| 摘要 |
1344060 Suspension polymerizing vinyl aromatic monomers BP CHEMICALS Ltd 14 June 1971 [19 June 1970] 29796/70 Heading C3P A process for producing non-spherical polymer particles containing not more than about 20% by wt. of spherical particles comprises (1) suspending a vinyl aromatic monomer as an aqueous solution of sufficient hydroxyethyl cellulose to maintain a stable suspension until at least 40% of the monomer is polymerized, but insufficient to maintain a stable suspension until complete conversion, (2) polymerizing the stably suspended monomer to at least 40% but less than complete monomer conversion, (3) adding sufficient hydroxyethyl cellulose and/or water to maintain a stable suspension until complete monomer conversion and. (4) continuing the polymerization. The preferred monomer is styrene. Preferably 0À02 to 0À05% by wt. (based on the monomer) of hydroxyethyl cellulose is added in stage (1), and 0À05 to 1À0% by wt. (based on the monomer plus polymer) in stage (4). The weight ratio of monomer plus polymer throughout the polymerization is suitably from 1 : 2 to 2 : 1. The temperature is preferably kept below 100‹ C. during the first polymerization stage and raised above this in the second polymerization stage. Examples are given, in which the initiator is a mixture of benzoyl peroxide and t-butyl perbenzoate, and stearic acid is present. The particles produced are flattened spheres. In one example hydroxyethylcellulose is added in stage 3 and in the other example water is added. |
