Research On The Post-chain Extension Of Aqueous Polyurethane Dispersions By MALDI Time-of-flight Mass Spectrometry

The post-chain extension process and the choice of chain extender are important for the molecular weight of aqueous polyurethane dispersions(APUDs)in the synthesis of APUDs by the prepolymer mixing process.There is a competitive reaction between the post-chain extension and water,because the post-chain extension reaction is located after emulsification and dispersion.The process of post-chain extension reaction is more complicated,due to the reactivity of the end groups and the ―cage effect‖.It is an important way to improve the performance of APUDs by looking for effective analysis methods and quantitative analysis of the post-chain extension reaction.Previously formerly,we used the ninhydrin color method to quantitatively analyze the post-chain extension,but this method is greatly affected by external factors and it cannot reflect the characteristics of the entire molecular chain.According to the reaction mechanism,after the post-chain extension using highly active primary amine as the post-chain extender,both water and polyamine participate in the extension reaction in four situations:(1)Water-determined(WD): The NCO reacts with water to form a terminal anmine group,and no further chain extension is performed,due to the environmental impact.(2)Water-chain extension(WE): after the NCO reacting with one water to form a terminal group,the amine group reacts with another NCO to form chain extension.(3)Diamine-determined(DD): The NCO and one end of the primary amine group in the chain extender are extended to obtain a molecular chain whose terminal group is still an amine group.(4)Diamine-chain extension(DE): After NCO group and diamine forming terminal amine group,the amine group reacts with another NCO group to form chain extension.We analyze the amount of NCO consumed by the above four reactions after post-chain extension to determine the four factors that affect the post-chain extension efficiency of the APUDs: temperature,particle size,degree of post-chain extension,post-chain extender.We use easily hydrolyzed polyester polyols to synthesize waterborne polyurethane.The formula guarantees that the content of isocyanate groups in the polyurethane prepolymer before post-chain extension is a certain amount.For different post-chain extension temperature,particle size,post-chain extension degree and the type of diamine post-chain extender,the polyurethane can be controlled to be hydrolyzed,dried and separated to obtain different hard segment fragments.Those four kinds of new hard segment structures were generated during the post-chain extension,which did not exist before post-chain extension.And then,we use MALDI-TOF to analyze the hard segments.Those four kinds of new hard segment structures were generated during the post-chain extension,which did not exist before post-chain extension.And then,we use MALDI-TOF to analyze the hard segments.The relative intensity of these molecules could be analyzed by Maldi-Tof MS spectra.Then the amount of NCO groups with consumed by Water-determined(WD),Water-chain extension(WE),Diamine-determined(DD)and Diamine-chain extension(DE)could be obtained.Then,the efficiency of post-chain extension under different conditions could be obtained,which provide a theoretical basis for further clarification of the chain extension reaction mechanism of APUDs.This study takes IPDI and TDI as representatives of aliphatic and aromatic isocyanates respectively,polyethylene glycol adipate as glycol,and the amount of DMPA to control the particle size.Ethylenediamine(EDA)、 1,6-hexanediamine(HMDA)and 1,3-Cyclohexane(1,3-BAC)are the post-chain extender.Explore the different temperature,particle size,degree of post-chain extension and the type of diamine post-chain extender,the influencing factors of the post-chain extension reaction,the study shows:(1)Research on post-chain extension of IPDI APUDs.The actual total chain extension efficiency referring to the sum of Diamine-chain extension and Water-chain extension were higher both higher temperature(40 ℃)and lower temperature(0 ℃-10 ℃);with the content of DMPA increasing(1.0 g-1.5 g-2.0 g-2.5 g),the particle size of the APUDs gradually decreases,the efficiency of Diamine-chain extension decrease;the total sum of Water-chain extension and Diamine-chain extension increase from 20% to 60% and decrease from 60% to 80%,with a maximum value around 60%.Hence,the optimum post-chain extension is when the amount of EDA is 60% of theoretical value.;EDA obtained high post-chain extension efficiency compared with HMDA and 1,3-BAC,because of EDA with low molecular weight and good water solubility among them.(2)Research on post-chain of TDI APUDs.The efficiency of Diamine-chain extension gradually decreases with temperature increasing(0 ℃、10 ℃、20 ℃、30 ℃、40 ℃),the lowest value is reached at 40 ℃,while the Water-chain extension efficiency reached the highest value at 40 ℃.The overall efficiency of Water-chain extension and Diamine-chain extension is greater at 0 ℃ and 40 ℃;with the content of DMPA increasing(1.0 g-1.5 g-2.0 g-2.5 g),the particle size of the APUDs gradually decreases,The efficiency of Diamine-chain extension gradually decreases,while the Water-chain extension efficiency is just the opposite;the total sum of Water-chain extension and Diamine-chain extension increase from 20% to 60% and decrease from 60% to 80%,with a maximum value around 60%.Hence,the optimum post-chain extension is when the amount of EDA is 60% of theoretical value.;EDA obtained high post-chain extension efficiency compared with HMDA and 1,3-BAC,because of EDA with low molecular weight and good water solubility among them.This has certain guiding significance for the selection of post-chain extenders in the synthesis of APUDs.