A kind of highly organsoluble polyimide and copolyimides were successfully synthesized from bicyclo（2.2.2）-oct- 7-ene-2,3,5,6-tetracarboxylic dianhydride （BCDA）, the commercial diamine 4,4＇-methylenedianiline （MDA） and the designed diamine 4,4＇-methylenebis-（2-tert-butylaniline） （MBTBA）. The polyimide from BCDA and MBTBA is highly soluble in conventional low boiling point solvents （such as chloroform, tetrahydrofuran） at room temperature. But the solubility of the copolyimides in conventional solvents decreased with the molar ratio of MBTBA and MDA decreased. When the molar ratio of MBTBA and MDA was larger than 7/3, the copolyimides can be soluble in low boiling point solvents at room temperature to form a transparent, flexible, tough film by solution casting. When the molar ratio of MBTBA and MDA was between 7/3 and 1/9, they can only be soluble in hot dipolar aprotic solvents （such as DMF, NMP etc.） and form films too. The copolyimide was only soluble in m-cresol when the molar ratio of MBTBA and MDA was lower than 1/9. The number-average molecular weights of the soluble copolyimides were larger than 5.8 × 1064 g/mol by GPC and their polydispersity indices were higher than 1.4. Only one glass transition temperature of these copolyimides was detected around 400℃ by DMA. The copolyimides did not show appreciable decomposition up to 430℃ in N2.
The amphiphilic multiarm copolymers were synthesized through the modification of commercially available hyperbranched polyesters（Boltorn H40） with N-ε-carbobenzoxy-L-Lysine N-carboxyanhydride（ZLys-NCA）.After being condensed with N-Boc-phenylalanine（Boc-^NPhe） and deprotected the Boc-groups in trifluoroacetic acid（TFA）,the original terminal hydroxyl groups were transformed into the amino groups and then initiated the ring-opening polymerization of ZLys-NCA.The hydrophilic poly（L-lysine） was grafted to the surface of Boltorn H40 successfully after the protecting benzyl groups were removed by the HBr solution in glacial acetic acid（33 wt%）.The resulting multiarm copolymers were characterized by the ^1H-NMR,GPC and FTIR.The arm length calculated by NMR and GPC analysis was about 3 and 13 lysine-units for H40-Phe-PLysl and H40-Phe-PLys2 respectively.Due to the amphiphilic molecular structure,they displayed ability to self-assemble into spherical micelles in aqueous solution with the average diameter in the range from 70 nm to 250 nm.The CMC of H40-Phe-PLysl and H40-Phe-PLys2 was 0.013 mg/mL and 0.028 mg/mL,respectively, indicating that H40-Phe-PLysl with shorter arm length is easier to self-assemble than H40-Phe-PLys2 with longer arm length.
A novel temperature-responsive hyperbranched multiarm copolymer with a hydrophobic hyperbranched poly(3-ethyl-3-(hydroxymethyl)oxetane)(HBPO) core and thermosensitive poly(N-isopropylacrylamide)(PNIPAM) arms was synthesized via the atom transfer radical polymerization(ATRP) of NIPAM monomers from a hyperbranched HBPO macroinitiator.It was found that HBPO-star-PNIPAM self-assembled into multimolecular micelles(around 60 nm) in water at room temperature according to pyrene probe fluorescence spectrometry,1H NMR,TEM,and DLS measurements.The micelle solution showed a reversible thermosensitive phase transition at a lower critical solution temperature(LCST)(around 32°C) observed by variable temperature optical absorbance measurements.Variable temperature NMR and DLS analyses demonstrated that the LCST transition originated from the secondary aggregation of the micelles driven by increasing hydrophobic interaction due to the dehydration of PNIPAM shells upon heating.The drug loading and release properties of HBPO-star-PNIPAM micelles were also investigated using prednisone acetate as a model drug.The micelles showed a much improved drug encapsulation efficiency and temperature-dependent sustainable release behavior due to the special micellar structure.The micelles exhibited no apparent cytotoxicity against human HeLa cells.
GUO Bo,SUN XiaoYi,ZHOU YongFeng & YAN DeYue College of Chemistry and Chemical Engineering,Shanghai Jiao Tong University,Shanghai 200240,China
