Synthesis of CO2-Based Block Copolymers via Chain Transfer Polymerization Using Macroinitiators: Activity, Blocking Efficiency, and Nanostructure

Controlled synthesis of polycarbonate diols and their polylactide block copolymers using amino-bis(phenolate) chromium hydroxide complexes

A diamine-bis(phenolate) chromium(III) complex, CrOH[L] ([L] = dimethylaminoethylamino-N,N-bis(2-methylene-4,6-tert-butylphenolate)), 2, in the presence of tetrabutylammonium hydroxide effectively copolymerizes CO2 and cyclohexene oxide (CHO) into a polycarbonate diol. The resultant low molar mass (6.3 kg mol-1) diol is used to initiate ring-opening polymerization of rac-lactide with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) giving ABA-type block copolymers with good molar mass control through varying rac-LA-to-diol loadings and with narrow dispersities. As the degree of rac-LA incorporation increases, the glass transition temperatures (Tg) are found to decrease, whereas decomposition temperatures (Td) increase. (Diphenylphosphonimido)triphenylphosphorane (Ph2P(O)NPPh3) was used as a neutral nucleophilic cocatalyst with 2, giving phosphorus-containing polycarbonates with an Mn value of 28.5 kg mol-1, a dispersity of 1.13, a Tg value of 110 °C and a Td value of over 300 °C. A related Cr(III) complex (4) having a methoxyethyl pendent group rather than a dimethylaminoethyl group was structurally characterized as a hydroxide-bridged dimer.

Enabling New Approaches: Recent Advances in Processing Aliphatic Polycarbonate-Based Materials

Aliphatic polycarbonates (aPCs) have become increasingly popular as functional materials due to their biocompatibility and capacity for on-demand degradation. Advances in polymerization techniques and the introduction of new functional monomers have expanded the library of aPCs available, offering a diverse range of chemical compositions and structures. To accommodate the emerging requirements of new applications in biomedical and energy-related fields, various manufacturing techniques have been adopted for processing aPC-based materials. However, a summary of these techniques has yet to be conducted. The aim of this paper is to enrich the toolbox available to researchers, enabling them to select the most suitable technique for their materials. In this paper, a concise review of the recent progress in processing techniques, including controlled self-assembly, electrospinning, additive manufacturing, and other techniques, is presented. We also highlight the specific challenges and opportunities for the sustainable growth of this research area and the successful integration of aPCs in industrial applications.

Sequence-Reversible Construction of Oxygen-Rich Block Copolymers from Epoxide Mixtures by Organoboron Catalysts

Switchable catalysis, in combination with epoxide-involved ring-opening (co)polymerization, is a powerful technique that can be used to synthesize various oxygen-rich block copolymers. Despite intense research in this field, the sequence-controlled polymerization from epoxide congeners has never been realized due to their similar ring-strain which exerts a decisive influence on the reaction process. Recently, quaternary ammonium (or phosphonium)-containing bifunctional organoboron catalysts have been developed by our group, showing high efficiency for various epoxide conversions. Herein, we, for the first time, report an operationally simple pathway to access well-defined polyether-block-polycarbonate copolymers from mixtures of epoxides by switchable catalysis, which was enabled through thermodynamically and kinetically preferential ring-opening of terminal epoxides or internal epoxides under different atmospheres (CO₂ or N₂) using one representative bifunctional organoboron catalyst. This strategy shows a broad substrate scope as it is suitable for various combinations of terminal epoxides and internal epoxides, delivering corresponding well-defined block copolymers. NMR, MALDI-TOF, and gel permeation chromatography analyses confirmed the successful construction of polyether-block-polycarbonate copolymers. Kinetic studies and density functional theory calculations elucidate the reversible selectivity between different epoxides in the presence/absence of CO₂. Moreover, by replacing comonomer CO₂ with cyclic anhydride, the well-defined polyether-block-polyester copolymers can also be synthesized. This work provides a rare example of sequence-controlled polymerization from epoxide mixtures, broadening the arsenal of switchable catalysis that can produce oxygen-rich polymers in a controlled manner.

Switchable Polymerization: A Practicable Strategy to Produce Biodegradable Block Copolymers with Diverse Properties

With the global demand for sustainable development, there has been an increasing interest in using natural biomass as raw resources to produce sustainable polymers as an alternative to petroleum-based polymers. Because monocomponent biodegradable polymers are often insufficient in performance, copolymers with well-engineered block structures are synthesized to reach wide tunability. Switchable polymerization is such a practical strategy to produce biodegradable block copolymers with diverse performance. This review focus on the performance of block copolymers bearing biodegradable polymer segments produced by diverse switchable polymerization. We highlight two main segments that are critical for biodegradable block copolymers, i. e., polyester and polycarbonate, summarize the multiple characters of materials from switchable polymerization such as antibacterial, shape memory, adhesives, etc. The state-of-the-art research on biodegradable block copolymers, as well as an outlook on the preparation and application of novel materials, are presented.

Intra- and Intermolecular Hydrogen Bonding in Miscible Blends of CO2/Epoxy Cyclohexene Copolymer with Poly(Vinyl Phenol)

In this study, we synthesized a poly(cyclohexene carbonate) (PCHC) through alternative ring-opening copolymerization of CO₂ with cyclohexene oxide (CHO) mediated by a binary LZn₂OAc₂ catalyst at a mild temperature. A two-dimensional Fourier transform infrared (2D FTIR) spectroscopy indicated that strong intramolecular [C–H···O=C] hydrogen bonding (H-bonding) occurred in the PCHC copolymer, thereby weakening its intermolecular interactions and making it difficult to form miscible blends with other polymers. Nevertheless, blends of PCHC with poly(vinyl phenol) (PVPh), a strong hydrogen bond donor, were miscible because intermolecular H-bonding formed between the PCHC C=O units and the PVPh OH units, as evidenced through solid state NMR and one-dimensional and 2D FTIR spectroscopic analyses. Because the intermolecular H-bonding in the PCHC/PVPh binary blends were relatively weak, a negative deviation from linearity occurred in the glass transition temperatures (T_g). We measured a single proton spin-lattice relaxation time from solid state NMR spectra recorded in the rotating frame [T_1ρ(H)], indicating full miscibility on the order of 2–3 nm; nevertheless, the relaxation time exhibited a positive deviation from linearity, indicating that the hydrogen bonding interactions were weak, and that the flexibility of the main chain was possibly responsible for the negative deviation in the values of T_g.

Sulfur-containing polymers derived from SO2: synthesis, properties, and applications

Sulfur-containing polymers enjoy the merits of excellent optical performance, degradation, chemical recyclability, and adhesive abilities toward metal ions. Recently, increasing attentions in both academic and industrial circles have been paid...

Orthogonally grown polycarbonate and polyvinyl block copolymers from mechanistically distinct (co)polymerizations

Mechanistically distinct polymerization systems can afford unique block copolymers that would not be accessible by mere sequential polymerization.

Boundary-directed epitaxy of block copolymers

Directed self-assembly of block copolymers (BCPs) enables nanofabrication at sub-10 nm dimensions, beyond the resolution of conventional lithography. However, directing the position, orientation, and long-range lateral order of BCP domains to produce technologically-useful patterns is a challenge. Here, we present a promising approach to direct assembly using spatial boundaries between planar, low-resolution regions on a surface with different composition. Pairs of boundaries are formed at the edges of isolated stripes on a background substrate. Vertical lamellae nucleate at and are pinned by chemical contrast at each stripe/substrate boundary, align parallel to boundaries, selectively propagate from boundaries into stripe interiors (whereas horizontal lamellae form on the background), and register to wide stripes to multiply the feature density. Ordered BCP line arrays with half-pitch of 6.4 nm are demonstrated on stripes >80 nm wide. Boundary-directed epitaxy provides an attractive path towards assembling, creating, and lithographically defining materials on sub-10 nm scales.

Synthesis of CO2-based polycarbonate-g-polystyrene copolymers via NMRP

The synthesis of CO₂-based APC-graft-polystyrene copolymers via NMRP.

Dual Nanopatterns Consisting of Both Nanodots and Nanoholes on a Single Substrate

Block copolymers (BCPs) with various nanostructures such as spheres, cylinders, gyroid, and lamellae, have received great attention for their application in nanolithography through nanopattern transfer to substrates. However, the fabrication of diverse geometries, shapes and sizes of nanostructure on a single substrate at the desired position could not be achieved because the nanostructure based on BCPs is mainly determined by the volume fraction of one block. Here, we synthesize polystyrene-hv-poly(methyl methacrylate) copolymer (PS-hv-PMMA), which contains a photocleavable linker at the junction point between PS and PMMA blocks. After vertically oriented PMMA cylindrical nanodomains in a thin film on a substrate were obtained, dual nanopatterns composed of high-density array of nanodots and nanoholes were successfully fabricated at the desired area on a single substrate using selective irradiation with a mask. The dual nanopatterns could be used to prepare metal (or metal oxide) nanostructure arrays consisting of both nanodots and nanoholes, which are utilized for smart sensors capable of simultaneously detecting two independent molecules on nanodots and nanoholes.

Nonionic Aliphatic Polycarbonate Diblock Copolymers Based on CO2, 1,2-Butylene Oxide, and mPEG: Synthesis, Micellization, and Solubilization

Carbon dioxide (CO₂) is a renewable carbon source that is easily available in high purity and is utilized as a co-monomer in the direct ring-opening polymerization of epoxides to obtain aliphatic polycarbonates. In this work, degradable aliphatic polycarbonate diblock copolymers (mPEG- b-PBC) are synthesized via catalytic copolymerization of CO₂ and 1,2-butylene oxide, starting from monomethoxy poly(ethylene glycol) (mPEG) as a chain transfer reagent. The polymerization proceeds at low temperatures and high CO₂ pressure, utilizing the established binary catalytic system ( R, R)-Co(salen)Cl/[PPN]Cl. Amphiphilic nonionic diblock copolymers with varying PBC block lengths and hydrophilic-lipophilic balance values between 9 and 16 are synthesized. The polymers are characterized via NMR and Fourier transform infrared spectroscopies as well as size exclusion chromatography, exhibiting molecular weights ranging from 2400 to 4100 g mol^-1 with narrow dispersities ( Đ = M_w/ M_n) from 1.07 to 1.18. Furthermore, the thermal properties, i.e., T_g, T_m, and T_d, are determined. Surface tension measurements prove that the amphiphilic polymers form micelles above the critical micelle concentration, whereas small-angle neutron scattering shows that they are of nearly spherical shape. Adding small amounts of the synthesized mPEG- b-PBC polymers to different microemulsion systems, we found that the polymers were able to strongly increase the efficiency of medium-chain surfactants to solubilize polar oils.

Waste not, want not: CO2 (re)cycling into block polymers

A new way to combine two different polymerisation reactions, using a single catalyst, results in efficient block polymer synthesis. The selective polymerisation of mixtures of l-lactide-O-carboxyanhydride and cyclohexene oxide, using a di-zinc catalyst in a one-pot procedure, allows the preparation of poly(l-lactide-b-cyclohexene carbonate). The catalysis near quantitatively recycles the carbon dioxide released during polyester formation into the subsequent polycarbonate block, with an atom economy of up to of 91%.