Position of RAFT Polymerization
RAFT, or Reversible Addition Fragmentation Chain Transfer, is one of the methods for reversibly controlling radical polymerization. It belongs to the family of living radical polymerization systems established in the late 1990s, and uses a chain transfer agent with a thiocarbonylthio structure to temporarily place growing radicals into a dormant state.
In ordinary radical polymerization, the process is usually
initiation
chain growth
termination
which becomes an irreversible sequence. As a result, the molecular weight distribution broadens, and it becomes difficult to produce polymers with uniform chain lengths.
In RAFT, growing chains repeatedly undergo reversible addition and fragmentation with the chain transfer agent. Because all chains share the same opportunities for growth, control of molecular weight and structure becomes relatively easy.
Main features
・does not require a metal catalyst
・aqueous reactions are possible
・applicable to many vinyl monomers
・easy to create block copolymers and graft structures
Patent Situation
RAFT is a relatively old technology, and the early core patents were filed in the late 1990s. Considering patent terms, many areas covering the basic concept itself have already passed beyond the protection period.
However, the actual intellectual property structure is not simple. Related patents are still being filed continuously.
The layers of patents can be broadly divided into three categories.
Basic concept
the principle of RAFT polymerization itself
Chemical species
specific RAFT agents
trithiocarbonates
xanthates
dithiocarbamates, etc.
Applications
specific materials
medical materials
surface modification
polymer end functionalization
For this reason, rather than being completely free as a technology, the intellectual property is in a state of dispersion according to each combination of application and chemical species.
In industrial fields, RAFT is widely used in areas such as adhesives, coatings, nanoparticle modification, and surfactants.
Relationship with Tire Materials
In tire materials, RAFT becomes meaningful not so much in the synthesis of the polymer backbone itself, but rather in the area of interface design.
Tire compounds consist of interactions among
polymer
filler
curing system
and performance is determined by these interactions.
The most important part is the interface between polymer and filler.
Current mainstream materials
・end-modified S-SBR
・Nd-BR
・silica-reinforced systems
These already have a mature industrial base. There is not a strong necessity for RAFT to replace them directly.
On the other hand, RAFT is well matched with the following areas.
Polymer end functionalization
・hydroxyl
・carboxyl
・epoxy
・thiol
These can be introduced to adjust affinity with silica and polar fillers.
Filler surface grafting
・silica
・carbon black
・cellulose nanofiber
The interface layer can be controlled by forming polymer brushes on the surface.
Reactive masterbatch
RAFT chain ends have a thiocarbonylthio structure. It is also possible to convert them during compounding or curing and use them as reaction points.
Aqueous composite design
It has good compatibility with emulsion polymerization, so designs in which nanofillers are compounded in the latex state can also be considered.
Meaning as a Materials Design Tool
When considering RAFT for tire materials, the important point is the following arrangement.
not
a mass production technology for the main-chain polymer
but rather use
as a tool to design interface structure
That is,
not
polymer design
but the design of interactions between polymer and filler
This is the correct positioning.
Application Areas
Areas with a high possibility of implementation
・CNF reinforced rubber
・rCB interface modification
・reactive masterbatch
・special tread materials
・small-lot high-performance materials
Rather than mass-produced PCR treads, it is more suitable for material fields that prioritize design freedom.
RAFT is already established as a polymer chemistry technology. In tire materials, it is easier to organize it as an auxiliary technology for interface design rather than as a leading polymer itself.