Linear polyamic acid, linear polyimide and thermoset polyimide

Linear polyimide represented by the formula (3):

• ##STR50## wherein S3 is one or more monovalent radicals represented by the formula (i) or the formula (j):
• ##STR51## wherein Q is a monovalent radical selected from a hydrogen atom, halogen atom, alkyl or alkoxy radical having 1.about.3 carbon atoms, cyano radical, or halogenated alkyl or halogenated alkoxy radical having 1.about.3 carbon atoms wherein hydrogen atoms of the alkyl or alkoxy radical are partly or totally or totally substituted with halogen atoms, m and n are respectively mol % of recurring units, m is 100.about.70 mol %, n is 0.about.30 mol %, fixed order or regularity is absent among the recurring units, and l is a polymerization degree and is an integer of 1.about.100.

Linear polyimide represented by the formula (5):

• ##STR52## wherein Q is a monovalent radical selected from a hydrogen atom, halogen atom, alkyl or alkoxy radical having 1.about.3 carbon atoms, cyano radical, or halogenated alkyl or halogenated alkoxy radical having 1.about.3 carbon atoms wherein hydrogen atoms of the alkyl or alkoxy radical are partly or totally substituted with halogen atoms, m and n are respectively mol % of recurring units, m is 100.about.70 mol %, n is 0.about.30 mol %, fixed order or regularity is absent among the recurring units, and l is a polymerization degree and is an integer of 1.about.100.

Linear polyimide represented by the formula (7):

• ##STR53## wherein S5 is one or more monovalent radicals of the formula (o) or the formula (p):
• ##STR54## m and n are respectively mol % of recurring units, m is 100.about.70 mol %, n is 0.about.30 mol %, fixed order or regularity is absent among the recurring units, and l is a polymerization degree and is an integer of 1.about.100.

Linear polyimide represented by the formula (9):

• ##STR55## wherein m and n are respectively mol % of recurring units, m is 100.about.70 mol %, n is 0.about.30 mol %, fixed order or regularity is absent among the recurring units, and l is a polymerization degree and is an integer of 1.about.100.