Molecular Characterization of Commercial Polymers

In the frame of the activities of IUPAC Macromolecular Division, samples of different commercial polymers have been sent to different laboratories in order to measure their molecular properties; molecular weights, molecular weights distribution, viscosity index, degree of branching and stereoregularity. The purpose of this work was to compare results obtained in different locations, not as it was done before on well defined monodisperse systems but on samples with broad distribution and in some cases branches. This report is a summary of the result collected on polystyrene, polyvinylchloride, low and high density polyethylene. It shows that there is a good agreement on viscosity values for all the samples. As for molecular weights, the agreement is good for polyvinylchloride, less good for polystyrene and very poor for polyethylene. Some explanations are proposed for these discrepancies but further work must be done in order to obtain better results. Two years ago the Division of Macromolecular Chemistry of the IUPAC decided to have a study made of a certain number of samples by laboratories which specialize in the characterization of polymers. The two main reasons for the study were: (1) It was essential to see if the same techniques used in different laboratories led to the same results; (2) It was interesting to compare different methods and to see if they led to similar conclusions and if, from this fact, one obtained precise information on certain characteristics of these samples (molecular parameters, degree of branching, stereoregularity, etc. ...). After discussions within the framework of the Division of Macromolecular Chemistry as well as within the framework of the Working Party on 'The Relationship of Performance Characteristics to Basic Parameters of Polymers' organized by Dr Barrett, it seemed to us preferable to carry out this study on commercial samples rather than on samples prepared under optimum conditions, that is as monodispersed as possible and not presenting ramifications. This decision was made in order to have conditions similar to those which industrial laboratories have to face, and to allow comparison of the measurements of polydispersity. Besides a similar study had already been undertaken by the IUPAC a few years ago on monodispersed samples of polystyiene1; we thought, therefore, that recent technical improvements might allow more complex problems to be solved.