PREPARATION OF POLYURETHANE MICROCAPSULES BY INTERFACIAL POLYCONDENSATION

The preparation of polyurethane capsules by interfacial reaction of di -and multiisocyanates (dissolved in toluene) and different di-and trio ls (dissolved in the aqueous phase) is investigated. Particular attent ion was paid to obtaining high yields and good mechanical resistance. The experimental conditions were chosen in order to obtain large capsu les in the diameter range 50-400 mu m since it is expected that for mi crocapsules prepared according to the same procedure, the mechanical r esistance will be still higher. Observations by optical and electronic microscope demonstrate that the wall structure is of the same type as for polyamide microcapsules with an internal dense layer of thickness about 0.6 mu m at the water side and a porous layer of about 2 mu m a t the organic side. The results show that the kinetics of capsule form ation are strongly dependent on the temperature reaction. Clean and su pple capsules presenting a smooth external surface are obtained when u sing moderate amounts of crosslinking agents and short poly(ethylene g lycol)s as diol. In these conditions, the porous structure of the wall is finer and more homogenous and the capsules am sufficiently supple to allow deformation without breakage. (C) 1998 Elsevier Science Ltd. All lights reserved.