In the field of polymer materials, Organic peroxides is used as an initiator for free radical polymerization, an initiator for graft reaction, a crosslinking agent for rubber and plastics, a curing agent for unsaturated polyester, and a molecular weight and molecular weight distribution regulator in the preparation of spinning grade polypropylene. Organic peroxides is the source of free radicals used in the following applications: ① initiator for free radical polymerization and copolymerization of vinyl and diene monomers; ② Vulcanizing agent for thermosetting resins; ③ Crosslinking agent for elastomers and polyethylene.
In addition to the above polymer material industry, Organic peroxides is used in the film industry as a photoinitiator and sensitizer, used in photosensitive polymer materials, photosensitive resins, etc., and also commonly used in the production of epoxy resin; In terms of medical materials, initiators composed of Organic peroxides and drugs are used to synthesize sustained-release drug delivery matrices (such as microspheres, pellets, drug films); In organic synthesis, Organic peroxides is mainly used as oxidant and epoxide. In addition, Organic peroxides is also used in disinfection of medical devices and food, bleaching agent, decolorizing agent, bactericide, cleaning agent, etc. in textile, paper and other daily chemical industries.
The decomposition temperature of a Organic peroxides at an effective rate largely determines its use. Other important factors include cost, solubility, and safety. Efficiency and types of free radicals generated, necessity of frozen storage and shipping, compatibility with production systems, potential impact on products, and ability to be activated. Organic peroxides can be decomposed into reactive radicals at a certain rate at high or room temperature.
All Organic peroxides are thermally unstable and decompose faster with the increase of temperature. The commonly used quantitative determination method for the reactivity of Organic peroxides is to measure the half-life, that is, the time required for a certain amount of peroxide to decompose to half of its initial amount at a certain temperature. Half life data of commercial Organic peroxides are now available on computer floppy disks. By using the computer menu program, suitable peroxides can be selected for a certain polymerization or process condition.
These free radicals can be added to unsaturated vinyl monomers such as styrene, vinyl chloride or Methyl methacrylate to initiate polymerization. Some free radicals also attack polymers such as PE to generate free radicals on the chain. When two such polymer radicals combine, a cross-linked structure is formed.
Vinyl compound polymerization
Organic peroxides provide the most effective way to initiate free radicals for polymerization. By selecting one Organic peroxides at half-life temperature, or using a mixture of two or more Organic peroxides, vinyl polymerization can be effectively carried out in a wide temperature range.
PVC is mainly produced through the suspension process. 2-Ethylhexyl peroxydicarbonate and tert butyl peroxydecanoate are excellent initiators, especially in relation to α- Cumyl peroxydecanoate or α- The mixed use of Kuji peroxyheptane ester. However, hyperacidity α- The use of cumyl ester can cause undesirable odor of Acetophenone in the resin. The odor of Acetophenone in the resin can be eliminated by using 1,1-dimethyl-3-hydroxy-butyl neoheptanoic acid as a low-temperature initiator component. Other advantages of using this initiator include increased productivity and reduced adhesion on the reactor wall. Due to improved processing and efficiency, tert amyl peroxyvalerate is now also used instead of azo initiator.
The resin used for high solid acrylic coatings uses peroxyesters and peroxyketals as initiators. When the solid content is 70% or higher, it is best to choose tert amyl peroxyesters and peroxyketals to obtain a narrow molecular weight distribution and low solution viscosity. Resins such as tert butyl peracetate and 3,3-di (tert amylperoxy) Ethyl butyrate can also be used to generate low residual amount of monomer. In addition, Organic peroxides with light stabilizer groups, such as hindered amine, are being actively developed to improve the performance of automotive coatings.
When EPS is produced by suspension polymerization, initiator including mixture of benzoic peroxide and tert butyl perbenzoate is usually used.
The reaction time required for residual styrene concentration below 0.1% can be shortened by replacing Tert-Butyl formate with O - tert amyl O - (2-ethylhexyl) - monoperoxycarbonate. Crystal PS and HIPS are usually prepared by continuous bulk polymerization, preferably using peroxyketal as the initiator.
polyolefin
Organic peroxides is used as initiator in the production of LDPE and ethylene copolymer. Peroxyesters are the best peroxide initiators due to their ability to provide a wide range of reactivity and good solubility when used at high temperatures and pressures. According to its efficiency, the most commonly used among peroxyesters is tert butyl peroxyoctanoate. Other varieties, in descending order of use, are tert butyl peracetate, Tert-Butyl acetate and tert butyl perbenzoate. If stronger reactivity is required, corresponding tert amyl peroxyesters can be used.
As a means to improve the strength of the foam film in the extruder, reducing the melting flow of LLDPE with Organic peroxides has attracted more and more people's interest. When higher processing temperatures are required, dialkyl peroxides are often used.
Polypropylene can be cracked with Organic peroxides to obtain narrow molecular weight distribution and increase fluidity. Select 2,5-dimethyl-2,5-ditert-butylperoxyhexane while meeting performance and FDA requirements.
Curing of polyester
Thermosetting polyester can be prepared by curing unsaturated polyester alkyd resin and monomer solution such as styrene with Organic peroxides. Many curing processes are carried out at room temperature by adding activators or accelerators to the resin, causing certain peroxides to decompose and form free radicals, thereby initiating curing.
The two most commonly used peroxides for polyester curing are benzoic acid peroxide and MEKP. Dimethylaniline is a typical tertiary aromatic amine, which is used to activate benzoic acid peroxide, and Cobalt(II) naphthenate is used to activate MEKP.
Both high-temperature cured sheet molding materials and overall molding materials are cured using metal molds and high-pressure at high temperatures. Tert-Butyl formate is the most widely used molding catalyst at 280-320 ° F. At present, some important processes for rapid curing operation cycles, as well as other peroxides, especially tert amyl peroxides, are becoming increasingly important in mold curing applications. Special examples include tert amyl benzoate and 1,1-di tert amyl peroxycyclohexane. Due to their faster reaction activity, shorter cycle time, and higher efficiency than their tert butyl counterparts, these two substances can save raw materials, shorten cycle time, and save energy.
A mixture of high-temperature and low-temperature initiators can improve production efficiency. However, according to the latest cost performance standards, tert amyl peroxyoctanoate is more important as a superior low-temperature initiator than tert butyl peroxyoctanoate.
MEKP type accelerators dominate the room temperature curing of unsaturated polyester. Together with transition metal salts (such as Cobalt(II) naphthenate), they are the most commonly used accelerators. Mixing dimethylaniline with transition metal salts can double the curing rate of the system. The most effective catalyst concentration is 0.5% to 2.0% of the resin. The concentration of the accelerator is variable, but usually between 0.05% and 0.3%. However, excessive accelerator concentration has an adverse effect on the final curing process.
The main feature of a room temperature curing system is that the peroxide and activator are only combined during curing. The most commonly used system is the catalyst injection system. The process includes the metering and mixing of catalysts and cured resins. For example, in a spraying system, mixing occurs in the spray fan (external mixing) or in the spray gun (internal mixing).
cross-linking
Organic peroxides are used for crosslinking saturated and unsaturated elastomers with thermoplastic resins. Dialkyl peroxides, especially dialkyl peroxides, have become the standard crosslinking agents for this process.
The free radicals derived from dialkyl peroxide derivatives are good hydrogen extractors. This is an important standard for thermoplastic resins such as LDPE, which only undergo cross-linking through the hydrogen abstraction mechanism.
In elastomers such as EPDM with unsaturated chains or containing crosslinking agents such as TAC, crosslinking is achieved through chain addition mechanism. In this case, peroxyketal is a very good crosslinking agent. If possible frost spraying issues are ruled out, using peroxyketal has a faster curing cycle.
It has been disclosed that there are new technologies that can increase users' ability to prevent early solidification when applying certain peroxides in blending processing. This new technology is applicable to most commercial dialkyl peroxides and peroxyketal Organic peroxides. Peroxides with lower temperature are allowed for elastomers, and faster curing time can be obtained by taking advantage of lower activation characteristics. For example, in the basic components of polybutadiene, the prevention of early curing grades of dicumyl peroxide and 1,3,5-trimethylcyclohexane can significantly prolong the curing time when similar curing states are generated.
Although dibutyl peroxide is the most commonly used in crosslinking processes, there are operational issues due to its solid nature. New peroxide liquid formulations, especially those with anti premature curing properties, are increasingly receiving attention. Similarly, it is expected that these formulas can be used in the crosslinking of LLDPE.
The rotational molding of HDPE can produce cross-linked structural products like storage tanks, which is a rapidly emerging field. Due to the high crystallization melting point of HDPE, most thermal stable Organic peroxides products, such as 2,5-dimethyl-2,5-di (tert butyl peroxide) hexyne-3, are most suitable for this purpose.