Study On Shape Memory And Self-healing Properties Of Brush Polyurethane

Shape memory material is a kind of intelligent material that can change the initial shape of the material and fix it under certain conditions,and can return to the initial shape under external stimuli.Compared with shape memory alloy,shape memory polymer has many advantages such as large deformation,short response time and various stimulation modes.However,shape memory polymer has a short service life and is prone to fatigue and crack during repeated deformation recovery.Shape-memory polymers with self-healing properties can effectively repair cracks or fractures of materials,thereby greatly improving the service life of materials.Existing research results show that brush-like polymer materials have potential self-healing ability due to the entanglement between side chains.In view of this,a series of brush-like polyurethane materials have been prepared in this paper to successfully integrate selfhealing properties and shape memory.The combination of performance and the mechanism of the brush-like structure of polyurethane and its self-healing properties and shape memory properties were studied.First,a quaternized monomer(MAB)was synthesized through the quaternization reaction between N-methyldiethanolamine(MDEA)and bromoalkanes of different chain lengths,and then it was mixed with hexamethylene diisocyanate(HDI).It was polymerized with triethylene glycol(TEG)and copolymerized according to a fixed feed ratio to prepare brush polyurethanes(SBPUs)with side chains of different lengths.The results showed that the length of the side-chain alkane will have a significant impact on the structure and performance of the polyurethane.When the number of carbon atoms in the side-chain alkane was less than 12,MAB was light yellow viscous liquid.At this time,the SBPUs prepared do not have Self-healing properties;when the number of carbon atoms in the side chain was greater than 12,MAB was white crystals,and the prepared SBPUs had better self-healing properties.The self-healing drive of this brush polyurethane stems from the winding action between the side chains.The principle is that the longer side chain moves to the other side of the section at high temperature,and winds with the side chain on the other side to achieve the "suture" of the fracture.Secondly,quaternized monomer(MAB22)was synthesized through a quaternization reaction between MDEA and 1-bromodocosadecane,and then MAB22 was copolymerized with HDI and TEG at different feed ratios to prepare a series of soft hardness.Brush polyurethanes(ABPUs)with different contents.The research results show that these ABPUs generally have good dual shape memory properties,but only when the TEG-HDI component is 40% can ABPUs have self-healing properties.This is because the occurrence of self-repair behavior requires sufficient movement of chain segment.When the content of hard segment is too high,a large number of crystals meet and seriously restrict the movement of chain segment,thus hindering the self-healing behavior.In addition,side alkanes mainly exist in hard segment components,and when the content of hard segment is low,the number of side alkanes involved in self-healing is small,resulting in low self-healing efficiency.Therefore,ABPUs can have selfhealing performance only when the component ratio of soft and hard segments reaches a certain appropriate value.Finally,pentaerythritol(PER)was used as a cross-linking agent to construct a partially cross-linked brush polyurethane,thereby improving its shape memory performance.HDI-MAB22-HDI prepolymer was synthesized by reacting MAB22 with HDI at a ratio of 1: 2,and then TEG chain extension and PER were added to prepare brush polyurethanes(PPUs)with partially crosslinked network structure.The research results show that compared with SBPUs,PPUs mechanical strength has the obvious improvement,but its self-healing efficiency declined,that is because the crosslinking structure hinders the side chain alkane chain segment motion,due to the introduction of the join point,PPUs shape memory performance is greatly improved,recovery rate of 99.2%,in addition,the crosslinking structure obvious two phase separation structure also brought PPUs triple shape memory performance.