Design,preparation And Structure-activity Relationship Of Side Chain Crystalizable Epoxy-based Phase Change Materials

Polymeric FSPCMs are encapsulated by chemical or physical interactions between polymers and SLPCMs.Compared with capsules or porous skeletons as shells,polymer-based stereotyped phase change materials have become the research point due to the advantages of designability of molecular networks,low cost,degradability/recyclability,deformability and composability.The existing polymeric phase change materials are mainly prepared using polyethylene glycol（PEG）.However,this type of polymeric phase change materials has the disadvantage of low latent heat and high enthalpy loss.The enthalpy of many of these systems has not achieved a major breakthrough due to the unclear influence on the enthalpy of the system based on the structure of the polymeric network.At the same time,the encapsulation mechanism of most systems and the characteristics of the polymer limit the design and regulation ability of the cross-linked network.Therefore,the development of new polymeric systems with high latent heat,low enthalpy loss,and efficient encapsulation of most types of SLPCMs based on the elucidation of the relationship between polymer network structure and phase change properties is the key to address the above frontier needs.In this paper,the network structure was designed with allyl epoxy（DADGEBA）as the main chain and crystallizable long-chain alkyl mercaptan（ODT）as the side chain.It was studied as a model compound to elucidate the3D network structure of this type of epoxy-based FSPCMs(EP_X-Y system)generated by the polarity and size of the curing agent on the crystalline morphology,encapsulation rate and the final phase change properties of the SLPCMs.The effect of the crystalline morphology,the encapsulation rate and the final phase change properties of the SLPCMs was studied.Based on this,a tunable comb/bottle brush epoxy network(z H-x D18_Pa-m)was designed to further increase the latent heat and reduce the enthalpy loss,while achieving UV curing,reprocessability and self-healing.It contributes to the study of the conformational relationships of epoxy-based set phase change materials and the structural design of other advanced polymeric set phase change materials.The main results achieved in the thesis are as follows:1.Using an epoxy resin（D18）with crystalline alkyl side chains and four structurally similar amine curing agents as model compounds,support networks with different polarity and spatial site resistance were constructed,and the effects of polarity and spatial site resistance of the cross-linked networks on the phase transition properties of D18/Bw polymer-based FSPCMs were systematically investigated by encapsulating bio-based beeswax（Bw）.The results show that:（1）curing agents with small molecular size and low polarity are favorable to achieve the maximum encapsulation rate of Bw;（2）curing agents with high polarity and large molecular size can promote the self-assembly effect of Bw,which is favorable to obtain higher enthalpy with the same Bw content,and in which the polarity effect plays a dominant role;（3）curing agents with higher polarity and smaller molecular size are favorable to balance the EP_X-Y system maximum encapsulation rate and enthalpy.In the EP_H-Y system with 1,3-cyclohexyldimethylamine as the curing agent,the highest encapsulation rate of Bw（close to 70 wt%）,but the highest enthalpy（146.2 J/g）was obtained for the EP_M-60 sample with m-phenylenedimethylamine as the curing agent（60 wt%Bw content）.Subsequently,different amounts of multi-walled carbon nanotubes（CNT）were introduced to improve the thermal conductivity of the EP_M-60 sample(The TC,electromagnetic interference（EMI）shielding performance and contact angle of the 30 wt%CNT-modified EP_M-60 samples could reach 1.37W/m K,37.4 d B,and 137o,respectively,while the enthalpy could be maintained at 101.1 J/g.This work helps to clarify the relationship between the cross-linking network structure and the phase transition properties of polymeric FSPCMs.At the same time,it provides theoretical guidance for the preparation and optimization of other high-enthalpy,high-reliability,and multifunctional polymeric FSPCMs with cross-linking network structures.2.On the basis of the above study,the molecular structure design for the preparation of high molecular weight linear prepolymers by regulating the grafting density of DADGEBA and performing chain expansion to increase the compatibility of polymer networks with SLPCMs and the physical entanglement of molecular chains to achieve further improvement in enthalpy and reduction in enthalpy loss.Ultraviolet（UV）curing was also introduced to achieve efficient preparation.Specifically,a type of photocurable and adjustable comb/bottlebrush epoxy-based FSPCMs was highly-efficiently prepared through the chain extension reaction of EP and octadecylamine（ODA）followed by thiol-ene click photocuring reaction,and the relationship between the network structure（molecular weight,graft density and crosslinking density）and the phase change properties was investigated in detail to obtain a high enthalpy and low enthalpy loss system.It was concluded that higher molecular weight and suitable grafting density as well as higher cross-linking density could balance the maximum encapsulation rate and phase change performance of paraffin.The best system(50H-50DA18_Pa-60)could be prepared by UV curing in only 13 min and could encapsulate 60 wt%of paraffin wax with an enthalpy of 150.1 J/g and a heat content loss of only0.7%compared to the theoretical enthalpy loss.Finally,the Diels-Alder（D-A）bond was introduced into the system to realize the recycble and self-healing ability of epoxy-based FSPCMs.This work not only proposes a strategy for the preparation of polymer-based FSPCMs by rapid photocuring method,but also provides theoretical guidance for the preparation and optimization of reprocessable polymeric FSPCMs with high enthalpy.