Chenyi Wang

Synthesis and properties of fluorinated polyimides with multi-bulky pendant groups

A new aromatic diamine monomer, 2,2′-bis[3,5-di(4-trifluoromethylphenyl)-4-(4-aminophenoxy)phenyl]sulfone, containing four pendant trifluoromethylphenyl group substituents was successfully synthesized via a three-step reaction from readily available reagents. A new series of fluorinated polyimides with multi-bulky pendant groups was prepared from the diamine monomer with three commercially available aromatic tetracarboxylic dianhydrides using one-step high-temperature polycondensation. The incorporation of multi-bulky pendant fluorinated groups and large non-coplanar structures brought about a great improvement in their properties. The resulting polyimides had excellent solubility and the maximum solubility even reached 20 wt% in NMP, CHCl3, and THF at room temperature. Their film displayed a light color and high optical transparency with the cut-off wavelengths ranging from 327 to 343 nm. They also possessed intrinsically low dielectric constant values of 2.69–2.85 (at 1 MHz) and low water absorption (0.59–0.68%). Moreover, these polyimides showed high glass transition temperatures (259–281 °C) and excellent thermal stability with 5% weight loss at temperatures over the range of 551–561 °C and 515–520 °C under nitrogen and air atmospheres, respectively. Compared to some trifluoromethyl-substituted polyimides, these polyimides with multi-bulky pendant groups possessed better solubility and lower cut-off wavelength and dielectric constants.

Synthesis of PBMA-b-PGMA Block Copolymers via ICAR ATRP and their Application in Polymer/Titanium Dioxide Hybrid Materials

Well-defined functional block copolymers, polybutyl methacrylate-b-polyglycidyl methacrylate (PBMA-b-PGMA), were successfully synthesized via initiators for continuous activator regeneration atom transfer radical polymerization ( ICAR ATRP) with pentamethyldiethylene-triamine (PMDETA) as a ligand and copper bromide (CuBr2 ) as a catalyst with concentration of 500 ppm. The PBMA-b-PGMA grafted with titanium dioxide (TiO2 ) nanoparticles was obtained through the reaction between the epoxide on the PGMA segment and amine group on the surface of modified TiO2 nanoparticles. Results showed that the PBMA-b-PGMA block copolymer with about same length of PBMA and PGMA segment could get highest graft ratio and about 17%wt TiO2 nanoparticles were successfully grafted onto the PBMA-b-PGMA block copolymer. The sizes of the PBMA-b-PGMA grafted nanoparticles were about 74 nm in ethyl acetate. The PBMA-b-PGMA grafted TiO2 nanoparticles showed very good dispensability in organic solvent (e.g. ethyl acetate) and polymer matrix. Polymethyl methacrylate (PMMA) containing 0.5%wt PBMA-b-PGMA grafted TiO2 nanoparticles showed strong absorption at about 300 nm and good transparency in visible region, which was attributed to good dispensability of PBMA-b-PGMA grafted TiO2 nanoparticles in PMMA matrix.

Low Concentration Limitations of Catalyst and Conventional Free Radical Polymerization in ICAR ATRP of Butyl Methacrylate With PMDETA as the Ligand

Low concentration limitations of the catalyst and conventional free radical polymerization are investigated in the system of initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) of butyl methacrylate (BMA), in which 2,2-azobisisobutyronitrile (AIBN) is used as a reducing agent, pentamethyldiethylenetriamine (PMDETA) as a ligand, copper bromide (CuBr2) as a catalyst and ethyl 2-bromoisobutyrate (EBiB) as an initiator. Results show that conventional radical polymerization happens in the early stage of the ICAR ATRP of BMA when the amounts of AIBN are 3∼25 times of the catalyst. And with the increase of the conversion, the BMA polymerization solely conducts the controlled radical polymerization (CRP). The low concentration limitations (based on monomer) of the catalyst required in ICAR ATRP of BMA with good controllability are found to be closely related to the molar ratio of initiator to catalyst, which is determined by the stability of the catalyst/ligand complex. The smaller molar ratio of initiator to catalyst allows lower concentration limitations of the catalyst.

Synthesis and characterization of amphiphilic graft copolymers with poly(ethylene glycol) as the hydrophilic backbone and poly(butyl methacrylate) as the hydrophobic graft chain

A series of amphiphilic graft copolymers with hydrophilic polyethylene glycol (PEG) backbone and different densities of hydrophobic poly(butyl methacrylate) (PBMA) side chains were synthesized via a strategy combining polycondensation and through activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) technology. The hydrophilic macro-ATRP initiators having different amounts of active side bromo atoms were first synthesized by reacting the small ATRP initiator which contains two hydroxyl groups with hexamethylene diisocyanate (HDI) and polyethylene glycol (PEG1000). By graft from technology, the amphiphilic graft copolymers were then synthesized via ARGET ATRP of butyl methacrylate (BMA) using the hydrophilic macro-ATRP initiators. The steric shield effects of the macro-initiator lowered the polymerization rate and final conversion of BMA. The amphiphilic graft copolymers in aqueous media had critical micelle concentration (CMC) in the range of 10−6 to 10−7xa0g/mL, which were determined by fluorescence method using pyrene as a probe. The aggregate sizes of the amphiphilic graft copolymers in different solvents changed greatly, which were due to different interactions between the amphiphilic graft copolymers and the solvents and the incompatibility between PEG and PBMA segments.