The Single-chain Mechanics Of Hydroproline-based Polyesters

Hydroproline-based polyesters(PPEs)are novel degradable aliphatic polyesters with high molecular weight and complete recyclability under mild and economic conditions.Because of that,PPEs can be used as a candidate to solve the environmental problems caused by the petroleum-based synthetic polymers.However,the study of the mechanical property of PPEs,which is important for the applications,has not been reported yet.In order to investigate the mechanical property of PPEs,herein,we utilized atomic force microscopy(AFM)-based single-molecule force spectroscopy(SMFS)and quantum mechanics(QM)calculations to study the mechanical property of PNC12PE(a kind of PPEs)in quasi-undisturbed environment at the single-molecule level.Besides,we discovered the effect of several solutions,which are often used to regulate the polyprolines conformation,on the mechanical property of PNC12 PE at the single-molecule level.Based on the above investigation,the main conclusions can be summarized as follows:(1)The inherent elasticity of PNC12 PE is obtained,exhibiting that the main chain of PNC12 PE is as soft as the common polymers with C-C backbone.In addition,the pyrrolidine rings in the main chain of PNC12 PE are mechanically stable(F < 2200 p N)during SMFS experiment,indicating that PNC12 PE is suitable for the applications requiring high mechanical stability.(2)Solution environment(DI water,nonane and 1-propanol)that are used to regulate the conformation of polyproline affect the mechanical properties of PNC12 PE.The hydrogenbonding interactions between water molecules and PNC12 PE have significant effect on the single-chain elasticity of PNC12 PE.The stretching of single PNC12 PE chain in the organic solvents with linear alkyl groups requires additional energy,which is negatively correlated with the polarity of the organic molecules containing the linear hydrocarbon groups.(3)The mechanical properties of PNC12 PE vary with the quasi-physiological conditions(PBS buffer and sodium chloride normal saline)and the neutral salt solutions(4 mol/L calcium chloride).Besides,there is a special relationship between the single-chain elasticity of PNC12 PE and the concentration of the sodium chloride solution.