Study On Precise Synthesis And Applications Of Cationic Polyacrylamides Via Aqueous RAFT Disnersion Polymerization

Cationic polyacrylamides(CPAMs)are arguably one of the most important water-soluble polymers.They are widely used in pulp industry,mining and sewage water treatment,especially as flocculants.However,the existing commercialized CPAMs mainly comprised linear random copolymers with high molecular weights,making them inefficient in cationic functionality,difficult to dissolve,and exhibit high viscosities in solutions.Designing and tailoring high-performance CPAMs with novel structures are badly needed.Moreover,the synthesis of CPAMs are usually conducted in solution of inversed emulsion systems,which limits the production efficiency and involves the use of organic solvents and emulsifiers.A dispersion polymerization in aqueous phase system is also needed to achieve high solid content.In this work,we developed a RAFT dispersion polymerization approach with aqueous solution of ammonium sulfate as the continuous phase,and random cationic copolymers were used as macro chain transfer agents(mCTAs)as well as stabilizers.The copolymer was first synthesized via aqueous RAFT solution polymerization of acrylamide(AM)and methacryloxyethyltrimethyl ammonium chloride.Block CPAM copolymers can be synthesized by chain extension of mCTA with AM.When phase separation occurred in this RAFT dispersion polymerization process,divinyl cross-linkers were added via a semi-batch strategy,and core-shell CPAMs with cationic copolymer arms and hyperbranched PAM cores can be obtained.These core-shell CPAMs show good flocculation performances and can be applied in sewage treatment and papermaking.This work investigated the kinetics of aqueous RAFT solution polymerization of AM using random CPAM copolymers.The effects of polymerization conditions on the kinetics were systematically investigated and a kinetic model for this system was established.Subsequently,RAFT dispersion polymerizations were conducted based on the solution ones.The phase separation phenomenon and effects of reaction conditions on the kinetics were also investigated.The reaction mechanism was hypothesized and a kinetic model for the RAFT dispersion polymerization system were developed.We also tailored core-shell CPAMs via semi-batch aqueous RAFT dispersion polymerization and studied the relationships between polymer structure and application performances as flocculants,drainage aids,and dry strength agents.Comparison was made with commercial products in order to evaluate the CPAMs.The main conclusions can be summarized into three points:1.A highly efficient approach to tailor high-performance CPAMs was developed.Random CPAM copolymers with high cationic fractions were introduced as mCTA and stabilizers in aqueous RAFT dispersion polymerization of AM.Precursors for core-shell CPAMs with concentrated cationic charge at the arm ends can be synthesized using this method.Green fabrication of CPAMs was achieved.2.The mechanism of aqueous RAFT dispersion polymerization of AM was unveiled by investigation into the phase separation and the reaction kinetics.It is shown that the mass enrichment and diffusion-control in dispersed phase are the main reasons for the accelerations in reaction rate when phase separation happened.Significant understanding of aqueous RAFT dispersion polymerization was provided by modeling of this unique system.3.We constructed and tailored core-shell CPAMs with hyperbranched PAM cores and cationic arms by combining RAFT dispersion polymerization and semi-batch strategy.The CPAMs have great performance in flocculation and paper dry strength aid,and also easy to dissolve.The tailor-made high-performance CPAMs synthesized via RAFT dispersion polymerization have promising industrial applications.The high efficiency approach can be used in producing other polymers with core-shell structures.