Perfectly alternating segmented polyimide‐polydimethyl siloxane copolymers via transimidization

Abstract

SYNOPSISNew strategies for the synthesis of perfectly alternating segmented polyimide-polydimethyl siloxane copolymers were developed by utilizing a transimidization method. Imide oligomers endcapped with 2-aminopyrimidine were reacted with aminopropyl terminated ( dimethyl siloxane ) oligomers to afford perfectly alternating segmented imide siloxane copolymers. The polymerization was conducted in solvents such as chlorobenzene and chloroform. High molecular weight, fully imidized perfectly alternating segmented imide siloxane copolymers were obtained within 2 h a t temperatures of 60-110°C. The mechanism of the reaction was further elucidated via model compounds and NMR characterization. The block copolymers exhibited two Tgs due to the microphase separation of the polyimide and polysiloxane phases. The Tg of the polyimide phase was a function of the length of the polyimide block. However, partial phase mixing was also evident from the DSC results on the imide siloxane copolymers prepared with low molecular weight polyimide segments. Thermooxidative stability and tensile properties of the perfectly alternating segmented imide siloxane copolymers were found to be principally dependent on the amount of poly (dimethyl siloxane) incorporated in the copolymer and did not correlate with the poly (dimethyl siloxane) or polyimide block lengths. The stress-strain behavior of both solvent cast films or molded films is also reported.

Synthesis of polyimides and segmented block copolyimides by transimidization

“…3-Nitro-5,6,9,10-tetrahydro [5]helicene-7,8-dicarboxylic anhydride 1 (2, 5.005 g, 12.60 mmol) and 2-aminopyridine (1.200 g, 12.76 mmol) were placed in o-dichlorobenzene (50 mL) and isoquinoline (5 drops) and stirred for 1 h in a three-necked, round-bottomed flask fitted with a nitrogen inlet and Dean-Stark trap, after which it was set to reflux overnight. The homogeneous solution was cooled and poured into pentane (600 mL), the yellow precipitate was collected and dried in vacuum (100°C, 5 mmHg) overnight; 5 6, 146.9, 146.2, 140.8, 140.5, 140.0, 139.7, 139.5, 139.3, 138.2, 137.0, 132.6, 130.9, 130.5, 129.3, 128.2, 127.2, 126.3, 125.9, 123.4, 122.9, 122.2, 120.9, 28.5, 28.4, 23.9, 23.9 …”

“…The homogeneous solution was cooled and poured into pentane (600 mL), the yellow precipitate was collected and dried in vacuum (100°C, 5 mmHg) overnight; 5 6, 146.9, 146.2, 140.8, 140.5, 140.0, 139.7, 139.5, 139.3, 138.2, 137.0, 132.6, 130.9, 130.5, 129.3, 128.2, 127.2, 126.3, 125.9, 123.4, 122.9, 122.2, 120.9, 28.5, 28.4, 23.9, 23.9 …”

“…3-Nitro-5,6,9,10-tetrahydro [5]helicene-7,8-dicarboxylic-(N-2-pyridyl) imide (3, 1.30 g, 2.74 mol) was dissolved in THF (50 mL) and acetic acid (0.5 mL) over PtO 2 (100 mg) and hydrogenated (60 psi) for 45 min. The solution was dried (MgSO 4 ) and removed to give a red solid that was dried in vacuum (100°C, 5 mmHg) overnight; 1.21 g (99% yield); m.p.…”

“…4 The use of electron deficient aryl amines, such as aminopyridines and aminopyrimidines, to block the anhydride group allowed for an exchange reaction to take place with an electron-rich (i.e., more basic) aryl amine (such as aniline). Since that time, except for one case, where the chemistry was used to prepare perfectly alternating polyimide-poly(dimethyl siloxane) block copolymers, 5 this reaction has been largely ignored. If the anhydride functionality of a target AB monomer can be directly masked by the formation of an imide moiety with an electron deficient heterocyclic amine (e.g., 2-aminopyridine or 2-aminopyrimidine), then this has the effect of rendering the anhydride functionality inert.…”

“…The tetrahydro [5]helicene core has been chosen as a model because our lab is familiar with its preparation and the properties of the polyimides that it produces. The synthesis and characterization of the polyimide and segmented copolyimides derived from AX monomer 4 via transimidization reaction are reported herein.…”