What is the main feature of the topic?
The main feature of this topic is the Reversible Addition-Fragmentation chain Transfer (RAFT) polymerization of N-acryloyl-L-phenylalanine (A-Phe-OH) where the carboxylics acid functional group is kept intact.
Furthermore this is achieved without the use of a protecting group, such as methyl esters, as seen below. Figure 1: Preservation of Carboxylic Acid Moiety
This article further examines the effect of chain transfer agents (CTA), solvents, temperature, and initiator molar ratio on the molecular weight distribution, and determines the optimal environment for direct polymerization.
Why is this topic important?
Carboxylic acid functional groups serve many purposes they confer to the polymer the ability to interact with a variety of substances. For example
The use of amino based monomers with carboxylic acid moiety is the ability to adapt the polymers for various interactions with substances such as metal ions, non-ionic proton-accepting polymers, their derivatives, and cationic polyelectrolytes. As such these polymers can serve as a way of delivering drugs to targeted zones.
Furthermore by polymerizing the monomers without the need for protecting groups serves a much more significant purpose on an industrial size. By avoiding the use of protecting groups one can avoid added steps in the industrial process, as such reducing the opportunities for errors to occur and avoiding additional costs associated with the protecting groups, for example added operation costs, capital costs.
Results
Describe a selection of the experimental results from the three papers. Show:
The results I will be discussing is the effect of solvent and CTA on polymerization.
Article 1:
Scheme:
Figure 2: RAFT Polymerization of Acrylamide Derivatives Containing l-Phenylalanine Moiety
Table 1: Effects of Temperature and Solvent on Polymerization of N-Acryloyl-L-phenylalanine (A-Phe-OH) with AIBN in the Presence of Benzyl 1-Pyrrolecarbodithioate (CTA 2) for 24 h entry temp,
°C solvent
(vol ratio) convn
% Mn
(theory) m Mw/Mn
(SEC)
(SEC)
1 60 1,4-dioxane 97 11 500 10 500 1.42
2 60 MeOH 94 11 200 12 800 1.3
3 60 MeOH/toluene (1/1) 94 11 200 8800 1.36e
4 60 MeOH/toluene (9/1) 91 10 800 7300 1.29
5 45 1,4-dioxane 84 10 000 7100 1.45
6 45 MeOH 76 9100 6500 1.25
7 45 EtOH 63 7600 5000 1.4
8 45 MeOH/toluene (9/1) 73 8700 5700 1.26
9 45 MeOH/1,4-dioxane (1/1) 73 8700 5500 1.3
10 45 DMF 90 10 800 7200 1.35
Time-conversion (circles) and first-order kinetic (squares) plots for the polymerization of N-acryloyl-L-phenylalanine (A-Phe-OH) with 2,2-azobis(isobutyronitrile) (AIBN) in the presence of benzyl 1-pyrrolecarbodithioate in methanol at 45 °C.
Time-conversion (circles) and first-order kinetic (squares) plots for the polymerization of N-acryloyl-L-phenylalanine (A-Phe-OH) with 2,2-azobis(isobutyronitrile) (AIBN) in the presence of benzyl 1-pyrrolecarbodithioate in methanol at 60 °C.
Article 2:
Figure 2: RAFT Polymerization of Acrylamide Derivatives Containing l-Phenylalanine Moiety
Conversion-time (squares) and the first-orderkinetic plots (circles) for the polymerization of N-acryloyl-L-phenylalanine methyl ester (A-Phe-OMe) with 2,2′-azobis-(isobutyronitrile) (AIBN) in the presence of benzyl 1-pyrrole-carbodithioate in dioxane at
60 °C (a)
90 °C
Article 3: entry CTA solvent convn
% Mn
(theory) m Mw/Mn
(SEC)
1 MeOH 97 - 93000 3.34
2 CTA 1 MeOH 72 6800 7600 1.26
3 CTA 1 EtOH 47 4200 5500 1.29
4 CTA 1 DMF 89 7800 7500 1.25
5 CTA 2 MeOH >99 9300 8000 1.3
6 CTA 2 EtOH >99 9300 6900 1.29
7 CTA 2 DMF >99 9300 6400 1.25
Time-conversion (circles) and first-order kinetic (squares) plots for the polymerization of N-acryloyl-4-trans-hydroxy-L-proline (A-Hyp-OH) with 2,2′-azobis(isobutyronitrile) (AIBN) in the presence of benzyl dithiobenzoate (CTA 1, see Scheme 2) in DMF at 60 °C Discussion
Article 1: Article 2 Article 3: From the schemes we can see that all the reactions follow a RAFT polymerization with all of the articles using AIBN as the initiator.
As we can see the results from all three articles come to the same conclusions:
1. Increasing temperature increases Mw/Mn
2. A properly chosen CTA can decrease Mw/Mn
3. Increasing temperature increases the rate of polymerization
What was interesting about the articles was the large difference each variable had on the polydispersity depending on the chemical. Changing the temperature by 20 degrees Celcius caused a much large difference for the first article when compared to the second article. Summary
Overall these articles ended up with similar conclusions where the solvent, CTA and temperature had significant effects on the polydispersity index of each polymer. Furthermore by trying different combinations of each one could end up with the optimal environment for the production of a polymer. However what was interesting was that the authors did not follow a similar process for describing the optimal conditions. In Article #1 they:
1. Determined the most favourable CTA
2. Test with 2 variables, temperature and solvent.
3. Test with the free variable of CTA to Initiator ratio at different temperatures.
In Article #2 the process was
1. Determine the most favourable CTA
2. Test with the free variable of CTA to Initiator ratio at different temperatures.
3. Test with 2 variables, temperature and solvent.
In Article #3 the process, which ignored temperature as a variable, was:
1. Test with 2 variables, CTA and solvent.
2. Tests with the free variable of CTA to Initiator ratio with different solvents.
Furthermore this was all done by the same author with very similar intentions in the articles. As such a suggestion would be to have a set article structure.
In the first article it would have been easier to understand the significance of the effect of temperature on the rate of polymerization had both graphs been superimposed or closer to each other making a comparison easier, as seen in Article #2. Furthermore in Article #3 it would have been interesting to see how a temperature change would have affected the polydispersity as well as the rate of conversion. Finally it would have been much more thorough had the articles gone into depth in determining the actual optimal conditions rather than proving that the variables do affect the system at hand. References
Matsuyama, M., Mori, H., & Endo, T. (2006). RAFT polymerization of acrylamide derivatives containing L-phenylalanine moiety and pH-responsive property. Paper presented at the Polymer Preprints, Japan, , 55(1) 169.
Sutoh, K., Mori, H., & Endo, T. (2005). Controlled radical polymerization of an acrylamide containing L-phenylalanine moiety. Paper presented at the Polymer Preprints, Japan, , 54(1) 180.
Mori, H., Kato, I., Matsuyama, M., & Endo, T. (2008). RAFT polymerization of acrylamides containing proline and hydroxyproline moiety: Controlled synthesis of water-soluble and thermoresponsive polymers. Macromolecules, 41(15), 5604-5615.
