Polymer Chemistry Course, KTE 080, 2014
Laboratory procedures in
Polymer & Materials Chemistry
1. Free Radical Bulk Polymerization of Styrene
This protocol describes the bulk polymerization of styrene at 60 oC using 2,2´azobisisobutyronitril (AIBN) as an initiator. The monomer styrene first has to be purified before it can be used. The purification is performed in order to remove inhibitors and impurities, which can have a detrimental effect on the reaction. Styrene is purified by passing the monomer through a column of activated basic aluminum oxide and by this treatment the inhibitors and impurities are adsorbed. The styrene used in this laboratory experiment has already been purified in this way, and has then been kept in a refrigerator to prevent thermal auto-initiation of the monomer.
In total 8 mL of the desired mixtures of initiator and styrene and pure styrene are added to reaction test tubes provided with glass stopcocks. A typical initiator concentration is around 1-8 g/L. The test tubes are shaken in order to properly homogenize the mixtures. Next, the tubes with the glass stopcock are secured with springs. In order to purge (remove) the oxygen, which will otherwise interfere with the polymerization, the tubes are evacuated using a vacuum connection, and are then filled with pure nitrogen gas. This process is repeated three more times to make sure that all the oxygen has been removed.
The polymerization reactions are performed in a heated water bath at 60 C for 2 hours. Note the exact reaction time in seconds! After 2 hours the polymerization is stopped by immersing the test tubes in an ice bath. The contents in the tubes are dissolved in 40 mL of toluene and the different polymers are then precipitated by adding the solutions slowly, drop-by-drop, into 400 mL of methanol under vigorous stirring. It is very important that the solution is added dropwise slowly to the methanol so that a fine polymer precipitate is formed! Styrene is soluble in methanol, while polystyrene is not. If the solution is added too quickly, monomeric styrene will be captured in the polystyrene, which will lead to the formation of a monomer-swollen lump of polymer, which in turn will cause much trouble in the next step. In order to obtain an appropriate drop rate, a separation funnel should be used. The precipitate is first collected by filtering off the precipitate using a glass filter crucible (weighed) and thoroughly washed with methanol and after that dried in an oven at 50C until a constant weight is achieved. Note the final weight of the samples. The dried samples are placed in marked vials and are kept for further analysis. Polymer solutions for analysis by size-exclusion chromatography should be prepared at least 24 hours prior to the analysis.
2. Free Radical Copolymerization of Styrene and Butyl
This protocol describes the bulk copolymerization of styrene and butyl methacrylate at 60 oC using 2,2´-azobisisobutyronitril (AIBN) as an initiator. The monomers first have to be purified before they can be used. The purification is performed in order to remove inhibitors and impurities, which can have a detrimental effect on the reaction. The monomers are purified by passing them through columns of activated basic aluminum oxide and by this treatment the inhibitors and impurities are adsorbed. The monomers used in this laboratory experiment have already been purified in this way, and have then been kept in a refrigerator to prevent thermal auto-initiation.
In total 8 mL of the desired mixtures of initiator, butyl methacrylate, and styrene are added to marked reaction test tubes provided with glass stopcocks. It is also suitable to homopolymerize styrene in one of the tubes. The initiator concentration should be kept constant in these experiments, and a suitable concentration is around 4 g/L. The test tubes are shaken in order to...
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