About Polyimide Resin
What is Polyimide Resin?
Figure 1. Structure of Polyimide Resin
Polyimide resin (abbreviated as PI) is a polymer compound that contains imide ring bonds within its molecular chains (Figure 1). Among them, aromatic polyimides—where the R group is aromatic—are widely used industrially. The first practical application began in the 1960s, when DuPont in the United States commercialized it as a film product under the brand name Kapton®.
Key Features
Heat Resistance
Exhibits minimal changes in physical properties over a temperature range of -196 °C to 300 °C, with a thermal decomposition temperature exceeding 500 °C. Physical properties remain stable even at extremely high temperatures.
Electrical Insulation
Dielectric constant and volume resistivity remain stable across a wide temperature range.
Chemical Resistance
Highly resistant to many organic solvents, acids, and alkalis.
Mechanical Strength
High tensile strength and modulus, with excellent dimensional stability.
Flame Retardancy
Self-extinguishing and difficult to ignite.
Low Outgassing
Releases minimal gas even in vacuum environments, making it suitable for space applications.
Types and Classification
| Thermosetting Polyimide | High Tg (glass transition temperature); used for coatings and film substrates |
|---|---|
| Thermoplastic Polyimide | Can be heat-molded; used in mechanical parts and industrial equipment |
| Soluble Polyimide | Highly soluble in organic solvents and easy to process |
| Non-Thermoplastic Polyimide | Most common type; excellent heat and chemical resistance, used in transportation equipment |
Main Applications
Electronics
Flexible printed circuits (FPC), semiconductor insulating films, motor coils, wires, etc.
Displays
Liquid crystal alignment films, organic EL pixel separation films
Automotive & Aerospace
Mechanical components, insulating protective films, heat-resistant materials for satellites
Semiconductor Manufacturing Equipment
Materials for machining, redistribution layers, buffer coatings
Synthesis Methods of Polyimide Resins
Two-Step Method (via Polyamic Acid) — Most Common Approach
Step 1: Synthesis of Polyamic Acid
- Raw Materials
Aromatic diamines (e.g., ODA) and aromatic tetracarboxylic acid dianhydrides (e.g., PMDA)
- Reaction
Conducted at room temperature in a non-protic polar solvent (such as NMP or DMAc) through a ring-opening addition reaction to produce polyamic acid
- Features
Produces high-molecular-weight polyamic acid with excellent processability
Step 2: Imidization (Dehydration Cyclization Reaction)
- Methods
■ Thermal Imidization: Heat at 250–300 °C to form imide rings through a dehydration cyclization reaction
■ Chemical Imidization: Use dehydrating agents (e.g., acylating agents) to carry out the reaction at room to moderate temperatures - Product
High heat-resistant polyimide resin
This method is also used in the production of representative polyimide films, such as Kapton®.Figure 2. Two-Step Synthesis of Polyimide (via Polyamic Acid)
One-Step Method (Direct Imidization)
- Overview
Polyimide is synthesized in a single step by directly reacting diamines with dianhydrides in a high-boiling-point solvent.
- Advantages
Shorter process and reduced reaction time
- Challenges
Difficult to control high molecular weight; reaction conditions are strict
Figure 3. One-Step Synthesis of Polyimide (Direct Imidization)
Three-Step Method (via Polyamic Acid Salt)
- Overview
Polyamic acid is converted to its salt, followed by dehydration cyclization to obtain polyimide.
- Features
Easier control of molecular structure, allowing design for specific applications
Vapor Deposition Method
- Applications
Formation of ultra-thin polyimide films (for MEMS and semiconductor applications)
- Method
Monomers are reacted in the vapor phase to form a polyimide film on the substrate
Representative Raw Materials Used in Synthesis
| PMDA | Pyromellitic dianhydride High heat-resistant polyimide (Kapton®) |
|---|---|
| ODA | Oxydianiline Improves flexibility and processability |
| BPDA | Biphenyl tetracarboxylic dianhydride High-elasticity polyimide (Upilex®) |
| PDA | p-Phenylenediamine Provides a rigid structure |
Figure 4. Polymer Categories Pyramid