Monte Carlo Simulation Of Amphiphilic Dendritic Polymer

Dendrimers have a novel three dimensional,hyperbranched structures.Unlike traditional polymers,dendrimers have attractive features like narrow polydispersity index,excellent control over molecular structure,availability of multiple functional groups at the periphery and cavities in the interior,nanoscopic size,which are widely applied in fields such as drug/gene delivery system,catalyst and nanomaterials.Most of the application of dendrimer are based on the so-call dense shell structure.However,studies prove that dendrimers with flexible spacers adopt dense core structure.It is believed that it might helpful to obtain dendrimers with dense shell structure by grafting linear polymer to the terminal groups.Such stratagem is applied in experiments to improve the solubility and load capacity and reduce the toxicity of dendrimers by introducing hydrophilic PEG chains to the terminal groups.However,the structure of such amphiphilic dendritic copolymer is not well examined.Among the many properties of dendrimers,understanding their conformation,or internal structure,provides a foundation for the development of application using dendrimers.In thesis,lattice Monte Carlo simulation was used to study the properties of amphiphilic dendritic polymer.Firstly,we study the structure of dendrimers.Then we further studied dendrimers modified by attaching long terminal segments.The influences of the length of grafting chain,grafting density and architecture were examined the thesis is organized as follows:The first chapter of this thesis gives a detailed description of dendrimers,its application,and the research background and current situation of amphiphilic dendritic polymers;The second chapter introduces the Monte Carlo simulation methods and related theories used in the research process,as well as the technical details such as the bond fluctuation method,Metropolis importance sampling.The third chapter studies the properties of a flexible dendrimer in an athermal solvent by lattice Monte Carlo simulation.Properties like the scaling relationship between size and molecular weight,the density profile and the distribution of terminal groups were examined.The results show a dense-core structure consistent with the literatures.The four chapter studies the properties of dendritic homopolymers(i.e.the grafted polymer and the dendrimer core have the same properties).The influence of parameters such as the length,the grafting density,the configuration of the grafting polymers and the number of dendrimer generations have been studied.The simulation results show that the polymer attachment can expand the dendrimer moiety in the core of the conjugate and also lead to a more ordered structure.Back-folding of the terminal segments of the dendrimer is reduced because of the additional steric effect imposed by the grafted polymers.Therefore,the periphery of the dendrimer becomes dense as compared to its unmodified counterpart.However,there exists no clear boundary between the core dendrimer and the attachment shell.The effect of attachment on the dendrimer structural behavior is found to increase with the length of attached chain.The expansion of the dendrimer moiety produces more free space inside and can thus enhance drug/gene encapsulation in principle.In chapter five,the interaction between the grafting chains and the dendrimer core has been introduced and the properties of the amphiphilic dendritic polymer were examined.The influence of structure parameters of the grafting polymer such as the length,the grafting density,the configuration and the number of dendrimer generations on this effect is studied.It is demonstrated that the incompatibility of grafting polymers with inner dendrimer units leads to formation of a “hollow” core with reduced polymer density in the dendrimer center.This effect is enhanced with addition in the number of dendrimer generations.It is established that the main factor determining the hollow core formation is the segregation between inner and terminal units because the main driving force for the effect is the localization of the terminal segments at the dendrimer periphery.These conclusions provide the basic theoretical basis for designing a novel amphiphilic dendritic polymer drug/gene delivery system.