Autoadhesion of High‐Molecular‐Weight Monodisperse Glassy Polystyrene at Unexpectedly Low Temperatures

2004 ◽  
Vol 43 (5) ◽  
pp. 925-934 ◽  
Author(s):  
Yuri M. Boiko ◽  
Jørgen Lyngaae‐Jørgensen
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Low Temperatures

I.—The Future of Synthetic Plastics

1944 ◽  
Vol 62 (1) ◽  
pp. 1-9
Author(s):  
H. W. Melville
Keyword(s):  
Mechanical Properties ◽  
Molecular Weight ◽  
High Molecular Weight ◽  
Mass Production ◽  
Low Temperatures ◽  
The Other ◽  
New Materials ◽  
Production Methods ◽  
Chemical Theory ◽  
Chemical Constitution

The term synthetic plastic covers such a wide variety of substances that it is an extremely difficult matter to attempt a definition—nor is it necessary for the purpose of this review. To the chemist plastics are solids of high molecular weight exhibiting properties which lie between those of liquids and solids: at sufficiently high temperatures they behave like liquids and at low temperatures like solids. These substances do not obey many of the laws which form the corner-stones of chemical theory, for their chemical constitution can be varied by indefinitely small degrees and it is possible mechanically to divide the molecule into parts. To the layman, on the other hand, plastics have come to mean substances used to fabricate, by mass-production methods, relatively trivial articles like ashtrays, ornamental door-knobs, etc. They tend to be regarded as substitutes which must necessarily be inferior to the materials, once used to make these domestic articles. Much, too, has been written to give the impression that we are on the verge of the plastics era. This is an optimistic exaggeration. Plastics are designed to play an important part as unique materials which can be built by the chemist to the specification of the engineer and the physicist. It is wrong to regard them as substitutes. They are new materials and must be used as such. The purpose of this survey is to indicate how synthetic plastics fit into a future economy in which their special chemical and mechanical properties find their proper application.

scholarly journals Comparison of Hydroxypropylcellulose and Hot-Melt Extrudable Hypromellose in Twin-Screw Melt Granulation of Metformin Hydrochloride: Effect of Rheological Properties of Polymer on Melt Granulation and Granule Properties

Macromol ◽  
2021 ◽  
Vol 2 (1) ◽  
pp. 1-19
Author(s):  
Amol Batra ◽  
Fengyuan Yang ◽  
Michael Kogan ◽  
Anthony Sosnowik ◽  
Courtney Usher ◽  
...  
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Low Temperatures ◽  
Extended Release ◽  
Metformin Hydrochloride ◽  
Drug Degradation ◽  
Twin Screw ◽  
Hot Melt ◽  
Melt Granulation ◽  
Metformin Hcl

High-molecular-weight hypromellose (HPMC) and hydroxypropyl cellulose (HPC) are widely known, extended-release polymers. Conventional high-molecular-weight HPMCs are preferred in extended-release applications but not widely used in twin-screw melt granulation due to processability difficulties at low operating temperatures and potential drug degradation if high processing temperatures are used. Conversely, high-molecular-weight grade HPC (Klucel®) can be used in melt granulation processes. The purpose of this study was to evaluate the processability and dissolution behavior of HPC GXF ((Klucel® GXF) and a recently introduced type of hot-melt extrudable HPMC (Affinisol®) in extended-release metformin hydrochloride formulations using twin-screw melt granulation. Powder blends were prepared with 75% w/w metformin HCl and 25% w/w polymeric binder. Blends were granulated at processing temperatures of 160, 140, 120 and 100 °C. HPMC HME 4M (Affinisol® 4M) provided a fine powder, indicating minimum granulation at processing temperatures lower than 160 °C, and the tablets obtained with these granules capped during tableting. In contrast, acceptable tablets could be obtained with HPC GXF at all processing temperatures. Rheological studies including capillary rheometry to measure steady shear rate viscosity, and rotational rheometry to obtain time and temperature superposition data, showed that HPC GXF had a greater thermoplasticity than HPMC HME 4M, which made granulation possible with HPC GXF at low temperatures. Tablets compressed with granules obtained at 160 °C with both binders showed comparable dissolution profiles. High-molecular-weight HPC GXF provided a better processability at low temperatures and adequate tablet strength for the melt granulation of metformin HCl.

scholarly journals Synthesis of Ultrahigh Molecular Weight Polymers with Low PDIs by Polymerizations of 1-Decene, 1-Dodecene, and 1-Tetradecene by Cp*TiMe2(O-2,6-iPr2C6H3)–Borate Catalyst

Molecules ◽  
2019 ◽  
Vol 24 (8) ◽  
pp. 1634 ◽  
Author(s):  
Kotohiro Nomura ◽  
Sarntamon Pengoubol ◽  
Wannida Apisuk
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Low Temperatures ◽  
Catalytic Activities ◽  
High Molecular Weight Polymers ◽  
Ultrahigh Molecular Weight ◽  
High Molecular Weight Poly

Polymerizations of 1-decene (DC), 1-dodecene (DD), and 1-tetradecene (TD) by Cp*TiMe2(O-2,6-iPr2C6H3) (1)–[Ph3C][B(C6F5)4] (borate) catalyst have been explored in the presence of Al cocatalyst. The polymerizations of DC and DD, in n-hexane containing a mixture of AliBu3 and Al(n-C8H17)3, proceeded with high catalytic activities in a quasi-living manner, affording high molecular weight polymers (activity 4120–5860 kg-poly(DC)/mol-Ti·h, Mn for poly(DC) = 7.04–7.82 × 105, after 20 min at −30 °C). The PDI (Mw/Mn) values in the resultant polymers decreased upon increasing the ratio of Al(n-C8H17)3/AliBu3 with decreasing the activities at −30 °C. The PDI values also became low when these polymerizations were conducted at low temperatures (−40 or −50 °C); high molecular weight poly(DD) with low PDI (Mn = 5.26 × 105, Mw/Mn = 1.16) was obtained at −50 °C. The TD polymerization using 1–borate–AliBu3 catalyst (conducted in n-hexane at −30 °C) afforded ultrahigh molecular weight poly(TD) (Mn = 1.02 × 106, Mw/Mn = 1.38), and the PDI values also decreased with increasing the Al(n-C8H17)3/AliBu3 ratio.

Synthesis of high molecular weight polyaniline at low temperatures

1996 ◽  
Vol 76 (1-3) ◽  
pp. 157-160 ◽  
Author(s):  
P.N. Adams ◽  
P.J. Laughlin ◽  
A.P. Monkman
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Low Temperatures

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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