Polymer Chemistry Blog

Block copolymer (BCP) assemblies are derived from covalently linked polymer chains and can undergo phase separation and thus find use in a wide range of applications including micropatterning, battery and electronic technologies. Metal-organic frameworks (MOFs) are another class of self-assembled matter consisting of crystalline networks with angstrom-scale order and permanent porosity. Owing to these advantageous properties, they can enable functions such as gas, energy storage, catalysis and selective-separation.

In the Johnson group, impressive efforts have been made to merge amorphous polymer networks with multi-component supramolecular assembly to generate soft materials with novel properties. In their current contribution, the group expands these types of hybrid materials by reporting a novel BCP where one block is a uniform benzene dicarboxylate (BDC)-based oligomer synthesized by iterative exponential growth (IEG), and the other is polystyrene (PS) prepared by atom transfer radical polymerization (ATRP). In order to achieve this, the authors initially synthesized the BDC-based oligomer with a defined end-functionality bearing an alkyne group that would allow for further diversification. This alkyne group was subsequently used to couple to azide-terminated polystyrene. In the presence of Zn ions, this BCP forms a “block co-polyMOF” (BCPMOF) material comprised of polyMOF domains embedded in a PS matrix.

The presented work is the first demonstration that it is possible to generate a crystalline polyMOF-amorphous polymer hybrid material from a single diblock copolymer. As such, BCPMOFs represent a new composite material that possesses the processability of the polymers while exhibiting enhanced stability towards ambient conditions when compared to the isolated MOFs. The ultimate goal of the group is to obtain BCPMOFs with robust mechanical properties, high surface areas, and tunable, well-defined domain sizes.

Tips/comments directly from the authors:

1. In the synthesis of the mono benzylated diethyl 2,5-dihydroxyterephthalate, A, UV absorbance can readily distinguish the starting material from the product. The starting material elutes before the product and can be isolated for reuse.
2. As noted in the supporting information, side products can occur during the coupling reaction to form L₁. It is critical that ethanol is used to maintain the ethyl ester.
3. The coupling reactions tend to require longer reaction times as the molecular weight of the reactants grows. Upon scaling up of the reactions, do not be temped to increase the concentration too much as it can lead to side product formation.
4. The same synthetic protocols were used to form polyMOFs and block co-polyMOFs: 2.5 eq Zn(II) per BDC unit in L_n, was combined with L_n(PS) in DMF, heated at 100°C for 24h, followed by DMF washings to remove excess Zn(II) and unreacted ligand. Unlike the purification and isolation of L₂ and L₄, special care was taken for L₄PS-Zn to use minimal organic solvent due to the solubility imparted by polystyrene.

Block co-polyMOFs: assembly of polymer-polyMOF hybrids via iterative exponential growth and “click” chemistry
Polym. Chem., 2017, 8, 4488-4493, DOI: 10.1039/c7py00922d

About the web writer

Dr. Athina Anastasaki is a web writer for Polymer Chemistry. She is currently a Global Marie Curie Fellow working alongside Professor Craig Hawker at the University of California, Santa Barbara (UCSB). Please visit this website for more information.

Phosphonic acid functionalized polymers find use in a wide range of applications such as metal protection, polymer electrolyte membranes flame retardancy and dentistry. This is thanks to their unique characteristics including their acidic nature, stability, proton conductivity and metal binding ability. Vinyl phosphonic acid (VPA) in particular is a structurally simple example of such monomers which is not only affordable but also provides with a polymer (PVPA) with phosphonic acid groups that are directly attached to the backbone.

Despite the popularity and applicability of this polymer, the polymerization of VPA is typically slow yielding incomplete conversions which necessitates the need for additional costly and time-consuming purification steps. Destarac, Harrisson and co-workers were capable to circumvent this by investigating the effect of adding various alkali hydroxides to the conventional (free radical) and reversible addition-fragmentation transfer polymerization/macromolecular design by interchange of xanthates (RAFT/MADIX) radical polymerizations. Both types of polymerizations were strongly affected by the addition of NaOH. The authors found that by adding 1 equivalent of NaOH they could significantly increase the rate of the polymerization and the final conversion for both conventional and RAFT/MADIX polymerizations while larger quantities led to retardation of the reaction. A wide range of alkali hydroxides were also studied including H⁺, Li⁺, K⁺ and NH₄⁺. It was shown that the dispersity of the final polymer decreases as the ionic radius of the counterion increases (H⁺ > Li⁺> Na⁺ > K⁺ > NH4⁺) while the acceleration of the polymerization follows the order Na⁺ > K⁺ > NH₄⁺> Li⁺ > H⁺). Overall, the fastest rates of polymerizations were obtained in the presence of 0.5 equivalent of NaOH, while the same concentration of KOH or NH₄OH allowed for a moderate acceleration on the polymerization rate combined with an improved control over the molar masses. Thus, this simple and cost-effective strategy can significantly improve the efficiency of the polymerization of VPA by simultaneously enhancing the reaction rate and the control over the molar masses.

Tips/comments directly from the authors:

1. Take care to control the temperature when neutralizing the VPA – the reaction is very exothermic!
2. Use NaOH for the most significant acceleration of polymerization and NH₄OH for the strongest reduction in dispersity of the polymer.
3. PVPA homopolymer can be precipitated in MeOH, but many PVPA-containing DHBCs must be purified by dialysis due to the small difference in solubility between PVPA and VPA and the low volatility of VPA.

Read this exciting research for free until 10/09/2017 through a registered RSC account.

Acceleration and improved control of aqueous RAFT/MADIX polymerization of vinylphosphonic acid in the presence of alkali hydroxides
Polym. Chem., 2017, 8, 3825-3832, DOI: 10.1039/c7py00747g

—————-

About the webwriter

Dr. Athina Anastasaki is a web writer for Polymer Chemistry. She is currently a Global Marie Curie Fellow working alongside Professor Craig Hawker at the University of California, Santa Barbara (UCSB). Please visit this website for more

Polyesters obtained from bio-derived monomers are often used as building blocks with the ultimate aim of meeting consumer demands for high-performance and sustainable materials. To this end, Reineke, Tolman, and Lillie sought to establish how changing the ratio of the sustainable D-glucaro-1,4:6,3-dilactone containing α, ω-diene (GDLU) and isosorbide undecanoate (IU) may influence the thermal, chemical and mechanical properties of the acyclic diene metathesis (ADMET)-derived polymers. The authors synthesized a series of random copolymers consisting of a range of GDLU and IU compositions and fully characterized them by uniaxial tensile testing, small-amplitude oscillatory shear rheology, X-ray scattering, and hydrolytic degradation testing.

It was found that small compositional changes have a detrimental impact on their mechanical performance and degradability. In addition, the authors investigated which carbohydrate-based building block was most important in promoting the elasticity and shape-memory abilities of this class of materials. To address this issue, GDL or isosorbide were replaced with a different sustainable diol, 2,5-bis(hydroxymethyl) furan. Studies of the resulting copolymers indicated that GDLU is responsible for imparting both elasticity and shape memory properties. Further, more economical and environmentally-friendly routes for the synthesis of GDLU and IU feedstocks were also explored.

Tips/comments directly from the authors:

1. Acetonitrile appears to be the essential solvent for the scandium triflate-catalyzed esterification of GDL with 10-undecenoic acid anhydride.
2. 10-Undecenoic acid anhydride can rapidly degrade on wet silica gel. To prevent this, oven dry (120 °C) the silica gel prior to its use and minimize the excess 10-undecenoic acid anhydride used in the reaction.
3. Due to the hydrolytic instability of GDL and GDL-containing polymers, they should be stored in a vacuum desiccator to protected from moisture to prevent degradation between uses.

Read this exciting research for free until 13/08/2017 through a registered RSC account.

Structure/property relationships in copolymers comprising renewable isosorbide, glucarodilactone, and 2,5-bis(hydroxymethyl)furan subunits
Polym. Chem., 2017, 8, 3746-3754, DOI: 10.1039/c7py00575j

—————-

About the webwriter

Dr. Athina Anastasaki is a web writer for Polymer Chemistry. She is currently a Global Marie Curie Fellow working alongside Professor Craig Hawker at the University of California, Santa Barbara (UCSB). Please visit this website for more

Block copolymers are of a great interest to the polymer chemistry community as they provide intermediate physicochemical properties when compared to the respective homopolymers. Sequential monomer addition, mechanistic transformation and coupling of different segments are three of the most popular approaches to obtain block copolymers. However, all these approaches suffer from several drawbacks such as being limited to monomers that can be polymerized only under the same polymerization mechanism or requiring extreme experimental precautions and elongated purification steps.

In order to address the latter challenge, Yagci, Yilmaz and co-workers developed the first metal free example of block copolymer formation in which they concurrently polymerize structurally different monomers from a junction point serving as two functional groups for each polymerization. Since atom transfer radical polymerization (ATRP) and ring opening polymerization (ROP) are not expected to interfere with each other and as such could be the ideal candidates for such a system. In order to test this hypothesis, a specifically designed initiator was synthesized possessing a tertiary bromine at one end (capable of initiating an ATRP reaction) and a hydroxyl functionality at the other end (capable for initiating a ROP reaction). Under carefully optimized conditions and in the presence of both the ATRP and ROP catalysts both methyl methacrylate (MMA) and ε- caprolactone could be simultaneously polymerized yielding a diblock copolymer with good agreement between theoretical and experimental value sand low dispersity values. Interestingly, the reaction took place on the roof of the chemistry department at Istanbul technical university utilizing natural sunlight as the light source. The applicability of this technique was further demonstrated by the simultaneous polymerization of different sets of monomers including n butyl acrylate- ε- caprolactone and methyl methacrylate-lactide combinations. As such, the successful combination of ATRP with ROP in the same reaction media allows for the facile one pot synthesis of block copolymers which can find use in further applications where excess of metals or inorganic residues would be undesirable.

Tips/comments directly from the authors:

1. All chemicals should be added into the reaction tube under nitrogen atmosphere in dark (perhaps by covering the outside of the tube with an aluminium foil) to avoid any premature light induced polymerization.
2. ROP polymerization can take place even in dark. Therefore, the ROP catalyst should be added last, and afterwards, the reaction tube should be exposed to sunlight as soon as possible. This way, one can provide the optimum conditions for the polymerizations to be realized simultaneously.
3. The method is best applicable in sunny days. Sunlight was deliberately selected as the most natural and simple way of light exposure. However, various other irradiation sources that emit in the wavelength regions matching with the absorption of appropriate sensitizers can also be used.

Read this exciting research for free until 17/07/2017 through a registered RSC account.

Block copolymer synthesis in one shot: concurrent metal-free ATRP and ROP processes under sunlight
Polym. Chem., 2017, 8, 2899-2903, DOI: 10.1039/c7py00069c

—————-

About the webwriter

Dr. Athina Anastasaki is a web writer for Polymer Chemistry. She is currently a Global Marie Curie Fellow working alongside Professor Craig Hawker at the University of California, Santa Barbara (UCSB). Please visit this website for more