Polymer membranes plasticization behaviour

Plasticization behaviour induced by condensable gases and vapours (e.g. carbon dioxide, hydrocarbons and other organic vapours) in polymer membranes is stiQ a painful problem in polymeric membrane-based gas separation applications [27,28]. Recently, novel hyperbranched polyimides were prepared from telechelic polyimides and an attempt was made to improve its gas separation performance and physical stability by obtaining plasticization-resistant materials [29-33] (see e.g. Chapters 4, 6 and 7 of this book). 

The mobility of polymer chains is larger for their polymer terminal chain ends as compared to that for the sections of macromolecules inside main chains. Therefore, plasticization may occur more easily around the polymer chain ends than in the polymer main chains. Moreover, if the number of polymer chain ends were minimized in a membrane, plasticization would be prevented. It is the hyperbranch structure that can create such behaviour in the case of rigid polymer chains. 

It is generally accepted that mass transport in dense polymer membranes takes place according to the well-known solution-diffusion mechanism [18,19]. For non-swelling and non-plasticizing species the amount of penetrant that can dissolve in the glassy polymer matrix depends on the available sorption sites and often a typical dual mode sorption behaviour is observed [20]. The number of Langmuir sorption sites is strongly related to the free volume distribution of the sample. 

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