Cocrystalline Copolyimides of Poly(ethylene 2,6-naphthalate)

Copolycondensation of N,N′-bis­(2-hydroxyethyl)-biphenyl-3,4,3′,4′-tetracarboxylic diimide (5–25 mol %) with bis­(2-hydroxyethyl)-2,6-naphthalate affords a series of cocrystalline, poly­(ethylene 2,6-naphthalate) (PEN)-based poly­(ester imide)­s. The glass transition temperature rises with the level of comonomer, from 118 °C for PEN itself to 148 °C for the 25% diimide copolymer. X-ray powder and fiber diffraction studies show that, when 5 mol % or more of diimide is present, the α-PEN crystal structure is replaced by a new crystalline phase arising from isomorphic substitution of biphenyldiimide for PEN residues in the polymer crystal lattice. This new phase is provisionally identified as monoclinic, C2/m, with two chains per unit cell, a = 10.56, b = 6.74, c = 13.25 Å, and β = 143.0°.将N,N'-双(2-羟乙基)联苯-3,4,3',4'-四羧酸二酰亚胺（N,N′-bis(2-hydroxyethyl)-biphenyl-3,4,3′,4′-tetracarboxylic diimide，投料占比5~25 mol%）与双(2-羟乙基)-2,6-萘二甲酸酯（bis(2-hydroxyethyl)-2,6-naphthalate）进行共缩聚反应，可制备得到一系列以聚2,6-萘二甲酸乙二酯（polyethylene 2,6-naphthalate, PEN）为基底的共结晶型聚酰亚胺酯（poly(ester imide)s）。随着共聚单体投料占比的提升，共聚物的玻璃化转变温度逐渐升高：纯PEN的玻璃化转变温度为118 ℃，当二酰亚胺单体投料占比为25 mol%时，共聚物的玻璃化转变温度可达148 ℃。X射线粉末衍射与纤维衍射研究表明，当二酰亚胺单体投料占比不低于5 mol%时，α晶型PEN的晶体结构将被全新晶相取代；该新晶相源于联苯二酰亚胺在聚合物晶格中对PEN链段的同晶取代。该新晶相暂被鉴定为单斜晶系，空间群为C2/m，每个晶胞内含两条聚合物链，晶胞参数为a = 10.56、b = 6.74、c = 13.25 Å，β = 143.0°。