Polymer Chemistry Blog

Sophie Guillaume is a member of the Advisory Board for Polymer Chemistry and a CNRS Research Director at the Institut des Sciences Chimiques de Rennes (ISCR), France.

Her research focuses on the development of green pathways for the synthesis and structure–property relationships of synthetic polymers (especially polyesters, polycarbonates, polyolefins, and polyurethanes). Areas of emphasis include biobased degradable polymers and functionalized and reactive (co)polymers for advanced industrial and biomedical applications.

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

Focus on polyurethanes

All articles are free to read until Sunday 5^th March.

Polyurethanes (PUs) are one of the most important classes of polymeric materials most widely used as coatings, adhesives, sealants, foams, or elastomers. These multiblock copolymers are formed by the stepwise addition of diols (or polyols) with diisocyanates (or polyisocyanates). Efforts to reduce their environmental impact and to improve their sustainability, resulted in the development of biobased monomers, and of greener processes towards non-isocyanate polyurethanes (NIPUs). Original PU materials with properties at least matching or improving those of the current PU market are thus being sought. To this end, functionalization introduced via the amine segment, the polyol moiety, or the repeating units’ pending groups, is a key parameter to tune towards the desirable characteristics and targeted applications. The biomedical field provides further opportunities for biocompatible and biodegradable PU materials which are widely used as nerve tissue scaffolds, vascular prostheses or drug delivery systems. However, their physical properties (mechanical properties, degradation performances and blood compatibility) still require improvements. These present trends are illustrated with the following top-picks.

Room temperature synthesis of non-isocyanate polyurethanes (NIPUs) using highly reactive N-substituted 8-membered cyclic carbonates

Alexander Yuen, Amaury Bossion, Enrique Gómez-Bengoa, Fernando Ruipérez, Mehmet Isik, James L. Hedrick, David Mecerreyes, Yi Yan Yang and Haritz Sardon
Polym. Chem., 2016, 7, 2105-2111

Current efforts in the polyurethane (PU) community aim at developing green strategies exempt of the use of toxic and dangerous isocyanates. Nowadays, the most promising route towards such non-isocyanate polyurethanes (NIPUs) is the aminolysis of dicyclic carbonates. H. Sardon and co-workers at the University of the Basque Country (Spain), have synthesized, at room temperature without the need for any additional catalyst, high molar mass NIPUs (up to 47 kg.mol1) from a (bis) N-substituted eight-membered cyclic carbonate (N-8CC) derived from renewable resources using a variety of diamines. These experimental results highlight the unique reactivity of this N-8CC over the smaller five- and six-membered cyclic carbonates, as further supported by computational insights which revealed a kinetically and theoretically more favourable ring opening of the N-8CC by an amine system.

Synthesis and hydrolytic properties of water-soluble poly(carbonate–hydroxyurethane)s from trimethylolpropane

Hiroyuki Matsukizonoa and Takeshi Endo
Polym. Chem., 2016, 7, 958-969

Poly(hydroxyurethane)s (PHUs) derived from the polyaddition of six-membered ring cyclic carbonates with diamines are promising non-isocyanate polyurethanes (NIPUs) alternatives to polyurethanes (PUs), as evidenced by T. Endo and co-worker at Kinki University (Japan). Such PHUs advantageously contain two primary hydroxyl groups in their side chains of repeating units, which improve the hydrophilicity and which can be chemically modified to design functional PHU materials. Original well-defined water-soluble poly(carbonate–hydroxyurethane)s comprising hydroxyurethane–carbonate–hydroxyurethane alternate structures were synthesized from trimethylolpropane and conventional diamines. Investigations of their hydrolytic properties in aqueous media at different pH values revealed their complete decomposition to their basic structures in carbonate buffers at pH 10.6 within one week.

Bio-based difuranic polyol monomers and their derived linear and cross-linked polyurethanes

Zehuai Mou, Shuo (Kelvin) Feng and Eugene Y. X. Chen
Polym. Chem., 2016, 7, 1593–1602

A series of linear and cross-linked polyurethanes (PUs) is reported by E. Chen and co-workers at Colorado State University (USA), from the catalysed polyadditions of diol, triol or tetraol derived from the biomass platform chemical 5-hydroxymethylfurfural (HMF) – one of the most value-added biomass building blocks or platform chemicals – with various diisocyanates in the presence of a catalyst (organocatalyst or dibutyltin dilaurate), respectively. The PU materials derived from the new diol monomer, namely 5,5’-bihydroxymethyl furil, and aromatic diisocyanates such as diphenylmethane diisocyanate, revealed valuable characteristics (Mn,SEC = ca. 40 kg mol−1, onset decomposition temperature = 234 °C, and Tg = 140 °C). Solvent casting from these PUs affords thin films ranging from brittle to flexible with a high strain at break of 300%.

An epoxy thiolactone on stage: four component reactions, synthesis of poly(thioether urethane)s and the respective hydrogels

Stefan Mommer, Khai-Nghi Truong, Helmut Keul and Martin Möller
Polym. Chem., 2016, 7, 2291–2298

The synthesis of a new epoxy thiolactone is described by H. Keul and M. Möller and co-workers at RWTH Aachen University (Germany), along with its ability to act in several concepts as a versatile tool towards polymeric materials. The reactivity of this epoxy thiolactone with an amine and catalytic amounts of a base, results in the selective ring opening of the thiolactone to generate an AB-type epoxy thiol monomer, which in situ starts a thiol-epoxy polymerization to ultimately form poly(thioether urethane)s (PTEUs). Besides the introduction of a new functionality – the organic residue – by the amine used for ring opening of the thiolactone, the PTEU backbone further exhibits a hydroxyl functionality. The latter increases the hydrophilicity of the polymer backbone and also provides a site for an additional functionalization. Two strategies were elaborated for the generation of functional gels from this epoxy thiolactone bis cyclic monomer, using a diamine or a triacrylate. These one pot processes are feasible and provide an interesting platform for a variety of polymer architectures hosting functionalities.

A novel biodegradable polyurethane based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(ethylene glycol) as promising biomaterials with the improvement of mechanical properties and hemocompatibility

Cai Wang, Yudong Zheng, Yi Sun, Jinsheng Fan, Qiujing Qina and Zhenjiang Zhao
Polym. Chem., 2016, 7, 6120-6132

A novel block polyurethane (PU) based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), 4,4’-diphenylmethanediisocyanate and poly(ethylene glycol) (PEG) was synthesized by Zheng and co-workers at the University of Science and Technology Beijing (China), from the polyaddition of PHBV diol with ,-diisocyanate telechelic PEG. The resulting PU films exhibited biodegradability at 37 °C in phosphate buffer solution (PBS) at pH 7.4, non-cytotoxicity towards the growth and proliferation of the bone marrow mesenchymal stem cells, and hemocompatibility. The degradation rate results indicate that PHBV-based PUs are more suitable for biomedical applications requiring a longer degradation period. Greater PHBV contents also favourably influenced the mechanical properties and the thermal stability of these PU films. These new PHBV based PU materials with better mechanical properties, biodegradability, hemocompatibility and biocompatibility, may find potential applications in blood vessel tissue engineering.

Thermo- and pH-sensitive shape memory polyurethane containing carboxyl groups

Qiuju Song, Hongmei Chen, Shaobing Zhou, Keqing Zhao, Biqing Wang and Ping Hu
Polym. Chem., 2016, 7, 1739-1746

A multi-functional polyurethane (PU) with both a thermo-induced triple shape memory effect and a pH-sensitive dual shape memory effect has been developed by Chen and Hu and co-workers at Sichuan Normal University (China). The two-step polyaddition of polyethylene glycol (PEG), and 4,4’-diphenylmethane diisocyanate, followed by polymerization of the resulting diisocyanate end-functionalized PEG with dimethylolpropionic acid afforded the desired PUs bearing pendant carboxyl groups. In PU with 30wt% of PEG, the glass transition of PEG chains and the association/disassociation of carboxylic dimers act as two switches to control the triple-shape memory effect, while the carboxylic dimer is affected by pH values to associate in acidic solutions (pH 2) and dissociate in alkaline solutions (pH 9) to induce the pH-sensitive shape memory. The carboxylic dimers play an important role in the construction of shape memory properties in these PUs. Indeed, PUs with too high or too low carboxylic content (e.g. with 20 or 40wt% of PEG) did not exhibit any shape memory properties.

Ben Zhong Tang is a member of Advisory Board for Polymer Chemistry and K. C. Cheong Professor of Science and Chair Professor of Chemistry and Biomedical Engineering at The Hong Kong University of Science and Technology (HKUST). His research interests include macromolecular chemistry, materials science, and biomedical theranostics.

Tang’s research group has been working on the development of new polymerization routes from alkyne reactions, and has succeeded in the syntheses of a number of new functional conjugated polymers from acetylenic monomers.
Professor Tang has published over 900 papers which have been cited more than 40,000 times, leading to an h-index of 101. He has been listed by Thomson Reuters as a Highly Cited Researcher in both areas of Chemistry and Materials Science. He received a Natural Science Award from the Chinese Government and a Senior Research Fellowship from the Croucher Foundation in 2007.

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

Focus on Luminogenic Polymers

All articles are free to read until Sunday 22^nd January.

 

CO₂/pH-responsive particles with built-in fluorescence read-out

Anne B. Mabire, Quentin Brouard, Anaïs Pitto-Barry, Rebecca J. Williams, Helen Willcock, Nigel Kirby, Emma Chapman and Rachel K. O’Reilly
Polym. Chem., 2016, 7, 5943–5948.

K. O’Reilly and collaborators at the University of Warwick (UK), Australian Synchrotron (Australia) and BP Exploration Operating Company, Ltd. (UK) synthesized fluorescent CO₂-responsive cross-linked polymeric particles via emulsion polymerization. In this system, a fluorescent monomer (aminobromomaleimide with high quantum yield was used as a probe for the core hydrophobicity; Poly(N,N-diethylaminoethylmethacrylate) and oligo(ethyleneglycol methacrylate) were utilized as the CO₂-responsive core-forming segment and the hydrophilic shell-forming block, respectively. The polymer particles became swollen and the corresponding fluorescence intensity drastically decreased through simple CO₂ bubbling. This contributed to the increased hydrophilicity of the particles. In addition, the swelling and emission processes were reversible by purging the mixture with nitrogen. The researchers also found that the ON/OFF cycles of fluorescence could be reproducible with CO₂/N₂ purges, indicating that the polymer can be used as a fluorescent sensor for CO₂ detection.

 


Conventional fluorophore-free dual pH- and thermo-responsive luminescent alternating copolymer

Biswajit Saha, Kamal Bauri, Arijit Bag, Pradip K. Ghorai and Priyadarsi De
Polym. Chem., 2016, 7, 6895–6900.

In this work, P. De and coworkers at Indian Institute of Science Education and Research Kolkata synthesized a group of dual pH- and thermo-responsive fluorescent copolymers with a poly(maleimide-alt-styrene) skeleton that is free of traditional fluorophores. The emission intensity of the copolymers increases with increasing pH and decreases with increasing temperature from 20 to 70 °C at pH 4.5. Density functional theory calculations show that the π molecular orbital is located over the benzene ring as the HOMO and the π* on the maleimide unit as the LUMO, suggesting that the through-space π–π interaction between the benzene ring and the neighboring carbonyl group of the maleimide unit is the origin of the unexpected fluorescence in the copolymers.

 


Unanticipated bright blue fluorescence produced from novel hyperbranched polysiloxanes carrying unconjugated carbon–carbon double bonds and hydroxyl groups
Song Niu, Hongxia Yan, Zhengyan Chen, Song Li, Peilun Xu and Xiaoli Zhi
Polym. Chem. 2016, 7, 3747–3755.

Fluorescent polymers containing no aromatic rings have attracted much interest due to their environmental benignancy, cytocompatibility and biodegradability. S. Niu, H. Yan and coworkers at Northwestern Polytechnical University (China) designed and prepared new hyperbranched polysiloxanes by a one-pot transesterification reaction of excessive neopentyl glycol with triethoxyvinylsilane. The resultant non-conjugated polysiloxanes show bright blue photoluminescence. Their emission intensities are increased when the polymers are more aggregated by increasing their molecular weights and concentrations, showing the photophysical effect similar to aggregation-induced emission. The interaction between the unconjugated C=C and –OH units in the tight aggregate was proposed to be critical for such strong unconventional luminescence.

 


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 and Feihe Huang
Polym. Chem., 2016, 7, 6178-6188.

Supramolecular brush copolymers (SBPs) fabricated from simple building blocks via non-covalent interaction have tremendous advantages, such as stimuli-responsiveness. X. Chen, F. Huang and coworkers at Zhejiang University (China) and National Institutes of Health (USA) constructed SBP-based supramolecular nanoparticles (SNPs), which were utilized as a self-imaging drug delivery vehicle by taking advantage of the photophysical effect of aggregation-induced emission. The fluorescence arising from tetraphenylethene and doxorubicin (DOX) was quenched due to the involved energy transfer relay effect. The silenced fluorescence was recovered at low pH and by reductase through the release of the loaded DOX, achieving in situ visualization of the drug release process. In vitro and in vivo experiments confirmed that the DOX-loaded SNPs showed excellent antitumor efficacy with negligible systemic toxicity. The present study provides a novel supramolecular method for the construction of self-imaging drug delivery systems, with promising applications in the field of cancer treatment.

 


Room temperature phosphorescence of 4-bromo-1,8-naphthalic anhydride derivative-based polyacrylamide copolymer with photo-stimulated responsiveness

Hui Chen, Lei Xu, Xiang Ma and He Tian
Polym. Chem., 2016, 7, 3989–3992

In this work, X. Ma, H. Tian and coworkers at the East China University of Science and Technology developed a new system of room temperature phosphorescence (RTP). The system was constructed from γ-cyclodextrin (γ-CD) and a polymer containing 4-bromo-1,8-naphthalic anhydride moiety (poly-BrNpA). While the aqueous solution of poly-BrNpA alone does not give any RTP signal, the poly-BrNpA/γ-CD binary system shows RTP emission centered at 580 nm with a lifetime of 0.32 ms. NMR spectroscopy was used to study the complexation behavior and to prove that the RTP of poly-BrNpA/γ-CD is from the host-guest interaction between poly-BrNpA and γ-CD. From poly-BrNpA/γ-CD, a pure organic RTP hydrogel was successfully prepared. Through incorporating azobenzene (Azo) unit, the RTP of the ternary mixture of poly-BrNpA/γ-CD/poly-Azo becomes reversibly tunable by the photo-isomerization of the Azo unit. This photo-regulation is achieved by the inclusion competition between the cis/trans isomers of the Azo unit and poly-BrNpA.

 


Synthesis and chiroptical properties of a π-conjugated polymer containing glucose-linked biphenyl units in the main chain capable of folding into a helical conformation

Tomoyuki Ikai, Syo Shimizu, Seiya Awata, Tomoya Kudo, Takayuki Yamada, Katsuhiro Maeda and Shigeyoshi Kanoh
Polym. Chem., 2016, DOI: 10.1039/c6py01759b

An optically active π-conjugated polymer containing chiral glucose-linked biphenyl units can interconvert between random-coil and helical-chain conformations in response to external environment, as demonstrated by T. Ikai et al. at Kanazawa University (Japan). The optically active polymer likely folds into a helical structure with a preferred handedness in the suspension containing high amounts of a poor solvent (acetonitrile), whereas the polymer conformation becomes a random coil in pure good solvent (chloroform). In addition, the chiral helical polymer shows efficient left-handed circularly polarized luminescence (CPL) with a green color. The solvent-dependent CPL signal change was also observed. The dissymmetry factor of the chiral helical polymer can reach 1.9×10^-2 in the film state. The researchers thus offer a new approach to functional materials through utilization of the chirality of abundant biomass resources.

Franck D’Agosto is a member of Advisory Board for Polymer Chemistry and CNRS research director at the University of Lyon in the group of Chemistry, Catalysis, Polymers and Processes (C2P2). D’Agosto’s research focuses on implementing original and simple chemistries to control the architecture of polymers both in the field of polyolefins and in aqueous dispersed media.

Work published almost 40 years ago exploited the livingness of poly(t-butyl styryl)-lithium chains to initiate the dispersion polymerization of styrene (St) or divinylbenzene in n-hexane, and indeed pioneered the concept of what is today called polymerization-induced self-assembly (PISA). Starting from hydrophilic polymers prepared by reversible-deactivation radical polymerization, emulsion or dispersion polymerization can now be conducted in water to generate block copolymer particles by PISA. Although PISA has not replaced conventional surfactant-containing emulsion polymerization in producing industrial-scale polymer latexes, it has rapidly evolved into a versatile tool capable of producing amphiphilic block copolymers directly in water at high solids contents and various micellar architectures in the absence of added cosolvents. PISA is now a mature topic for which scientists are investigating new uses.

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

Focus on polymerisation-induced self-assembly (PISA)

1. Synthesis of zwitterionic, hydrophobic, and amphiphilic polymers via RAFT polymerization induced self-assembly (PISA) in acetic acid
D. Das, D. Gerboth, A. Postma, S. Srinivasan, H. Kern, J. Chen, D.M. Ratner, P.S. Stayton, A.J. Convertine, Polym. Chem., 2016, DOI:10.1039/C6PY01172A.

By Dr. Ming Liang Koh. Ming obtained his PhD at the University of Sydney. Following a postdoctoral position at the University of Warwick, he is currently researching hybrid inorganic-organic latexes in the group of C2P2 at the University of Lyon.

While PISA has quickly matured as a topic, fundamental research still plays an important role to further widen opportunities. In this study, Das et al. considered the difficulty in marrying the poor solubility of hydrophobic monomers in aqueous media with the poor solubility of zwitterionic polymers in organic solutions.

This is often the dilemma encountered when one wants to incorporate prodrug monomers with hydrolytically unstable linkages into a polyionic scaffold. RAFT polymerizations of a hydrophilic sulfobetaine monomer (2-(N-3-sulfopropyl-N,N-dimethyl ammonium)ethyl methacrylate, DMAPS) and hydrophobic lauryl methacrylate (LMA) was then considered in acetic acid using solvophilic macroRAFT composed of hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) methyl ether methacrylate (O300). Well-defined amphiphilic block copolymers were produced using PISA.

This was successfully applied to copolymerizations of DMAPS with LMA and/or other biorelevant hydrophobic methacrylates incorporating hydrolytically sensitive links that were successfully preserved in a poly(DMAPS) scaffold. The preparation of macrophage targeting mannose-functionalized solvophilic macroRAFT also allowed the design of original polymeric prodrug nanoparticles.


2. Synthesis, characterisation and Pickering emulsifier performance of poly(stearyl methacrylate)–poly(N-2-(methacryloyloxy)ethyl pyrrolidone) diblock copolymer nano-objects via RAFT dispersion polymerisation in n-dodecane
V. J. Cunningham, S. P. Armes and O. M. Musa, Polym. Chem., 2016, 7, 1882–1891

By Dr. Samuel Pearson. After obtaining his PhD in Australia, Sam completed a postdoctoral position in C2P2 group at the University of Lyon and is currently a Marie Curie individual fellow at the University of Pau. His research interests include light-responsive polymers, self-assembly systems, and polymer/inorganic nanohybrids.

The Armes group has been pivotal in developing novel PISA systems, and this latest paper in Polymer Chemistry exploits PISA-derived nanospheres as Pickering emulsifiers with a surprising twist. A stearyl methacrylate-based macroRAFT agent was chain extended in n-dodecane with N-2-(methacryloyloxy)ethyl pyrrolidone – a more polar core-forming monomer than previously employed by the authors – to give very fast polymerisation and a typical range of self-assembly morphologies captured in a detailed phase diagram.

Using low shear mixing, the spherical nano-objects proved effective as Pickering stabilisers for water-in-oil emulsions, as expected for such hydrophobic particles. At high shear, however, entirely unexpected behavior was observed: the particles inverted to give hydrophilic nanospheres stabilising oil-in-water emulsions, presenting a new puzzle and new opportunities in PISA research.

3. Room temperature synthesis of poly(poly(ethylene glycol) methyl ether methacrylate)-based diblock copolymer nano-objects via Photoinitiated Polymerization-Induced Self-Assembly (Photo-PISA)
J. Tan, Y. Bai, X. Zhang and L. Zhang, Polym. Chem., 2016, 7, 2372–2380.

By Dr. Winnie Nzahou Ottou. Winnie is a post-doctoral research fellow at the University of Lyon in the group of C2P2. Her research focuses on catalytic olefin polymerization and the design of new functionalized polyolefins through both in situ reactions and post-polymerization modifications.

In this study, Tan, Zhang et al. report the photoinitiated polymerization-induced self-assembly (photo-PISA) of 2-hydroxypropyl methacrylate (HPMA) using poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA) as macro-RAFT agents at 25 °C in water.

By a simple “ON/OFF” switch of the light source and by tuning the reaction parameters (e.g. solids content, degree of polymerization and molecular weight of the macro-RAFT agent), a series of PPEGMA-b-PHPMA diblock copolymer nano-objects with controllable morphologies (worms, spheres, and vesicles) were thus obtained. Interestingly, PPEGMA₁₄-PHPMA₂₀₀ nanoparticles (15% w/w) were found to exist as a soft physical worm gel at 25 °C and changed to spheres at 4 °C.

However, this transformation was irreversible presumably due to the effective steric stabilization effect of PPEGMA on the PHPMA-based nanoparticles. Zhang and coworkers then expand the scope of photo-PISA for the synthesis of various block copolymers nano-objects, and also provide an efficient method for making a new class of light and thermo-responsible biomaterials.

4. Surface-initiated polymerization-induced self-assembly of bimodal polymer-grafted silica nanoparticles towards hybrid assemblies in one step
Y. Zheng, Y. Huang, Z. M. Abbas and B. C. Benicewicz, Polym. Chem., 2016, 7, 5347–5350.

By Dr. Arne Wolpers. Arne obtained his PhD in Germany and is currently a postdoctoral researcher at the University of Lyon in the group of C2P2. His research focuses on the polymerization of ethylene using reversible-deactivation radical-polymerization (RDRP) techniques under mild conditions and the further processing of polyethylene.

With their great expertise on polymer nanocomposites, researchers of the Benicewicz group demonstrated the first case of surface-initiated polymerization-induced self-assembly (SI-PISA) of nanoparticles, offering a facile and efficient one-step procedure to prepare hybrid assemblies.

In this context, rather than performing conventional chain-extension, by utilizing a surface-immobilized RAFT agent, silica nanoparticles grafted from with solvophilic poly(2-hydroxyethyl methacrylate) (PHEMA) were successively grafted from for a second time in methanol with solvophobic poly(benzyl methacrylate) (PBzMA). The growth of PBzMA was well-controlled and with increasing molar mass, the nanoparticles assembled into a variety of one-dimensional structures.

The obtained assemblies were very stable and exhibited high nanoparticle concentrations. The manifold possibilities to tune the presented system and thus the formed hybrid structures indicate the potential of SI-PISA as a powerful new tool in the field of polymer nanocomposites.