Helical Configuration of Poly(iminomethylenes). Screw Sense of Polymers Derived from Optically Active Alkyl Isocyanides

Beijnen, A.J.M. van; Nolte, Roeland J. M.; Drenth, W.; Hezemans, A.M.F.; Coolwijk, P.J.F.M. van de

doi:10.1021/ma60078a011

Cited by 40 publications

(19 citation statements)

References 9 publications

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“…In fact, the polymers in this study displayed extremely high viscosity indices ( α ) in the Mark–Houwink–Sakurada plot, η = kM α , in which η and M are the intrinsic viscosity and absolute molecular weight, respectively, and k is a constant. For example, poly( sec ‐octylisocyanide) displays a large α value (1.75),15a and so does poly(butylisocyanate) (1.83),15b owing to its rigid helical conformation. Some substituted helical polyacetylenes also display large α values owing to the conjugated main chain, including poly( N ‐propargyl‐ n ‐hexanamide) (0.98),16 poly( n ‐hexylpropiolate) (1.2),17 and poly( p ‐phenoxycarbonylphenylacetylene) (0.97) 18.…”

Section: Resultsmentioning

confidence: 99%

Synthesis and Helical Structure of Poly(1‐methylpropargyl ester)s with Various Side Chains

Suzuki

Shiotsuki

Sanda

et al. 2008

Chemistry An Asian Journal

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Optically active 1-methylpropargyl esters bearing various substituents were polymerized with [(nbd)Rh](+)[eta(6)-C(6)H(5)B(C(6)H(5))(3)](-) (nbd=norbornadiene) as a catalyst to afford the corresponding poly(1-methylpropargyl ester)s with moderate molecular weights in good yields. The polymers have a cis-stereoregular structure, which was determined by (1)H NMR spectroscopy. Large optical rotations and clear CD signals demonstrated that all these polymers take on a helical structure with a predominantly one-handed screw sense. The polymers exhibited large viscosity indices in the range 1.14-1.75. Chiral amplification was observed in R/S copolymerization. Conformational analysis revealed that the polymers form a tightly twisted helical structure with a dihedral angle of 70 degrees at the single bond of the main chain.

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Section: Resultsmentioning

confidence: 99%

Synthesis and Helical Structure of Poly(1‐methylpropargyl ester)s with Various Side Chains

Suzuki

Shiotsuki

Sanda

et al. 2008

Chemistry An Asian Journal

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“…For these measurements, the polymer was dissolved in acetonitrile (0.1−0.6 mg mL −1 ) and the intrinsic viscosity of these solutions was measured at 25 °C. The average viscosity molecular weight M v of the polymer was calculated using the Mark–Houwink equation using previously determined Mark–Houwink parameters of K = 1.4 × 10 −9 and a = 1.75 . This yielded an average viscosity molecular weight of 413 kg mol –1 , which corresponds to an average stretched polymer length of 163 nm.…”

Section: Methodsmentioning

confidence: 99%

Tuning Hydrogel Mechanics Using the Hofmeister Effect

Jaspers

Rowan

Kouwer

2015

Adv Funct Materials

114

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6503wileyonlinelibrary.com mechanical properties. The large morphological and volume change at the LCST of PNIPAM-based gels [ 10 ] make mechanical studies meaningless. A series of studies on the Hofmeister effect on supramolecular hydrogels showed a dependence of the mechanical properties, but this was merely induced by the hugely different morphologies found for the different assembly conditions of the gels. [11][12][13] Here, we describe for the fi rst time that we can use the Hofmeister effect to controllably manipulate the mechanical properties of polymer hydrogels. As expected, the addition of salts directly affects the gelation temperature and, for our thermoresponsive hydrogel, this changes the stiffness of the gel over two orders of magnitude at a constant temperature, for instance 37 °C. We construct hydrogels that range from very soft to stiff, but all at identical concentration. To achieve such change in mechanical response, one commonly needs to vary parameters such as concentration, morphology and bundle (or fi ber) diameter and stiffness. [ 14 ] Some of these are diffi cult to control, while others simultaneously change many important network characteristics; for instance, the concentration changes the biomedically relevant pore size and stiffness of the gel (as well as nonlinear gel properties). The salts, however, are able to shift the mechanics, without changing porosity and network morphology.The polymers we use are ethylene glycol-functionalized polyisocyanides (PICs, Figure 1 b), which form a thermoreversible gel upon heating when dissolved in water. [ 15 ] At the LCST, the polymers become hydrophobic and form a network of entangled semi-fl exible bundles of polymer chains. The mechanical properties of the PIC hydrogels mimic those of biological gels, [ 15 ] including the nonlinear mechanics at large stress (or strain), which is markedly different than that of other synthetic hydrogels. The mechanics of PIC hydrogels is readily tuned by changing concentration, temperature, and polymer length. [ 16 ] Here, we add two additional parameters to this list: the nature of the salt (more precisely the anion) and its concentration.For a long time, the molecular basis of the Hofmeister series was related to the effect of ions on the bulk structure of water. [ 17 ] More recently, however, it was shown that salts generally do not affect the bulk water structure. [ 18,19 ] Instead, more recent theories hypothesize that direct interactions between ions and macromolecules and their fi rst hydration shell can explain the effects fi rst described by Hofmeister. [ 7,[20][21][22][23] The Hofmeister effect is usually more pronounced for anions than for cations and some ions have a stronger effect than others. The general order of the anions, termed the Hofmeister series is shown in Figure 1 a. [ 7,24 ] The ions on the The mechanical properties of hydrogels are commonly modifi ed by changing the concentration of the molecular components. This approach, however, does not only change hydrogel mechanics, but also th...

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“…The polymers obtained from ( R ) -222 , ( R ) -223 , and ( R ) -224 have M -helical conformation with helical excess of 62%, 56%, and 20%, respectively [369] . The polymerization of optically active ( S ) -225 also gives a polymer with M -helicity.…”

Section: Polymerization Of Isocyanidesmentioning

confidence: 98%