Stimuli-responsive Poly(vinyl Alcohol) Derivatives:Synthesis,Characterization And Application

Smart polymers have a wide range of applications in many fields.Smart polymers are characterized by their stimuli-responsive behavior,which is basically determined by the functional groups present in the polymer chain or on the polymer chain.As a widely used water-soluble polymer,polyvinyl alcohol?PVA?has excellent biocompatibility,and it has special significance for imparting a responsive function.In this paper,polyvinyl alcohol was functionalized by a post-synthesis modification method,and a series of polyvinyl alcohol derivatives with multiple stimuli-responsive properties were obtained,and their properties and functional applications were further studied.Specifically,the work of this paper includes the following three parts:First,a series of thermosensitive and pH-sensitive of PVA-based polymers PVA-DEEDA-t with different degrees of substitution were synthesized by coupling N,N-diethyl-1,2-ethanediamine?DEEDA?with urethane linkages on PVA.The turbidity test,nuclear magnetic resonance?NMR?and dynamic light scattering?DLS?techniques were used to fully characterize the macroscopic and microscopic phase transition behavior of PVA-DEEDA-t.According to the degree of substitution of DEEDA?14.1-20.9%?,the turbidity measurements showed that the aqueous solution of PVA-DEEDA-t had a tunable low critical solution temperature?LCST?in the wide temperature range of 24 to 58°C.In addition,the pH-responsive property allows the LCST of PVA-DEEDA-t to be turned"on"or"off"by adjusting the acidity of the aqueous solution.Different NMR techniques,such as two-dimensional NOESY and PFG NMR,determine the relationship between conformation and properties during the phase transition at the molecular level.Second,the importance of the chain length of tertiary amines and alkyl groups on the N-alkylcarbamate groups for the response performance was studied.A series of novel biocompatible polymer families with CO2 switchable LCSTs was obtained by post-synthetic modification of PVA with different alkylamine motifs..These polymers show tunable LCST by adding/removing CO₂,outstanding cell compatibility and distinguishable solution behavior.In general,more hydrophobic terminal amines result in lower LCST.A comparative study of PVA-C2-Me without terminal amines and PVA-C3-NEt with diethylamino groups revealed the importance of side chain amines for the LCST phase transition mechanism.For PVA-C3-NEt,LCST behavior is due to hydrogen bonding and hydrophobic interactions with terminal tertiary amines.Even at low temperatures,PVA-C2-Me in solution may have a globular conformation.Heating causes slow agglomeration without forming hydrogen bonds between C=O...H-N.Thus,the observed thermally induced phase transition of PVA-C2-Me may be related to hydrophobic interactions rather than hydrogen bonding.Heating can cause changes in the pKa of PVA-C2-NEt and PVA-C3-NEt,which favor CO₂ absorption/desorption cycles.This work demonstrates the importance of the alkylamine motif in the behavior of thermosensitive polymer solutions and its potential as an absorbent for carbon dioxide absorption.Third,in order to explore the practical application of PVA-based responsive functional polymers,we first performed cytotoxicity tests on different N-alkyl substituted PVA derivatives.The results show that it has good biocompatibility.In addition,the polymer of PVA-DEEDA-90h was converted into a gel and a membrane.The PVA-DEEDA-90h gel obtained by adding borax can be used for controlled release of drugs?eg,RhB?due to its temperature and pH-dependent permeability.The PVA-DEEDA-90h film cast on ITO glass forms a smart interface with high sensitivity to pH and temperature,with adjustable wettability and interface ion migration.