Jiangtao Liu

Dispersion polymerization of styrene in aqueous ethanol media using poly(ethylene oxide) macromonomer as a polymerizable stabilizer

Abstract The kinetics of dispersion polymerization of styrene with a small amount of ω-methoxy poly(ethylene oxide)40 undecyl-α-methacrylate macromonomer (PEO-R-MA-40) in the ethanol-water media was studied. A maximum and constant rate of polymerization for this system appeared at the 18%—55% conversion of styrene to polystyrene. However, only 50% of the amphiphilic PEO macromonomer was found to be grafted in the copolymer (stabilizer) after 10 h of polymerization at 65°C. But as high as 98.5% conversion of styrene to polymer was attained. The initial rate of polymerization follows the scaling relationship, (Rp)i ∞ [PEO-R-MA-40]00 [styrene]00.92 [AIBN]00.90. It increased with increasing temperature but decreased with increasing water content because of the solvency effect in the reaction medium. The molecular weight Mw of polymer increased with increasing conversion of styrene up to about 55%. It then decreased slightly towards higher conversions, leading to a broader molecular weight distribution. The activation energies for the dispersion polymerization in the initial stage (

Precise Molecular Sieving Architectures with Janus Pathways for Both Polar and Nonpolar Molecules

Precise molecular sieving architectures with Janus superhighways are constructed via a molecularly engineered interfacial reaction between cyclodextrin (CD) and trimesoyl chloride (TMC). Interestingly, the CD/TMC nanofilms constructed with both hydrophobic inner cavities and hydrophilic channels exhibit exceptionally high permeances for both polar and nonpolar solvents. The precise molecular sieving functions are determined by the type of CD building blocks and the inner cavities of intrinsic 3D hollow bowls. Positron annihilation spectroscopy (PAS) confirms that a larger inner CD cavity tends to generate a larger free volume and higher microporosity. Based on the rejection ratio of various dyes, the estimated molecular weight cutoff of CD/TMC nanofilms follows the trend of α-CD/TMC (320 Da) <β-CD/TMC (400 Da) <γ-CD/TMC (550 Da), which is in strict accordance with the orders of their free volumes measured by PAS and inner cavity sizes of α-CD <β-CD <γ-CD. This kind of novel CD/TMC molecular sieving membrane with intrinsic microporosity containing tunable pore size and sharp pore-size distribution can effectively discriminate molecules with different 3D sizes.

Flexible thermally treated 3D PIM-CD molecular sieve membranes exceeding the upper bound line for propylene/propane separation

Polymers of intrinsic microporosity (PIM) incorporated with beta-cyclodextrin (β-CD) (referred to as PIM-CD) are prepared via nucleophilic substitution copolymerization and then thermally treated at elevated temperatures from 300 to 600 °C. After the decomposition of thermally labile CD, the spaces originally occupied by CD convert to micro-pores and cross-linking points in the polymer matrix. The thermally induced three-dimensional (3D) cross-linking network not only possesses ultra-fine micro-pores and interconnected microvoids but also shows a superior molecular sieve ability for propylene/propane separation. The C3H6/C3H8 selectivity of the thermally treated membranes increases remarkably, about 3 times compared to that of the original untreated membranes. In particular, the PIM-CD membranes thermally treated at 300 or 400 °C are flexible, and they have C3H6/C3H8 separation performance exceeding the upper bound line in both pure and mixed gas tests. As observed from the gas sorption isotherms, membranes with a higher content of CD units have a higher gas sorption capacity. Additionally, the diffusivity selectivity of PIM-CD membranes after thermal treatment increases more quickly than that of the PIM membrane and contributes more to the permeability selectivity.

Preparation, characterization, and properties of poly(thioether ether imide)s from isomeric bis(chlorophthalimide)s and bis(4-mercaptophenyl) ether

A series of isomeric poly(thioether ether imide)s (PTEIs) containing both thioether and ether linkages were prepared by aromatic nucleophilic substitution reaction of isomeric bis(chlorophthalimide)s (BCPIs) with bis(4-mercaptophenyl) ether (BMPE). The inherent viscosities of synthesized polymers were found in the range of 0.41–0.86 dL g−1 in N-methyl-2-pyrrolidone at 30°C. The glass transition temperature (T g) of the isomeric PTEIs were 210–242°C and increased by increasing the content of 3-substituted phthalimide unit in the polymer backbone. The 5% weight loss temperature values reached up to 525–539°C under nitrogen and 523–534°C in air atmospheres, respectively, which indicated this kind of polyimide possessed excellent thermal stability. Flexible films could be cast from the polymer solution. The PTEI films exhibited moderate mechanical properties with tensile strengths of 106–127 MPa, elongations at break of 8.6–11.5%, and tensile moduli of 2.2–2.8 GPa, respectively. Dynamic mechanical thermal analysis results illustrated that the storage moduli (E′) of PTEI (a–e) almost completely maintained at about 2.3 GPa before reaching the corresponding T g. It is noted that the minimum melt viscosity of isomeric PTEIs (a′–e′) decreased by increasing the content of unsymmetrical 3,4′-substituted phthalimide unit in the polymer main chain.

Synthesis of organosoluble and transparent phenolphthalein-based cardo poly(ether sulfone imide)s via aromatic nucleophilic substitution polymerization

A series of cardo poly(ether sulfone imide)s (PESI-C) containing bulky phthalide groups were prepared via aromatic nucleophilic substitution reaction of phenolphthalein with 4,4′-difluorodiphenyl sulfone and 4,4′-bis(4-fluorophthalimido)diphenyl ether (BFPI). The glass transition temperatures and 5% weight loss temperatures in nitrogen of the resulting PESI-C increased from 258°C to 278°C and from 468°C to 495°C with increasing the content of imide moiety in the polymer chain, respectively. These PESI-C films were transparent and essentially colorless and exhibited good mechanical properties with tensile strengths of 91–124 MPa, elongations at break of 6.9–12.8%, and tensile moduli of 2.2–2.8 GPa, respectively. It is noted that the tensile strengths, elongations at break, and tensile moduli of PESI-C also increased with increasing the content of BFPI in the copolymerization, indicating that the properties could be adjusted by controlling the ratio of BFPI and 4,4′-difluorodiphenyl sulfone.

Preparation, characterization, and properties of poly(thioether imide)s from isomeric bis(chlorophthalimide)s and bisthiophenols

A series of isomeric poly(thioether imide)s (PTIs) containing thioether linkages were prepared by aromatic nucleophilic substitution reaction of isomeric bis(chlorophthalimide)s (BCPIs) and bisthiophenols. The glass transition temperatures (T gs) of the isomeric PTIs were 190–264°C, the 5% weight loss temperature (T 5%) reached up to 441–508°C under nitrogen and 472–520°C in air atmospheres, respectively. It was found that the T g values of the PTIs from three isomeric BCPIs with the same bisthiophenol increased in the order of 4,4′-BCPI < 3,4′-BCPI < 3,3′-BCPI, while the T 5% values gradually decreased in the order of 4,4′-BCPI > 3,4′-BCPI > 3,3′-BCPI. Flexible films that could be cast from the polymer solutions exhibited good mechanical properties with tensile strengths of 91–121 MPa, elongations at break of 8–12%, and tensile moduli of 2.2–2.6 GPa. The minimum melt viscosity of isomeric PTIs decreased with increasing the content of asymmetric 3,4′-substituted phthalimide unit, and the PTI (2c) showed the lowest melt viscosity about 760 Pa·s at 264°C among these isomeric polymers.

Advanced Anti-Fouling Membranes for Osmotic Power Generation from Wastewater via Pressure Retarded Osmosis (PRO)

A facile and versatile approach was demonstrated for the fabrication of low-fouling pressure retarded osmosis (PRO) membranes for osmotic power generation from highly polluted wastewater. A water-soluble zwitterionic random copolymer with superior hydrophilicity and unique chemistry was molecularly designed and synthesized via a single-step free-radical polymerization between 2-methacryloyloxyethyl phosphorylcholine (MPC) and 2-aminoethyl methacrylate hydrochloride (AEMA). The P[MPC- co-AEMA] copolymer was then chemically grafted onto the surface of PES/Torlon hollow fibers via amino groups coupling of poly(AEMA) with the polyimide structures of Torlon, leaving the zwitterions of poly(MPC) in the feed solution. Because of the outstanding hydrophilicity, unique cationic and anionic groups, and electrical neutrality of the zwitterionic brush, the newly developed membrane showed great resistances to both inorganic scaling and organic fouling in PRO operations. When using a real wastewater brine comprising multifoulants as the feed, the P[MPC- co-AEMA] modified membrane exhibits a much lower flux decline of 37% at Δ P = 0 bar after 24-h tests and a smaller power density decrease of 28% at Δ P = 15 bar within 12-h tests, compared to 61% and 42% respectively for the unmodified one. In addition to the low fouling tendency, the modified membrane shows outstanding performance stability and fouling reversibility, where the flux is almost fully recovered by physical backwash of water at 15 bar for 0.5 h. This study provides valuable insights and strategies for the design and fabrication of effective antifouling materials and membranes for PRO osmotic power generation.