Method for the preparation of graft polymer dispersions having broad particle size distribution without wildly fluctuating viscosities

摘要

A method for preparing graft polymer dispersions having broad particle size distribution without wildly fluc­tuating viscosities is disclosed. The method comprises:(a) preparing intermediate graft polyol disper­sions containing 30 percent by weight or less solids to achieve a broad distribution of partial sizes in a continuous process by feeding a suffi­cient amount of an ethylenically unsaturated mon­omer and a free radical initiator into a flow re­actor at a temperature sufficient to promote poly­merization, and(b) charging the intermediate graft polymer dis­persion of (a) to a semi-batch reactor as seeds for further grafting to increase the solids content of the dispersion to above 30 percent by weight by feeding an effective amount of an ethylenically unsaturated monomer and a free radical initiator into the semi-batch reactor at a temperature suf­ficient to promote the growth of the seeds, whereby the seed particles generally grow larger but retain the characteristic of broad size distribution. The graft polymer so formed is useful in the production of polyurethanes.