Esters of terephthalic acid

Polyethylene terephthalate is prepared by polymerizing bis-(hydroxyethyl) terephthalate obtained by heating together terephthalic acid, ethylene glycol and bis-(hydroxyethyl) terephthalate, the latter having been present at the start of the reaction. In an example bis(hydroxyethyl) terephthalate obtained as above is polymerized by heating in the presence of antimony oxide under vacuum. Specification 578,079, [Group IV], is referred to.ALSO:Bis-(hydroxyethyl) terephthalate containing some low molecular weight polyester derived therefrom, is prepared by heating terephthalic acid with ethylene glycol, some bis-(hydroxyethyl) terephthalate being present at the start of the reaction. The process may be a semi-continuous one wherein on completion of the esterification a part of the product is mixed with more ethylene glycol and terephthalic acid and the esterification is repeated. In examples, a mixture of terephthalic acid, ethylene glycol and bis-(hydroxyethyl) terephthalate is heated to boiling while the water of condensation is distilled off, to yield bis-(hydroxyethyl) terephthalate. The bis-(hydroxyethyl) terephthalate may be polymerized to polyethylene terephthalate (see Group IV (a)). The Provisional Specification also refers to the preparation of bis-(hydroxyalkyl) terephthalates by heating terephthalic acid with a glycol of the formula HO(CH2)nOH, where n is an integer from 3 to 10, some of the bis-(hydroxyalkyl) terephthalate being present at the start of the reaction. Specification 578,079, [Group IV], is referred to.