A versatile living polymerization method for aromatic amides.

Polycondensation polymers typically follow step-growth kinetics assuming all functional groups are equally likely to react with one another. If the reaction rates with the chain end can be selectively accelerated, living polymers can be obtained. Here we report on two chlorophosphonium iodide reagents that have been synthesized from triphenylphosphine and tri(o-methoxyphenyl)phosphine. The former activates aromatic carboxylic acids as acid chlorides in the presence of secondary aromatic amines and the latter even in the presence of primary aromatic amines. These reagents allow p-aminobenzoic acid derivatives to form solution-stable activated monomers that polymerize in a living fashion in the presence of amine initiators. Other aryl amino acids and even dimers of aryl amino acids can be polymerized in a living fashion when slowly added to the phosphonium salt in the presence of an amine initiator. Diblock copolymers and triblock terpolymers of aryl amino acids can be prepared even in the presence of electrophilic functional groups.

Oxanorbornenes: promising new single addition monomers for the metathesis polymerization.

Higher ring-opening metathesis propagation rates of exo-norbornene derivatives over endo derivatives are well established in the literature. Here, we report for the first time that endo-isomers of oxanorbornene derivatives show higher reactivity towards ring-opening metathesis with Grubbs' 3rd generation catalyst (G3) than the corresponding exo-isomers. A very high selectivity for the reaction of G3 with endo over the exo-isomers could be shown. Furthermore, single molecular addition of the endo-isomers with G3 was observed. On the other hand, pure exo-monomers could successfully be homopolymerized. Mixtures of exo- and endo- monomers, however, prevented the homopolymerization of the exo-monomer. Such mixtures could successfully be copolymerized with cycloalkenes, resulting in alternating copolymers. An oxanorbornadiene derivative could be shown to undergo single addition reactions, exploited in the preparation of mono-end functional ROMP polymers. These could be selectively derivatized via endgroup selective thiol-ene click reactions. A thiol and alcohol end functional ROMP polymer was synthesized, and the efficient end functionalization was confirmed by 1H NMR spectroscopy and MALDI-ToF spectrometry.

Towards Polymers with Molecular Auxeticity.

For many decades, it has been challenging to synthesize auxetic materials at the molecular level. Auxetic materials exhibit counterintuitive behavior; they expand perpendicularly to the direction in which they are stretched. An aromatic macrocycle containing a sequence of N-substituted and N-unsubstituted amides was designed to resemble the re-entrant structure found in macromolecular auxetic materials. Upon application of tensile force, bent cis amides change to linear trans amides. This was anticipated to trigger the expansion of the macrocycle perpendicular to the direction of the applied force. To investigate the proposed configurational change by atom force microscopy (AFM), we designed and prepared a cis-trans aramide motif incorporated into an end-functionalized polymer which ensured covalent attachment to the AFM tip. At large extensions, polymer chains were envisioned to unfold and induce cis-trans isomerization.

Telechelics Based on Catalytic Alternating Ring-Opening Metathesis Polymerization.

We describe a protocol to synthesize alternating telechelic ROMP copolymers of 7-oxa-norbornene derivatives and cycloalkenes under catalytic conditions. These copolymers were synthesized using Grubbs' second-generation catalyst. The sterically less hindered backbone double bonds of the resulting alternating copolymers facilitate the chain transfer (secondary metathesis) reactions. In the presence of symmetrical chain transfer agents (CTA), alternating copolymers could be synthesized catalytically. This procedure allows the synthesis of telechelic polymers based on potentially functional 7-oxa-norbornene derivatives under thermodynamic equilibrium conditions. The molar mass of the alternating copolymer was controlled by the monomer to CTA ratio. The end group of the copolymers synthesized in the catalytic manner was addressed by the CTA functionality, yielding telechelic copolymers in excellent yields. 1H NMR spectroscopy, MALDI-ToF mass spectrometry, and SEC analysis confirmed the chemical identity of the alternating telechelic copolymers with excellent control over the molar mass.

Magnetic pH-responsive nanocarrier with long spacer length and high colloidal stability for controlled delivery of doxorubicin.

A novel magnetic nanocarrier with long spacer length and high colloidal stability has been prepared for effective delivery of doxorubicin (DOX). First, poly(amidoamine) (PAMAM) dendrimer was grown up onto the surface of superparamagnetic iron oxide nanoparticles to increase the loading amount of amine groups. Then, terminal amine groups were functionalized by polyethylene glycol dimethylester to increase the spacer length. Then anticancer drug DOX was covalently attached onto the system by hydrazone bond to forms a pH-sensitive nanocarrier. This system is designed to combine the advantage of magnetic targeting, high drug loading capacity, and controlled release.