Thermoreversible Supramacromolecular Ion Gels via Hydrogen Bonding

Abstract

We report the thermoreversible viscoelastic properties of a supramolecular ion gel. Two building blocks were used to form “supramacromolecules”. An ABA triblock copolymer ( M n = 50 000, poly(2-vinylpyridine)-b-poly(ethyl acrylate)-b-poly(2-vinylpyridine)) (P2VP−PEA−P2VP), with a mole ratio of 0.1/0.8/0.1 as a telechelic polymer, and a poly(4-hydroxystyrene) (PHS) homopolymer, with M n = 6600 as a connector, form a physical gel via hydrogen bonding between P2VP and PHS. The thermally stable, hydrophobic ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) provided a good solvent medium for PEA from room temperature up to at least 160 °C. A solution containing 10 wt % P2VP−PEA−P2VP and 4% PHS was a liquid at elevated temperatures but on cooling formed a network at 141.5 °C. Dynamic shear moduli obtained as a function of frequency at various temperatures from 30 to 160 °C could be superposed to form excellent master curves, with a distinct plateau modulus extending over more than 11 orders of magnitude in frequency. The longest relaxation time inferred from the time−temperature superposition shift factors showed a similar 11 order of magnitude increase on cooling. This remarkable temperature sensitivity of the supramacromolecular ion gel is attributed to the formation of multiple hydrogen bonds between a given P2VP block and PHS cross-linker. A hydrogen bond energy of 13 kJ/mol was estimated from temperature-dependent FTIR measurements, and a straightforward analysis yielded an estimate of the number of hydrogen bonds per P2VP block as a function of temperature. This system is distinct from other supramolecular hydrogen-bonded polymers, and from hydrophobically modified associating polymers, in that below the gelation temperature the number of physical cross-links is independent of temperature, but the strength of each association, namely, the number of active hydrogen bonds within a particular cross-link site, increases strongly on cooling.

Living Radical Polymerization by the RAFT Process - A Second Update

“…In the case of bis-RAFT agents sequential polymerization of two monomers will yield a triblock. [269] BA [270] MA [270] NIPAM [269,[271][272][273] 420 [274] BA [281] DA [281] St [71,275] 2VP [276] NVP [103] NIPAM/274 [153] DEHEA [280] MA [281] TMAPMA/PEGMA/NIPAM [277] (PEGMA/320) [165] tBA [280] BA/AA [279] (PEGMA/344) [165] 331 [159] AEMA/325/328 [278] DEHEA-b-ODA [280] DMAM-b-331 [159] DMAM-b-331-b-NIPAM [159] DEHEA-b-tBA [280] NIPAM-b-DMAM [272] 2VP-b-EA [276] tBA-b-DEHEA [280] AEME/328/342 [278] 105 [282] [282] PEGA-b-St [282] 106 [188] [188] EHA-b-MA [188] S S S…”

“…MMA [296] St [296] 128* [283] S S C 12 H 25 S CO 2 H AA [91] CA [297] tBA [298] MA [299] (BMA) [300] (BMA) [300] CMA [301] MMA [122,283] (MMA) [122] BAM [302] DEAM [302,303] DMAM [302,303] EMAM [302,303] NIPAM [302][303][304][305][306] PAM [302,306] MVK [307] PVK [307] 297 [308] tBS [276] CMS [309] HMS [309] St [91,300,309] (St) [300] 4VP [310] Ip [311] 320 [312] 325 [100] 327 [309] 331 [313] 332 [313] NVP [103] 331-b-St [313] tBA-b-Ip [298] tBA-b-St [298] tBA-b-IP-b-St …”

“…Recently, several groups have reported that the polymerization of monomers with primary amine functionality (273)(274)(275)(276) (Table 16) can be effectively controlled with the monomer as the ammonium salt and with no or minimal loss of the RAFT end-group. [90,152,153,166] Some of the more exotic monomer subjected to RAFT polymerization are included in the tables that follow.…”

Model Transient Networks from Strongly Hydrogen-Bonded Polymers

“…Additionally, supramolecular gels based on hydrogen bonding in ionic liquids have been demonstrated and their rheological properties related to the strength and number of hydrogen bonds as well as stoichiometry of donor and acceptor units. 29,30 To broaden the scope and applicability of supramolecular polymer chemistry, many new strongly hydrogen-bonding moieties have been synthesized [31][32][33][34][35][36][37] and incorporated into networkforming materials. [12][13][14][15][38][39][40][41] The strength and specificity of multiple-hydrogen-bonded (MHB) groups vary widely, from weakly complementary pyridine-phenol pairs 42 to extremely strong, self-complementary 6-H-bonded dimers.…”

Creation and control of new morphologies via supramacromolecular self-assembly

“…In addition, we describe the interesting A useful design for building supramolecular networks of polymers is to blend two polymers in a non-volatile solvent. 53,54 One of the two polymers used in this design is an ABA triblock copolymer that has two proton acceptor A blocks, and the other is a C homopolymer that functions as a multifunctional crosslinker with many proton-donor groups. A thermally stable IL is used as the non-volatile solvent and plasticizer to make the supramolecular polymer networks soft and flexible.…”