Accurate characterization of new materials is vital to verify their chemical identity and to understand their properties. However, with polymers, this can be far from trivial. Polymeric organic materials can be amorphous, crystalline, or semi-crystalline, and their physical states can range from solids to oils and gels. The presence of a range of chain lengths can further add to the complexity. In addition, solvents can have a significant impact causing swelling or contraction, affecting the surface area, surface energy, and overall polymer activity.
Guidelines for method selection
To address the challenges inherent to the characterization of polymeric materials, a combination of techniques is usually required. For good scientific practice, at least one analytical technique should give an indication of purity, and it is advisable to use at least one technique that addresses each of the following three areas:
Chemical characteristics; Including identification of functional groups, chemical bonds, intentionally and non-intentionally added chemicals and components, and intermolecular interactions.
Molecular characteristics; Including behavior in different solvents, molecular weight (MW), scattering behaviors, and crosslink density.
Bulk mechanical and dynamic properties; Including thermal properties, viscoelasticity, mechanical strength, compressibility, relaxation, and creep.
There are several analytical techniques for studying each of these areas, with the technique chosen depending on the nature of the polymer. This is useful, as in some instances a particular polymer may not give clear data under a particular testing regimen. Table 1 outlines some of the common testing techniques used to probe different aspects of a polymeric material. Usually, at least one technique from each category (chemical, molecular, and bulk level) is used.
Table 1: Commonly used analytical techniques for polymer characterization
Analytical technique | Chemical bonds* | Intra- and intermolecular interactions* | MW distribution** | Solvent properties** | Thermal behavior*** | Bulk structure*** | Bulk behavior*** |
NMR (liquid) | x | x | x | x |
| ||
FTIR | x | x |
|
|
|
| |
Raman | x | x |
|
|
|
| |
Mass spectrometry |
|
| x |
|
|
| |
SEC/GPC |
|
| x |
|
|
| |
AFM |
| x |
|
| x |
| |
TGA |
|
|
| x |
|
| |
DSC |
|
|
| x |
|
| |
Microscopy |
|
|
|
| x |
| |
NMR (Solid-state) | x | x |
|
| x |