Molecular Weight Distribution of Two Types of Living Chains Formed during Nitroxide‐Mediated Polymerization of Styrene

2021 ◽  
pp. 2000624
Author(s):  
Kyoungho Kim ◽  
Jieun Lee ◽  
Hong Y. Cho ◽  
Eun Ho Lee ◽  
Seo‐Hui Lee ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Nitroxide Mediated Polymerization

Nitroxide-mediated polymerization of methyl methacrylate by 4,4′-dimethoxydiphenyl-based alkoxyamine

RSC Advances ◽  
2016 ◽  
Vol 6 (77) ◽  
pp. 73842-73847 ◽  
Author(s):  
Zhecheng Zhu ◽  
Guorong Shan ◽  
Pengju Pan
Keyword(s):  
Molecular Weight ◽  
Methyl Methacrylate ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Linear Increase ◽  
Narrow Molecular Weight Distribution ◽  
Nitroxide Mediated Polymerization

4,4′-Dimethoxydiphenyl nitroxide-based alkoxyamine was prepared and used to control the polymerization of methyl methacrylate. Linear increase in molecular weight with conversion and narrow molecular weight distribution was up to 65% conversion.

scholarly journals Thermal Pyrolysis of Polystyrene Aided by a Nitroxide End-Functionality Improved Process and Modeling of the Full Molecular Weight Distribution

Polymers ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 160
Author(s):  
Antonio Monroy-Alonso ◽  
Almendra Ordaz-Quintero ◽  
Jorge C. Ramirez ◽  
Enrique Saldívar-Guerra
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Molar Ratio ◽  
Pyrolysis Process ◽  
Thermal Pyrolysis ◽  
Initial Stage ◽  
The Mathematical Model ◽  
Nitroxide Mediated Polymerization ◽  
Initial Heating

A significantly improved thermal pyrolysis process for polystyrene (PS) is reported and mathematically modeled, including the description of the time evolution of the full molecular weight distribution of the polymer during its degradation by direct integration of the balance equations without simplifications. The process improves the styrene yield from 28–39%, reached in our previous report, to 58–75% by optimizing the heating ramp during the initial stage of the pyrolysis process. The process was tested at 390 and 420 °C on samples of conventional PS synthesized via free-radical polymerization (FRP) and PS with a nitroxide end-functionality synthesized via nitroxide mediated polymerization (NMP) with three levels of the nitroxide to initiator (N/I) molar ratio: 0.9, 1.1 and 1.3. The NMP-PS produced with N/I = 1.3 generates the highest styrene yield (75.2 ± 6.7%) with respect to the best FRP-PS yield (64.9 ± 1.2%), confirming the trends observed in our previous study. The mathematical model corrects some problems of a previous model that was based on assumptions that led to significant errors in the predictions; this is achieved by solving the full molecular weight distribution (MWD) without assumptions. The model provides further insight into the initial stages of the pyrolysis process which seem to be crucial to determine the chemical paths of the process and the styrene yield, as well as the influences of the initial heating ramp used and the presence of a nitroxide end-functionality in the polymer.

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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