Determination of the Molecular Weight of Polymers

The molecular weight of the polymer is an extremely important variable, which represents the average value of the distribution of various constituent molecules with different chain lengths included in the whole polymer. The molecular weight of the polymer directly affects its physical properties of the polymer. NMR provides a simple, convenient, and fast analytical method for polymer characterization.

As an expert in the field of nuclear magnetic resonance, Creative Biostructure can conduct routine determination of number-average molecular weight (Mn) analysis for polymers with Mn value below 3000 based on ¹H NMR technology.

¹H NMR has the following advantages in the application of molecular weight analysis of polymers：

The signal intensity of ¹H NMR is not affected by different nuclear superheat effects;

Similarly, the signal response is not sensitive to the dipole relaxation rate;

The chemical shifts of some groups in ¹H NMR spectra are better resolved;

The signal-to-noise ratio in ¹H NMR is usually better.

Our Principles

The principle of using ¹H NMR to determine the molecular weight of polymers is that in the ¹H NMR spectra of polymers, the occupied area of protons of monomer units at specific chemical shifts reflects the whole molecule.

Compared with the standard proton, each proton of a given monomer occupies a fixed area, so the total number of such protons at a fixed chemical shift can be calculated from the peak area of a specific shift. The total number of protons that can be obtained from a specific monomer can easily calculate the number of repeated units of the polymer.

Prerequisites of Our Service

We will consider the following conditions to determine whether the polymer to be tested meets the technical conditions of ¹H NMR spectrum:

• In the ¹H NMR spectrum, the intensity peak area generated by the same kind of proton at a specific chemical shift should be additive.
• The proton peaks in different groups should not overlap (however, when the molecular weight of the polymer is large, there is a possibility of overlap.)
• The proton resolution of different segments of the copolymer should be similar.

Our Methods for Determination of Mn

We have three methods to determine polymer Mn.

Method 1

By introducing a characteristic terminal group with a known number of protons. After introducing a group with known proton number at the end of the polymer, the strength of different protons in the polymer monomer unit at different chemical shifts is compared with the strength of known protons, so as to calculate the total number of protons in the polymer.

Method 2

By using a specific single group with a fixed number of protons as the internal standard. When the polymer contains a single group with a fixed number of protons, these protons can be used as the internal standard for the determination of DP by ¹H NMR spectroscopy.

Method 3

The peak area at the corresponding chemical shift is expressed according to the total number of two or three specific types of prominent protons, and the equation is solved. Sometimes the peak in the H-NMR spectrum of the polymer is very prominent, so it can be clearly expressed by the proton number of the monomer under the corresponding chemical shift.

Creative Biostructure is committed to providing high-quality NMR analysis services to advance the life sciences fields. If you have any questions or needs, please contact us and our customer service staff will help you the first time.

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