Swelling of Ultrathin Molecular Layer‐by‐Layer Polyamide Water Desalination Membranes

Abstract

The water vapor swelling behavior of ultrathin crosslinked aromatic polyamide (PA) films, synthesized via molecular layer‐by‐layer deposition, is characterized via specular X‐ray reflectivity. The results show that these films expand only along the thickness direction and their maximum swelling ratio can be controlled by the specific diamine monomer chemistry. By measuring the swelling ratio as a function of water activity, the Flory interaction parameter and monomers between crosslinks of these PAs are characterized using the Flory‐Rehner and the Painter‐Shenoy thermodynamic swelling models. Comparing the monomers between crosslink calculated from the swelling theories with values obtain from chemical analysis indicate that the PS model gives a more accurate description of the PA networks. This suggests that these low functionality but highly crosslinked networks swell via a combination of chain expansion and topological rearrangement. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1647–1655

Synthesis and characterization of polyimides from 4‐(diphenyl phosphine oxide)phenyl pyrromellitic dianhydride

“…In addition, the amount of residue at 800 C in air was high and correlated well to the phosphine oxide content in polyimides (Table II). In the TMA analysis, the POPPMDA-mDAPPO polyimide exhibited a CTE value of 28 ppm/ C, which is similar to the CTE of PI-3(30 ppm/ C) reported by Chen, 6 but smaller than that of Type HN polyimide film (34 ppm in 30-400 C range). 35 However, CTE of the POPPMDA-mDAPPO polyimide was still higher than that of Cu substrate (17 ppm/ C) and thus copolymerization with pPDA was attempted, resulting in 19 and 17 ppm/ C of CTE values, which are similar to or same as that of Cu foil (Table III).…”

“…The results clearly demonstrate the effect of two phosphine oxide moieties in the POPPMDA-mDAPPO polyimide, compared to only one moiety found in PPMDA-mDAPPO, as well as the usefulness of the modified T-peel samples which do not require a thermal lamination process. The peel strength of POPPMDA-mDAPPO (134 g/mm) can be also compared with those of PyraluxV R AC(119), 36 PyraluxV R TK(124), 37 PI-3(128), 6 PyraluxV R AX(137), 38 PI-4(160), and PyraluxV R AP (160 g/mm). 39 These results clearly demonstrate the successful structural modification of polyimides to obtain low CTE and high peel strength.…”

“…A novel dianhydride monomer, POPPMDA, was synthesized via a 3-step process (Scheme 1); (1) preparation of 4-(diphenyl phosphine oxide)phenyl boronic acid (POBB), (2) Suzuki cross coupling reaction of POBB with B4MB to produce 4-(diphenyl phosphine oxide)phenyl tetramethyl benzene (POP4MB), and (3) oxidation and cyclodehydration of POP4MB to produce POPPMDA. The monomer and its intermediates were characterized by FT-IR (Shimadzu, FTIR 8400S) and NMR (JEOL, JNM-LA300WB, 300MHz) using CDCl 3 or deuterated dimethyl sulfoxide (DMSO-d 6 ). The chemical shifts in NMR were calibrated using tetarmethylsilane ( 1 H) or phosphoric acid ( 31 P) as the internal standard.…”

“…[6][7][8] However, the insolubility of these polyimides due to their high chain rigidity has led to the use of poly(amic-acid)s to prepare polymeric films. This, in turn, requires the thermal conversion of poly(amic-acid)s to polyimides, a process that is accompanied by large volume shrinkage and thus large residual stress.…”

“…[21][22] In comparison, the direct casting of polyimide solution onto the Cu foil 23 is a cost advantageous method, but requires soluble polyimides with low CTE and excellent adhesion. Since lowering the CTE with monomers possessing high chain rigidity is well understood, [6][7][8] and soluble polyimides can be prepared by solution or chemical imidization, 24 the remaining hurdle is improving adhesion. This can be achieved by the surface modification of Cu foil by tie-layer coating of Cr, Ti, or polymers, [25][26] or structural modification of polyimides with adhesion promoting groups such as pyridine 27 or phosphine oxide groups.…”