, Et, i-Pr, Np) with B(C6F5)3 result in the formation of the alkylborate salts Li[RB(C6F5)3]. Metathesis reactions of these with Ph3CCl and chloride salts of (Ph3P)2N+, PMePh3+, and HNMe2Ph+ proceed with varying degrees of success, as shown by NMR spectroscopy and electrospray mass spectrometry, and the compounds [PPN][EtB(C6F5)3], [PMePh3][NpB(C6F5)3], and [HNMe2Ph][NpB(C6F5)3] have been characterized crystallographically. All three anions assume the expected pseudotetrahedral structures with normal B−aryl bond lengths and R−B−aryl and aryl−B−aryl bond angles. The compound [HNMe2Ph][NpB(C6F5)3] reacts with Cp2ZrMe2, (Indenyl)2ZrMe2, and SBIZrMe2 to give propylene polymerization catalysts that are significantly more active and give higher molecular weight polypropylene than do the catalysts obtained using B(C6F5)3. Thus the [NpB(C6F5)3]- anion is for steric reasons more weakly coordinating than is [MeB(C6F5)3]-.

Chiral Indenes and Group‐4 Metallocene Dichlorides Containing α‐ and β‐Pinenyl‐Derived Ligand Substituents: Synthesis and Catalytic Applications in Polymerization and Carboalumination Reactions

AbstractThe synthesis and characterization of chiral bis(indenyl)zirconium dichlorides containing β‐pinenyl‐derived ligand substituents is reported. Unbridged metallocene complexeshaving the {[(1S,2S,5S)‐6,6‐dimethylbicyclo[3.1.1]hept‐2‐yl]methyl}dimethylsilyl substituent in both 1‐ and 2‐positions of the indenyl moiety were prepared and isolated in moderate to low yields by reaction of the corresponding indenyllithium salts with ZrCl4 followed by work‐up and crystallization procedures. The corresponding tetrahydroindenyl complexes were obtained in excellent yields by catalytic hydrogenation of the indenyl six‐membered rings. In a complementary approach, a synthetic route to α‐pinenyl‐substituted indenyl ligand analogues was briefly evaluated, which however, suffered from low yields. Selected β‐pinenyl‐substituted indenyl complexes were scanned as catalysts for the dehydropolymerization of phenylsilane upon activation with nBuLi, for polymerization of ethylene and propylene upon activation with methylaluminoxane (MAO) as well as for enantioselective carboalumination of 1‐octene with triethyl‐ and trimethylaluminum. The bis(indenyl) complexes catalyzed the carboalumination reaction, albeit only low yields (8–16 %) and low enantioselectivities (ee = 0.5–10 %) were obtained. The 2‐substituted bis(indenyl)zirconocene/MAO catalyst system produced atactic low‐molecular weight polypropylene with low polymerization activity whereas both 1‐ and 2‐substituted complexes showed high activities in ethylene polymerization producing polyethylenes with high molecular weights (Mw &gt; 440000). (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2005)

High modulus/tenacity filaments from blends of different molecular weights of polypropylene

AbstractPolypropylene (PP) filaments are prepared by blending two different molecular weight components of PP. A melt‐spinning process to produce filaments includes mixing of components, extrusion, and two‐stage drawing, followed by a unique Gradient Drawing™ process. Blending results in highly deformable as‐spun filaments with high draw ratios. For 90:10 blends of PP samples with melt flow indexes of 35 and 3, a high level of crystallinity and crystalline and amorphous orientations are obtained. A sonic modulus of 28 GPa, dynamic modulus of 20 GPa, tensile modulus of 16 GPa, and tenacity of 667 MPa are achieved. These samples are dimensionally stable up to ∼100°C. All steps in the production of the filaments are continuous. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1021–1028, 2005

The interfacial conformation of polypropylene glycols and foam behaviour

The foam behaviour of low molecular weight polypropylene glycols (PPG) was investigated as a function of concentration and molecular weight (190–2000 g mol −1). For each polypropylene glycol, foam stability increases with concentration and passes through a maximum, beyond which foamability is suppressed as the solubility limit of the glycol is exceeded and droplets of glycol form. Light-scattering data as well as static and dynamic surface tension results provide the key information leading to these interpretations. A maximum in foamability was observed for the PPG molecules with increasing molecular weight (caused by a change in molecular conformation at the interface). This suppresses the Marangoni effect and leads to a decrease in foam stability.

Structure and Properties of Elastomeric Polypropylene from C2 and C2v-Symmetric Zirconocenes. The Origin of Crystallinity and Elastic Properties in Poorly Isotactic Polypropylene

A comparative analysis of the structure and mechanical properties of two elastomeric amorphous and semicrystalline polypropylenes samples, produced with C2v-symmetric and chiral C2-symmetric ansa-zirconocene catalysts, respectively, is presented. The poorly isotactic polypropylene (iam-PP) of medium molecular weight, prepared with the chiral C2-symmetric catalyst, slowly crystallizes, by aging at room temperature or by stretching, in a continuum of disordered modifications intermediate between α and γ forms of isotactic polypropylene. Structural and morphological transformations occur during stretching. Disordered α/γ modifications, containing a high fraction of perpendicular chains, present in the unoriented film, transform by stretching at high deformations into structures more similar to the α form with a high content of parallel chains. The development of the small level of crystallinity induces elastic properties. The small crystalline domains in the amorphous matrix, indeed, act as physical knots of the elastomeric lattice. This poorly isotactic iam-PP sample shows, instead, poor elastic properties and viscous flow at high deformations in the amorphous state, before crystallization, because of the not high molecular weight. The unique crystallization mode of the iam-PP sample explains the remarkable enhancement of elastic properties in low stereoregular polypropylene upon development of crystallinity. The fully amorphous high molecular weight atactic polypropylene (a-PP), prepared with the C2v-symmetric catalyst, presents elastic behavior only in a small deformation range (up to 300% strain) and experiences viscous flow of the chains at high deformations. The elasticity arises from the physical network generated by the high degree of entanglement of the polymeric chains generated by the high molecular weight of the sample. The poorly isotactic iam-PP sample, before crystallization, presents much poorer elastic properties than the a-PP sample because of the lower molecular weight. After crystallization, it shows better elastic properties in a large range of deformation with higher strength, notwithstanding the lower molecular weight, due to the presence of crystallinity.

The effects of SEBS- g-maleic anhydride reaction on the morphology and properties of polypropylene/PA6/SEBS ternary blends

Ternary blends, based on 70% by weight of polypropylene (PP) with 30% by weight of a dispersed phase, consisting of 15% polyamide-6 (PA6) and 15% of a mixture comprising varying ratios of an unreactive poly[styrene- b-(ethylene- co-butylene)- b-styrene] (SEBS) triblock copolymer and a reactive maleic anhydride-grafted SEBS- g-MA, were produced via melt blending in a co-rotating twin-screw extruder. TEM revealed the blend containing only non-reactive SEBS to exhibit individual PA6 and SEBS dispersed phases. However, the progressive replacement of SEBS with reactive SEBS- g-MA increased the degree of interfacial reaction between the SEBS and PA6 phases, thus reducing interfacial tension and providing a driving force for encapsulation of the PA6 by the SEBS. Consequently, the dispersed-phase morphology was observed to transform from two separate phases to acorn-type composite particles, then to individual core-shell particles and finally to agglomerates of the core-shell particles. The resultant blends exhibited significant morphology-induced variations in both thermal and mechanical properties. DSC showed that blends in which the diameter of the PA6 particles was reduced to ≤3 μm by the increasing interfacial reaction exhibited fractionated PA6 crystallisation. In general, mechanical testing showed the blends to exhibit inferior low-strain tensile properties (modulus and yield stress) compared to the matrix PP, but superior ultimate tensile properties (stress and strain at break) and impact strength. These changes are discussed with reference to composite models.

Synthesis of the new, weakly coordinating anions [RB(C6F5)3]−(R = CH2Me, CHMe2, CH2CMe3); utilization of [HNMe2Ph][Me3CCH2B(C6F5)3] to activate zirconocene catalysts for propylene polymerization

The compound [HNMe2Ph][NpB(C6F5)3](Np =(CH3)3CCH2) reacts with dimethylzirconocenes to give active propylene polymerization catalysts which are significantly more active and give higher molecular weight polypropylene than do the catalysts obtained using B(C6F5)3; the [NpB(C6F5)3]- anion is for steric reasons more weakly coordinating than is [MeB(C6F5)3]-.

Effect of Carbon Dioxide on the Interfacial Tension of Polymer Melts

Supercritical CO2 is a promising solvent for application in polymer blending and foaming. Interfacial tension is a key parameter in determining the bubble nucleation and growth rates, as well as droplet breakup in blending. However, very limited data are available in the literature for CO2−polymer systems. In this work, pendant drops were imaged in a high-pressure, high-temperature view cell for determining the interfacial tension between polystyrene (PS) and CO2 (210−230 °C and pressure up to 140 atm), and between polystyrene and two different molecular weight polypropylenes (PP) (both saturated with CO2 at 220 °C and pressures up to 165 atm). The interfacial tensions in polymer/CO2 and polymer/polymer systems decrease significantly with increasing CO2 pressure and then level off at higher CO2 pressures. Density gradient theory combined with an equation of state was applied in predicting the interfacial tension between PS and CO2 starting from only the surface tension data of pure PS at the temperature o...

Dielectric α-relaxation and ionic conductivity in propylene glycol and its oligomers measured at elevated pressure

Structural dynamics and volume were measured as a function of both temperature and pressure for a propylene glycol and its oligomers (PPG), and the results compared with previous data on higher molecular weight polypropylene glycols. PPG is of special interest because the terminal groups form hydrogen bonds; thus, by studying different molecular weights, the manner in which hydrogen bonding influences the dynamics in the supercooled regime can be systematically investigated. The fragility (Tg-normalized temperature dependence) of the dimer and trimer of PPG increases with pressure, similar to results for other H-bonded liquids, but different from van der Waals glass formers. This behavior is believed to be due to the effect of pressure in decreasing the extent of hydrogen bonding. From the combined temperature and volume dependences of the relaxation times, the relative degree to which thermal energy and volume govern the dynamics was quantified. With decreasing molecular weight, the relative contribution of thermal energy to the dynamics was found to strongly increase, reflecting the role of hydrogen bonding. By comparing the ionic conductivity and the dielectric relaxation times, a decoupling between rotational and translational motions was observed. Interestingly, this decoupling was independent of both pressure and molecular weight, indicating that hydrogen bonds have a negligible effect on the phenomenon.

Effect of composition and comonomer type on the rheology, morphology and properties of ethylene-α-olefin copolymer/polypropylene blends

The rheology, morphology, thermal and mechanical properties of blends containing low molecular weight polypropylene (PP) and metallocene-based ethylene-α-olefin copolymers (ECs) have been investigated. Evaluation of the thermo-rheological properties of the blends showed that they are immiscible, both in the solid and melt state, over the whole range of compositions. Rheological properties were correlated to blend morphology, by using the Palierne emulsion model. The resulting low values of interfacial tension confirmed excellent compatibility between the phases. Addition of ECs in PP resulted in significant ductility improvement. The transition from plastic to elastomeric properties coincided with phase inversion. The butene-based EC was found to be the most beneficial in terms of impact properties. Fine morphologies, with sub-micron sizes of the dispersed phase, were obtained upon post-extrusion shearing of the blends.

Synthesis and characterization of high-molecular-weight syndiotactic amorphous polypropylene.

Heterocycle-fused titanium indenyl silylamido dimethyl complexes produce very high molecular weight polypropylene having a prevailingly syndiotactic microstructure with syndiotactic pentad contents rrrr up to 40-55% (sam-PP). The samples are basically amorphous and may slowly develop a low level of crystallinity (16-20%) at room temperature. A structural characterization has shown that sam-PP samples crystallize in disordered modifications of the helical form I of syndiotactic polypropylene (s-PP). The stretching of compression-molded films of sam-PP samples produce oriented crystalline fibers in the trans-planar mesomorphic form of s-PP. The low stereoregularity prevents the formation of the ordered trans-planar form III of s-PP, which instead is obtained in stretched fibers of the highly stereoregular and crystalline s-PP. The trans-planar mesomorphic form, obtained in stretched fibers, in turn transforms into the helical form I upon releasing the tension. The analysis of the mechanical properties has shown that sam-PP samples show good elastic behavior in a large range of deformation with remarkable strength, due to the presence of crystallinity. A comparison with the mechanical properties of less syndiotactic and fully amorphous samples is reported. These fully amorphous samples present lower strength and experience rapid viscous flow of the chains at high deformations and/or by application of stresses for long times. The higher strength in the semicrystalline sam-PP samples makes these materials interesting thermoplastic elastomers showing high toughness and ductility.

Asymmetric Metallocene Catalysts Based on Dibenzothiophene: A New Approach to High Molecular Weight Polypropylene Plastomers

Synthesis and polymerization data of a series of new sulfur-containing C1-symmetric metallocenes, rac-[1-(9-η5-fluorenyl)-2-(2-methylbenzo[b]indeno[4,5-d]thiophen-1-η5-yl)ethane]zirconium dichloride (7a), rac-[1-(9-η5-fluorenyl)-2-(2-methylbenzo[b]indeno[4,5-d]thiophen-1-η5-yl)ethane]hafnium dichloride (7b), rac-[1-(9-η5-fluorenyl)-2-(2-methylbenzo[b]indeno[4,5-d]thiophen-1-η5-yl)ethane]hafnium dimethyl (7c), and rac-[1-(9-η5-fluorenyl)-2-(2-methylbenzo[b]indeno[4,5-d]thiophen-3-η5-yl)ethane]zirconium dichloride (8), are reported. The characteristic structural feature of these complexes is the 2-methyl-1H-benzo[b]indeno[4,5-d]thiophene moiety (3: MBIT), which was derived from dibenzothiophene. In the case of 7a−c the MBIT unit shows a “back” orientation, whereas in 8 it is directed to the “front” of the tetrahedral metallocene dichloride species, which was unambiguously illustrated by X-ray structure analysis. Propylene polymerization experiments revealed higher activity and stereoselectivity for 7a/MAO ...

Polyethylene glycol-water and polypropylene glycol-water solutionsas benign reaction solvents

Aqueous solutions of low molecular weight polypropylene and polyethylene glycol are proposed for use as novel, safe, environmentally friendly solvents. Not only are these solvents relatively nontoxic, but they are also nonvolatile, which eliminates the possibility of fugitive gaseous emissions. Many organic compounds have been found to be soluble in these polyglycol solutions; thus, they could be used as replacement solvents in various chemical processes. One use of the solvents could be as the medium for conducting chemical reactions, and this has been investigated. In particular, three classes of organic reactions, S N 1, S N 2, and Diels-Alder, have been conducted in the polyglycol solutions. Rate constants were obtained and compared to those for the traditional organic solvents. For the S N 1 reaction and the Diels-Alder reactions, the rate constants in the polyglycol solvents were greater than those found for the frequently used organic solvents.