Selectivity in Propylene Polymerization with Group 4 Cp−Amido Catalysts

1997 ◽  
Vol 16 (13) ◽  
pp. 2879-2885 ◽  
Author(s):  
Andrew L. McKnight ◽  
Md. Athar Masood ◽  
Robert M. Waymouth ◽  
Daniel A. Straus
Keyword(s):  
Propylene Polymerization ◽  
Group 4

Stereoselective and regioselective propylene polymerization with group 4 bisphenolate ether complexes

2012 ◽  
Vol 50 (13) ◽  
pp. 2604-2611 ◽  
Author(s):  
Sören Randoll ◽  
Elizabeth T. Kiesewetter ◽  
Robert M. Waymouth
Keyword(s):  
Propylene Polymerization ◽  
Group 4

scholarly journals Propylene Polymerization and Deactivation Processes with Isoselective {Cp/Flu} Zirconocene Catalysts

Catalysts ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 959
Author(s):  
Xavier Desert ◽  
Thierry Roisnel ◽  
Vincent Dorcet ◽  
Katty Den Dauw ◽  
Aurélien Vantomme ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Dft Calculations ◽  
Isotactic Polypropylene ◽  
13C Nmr ◽  
13C Nmr Spectroscopy ◽  
Propylene Polymerization ◽  
Activation Process ◽  
Dormant State ◽  
Group 4 ◽  
New Compounds

Industrially relevant single-site precatalysts used to produce isotactic polypropylene (iPP) include C2-symmetric {SBI} and C1-symmetric {Cp/Flu} complexes of group 4 metals. While the latter can produce iPPs with a higher degree of isotacticity, they also suffer from poor productivity compared to their {SBI} counterparts. Several causes for this trend have been suggested—2,1-Regioinsertions are frequently pointed out, as they are suspected to drive the catalyst into a dormant state. While this event does not seem to significantly impact the productivity of {SBI} systems, the influence of these regioerror is poorly documented for isoselective {Cp/Flu} precatalysts. To address this issue, new Ph2X(Cp)(Flu) (Ph2X = Ph2C, FluC, Ph2Si) proligands (2a–k) and some of the corresponding dichlorozirconocenes (3a–h,k) were synthesized. These new compounds were characterized and tested in homogeneous propylene polymerization at 60 °C and the amounts of regioerrors in the resulting polymers were examined by 13C NMR spectroscopy. A possible correlation between poor productivity and a high number of regioerrors was investigated and is discussed. Furthermore, a C-H activation process in the bulky nBu3C substituent upon activation of 4c (the dimethylated analog of 3c) by B(C6F5)3 has been evidenced by NMR; DFT calculations support this C-H activation as a deactivation mechanism.

Isospecific propylene polymerization with unbridged Group 4 metallocenes

1993 ◽  
Vol 115 (16) ◽  
pp. 7529-7530 ◽  
Author(s):  
Abbas Razavi ◽  
Jerry L. Atwood
Keyword(s):  
Propylene Polymerization ◽  
Group 4

Chiral-at-ansa-Bridged Group 4 Metallocene Complexes {(R1R2C)-(3,6-tBu2Flu)(3-R3-5-Me-C5H2)}MCl2: Synthesis, Structure, Stereochemistry, and Use in Highly Isoselective Propylene Polymerization

2011 ◽  
Vol 30 (2) ◽  
pp. 263-272 ◽  
Author(s):  
Evgeny Kirillov ◽  
Nicolas Marquet ◽  
Manuela Bader ◽  
Abbas Razavi ◽  
Vincenzo Belia ◽  
...  
Keyword(s):  
Propylene Polymerization ◽  
Group 4 ◽  
Metallocene Complexes

Propylene Polymerization with Bis(phenoxy-imine) Group-4 Catalysts Using iBu3Al/Ph3CB(C6F5)4 as a Cocatalyst

2002 ◽  
Vol 23 (18) ◽  
pp. 1118-1123 ◽  
Author(s):  
Junji Saito ◽  
Mitsuhiko Onda ◽  
Shigekazu Matsui ◽  
Makoto Mitani ◽  
Rieko Furuyama ◽  
...  
Keyword(s):  
Propylene Polymerization ◽  
Imine Group ◽  
Group 4

Morphological Changes in the Rat Granulosa Cell Surface During Differentiation Induced by Estradiol and Gonadotropins

1977 ◽  
Vol 35 ◽  
pp. 484-485
Author(s):  
P. Bagavandoss ◽  
JoAnne S. Richards ◽  
A. Rees Midgley
Keyword(s):  
Cell Surface ◽  
Granulosa Cell ◽  
Morphological Changes ◽  
Follicular Development ◽  
Female Rats ◽  
Functional Changes ◽  
Group 4 ◽  
Group 3 ◽  
Group 5 ◽  
Group 2

During follicular development in the mammalian ovary, several functional changes occur in the granulosa cells in response to steroid hormones and gonadotropins (1,2). In particular, marked changes in the content of membrane-associated receptors for the gonadotropins have been observed (1).We report here scanning electron microscope observations of morphological changes that occur on the granulosa cell surface in response to the administration of estradiol, human follicle stimulating hormone (hFSH), and human chorionic gonadotropin (hCG).Immature female rats that were hypophysectcmized on day 24 of age were treated in the following manner. Group 1: control groups were injected once a day with 0.1 ml phosphate buffered saline (PBS) for 3 days; group 2: estradiol (1.5 mg/0.2 ml propylene glycol) once a day for 3 days; group 3: estradiol for 3 days followed by 2 days of hFSH (1 μg/0.1 ml) twice daily, group 4: same as in group 3; group 5: same as in group 3 with a final injection of hCG (5 IU/0.1 ml) on the fifth day.

Correlation of γ-radioactivity and Scanning Electron Microscopy in measurement of retention of 111Indium-labeled canine endothelial cells on synthetic vascular grafts

1989 ◽  
Vol 47 ◽  
pp. 886-887
Author(s):  
E.J. Prendiville ◽  
S. Laliberté Verdon ◽  
K. E. Gould ◽  
K. Ramberg ◽  
R. J. Connolly ◽  
...  
Keyword(s):  
Blood Flow ◽  
Ex Vivo ◽  
Vascular Grafts ◽  
Retention Data ◽  
Vascular Prostheses ◽  
Group 4 ◽  
Human Fibronectin ◽  
Insufficient Time ◽  
Group 3 ◽  
Group 2

Endothelial cell (EC) seeding is postulated as a mechanism of improving patency in small caliber vascular grafts. However the majority of seeded EC are lost within 24 hours of restoration of blood flow in previous canine studies . We postulate that the cells have insufficient time to fully develop their attachment to the graft surface prior to exposure to hemodynamic stress. We allowed EC to incubate on fibronectin-coated ePTFE grafts for four different time periods after seeding and measured EC retention after perfusion in a canine ex vivo shunt circuit.Autologous canine EC, were enzymatically harvested, grown to confluence, and labeled with 30 μCi 111 Indium-oxine/80 cm 2 flask. Four groups of 5 cm x 4 mm ID ePTFE vascular prostheses were coated with 1.5 μg/cm.2 human fibronectin, and seeded with 1.5 x 105 EC/ cm.2. After seeding grafts in Group 1 were incubated in complete growth medium for 90 minutes, Group 2 were incubated for 24 hours, Group 3 for 72 hours and Group 4 for 6 days. Grafts were then placed in the canine ex vivo circuit, constructed between femoral artery and vein, and subjected to blood flow of 75 ml per minute for 6 hours. Continuous counting of γ-activity was made possible by placing the seeded graft inside the γ-counter detection crystal for the duration of perfusion. EC retention data after 30 minutes, 2 hours and 6 hours of flow are shown in the table.

In-vivo evaluation of the effect of cyanoacrylate on prosthetic vascular graft infection – does cyanoacrylate increase the severity of infection?

VASA ◽  
2020 ◽  
Vol 49 (4) ◽  
pp. 281-284
Author(s):  
Atıf Yolgosteren ◽  
Gencehan Kumtepe ◽  
Melda Payaslioglu ◽  
Cuneyt Ozakin
Keyword(s):  
Vascular Graft ◽  
Graft Infection ◽  
Vascular Graft Infection ◽  
Group 4 ◽  
Significant Difference ◽  
Group 3 ◽  
Group 2 ◽  
Prosthetic Vascular Graft Infection ◽  
Group 1

Summary. Background: Prosthetic vascular graft infection (PVGI) is a complication with high mortality. Cyanoacrylate (CA) is an adhesive which has been used in a number of surgical procedures. In this in-vivo study, we aimed to evaluate the relationship between PVGI and CA. Materials and methods: Thirty-two rats were equally divided into four groups. Pouch was formed on back of rats until deep fascia. In group 1, vascular graft with polyethyleneterephthalate (PET) was placed into pouch. In group 2, MRSA strain with a density of 1 ml 0.5 MacFarland was injected into pouch. In group 3, 1 cm 2 vascular graft with PET piece was placed into pouch and MRSA strain with a density of 1 ml 0.5 MacFarland was injected. In group 4, 1 cm 2 vascular graft with PET piece impregnated with N-butyl cyanoacrylate-based adhesive was placed and MRSA strain with a density of 1 ml 0.5 MacFarland was injected. All rats were scarified in 96th hour, culture samples were taken where intervention was performed and were evaluated microbiologically. Bacteria reproducing in each group were numerically evaluated based on colony-forming unit (CFU/ml) and compared by taking their average. Results: MRSA reproduction of 0 CFU/ml in group 1, of 1410 CFU/ml in group 2, of 180 200 CFU/ml in group 3 and of 625 300 CFU/ml in group 4 was present. A statistically significant difference was present between group 1 and group 4 (p < 0.01), between group 2 and group 4 (p < 0.01), between group 3 and group 4 (p < 0.05). In terms of reproduction, no statistically significant difference was found in group 1, group 2, group 3 in themselves. Conclusions: We observed that the rate of infection increased in the cyanoacyrylate group where cyanoacrylate was used. We think that surgeon should be more careful in using CA in vascular surgery.

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