Synthesis and characterization of polynaphthalimides copolymers and their reduced graphene oxide composites

Author(s)

Heloisa Moretti Passos

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
• Defense date: 2022-03-25

Examining board members

Maria Isabel Felisberti; Cesar Liberato Petzhold; Thiago Ferreira da Conceição; Cláudia Longo; Camila Alves de Rezende

• Advisor: Maria Isabel Felisberti

Abstract

Polyimides are high performance polymers whose properties can be modulated through structural modifications. Until 2019, the two-step polycondensation route, used for the synthesis of 5-membered polyimides since the 1960s, was reported in the literature as being unfeasible for 6-membered dianhydrides in the production of polynaphthalimides (PNI). In this work, the two-step polycondensation route for PNI based on 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA, dianhydride 6) and 4,4'-(9-fluorenylidene)dianiline (FNDA, diamine S) was successfully conducted under mild conditions (40 °C, 4 h, no catalyst), resulting in the aminolysis of dianhydride 6 and minimizing early imidization. The neutralization of the polyamic acid intermediate (PAA), generating the salt (PAAS) resulted in a significant increase in the degree of imidization, because the amine acts as a catalyst for imidization, which is undesirable. PAA and PAAS formation, as well as imidization and PNI formation, were confirmed by GPC, 1H NMR, 13C NMR and FTIR. The optimal synthesis condition was also evaluated for PNI based on dianhydride 6 and hexamethylenediamine (HMD, diamine L) or 1,5-diaminonaphthalene (DAN, diamine N). However, polymerization with diamine L is very fast, compromising the homogenization of the medium, while polymerization with 4,4'-(1,3-phenylenedioxy)dianiline (PDODA, diamine F) proved to be unfeasible at 40 °C and led to partial conversion at 60 °C. Copolymers based on the diamines S, L and F and on dianhydride 6 and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA, dianhydride 5) and diamine F were synthesized and characterized according to their thermal, mechanical, dynamic-mechanical and dielectric properties. Polymers based on diamine S and diamines S and L were amorphous, while those based on F diamine were semicrystalline. The polymers showed glass transition temperatures above 219 °C, melting temperatures between 303 °C and 460 °C and degradation temperatures between 490 °C and 585 °C. Copolymers based on diamine L and diamine S showed a block-like structure, characterized by presenting two glass transitions and two-step degradation. The electrical conductivity of copolymers increased with the increase in the dianhydride 6 molar fraction, and the dielectric constant was between 2 and 5. The fabrication of polyimide/graphene composites was carried out using graphene oxide, which was thermally reduced in situ during the thermal imidization of polyimides, confirmed by infrared and Raman spectroscopy. The partial aggregation of the filler in the composites compromised the performance in relation to mechanical and electrical properties, despite the adhesion between the filler and the polymer matrix (AU)

• FAPESP's process: 16/22724-9 - Synthesis and characterization of polinaphthalimides copolymers and their reduced graphene oxide composites
• Grantee: Heloisa Moretti Passos
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)