| 摘要 |
Polymers are crosslinked during processing by extrusion, at a temp. between their softening pt. and decompsn. temp., by injecting at one or more positions between the feed and discharge points, a crosslinking agent reactive with the COOH gps. Opt. a blowing agent may be mixed with the polymer to cause foam formation. The copolymer is obtd. from at least 60 (pref. 80-99.9) wt.% of monomers of formula (I) (where G is H or methyl; and Ar is opt. alkyl and halo-ring substd. 6-10C aryl gp.); with one or more comonomers of formula X-C-(CH2)nCOOH (where Z is H, 1-4C alkyl and carboxyl; X is methylene and 2-5C alkenyl, opt. carboxylated (providing X and Z together carry only 1 COOH); and n is 0-4); and a balance, if any of other copolymerisable ethylenic monomers and natural and synthetic elastomers. Crosslinking is effected during processing in a simple one-stage procedure which is esp. suited to the prodn. of very good quality foamed articles by shaping the extrudate e.g. into board, sheet or film or by injection into a mould. Such foams resist collapse at temps. significantly higher than unmodified foams can accommodate. In an example, a styrene-acrylic acid copolymer having wt. ave. mol. wt. 215,000 and contg. 8 wt.% acrylic acid was extruded into expandable beads contg. 14 pts. wt. per 100 of Cl3CF. The granules were re-extruded into foam (die temp. 175 deg.C) using 1% talc as nucleator, and adding 0.11 wt.% of (III). The extruded foam was of excellent quality and had density 4.4 lb/cu.ft. Omitting (III) resulted in a collapsed foam of density 13.6 lb/cu.ft. |
