Importance

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Abstract

In a process for producing a semipermeable composite membrane which comprises forming on a microporous substrate a thin layer of a polymeric material comprising a polyamino polymer containing at least 1 milliequivalent, per gram of the polymer in the dry state, of active amino groups selected from primary amino groups and secondary amino groups, and thereafter interfacially crosslinking a surface portion of said thin layer with a crosslinking agent having at least two functional groups (a) capable of easily reacting with either the primary or secondary amino groups or both in said polymer; the improvement wherein (1) said polymeric material contains dispersed therein a polyfunctional compound having at least two functional groups (b) substantially incapable of reacting with the primary or secondary amino groups in said polymer at a temperature at which the interfacial crosslinking is carried out, but capable of reacting easily with either the primary or secondary amino groups or both in said polymer at a temperature at least 30.degree. C. higher than said crosslinking temperature, and (2) the interfacially crosslinked thin layer is heated to a temperature at which said polyfunctional compound reacts with the primary or secondary amino groups or both in said polymer.

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First Claim