Seeded Polymerization of Conjugated Diene Copolymers

The patent changes the polymerization mechanism by introducing a reversible addition-fragmentation chain transfer agent (RAFT agent) to control the molecular weight distribution. This parameter change in the polymerization process allows achieving narrow molecular weight distribution (Mw/Mn ≤ 2.5) while maintaining the emulsion polymerization framework, thus improving fuel efficiency without completely redesigning the synthesis process

The patent uses a hydrophilic RAFT agent as an intermediary substance to control the polymerization process. The hydrophilic nature of the RAFT agent allows it to be effectively dispersed in the aqueous emulsion system, enabling controlled radical polymerization mechanism while maintaining processability. This intermediary facilitates the transition from conventional uncontrolled polymerization to controlled polymerization with narrow molecular weight distribution

The patent changes the key parameter of the RAFT agent from hydrophobic to hydrophilic by selecting specific molecular structures (containing polar groups such as carboxyl, hydroxyl, or ether groups). This parameter change enables the RAFT agent to be effectively dissolved and dispersed in the aqueous emulsion system, ensuring uniform distribution and active participation in the polymerization process, thus maintaining high reaction rates while achieving narrow molecular weight distribution

The patent employs a hydrophilic RAFT agent that can be effectively used at low concentrations (0.1-5 wt% based on total monomer) to control the polymerization process. The hydrophilic nature ensures the agent remains accessible and active throughout the reaction, preventing droplet encapsulation and ensuring continuous chain transfer activity, thereby maintaining fast reaction rates

The patent applies partial action by stopping the polymerization at a controlled conversion rate (50-90%) rather than allowing it to proceed to 100%. This partial conversion is sufficient to achieve the desired molecular weight distribution and incorporate the third monomer effectively, while preventing the formation of gel. The controlled conversion rate optimizes the balance between monomer conversion and gel prevention

The hydrophilic RAFT agent serves as an intermediary that mediates the polymerization process to prevent gel formation. By controlling the chain transfer reactions and maintaining active chain ends throughout the process, the RAFT agent prevents the formation of dormant gel structures even at high conversion rates, thereby maintaining workability and dispersibility while enabling effective third monomer incorporation

The patent replaces tert-dodecyl mercaptan with a hydrophilic RAFT agent as an intermediary substance to control molecular weight. The RAFT agent operates through a reversible addition-fragmentation mechanism that prevents the formation of gel structures, unlike the conventional mercaptan approach. This intermediary enables efficient polymerization while eliminating the harmful gel byproduct through controlled chain transfer reactions

The patent changes the molecular weight control mechanism from irreversible chain transfer (mercaptan) to reversible addition-fragmentation chain transfer (RAFT). This parameter change in the control mechanism allows maintaining polymerization efficiency while preventing gel formation. The reversible nature of RAFT ensures continuous chain activity and uniform molecular weight distribution without generating gel