Nowadays, polymeric materials are inescapable in our modern societies and cover a broad range of applications in areas such as automobiles, textiles, packaging, medical and pharmaceutical, to name just a few. This increasing complexity in applications has driven the need to produce new, and often highly complex, polymeric materials. Accurate and detailed sample characterisation is vital to this process.It is predicted that the 3D structure of a polymer will have functional importance as synthetic polymers become increasingly sophisticated. Traditional techniques used by the polymer industry cannot measure 3D shape, which is greatly influenced by the flexibility of the polymer chain.Travelling wave ion mobility separations coupled with quadrupole time-of-flight (QTof) mass spectrometry provide unique capabilities for 3D shape characterization.Different polymers were prepared for analysis; a random and a block co-polymer containing poly ethylene glycol (PEG) and poly propylene glycol (PPG) repeat units and a polylactide. Samples were introduced to the electrospray source of a SYNAPT G2 HDMS instrument via direct infusion. Ion mobility data were processed using MassLynx v4.1 and DriftScope v2.6.DriftScope can be used to generate mobility plots that display mass to charge ratio on the x-axis, drift time on the y-axis, and ion intensity represented by color. If we observe a roughly straight, diagonal line in the mobility plots this tells us that as the polymer increases in mass there is a predictable relationship with its size. A bend, or a kink, in the ion series indicates that as the polymer increases in mass the 3D arrangement of the polymer chain changes and possibly folds back on itself.Both co-polymer samples contained PEG and PPG repeat units and had an average molecular weight of approximately 2000 Da. For the block co-polymer, the area with the highest ion intensity runs roughly diagonally across the plot. This is in contrast to the random co-polymer where we see a greater number of bends, or kinks, in the ion series. This means that we can draw some conclusions about the 3D structure and flexibility of the two polymers. The block co-polymer has the most linear relationship between mass and shape.Recently, academic research has been carried out on polylactides to determine the degree of polymerization at which the folding occurs, for a given charge state. Calibrating the mobility cell with a known standard allows collision cross section areas to be calculated. This information can then be used to confirm calculated 3D structures for the polymer at various degrees of polymerization and charge state.

Using ion mobility for "shape-selective" characterization of polymers

247th National Meeting (2014)

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