The Chemistry of the Active Molecules Formed in the Mechanical Degradation of Polymers

1957 ◽  
Vol 30 (4) ◽  
pp. 1162-1165
Author(s):  
A. A. Berlin
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Polyvinyl Acetate ◽  
Covalent Bond ◽  
Ultrasonic Waves ◽  
Mechanical Degradation ◽  
Specific Viscosity ◽  
Mechanical Destruction ◽  
Fluid State ◽  
Polymeric Chains

Abstract At the present time there is a multitude of data indicating that when polystyrene, natural rubber, polyvinyl acetate, cellulose, starch, proteins and other high molecular weight compounds are mechanically ground up, a degradation of the polymeric chains is observed. The mechanical scission of macromolecules during grinding in a colloid or ball mill, or when they are broken down on mill rolls, proceeds most rapidly at temperatures below the range of the viscous-fluid state, since under these conditions the forces of intermolecular interaction are considerably greater than the strength of the covalent bond. However, the mechanical destruction of macromolecules is also possible through certain mechanical effects acting on solutions of polymers. Thus, for instance, the force of friction generated in the flow of a 0.05% solution of polystyrene (Mcp=6×105) in tetralin through a platinum capillary is due to the scission of macromolecules, which brings about a 30% decrease in the specific viscosity. The significant gradients in the rate and in the forces of friction and cavitation developed in polymer solution through the action of ultrasonic waves with frequencies of the order of 200–300 kilocycles/sec. are due to the mechanical scission of macromolecules of polystyrene, rubber, polyvinyl acetate, cellulose and a number of other high molecular weight compounds.

Titanium amidate complexes as active catalysts for the synthesis of high molecular weight polyethylene

2015 ◽  
Vol 93 (7) ◽  
pp. 775-783 ◽  
Author(s):  
Patricia Horrillo-Martinez ◽  
David C. Leitch ◽  
Scott A. Ryken ◽  
Robert K. Thomson ◽  
J. David Beard ◽  
...  
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Ethylene Polymerization ◽  
Catalytic Polymerization ◽  
Binding Motifs ◽  
Co Catalyst ◽  
Multiple Binding ◽  
Polymeric Chains ◽  
Ultra High Molecular Weight

A series of titanium and zirconium bis(amidate) complexes of the type L2MX2, where L is an amidate ligand, and X is either –NMe2 or –Cl, were prepared in 60%–83% yield and fully characterized. Multiple binding motifs are observed as the amidate ligand can bind in κ1- and κ2-modes. These complexes were then subjected to screening the catalytic polymerization of ethylene. All catalysts, after reaction with suitable co-catalyst, were functional for ethylene polymerization, though not for the copolymerization of ethylene and longer linear 1-alkenes. Polyethylene was formed in the range of 1000–4000 kDa, and with PDI values as low as 1.3. These long polymeric chains are considered as ultra-high molecular weight polyethylene (UHMWPE).

Microtubule motors and other maps

1990 ◽  
Vol 48 (3) ◽  
pp. 1-1
Author(s):  
Richard B. Vallee
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Cytoplasmic Dynein ◽  
Organelle Transport ◽  
Structural Components ◽  
Microtubule Associated Proteins ◽  
Microtubule Motors ◽  
Associated Proteins ◽  
The Subject ◽  
Intracellular Motility

Microtubules are involved in a number of forms of intracellular motility, including mitosis and bidirectional organelle transport. Purified microtubules from brain and other sources contain tubulin and a diversity of microtubule associated proteins (MAPs). Some of the high molecular weight MAPs - MAP 1A, 1B, 2A, and 2B - are long, fibrous molecules that serve as structural components of the cytamatrix. Three MAPs have recently been identified that show microtubule activated ATPase activity and produce force in association with microtubules. These proteins - kinesin, cytoplasmic dynein, and dynamin - are referred to as cytoplasmic motors. The latter two will be the subject of this talk.Cytoplasmic dynein was first identified as one of the high molecular weight brain MAPs, MAP 1C. It was determined to be structurally equivalent to ciliary and flagellar dynein, and to produce force toward the minus ends of microtubules, opposite to kinesin.

Studies on the Functionality of Newly Synthesized Fibrinogen after Treatment of Acute Myocardial Infarction with Streptokinase, Increase in the Rate of Fibrinopeptide Release

1993 ◽  
Vol 70 (06) ◽  
pp. 0978-0983 ◽  
Author(s):  
Edelmiro Regano ◽  
Virtudes Vila ◽  
Justo Aznar ◽  
Victoria Lacueva ◽  
Vicenta Martinez ◽  
...  
Keyword(s):  
Myocardial Infarction ◽  
Acute Myocardial Infarction ◽  
Molecular Weight ◽  
Steady State ◽  
High Molecular Weight ◽  
Coronary Arteries ◽  
Risk Index ◽  
Weight Fraction ◽  
High Molecular Weight Fraction ◽  
Fibrinopeptide A

SummaryIn 15 patients with acute myocardial infarction who received 1,500,000 U of streptokinase, the gradual appearance of newly synthesized fibrinogen and the fibrinopeptide release during the first 35 h after SK treatment were evaluated. At 5 h the fibrinogen circulating in plasma was observed as the high molecular weight fraction (HMW-Fg). The concentration of HMW-Fg increased continuously, and at 20 h reached values higher than those obtained from normal plasma. HMW-Fg represented about 95% of the total fibrinogen during the first 35 h. The degree of phosphorylation of patient fibrinogen increased from 30% before treatment to 65% during the first 5 h, and then slowly declined to 50% at 35 h.The early rates of fibrinopeptide A (FPA) and phosphorylated fibrinopeptide A (FPAp) release are higher in patient fibrinogen than in isolated normal HMW-Fg and normal fibrinogen after thrombin addition. The early rate of fibrinopeptide B (FPB) release is the same for the three fibrinogen groups. However, the late rate of FPB release is higher in patient fibrinogen than in normal HMW-Fg and normal fibrinogen. Therefore, the newly synthesized fibrinogen clots faster than fibrinogen in the normal steady state.In two of the 15 patients who had occluded coronary arteries after SK treatment the HMW-Fg and FPAp levels increased as compared with the 13 patients who had patent coronary arteries.These results provide some support for the idea that an increased synthesis of fibrinogen in circulation may result in a procoagulant tendency. If this is so, the HMW-Fg and FPAp content may serve as a risk index for thrombosis.

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