Design,Preparation And Properties Of Bio-based Cross-linked Polymers Based On Amide Bonds

Nowadays,polymer materials play an important role in social development and daily life.However,the development of polymer materials depends heavily on non-renewable petrochemical resources.The petrochemical resource crisis will affect the development of polymer materials,and the consumption of traditional polymer materials will further aggravate the energy crisis.Therefore,it is imperative to develop sustainable polymer materials based on biomass.Thermosetting polymers are widely used for the outstanding mechanical properties,thermal stability,solvent resistance,wear resistance and dimensional stability derived from their chemical crosslinking network structure.However,the chemical crosslinking network structure makes thermosetting materials difficult to be reprocessed and recycled,which greatly limits the application potential of thermosetting materials in some emerging fields.Therefore,it is necessary to improve the reprocessability of thermosetting materials.Amide group,which could form hydrogen bonds between each other,is widely used in the structural design of polymer materials.The existence of hydrogen bond can increase the intermolecular force,so the mechanical properties of materials can be improved by introducing amide groups.In order to alleviate the crisis of petrochemical resources,promote the sustainable development and application of thermosetting polymer materials,and take into account the mechanical properties and stability of thermosetting materials,a series of high-performance,bio based and cross-linked polymers were designed and prepared by introducing amide bonds into molecular chain.The specific research contents and results are as follows:(1)Design,preparation and properties of bio-based polyamides with high performance based on amide bonds and hydrogen bonds.Firstly,a novel biobased tetraester,i.e.tetramethyl piperazine-N,N'-bis(2-methylene butanedioate)(TMPB)was synthesized through a highly efficient and atom economical Michael addition using dimethyl itaconate(DMI)and piperazine(PZ).Then,several cPITAs with double crosslinking network based on amide bonds and hydrogen bonds were prepared through bulk polycondensation of TMPB with bio-based diamines.The existence of hydrogen bonds was verified by in-situ infrared,and the effects of reaction temperature,curing time and crosslinking density on the properties of cPITAs were investigated.It was found that high pre-curing temperature and post-curing temperature,long curing time and short chain length were beneficial to increase the crosslinking density and Tg,leading to the improvement of thermal stability and mechanical properties of the cPITAs.cPITAs exhibited Tg ranging from 58 to 72?,tensile strength up to 84 MPa,and strain at break from 12%to 17%.Compared with traditional linear polyamide,the cPITAs prepared in this paper are based on renewable resources,which is adapted to sustainable development.Moreover,the preparation method of cPITAs is easy to industrialize.The cPITAs with excellent mechanical properties are expected to become a new type of renewable thermosetting polymer and be applied in simultaneous interpreting materials,adhesives,coatings and other fields.(2)Design,preparation and properties of(Amide-Imine)-based dynamic crosslinked Polymers.Firstly,NH2-terminated PreP(Am-In)s with adjustable content of amide bonds and imine bonds were prepared.Oxamide diethyl ester(HDODE)with regular structure was selected to provide the amide bonds,and 1 mol HDODE can provide 4 amide bonds of 4 molecules.The benzene ring is favorable to stabilize imine bonds,so p-benzaldehyde(TPA)is selected to provide imine bonds.Then,trimethyl citrate was used as cross-linker to react with PreP(Am-In)for the preparation of dynamic crosslinked P(Am-In)s with amide bonds as crosslinking point.Under the premise of similar degree of crosslinking,the relationship between the content of amide/imine bond and the repeatability,self-repair,stability and creep resistance of the polymer were studied,respectively.The results showed that with the increase of amide bonds accompanied by the decrease of imine bonds in backbones,the tensile strength and T5%of P(Am-In)s were increased by 132%and 17.2? to reach a maximum of 45.1±2.6 MPa and 298.0?,respectively.In addition,due to the existence of H-bonds,P(A1.5-11.5)displayed more excellent creep resistance than P(A0I3).P(A1.5-I1.5)occurred no creep at 60 ?,while contrastively there was 14%creep of P(A0-I3)at the lower temperature of 30?.Moreover,the presence of dynamic imine bonds endowed the reprocessability,self-healing property and degradability to the poly(amide-imine)networks.The content of imine bonds has a great influence on the reprocessability of P(Am-In)s.when the content of imine bonds in the main chain is less than 1/3,the reprocessability of P(Am-In)s disappeared.(3)On the basis of the study of(amide-imine)based dynamic crosslinked polymer,the functional modification and complete biogenic modification were explored.Firstly,NH2-terminated fully bio-based PrePAs only containing amide bonds was prepared by the polycondensation of diacid(or diester)and diamine.The bio-based dimeric acid(DIA)with long alkane branches was selected as one of the reactants for the purpose of improving the flexibility and hydrophobicity of the system.The imine bond is easy to hydrolyze when it meets water,and the polymer can better protect the imine bond when it is hydrophobic.Then,bio-based tri-aldehyde phosphate(TPV)was prepared from vanillin.Finally,through the condensation reaction between PrePAs and TPV,fully bio-based cPIAs with reprocessability were prepared successfully,which could promote the sustainable development from synthesis to application of thermosetting materials.The effects of amide bonds on the dynamic properties such as relaxation,creep resistance and reprocessability of the cPIAs were further studied.The results showed that the existence of amide bond and crystal structure could improve the mechanical properties,thermal stability and creep resistance of the polymers,which was consistent with the previous conclusion.The rigidity of material could also enhance the creep resistance of the material.The existence of crystalline structure affected the stress relaxation properties of the materials,increased the activation energy Ea of dynamic exchange reaction,and weakened the stress relaxation ability of the cPIAs.The introduction of DIA increased the flexibility of the cPIAs,which is conducive to the reprocess.In addition,alkane branched chains of DIA increased hydrophobicity of cPIAs which could protect the imine bonds.