Crosslinking of isocyanate functional acrylic latex with telechelic polybutadiene. III. Application of a diffusion model

摘要

The diffusion and reaction of amino-telechelic polybutadiene (PBD-NH2) in poly(styrene-butyl acrylate/TMI(R)) (PSBT) was studied. A monodisperse poly(St/Ba/TMI) seed latex was prepared by semicontinuous emulsion polymerization. Two core/shell latices were also prepared semicontinuously, using the seed latex as the core and poly (St/BA) as the shell. These monodisperse latices were mixed with equivalent amounts of the telechelic PBD-NH2 artificial latex before casting into films. The consumption of the TMI in these films was monitored by FTIR as a function of time and the NH2/TMI ratio. The results showed that without the PSB shell, the pSBT particles (80 nm radius) could be penetrated by the PBD-NH2 completely. A 24 nm PSB shell was found to act effectively as a barrier to preventing the penetration of the PBD-NH2 inside the particles. This was consistent with previous TEM results, indicating that the crosslinking between the isocyanate in the PSBT particles and the amine in the PBD-NH2 particles provided the driving force for the chain diffusion. A diffusion model was established for the PSBT/PBD-NH2 system. Assuming steady-state diffusion, the effective diffusion coefficients were calculated based on the experimental data. This lead to the estimation of the surface coverage of the PBD-NH2 on the PSBT particles in the latex films. A film formation and crosslinking mechanism was proposed for the PSBT/PBD-NH2 latex blend system. In the absence of crosslinking reactions, the two incompatible polymers tended to completely phase separate during the film formation. However, with the crosslinking reactions, the PBD-NH2 will be bound to the PSBT particle surfaces, forming a PSBT-PBD copolymer interphase. This interphase facilitates the diffusion oft he PBD-NH2 into the PSBT particles. (C) 1998 John Wiley & Sons, Inc J Appl Polym Sci 69: 985-993, 1998. [References: 5]