Self-assembly Of PH/Thermo Dual Responsive PDMAEMA-based Polyelectrolytes And Their Appliactaion In Salt-free Reactive Dyeing

The traditional dyeing process of reactive dyes requires a large amount of inorganic salt(30?150 g/L),which is used to eliminate the electrostatic repulsion between the anionic reactive dyes and cotton fibers,and to increase the dye uptake and fixation of reactive dyes.After dyeing,the inorganic salt is difficult to be degraded in dyeing wastewater,and the burden of wastewater treatment is heavy,which is easy to cause environmental pollution.Cationic modification of cotton fiber is one of the effective approaches to improve the affinity between cotton fiber and reactive dyes,increase the dye uptake and fixing rate.However,the reported cationic agents which were used to modify cotton showed many defects,such as the difficulty in control of molecular weight,poor levelness and penetrability of the treated fibers,effect on color shade and low color fastness.To solve the problems above,dual stumuli-responsive poly(2-(dimethylamino)ethyl methacrylate)-based polyelectrolytes were designed and fabricated via molecular design and living radical polymerization technology in this study.Modification of cotton with these polyelectrolytes was successfully adopted to improve and control dye adsorption on fabric through their adaptive responsive behavior.Some excellent results of salt-free reactive dyeing performance of cationic cotton were obtained.The research contents are as follows:Controllable preparation and characterization of pH/temperature responsive PDMAEMA-based polyelectrolytes.A series of well-defined PDMAEMA-based polyelectrolytes with controlled molecular weight and low polydispersity were synthesized,including cationic polyelectrolyte PDMAEMA,QPDMAEMA and amphoteric polyelectrolyte PDMAEMA-b-PMAA.The polymerization of these polyelectrolytes was based on the activators regenerated by electron transfer atom transfer radical polymerization(ARGET ATRP)technology,using CuBr2/PMDETA as catalytic system,ethyl ?-bromoisobutyrate and ascorbic acid as initiator and reductant,respectively.The structures of PDMAEMA-based poly electrolytes were characterized by 1H-NMR,FT-IR and GPC methods.Based on the influence of reaction conditions on the polymerization,the optimum synthesis conditions of polymerization were determined.Meanwhile,the kinetics of ARGET ATRP polymerization of PDMAEMA and its chain propagation were investigated as well.The results are as follows:when T=60?,t=6.0 h,v[EAc]:v[M]=50%,[M]0=3.95 M,feed ratio of[EBiB]/[CuBr2]/[PMDETA]/[AA]=1/0.05/0.25/0.50,PDMAEMA-Br polymer with different molecular weight and low molecular weight distribution(Mw/Mn<1.19)were synthesized by changing the ratio of[M]0/[I]0.PDMAEMA-b-PBMA block copolymer with different molecular weight and block ratio,low molecular weight distribution(Mw/Mn<1.24)were synthesized by using PDMAEMA-Br as macromolecular initiator.The optimum reaction conditions are T=60?;t=6.0 h,v[EAc]:v[M]=50%,[M]0=3.95 M,[PDMAEMA-Br]/[CuBr2]/[PMDETA]/[AA]=1/0.05/0.25/0.50.Dynamic data showed that the concentration of propagating chain radical of polymerization of PDMAEMA and its chain propagation maintained relatively constant at the optimum conditions.Meanwhile,the polymerization was provided with higher apparent reaction rate constants and shorter induction period.Products with narrow molecular weight distributions(Mw/Mn=1.10?1.21)were obtained with highly efficient and controllable polymerization.Quaterisation and acidification reactions were proceeded to achieve polyelectrolyte QPDMAEMA with different cationic degrees and amphoteric polyelectrolytes PDMAEMA-b-PMAA,using PDAMAEMA and PDMAEMA-b-PBMA as raw material and dimethyl sulfate,hydrochloric acid as reactant,respectively.The 1H-NMR,FT-IR and GPC results showed that the structure of as-synthesized polymer with targeted molecular weight were accurate.Dual pH/temperature responsive behaviors of PDMAEMA-base polyelectrolyte solutions.The aqueous solution properties of PDMAEMA-base polyelectrolytes were investigated in detail through ultraviolet-visible spectroscopy,dynamic light scattering and dynamic surface tension methods.The self-assembly mechanism of PDMAEMA-base poly electrolyte which triggered by the external environmental factors were studied in-depth by exploring the dual sensitivity and aggregation behaviors under different temperature and pH.At the same time,the factors(molecular weight,structure of polyelectrolyte and block ratio)which affect the behaviors of the aggregation were analyzed particularly.The results showed that the positive charges of tertiary amine polyelectrolyte PDMAEMA,which existed as protonated form in acid medium,raised with the increase of molecular weight;The aqueous solution surface activity increased,caused by the gradual deprotonation of tertiary amine groups of polymers when pH increased.Its aqueous solution surface tension showed double linear change at the temperature closed to LCST,and reduced with the increase of the degree of polymerization.The transmittance of micellar solution at LCST decreased rapidly from 100%to 0 in alkaline condition,demonstrating a good response performance of temperature.As a typical cationic polyelectrolyte,quaternized polyelectrolyte QPDMAEMA was insensitive to the external stimulation due to the quaternarization of tertiary amine groups.Compared with tertiary amine polyelectrolyte PDMAEMA,the charges of QPDMAEMA remained positive or neutral under alkaline conditions because of the strong hydrophilicity of quaternary ammonium groups.Under acidic pH,molecule dissociated into single-stranded structure,suggesting that the conformation of chains was random coils shape.In alkaline medium,a general trend of decreasing with particle sizes can be observed due to the neutralization of unquaternarized tertiary amine groups and weakened inter-atomic forces among molecular chains.Amphoteric polyelectrolytes PDMAEMA-b-PMAA exhibited good pH/temperature sensitive performance in aqueous solution.Away from the isoelectric point of PDMAEMA137-b-PMAA16 and PDMAEMA118-b-PMAA47,the stable chains in the water lead to the nonexistence of LCST;Under alkaline condition(pH 11.5),the hydrogen bonding were broken with the raised temperature,resulting in the formation of stable micelle with PDMAEMA as core and highly negative charged PMAA segments as shell in aqueous solution.Specific assembling behaviors of PDMAEMA118-b-PMAA47 were found close to the IEP,namely the small size micelles were formed by the attraction between positively charged segments and negatively charged ones at ambient temperature.With temperature increased,it is difficult to form large aggregates.The application of pH/temperature responsive PDMAEMA-base polyelectrolyte in salt-free reactive dyeing.Tertiary amine poly electrolyte PDMAEMA,quaternarized polyelectrolyte QPDMAEMA and amphoteric polyelectrolytes PDMAEMA-b-PMAA were designed and adopted to modify cotton fibers as salt-free dyeing auxiliaries.The effects of the molecular weight and distribution,cationic degrees,block ratio of PDMAEMA-based poly electrolytes on salt-free dyeing performance were investigated.The results showed that,with the increase of the molecular weight of additives,the exhaustion E%increased and reactivity R%decreased,the fixation rate F%first increased and then decreased due to the combined action of the variation tendency of E%and R%?Uneven dyeing degree Sr increased with the increment of molecular weight(Mn),molecular weight distribution(Mw/Mn)and cationic degree,leading to the poor levelness of dyed modified fiber.Meanwhile,the salt-free dyeing performance of cotton modified with three different kinds of additives varied pre-treatment and dyeing procedures were compared.To obtain the optimum pre-treatment and salt-free dyeing conditions of three additives,the effects of additive dosage,dipping temperature,dipping time,baking temperature and alkali dosage on dye uptake were studied.The salt-free dyeing mechanism of the cotton after modification with PDMAEMA-based polyelectrolytes was illustrated by SEM,fabric surface potential tests.The analysis results indicated that PDMAEMA-based polyelectrolyte exhibited different charges under different pH due to the features of "protonation-disprotonation" of tertiary amine side-groups.The static gravitational forces between additives and cotton/hydrolysed dyes were weakened due to the neutral or electronegative charges of additives under alkaline pH,which is beneficial of the desorption of the hydrolyzed dyes during the fixing stage,solving the problems of low friction fastness and color change for salt-free dyeing of cationic cotton fabric.The adsorption of reactive dyes on PDMAEMA-based polyelectrolyte treated cotton showed that it was in accordance with the Langmuir adsorption model,suggesting that the dye adsorption on modified fabric depended on electrostatic forces.Isothermal dyeing rate curve at 30? accorded with pseudo-second order kinetic model of adsorption,which means that the adsorption of dyes on the modified fibers belongs to chemical adsorption.Furthermore,PDMAEMA-base polyelectrolyte aqueous solutions showed surface activity under alkaline conditions,acting as retarding agents in the dyebath.It can solve uneven dyeing problem of cationic cotton caused by "rapid dyeing" and obtain salt-free reactive levelling dyeing.Salt-free dyeing results showed that there is no shading performance of dyed cotton after modification.Compared with conventional reactive dyeing,modification with PDMAEMA-based polyelectrolyte improved the dye uptake of reactive dyes,increased the color fixation rate by 4?16%,made leveling performance is superior to conventional dyeing.In addition,cotton treated with PDMAEMA-b-PMAA showed best performance of apparent color depth,levelling properties and color fastness,equal or higher than conventional dyeing results with salt.