Tandem Metathesis Depolymerization-Cyclopolymerization And Properties Of Rubbery Block Copolymers

Rubber materials as indispensable strategic resource,which were wildely used in defense military and security,aerspace,and industrial production fields.In order to expand the research and application fields of natural rubber（NR）and realize the structural transformation and performance optimization at the molecular level of NR,it was of great significance to develop new rubber-based functional polymers.Herein,modification of NR was studied as follows:Metathesis depolymerization（MDP）of NR was readily conducted to afford depolymerized NR（d NR_x）bearing the living chain end,which can initiate metathesis cyclopolymerization（MCP）of 4-（1-methyl-3-undecyl imidazolium hexafluorophosphate）ester-1,6-heptadiyne（Im HD）and 4-（2-hexyldecyl carbonyloxymethyl）-1,6-heptadiyne（HCHD）to creat a new tandem MDP-MCP method.Block copolymers consisting of rubbery d NR_x segment and plastic PA segment were achieved by this newly constructed tandem MDP-MCP strategy.The triblock copolymers containing flexible d NR_x segment and rigid ionic PA segment possessed good mechanical properties,and exhibited distinctive damping performance with unique relaxation plateau covered a broad temperature range,which could be further enhanced by modifying triblock copolymers with the bromo-functionalized triazolinedione derived from biobased oleic acid.Specifically,(d NR_x2-b-PHCHD₁₀₀-b-PIm HD₅₀)-40%Br UZ showed a superior damping performance with a strong damping peak（tanδ=0.57）and wide（35）T from-23 to 39 ^oC.Therefore,the reconstruction of unsaturated polymers by the MDP-MCP method with broad application prospects opens up a convenient new route for the preparation of functional rubbery-plastic block copolymers.4-[（3-Phenyl acrylate）methyl ester]-1,6-heptadiyne（Cin HD）was designed and prepared.The corresponding d NR_x2-b-PCin HD₁₀₀ was obtained by tandem MDP-MCP reaction,which consisted of Cinnamate side group.The test results of UV-visible absorption spectrum showed that the sample in solution and in film both undergo a certain degree of[2+2]photocyclization when irradiated with 365 nm UV light for about 2 h.Meantime,dynamic light scattering（DLS）demonstrated that the self-assemblies for d NR_x2-b-PCin HD₁₀₀ before UV crosslinking with D_h of 29 nm and after UV crosslinking with further decreased D_h of 12 nm were observed in the selective solvent chloroform.Comparing the damping properties of d NR_x2-b-PCin HD₁₀₀before and after UV crosslinking,it was found that the maximum damping value of the material after crosslinking increased from 0.38 to 0.43,and the effective damping temperature range was broadened by nearly 20 ^oC.After the[2+2]photocyclization reaction,the polymer molecular chain becomed compact which increases the internal friction of the molecular chain,thereby enhancing the damping performance of the material.It also shows that there is a close relationship between the macroscopic properties of the material and the the microscopic molecular structure.Therefore,photochemical crosslinking is also an effective method to improve polymer functionality.