Challenges in Specialty Polymer Analysis

Specialty polymers cover a wide range of molecular structures and include functionalized monomers, oligomers and polymers. Their functionalisation, molecular structural and electronic properties have been developed for highly specialised applications and as a result there are scores of complex, highly sophisticated species in this chemical category.  Applications for specialty polymers include formulated liquid coatings products (e.g. inks, varnishes and lacquers), organic electronic materials (e.g. OLEMs), formulation additives (such as surfactants, dispersants, rheology control agents), aids to polymerization, pigments and dyes. This article discusses some of the major challenges to specialty polymer characterisation.

Polymer Molecular Weight Determination for Registration Requirements

When novel polymers are presented for registration it is necessary that the number average molecular weight data is available. Frequently, performance polymers contain components of widely varying molecular weight and composition so that the generation of appropriate molecular weight data which meets the regulatory guidelines is a key component of successful new product registration, especially with regard to the presence of low molecular weight oligomers. This data is critical to the registration process and can influence which registration category will apply for a new product determining, for example, whether new products can fall into the category “polymer of low concern“. Sophisticated analytical technology is available to address these issues and these include those listed below.

• SEC (Size-exclusion chromatography) - also known as GPC, (Gel Permeation Chromatography)

• MALLS (Multi Angle Laser Light Scattering), for determination of absolute molecular weight

• SEC-MALLS

• Viscometry

• SEC-Viscometry-RALLS (Right Angle Laser Light Scattering)

• MALDI-TOF MS (Matrix-Assisted Laser Desorption / Ionization Time of Flight Mass Spectrometry)

Further Polymer Characterisation

A wealth of structural information can be obtained using Nuclear Magnetic Resonance Spectroscopy (NMR).  The monomer type, level and distribution e.g. block or random, polymer chain branching , polymer sequencing , polymer tacticity, polymer molecular weight and polymer end-groupings can all be determined or investigated using NMR.  In Example 1 ¹H and ¹³C NMR has been used to study a block copolymer.  Quantitative ¹³C NMR experiments were essential in determining the amounts of each of the major monomers present.  Also the chemical shift of the CCl₂ group of the central monomeric unit in a block helped deduce the monomer units present on either side of this group, thus enabling determination of the sequence lengths for vinylidene chloride (or ‘blockiness’ of the polymer).

Other NMR techniques can also be employed to explore specialty polymeric structures. When appropriate this can include the use of different nuclei (for example, ¹⁹F, ²⁹Si ³¹P ¹¹B, ¹⁵N, ²⁷Al) and/or the use of 2D NMR experiments including COSY, TOSCY, NOESY, ROESY and others.  Magic Angle Spinning NMR is yet another approach particularly suited to gels and soft solids.  The analysis of oligonucleotides using ¹H NMR, for example, was not very successful due to the large number of peaks observed across the spectrum from the various functional groups present.  An illustration of this can be improved is shown in Example 2; here the use of ³¹P NMR reveals how phosphorus atoms in the sample are coupled via hydrogen atoms yielding additional structural information.

Intertek Analytical Services offer a wide range of characterization capabilities allowing detailed characterization of monomers, oligomers and polymer materials.  Through the application of technologies discussed in this article Intertek Analytical Services can support process optimization, scale up, regulatory submissions and the development and manufacture of pharmaceuticals, biopharmaceuticals and polymeric pharmaceutical ingredients.

Polymers studied include a large range of performance polymers such as acrylics, polyesters, polyethers, polyurethanes and naturally derived polymers such as cellulosics, carbohydrates and polysaccharides, and biological polymers. Oligomers studied include a range of functional prepolymers, telechelic oligomers and branched oligomers of various architectures. A wide range of standard and speciality monomers are analysed in the laboratory, including functional monomers with hydroxyl, isocyanate, carboxylic acid, epoxy functionality.

Please contact Intertek now to find out if we can provide a polymer characterisation service for your organization by emailing ASGenquiries@intertek.com or visit www.intertekasg.com.