NMR

Determination of the Polyoxyethylene(POE) Percentage in Poloxamers

Background

Application Note 3Poloxamers are an important category of polymers with significant applications in industry, especially forpharmaceutical, cosmetic and personal care products.The most common uses are related to its surfactantproperties. In the cosmetics and personal care products, Poloxamers are used for various formulations
including mouthwashes, lens cleaning solutions, skin cleansers, shampoos and conditioners. In thepharmaceutical industry, Poloxamers are used as suspension and emulsifying agents, coating materialsand importantly as components of drug delivery systems. The United States Pharmacopeia and The
National Formulary (USP–NF) specifies 5 different types of poloxamers with different chain lengths of x and y (see Figure 1).
Poloxamers are non-ionic block copolymers comprising aAnalysis

central polyoxypropylene block flanked by two polyoxyethylene

The method for performing the NMR analysis involves

blocks (figure 1). The central block is hydrophobic while thecollecting a 1-dimensional 1H spectrum and integrating theflanking blocks are hydrophilic resulting in a polymer which is anregion around 1.1 ppm (region 1) corresponding to the -CH3

amphiphile and suitable for use as a non-ionic surfactant. The

group on the polyoxypropylene block and the region aroundamphiphilic character of the polymer is dependent on the chain

3.7 ppm (region 2) corresponding to the -CH2- and -CH-

lengths and can be tailored for specific applications.

groups on all three blocks.
The percentage of polyoxyethylene in the polymer
can be evaluated from 3300a / (33a𝛼+  58)where a = (I2 / I1) – 1 and I1 and I2 are the integrals of region
one and two respectively.

Figure 1: Structure of generic poloxamer

The method relies on integrating regions of the spectrum
containing multiple peaks, but does not require that thesePoloxamers are identified by their poloxamer number whichpeaks are fully resolved, simply that region one and region two

takes the form “P abc”, where the number ab multiplied by

are well separated.

100 is the mass per mole of polyoxypropylene in the polymer
and c multiplied by 10 is the percentage of polyoxyethylene.

Figure 2 shows the 1H spectrum of poloxamer 188 acquired atFor example, poloxamer p188, contains 1800 g/mol

1.4 T, 1H resonance frequency of 60 MHz. The data is a single

polyoxypropylene and 80% polyoxyethylene.

scan collected over a large spectral width, 5.2 KHz with 64K
complex data points that are zero filled on acquisition. Thespectrum shows that the two integral regions are sufficiently
well separated to allow integration.

Figure 2: 1H spectrum of poloxamer 188 in CDCL3

The results of integrating the spectra of four commercially available
poloxamers are given in table 1. The reproducibility of the NMR results wasdetermined by collecting 16 spectra for each sample and calculating the% of polyoxyethylene from each data set. An average value and standard
deviation were determined from these results. The estimate show excellent
comparison with the values implied by the poloxamer.

NamePoloxamer number% POE(NMR)% POE(p-number)

Kolliphor P188

P 188

82.1 ± 0.680

Kolliphor P407

P 407

72.4 ± 0.470

Pluronic F127

P 367

73.8 ± 0.670Synperonic F108P 308

83.4 ± 0.880

Table 1: % of polyoxyethylene in a poloxamer determined by NMR at 60 MHz.
The numbers are compared to the values associated with the poloxamer number.

visit nmr.oxinst.com/x–pulse for more information or email magres@oxinst.com

5201

This publication is the copyright of Oxford Instruments plc and provides outline information only, which (unless agreed by thecompany in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or regarded as
the representation relating to the products or services concerned. Oxford Instruments’ policy is one of continued improvement. Thecompany reserves the right to alter, without notice the specification, design or conditions of supply of any product or service. Oxford
Instruments acknowledges all trademarks and registrations. © Oxford Instruments plc, 2019. All rights reserved. Part no: PO-AN-0919