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.

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.

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.

scholarly journals Molecular Weight Distribution of Kerogen with MALDI-TOF-MS

2020 ◽  
Author(s):  
Hyeonseok Lee ◽  
Mohammadreza Shokouhimehr ◽  
Mehdi Ostadhassan ◽  
Bo Liu ◽  
Arash Abarghani
Keyword(s):  
Mass Spectrometry ◽  
Molecular Weight ◽  
Organic Matter ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Rate Of Change ◽  
Molecular Structures ◽  
Thermal Maturity ◽  
Maldi Tof ◽  
Fine Grain

<p>Kerogen is an amorphous organic matter (AOM) in fine grain sediments, which produces petroleum and other byproducts when subjected to adequate pressure and temperature (deep burial conditions). Chemical characteristics of kerogen by considering its biogenic origin, depositional environment, and thermal maturity has been studied extensively with different analytical methods, though its molecular structure is still not fully known. In this study, conventional geochemical methods were used to screen bulk rock aliquots from the Bakken Shale with varying thermal maturities. Organic matter was isolated from the mineral matrix and then a mass spectrometry method was utilized to quantify molecular weight distribution (MWD) of four different kerogens at various thermal maturity levels (immature to late mature). Furthermore, to complement mass spectrometry, Fourier transform infrared (FTIR) spectroscopy was employed as a qualitative chemical and structural investigation technique. The MWD of four samples was obtained by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, and the results are correlated with the absorption indices (CH<sub>3</sub>/CH<sub>2</sub> ratio and aromaticity) calculated from the FTIR attenuated total reflectance (ATR) method. The results showed when the degree of maturity increases, the aliphatic length shortens, and the branching develops, as well as the aromatic structure becomes more abundant. Moreover, based on the MWD results, higher maturity kerogen samples would consist of larger size molecular structures, which are recognized as more developed aromatic, and aliphatic branching stretches. The combination of infrared spectroscopy (AFT-FTIR) and mass spectrometry (MALDI-TOF) provided MWD variations in kerogen samples as a function of maturity based on varying absorption indices and revealed the rate of change in molecular mass populations as a function of thermal maturity.</p>

scholarly journals Assessment of the Molecular Weight Distribution of Tannin Fractions through MALDI-TOF MS Analysis of Protein−Tannin Complexes

2007 ◽  
Vol 79 (6) ◽  
pp. 2239-2248 ◽  
Author(s):  
C. Mané ◽  
N. Sommerer ◽  
T. Yalcin ◽  
V. Cheynier ◽  
R. B. Cole ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Maldi Tof Ms ◽  
Maldi Tof ◽  
Ms Analysis ◽  
Tof Ms
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