Polymerization
Source: Vy M. Dong and Jan Riedel, Department of Chemistry, University of California, Irvine, CA
Polymers are made from macromolecules, which are comp…
1. Preparation
- To a 250 mL beaker, add 3 mL (14 mmol) of sebacoyl chloride in 100 mL n-hexane.
- To a 150 mL beaker, add 4.4 g (38 mmol) of 1,6-diaminohexane in 50 mL distilled water.
- Add approximately 5 drops of a phenolphthalein solution to the 1,6-diaminohexane solution.
2. Surface Polymerization
- Overlay carefully the aqueous solution with the sebacoyl chloride solution.
- Note that a thin layer will form at the interface of the aqueous solution and the organic solution.
- Note that the added phenolphthalein will make the interface visible.
3. Collecting the Polymer
- Pull the formed polyamide film from the interface with tweezers and wrap it around a glass rod.
- Wind the polyamide on the glass rod.
- Wash the polymer with acetone and then with copious amounts of water.
- Dry the polymer at 50 °C under reduced pressure.
Synthetic polymers are not only ubiquitous in everyday life, but have numerous applications across the applied and basic sciences.
Polymerization is a process used to create macromolecular compounds known as polymers.
These macromolecules are made up of a large number of repeating units known as monomers. Materials made up of these large molecules have unique chemical, mechanical, and thermal properties.
This video will illustrate principles of polymerization, the synthesis of polyamide-6,10, and cover some applications of polymerization.
There are several ways to classify polymerization. A common way is by its growth characteristics, either chain-growth or step-growth polymerization. In chain-growth, monomers are added to the end of an ever-lengthening chain of molecules. This continues until the monomer is exhausted or growth is inhibited.
In step-growth polymerization, bi-functional or multi-functional monomers initially react to form dimers and trimers. As the reaction proceeds these compounds combine to form larger oligomers. The reaction continues until long polymer molecules are formed.
Another way to classify polymerization is based on the reaction mechanism. One category is addition polymerization, where monomers add together without the formation of a byproduct. For example, when a vinyl chloride monomer forms a free radical, it attacks other monomer molecules successively propagating a long chain molecule, known as polyvinylchloride or PVC.
In the other mechanism, condensation polymerization, molecules with complementary functional end units react, releasing a byproduct in the form of water or a small molecule. The reactants can be monomers, or higher molecular weight intermediates.
An important polymer made from this process is a polyamide, better known as nylon. In this synthesis, a dicarboxylic acid chloride condenses with a diamine to form a polyamide and releases hydrogen chloride. As the reaction proceeds, monomer is consumed to form dimers and trimers, which react to form larger oligomers. Oligomers will then condense to form large molecular weight polymers.
Now that the basics of polymerization have been covered, let's take a look at the step-growth condensation reaction of polyamide using surface polymerization; a process where polymerization occurs at the interface of a heterogeneous mixture, consisting of an aqueous and an organic phase.
First, prepare the reaction solutions for the polymerization. In a beaker, mix 3 mL of sebacoyl chloride to 100 mL hexane. In a separate beaker, add 4.4 g of 1,6-diaminohexane to 50 mL of distilled water.
Add roughly 5 drops of a phenolphthalein solution to the aqueous diaminohexane solution.
Next, carefully overlay the sebacoyl chloride solution onto the aqueous solution containing the diaminohexane. A thin layer will form at the interface of the two phases. The visibility of the layer is enhanced by the phenolphthalein.
Finally, the polymer must be collected. Using a pair of tweezers, pull the formed polyamide film and wrap it around a glass rod. Wind the polyamide onto the glass rod.
Then wash the polymer with acetone, followed by copious amounts of water. Once this is complete, dry at 50 ?C under reduced pressure.
A hollow, long strand of polyamide is obtained from this process.
Polymerization is used in many scientific and engineering applications. Here, we cover some of these applications.
Photo-polymerization utilizes light to initiate the reaction. Using masks, three-dimensional polymer structures can be fabricated in a layer-by-layer fashion. This system, which uses an off-the-shelf digital projector and photosensitive resins, can produce 3D objects with sub-100 ?m resolution, enabling fundamental studies in mechanics and materials science, and emerging fields such as tunable metamaterials.
Despite advances in the synthesis of nanoparticles, the ordered assembly of nanoparticles remains a challenge. In this application, metal nanoparticles coated in polystyrene-block-poly(acrylic acid) are polymerized into chain structures. The polymer synthesis techniques allow for the control of the length and width of nanoparticle chains.
Biocompatible polymers have become an indispensable tool in the biological sciences. For example, density gradient multilayered polymerization allows for the creation of biocompatible-layered matrices that have distinct chemical and mechanical properties. This technique enables biomedical and basic research into cellular response in complex 2-D and 3-D environments.
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Q1: What is the difference between chain-growth and step-growth polymerization?
Chain-growth polymerization adds monomers sequentially to the end of an ever-lengthening chain until monomers are exhausted or growth is inhibited. Step-growth polymerization involves bi-functional or multi-functional monomers reacting to form dimers and trimers, which combine into larger oligomers and eventually long polymer molecules.
Q2: How does addition polymerization differ from condensation polymerization?
Addition polymerization combines monomers without releasing a byproduct, such as vinyl chloride forming polyvinylchloride (PVC) through free radical propagation. Condensation polymerization involves molecules with complementary functional groups reacting and releasing a byproduct like water or hydrogen chloride, as occurs in nylon synthesis.
Q3: What happens during the synthesis of polyamide-6,10?
A dicarboxylic acid chloride condenses with a diamine, releasing hydrogen chloride as a byproduct. Monomers are consumed to form dimers and trimers, which react to form larger oligomers. These oligomers then condense to form high molecular weight polyamide polymers through step-growth condensation.
Q4: What is surface polymerization and how is it used in nylon synthesis?
Surface polymerization occurs at the interface between heterogeneous phases—an aqueous and organic layer. In nylon synthesis, sebacoyl chloride in hexane is overlaid onto an aqueous diaminohexane solution. A thin polymer film forms at the interface and is collected by wrapping around a glass rod, then washed and dried.
Q5: How does photo-polymerization enable three-dimensional object fabrication?
Photo-polymerization uses light to initiate polymer reactions. Masks and photosensitive resins allow layer-by-layer fabrication of three-dimensional structures with sub-100 micrometer resolution. This technique enables fundamental studies in mechanics and materials science, and emerging fields such as tunable metamaterials.
Q6: What role do biocompatible polymers play in biological research?
Biocompatible polymers are indispensable tools in biological sciences. Density gradient multilayered polymerization creates biocompatible-layered matrices with distinct chemical and mechanical properties. These matrices enable biomedical and basic research into cellular response in complex two-dimensional and three-dimensional environments.
Q7: How are metal nanoparticles assembled using polymer synthesis techniques?
Metal nanoparticles coated in polystyrene-block-poly(acrylic acid) are polymerized into chain structures. Polymer synthesis techniques allow precise control of the length and width of nanoparticle chains, addressing the challenge of ordered assembly of nanoparticles in materials science applications.