Journal of Thermal Analysis and Calorimetry, Vol. 76 (2004) 1069–1078 CHARACTERISATION OF THE COMONOMER COMPOSITION AND DISTRIBUTION OF COPOLYMERS USING CHEMOMETRIC TECHNIQUES J. Hughes * , R. Shanks and F. Cerezo Applied Chemistry, RMIT University, GPO Box 2476V, Melbourne, 3001, Australia (Received January 26; in revised form March 29, 2004) Abstract Chemometric techniques have been applied to FTIR and DSC data to correlate polymer composi- tion. Since structural differences in the polymers with only hydrocarbon structure, often cause subtle changes in spectra, the ability of chemometric techniques is required to discern these differences. FTIR spectra and thermal fractionation using DSC were measured for 28 types of polyethylenes (PE) varying in chain branching type, content and distribution. Unsupervised clustering methods such as principal component analysis (PCA) and supervised discriminant analysis were used to clas- sify the PEs according to their structural class. The DSC data was the more successful in both classi- fying PEs according to their class. Keywords: chemometrics, DSC, discriminant analysis, polyethylenes, thermal fractionation Introduction Commercial polyethylenes are marketed in three general grades; high-density poly- ethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethyl- ene (LLDPE). HDPE is a linear polyethylene with no branching. LDPE is a polyeth- ylene with both short-and long-chain branching. LLDPE is a copolymer of ethylene and 1-olefins, with short-chain branching. The densities for LLDPEs are normally about 0.920 g cm –3 . Many new polyethylenes have been prepared using typically metallocene cata- lysts, and they are now commercially available. They provide a combination of more evenly spaced branches, increased branch content, narrow branch distribution, nar- row molar mass distribution and in some cases long chain branching. Polyethylenes, with densities between 0.89–0.91 g cm –3 are called very low-density polyethylene (VLDPE) and those with densities less than 0.89 g cm –3 are called ultra low-density polyethylene (ULDPE). 1388–6150/2004/ $ 20.00 © 2004 Akadémiai Kiadó, Budapest Akadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht * Author for correspondence: E-mail: jeff.hughes@rmit.edu.au