Study Of Self-healing Polyurethane Based On Thermoreversible Diels-Alder Reaction

Polymeric materials may easily suffer from damages including chemical attack,radiation damage, mechanical abrasion, impact and thermal decomposition-alone or incombination in their manufacture and use, then the microcraks generated inside of thematerials, which are hard to be found and repaired artificially. With the propagationof cracks, the macroscopic cracks would form, the mechanical performance (such astensile strength, compression performance, and etc.) would rapidly reduce andultimately the using life of the material would be diminished. As novelly intelligentmaterials, self-healing polymeric materials simulating the self-healing mechanism oforganisms to heal the microcracks by theirselves to prolong theirs using life. Withmore and more attention, self-healing technology has great development prospectsand application value. At present, polymeric materials based on thermoreversibleDiels-Alder (DA) bonds stands out among many repair approaches. These materialscan repair the cracks by retro-DA and DA reaction only in the heat treatment, withoutcatalyst, monomers or other special treatment, in addition, the approach has highremediation efficiency and multiple healing events.In this thesis, a preliminary kinetic study of the DA reaction between modelcompounds (furfuryl alcohol (FA) and BMI) by attenuated total reflection infrared(ATR-IR), UV-Vis and in situ1H NMR spectroscopies. The results show that themodel reaction follows third-order kinetics, and reaction perform best in thetemperature range of60~70oC, retro-DA reaction would become dominated and hinder DA reaction if the reaction temperature at or above70oC. In addition, apolyurethane prepolymer bearing two furan groups (MPF) was synthesized by twosteps, and in situ1H NMR spectroscopies was selected as the analytical method ofchoice to study the DA reaction between MPF and BMI, and the most beneficialexperimental conditions to maximize conversion were identified.To give polyirethane self-healing property, using the reaction characteristics ofisocyanate, a polyurethane prepolymer bearing two furan rings (MPF) wassynthesized. A linear polyurethane exhibiting self-healing ability was synthesized byDiels-Alder (DA) reaction between MPF and BMI below80oC.Thermoreversible property of the linear polyurethane was studied by1H NMR,Differential Scanning Calorimetry (DSC) and Gel Permeation Chromatography (GPC)analysis. High performance of thermal remendability of the self-healing polyurethanewas observed by Polarized Optical Microscope (POM), and the mechanical propertieswere also investigated by Tensile Measurements. The results revealed that the knifecut could be disappeared at120oC in5min. The healed film could reach as much as80%of the original one and the healing process could be performed at the sameposition for many times. The research also revealed that the reversible DA bonds notonly endowed the polyurethane material thermal remendability, but also improvedmechanical properties of the traditional materials.