Thermomechanical characterization of thermoplastic polyimides containing 4,4'‐methylenebis(2,6‐dimethylaniline) and polyetherdiamines

Abstract

In this work, we synthesized polyimides by incorporating an aromatic diamine monomer with a methylene linker, 4,4'‐methylenebis(2,6‐dimethylaniline) (MBDMA), to make a robust main chain along with aliphatic polyetherdiamine backbone linkers to reduce rigidity. We designed the polymers to exhibit thermal properties in between those of conventional aromatic polyimides and polymers with wholly aliphatic ether diamine links. Through dynamic mechanical analysis and differential scanning calorimetry, it is shown that control of the molar ratios of the aromatic MBDMA (4,4'‐methylenebis(2,6‐dimethylaniline)) and the composition and size of the aliphatic polyetherdiamine can be used to tune the glass transition. The polymers were characterized by GPC, FTIR, NMR, thermomechanical and calorimetric analysis, and microhardness testing. POLYM. ENG. SCI., 59:221–232, 2019. © 2018 Society of Plastics Engineers

Thermomechanical characterization of thermoplastic polyimides to improve the chain collaboration via ureidopyrimidone endcaps

“…The introduction of a terminal UPy linker was made to influence the interaction and connection between the chains. In contrast to other works , the increased molecular weight was acceptable due to the previous modifications in the backbone that gave the backbone the required flexibility and processability. Furthermore, the glass transition temperatures and properties were tuned by controlling the stoichiometric ratio of MBDMA to aliphatic polyetheramines along with the molecular weight of the polyetheramine itself.…”

“…The main variation in all the series comes from the addition of a terminal UPy linker that can interact to form four hydrogen bond links and connect the chains in series (essentially, mimicking the lengthening of the chains). Aromatic PIs are recognized for having high thermal stability, but when the aromaticity is lessened with the incorporation of aliphatic monomers, the temperature stability decreases . Though the addition of UPy to these sets of flexible PIs does not increase aromaticity or rigidity, per se , its ability to allow the connection of the chains in series could increase the entanglement of the chains, which can also increase the temperature stability.…”

“…To counteract the deficiency in processability, researchers have modified these materials through the breaking of the aromatic moieties, so that these materials can have thermoplastic behavior by augmenting their flexibility and lowering thermal transitions. To do so, the conventional procedure is to disrupt the order of the aromatic backbone . The glass transition temperatures of these modified aromatic PIs remain particularly elevated; these temperatures range from 215°C to 310°C , which makes them energetically inefficient for processing.…”

“…This result evidenced the need for the highly ordered, stiff backbones of conventional aromatic PIs to maintain higher glass transition temperatures. Our previous research showed that a broad range of tractable glass transition temperatures can be reached through the introduction of 4,4′‐methylenebis (2,6‐dimethylaniline) (MBDMA) into the backbone; the lowest glass transition temperature obtained was 22°C and the highest glass transition temperature reached was 101°C . The structure proposed provided the option to broaden the glass transition range.…”

“…These thermal properties provide a large range of operational conditions for flexible materials. As mentioned above, when PIs have flexible backbones , their thermal transitions are lowered, and they lose their valuable characteristics for which they are known for. The complement of hydrogen bonding provides advantageous solvent resistance, garnering attention as thermally resilient thermoplastics.…”