Lightly Crosslinked Polyimides with Phenylethynyl Pendants for Shape-Memory Effect and Programmed Enhancement in Tg and Modulus

A method for fabricating a shape memory polymer into a three-dimensional object, comprising:

• a) treating a solution comprising:
• (i) a polymeric intermediate comprising repeat units and non-terminal, phenylethynyl moieties, each of said repeat units comprising one of said non-terminal, phenylethynyl moieties;
• said polymeric intermediate being selected from the group consisting of a poly(amic acid) intermediate, a poly(amide-amic acid) intermediate, a copolymer intermediate of poly(amic acid) and poly(amide-amic acid), and mixtures thereof;
• (ii) a solvent;
• with a multi-functional crosslinking agent to thereby form a sol-gel comprising a crosslinked poly(amic acid), a crosslinked poly(amide-amic acid) and/or a crosslinked copolymer of poly(amic acid) and poly(amide-amic acid), said crosslinked poly(amic acid), a crosslinked poly(amide-amic acid) and/or a crosslinked copolymer of poly(amic acid) and poly(amide-amic acid) comprising repeat units and non-terminal, phenylethynyl moieties each of said repeat units comprising one of said non-terminal, phenylethynyl moieties, said multi-functional crosslinking agent comprising at least a tri-functionalized amine crosslinking agent when said polymeric intermediate is anhydride end-functionalized and said multi-functional crosslinking agent comprising at least a tri-functionalized anhydride crosslinking agent when said polymeric intermediate is amine end-functionalized;
• b) forming a film of said sol-gel on a substrate to provide a laminated substrate;
• c) evaporating at least a portion of the solvent from the sol-gel by heating the sol-gel to a temperature in a range of about 50° C. to about 100° C. at a pressure less than about atmospheric pressure;
• d) forming the laminated substrate into a first configuration that is in a three-dimensional form;
• e) imidizing, via heating, said sol-gel to provide the shape memory polymer having a permanent shape corresponding to the first configuration, wherein the shape memory polymer comprises a crosslinked polyimide, a crosslinked poly(amide-imide) and/or a crosslinked polyimide poly(amide-imide) copolymer comprising repeat units and non-terminal, phenylethynyl moieties each of said repeat units comprising one of said non-terminal, phenylethynyl moieties;
• and
• f) removing the substrate from the laminated substrate to provide the three-dimensional object comprising the shape memory polymer;
• g) optionally, heating said shape memory polymer to a temperature of from about 210° C. to 250° C. and then placing said shape memory polymer under tension to a new shape.