Foamable polyetherimide resin formulation

A concentrated polyetherimide resin containing from about 15 to 50% by weight of a blowing agent of the structural formula:

• ##STR20## where "a" is an integer equal to 1 or 2, R is a monovalent radical when "a" is 1 and R is a divalent radical when "a" is 2 and R is selected from alkyl radicals and aryl radicals, alkylene radicals, arylene radicals, substituted aryl radicals or substituted arylene radicals and R.sub.1 and R.sub.2 are monovalent or divalent radicals which can be the same or different selected from hydrogen, alkyl, alkylene, a cyclo-aliphatic ring including R.sub.1 and R.sub.2 alkoxy radicals and aryloxy radicals;
• and wherein the polyetherimide is represented by the formula:
• ##STR21## where "b" is an integer from 10 to 10,000, Z is a member selected from the class consisting of:
• (1) ##STR22## and (2) divalent organic radicals of the general structural formula:
• ##STR23## where X is a member selected from the class consisting of divalent radicals of the formulas, ##STR24## where q is 0 or 1, y is an integer from 1 to 5, and the divalent bonds of the --O--Z--O-- radical are situated on the phthalic anhydride end groups, e.g., in the 3,3', 3,4', 4,3' or the 4,4' positions and R', is a divalent organic radical selected from the class consisting of aromatic hydrocarbon radicals having from 6 to about 20 carbon atoms and halogenated derivatives thereof, alkylene radicals and cycloalkylene radicals having from about 2 to about 20 carbon atoms, C.sub.(2-8) alkylene terminated polydiorganosiloxane, and divalent radicals of the formula:
• ##STR25## where Q is a direct bond or a member selected from the class consisting of ##STR26## and x is an integer from 1 to 5.

A process for producing a foamable thermoplastic resin comprising contacting a polyetherimide resin with a chemical blowing agent in a molten state but below the decomposition temperatures of said blowing agent wherein said blowing agent is of the formula:

• ##STR27## where "a" is an integer equal to 1 or 2, R is a monovalent radical when "a" is 2 and R is a divalent radical when "a" is 2 and R is selected from alkyl radicals and aryl radicals, alkylene radicals, arylene radicals, substituted aryl radicals or substituted arylene radicals and R.sub.1 and R.sub.2 are monovalent or divalent radicals which can be the same or different selected from hydrogen, alkyl, alkylene, a cyclo-aliphatic ring including R.sub.1 and R.sub.2 alkoxy radicals and aryloxy radicals;
• and wherein the polyetherimide is represented by the formula:
• ##STR28## where "b" is an integer from 10 to 10,000, Z is a member selected from the class consisting of:
• (1) ##STR29## and (2) divalent organic radicals of the general structural formula:
• ##STR30## where X is a member selected from the class consisting of divalent radicals of the formulas, ##STR31## where q is 0 or 1, y is an integer from 1 to 5, and the divalent bonds of the --O--Z--O-- radical are situated on the phthalic anhydride end groups, e.g., in the 3,3', 3,4', 4,3' or the 4,4' positions and R', is a divalent organic radical selected from the class consisting of aromatic hydrocarbon radicals having from 6 to about 20 carbon atoms and halogenated derivatives thereof, alkylene radicals and cycloalkylene radicals having from about 2 to about 20 carbon atoms, C.sub.(2-8) alkylene terminated polydiorganosiloxane, and divalent radicals of the formula:
• ##STR32## where Q is a direct bond or a member selected from the class consisting of ##STR33## and x is an integer from 1 to 5.