SYNTHESIS AND CHARACTERIZATION OF POLY(PHTHALAZINONE ETHER NITRILE)-POLYDIMETHYLSILOXANE BLOCK COPOLYMERS

Abstract

High molecular weight block copolymers with different backbone compositions were synthesized from eugenol end-capped polydimethylsiloxane(PDMS)and fluorophenyl-terminated poly(phthalizinone ether nitrile)(PPEN)oligomers.These oligomers of PPEN were prepared via S_NAr step-growth polymerization from 4-(4-hydroxylphenyl)(2H)-phthalazin-1-one(DHPZ)and 2,6-difluoro-benzonitrile(DFBN)using DMSO as solvent at 180℃.The oligomers with well-defined fluoro-terminated and various quantitative molecular weights were obtained by using an excess of DFBN.The number-average molecular weight(M_n)values of PPEN oligomers ranged from 3100 to 10500.The eugenol terminated PDMS oligomers were prepared by reacting silane terminated PDMS with eugenol in toluene via the well-known Pt-catalysed hydrosilation reaction.The phenol-group of eugenol was protected by trimethylchlorosilane in the hydrosilation to avoid side reactions and loss of functional group,and the aryl-trimethylsilyl ethers can be cleaved by refluxing in aqueous methanol.The M_n values of PDMS oligomers were 4550 and 7220,respectively.The block polycondensation was carried out in the presence of dimethyl sulfoxide/o-dichlorobenzene and K_2CO_3 as solvents and catalyst at 180℃ by the S_NAr reaction.The M_n values of block copolymers ranged from 19400 to 25100.The results of GPC indicated that reaction of two oligomers occurred and then the higher molecular weight copolymers were obtained.It further suggested that the new synthesis method is an effective and convenient approach to prepare similar PDMS based block copolymers.The structure of copolymers obtained was characterized by FTIR and 1H-NMR.Differential scanning calorimetry analysis indicated that the block copolymers showed two glass-transition temperatures(T_g) at-98～-90℃ and 255～287℃,respectively.The distinct two T_g's in the block copolymers suggested that microphase separation occurred in the block copolymer.The copolymer also showed a high thermal stability with 10% weight-loss temperatures in excess of 450℃ in nitrogen according to thermogravimetric analysis.The migration of PDMS segments to the copolymer surface was observed directly by atomic force microscope(AFM) and transmission electron microscope(TEM).PDMS expanded to the continuous phase on the surface,suggesting that PDMS segments were rich on the surface.The PPEN phase as the particle cavities was dispersed in copolymer surfaces with diameters of 0.1～0.3 nm.