Preparation And Properties Of Thermoplastic Elastomers Based On Myrcene By RAFT Emulsion Polymerization

The utilization of monomers to synthesis rubber presents significant environmental concerns as these monomers are often derived from non-renewable fossil sources.The manufacturing process requires irreversible chemical cross-linking and precise control,leading to increased production costs.Moreover,once discarded,these products present difficulty in recycling,thereby creating an undeniable negative impact on the ecosystem of nature and the living environment of humans.In contrast,thermoplastic elastomers,commonly referred to"third-generation rubber,"have unique advantages due to their physical cross-links.They exhibit high elasticity similar to vulcanized rubber at room temperature and plastic-like molding and processing properties at high temperatures.Thermoplastic elastomers can be repeatedly processed and used multiple times,leading to lower production costs and reduce environmental impact.To address the limitations of using petroleum-based diene monomers,this project utilized myrcene,a bio-based monomer derived from biomass resources.Myrcene is found in essential oils extracted from various plants.Myrcene’s structure is similar to isoprene,making it an ideal substitute for petroleum-based diene monomers.The RAFT surfactant-free emulsion polymerization,a novel polymerization method,was employed in this project.The method combines RAFT technology and emulsion polymerization technology,providing high reaction activity,controllable molecular weight,and molecular weight distribution,and controllable sequence structure.A dual-functional macromolecule RAFT reagent was used.First,both monomers were homopolymerized.Then the block copolymerized a series of three-block copolymers of tert-butylacrylate-b-myrcene-b-tert-butyl acrylate were synthesized.To verify the controllable activity of RAFT polymerization,the changes in conversion,particle size,and molecular weight were studied during the reaction process.The properties of the five groups of different feed ratios of the three-block copolymers were also analyzed,and their hydrolysis and carboxylation modification were carried out to further explore their potential applications.In our initial endeavor,we endeavored to synthesize and characterize an amphiphilic Macro-RAFT AA₂₀-b-St₅ agent,which had the potential to be utilized in the homopolymerization of tert-butyl acrylate and the block copolymerization of tert-butyl acrylate and lauryl methacrylate.Through the utilization of the RAFT emulsion polymerization technique,we proceeded to analyze the conversion,particle size,and molecular weight of both processes over time.The outcomes of our research indicated that the mid-stage polymerization rate was the most expeditious and consistent when utilizing the RAFT emulsion polymerization method,and the ultimate conversion rate exceeded 95%.During the emulsion,the latex particle size underwent three distinct stages:nucleation,constant rate,and slowing down periods,ultimately resulting in a final latex particle size increase to 105 nm.The molecular weight distribution,however,remained within a narrow range.Upon the addition of the second monomer lauryl methacrylate,the monomer conversion rate remained above 90%for a specific period,and the latex particle size continued to increase,ultimately reaching 150 nm.The molecular weight increased correspondingly,as the molecular weight and distribution expanded from 5.9w,1.1 at the conclusion of the first polymerization to 11.8w,1.8 at the end of the second polymerization.Consequently,our research concluded that the usage of the amphiphilic Macro-RAFT AA₂₀-b-St₅ agent could result in an effective and well-controlled emulsion polymerization process for the production of block copolymers.We then proceeded to synthesize five groups of tert-butyl acrylate triblock copolymer thermoplastic elastomers,with feeding ratios ranging from 20%to 60%.The molecular weight of BMB20 to BMB60 ranged from 5.7 to 7.3w,with a molecular weight distribution ranging from 1.2 to 1.7.We characterized the thermal properties of BMB20BMB60 using DSC,TGA,and DTG,which showed two glass transition temperatures:-58℃for polylaurene and 40℃for polytert-butyl acrylate.The decomposition temperature of BMB20～BMB60 ranged from 390℃to 500℃.The tensile strength of the five groups of thermoplastic elastomers increased from0.8MPa of BMB20 to 3.8MPa of BMB60,while the elongation at break decreased from 394%to 81%.As the chain length of the polytert-butyl acrylate segment increased,the chain length of the polylaurene segment decreased,and the chain length between adjacent crosslinkingpoints became shorter,resulting in the modulus increasing from 0.8MPa to 32MPa.BMB40 was selected as the blank group for hydrolyzed carboxyl modification.After hydrolysis,the chain compliance of the hard BMB decreased,and the glass transition temperature ultimately increased to 58℃,while the glass transition temperature of the soft polylaurene ultimately increased to-44℃.Concerning mechanical properties,the tensile strength of BMB40 was1.08MPa,the elongation at break was 254%,and the modulus was 0.51MPa.As the hard segment carboxylation increased,the final tensile strength of BMB40-60h was 1.56MPa,elongation at break was 170%,and modulus was 1.60MPa.