Polymer Gels

I- Purpose/Objective:

 

The purpose of this laboratory is to enable you to get molecular level of understanding on polymerization chemistry, physical crosslinking, chemical crosslinking, and the related design issues and applications. We will conduct a series of radical polymerization, photo-polymerization, physical crosslinking, and chemical crosslinking.


For the biopolymer gel experiment, we will use alginic acid. Sodium alginate (alginic acid sodium salt) will be dissolved in doubly distilled water. The solubility, diffusion, ion exchange, and physical crosslinking of this biopolymer will be explored by adjusting pH and adding various multivalent ions. We will also prepare acrylamide gels by radical polymerization of formulated acrylamide and bis-acrylamide mixture solution. The resulting gels will be used to separate protein markers with different molecular weights through electrophoresis. We will also apply photopolymerization to make smart functional polymer gels. Butyl acrylate and a custom synthesized bifunctional crosslinker will be photopolymerized by using a photoinitiator and UV irradiation. Shape memory phenomenon of the resulting polymer gel will be explored and analyzed.


This lab involves five major tasks, which we have scheduled in a sequence in order to minimize bottlenecks:

  • Biopolymer gels: physical crosslinking of alginic acid
  • Acrylamide gels: radical polymerization and chemical crosslinking of acrylamide and bis-acrylamid
  • Electrophoresis: electrophoretic separation of protein markers by using acrylamide gels
  • Photopolymerization of butyl acrylate and bifunctional crosslinkers to make a shape memory polymer
  • Shape memory transition experiment of the photopolymerized shape memory polymer

 


II - Experimental Procedure:

A. Biopolymer gels1

 

Each group will be given 2% aqueous sodium alginate solution, 2 wt% Ca(NO3)2 solution, 2 wt% NaHCO3 solution, 2 wt% CuSO4solution, 10 wt% CuSO4 solution, concentrated NH3 solution, a NaOH buffer at pH 12, and saturated NaCl solution. You will do the following experiments.

  • Precipitation and solubility: Into 2% aqueous sodium alginate solution add gradually small amount of HCl until alginic acid start to precipitate. Measure the pH of the solution when the precipitation occurs.

 

  • Alginate beads: Slowly add 5 drops of 2% aqueous sodium alginate solution to a 10 ml of 2 wt% Ca(NO3)2 solution and 2 wt% NaHCO3, respectively. Observe any changes every 5 minute for at least 30 minutes. Repeat the same ion exchange experiment by adding 5 drops of 2% aqueous sodium alginate solution to 2 wt% CuSO4 solution and 10 wt% CuSO4 solution, respectively. Observe any differences between the beads in these CuSO4 solutions.

 

  • Ion exchange: Add 10 drops of 2% aqueous sodium alginate solution into 2 wt% Ca(NO3)2 solution. Remove immediately two beads once they are formed and add them into a saturated NaCl solution. Observe any changes in the beads periodically. Take additional 6 beads from the solution and rinse the beads with doubly distilled water several times. Place 3 beads into a concentrated NH3 solution and a NaOH buffer at pH 12, respectively. Observe any changes in the beads treated with the two different bases, NH3 and NaOH.


B. Acrylamide gels2

Each group will prepare an acrylamide/bisacrylamide gel plate for electrophoresis of protein markers. Use the following information and table when preparing the gel. Group 1 will make a 9% gel, group 2 will make a 12% gel, and group 3 will make a 15% gel.

Gel Stock Solution: Tris•Cl/SDS, pH 8.45 (3.0 M Tris•Cl containing 0.3 % SDS)
Dissolve 182 g of Tris base in 300 ml of dd-water. Adjust pH with 1N HCl to 8.45. Add water to 500 ml total volume. Filter it though 0.45μl filter. Add 1.5g SDS.

Stacking buffer:
Add 357 ml of dd-water to 143 ml of the Gel stock solution.

Separating buffer:
Add 95 ml of glycerol and 55 ml of dd-water to 300 ml of the Gel stock solution.

 

 


C. Electrophoresis2

Proteins can be separated by electrophoresis in an acrylamide polymer gel plate primarily based on their molecular mass. Proteins are dissolved in a solution containing sodium dodecyl sulfate (SDS), a negatively charged denaturing agent. SDS will form a complex with a denatured protein and the net negative charge of the complex will be proportional to the molecular mass of the protein. The negatively charged complex will migrate along the electric field applied to the acrylamide gel plate. You will electrophorese a protein marker, BioLabs P7708S, by using the acrylamide gel plate prepared in the experiment described above. Observe the mobility of proteins of different molecular masses also their mobility difference in polymer gel plates with different densities.


D. Photopolymerization3

In this experiment, butyl acrylate and a custom synthesized bifunctional crosslinker will be photopolymerized by using a photoinitiator and UV irradiation. You will mix a photoinitiator, butyl acrylate, and the crossliker at a certain weight per cent and infiltrate a thin class tube with the mixture. UV irradiation for one hour on the reaction mixture in the class tube will give a solid polymer rod after removing the class tube. Observe the difference in mechanical properties of the resulting polymer rods depending on the mixing ratio of butyl acrylate and the crosslinker.


E. Shape memory experiment3,4

Shape memory phenomenon of the resulting polymer gel will be explored and analyzed. The polymer rod produced in the above experiment would be glassy in room temperature and become flexible above the melting temperature of the crosslinker. You will change the shape of the polymer rod in hot water into a temporary form. Cooling the temporary form at room temperature will fix the temporary shape. The polymer rod in the temporary shape will recover the original rod shape when it is immersed in a water bath at a high temperature.


III - Theory/Background Information:


IV - Theory/Background References:

  1. Teegarden, D.M. Polymer Chemistry, Introduction to an Indispensable Science, NSTA press, chapters 3 and 6, and section 4, 2004.; Waldman, A.S. et al. “The alginate demonstration: Polymers, food science, and ion exchange” Journal of Chemical Education 1998, 75, 1430.

  2. Stryer, L. Biochemistry 4th Ed. Freeman, NY, chapter 3, 1995.
  3. Lendlein, A.; Kelch, S. Angew. Chem. Int. Ed. 2002, 41, 2034.; Lendlein, A.; Langer, R. Science 2002, 296, 1673.; Aoyagi, T.; Miyata, F.; Nagase, Y. Journal of Controlled Release 1994, 32, 87.
  4. Osada, Y., Matsuda, A. Science 1995, 376, 219.

V- Activity Schedule:


VI -Format and Important Questions for Lab Report:

  1. This laboratory experiment consists of several separate but related tasks. List the five major tasks and describe briefly what will be done in each.
  2. Which specific polymers will be prepared in this lab? Give their repeat units.
  3. Explain two different crosslinking methods.
  4. What is electrophoresis and how does this method work for protein separation?
  5. Explain the relation between the ratio of monomer and crosslinker and the mechanical properties of the resulting polymer.
  6. Explain the mechanism of addition polymerization in terms of initiation, propagation, termination, and disproportionation.
  7. A material scientist synthesized poly(vinyl chloride)s with the following molecular weight data to make blood bags. Calculate the number average and weight average molecular weight, respectively. What is the polydispersity?



  8. What does pKa value means?
  9. Regarding the shape memory gel experiment, what kind of molecular force is designed to hold the temporary shape in this particular experiment?