Study On Controlling Sequence Structure Of Comb-like Macromolecules By Semi-batch Miniemulsion RAFT Polymerization

Biological macromolecules such as DNA and proteins play an important role in sustaining life.Their complex functions are based on precisely well-defined chain structures and self-assembling behaviors through intra-or inter-molecular actions.To mimic the structures and properties of bio-macromolecules,polymers with well-defined chain structures and specific topologic structures become the target of design and synthesis based on structure-function relationship.Comb-like macromolecules have more designable freedoms because their back-bones and branched chains can be independently designed and synthesized.Up to now,many living polymerization techniques based on different polymerization mechanisms have been used to control sequence structure of macromolecular chains.Among“living”radical polymerization techniques,reversible addition fragmentation chain transfer(RAFT)polymerizations have more applications in constructing non-linear macromolecules because of flexible grafting methods.In this paper,macromolecules with branched chains were synthesized by ROMP as the RAFT reagent,comb-like macromolecules with branched chains with controlled sequence structure were synthesized through a miniemulsion RAFT polymerization of 4-vinylpridiene(4VP)and t-butyl acrylate(tBA)in a semi-batch manner.The effect of molecular sequences on molecular sizes and self-assembly behavior was studied.And the effect of comb-like macromolecules aggregates on the hydrophilicity of substrates was studied also.The main research contents and results are as follows:1.First of all,Macro-CTA was synthesized by ROMP of norbornene derivatives anchoring RAFT agent.According to ~1HNMR,the degree of polymerization is 27 and M_n is calculated to be 1.28×10~4 g/mol.Comb-like macromolecules with different gradient P(4VP-b-tBA)branches were synthesized through a semi-batch miniemulsion RAFT polymerization of 4VP and tBA controlled by Macro-CTA.According to ~1HNMR,the grafting ratio and M_n of comb-like macromolecules with two gradient blocks are calculated to be 52%and4.80×10~4g/mol.The grafting ratio and M_n of comb-like macromolecules with four gradient blocks were calculated to be 50%and 1.20×10~5 g/mol.When the ratio of the chain transfer agent and initiator decreased from 2:1 to 1:1,the grafting ratio and M_n of comb-like macromolecules with four gradient blocks are calculated to be 28%and3.40×10~4g/mol;2.In order to prepare accurate multiblock copolymers,the reaction time was extended and the initiator was added so that the monomers could polymerize completely on the basis of synthesis of gradient block polymers.In contrast,the polymerization behavior of linear copolymers was studied.When the branched chains are two blocks,M_n of comb-like macromolecule is 2.31×10~5 g/mol,PDI is1.31,the grafting ratio is 55%,and the average compositions of the branched chains(4VP+tBA)are 72+69,while PDI of the linear copolymers is 1.28,and the average compositions of chains(4VP+t BA)are 95+96.When the branched chains are four blocks,M_n of comb-like macromolecule is 2.41×10~5 g/mol,PDI is 1.36,the grafting ratio is 57%,and the average compositions of the branched chains are 67+69,while PDI of the linear copolymers is 1.30,and the average compositions of chains are94+96.When the branched chains are forty blocks,M_n of comb-like macromolecule is 2.20×10~5 g/mol,PDI is 1.38,the grafting ratio is 51%,and the average compositions of the branched chains are 68+67,while PDI of the linear copolymers is 1.33,and the average compositions of chains are 93+94.The size of polymers with different sequence structures of branched chains is different by analyzing the molecular size of the DMF solution(0.01wt%)of the comb-like macromolecules.The more blocks of the polymer contains,the smaller the size is.The PDI of the linear copolymers is smaller than that of the comb-like macromolecule,which is due to the limited activity of chain transfer agent;3.In order to explore the effect of sequence structures on the size of comb-like macromolecules aggregates,different concentrations of comb-like macromolecule DMF solution were dried and analyzed by microscope.The results of optical microscope show that the more blocks P(4VP-b-tBA)branches contain,the smaller the particle size of comb-like macromolecules aggregates is.Furthermore,the effects of these aggregates on the contact angle of the substrate have been studied.The results show that the two blocks comb-like macromolecules of the branched chains can enhance the hydrophobicity of the substrate,while the four blocks and forty blocks of comb-like macromolecules can improve the hydrophilicity of the substrate.Finally,the surface energy of the blank substrates and substrates with comb-like macromolecules is calculated.P(4VP-b-tBA)branches and forty blocks P(4VP-b-tBA)branches could enhance the hydrophilicity of the interface.The surface energy of blank substrates and different substrates with comb-like macromolecules with different block P(4VP-b-tBA)branches was calculated;...