Viscoelasticity and Curing Conditions

The shift of Tg of the PBMA-enriched phase toward low temperatures depends on the PBMA formation rate. It seems that the lower is the PBMA formation rate, the more favorable are the conditions for the intermolecular interaction between forming PBMA macromolecules and the PU network being formed, and the lower is the Tg of PBMA in the semi-IPN. 

The viscoelastic behavior of the semi-IPNs obtained at the highest PBMA and the lowest PU network formation rates is somewhat unusual. The smallest Too value of the PU-enriched phase indicates a more defective structure of the network. This fact can be interpreted as follows it is possible that in this case the earlier formed PBMA phase has the form of disperse inclusions, while the PU network is formed in the presence of such a polymeric filler and, as was ascertained elsewhere [180], a more defective network structure develops in such cases. 

It seems interesting to compare viscoelastic properties of semi-IPNs obtained with the use of BMA monomer and those made of PBMA. The temperature dependencies of the mechanical losses for these systems are shown in Fig. 41. This figure shows that the method of PBMA introduction (monomer or previously prepared polymer) radically changes the semi-IPN structure and its viscoelastic properties. Of course, in all cases the semi-IPNs are incompatible heterogeneous systems, but significant changes in glass 

Knowledge of the general principles that govern the viscoelastic and mechanical properties of IPNs allows us to obtain various polymeric materials on their basis. Because of this, up to now many pubhcations have appeared where these properties are studied [203-208]. 

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