Thermal degradation of new copolymers from pyromellitic anhydride Giorgio Montaudo*, Concetto Puglisi Dipartimento di Scienze Chimiche, Universitb di Catania and/stituto per/a Chimica e/a Tecno/ogia dei Material/Po/imerici, Consig/io Naziona/e de//e Ricerche, Via/e A. Doria 6, 95125 Catania, Italy Niyazi Bi.cak~ Technical University of Istanbu/, Department of Chemistry, Ayazaga kampusu, Mas/ak, /stanbu/, Turkey and Andrzej Orzeszko~ Agricultural University, Institute of Chemistry, UL Rakowiecka 26/30, 02-528 Warsaw, Poland (Received 21 December 1988; accepted 24 February 1989) A series of new copolyimides has been synthesized from pyromellitic anhydride. Copoly(imide esters) and copoly(imide amides) were synthesized from bis(N-methylcarboxychloride)pyromellitimide with diols and amines, respectively. One copoly(imide amine) was obtained from bis(N-allyl)pyromellitimide and piperazine via the Michael reaction. The thermal degradation of the copolymides obtained was studied by direct pyrolysis mass spectrometry. Our results show that a selective//-CH hydrogen transfer reaction occurs in copoly(imide esters) containing 1,3-propyl and 1,6-hexane diols, while an intramolecular ester exchange process takes place in copoly(imide ester) with a neopentylglycol moiety. Copoly(imide amide) containing 1,6-hexane diamine decomposes by an N-H hydrogen transfer process, although extensive crosslinking is observed, while that containing piperazine decomposes by an ct-CH hydrogen transfer. In contrast, copoly(imide amine) undergoes a very selective depolymerization process, yielding bis(N- allyl)pyromellitimide and piperazine. (Keywords: thermal degradation mechanisms; mass spectrometry; direct pyrolysis m.s.; polyimide copolymers) INTRODUCTION Polyimides are well known and their thermal decompo- sition behaviour has been extensively investigated 1-1°. These polymers present processing problems and con- siderable effort is still being devoted to improving these properties. Copolymerization of imides with flexible monomer units has been reported more recently 11-15 We have synthesized a series of copolymers from pyromellitic anhydride: poly(imide esters), polymers I-III in Table I; poly(imide amides), polymers IV and V in Table I; and one poly(imide amine), polymer VI in Table 1. These copolymers were synthesized starting from monomers 1 and 2, according to equations (1) and (2), respectively: 0 0 // o ~ ~ o + H2N__CH2__COOH (1) Imidization 1- (2) SOCl 2 // It O O O O Cl--C- CHz-:/~~N- CHo" C-CI 0 0 Monomer 1 1 + X--R--X Copolymers I-V x =OH, NH2, NH * To whom correspondenceshould be addressed t On leave from Istanbul, Jan-Dec 1988 On leave from Warsaw, June-Oct 1988 O O 0 O + H2N---CH2--CHB~CH 2 ~- o o CH2= CH -- C Ha-- N ~ ~ N -- CH=-- CH -- CH2 O O 2+ .a/--'xN. ~ Copolymer VI x_../ Monomer 2 In the present study, our main interest has been directed towards the investigation of the thermal degra- dation pathways of these copolyimides by thermogravi- metry (t.g.) and by direct pyrolysis mass spectrometry (d.p.m.s). In the d.p.m.s, technique 16, polymers were introduced via the direct insertion probe of the m.s. and the temperature increased gradually until thermal degra- dation reactions occur; the volatile compounds formed were then ionized and detected as soon as they are formed. A general advantage of this technique is that pyrolysis is accomplished under high vacuum, and therefore the thermal products are volatilized and readily removed from the hot zone. This, together with the low probability of molecular collision and fast detection, reduces the occurrence of secondary reactions, so that the probability of detecting primary thermal degradation products is enhanced. A series of temperature-time 0032-3861/89/122237-09503.00 © 1989 Butterworth& Co. (Publishers) Ltd. PO LYM ER, 1 989, Vol 30, December 2237