30 CHROMATOGRAPHY
SUCCESS GPC system
Regina Roemling describes a tool to determine the process property relations in polymers
G
el permeation chromatography (GPC) coupled to a differential refractive index (RI) detector is the most widely used analytical technique for obtaining molar mass averages and distributions of polymers. Te excellent reproducibility of GPC analyses on the EcoSEC GPC system, together with the dedicated calculation software enable the precise determination of the molar mass of a polymer. Tis allows establishing direct relations between the degree of polymerisation and the molar mass, leading to the characterisation of process properties. Traditionally, molar mass averages and distributions are obtained via a peak position calibration involving a series of standards of known molar mass analysed by GPC with RI detection. GPC/ RI continues to be heavily employed as it provides excellent day-to-day reproducibility and is ideal for quality control procedures.
PVC case study Polyvinyl chloride (PVC) is a thermoplastic polymer that has the property of softening under temperature and hardening when cooled. Te average molecular weight and the molar mass distribution (MMD) of PVC extensively influence its properties. Te number of monomer units in a polymer chain is referred to as the degree of polymerisation (DP). Synthetic polymers always comprise a set of macromolecules of varying DP and respectively varying molecular weight. In general, increasing DP values correlate with higher melting temperature and higher mechanical strength. Te molar mass averages
www.scientistlive.com Fig.1. Molar mass distributions. PVC 6 (DP = 620-660) and PVC 13 (DP = 1270-1370)
and molar mass distributions of two PVC samples, PVC 6 (DP = 620-660) and PVC 13 (DP = 1270-1370), were determined via a dual flow RI detector using the EcoSEC GPC system and semi-micro TSKgel GPC columns in THF. Each sample was injected three times with excellent reproducibility. Fig. 1 depicts the differential and cumulative distributions of molar masses. Even though the amount of crystalline
regions of PVC is low, many researchers study the crystallisation behaviour. Te crystallinity of PVC is inversely proportional to molar mass. PVC 6 showing a low molar mass indicating a higher crystallinity is attractive for the production of rigid plates, blow bottles,
injection moulding, etc. Because the tensile strength decreases with increasing molar mass, PVC 13 can be used for flexible films, sheets, artificial leathers, wires, cables and tapes.
Results show the value of the tool GPC analysis revealed the direct relationship between the degree of polymerisation (DP) and the molar mass of PVC 6 and PVC 13. It is a great tool to investigate the process property relations in polymers.
Regina Roemling is with Tosoh Bioscience.
www.tosoh.com
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