A Computer Simulation Study Of Supramolecular Interfacial Polymerization

Because of the dynamic and reversible nature of non-covalent interactions,supramolecular polymers possess superior characteristics like reversibility,degradability,self-healing and stimulus-responsiveness.Therefore,they have been widely utilized in materials and biomedicine fields.Generally speaking,there are two strategies to prepare supramolecular polymers: one is the conventional method,i.e.,firstly synthesize bifunctional monomers via covalent polymerization,and then prepare supramolecular polymers through supramolecular polymerization between monomers.The other is the covalent polymerization of supramolecular monomer.In this method,supramolecular monomers are first prepared by non-covalent interactions,and then they are able to be used to synthesize supramolecular polymers by covalent polymerization.The latter strategy is more controllable.If the two reactive monomers are immiscible,solution polymerization cannot be used to prepare supramolecular polymers.Under these conditions,interfacial polymerization can be used to prepare supramolecular polymers.Researchers have successfully prepared the supramolecular polymers through interfacial polymerization of supramolecular monomer,and they found that interfacial polymerization can generate higher molecular weight products than solution polymerization.There are still some important problems need to be solved or clarified on this issue.For example,whether the theory of polymer physics is applicable to supramolecular polymers? What is the formation process of supramolecular polymerization? As is known to all,molecular weight distribution is important and will affect polymer properties such as mechanical properties,processing properties,and phase separation behavior,etc.Thus,how to precisely control the molecular weight and distribution of supramolecular polymers? Moreover,theoretical and computer simulation investigations,which are focused on the process of supramolecular interfacial polymerization are rarely reported.These challenges are greatly bound to affect our further comprehensive understanding of the supramolecular interfacial polymerization.In this paper,the dissipative particle dynamics simulation method combined with a stochastic reaction model is used to simulate the supramolecular interfacial polymerization at the liquid-liquid interface.Regarding to interfacial polymerization,we can easily think of emulsion interfacial polymerization,because in the same situation,the emulsion has a larger liquid-liquid interfacial region,which can effectively increase the yield.Moreover,emulsions with nanosized and hollow nanocapsule structure possess excellent properties and have potential application in the fields of materials science and biomedicine.So we also simulate supramolecular emulsion interfacial polymerization.In the above two systems,we simulate the preparation of supramolecular polymers at the interface,and obtain detailed analysis on the formation theory,process,and molecular weight distribution of the products.The specific research content is as follows:(1)We simulate the supramolecular interface polymerization induced at the oilwater interface.We first consider a comparison study on interfacial polymerization and solution polymerization,and find that products obtained by interfacial polymerization with higher molecular weights than solution polymerization.This result reproduces the experimental results well.We explore the growth of the degree of polymerization at different reaction times and find that supramolecular interfacial polymerization still obeys the characteristics of second-order reaction kinetics as that of the solution polymerization.We also find that at different stages of polymerization reaction,the molecular weight distribution of the products can be described by the Flory distribution.In addition,the influence of the concentration of reactive monomer and solvent incompatibility on the polymerization reaction is explored,and it is found that choosing an appropriate reactive monomer concentration and solvent incompatibility is beneficial to obtain high molecular weight products.Through these research results,we propose an optimized scheme for improving the experimental technology of supramolecular interfacial polymerization.It is not only able to provide theoretical guidance for the better design of new supramolecular systems,but also provide ideas for the synthesis of supramolecular polymers with higher molecular weight.(2)We simulate the supramolecular emulsion interface polymerization induced at the droplet interface(oil-in-water)between water and oil phase.We consider a comparative study on supramolecular emulsion interfacial polymerization and supramolecular interfacial polymerization,and find that emulsion interfacial polymerization can obtain higher yields than interfacial polymerization.However,due to its obvious interface curvature,its average chain length of products is lower than the latter.The influence of the reactive monomer concentration and stoichiometric ratio on the polymerization reaction is explored.It is found that the reactive monomer concentration not only affect the polymerization products,but also further affect the conformation of the emulsion and its practical application such as drug release rate and permeability.By simulating polymerization occurring on the emulsion droplet of different sizes,we find that the molecular weight distribution of products deviates from the Flory distribution.It is attributed to that the emulsion curvature has an obvious effect on the polymerization reaction rate and further influences the growth of polymeric products.In addition,we obtain the molecular weight distribution for the emulsions whose size distribution conforms to the Gaussian distribution,so that the molecular weight distribution may be predicted according to the corresponding emulsion size distribution.This study helps to better understand the thermodynamic and dynamic factors that may affect the degree of polymerization and molecular weight distribution of products in supramolecular emulsion interfacial polymerization,and is thereby possible to guide experimentalists for the precise control of supramolecular materials.