Effect of Small Molecule Antiplasticisers

Some small molecule additives, called antiplasticisers, miscible with BPA-PC, lead to an increase of both modulus and yield stress at room temperature [14, 15]. In contrast, the toughness and the elongation at break decrease. 

It has been recognised for a long time that the antiplasticisers induce a decrease of the f3 transition peak intensity [16]. 

Such an effect of small molecule antiplasticiser is not specific to BPA-PC. It seems to occur with most polymers undergoing a transition originating from motions in the main chain. In the present paper, the effects of antiplasticisers on the f3 transition of poly(ethylene tere-phthalate) and epoxy networks are analysed in Sects. 4 and 7, respectively. 

One of the most efficient antiplasticiser for BPA-PC is Aroclor 1254, which consists of a polychlorinated bi-phenyl with five chlorine substituents it will be denoted AP. The results reported here deal with this additive. 

Dependence of the dynamic mechanical tan 8 on temperature [17] is shown in Fig. 70 for pure BPA-PC and for mixtures with 10 and 30wt% AP. 

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Furthermore, the effect of miscible small molecule additives, antiplasticisers, on the secondary transition, is worth analysing in order to reach a deeper understanding of the involved molecular motions. 

It appears that it is mostly the high-temperature part of the fi transition which is suppressed, leading to a downward shift of the peak maximum. As presented in Fig. 71, the strength of the fi relaxation, expressed by the area under the dynamic mechanical loss, peak, Rsec, decreases much more rapidly with increasing the AP concentration that it should according to a dilution effect. It is worth pointing out that a similar behaviour has been reported, a long time ago, on the same system [53] and is encountered in BPA-PC-antiplasticiser mixtures, irrespective of the specific nature of the antiplasticiser small molecule [16,17,53,54]. 

In a way similar to that described for polyethylene fere-phthalate (Sect. 4.2), some antiplasticiser small molecules with a specific chemical structure are able to affect the ft transition and the yield stress of epoxy resins, but they do not have any effect on the y transition. In the case of HMDA networks, an efficient antiplasticiser, EPPHAA, whose chemical structure is shown in Table 8, has been reported [69]. The investigation of such antiplasticised epoxy networks by dynamic mechanical analysis as well as solid-state NMR experiments [70] can lead to a deeper understanding of the molecular processes involved in the ft transition and of their cooperativity. 

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