PDMS-CAB IPNs

The absence of phase segregation has been confirmed by DMTA measurements. Indeed, PDMS/CAB IPNs show only one mechanical relaxation lying between those of the single CAB and PDMS networks (Fig. 1). 

In order to check whether the mechanical properties of the PDMS network are really improved by the CAB network introduction in a final IPN material, the stress-strain curves of PDMS/CAB IPNs with different compositions were recorded (Fig. 2). The PDMS and CAB single networks break when less than 10 and 5% strains are applied respectively. On the other hand, the elongation at break is over 150% for the PDMS/CAB (50/50) IPN. Thus, the poor mechanical properties of the PDMS... 

Fig. 2 Stress-strain curves of PDMS (a) and CAB (e) single networks and of PDMS/CAB IPNs with different compositions (b) 75/25, (c) 50/50 and (d) 25/75. Deformation rate Imm.min" -T=35°C.[16]...

These results summarize a large amount of work carried out in our laboratory on polysiloxane based Interpenetrating Polymer Networks (IPNs). First, a polydimeth-ylsiloxane (PDMS) network has been combined with a cellulose acetate butyrate (CAB) network in order to improve its mechanical properties. Thanks to a perfect control of the respective formation rates of networks it has been possible to avoid polymer phase separation during the IPN synthesis. Indeed, PDMS/CAB IPNs are transparent and only one mechanical relaxation was detected by DMTA measurements which are characteristic of trae IPNs. In addition, a synergy effect is observed on the stress-deformation curves. Second, a PDMS network was combined with a fluorinated polymer network and the resulting IPNs can also be considered as true IPNs. In this case, a synergy of the surface properties was displayed. 

First, PDMS network was combined to a cellulose acetate butyrate (CAB) network into an IPN architecture in order to improve the thermomechanical properties of PDMS network (Scheme 1). The linear CAB can be cross-linked through its free OH groups with a Desmodur N3300 pluri-isocyanate. The alcohol/isocyanate reaction is catalyzed by DBTDL leading to urethane cross-links. Simultaneously, PDMS oligomers must be cross-linked independently in order to form the PDMS network. In order to carry out independent cross-linking reactions. 

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