Vinyl Carboxylate Applications
Currently, there are no other vinyl carboxylates that are being used in such large quantities as vinyl acetate, but because of the diversified structure of these substances, their possibilities are limitless. Following is an introduction to only a fraction of the applications for vinyl carboxylates.
- Controlling of plastic softness (Tg) and other properties (used as a copolymerization monomer)
- Using vinyl carboxylates with functional groups as cross-linking sites
- Use in optically active substance splitting reactions
- Use in photo hardening and cross-linking reactions
Controlling of plastic softness (Tg) and other properties (used as a copolymerization monomer)
When synthesizing polymers, producing a product with just one type of monomer is not common. Instead, usually a variety of monomers are copolymerized to approach the desired properties such as the plastic's hardness and solubility in solvents.
Vinyl carboxylates are very useful as this type of modification monomer.
For example, a polymer polymerized using only vinyl pivalate will produce a transparent, hard plastic (Tg: 86°C). Copolymerizing this type of monomer that produces a hard polymer makes it possible to produce a plastic that does not soften easily even at higher temperatures.
Conversely, a plastic with flowability at room temperature can be obtained by polymerizing a straight-chained aliphatic vinyl carboxylate like vinyl laurate. Copolymerizing this type of monomer that produces a "soft" polymer makes it possible to obtain a soft "internal plasticity" plastic without raising its temperature.
(Tg: Glass Transition Temperature): This is the temperature at which a polymer changes from a hard glass-like state to a soft state.
A plastic's properties can be modified in other cases using copolymerization to obtain specified objectives, such as controlling the solubility in solvents, increasing the dispersability of pigments, or adding cross-links.
The plastic in the illustration was copolymerized with vinyl carboxylate to adjust the softness, solubility, and pigment dispersability.
Using vinyl carboxylates with functional groups as cross-linking sites
- Example: Acrylic rubber cross-link site monomer
- Vinyl monochloroacetate has an active chlorine atom, so the reactivity of this chlorine atom can be used to cause a reaction.
The following is an example of using this active chlorine atom as an acrylic rubber cross-link site (area that reacts with a cross-linking agent).
Acrylic rubber is a rubber with excellent heat resistance and oil resistance and is mainly used as a material in parts that require both resistance to high temperatures and oil, such as for parts used in the automobile engine compartments.
A few percent of vinyl monochloroacetate (shown in red in the illustration) is copolymerized with various acrylic ester monomers.
Using an amino based or other cross-linking agent here will quickly form cross-links. Since the chlorine atom that forms the leaving group of the vinyl monochloroacetate is very active, the formation of the cross-link is very fast compared to when using 2-chloroethylvinylether, which is also a chlorine base vinyl monomer, and secondary vulcanization is in some cases unnecessary.
Use in optically active substance splitting reactions
Most of the proteins found in organisms are optically active substances. Optically active substances exhibit different behavior even when they have the same chemical formulas, as shown in the following illustration, because they have a different three-dimensional structure.
(These are diagrams of D Type and L Type molecules. They have the same chemical formula, but reversed three-dimensional structures.)
In an organism, the functions of the D Type and L Type molecules are normally not the same. One is used as a pharmaceutical, and the other one exhibits toxicity. Therefore, accurately extracting only one type (optical resolution) when multiple optically active substances are mixed together (racemic body) is an important point when producing pharmaceuticals, fragrances, agricultural chemicals, or synthesizing intermediate substances.
Vinyl carboxylate is especially useful for optical resolution reactions when the optical resolution target is racemic alcohol.
The same reaction can be done using carboxylic acid methyl or ethyl ester, but in this case the byproducts of methanol or ethanol remain easily in the reaction system, so equilibrium could be reached before the reaction is complete. Using vinyl carboxylate, the vinyl group is converted into acetaldehyde, which has a lower boiling point and is desorbed, so it is easy to remove from the reaction system, thus allowing the reaction to efficiently proceed until it is completed.
The reaction itself is very simple, so it can be used for a wide variety of reactions from those in a beaker to industrial scale.
The problem is that the reaction only selects one of the types, so the maximum yield when performed normally is 50%, but this is a very useful reaction when the remaining substance can easily be re-racemized or the product is a high value-added product.
Use in photo hardening and cross-linking reactions
Recently, there has been much interest in reactions using high energy beams, such as ultraviolet rays, gamma rays, or electron beams. The interest is not only in easily starting polymerization using light, but also in reactions, such as cross-linking.
Because heat is not used to initiate a reaction, there is very little change in properties caused by heat. Using an adhesive as an example, conventional adhesives require heating to start the hardening reaction, or the reaction generates heat, and the swelling from heating or the contracting from cooling has caused the adhesive resin to crack or separation to occur between the adhesive and the base material.
Compared to this, no swelling from heating occurs during a photo-hardening reaction, so this reaction has excellent dimensional stability and is used where dimensional stability is required, such as in adhesives for electronics materials.
Progress is also being made for applications of this kind of cross-linking or polymerization using a photoreaction for photo-hardening coatings that do not use a solvent.