units (Figure 5-2). The 1H NMR spectrum of the hydrosilylated PB revealed a strong decrease in the intensity of the signal corresponding to the -CH=CH2 (3 = 4.9 ppm) protons. Furthermore, the appearance of intense peaks at 3 = 1.2 and 3.8 ppm corresponding respectively to the -Si- OCH2CH3 methyl protons and the -Si-OCH2CH3 methylene protons is indicative of a high degree of conversion. However, some pendant double bonds remained unreacted after hydrosilylation (Figure 5-3). Based on the integration values of the signals at 3 = 4.9 and 5.4 ppm, a conversion of 75 % of the 1,2-PB pendant double bonds was found, assuming that triethoxysilane reacts predominantly with the 1,2-PB units as previously demonstrated.221 This result was confirmed by FTIR spectroscopy as shown in Figure 5-4, where the absorbance peaks at 3100 cml (=CH2 anti-symmetric stretch) and 1640 cm-l (alkenyl -HC=CH2 Stretch) strongly decreased in intensity after hydrosilylation. 5.2.1.2 Cross-linking reaction at the A/W interface After characterization of the PB68-CO-PB(Si(OEt)3)136 triethoxysilane-functionalized PB, its A/W interfacial cross-linking by self-condensation of the triethoxysilane groups was studied. This 2D acid-catalyzed condensation reaction involves two different steps as shown in Figure 5- 5: hydrolysis of the ethoxy groups with elimination of ethanol, followed by condensation between the resulting silanols. Several isotherms were first recorded after different reaction times (subphase pH = 3.0) as shown in Figure 5-6 with a fast barrier compression speed (100 mm/min) to prevent additional cross-linking during monolayer compression. As the reaction time is increased, the isotherms shift toward the low mean molecular area region because of the irreversible loss of ethanol and water molecules into the water subphase during the hydrolysis and condensation steps, respectively. As shown in Figure 5-7, the monolayer's static elastic modulus E, (calculated from Equation 3-1101) significantly increases versus reaction time,