The Application Of Degradable Poly(Benzyl Ether)on Adhesive And Polypeptide Synthesis

Different from those stable polymeric materials used traditionally,degradable polymers can break down under pre-designed,specific and mild conditions.The diversity of polymers’structures also brings diversified modes for polymer degradation,such as the chain break-downs on random positions along a biodegradable polymer with certain enzymes present,and domino-type self-elimination cascades for self-immolative polymers triggered by the removal of chain-end caps in certain scenarios.Poly（benzyl ether）is a type of self-immolative polymer with sequentially connected benzyl phenyl ethers on its backbone.The corresponding monomer is easy to make,and can undergo controlled polymerization processes under mild conditions.In these polymers,both the end-cap and the monomer can have its structure independently regulated,which provides the possibility to create modular structures for different application scenarios.In addition to its conventional self-immolative degradation mode involving sequential 1,6-eliminations,we found that poly（benzyl ether）s can also be rapidly degraded through ether bond cleavage under strong acid conditions.Based on these two different degradation modes,we designed an AB-type modular dismantling adhesive based on poly（benzyl ether）,which can achieve high adhesion strength and high stability on a variety of material surfaces,meanwhile with the capability of being dismantled quickly and controllably.In addition,we designed a poly（benzyl ether）-basedɑ-amino acid-N carboxy anhydride（NCA）ring-opening polymerization macroinitiator.Thanks to the poly（benzyl ether）skeleton,the NCA polymerization initiator can be used to rapidly prepare modifiable polypeptides.The prepared polypeptides can be easily modified by functional small molecules,and more importantly,they can be directly used to modify organic semiconductors and two-dimensional inorganic nanosheets.In the work related to AB-type modular dismantling adhesives,we designed and synthesized three kinds of poly（benzyl ether）s with different end caps（component A）and seven small molecular organic azides（component B）.The modular construction of the polymers allows the polymeric adhesive system to be used for the bonding of different substrates.Benefiting from the multivalent structure generated by the azide-alkyne cycloaddition reactions after AB mixing,the adhesive exhibits high bonding strength（lap-shear）of up to 11 MPa.The phenyl ring-rich structure of poly（benzyl ether）makes the adhesive sufficiently hydrophobic,allowing it to be used in wet or underwater environments.By adjusting the end-cap’s structure,the adhesive can be degraded under the action of different triggering agents,thereby realizing the non-destructive disassembly of the adhered surfaces.Since it is necessary have the lone pair of electrons on the leaving phenolic anion and the breaking C-Oσ-bond in anti-periplanar positions during the degradation of poly（benzyl ether）s,the disassembly of the adhesive requires that the end group of the poly（benzyl ether）has some degree of rotational freedom,which is satisfied by the presence of a suitable swelling solvent.Therefore,both a triggering agent and a suitable solvent are needed to achieve degradation.This feature provides AND-gated control of the disassembly of the adhesive,ensuring the reliability of the adhesive without affecting the dismantlability of the adhesive.In the work related to polypeptide materials,we found that strong acid can rapidly degrade poly（benzyl ether）s.Different from the domino-like self-eliminating degradation reported previously,the use of excess HCl in aprotic solvents can instantly degrade poly（benzyl ether）s to benzhydryl chloride derivatives（BHD-X）,and this degradation process is not influenced by the end-caps.When poly（benzyl ether）s are degraded using acids with non-nucleophilic anions such as bis（trifluoromethane）sulfonimide（TFSI）,the degradation is more inclined to generate BHD⁺cations,which can react rapidly with nucleophiles such as thiols or alcohols.We successfully achieved the controllable ring-opening polymerization of crude NCAs using poly（benzyl ether）with amino groups on the side chains（PBE-g-NH₂）in a biphasic polymerization system of chloroform and phosphate buffer to obtain polypeptide brushes with poly（benzyl ether）backbones（PBE-g-polypeptide）s.The backbone can be rapidly degraded by strong acid（HX）,which can be completed within a few seconds.The free polypeptide obtained after backbone degradation has low dispersity（<1.2）,and can be quickly modified by alcohols or thiols.As a result,we achieved extremely efficient preparation and modification of polypeptides,and the entire process starting from NCA monomer synthesis to peptide synthesis and modification can be completed within 3.5 hours.Considering that BHD-polypeptides have highly reactive end groups,we tried to use BHD-polypeptides to directly construct functional hybrid materials.We successfully modified the organic semiconductor,poly（3-hexylthiophene）（P3HT）,with TFSI-degraded BHD-PBLG（PBLG=poly（γ-benzyl-L-glutamate））to obtain conductive P3HT-g-polypeptides.Benefiting from the large steric hindrance（15 k Da）of PBLG,the polaron generated on the main chain of P3HT after doping can be protected by the PBLG side chains,which makes P3HT-PBLG more biocompatible.At the same time,due to the large molecular weight of PBLG,the mass of PBLG in P3HT-PBLG is several times higher than that of P3HT,so that P3HT-PBLG has more characteristics of polypeptides.Freshly prepared PBLG-BHD can also be used to directly modify MoS₂ 2D nanosheets,and the modified MoS₂-PBLG shows better organic solvent dispersibility than pristine MoS₂ nanosheets.MoS₂-PLG,obtained by reducing the benzyl protecting groups of PBLG in MoS₂-PBLG,has better dispersibility in water,and such surface-modified MoS₂ can be used as a catalyst to mediate the reduction of nitro groups by sodium borohydride,and it shows better catalytic activity than the unmodified MoS₂ nanosheets.