PU-PBMA mixtures

Sample Preparation. For each of the xx, lx, and xl mixtures, three PU PBMA compositions, 3 7, 5 5, and 7 3, were made with the 11 mixture, only the 5 5 composition was prepared. An equivalent weight ratio of 0.95 for OH NCO was maintained for the PU components a 3.5 1 (by weight) BD TMP mixture was used for the PU(x) samples. Samples containing PBMA(x) were made with a 60 1 (mole ratio) BMA TMGDM mixture. These ratios yield a calculated Me of 1700 and 4200 g/mol for the PU(x) and PBMA(x), respectively. In each mixture, 0.05 wt.%... 

A polyurethane (PU)/poly(n-butyl methacrylate) (PBMA) system has been selected for an investigation of the process of phase separation in immiscible polymer mixtures. Within this system, studies are made of the XX, lx, xl, and the 11 forms. In recognition of the incompatibility of PBMA with even the oligomeric soft segment precursor of the PU, no attempt was made to equalize the rates of formation of the component linear and network polymers. Rather, a slow PU formation process is conducted at room temperature in the presence of the PBMA precursors. At suitable times, a relatively rapid photopolymerization of the PBMA precursors is carried out in the medium of the slowly polymerizing PU. The expected result is a series of polymer mixtures essentially identical in component composition and differing experimentally only in the time between the onset of PU formation and the photoinitiation of the acrylic. This report focuses on the dynamic mechanical properties cf these materials and the morphologies seen by electron microscopy. 

The detailed investigation of this process was done using two types of semi-IPNs made of cross-linked PU and linear PBMA [202]. The difference between these two cases is that in one case the previously polymerized PBMA was introduced into the reaction mixture for PU network formation, whereas in the other case the reactions of PU formation and BMA polymerization proceeded simultaneously. PU based on POPG and TDI-TMP adduct was formed under the action of dibutyltin laurate (catalyst). The kinetics of PU network formation and BMA polymerization were studied by calorimetry. The kinetic parameters of the reaction for pure PU and for PU in the presence of the second component were found from equation of the second-order reaction ... 

The comparison of the reduced rates of PBMA formation, Wred = y/ y where V = dM/dt is the amount of unreacted monomer and M is monomer concentration, in the semi-IPN and the initial rate (Fig. 68) shows an increase in Wred of PBMA formation in the mixture with respect to the initial one (Fig. 68, curves 11 and 15b, 10 and 13, 9 and 14). This, according to [311], may be due to an increase of the initial viscosity of the semi-IPN system, which rises in the course of PU and PBMA formation, thereby sharply reducing the termination constant Kt and accordingly increasing the Kg/Kt ratio and the chain growth rate Vg with increasing completeness of reaction, according to Eq. 152. 

Figure 69 presents kinetic curves for PU and PBMA for various ratios in the mixture 85 15, 75 25, and 65 35 mass % at a constant molar concentration of the catalyst (1.4 x 10 moM ) and various initiator concentrations. Calculated W ed values for PBMA in the mixture show that the PBMA formation rate increases for experiment 19 to experiment 17 over the initial one (curves 19a, 18a, 17a), which is due to the increase in the system viscosity in experiment 17 it is higher than in experiment 19, and hence Kt decreases, while Kg and K increase. The PU formation rate in the mixture decreases compared to the initial one from experiment 17 to experiment 19 (curves 19a, 18a, 17a). 

All the potential compatibiUzers were introduced into the reaction mixture for IPN formation before the beginning of the reaction. To establish the pecuUarities of IPN formation in the presence of compatibilizers, special simultaneous kinetic investigations of the formation of PU and PBMA in IPNs were performed using differential calorimetric methods [285]. 

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