Polytetramethylene Ether Glycol: Effect of Concentration, Molecular Weight, and Molecular Weight Distribution on Properties of MDI/BDO-Based Polyurethanes

1982 ◽  
Vol 55 (1) ◽  
pp. 76-87 ◽  
Author(s):  
E. Pechhold ◽  
G. Pruckmayr
Keyword(s):  
Molecular Weight ◽  
Low Temperature ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Soft Segment ◽  
Hydrolytic Stability ◽  
The Other ◽  
Molecular Weight Range ◽  
Weight Range ◽  
Other Hand

Abstract Hardness, modulus, and tear strength of PTMEG-based polyurethanes are mainly affected by the hard-segment (MDI/BDO) concentration. On the other hand, PTMEG molecular weight mainly influences low-temperature and dynamic properties. Resilience and hydrolytic stability are affected by both soft-segment concentration and chain length. PTMEG of narrow molecular weight distribution yields softer polyurethanes with considerably longer elongation at break. Broad molecular weight distribution is advantageous only at the lower molecular weight range (650 and 1000), giving rise to improved resilience and low-temperature performance. Polyurethanes made from PTMEG of low molecular weight (Mn≤1000) have inherent drawbacks due to poor phase separation (high Tg) and limits in soft segment concentration (∼63% maximum for PTMEG 1000). The only advantage they offer is easier processability (lower viscosity and melting temperature). On the other hand, PTMEG above 2100 offers little property advantages and is more difficult to handle. Optimum overall polyurethane properties can be achieved with PTMEG in the molecular weight range of 1800 to 2100. It is conceivable that PTMEG-based polyurethanes made with different diisocyanates, curatives, curative/NCO ratios, or in the presence of triols or catalysts may show similar trends as the MDI/BDO formulations described in this study.

Rubber Hydrocarbon in Freshly Tapped Latex

1954 ◽  
Vol 27 (4) ◽  
pp. 1061-1067 ◽  
Author(s):  
G. F. Bloomfield
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Molecular Weight Range ◽  
Considerable Heterogeneity ◽  
Weight Range ◽  
Molecular Material ◽  
Wide Range ◽  
Soluble Fractions

Abstract Investigations carried out in Malaya have shown that rubber hydrocarbon in fresh latex is already a high molecular material but of considerable heterogeneity. Latex is separable into non-rubber constituents and rubber hydrocarbon, which is itself separable into microgel, soluble fractions covering a wide range of molecular weight, and low-molecular oxygenated fractions. The molecular weight distribution of the soluble hydrocarbon material is weighted heavily in the higher molecular weight range of half million to five million, with an average around one million. Coagulated rubber contains macrogel in addition to the microgel component of the latex. The microgel component of latex hydrocarbon has been used as a “marker” to indicate from what regions of a tree rubber is withdrawn on tapping.

scholarly journals Ring-Opening Polymerisation ofrac-Lactide Using a Calix[4]arene-Based Titanium (IV) Complex

2010 ◽  
Vol 2010 ◽  
pp. 1-6 ◽  
Author(s):  
Marco Frediani ◽  
David Sémeril ◽  
Dominique Matt ◽  
Luca Rosi ◽  
Piero Frediani ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Thermal Treatment ◽  
Microwave Irradiation ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Ring Opening ◽  
The Other ◽  
Maldi Tof ◽  
Other Hand ◽  
First Time

cone-25,27-Dipropyloxy-26,28-dioxo-calix[4]arene titanium (IV) dichloride(1)has been assessed in the ring-opening polymerisation ofrac-lactide (L,D-LA). The polymers formed (PLDA) turned out to display an isotactic stereoblock microstructure (determined by NMR) despite the fact that the catalyst hasC2vsymmetry. Two techniques were applied for initiating the polymerisation reaction, microwave irradiation, and conventional thermal treatment. The polymers obtained were all characterised by NMR, IR, HPLC-SEC, DSC, and MALDI-TOF analysis. The use of microwave irradiation, applied for the first time to calixarene-based catalysts in the presence of therac-lactide monomer, increased the polymerisation rate compared with that obtained by the other method. On the other hand, standard thermal treatment enabled a slightly better control than microwave irradiation over the molecular weight and molecular weight distribution of the polylactides formed.

Viscoelastic Characterization of Long Branching and Gel in Butadiene-Acrylonitrile Copolymer Elastomers

1980 ◽  
Vol 53 (1) ◽  
pp. 14-26 ◽  
Author(s):  
N. Nakajima ◽  
E. R. Harrell
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
General Rule ◽  
The Other ◽  
Model Systems ◽  
Newtonian Flow ◽  
Long Chain Branching ◽  
Linear Viscoelastic ◽  
Definition Of

Abstract Difficulties in relating long-chain branching to processability may be attributable to two causes: one is the definition, pertinent to processability, of what long branches are and the other is a method of determining long branching which is free from interference by other material variables, such as molecular weight distribution, gel, and “short” branches. Measurements of the dilute solution properties are tedious, time-consuming, and require skill for precision. In addition, the requirement for filtering the solution practically obliterates the result, regardless of how precise the measurement may be, because elastomers, as a general rule, have or are suspected to have an insoluble gel fraction. Recent advances in viscoelastic studies of model polymers show that the branches must be 2–3 times longer than the “entanglement coupling” distance in order to exhibit enhancement of viscosity in the Newtonian flow. Whereas Newtonian flow provides a precise definition of the long branches, it is not accessible for most of the elastomers. In the observed time scale, the linear viscoelastic properties as well as the steady-state viscosities are affected not only by branches but also by gels and molecular weight distribution. When these material variables are changed one at a time in the properly designed model systems, their effects are separately observable. On the other hand with a sample of unknown background, the effect of long branching is usually inseparable from those of other variables.

The molecular weight distribution (MWD) and the properties of polyarylate F-2 solutions produced by low temperature polycondensation

1970 ◽  
Vol 12 (6) ◽  
pp. 1484-1491 ◽  
Author(s):  
L.V. Dubrovina ◽  
S.A. Pavlova ◽  
V.A. Vasnev ◽  
S.V. Vinogradova ◽  
V.V. Korshak
Keyword(s):  
Molecular Weight ◽  
Low Temperature ◽  
Molecular Weight Distribution ◽  
Weight Distribution

Study of recycled polyethylene materials as asphalt modifiers

2006 ◽  
Vol 33 (8) ◽  
pp. 968-981 ◽  
Author(s):  
Susanna Ho ◽  
Ronaca Church ◽  
Kristel Klassen ◽  
Barkley Law ◽  
Daryl MacLeod ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Low Temperature ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Phase Distribution ◽  
Low Density Polyethylene ◽  
Low Density ◽  
Direct Tension ◽  
Bending Beam Rheometer ◽  
Asphalt Modification

There has been interest in modifying asphalt with polyethylene materials, which are a major plastic waste substance, especially low-density polyethylene (LDPE). In this study, combinations of three low molecular weight polyethylene (PE) wax materials and three recycled LDPE materials were used as asphalt modifiers. The modified asphalts were studied using the SuperpaveTM MP1 and MP1a specifications, 1% direct tension test (DTT) failure strain criteria, phase separation, and microscopy. When the molecular weight distribution of the polyethylene modifiers was widened, the bending beam rheometer thermal stress curve of the modified asphalt shifted to the low-temperature end, giving a better critical cracking temperature. Not all recycled LDPE are the same. When using recycled LDPE in asphalt modification, we have to consider the LDPE properties, such as molecular weight and molecular weight distribution, which have been found to play important roles in asphalt's low-temperature properties, hot storage stability, and polymer phase distribution. This study showed that LDPE with lower molecular weight and wider molecular weight distribution are more suitable materials for asphalt modification, compared with high molecular weight LDPE with very narrow molecular weight distribution.Key words: superpave, low-density polyethylene (LDPE), polyethylene, asphalt, recycled, bending beam rheometer (BBR), direct tension tests (DTT), molecular weight distribution, low-temperature grading.

Extraction and Partial Purification of Protease from Bilimbi (Averrhoa bilimbi L.)

2013 ◽  
Vol 10 (2) ◽  
pp. 29
Author(s):  
Normah Ismail ◽  
Nur' Ain Mohamad Kharoe
Keyword(s):  
Molecular Weight ◽  
Protein Content ◽  
Ammonium Sulfate ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Protease Activity ◽  
Protein Concentration ◽  
Temperature Stability ◽  
Partial Purification ◽  
Ammonium Sulfate Precipitation

Unripe and ripe bilimbi (Averrhoa bilimbi L.) were ground and the extracted juices were partially purified by ammonium sulfate precipitation at the concentrations of 40 and 60% (w/v). The collected proteases were analysed for pH, temperature stability, storage stability, molecular weight distribution, protein concentration and protein content. Protein content of bilimbi fruit was 0.89 g. Protease activity of both the unripe and ripe fruit were optimum at pH 4 and 40°C when the juice were purified at 40 and 60% ammonium sulfate precipitation. A decreased in protease activity was observed during the seven days of storage at 4°C. Molecular weight distribution indicated that the proteases protein bands fall between IO to 220 kDa. Protein bands were observed at 25, 50 and 160 kDa in both the unripe and ripe bilimbi proteases purified with 40% ammonium sulfate, however, the bands were more intense in those from unripe bilimbi. No protein bands were seen in proteases purified with 60% ammonium sulfate. Protein concentration was higher for proteases extracted with 40% ammonium sulfate at both ripening stages. Thus, purification using 40% ammonium sulfate precipitation could be a successful method to partially purify proteases from bilimbi especially from the unripe stage. 

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