Archive for August, 2016

Paper of the month: Quantitative end-group functionalization of PNIPAM from aqueous SET-LRP via in situ reduction of Cu(II) with NaBH4

Gavrilov et al. report the quantitative and in situ functionalization of PNIPAM in aqueous media.

One major issue in aqueous copper mediated approaches is the hydrolysis of the halide end group which significantly compromises the end group fidelity of the resulting materials and therefore limits post polymerization modifications. In this current contribution, Monteiro and co-workers have carefully investigated the kinetics of hydrolysis of poly(N-isoproplyacrylamide) (PNIPAM) obtained via a new single electron transfer (SET) polymerization method to reduce Cu(II) directly and quantitatively to Cu(0). It was shown that the rate of hydrolysis is independent of the molecular weight of the polymer and the copper content in solution and reaches completion in approximately 15 hours.

In order to circumvent the hydrolysis issue, the authors elegantly conducted an in situ azidation of the bromine end group resulting in the quantitative transformation of the bromine end groups in a matter of 30 seconds, as indicated by matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-ToF-MS). This is quite a remarkable achievement given that organic solvents facilitate the same process in much longer reactions times, ranging from 10 to 24 hours. The fast reaction rate can be attributed to the enhanced solubility of sodium azide in water and the greater ion pair separation that facilitates nucleophilic attack.

In an attempt to further confirm the data obtained by MALDI-ToF-MS, the azide terminated PNIPAM was subsequently coupled to alkyne functional polymers (after purification) with coupling efficiencies greater than 97%. Thus, it was demonstrated that this approach can not only overcome the hydrolysis issues but also allow rapid synthesis of functional materials.

Tips/comments directly from the authors:

  1. The method of addition of the reactants is important, and by varying the order of addition the polymerizations rates can vary.
  2. It is important to note that the NaBH4 is hygroscopic, and care should be taken to store it in a water-free environment as errors can arise from weighting wet reagents.
  3. We believe that quantitative information can be obtained from the molecular weight distribution using the SEC/LND-model. This is especially important when determining quantitative coupling information of end-groups at high polymer molecular weights, as conventional techniques such as NMR and MALDI-ToF lose sensitivity. We use the weight distribution (i.e. w(M)) as the total weight of the reactants and products remains constant over the reaction; thus, the area under the w(M) vs M curve is the same before and after the reaction.

Read this exciting research for free until 30/09/2016 through a registered RSC account:

Quantitative end-group functionalization of PNIPAM from aqueous SET-LRP via in situ reduction of Cu(II) with NaBH4
M. Gavrilov, Z. Jia,, V. Percec and M.J. Monteiro
Polym. Chem., 2016, 7, 4802-4809
DOI: 10.1039/C6PY00968A

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About the webwriterAthina Anastasaki

Dr. Athina Anastasaki is a web writer for Polymer Chemistry. She is currently an Elings fellow working alongside Professor Craig Hawker at the University of California, Santa Barbara (UCSB).

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Focus on: Cationic Polymerisation

Cationic polymerisation is a type of chain growth polymerisation which proceeds through the reaction of a cationic initiator with monomer, followed by further propagation. Cationic “living” polymerisation is well-known to produce precise polymers with narrow molecular weight distributions. Initial investigations in cationic polymerisation were reported as early as the beginning of the 20th century, whilst further developments in the 1970s and 80s have led to vast growth in this field of study. Now, many different monomer types can be successfully polymerised, including: styrenic, vinyl ethers, isobutene, and heterocyclic monomers, such as: lactones, lactams and cyclic amines.

Three articles appearing in Polymer Chemistry this month have described the use of cationic polymerisation to polymerise either oxazolidine based monomers or p-methylstyrene. In the case of the cyclic oxazolidine monomers the polymerisation is termed cationic ring-opening polymerisation, and in both cases the resulting polymers are interesting for biomedical applications. The polymerisation of p-methylstyrene was conducted in ionic liquids as a green substitute for organic solvents.

ToC image

1. Cationic ring-opening polymerization of protected oxazolidine imines resulting in gradient copolymers of poly(2-oxazoline) and poly(urea)
Meike N. Leiske, Matthias Hartlieb, Fabian H. Sobotta, Renzo M. Paulus, Helmar Görls, Peter Bellstedt, Ulrich S. Schubert
Polym. Chem., 2016, 7, 4924-4936; DOI: 10.1039/C6PY00785F

A Boc-protected oxazolidine monomer was synthesised and utilized to prepare poly(urea)s through  cationic ring opening polymerisation. The polymerisations were studied and resulting homopolymers and copolymers were characterised and subsequently deprotected. Through deprotection and solvent switch to water self-assmebled nanostructures were obtained, which will be further investigated for their biological application.

2. Cationic polymerization of p-methylstyrene in selected ionic liquids and polymerization mechanism
Xiaoqian Zhang, Wenli Guo, Yibo Wu, Liangfa Gong, Wei Li, Xiaoning Li, Shuxin Li, Yuwei Shang, Dan Yang, Hao Wang
Polym. Chem., 2016, 7, 5099-5112; DOI: 10.1039/C6PY00796A

The authors describe extensive experimental and computational investigations of the cationic polymerisation of p-methylstyrene in ionic liquids. Using quantum chemically based computations (the COSMO-RS method) following by solubility and viscosity measurements, a range of ionic lquids were screened. Subsequently, cationic polymerisation were investigated using various initiating systems.

3. Formation of polyoxazoline-silica nanoparticles via the surface-initiated cationic polymerization of 2-methyl-2-oxazoline
G. Bissadi, R. Weberskirch
Polym. Chem., 2016, 7, 5157-5168; DOI: 10.1039/C6PY01034B

Silica nanoparticles were modified to bear initiating sites to polymerise 2-methyl-2-oxazoline from the surface. This cationic surface-initiated grafting-from polymerisation resulted in higher grafting densities compared to previous grafting-to studies, and the molecular weight of the grafted polymer could be tuned by varying the monomer/initiator ratio. The resulting polymer-grafted nanoparticles were conjugated with biomolecules for fluorescence imaging and targeting for biomedical applications.


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About the webwriterFiona Hatton

Dr. Fiona Hatton is a web writer for Polymer Chemistry. She is currently a postdoctoral researcher in the Armes group at the University of Sheffield, UK. Find her on Twitter: @fi_hat

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Advisory Board Top Picks: Tom Davis and Nghia Truong

Tom Davis is a member of Advisory Board for Polymer Chemistry and the Monash–Warwick Professor of medical nanotechnology at Monash University, Australia. Prof. Davis’ research focuses on the application of polymer science and nanotechnology to therapeutic applications, and enhancing the fundamental understanding of how nanomaterials interact with biological systems.

Nghia Truong is a member of the RSC Advances Reviewer Panel and a research fellow at Monash University, Australia. His research focuses on engineering the size, shape, surface, core, and function of polymeric nanoparticles for applications in nanomedicine, using a variety of techniques including emulsion polymerization, self-assembly, polymerization-induced self-assembly, temperature-induced morphological transformation, and click chemistry.

You can find all Advisory Board’s Top Picks papers in our web collection.

Focus on nanoparticle shapes (Prof. Tom Davis, Monash University, Australia and Dr. Nghia Truong, Monash University, Australia).

Shape plays an important role in functional properties of nanoparticles, and as a result, their utility in many applications. Polymer chemists with powerful synthetic techniques have recently made significant contributions expanding our ability to make complex nano-shapes. In 2016, many excellent Polymer Chemistry publications have appeared describing the synthesis and assembly of polymers into tertiary structures.   Below we highlight some that have caught our eye.

1. Multicompartment morphologies self-assembled from fluorinated ABC triblock terpolymers: the effects of flexible and rigid hydrophobic moieties

Sen Li, Jinlin He, Mingzu Zhang, Hairong Wang and Peihong Ni

Polym. Chem., 2016, 7, 1773–1781

Li et. al. self-assemble fluorinated triblock terpolymers into five types of reproducible shapes including sphere, tube, rod, hamburger, and flower. Interestingly, rod-like aggregates have a uniform zig-zag pattern. This work reveals the fact that flexibility or rigidity of hydrophobic segment and polymer concentration have a big influence on the shape of nanoparticles.

2. Disk-like micelles with cylindrical pores from amphiphilic polypeptide block copolymers

Xue Lin, Xiaohua He, Chaoqun Hu, Yuxiang Chen, Yiyong Mai and Shaoliang Lin

Polym. Chem., 2016, 7, 2815–2820

A rare and complex shape such as a nanodisk with cylindrical pores has recently been achieved by self-assembly of the amphiphilic block copolypeptide poly(ethylene glycol)-block-poly(γ-benzyl-L-glutamate) (PEG-b-PBLG) in solution. Spherical micelles and vesicles can also be prepared by tuning the ratio between the hydrophilic block and hydrophobic block in PEG-b-PBLG copolymers.

3. Salicylaldehyde-functionalized block copolymer nano-objects: one-pot synthesis via polymerization-induced self-assembly and their simultaneous cross-linking and fluorescence modification

Jianbing Huang, Hanjun Zhu, Hui Liang and Jiang Lu

Polym. Chem., 2016, 7, 4761–4770

Beside traditional self-assembly, RAFT-mediated emulsion and dispersion polymerization is a very useful technique to simultaneously synthesise block copolymers and form nanoparticles with different shapes. Using this technique, Huang et. al. can crosslink and functionalise spheres, worms, and vesicles with salicylaldazine moieties. These moieties endow the nano-objects with strong orange fluorescence in water, organic solutions or solid state via an aggregation-induced emission mechanism.

4. Microwave-assisted synthesis of block copolymer nanoparticles via RAFT with polymerization-induced self-assembly in methanol

Elden T. Garrett, Yiwen Pei and Andrew B. Lowe

Polym. Chem., 2016, 7, 297–301

Andrew Lowe and coworkers have reported the use of microwaves to further assist RAFT-mediated dispersion polymerization and the formation of nanoparticles with various shapes. The work shows the benefits of microwave-assisted syntheses of nanoparticles in alcoholic solvents.

5. Addition of water to an alcoholic RAFT PISA formulation leads to faster kinetics but limits the evolution of copolymer morphology

E. R. Jones, M. Semsarilar, P. Wyman, M. Boerakker and S. P. Armes

Polym. Chem., 2016, 7, 851–859

Besides using a microwave, the addition of water into alcoholic solvents also increases the rate of RAFT-mediated dispersion polymerization. On the other hand, Armes and coworkers find that in the presence of water, only kinetically-trapped spheres are obtained. This work and other works using aqueous RAFT-mediated emulsion polymerizations create a currently unclear question about the mechanism of the in-situ formation of various nanoparticle shapes in water.

Review article

Theoretical simulations of nanostructures self-assembled from copolymer systems

Zhanwen Xu, Jiaping Lin, Qian Zhang, Liquan Wang and Xiaohui Tian

Polym. Chem., 2016, 7, 3783–3811

Beside powerful synthetic techniques, theoretical simulations offer a useful approach for the understanding and prediction of the formation of polymeric nanostructures. The review by Xu et al. gives a nice overview of the simulation investigations of many self-assembled nanostructures. By tailoring the molecular architectures of block copolymers, nanoparticles with desired shapes can be achieved. Challenges and further developments for theoretical simulations are also discussed in this useful review.

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5th Zing Polymer Chemistry Conference

We are proud to announce the 5th Zing Polymer Chemistry Conference will take place in Dublin (Ireland).

The field of polymer chemistry has experienced a renaissance over the last few last years with the discovery of novel mechanisms to control polymer structure, molecular weight, and functionality. Moreover, the preparation of new polymeric materials with stimuli-responsive or dynamic characteristics have led to novel biomedical materials, polymers for electronic applications, and many other advanced materials. Indeed, polymer science is more exciting than ever before.

This conference will be held 5th – 8th August 2016 and will feature recent developments in the area of polymer synthesis and applied science and intends to gather researchers interested in the forefront polymer science and its future applications.

Several Editorial Board members of Polymer Chemistry will be attending:

Eva M. Harth (Vanderbilt University): Conference Chair
David M Haddleton (University of Warwick): Plenary speaker with the talk ‘Sulfur free RAFT in emulsion for multi-block copolymer synthesis
Emily B. Pentzer (Case Western Reserve University): Invited speaker with the talk ‘Polymerization of Silyl Ketenes
Masami Kamigaito (Nagoya University): Invited speaker with the talk ‘New Developments in Controlled Radical and Cationic Polymerizations

We look forward to welcoming you for the 5th Zing Polymer Chemistry Conference!

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