Polymer Chemistry Blog

This month we focus on 3 articles published in Polymer Chemistry which report the use of naturally occurring polymers. As opposed to synthetic polymers, naturally occurring polymers are produced by living organisms in nature. Classes of naturally occurring polymers include proteins, polynucleotides, polyisoprenes, lignin and polysaccharides. These polymers can be extracted and utilised in various applications. In particular, polysaccharides such as cellulose and chitosan are cheap and abundant, biodegradable and are being used increasingly due to growing environmental concerns. Here, chitosan and/or celluose are utilised for the preparation of hydrogels, cellulose modification, and with thermo-conductive carbon nanotubes, exemplifying the broad versatility of these naturally occurring polymers.

1. Highly cost-effective and high-strength hydrogels as dye adsorbents from natural polymers: chitosan and cellulose
Hu Tu, Yi Yu, Jiajia Chen, Xiaowen Shi, Jialin Zhou, Hongbing Deng, Yumin Du
Polym. Chem., 2017, 8, 2913-2921; DOI: 10.1039/C7PY00223H

The authors decribe the preparation of composite hydrogels comprising chitosan, cellulose and rectorite for use as adsorbents for waste water treatment. The hydrogels had good elasticity and strength with the ability to restore their shape after compression. The adsorption efficiency was demonstrated with a dye molecule, which was adsorbed from solution. In addition these materials show promise as adsorbents for heavy metals.

2. Tandem modification of amphiphilic cellulose ethers for amorphous solid dispersion via olefin cross-metathesis and thiol-Michael addition
Yifan Dong, Laura I. Mosquera-Giraldo, Lynne S. Taylor, Kevin J. Edgar
Polym. Chem., 2017, 8, 3129-3139; DOI: 10.1039/C7PY00228A

The combination of olefin cross-metathesis and thiol-Michael addition chemistries have been used to functionalise cellulose derivatives. This methodology allowed for the design of certain cellulose-based polymers for potential use in amorphous solid dispersion, which can enhance the bioavailability of a poorly soluble drug. Mild reaction conditions and functional group tolerance make this strategy appealing for use with other polysaccharides.

3. Thermo conductive carbon nanotube-framed membranes for skin heat signal-responsive transdermal drug delivery
Ji-Hye Kang, Han-Sem Kim, Ueon Sang Shin
Polym. Chem., 2017, 8, 3154-3163; DOI: 10.1039/C7PY00570A

Smart carbon nanotube (CNT)-framed membranes were prepared from CNTs, chitosan and a thermoresponsive polymer, with an LCST around body temperature. The chitosan was used as a biocompatible adhesive to give cohesion to the CNTs. The loading and release of bovine serum albumin (BSA) was investigated and a high loading capacity was found, with temperature-dependent release of the BSA. The hybrid memberanes show potential as patch type transdermal drug delivery devices.

Read these articles for free until July 17^th

About the webwriter

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

Self-assembly of block copolymers is well-known to form polymeric particles with various morphologies, for example, spherical, cylindrical and vesicular morphologies. This month we focus on three research articles published in Polymer Chemistry involving polymer self-assembly.

Polymer self-assembly is driven by the respective solubilities of the blocks of the copolymer in the solvent media present. For example, when water is the desired media the polymer is designed so that one block is water soluble and one block is water insoluble. Either post-polymerisation self-assembly, or in situ polymerisation-induced self-assembly can be employed to form a range of particle morphologies. Post-polymerisation self-assembly typically relies on a solvent switch technique whereby the block copolymer is dissolved in a good solvent for the whole polymer, and is subsequently added to another miscible solvent which is a good solvent for one block and a non-solvent for another. On the other hand, polymerisation-induced self-assembly involves the chain extension of a soluble stabiliser block with a monomer, which when polymerised is insoluble, therefore the polymerisation of the monomer drives the self-assembly process.

The first two articles here utilise polymerisation-induced self-assembly, whilst the third employs post-polymerisation self-assembly. Interestingly, all of the articles highlighted here have employed reversible addition-fragmentation chain-transfer (RAFT) polymerisation as the polymerisation technique of choice to prepared the polymers studied.

1. In situ synthesis of a self-assembled AB/B blend of poly(ethylene glycol)-b-polystyrene/polystyrene by dispersion RAFT polymerization
Bing Yuan, Xin He, Yaqing Qu, Chengqiang Gao, Erika Eiser, Wangqing Zhang
Polym. Chem., 2017,8, 2173-2181; DOI: 10.1039/C7PY00339K

In this article, the authors present the self-assembly of diblock copolymers and homopolymers through a dispersion RAFT polymerisation. The use of a poly(ethylene glycol) macromolecular chain-transfer agent (macro-CTA) and a small molecule CTA led to the formation of various self-assembled morphologies that were considerably different from the pre-synthesised equivalent blends. Morphologies obtained include: vesicles, compartmentalized vesicles and porous nanospheres.

2. RAFT/MADIX emulsion copolymerization of vinyl acetate and N-vinylcaprolactam: towards waterborne physically crosslinked thermoresponsive particles
Laura Etchenausia, Abdel Khoukh, Elise Deniau Lejeune, Maud Save
Polym. Chem., 2017, 8, 2244-2256; DOI: 10.1039/C7PY00221A

Here, the RAFT/MADIX batch emulsion copolymerisation of vinyl acetate (VAc) and N-vinyl caprolactam (VCL) was performed using a poly(ethylene glycol) macro-CTA. The resulting particles were physically crosslinked and thermoresponsive, and particles with a core composition of VAc and VCL of 47:53 exhibited a reversible swelling-to-collapse transition with heating. The hydrolysis of VAc units to vinyl alcohol gave thermoresponsive biocompatible statistical copolymers.

3. CO₂-Triggered UCST transition of amphiphilic triblock copolymers and their self-assemblies
Shaojian Lin, Jiaojiao Shang, Patrick Theato
Polym. Chem., 2017, 8, 2619-2629; DOI: 10.1039/C7PY00186J

RAFT polymerisation was used to prepare triblock copolymers consisting of poly[(ethylene glycol)methyl ether]-b-poly(acrylamide-co-acrylonitrile)-b-poly(diethylamino ethyl methacrylate), which self-assembled in water to form vesicles. As this triblock copolymer contains a temperature responsive segment and a CO₂ responsive block, a morphological transition from vesicles to micelles could be achieved with a CO₂ purge, and then to unimers with an increase in temperature.

Read these articles for free until June 21^th

About the webwriter

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

This month the focus is on Polymers and Rotaxanes, inspired by a recent lecture I attended, given by Sir J. Fraser Stoddart. He received the Nobel Prize in Chemistry in 2016, which was awarded jointly between himself, Jean-Pierre Sauvage and Bernard L. Feringa. His talk, which was part of the Krebs series of lectures at the University of Sheffield, featured his research in the field of mechanically interlocked molecules: rotaxanes and catenanes, which led to his pioneering work on “Molecular Machines”, for which the Nobel Prize was awarded.

Rotaxanes and catenanes are mechanically interlocked molecules; rotaxanes consist of a dumbbell shaped unit, with an encircled ring trapped by the dumbbell ends, whilst catenanes contain a number of interlocked macrocycles. The pioneering work of the Nobel laureates mentioned above has seen these systems developed, whereby through controlling the complexity and chemical functionality of the interlocked structures, work is possible, therefore leading to the term “Molecular Machines”.

Whilst rotaxane and catenane chemistry is well established, the same concept applied in polymer chemistry is currently a smaller area of research interest. However, this area of polymer chemistry research is emerging, with one article featured in Polymer Chemistry this month on the use of a non-polymeric rotaxane crosslinker to form toughened polymer networks. Looking back at previous Polymer Chemistry issues, two further articles utilising rotaxanes have been highlighted below.

1. A vinylic rotaxane cross-linker for toughened network polymers from the radical polymerization of vinyl monomers
J. Sawada, D. Aoki, M. Kuzume, K. Nakazono, H. Otsuka, T. Takata
Polym. Chem., 2017, 8, 1878-1881; DOI: 10.1039/c7py00193b

The authors describe the use a non-polymeric rotaxane crosslinker (RC), with two polymerisable vinyl groups, one on each constituent of the rotaxane unit, for the preparation of rotaxane crosslinked polymers (RCP). The RCPS were prepared via the free radical polymerisation of either butyl acrylate or ethylhexyl acrylate with the RC. The RCPs showed a higher toughness and fracture energy when compared with an equivalent polymer crosslinked with a standard divinyl monomer.

2. Mechanically linked poly[2]rotaxanes constructed from the benzo-21-crown-7/secondary ammonium salt recognition motif
Peng Wang, Zhao Gao, Ming Yuan, Junlong Zhua, Feng Wang
Polym. Chem., 2016, 7, 3664-3668; DOI: 10.1039/c6py00494f

Here, poly[2]rotaxanes were prepared through Cu(I) catalysed click polymerisation of the individual rotaxane units to give a linear polymer. The rotaxane monomer was prepared via a so-called “threading-followed-by-stoppering” strategy. The rheological properties of the poly[2]rotaxanes were investigated and exhibited shear-thinning behaviour not observed for the poly(caprolactone) precursors.

3. Phototriggered supramolecular polymerization of a [c2]daisy chain rotaxane
Xin Fu, Rui-Rui Gu, Qi Zhang, Si-Jia Rao, Xiu-Li Zheng, Da-Hui Qu, He Tian
Polym. Chem., 2016, 7, 2166-2170; DOI: 10.1039/c6py00309e

The formation of a polyrotaxane was achieved through the initial protection of two 2-ureido-4-pyrimidinone (Upy) end groups with photolabile coumarin groups. Exposure to UV light removed the coumarin protecting groups, which led to the self-assembly of the Upy groups and supramolecular polymerisation of the [c2] daisy chain rotaxane monomer. This work represents an interesting stimuli-responsive supramolecular polymers utilising rotaxanes.

Read these articles for free until May 21^th

About the webwriter

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

Carbon dioxide constitutes a small amount of our atmosphere (currently around 0.04%) however it is vital for the survival of life on our planet. CO₂ has been found to be a useful trigger for stimuli-responsive materials as it is benign, abundant, “green” and inexpensive. The reversible self-assembly of polymers and their response to the presence of CO₂ has been of particular interest, for example in biomedical applications.

There is also a growing interest in carbon capture as environmental concerns increase, due to the rise in CO₂ levels since the industrial age. Carbon capture has been proposed as a method to reduce the amount of CO₂ in the atmosphere. Therefore several researchers have been interested in preparing materials which could be used absorb and store CO₂ to remove it from the atmosphere.

This month we look at three articles published in Polymer Chemistry; two articles which describe CO₂ responsive polymers, and one which investigates materials for CO₂ absorption.

1. Oxygen and carbon dioxide dual gas-responsive homopolymers and diblock copolymers synthesized via RAFT polymerization
Xue Jiang, Feng Chun, Guolin Lu, Huang Xiaoyu
Polym. Chem., 2017, 8, 1163-1176; DOI: 10.1039/C6PY02004F

Firstly a monomer containing both O₂ and CO₂ responsive groups was prepared (containing a CF₃ and tertiary amine group), and polymerised by reversible addition-fragmentation chain-transfer (RAFT) polymerisation. This polymer and a diblock copolymer containing PEG, showed responsivity when O₂ and CO₂ were bubbled through the solution compared with N₂. The results suggest potential biomedical applications for the PEG containing polymer which formed micelles in solution.

2. CO₂-Responsive graft copolymers: synthesis and characterization
Shaojian Lin, Anindita Das, Patrick Theato
Polym. Chem., 2017, 8, 1206-1216; DOI: 10.1039/C6PY01996J

Through a combination of controlled radical polymerisation and a grafting-to post-polymerisation modification, the authors describe the synthesis of CO₂ responsive graft-copolymers, where the incorporation of a tertiary amine monomer imparts the CO₂ responsive behaviour. The graft copolymers could be self-assembled to form vesicles in aqueous media, which swelled upon purging with CO₂, for applications such as responsive drug delivery vehicles.

3. Microporous polyimide networks constructed through a two-step polymerization approach, and their carbon dioxide adsorption performance
Hongyan Yao, Na Zhang, Ningning Song, Kunzhi Shen, Pengfei Huo, Shiyang Zhu, Yunhe Zhang, Shaowei Guan
Polym. Chem., 2017, 8, 1298-1305; DOI: 10.1039/C6PY01814A

In contrast to the two previous articles, this paper reports the preparation of microporous polyimide networks, through polycondensation reaction and subsequent crosslinking. The formation of micropores was promoted due to the crosslinked structure, which restricted macromolecular conformational changes. The materials exhibited BET surface areas up to 497 m²g^-1, with comparable CO₂ uptake values to other microporous polyimides prepared from rigid tri-dimensional monomers.

Read these articles for free until April 16^th

About the webwriter

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

This month we look at three articles that feature in Polymer Chemistry that report the use of polymers in emulsions.  Both in emulsion polymerisation and high internal phase emulsions.

Emulsion polymerisation can be utilised to prepare polymers as polymeric particles with high solids content, and is commonly used in industry and academia alike. Seeded emulsion polymerisation is a technique where a seed particle is utilised in an emulsion polymerisation, to overcome any variability in the nucleation step.

High internal phase emulsions (HIPE) are those that have a droplet (internal) phase that constitutes 74.05% or more of the total emulsion volume. PolyHIPEs have gained a great deal of interest, where the polymerisation occurs in the continuous phase forming voids around the dispersed droplets, leading to highly porous materials.

1. Impressed pressure-facilitated seeded emulsion polymerization: design of fast swelling strategies for massive fabrication of patchy microparticles
Lei Tian, Xue Li, Panpan Zhao, Zafar Ali, Qiuyu Zhang
Polym. Chem., 2016, 7, 7078-7085; DOI: 10.1039/C6PY01778A

The authors present a pressure-facilitated seeded emulsion polymerisation of poly(glycidyl methacrylate)/poly(styrene), whereby the utilisation of high pressure and temperature allowed for an accelerated seed swelling process, overcoming typical disadvantages of seeded emulsion polymerisation.  The resulting particles could be designed to be patchy and anisotropic in shape, through tuning the polymerisation time and dibutyl phthalate/styrene ratios.

2. Rational design of functionalized polyacrylate-based high internal phase emulsion materials for analytical and biomedical uses
Gloria Brusotti, Enrica Calleri, Chiara Milanese, Laura Catenacci, Giorgio Marrubini, Milena Sorrenti, Alessandro Girella, Gabriella Massolini, Giuseppe Tripodo
Polym. Chem., 2016, 7, 7436-7445; DOI: 10.1039/C6PY01992G

PolyHIPEs (with water contents of 80-90%) were designed through the polymerisation of (meth)acrylate monomers: butyl acrylate, glycidyl methacrylate and trimethylolpropane triacrylate as the oil phase. Various parameters were optimised, such as the monomer, cross-linker and surfactant concentrations, to give structural porous polyHIPEs with interesting morphology, thermal stability and porosity. The materials have potential for the immoblization of biomolecules for various applications.

3. Closed-cell and open-cell porous polymers from ionomer-stabilized high internal phase emulsions
Tao Zhang, Zhiguang Xu, Qipeng Guo
Polym. Chem., 2016, 7, 7469-7476; DOI: 10.1039/C6PY01725H

PolyHIPEs were prepared, utilising an ionomer as a stabiliser and either styrene (Sty) or butyl acrylate (BA) as the continuous phase. Sty based polyHIPEs resulted in closed-cell pores, whereas BA gave open-cell structures. When increasing the internal phase, the average pore diameters in the Sty polyHIPES decreased, whilst the average pore diameters for the BA polyHIPEs increased. Also, the amphiphilicity of the polyHIPEs could be tuned by simply exposing them to different water of different pH values.

Read these articles for free until March 17^th

About the webwriter

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

This month we focus on three articles appearing in Polymer Chemistry which report various types of Supramolecular Polymerisation. Supramolecular polymers are polymers formed through reversible non-covalent bonds, such as hydrogen bonding, π-π interactions, coordination and host-guest interactions. Advantages of supramolecular polymers include self-healing properties, improved processability, degradability and recyclability; these materials have found applications in fields including optoelectronics, tissue engineering, drug delivery, gene transfection, self healing films and networks to name a few. The articles highlighted this month demonstrate supramolecular polymerisation directed by coordination and host-guest interactions.

1. Ligand effects on cooperative supramolecular polymerization of platinum(II) acetylide complexes
Zhao Gao, Junlong Zhu, Yifei Han, Xiaoqin Lv, Xiaolong Zhang, Feng Wang
Polym. Chem., 2016, 7, 5763-5767; DOI: 10.1039/C6PY01440B

The authors present the formation of helical nano-fibers and organogels by supramolecular polymerisation of a rod-like platinum(II) acetylide monomer with less bulky ligand substituents. The self-assembly mechanism was found to be through a cooperative nucleation–elongation mechanism, and the more-bulky monomers showed no aggregation. These results highlight the importance of minor monomer variations on the supramolecular polymerisation mechanism.

2. Supramolecular main-chain polycatenanes formed by orthogonal metal ion coordination and pillar[5]arene-based host–guest interaction
Hao Xing and Bingbing Shi
Polym. Chem., 2016, 7, 6159-6163; DOI: 10.1039/C6PY01617K

The combination of catenanes and supramolecular polymers has been reported here, where the authors show the orthogonal use of coordination between zinc ions and terpyridyl groups and pillar[5]arene host-guest interactions. The materials exhibited glue-sol transitions with a change of temperature or hydroxide ion concentration. The mechanical properties were assessed by rheology, which showed improvement compared with a supramolecular polymer without catenane functionality.

3. Pillar[5]arene-based amphiphilic supramolecular brush copolymers: fabrication, controllable self-assembly and application in self-imaging targeted drug delivery
Guocan Yu, Run Zhao, Dan Wu, Fuwu Zhang, Li Shao, Jiong Zhou, Jie Yang, Guping Tang, Xiaoyuan Chen Feihe Huang
Polym. Chem., 2016, 7, 6178-6188; DOI: 10.1039/C6PY01402J

Supramolecular brush copolymers were prepared utilising host-guest interactions between pillar[5]arene and a viologen salt. The supramolecular brush copolymers self-assembled into single chain nanoparticles which were fluorescent due to the aggregation-induced emission effect. Doxorubicin loading was achieved and biotin labelling resulted in targeted drug delivery and imaging capabilities. The single-chain nanoparticles showed excellent anti-tumour efficacy with limited systemic toxicity in vivo.

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About the webwriter

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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About the webwriter

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

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.

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 webwriter

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