Thermal Decomposition of Dendrimer Particles
My research
The purpose of my research is to monitor the decomposition of
the dendrimer particle as it is heated to different temperatures. Infrared
Spectroscopy and Thermal Gravimetric Analysis are the two main ways to monitor
this decomposition. It is hypothesized that the data obtained from the two
methods will support each other.
What is a Dendrimer?
Dendrimers are hyperbranched polymers that have a well
defined structure characterized by three distinct features: a central core,
repetitive branching units, and terminal groups. Dendrimer particles are
usually spherical in shape and contain interior void spaces. The dendrimer is
grown outward from the central core to the terminal functional groups. As the
generation of the dendrimer increases, the number of terminal groups increases.
G4-OH, the main dendrimer used in this research, has 64 terminal groups while
the G2-OH has 16. Another distinct feature of the dendrimer is the appearance of
the amide I, II peaks (with wavenumbers of 1640 cm-1 and 1550 cm-1 respectively)
in the unique spectrums obtained from different vibrational spectroscopies such
as Infrared spectroscopy.
Source: Meijer and coworkers, Polym. Mater. Sci. Eng., 73, 123 (1995)
What happens as the dendrimer particle decomposes?
Thermal decomposition refers to a chemical reaction where a
single compound breaks up into two or more simpler compounds or elements when
heated. As the dendrimer particles are heated to higher temperatures, their
bonds, specifically their signature amide peaks, are broken.
Why use dendrimers?
One application of the dendrimer is to create metal
catalysts on the nano-scale. The metal catalysts are formed in the
interior voids of the dendrimer. Once the catalyst is formed, the dendrimer must
be removed before the catalyst can be used. One method of removal is thermal
decomposition.
Methods of monitoring the dendrimer particle decomposition
Thermal Gravimetric Analysis (TGA)
TGA examines the process of
weight changes as a function of time, temperature, and other conditions that may
be created within the apparatus. For this research project, TGA will be used to
monitor the weight loss of polymeric dendrimer particles as they are thermally
decomposed.
Infrared Spectroscopy
Infrared spectroscopy involves the absorption of infrared
light causing chemical bonds to bend and stretch. Each stretch corresponds to a
particular functional group and frequency. For example, the stretching of a
carbon-hydrogen bond occurs at a frequency of around 3000 cm-1. Thus, Infrared
Spectroscopy can be used to identify functional groups and types of bonds in a
given molecule.
The dendrimer particles have characteristic amide I and amide
II peaks that occur at 1640 cm-1 and 1550 cm-1 respectively. As the dendrimer
decomposes, the intensity of these peaks slowly decreases in the Infrared
spectrum. Once the peaks have completely vanished, the dendrimer bonds have been
fully broken.
Results
Infrared Spectroscopy
G4-OH
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| Before heating | After Heating to 150ºC |
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| After Heating to 200ºC | After Heating to 225ºC |
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| After Heating to 250ºC | After Heating to 275ºC |
*As these graphs show, the empty G4-OH dendrimer particles begins decomposing between 150-200ºC and is mostly decomposed by 275ºC. This data is taken as a reference for the Pt G4-OH dendrimer particles.
Pt G4-OH
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| Before Heating | After Heating to 150ºC |
 |
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| After Heating to 200ºC | After Heating to 225ºC |
 |
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| After Heating to 250ºC | After Heating to 275ºC |
*When compared to the empty G4-OH dendrimer particle data, it is clear that the Pt nanoparticles catalyze the decomposition process. In this case, the dendrimer particle is completely decomposed after 200ºC rather than 275ºC.
TGA
*data coming soon!