CROSS-LINKING OF ISOCYANATE FUNCTIONAL ACRYLIC LATEX WITH TELECHELIC POLYBUTADIENE - III - APPLICATION OF A DIFFUSION-MODEL

The diffusion and reaction of amino-telechelic polybutadiene (PBD-NH2) in poly(styrene/n-butyl acrylate/TMI(R)) (PSBT) was studied. A monodi sperse poly(St/Ba/TMI) seed latex was prepared by semicontinuous emuls ion polymerization. Two core/shell latices were also prepared semicont inuously, using the seed latex as the core and poly (St/BA) as the she ll. These monodisperse latices were mixed with equivalent amounts of t he telechelic PBD-NH2 artificial latex before casting into films. The consumption of the TMI in these films was monitored by FTIR as a funct ion 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 t he 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 p articles. This was consistent with previous TEM results, indicating th at the crosslinking between the isocyanate in the PSBT particles and t he amine in the PBD-NH2 particles provided the driving force for the c hain diffusion. A diffusion model was established for the PSBT/PBD-NH2 system. Assuming steady-state diffusion, the effective diffusion coef ficients were calculated based on the experimental data. This lead to the estimation of the surface coverage of the PBD-NH2 on the PSBT part icles in the latex films. A film formation and crosslinking mechanism was proposed for the PSBT/PBD-NH2 latex blend system. In the absence o f crosslinking reactions, the two incompatible polymers tended to comp letely phase separate during the film formation. However, with the cro sslinking reactions, the PBD-NH2 will be bound to the PSBT particle su rfaces, forming a PSBT-PBD copolymer interphase. This interphase facil itates the diffusion oft he PBD-NH2 into the PSBT particles. (C) 1998 John Wiley & Sons, Inc J Appl Polym Sci 69: 985-993, 1998.