*2.1. Materials*

N-methyl-2-pyrrolidone (N-MP, 98%, Aldrich, St. Louis, MO, USA), toluene (analytical grade) methylene chloride, chloroform, THF, DMF (all reagent grade, Vekton, Voronezh, Russia), trimethylamine (≥99%, Aldrich, Overijse, Belgium), and pyridine (99%, Acros Organics, NJ, USA) were purified through standard techniques. 3,3 ,4,4 - (1,3-diphenoxybenzene)tetracarboxylic dianhydride (99%, Ambinter Stock Screening Collections, China), 2,4-diaminophenol dihydrochloride (98%, Lancaster, Eastgate, White Lund, Morecambe, England), and potassium iodide (≥99.5%, Aldrich, St. Louis, MO, USA) were dried at elevated temperature in a vacuum prior to synthesis. 2-Hydroxyethyl methacrylate (HEMA) (99%, Acros Organics, UK) and ε-caprolactone (99%, Aldrich, St. Louis, MO, USA) were distilled twice under vacuum. Copper(I) chloride (99%, Aldrich, St. Louis, MO, USA) was stirred in glacial acetic acid overnight, filtered, and washed with argon-purged methanol (reagent grade, Vekton, Russia). Sn(II) 2-ethyl hexanoate (Sn(EH)2) (~95%, Aldrich, Japan) was distilled under vacuum. 2-Bromoisobutyryl bromide (98%, Aldrich, St. Louis, MO, USA), 2,2'-bipyridine (bpy) (≥99%, Aldrich, St. Louis, MO, USA), sodium azide (NaN3) (≥99.5%, Aldrich, St. Louis, MO, USA), propargyl alcohol (99%, Aldrich, Steinheim, Germany), N,N,N ,N,N-pentamethyldiethylenetriamine (PMDETA) (99%, Aldrich, Steinheim, Germany), copper(I) bromide (CuBr) (98%, Aldrich, St. Louis, MO, USA), and LiBr (≥99%, Aldrich, St. Louis, MO, USA) were used without additional purification.

#### *2.2. Synthesis of PI-g-PHEMA as Branched Multicenter Macroinitiator with Hydroxyl Groups in Each Repeating Unit of the Side Chains of the Grafted Copolyimide*

The polyimide multifunctional macroinitiator with initiating groups in almost every monomer unit was obtained by polycondensation of dianhydride of 3,3 ,4,4 -(1,3 diphenoxybenzene)-tetracarboxylic acid and 2,4-diaminophenol, its phenol groups being further modified by 2-bromoisobutyryl bromide. The initial PI1 and the related PI2 multifunctional macroinitiator (Figure 1, see Result and Discussion section) were synthesized using procedures described in our previous publications [28–30].

To obtain a brush-type macroinitiator with hydroxyl groups in the side chains, graft copolyimide PI-*g*-PHEMA was synthesized by polymerization of 2-hydroxyethyl methacrylate (HEMA) on PI2 macroinitiator (Figure 1) by the ATRP. A typical synthesis procedure was as follows. A weighed portion of PI2 (0.075 g, 0.11 mmol per initiating group) and 2,2 -bipyridine (0.052 g, 0.33 mmol) was placed into a 25 mL Schlenk flask equipped with a magnetic stirrer, then DMF (16.5 mL, 0.21 mol) and HEMA (3.65 mL, 0.03 mol) were added with the syringe. The solvent, monomer, and syringes were purged with argon. The flask was sealed with a rubber septum, and the mixture was stirred until the powder was completely dissolved. Then, three freeze−pump−thaw cycles were carried out (evacuation for 15 min), after which the flask was filled with argon. After opening the septum in

a stream of argon, CuCl (0.011 g, 0.11 mmol) was added to the reaction mixture, after which the flask was closed again with the septum. Three more freeze−pump−thaw cycles (evacuation for 15 min) of the reaction mixture were carried out. The flask was filled with argon and thermostated in an oil bath, and placed on a magnetic stirrer with a temperature controller, at 30 ◦C.

After a given reaction time, the reaction mixture was quickly cooled to room temperature and diluted two times with THF. To remove copper salts from the mixture, reaction solution was passed through a column filled with Al2O3, then concentrated using a rotary evaporator, and the polymerization product was precipitated into a water/methanol mixture with a volume ratio of 1/6. The filtered powder was dried under vacuum at 50 ◦C.
