Acrylic rubber, also known as ACM (Acrylic Copolymer Monomer), is a synthetic rubber characterized by its specific chemical composition which grants it unique properties, particularly resistance to heat and oils.
Defining the Chemical Structure
The chemical structure of acrylic rubber is not a simple repeating unit like many polymers. Instead, it is defined by its composition as a copolymer or terpolymer. This means it is formed by linking together two or three different types of monomer units in a long chain.
Based on the provided reference, acrylic rubber is primarily composed of:
- Ethyl Acrylate: This is the main monomer unit forming the backbone of the polymer chain.
- Other Acrylates: Additional acrylate monomers are included alongside ethyl acrylate. Common examples might include butyl acrylate or 2-ethylhexyl acrylate, which can modify the rubber's properties.
- Vulcanisation-Supporting Monomer: A small amount of a third, specific monomer is incorporated. This monomer contains reactive sites (like carboxylic groups, epoxy groups, or active chlorine) that are essential for the process of vulcanization or curing. Vulcanization creates cross-links between the polymer chains, transforming the material from a plastic state into an elastic rubber.
Essentially, the chemical structure is a long polymer chain consisting of randomly arranged (or sometimes blocky) units derived from these one or two main acrylates and the small amount of the vulcanization-supporting monomer.
How Acrylic Rubber is Produced
The process by which these monomers are linked together significantly impacts the final structure and properties of the rubber. The reference mentions two primary production methods:
- Radically Initiated Emulsion Polymerisation: In this method, monomers are dispersed as tiny droplets in water, and polymerization is initiated by free radicals. This is a common method for producing many types of synthetic rubber and plastics.
- Suspension Polymerisation: This method involves suspending larger droplets of monomers in water, where polymerization occurs within the droplets.
Both processes result in the formation of the long polymer chains that constitute acrylic rubber.
Key Structural Components in Detail
Let's look closer at the monomers that define the structure:
Main Acrylate Monomers
The primary building blocks are esters of acrylic acid. The general structure of an acrylate ester monomer is:
O
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CH₂=CH-C-O-RWhere 'R' is an alkyl group. For Ethyl Acrylate, R is an ethyl group (-CH₂CH₃). Other acrylates used would have different 'R' groups.
Vulcanisation-Supporting Monomer
This monomer is crucial for enabling the rubber's elasticity. It introduces specific functional groups into the polymer chain. For example:
- A monomer with a carboxylic acid group (-COOH) allows for curing with diamines or epoxides.
- A monomer with an epoxy group might cure via reactions with acids or amines.
- A monomer with an active chlorine might cure with amines or thioureas.
The presence of these groups at specific points along the polymer chain allows for the formation of cross-links during the curing process, which is fundamental to the performance of acrylic rubber.
Summary of Structure
| Component | Description | Function in Structure |
|---|---|---|
| Ethyl Acrylate | Primary monomer (acrylate ester) | Main backbone of the polymer chain |
| Other Acrylates | Secondary acrylate monomers | Modifies properties (e.g., flexibility) |
| Vulcanisation-Supporting Monomer | Small amount of a monomer with reactive functional groups | Enables cross-linking (vulcanization) |
This combination of monomers forms a flexible yet strong polymer network after curing, suitable for demanding applications.
