NMR

Determination of the Polyoxyethylene(POE) Percentage in Poloxamers

Background

Application Note– Pulsar 003

Poloxamers 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 materials
and 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
blocks (figure 1). The central block is hydrophobic while theThe method for performing the NMR analysis involves

flanking blocks are hydrophilic resulting in a polymer which is ancollecting a 1-dimensional 1H spectrum and integrating theamphiphile and suitable for use as a non-ionic surfactant. The

region around 1.1 ppm (region 1) corresponding to the -CH3

amphiphilic character of the polymer is dependent on the chaingroup on the polyoxypropylene block and the region around

lengths and can be tailored for specific applications.

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

Poloxamers are identified by their poloxamer number whichcontaining multiple peaks, but does not require that thesetakes the form “P abc”, where the number ab multiplied bypeaks are fully resolved, simply that region one and region two

100 is the mass per mole of polyoxypropylene in the polymer

are well separated.

and c multiplied by 10 is the percentage of polyoxyethylene.
For example, poloxamer p188, contains 1800 g/mol
polyoxypropylene and 80% polyoxyethylene.

Figure 2 shows the 1H spectrum of poloxamer 188 acquired at
1.4 T, 1H resonance frequency of 60 MHz. The data is a single
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 wasOxford Instruments
Industrial Analysis

determined 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 ± 0.670

Synperonic 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.

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