Meta-aramid polymer with grid structure, and preparation method therefor and use thereof

A meta-aramid polymer with a grid structure whose structural formula is as follows:

• wherein m, n, x and y represent polymerization degrees;
• each of R1 and R2 is alkyl groups with 3-5 carbon atoms;
• and
• wherein the meta-aramid polymer is prepared from a method comprising the following steps:
• (1) polycondensation:
• preparing a meta-aramid polymer by using solution polymerization including dissolving m-phenylenediamine (MPD) in an organic solvent, then adding isophthaloyl chloride (IPC) into a solution in 4 stages for polycondensation, independently 1st polycondensation stage, 2nd polycondensation stage, 3rd polycondensation stage and 4th polycondensation stage, adding an alkylating agent and a metal halide in the 1st and 2nd polycondensation stages, and controlling a reaction temperature, a stirring speed, reaction time and a system viscosity of each stage so as to obtain a prepared polymer solution comprising a polymer molecular structure with a grid structure;
• and
• (2) washing:
• washing the prepared polymer solution in an aqueous solvent, and removing an oligomer and a metal salt in the polymer by water washing for 3 times so as to obtain the meta-aramid polymer with the grid structure;
• when the m-phenylenediamine (MPD) is dissolved in the organic solvent, the solution is kept at 0-10° C., the isophthaloyl chloride (IPC) is divided into 4 equal parts by weight and added into a system in the 4 stages for the polycondensation, the polycondensation in the 4 stages is defined as polycondensation 1, polycondensation 2, polycondensation 3 and polycondensation 4 respectively;
• the reaction temperature of the polycondensation 1 is 5-10° C., the stirring speed is 500-1,000 r/min, the alkylating agent and the metal halide are added, the reaction time is 30-60 min, a neutralizing agent is added, a reaction byproduct is removed, and the system viscosity is 100-300 mPa·s after the polycondensation 1 is completed;
• the reaction temperature of the polycondensation 2 is 10-30° C., the stirring speed is 500-700 r/min, the alkylating agent is added again, the reaction time is 30-45 min, the neutralizing agent is added, a reaction byproduct of this stage is removed, and the system viscosity is 500-1,000 mPa·s after the polycondensation 2 is completed;
• the reaction temperature of the polycondensation 3 is 25-45° C., the stirring speed is 200-350 r/min, the reaction time is 15-20 min, and the system viscosity is 2,000-3,000 mPa·s after the polycondensation 3 is completed;
• and the reaction temperature of the polycondensation 4 is 40-55° C., the stirring speed is 80-200 r/min, the reaction time is 10-30 min, and the system viscosity is 100,000-150,000 mPa·s after the polycondensation 4 is completed;
• the alkylating agent is chloro or bromo alkylolefin;
• and the metal halide is one of AlCl3, FeCl3, SbCl5 and SnCl4.