Polymer Sequence Regulation Based On Latent Monomer Strategy

The precise sequence structure of biomacromolecules(deoxyribonucleic acid and proteins)plays a key role in the biological diversity and complexity.Inspired by nature,sequence regulation of synthetic polymers has become a hot topic in the field of polymer research.The research of sequence-controlled polymers covers the fields of life science and polymer science.In the field of life science,precise synthesis,characterization and sequencing of proteins and deoxyribonucleic acid(DNA)not only pioneered the gene research,but also led to the emergence of biological materials with complex and precise sequence structures.In the field of polymer science,the properties of polymers are closely related to their chain structure(e.g.,molecular weight and molecular weight distribution,sequence,stereoisomerism,and topological structure).In recent years,sequence regulation has become one of the most important strategies to regulate polymer properties,and study the structure-property relationship of polymers.With the development of polymer synthesis,a variety of synthetic strategies for the polymer sequence regulation have been reported;however,these synthetic strategies have their own limitations,such as the narrow range of monomers,complex synthesis,tedious operation and so on.Therefore,it is still an important and challenging research topic in the field of polymer synthesis to develop facile and efficient synthetic strategies for the polymer sequence regulation and enrich the sequence structure of synthetic polymers.The latent monomer strategy opens a new window for the polymer sequence regulation.In this dissertation,the furan-protected maleimide was used as the latent monomer,and the kinetic difference of its retro Diels-Alder(D-A)reaction at high and low temperature was used to control the release of the latent monomer through programmable controlled temperature.The latent monomer strategy,as an efficient synthetic strategy for the polymer sequence regulation,has been widely used in polymer synthesis.Currently,the latent monomer strategy is mainly based on programmable controlled temperature,which is suffered from the single regulation method,limited structures of latent monomers,and lack of sequence diversification.This motivates us to further improve and enrich the latent monomer strategy for the synthesis of polymers with different sequences.This dissertation focuses on enriching the structure of maleimide-based latent monomers,aiming to diversify polymer sequences and sequence regulation methods through latent monomer strategy.The research is carried out as the following five aspects:1)In this work,the alkynyl-containing latent monomer was designed and synthesized to further enrich the sequence structure of synthetic polymers.This latent monomer was controllably inserted into the polymer main chain by programmable controlled temperature to synthesize multi-block sequence-controlled polymers.An advanced sequence-controlled polymer with complex sequence distribution was synthesized by taking advantage of the variability of programmable controlled temperature mode,showing the great flexibility of the latent monomer strategy.In addition,the symmetrical multi-block copolymer was synthesized via bifunctional chain transfer reagent,which further enriched the sequence structure of synthetic polymers.This work not only enrichs the sequence regulation of synthetic polymers through the variable programmable controlled temperature,but also successfully build a "clickable" reaction platform for the synthesis of funcational sequence-controlled polymers.2)At present,there are not many latent monomers suitable for the regulation sequence of polymer,and the species of latent monomers can be further enriched according to the difference of the retro D-A reaction kinetics of latent monomers.In this work,the structure of the conjugated diene was designed to affect the retro D-A reaction behavior of the cycloadduct.Based on this,we designed a dithiophenyl furan as the new conjugated diene to synthesize the dithiophenyl furan protected N-methylmaleimide(DTFMMI)as a new latent monomer,and the latent monomer is expected to have high kinetic stability towards retro D-A reaction.The monomer design was also supported by the theoretical calculation,that is,DTFMMI has a significantly higher activation energy of the retro D-A reaction than that of the furan-protected N-hydroxyethyl maleimide(FMOH),showing higher kinetic stability towards retro D-A reaction.In this work,DTFMMI and styrene were copolymerized in one shot to synthesize binary sequence-controlled copolymers through programmable controlled temperature.In order to further enrich the polymer sequences,two latent monomers(DTFMMI and FMOH)were copolymerized with styrene and naked maleimide to synthesize sequence-controlled quadripolymers.This work utilizes the difference in the retro D-A reaction behavior between different latent monomers to synthesize diverse sequence-controlled polymers in one shot via programmable controlled temperature,which further enriches the sequence structure of synthetic polymers and expands the application of latent monomer strategy for the polymer sequence regulation.3)The latent monomer strategy is mainly based on programmable controlled temperature to regulate polymer sequences and the regulate mode is monotonous.In order to enrich the operation for sequence regulation,the spatiotemporal controllable"photo-control" was introduced to the latent monomer strategy.The above mentioned dithiophenyl furan protected N-methylmaleimide(DTFMMI)can lock and unlock the retro D-A reaction with the light irradiation."Ring-open" dithiophenyl furan protected N-methylmaleimide(DTFMMI-o)transforms to "ring-closed" isomer(DTFMMI-c)via ultraviolet irradiation.The "ring-closed" isomer(DTFMMI-c)is less prone to undergo retro D-A reaction due to its structure rigidity and the disappearance of cyclohexene double bond.With the blue light irradiation,DTFMMI-c transforms to its "ring-open"isomer(DTFMMI-o)and the restores the cyclohexene double bond,which promotes the retro D-A reaction.Based on the difference in the retro D-A reaction behavior of the two isomers and their reversible photoisomerization,the polymer sequences can be well-regulated via photo-thermal dual-control.At the constant polymerization temperature,the polymerization behavior changes significantly with the isomerization from "ring-closed"isomer to "ring-open" isomer via visible light irradiation(blue light),leading to the regulation of polymer sequences.In addition,through the combination of programmable controlled temperature and visible light switch,the release of monomers can be well-regulated to enrich the sequence of synthetic polymer.This work realizes the regulation of polymer sequence via light,and provides a new synthesis strategy.4)Environmental stimuli can also directly activate the retro D-A reaction of latent monomers.Ultrasound,as a special mechanical force,has a significant activation effect on the retro D-A reaction of maleimide-based D-A adducts.In this paper,the retro D-A reaction activated by mechanical force is applied to the latent monomer strategy.At constant polymerization temperature,the retro D-A reaction of latent monomer was activated by applying mechanical force,and maleimide was released to participate in polymerization.The sequence distribution of maleimide monomer in polymer can be controlled by controlled ultrasonic modes.In this work,mechanical force is cleverly used as a new and convenient method to achieve the sequence regulate of the polymers,which expands the regulation mode of latent monomer strategy and enriches the sequence structure of synthetic polymers.5)Polymers with specific topologies have attracted increasing attention due to their unique properties and specific applications,but the synthesis of polymers with specific topologies often requires precise molecular design.Inspired by the sequence regulation of polymer,polymers with different topological structures can also be constructed by the latent monomer strategy via one shot.In this work,macro-latent monomers based on maleimide were designed and synthesized.The latent monomer strategy and the grafting through method were combined to control the release and polymerization of macro-latent monomers,building the polymer topologies in situ during polymerizations.This means that different topologies can be prepared at different time points during the polymerization(including star shape/T shape,π shape and brush structure with adjustable grafting density,etc.).Based on the multi-reactivity of maleimide which is used as the macro-latent monomer,the composition of the macro-latent monomer can be easily diversified.In this work,a variety of polymer topologies were prepared via one-shot latent monomer strategy in combination with the grafting through method,and the grafting density could be well-adjusted by programmable controlled temperature.This work provides a simple and efficient synthesis strategy for polymers with diverse topologies.