PDMDAAC is a polycationic fixing agent, it is mainly used for fixing reactive dyes, and generally does not produce discoloration and reduce light fastness.
PDMDAAC is prepared by the reaction of dimethylamine and allyl chloride in the presence of alkali to produce dimethyl diallyl ammonium chloride (DMDAAC), and then the monomer is polymerized by free radical in the presence of initiator.
PDMDAAC has high density of positive charge, good water solubility and easy control of molecular weight distribution. So far, PDMDAAC has been applied in the printing and dyeing industry as a non-toxic and efficient dye fixing agent. The properties of polymers are closely related to their molecular weight and its distribution. For the same monomer, there are great differences in properties due to different molecular weight or molecular weight distribution. There are many factors affecting the properties of polymers, such as initiator variety, dosage, monomer concentration, impurity content, reaction time, pH and so on.
PDMDAAC color fixing agent was successfully developed and put into production by Calgon company and Halliburton company, subsidiaries of Merck company in the United States in the 1970s. It has the characteristics of high color fastness, good color fastness to light and low dosage. It is better for reactive dye fixation than for direct dye. Direct dye dyeing and fixation can be carried out in the same bath. The synthesis of color fixing agent PDMDAAC began to be studied in China in the 1990s.
The synthesis of PDMDAAC is divided into two parts: (1) the synthesis of monomer, DMDAAC is formed by tertiary amination and quaternization of chloropropene with dimethylamine and sodium hydroxide; (2) In the polymerization process, DMDAAC is polymerized by free radical under the action of initiator to form PDMDAAC. In the reports related to the synthesis of PDMDAAC, the polymerization mode is mainly aqueous solution, and the initiators used are divided into peroxy, azo and composite. However, because DMDAAC has good water solubility, typical persulfates are used in the synthesis of PDMDAAC. Compared with persulfate initiators, azo initiators have many advantages, such as stable properties, almost all of their decomposition is a first-order reaction, only one free radical is formed, there is no side reaction, no chain transfer and branching structure, mild polymerization conditions and so on. Common azo initiators are hydrochloride of azodiisobutyronitrile and azoamidine. Azodiisobutyronitrile has certain toxicity and low solubility in water. Azoamidine hydrochloride has good water solubility and non toxicity. It has been used abroad to initiate the polymerization of DMDAAC since 1980s; This kind of initiator has been used in the polymerization of DMDAAC since the mid-1990s.
Because DMDAAC is a water-soluble allyl quaternary ammonium salt, the tendency of chain transfer is particularly strong during polymerization. In order to obtain high water solubility and polymerization efficiency, the monomer conversion rate must be as low as possible. Ammonium persulfate is a water-soluble initiator, but the oxygen free radical produced by its induced decomposition has strong hydrogen abstraction ability. Ammonium persulfate itself is an oxidant. In the polymerization process, the pH of the system is reduced due to ionization reaction, and the residual initiator affects the stability of the polymer. These shortcomings make it difficult to obtain polymers with high molecular weight and high conversion by persulfate catalysis.
