4,4′-Oxydiphthalic anhydride, commonly abbreviated as ODPA, is an aromatic dianhydride identified by CAS 1823-59-2. It is also referred to as 4,4′-oxydiphthalic dianhydride in polymer and materials science literature.
ODPA is mainly associated with the development of polyimide materials. Its molecular structure combines aromatic rings, two anhydride functionalities and an ether linkage. These structural elements make ODPA relevant when polymer scientists need to control the balance between backbone rigidity and molecular mobility in an aromatic polymer system.
The role of ODPA should not be interpreted as a simple relationship in which one monomer determines one final material property. Polyimide behavior depends on the complete molecular architecture, including the selected dianhydride, the corresponding diamine, molecular weight, polymer morphology and material processing history.
For this reason, ODPA is best understood as a structural monomer used in polyimide molecular design, rather than as a general-purpose additive.
What Is ODPA?
ODPA belongs to the class of aromatic tetracarboxylic dianhydrides.
Its molecular formula is C16H6O7, and its molecular weight is approximately 310.21 g/mol. NIST identifies CAS 1823-59-2 as 4,4′-oxydiphthalic dianhydride and reports a molecular weight of 310.2146.
The term “dianhydride” is important when discussing ODPA.
The molecule contains two cyclic anhydride functionalities. In polyimide chemistry, aromatic dianhydrides form one of the major monomer families used to construct imide-containing polymer backbones.
ODPA also contains an oxygen atom connecting two aromatic structural units. This ether linkage distinguishes it from dianhydrides built around more rigid directly connected aromatic frameworks.
The combination of these structural features explains why ODPA appears frequently in studies of polyimide and polyetherimide systems.
It also explains why its performance cannot be evaluated only from basic properties such as molecular weight or melting point. The position and connectivity of the functional groups influence how the monomer becomes incorporated into a polymer backbone.
Key Physical and Chemical Properties of ODPA
| Property | Information |
| Chemical Name | 4,4′-Oxydiphthalic Anhydride |
| Common Abbreviation | ODPA |
| CAS Number | 1823-59-2 |
| Molecular Formula | C16H6O7 |
| Molecular Weight | 310.21 g/mol |
| Chemical Class | Aromatic Dianhydride |
| Appearance | White powder |
| Purity | ≥99% |
| Melting Point | 225–229°C |
The principal identification and product parameters relevant to the Starsky Chemical ODPA listing are shown above.
The CAS number, molecular formula and molecular weight establish the chemical identity of the material. These identifiers are particularly important because oxydiphthalic anhydride can exist in different positional forms.
Purity is another relevant specification for polymer-grade monomers. In high-molecular-weight polymer systems, monomer quality and impurity control can affect repeatability and the interpretation of downstream material data.
The Starsky Chemical specification currently lists ODPA purity at ≥99%.
The reported 225–229°C melting-point range provides another physical-property reference. Melting point can support material characterization, but it should not be used alone to determine chemical identity, purity or suitability for a specific polymer system.
For technical qualification, chemical identity, analytical results, batch consistency and application-specific requirements need to be considered together.
Understanding the Molecular Structure of ODPA
The technical relevance of ODPA comes primarily from its molecular architecture.
Aromatic Structure
ODPA contains two aromatic ring systems.
Aromatic structures are widely used in high-performance polymer chemistry because they generally provide greater backbone rigidity than many aliphatic structural units.
Higher molecular rigidity can influence thermal behavior, dimensional response and chain packing. These relationships are not universal. A polymer containing ODPA can behave very differently depending on the diamine paired with it and the resulting molecular structure.
The aromatic portion of ODPA should therefore be considered one contributor to polymer behavior rather than an independent guarantee of heat resistance or mechanical strength.
Dianhydride Functionality
The two anhydride functionalities define ODPA’s role as a dianhydride monomer.
This creates a clear distinction between ODPA and aromatic diamines such as 4,4′-oxydianiline, or ODA.
From a polymer-design perspective:
The selection of both components determines the repeating molecular structure of the resulting polyimide.
Studies of polyimide systems consistently show that changing either the dianhydride or diamine structure changes material behavior. Research comparing different dianhydride and diamine architectures has examined their effects on properties such as chain mobility and polymer structure.
Ether Linkage
ODPA contains an ether oxygen between its aromatic structural units.
This feature gives the molecule a different degree of rotational freedom from a completely rigid aromatic dianhydride structure.
The distinction is important because polyimide design frequently involves a balance between two competing structural requirements:
A highly rigid backbone may provide advantages for certain thermal or dimensional properties, while greater chain mobility may affect processing behavior, morphology and mechanical response.
The ether linkage in ODPA contributes to this structural balance, but it does not independently determine the properties of the finished polyimide.
What Role Does ODPA Play in Polyimide Materials?
ODPA is primarily relevant as a dianhydride monomer used in polyimide chemistry.
Polyimides are polymers containing imide groups within their molecular structure. Aromatic polyimides have been extensively studied because their molecular architectures can be designed for demanding thermal, mechanical, electrical and dimensional requirements.
ODPA contributes the dianhydride-derived portion of the polymer backbone.
The diamine selected for the same polymer system contributes another major structural component. Changing either monomer changes the geometry, flexibility and intermolecular interactions of the polymer chain.
Research literature contains many ODPA-based polyimide systems prepared with different diamine structures. This diversity itself demonstrates an important engineering point: there is no single set of properties that can accurately describe all “ODPA polyimides.”
ODPA-based polymers may differ in:
- · molecular-chain rigidity;
- · glass-transition behavior;
- · thermal response;
- · mechanical characteristics;
- · solubility characteristics;
- · moisture interaction;
- · dielectric behavior;
- · film morphology.
These characteristics depend on the complete polymer structure.
Primary research on ODPA-containing polyimides has evaluated how molecular design changes properties across different polymer systems, including copolyimides and ODPA-based polyetherimides.
For technical users, the useful question is therefore not simply:
A more accurate question is:
That distinction is important in research, material development and product specification.
Why the Ether Linkage Matters in ODPA-Based Polymer Design
The ether linkage is one of the main structural reasons ODPA is differentiated from other aromatic dianhydrides.
A polymer backbone consisting only of highly rigid aromatic units can show restricted segmental movement. Introducing an ether-containing structural unit changes the rotational freedom available along the molecular chain.
That change can influence chain packing, molecular mobility and the relationship between thermal performance and processing characteristics.
No universal numerical improvement can be assigned to the ether linkage.
A claim such as “ODPA increases flexibility by a certain percentage” would be technically unreliable without defining the complete polymer formulation and test method.
The actual result depends on factors including:
- · diamine structure;
- · molecular weight;
- · polymer sequence;
- · intermolecular interactions;
- · morphology;
- · test temperature;
- · material form.
Research comparing polyimides with different dianhydride structures supports this structure-property approach: monomer architecture affects the resulting polymer, but the effect needs to be evaluated within the complete molecular system.
This is why ODPA is useful in polymer design discussions. Its significance lies in the structural options it introduces, not in one isolated performance number.
Where Are ODPA-Based Polyimide Materials Relevant?
Starsky Chemical identifies polyimide material preparation as the primary application direction for its ODPA product.
From a broader materials-science perspective, polyimide systems are studied when a combination of properties is required rather than one single performance parameter.
Typical technical requirements may include:
These application categories should not be interpreted as automatic performance claims for ODPA itself.
A monomer does not have the same mechanical, dielectric or thermal properties as the finished polymer produced from it.
The finished material must be evaluated using data from the actual polymer formulation and relevant material test methods.
What Matters When Evaluating ODPA as a Polymer Monomer?
Chemical Identity
The complete chemical name and CAS number should be clearly established.
For 4,4′-ODPA, the relevant CAS number is 1823-59-2. NIST records the compound as C16H6O7 with a molecular weight of 310.2146.
This identification is important because positional oxydiphthalic anhydride isomers should not automatically be considered interchangeable.
Purity
Purity provides a basic measure of the proportion of the intended chemical component.
Starsky Chemical currently specifies ≥99% purity for its ODPA listing.
For polymer development, purity should be interpreted together with the analytical method, impurity profile and the requirements of the intended material system.
Physical Characteristics
Appearance and melting-point range provide additional characterization information.
Starsky’s current specification describes the material as a white powder with a melting point of 225–229°C.
These parameters are useful references but do not replace chemical analysis.
Batch Consistency
Repeatability becomes increasingly important when development moves from initial material screening to ongoing polymer evaluation.
A single acceptable sample does not establish long-term material consistency.
Quality teams therefore need to interpret individual analytical data within their own validated incoming-material specifications.
ODPA and Other Aromatic Dianhydrides
ODPA is one member of a broader family of aromatic dianhydride monomers used in polyimide research and materials development.
Different dianhydrides differ in molecular rigidity, symmetry, substituent structure and linkage type.
These differences change the molecular backbone produced when the dianhydride is combined with a given diamine.
ODPA should therefore not be classified simply as “better” or “worse” than another aromatic dianhydride.
The technically meaningful comparison depends on the targeted polymer architecture and the required balance of thermal, mechanical, dielectric and processing characteristics.
That topic deserves separate treatment because meaningful comparison requires examining the molecular structures of the complete polymer systems rather than comparing isolated commercial specifications.
Safety and Regulatory Considerations
ODPA is an industrial chemical and should be evaluated within an appropriate chemical-safety framework.
A technical article cannot replace a current Safety Data Sheet, workplace risk assessment or applicable chemical regulations.
Organizations working with polymer raw materials should use the current SDS and their own EHS requirements when assessing hazards, occupational exposure controls and regulatory obligations.
Product performance information and chemical-safety information serve different purposes. Both need to be considered during technical material qualification.
Frequently Asked Questions About ODPA
What is ODPA?
ODPA is the common abbreviation for 4,4′-oxydiphthalic anhydride, also widely referred to as 4,4′-oxydiphthalic dianhydride. It is an aromatic dianhydride used in polymer and materials research, particularly in polyimide systems.
What is the CAS number of ODPA?
The CAS number of 4,4′-ODPA is 1823-59-2.
What is the molecular formula of ODPA?
ODPA has the molecular formula C16H6O7 and a molecular weight of approximately 310.21 g/mol.
Is ODPA an anhydride or a dianhydride?
ODPA contains two anhydride functionalities and is therefore classified as an aromatic dianhydride in polymer chemistry. The shorter name “4,4′-oxydiphthalic anhydride” is widely used, but “4,4′-oxydiphthalic dianhydride” describes its functional role more explicitly.
What is ODPA mainly associated with?
ODPA is mainly associated with the development of polyimide materials. Its dianhydride groups allow the molecule to become part of an imide-containing polymer backbone, while its aromatic rings and ether linkage contribute specific structural characteristics to that backbone.
Why is ODPA relevant to polyimide molecular design?
ODPA combines aromatic structural units with an ether linkage. This architecture introduces a different balance of rigidity and molecular mobility from dianhydrides with more rigid backbone structures. The actual effect depends on the diamine and complete polymer architecture, so ODPA should be evaluated as part of a monomer system rather than as an isolated determinant of performance.
Conclusion
4,4′-Oxydiphthalic anhydride, or ODPA, is an aromatic dianhydride identified by CAS 1823-59-2. Its importance in materials science comes from the combination of dianhydride functionality, aromatic structure and an ether linkage.
ODPA is primarily associated with polyimide molecular design, where the dianhydride structure works together with the selected diamine to define the polymer backbone.
For technical evaluation, chemical identity, purity, physical characteristics, batch consistency and the complete polymer architecture should be considered together. Statements about thermal, mechanical or dielectric performance should be based on data from the finished polymer system rather than inferred from ODPA alone.
Post time: Aug-17-2026