Research On Stimuli-Responsive Polyvinylacetone And The Derivative Functional Materials

In this dissertation,emphasis is placed on the investigation of polyvinylaceton (PVKA),a stimuli-responsive polymer,and the derivative functional materials,which actually involves three main aspects:(1)the controllable synthesis processes to PVKA,(2)the characterization of the properties of the polymeric materials,and(3) the synthesis of the derivative functional materials utilizing the properties of PVKA. And the works under the guidance could be summarized as follows:1.With p-toluene sulfonic acid(PTS)and tetrabutylammonium bromide(TBAB) as the catalysts,PVKA was synthesized by ketalizing poly(vinyl alcohol)(PVA)with acetone.The structure of the product both swelled and dissolved in dimethyl sulfoxide-d₆(DMSO-d₆)was confirmed,which revealed the structural change in PVKA due to the semi-hydrolysis during its dissolution in water.Those effects,such as temperature,the composition of the reaction media(the ratio of water to DMSO), the catalyst(e.g.CTAB and Triton^?X-100),and other conditions,on the ketalization degree(D_H,that is the modification degree of PVA)of the product were probed from experimental viewpoint.Compared with the literature method reported previously,the present method exhibites evident advantages,such as the bearing with water to some extent,the higher ketalized PVKA,the easier control on ketaiization degree,etc.This is the first time of report,to our best knowledge,that synthesizing polyvinylketal under phase transfer catalyst conditions.The present study may lead to a further investigate of attractive intrinsic properties of PVKA.2.PVKA is a hydrolysable polymer,whose hydrolysis time could be controlled by the pH value of water,temperature,and ketalization degree:the closer the pH value to neutral,the lower the hydrolysis rate;the elevated temperature favor hydrolysis;and the lower the initial ketalization degree,the more easily the hydrolysis proceeds in acidic water.The hydrolysis of PVKA leads to PVA.PVKA of D_H=0.28-0.6 exhibited temperature-induced phase transition in water,and the lower critical solution temperature LCST≈33～45℃.Moreover,we also investigated PVKA/TBAB complexes that generated a series of self-assembled superstructures in the selective solvent composed of DMSO and acetone.3.Further investigations found that the complete hydrolysis time of PVKA(D_H =0.533)could be greatly shortened in existence of Ag⁺,which would be simultaneously reduced to form Ag nanostructures of various morphologies.Cu₂O polyhedral micro/nanocrystals could also be synthesized in aqueous solution of amphiphilic PVKA(D_H=0.549)under ambient conditions,via natural oxidation of copper metal by naturally dissolved oxygen in water;however,herein PVKA possibly works as the role like catalyst,which changes the microenvironment for the electrochemical reaction,whilst the D_H keeps nearly the same.4.As an important extended research,the polymer/inorganics hybrid nanomaterials were synthesized under ⁶⁰Coγ-ray irradiation,utilizing the properties of PVKA.Because of the spatial interactions coming from the rigid six-membered ketal rings,which would make the neighbouring groups become unreactive,the low hydrolysis rate of the PVKA in dilute acidic solution hinders and then slows down the cross-linking of the PVA chains yielded,also resulting in a low cross-link density, which favors the growth of inorganics inside to form different structures.Those hybrids as Ag/cross-linked PVA cable-like nanohybrids,Ag/Cu20/cross-linked PVA dendritic assemblies,Ag/Cu₂O/cross-linked PVA propeller-like assemblies,and Bi₂S₃/Cross-linked PVA 3D dendritic nanohybrids were developed,and the proper explanation on both the reaction mechanism and the formation mechanism were proposed.Moreover,the optical and other properties were also explored.5.We developed an easy strategy of using ⁶⁰Coγ-ray irradiation to graft PVA and PVKA onto multi-walled carbon nanotubes(MWCNTs)without the use of aggressive acid treatment,all in a single processing step.We also tried to decorate MWCNTs with Ag nanoparticles relying on those covalently bonded polymers,via one-step covalent grafting of the polymer to the surface of MWCNTs,and simultaneous reducing of Ag⁺ ions to Ag which are then efficiently anchored onto the MWCNTs.This is the first time of report,to the best of our knowledge,that fabricating metalliferous polymer/CNT hybrids underγ-ray irradiation.It is envisioned that this simple but efficient method could be extended to fabricate other similar CNT-based hybrids.On summary,utilizing the character of the macromolecular reaction on PVA, PVKA of controllable ketalization degree was synthesized via ketaling PVA with acetone,in which the ratio of hydrophilic/hydrophobic structure units(alcohol/ketal ring units)was tunable and thus tailoring the properties of the founctional materials, and we also successfully extended our research to synthesizing a series of derivative functional materials as described in this dissertation.