GB849027A - Improvements in polymers of ethylene - Google Patents

Abstract

A homo-polymer of ethylene characterised by an average molecular weight above 50,000, a melting point above 125 DEG C., a density above 0,94, a modulus of elasticity at 23 DEG C. of at least 60,000 p.s.i., an ultimate tensile strength above 2500 p.s.i. when measured at 23 DEG C., at an extension rate of 20 inches/minute, a melt index as measured by A.S.T.M. test D1238-52T of at least 0,2 gram/10 minutes, and the ability to resist cracking for a period of at least 7 days continuous exposure to air at 80 DEG C. when moulded strips-of same are cut and stressed in the manner described on pages 25-26 of A.S.T.M. Bulletin No. 218, published December 1956 by reacting a homopolymer of ethylene having the above properties except that it is susceptible to embrittlement, stress cracking and other forms of degradation at a temperature above 80 DEG C., with a free radical generating compound which does not boil below 100 DEG C. at atmospheric pressure and which decomposes to form free radicals in the range of 140 DEG to 200 DEG C. and which is present in an amount of from 0,1 to 0,4 parts by weight per 100 parts of polyethylene, by decomposing by heat the free radical generating compound. The reaction with the free radical compound may be effected in the presence of carbon blacks, antixoidants, and plasticisers. If desired these ingredients may also be compounded with the aftertreated polymer. The free radical compounds may be peroxides or hydroperoxides, compounds containing an <N-Cl grouping, metal alkyls, amine oxides, hydrasine salts, organic disulphides, and azo compounds. The preferred compound is dicumyl peroxide. In Example 2, the reaction with cicumyl peroxide is carried out in the presence of carbon black and phenyl-beta-naphthalmine and the product extruded into pipes.