Formation of Nanostructured Poly(dicyclopentadiene) Thermosets Using Reactive Block Polymers

Reaction-induced phase transitions with block copolymers in solution and bulk

Reaction-induced phase transitions use chemical reactions to drive macromolecular organisation and self-assembly. This review highlights significant and recent advancements in this burgeoning field.

Molecular Engineering of Nanostructures in Disordered Block Polymers

A series of symmetric poly(methyl methacrylate-stat-styrene)-block-polylactide (P(MMA-s-S)-b-PLA) diblock terpolymers with nearly constant molar masses yet varying block interaction parameters were synthesized as a model system to probe the extent and utility of composition fluctuations in the disordered state. A combination of differential scanning calorimetry, dynamic mechanical analysis, and small-angle X-ray scattering revealed that a broad range of segregation strengths ranging from what we ascribe to essentially a mean-field disordered to a fluctuating disordered to an ordered system could be readily obtained by tuning the molar fraction of styrene in these diblocks. The P(MMA-s-S)-b-PLA diblocks were annealed above their order-disorder transition temperatures (T_ODT) and rapidly quenched to low temperatures to trap the disordered state via vitrification, as confirmed by scanning electron microscopy. Small-angle X-ray scattering and N₂ sorption analysis post-removal of PLA demonstrated that a transition from a very weakly structured, mean-field-like melt to a bicontinuous fluctuating disordered state occurred with increasing segregation strength. This work demonstrates that the extent of microphase segregation as well as the domain continuity of the disordered block polymer melt can be tuned using both synthetic design and thermal stimuli, guiding the design of disordered block polymers with targeted nanostructures that have potential technological utility.

Thiol-ene polymerization for hierarchically porous hybrid materials by adding degradable polycaprolactone for adsorption of bisphenol A

Hierarchically porous materials with multiple pore structures have the potential application in catalysis, separation or bioengineering. A concept was introduced to design and fabricate hierarchically porous hybrid materials (HPHMs) simultaneously containing mesopores and macropores. The proof-of-concept design was demonstrated by fabrication of several kinds of hybrid materials by adding degradable polycaprolactone (PCL) additive, which was simple and easy-operating. The specific surface areas of HPHMs prepared with polyhedral oligomeric vinylsilsesquioxanes (vinylPOSS) and 1,4-dithiothreitol (DTT) could reach 727 m²/g by adding 25% PCL additive, while the HPHMs were imperforate prior to degradation of PCL. The characterization further indicated that the macropores could be controlled by the amount of PCL additive. Moreover, the porous properties of HPHMs were influenced by the molecular weight of PCL. Other dithiols compounds were also successful in preparing HPHMs with high specific surface areas over 400 m²/g. Due to hydrophobic interaction and hydrogen bond interaction, the HPHM exhibited good adsorption ability for bisphenol A (BPA) in aqueous solution. Adsorption equilibrium could be achieved within 30 min, and the adsorption capacity was up to 157.4 mg/g. Meanwhile, the removal efficiency was found to be 95.37% for BPA.

Photonic Resins: Designing Optical Appearance via Block Copolymer Self-Assembly

Despite a huge variety of methodologies having been proposed to produce photonic structures by self-assembly, the lack of an effective fabrication approach has hindered their practical uses. These approaches are typically limited by the poor control in both optical and mechanical properties. Here we report photonic thermosetting polymeric resins obtained through brush block copolymer (BBCP) self-assembly. We demonstrate that the control of the interplay between order and disorder in the obtained photonic structure offers a powerful tool box for designing the optical appearance of the polymer resins in terms of reflected wavelength and scattering properties. The obtained materials exhibit excellent mechanical properties with hardness up to 172 MPa and Young's modulus over 2.9 GPa, indicating great potential for practical uses as photonic coatings on a variety of surfaces.

Highly conductive anion exchange membrane for high power density fuel-cell performance

Anion exchange membrane fuel cells (AEMFCs) are regarded as a new generation of fuel cell technology that has the potential to overcome many obstacles of the mainstream proton exchange membrane fuel cells (PEMFCs) in cost, catalyst stability, efficiency, and system size. However, the low ionic conductivity and poor thermal stability of current anion exchange membranes (AEMs) have been the key factors limiting the performance of AEMFCs. In this study, an AEM made of styrenic diblock copolymer with a quaternary ammonium-functionalized hydrophilic block and a cross-linkable hydrophobic block and possessing bicontinuous phases of a hydrophobic network and hydrophilic conduction paths was found to have high ionic conductivity at 98 mS cm(-1) and controlled membrane swelling with water uptake at 117 wt % at 22 °C. Membrane characterizations and fuel cell tests of the new AEM were carried out together with a commercial AEM, Tokuyama A201, for comparison. The high ionic conductivity and water permeability of the new membrane reported in this study is attributed to the reduced torturosity of the ionic conduction paths, while the hydrophobic network maintains the membrane mechanical integrity, preventing excessive water uptake.

One-Step Synthesis of Cross-Linked Block Polymer Precursor to a Nanoporous Thermoset

Using a simultaneous block polymerization/in situ cross-linking from a heterofunctional initiator approach, we produced a nanostructured and cross-linked block polymer in a single step from a ternary mixture of monomers and used it as a precursor for a cross-linked nanoporous material. Using 2-(benzylsulfanylthiocarbonylsulfanyl)ethanol as a heterofunctional initiator, simultaneous ring-opening transesterification polymerization of d,l-lactide in the presence of tin 2-ethylhexanoate as a catalyst and reversible addition-fragmentation chain transfer polymerization of styrene at 120 °C produced a polylactide-b-polystyrene (PLA-b-PS) block polymer. Incorporation of divinylbenzene in the polymerization mixture allowed in situ cross-linking during the simultaneous block polymerization to result in the cross-linked block polymer precursor in one step. This material was converted into cross-linked nanoporous polymer by etching PLA in a basic solution.

Separation of cis-fatty acids from saturated and trans-fatty acids by nanoporous polydicyclopentadiene membranes

This article describes the separation of mixtures of fatty acid salts using a new organic solvent nanofiltration membrane based on polydicyclopentadiene (PDCPD). Mixtures of free fatty acids could not be separated by the membranes because they permeated at similar rates. When triisobutylamine was added to the fatty acids, the cis-fatty acid salts (oleic, petroselinic, vaccenic, linoleic, and linolenic acid) had slower permeation though the membranes than saturated (stearic acid) and trans-fatty acid (elaidic acid) salts. The reason for the difference in permeation was due to the formation of stable salt pairs between the amine and fatty acids that increased their cross-sectional areas. The fatty acid salts derived from saturated and trans-fatty acids were smaller than the critical area cutoff for the PDCPD membranes, so they readily permeated. In contrast, the fatty acid salts derived from the cis-fatty acids had critical areas larger than critical area cutoff of the PDPCD membranes and had slowed permeation. The partitioning coefficients of fatty acids and fatty acid salts were investigated to demonstrate that they were not responsible for the difference in permeation. The use of pressure was investigated to greatly accelerate the permeation through the membranes. For a solvent mixture of 35/65 (v/v) toluene/hexanes, the permeation of solvent was approximately 39 L m(-2) h(-1). This value is similar to values reported for permeation through membranes used in industry. The separation of a mixture of fatty acids based on the composition of soybean oil was investigated using pressure. The saturated fatty acid salts were almost completely removed from the cis-fatty acid salts when iBu(3)N was used as the amine to form the salt pairs. The separation of the cis-fatty acids found in soybean oil was investigated with Pr(3)N as the amine. The oleic acid salt (oleic acid has one cis double bond) preferentially permeated the membrane while the linoleic (two cis double bonds) and linolenic (three cis double bonds) salts were partly retained. The separation of fatty acids using membranes may have real applications in industry to purify fatty acids on a large scale.

Functionalized Nanoporous Membranes from Reactive Triblock Polymers

Hydrophilic and stimuli responsive nanoporous poly(dicyclopentadiene) membranes are prepared using reactive ABC triblock polymers consisting of a chemically etchable ‘A’ block, poly(lactide), various functionalized ‘B’ blocks, and a metathesis-reactive ‘C’ block, poly(styrene-stat-norbornenylethylstyrene).A membrane with a bicontinuous structure is formed by reaction-induced phase separation during the metathesis crosslinking of dicyclopentadiene in the presence of the ABC triblock polymers. Selective etching of the poly(lactide) block exposed the functionality contained in the B block. Hydrophilic membranes are prepared from a triblock polymer with a poly(N,N-dimethylacrylamide) B midblock as evidenced by static contact angle measurements in comparison to AC diblock templated membranes. Temperature responsive membranes are prepared from a triblock polymer with a poly(N-isopropylacrylamide) B block.