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

✍ Scribed by Jiangtian Xu; Victoria L. Dimonie; E. David Sudol; Andrew Klein; Mohamed S. El-Aasser

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 250 KB
• Volume: 69
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(19980801)69:5<985::aid-app18>3.0.co;2-n

✦ Synopsis

The diffusion and reaction of amino-telechelic polybutadiene (PBD-NH 2 ) in poly(styrene/ n-butyl acrylate/TMI) (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-NH 2 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 NH 2 /TMI ratio. The results showed that without the PSB shell, the PSBT particles (80 nm radius) could be penetrated by the PBD-NH 2 completely. A 24 nm PSB shell was found to act effectively as a barrier to preventing the penetration of the PBD-NH 2 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-NH 2 particles provided the driving force for the chain diffusion. A diffusion model was established for the PSBT/PBD-NH 2 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-NH 2 on the PSBT particles in the latex films. A film formation and crosslinking mechanism was proposed for the PSBT/PBD-NH 2 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-NH 2 will be bound to the PSBT particle surfaces, forming a PSBT-PBD copolymer interphase. This interphase facilitates the diffusion of the PBD-NH 2 into the PSBT particles.