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Recent progress in ring-opening (co)polymerization of γ-butyrolactone (γBL) in the presence of various initiating/catalyst systems has been reviewed. Low reaction temperatures and high monomer concentrations are critical for the success of such polymerization, regardless of the different initiating/catalyst systems.
The implementation of Direct Heteroarylation Polymerization (DHAP) in the synthesis of well-defined and defect-free materials for organic electronics is still in its early stages but giant leaps have been made over the past few years to improve and stir the selectivity of the reaction to avoid unwanted side-reaction such as β-branching or homocoupling. DHAP has proven to be an efficient, cost-effective, green and scalable polymerization method now competing or even surpassing well-established Suzuki-Miyaura or Migita–Stille cross-coupling polymerization methods. This focus review puts emphasis on the synthetic strategies that made DHAP successful.
Sequence precise regulation provides the possibility to probe the fundamental relationship between structure and properties in artificial polymers. Recent progress in sequence regulation through maleimide chemistry is focused on in this review, which put emphasis on the development of three strategies taking advantages of the versatile chemical properties of maleimide.
We have developed sequential multicomponent reaction and interconvertible hybrid copolymerization methods to prepare sequence-controlled polymers. The sequential multicomponent reaction combines more than two different multicomponent reactions in one pot to prepare periodic sequence˗controlled polymers with sufficient molecular diversity. The interconvertible hybrid copolymerization method uses trithiocarbonate compounds to combine radical polymerization of vinyl monomers and anionic ring-opening polymerization of thiirane monomers, resulting in hybrid multiblock sequence-regulated polymers.
A new thermally latent cocatalyst, based on 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), has been specifically designed for “on-demand” synthesis of polyurethanes in the presence of DBTL as catalyst. This nitrophenyl-based isocyanurate cocatalyst exhibited a low cleavage temperature keeping the system almost inactive at 20 °C and allowing fast polymerization only after increasing temperature up to 60 °C by the release of active DBN.
Pd-initiated polymerization of diazoacetates containing oligo(ethylene glycol)-substituted cyclotriphosphazenes was conducted to yield carbon-carbon main chain polymers bearing an oligo(ethylene glycol)-substituted cyclotriphosphazene on every main chain carbon atom. The resulting organic–inorganic poly(substituted methylene)s were found to show an LCST-type phase separation in aqueous media, and thus their thermosensitive behavior was evaluated by turbidity measurements.
We introduce a facile method to convert the bromine end of the polymer into a hydroxyl group. For this, bromine-terminated polystyrene (PS-Br) was prepared by atom transfer radical polymerization. The bromine groups of the PS-Br could be directly converted to hydroxyl groups by using Ag+ as the Lewis acid in water/acetone. The conversion yield was investigated by 1H nuclear magnetic resonance spectroscopy, high-performance liquid chromatography, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.
Photoswitchable and interconvertible cationic/radical copolymerization was investigated by combining a Lewis acid-catalyzed cationic polymerization with a photoinduced electron/energy transfer (PET)-reversible addition-fragmentation transfer (RAFT) polymerization, in which the dormant terminal group of the RAFT polymerization was employed as the dual mediator for cationic and photoradical polymerizations. Zinc porphyrin complex (ZnTPP) as the photoredox catalyst and bulky boron-based Lewis acid, B(C6F5)3, was successfully combined to induce the concurrent and interconvertible cationic/radical copolymerization of vinyl ether and methyl acrylate under visible light irradiation.
A new nickel diphosphine catalyst was synthesized and evaluated for Suzuki–Miyaura cross-coupling polymerization. The diphosphine is comprised of two electronically and sterically distinct phosphine donors, a PPh2 group and a PEt2 group. The catalyst was employed to bring about controlled polymerization of a 3-hexylthiophene monomer to afford poly(3-hexylthiophene). The catalyst was particularly effective for bringing about this polymerization in the presence of excess free ligand. The catalyst resting state was also probed using NMR spectroscopy and an externally initiated catalyst.
Vinylcycloalkanes with 12-, 15-, and 21-membered rings were synthesized from commercially available cycloalkanones or cycloalkyl carboxylic acids derived from malonate and ω-bromo-α-alkenes. Pd complexes with diimine ligands promoted the isomerization polymerization of vinylcycloalkanes with 15- and 21-membered rings to afford polymers having cycloalkylene groups in the main chain. Vinylcycloheneicosane with a 21-membered ring afforded polymers with Mn up to 9700, whereas vinylcycloalkanes with smaller ring sizes (8- and 12-membered rings) yielded oligomers with Mn = 720–1600.
Alkali metal carboxylates, which are readily available and widely used as food additives, were found to promote the ring-opening polymerization (ROP) of trimethylene carbonate (TMC) to produce poly(trimethylene carbonate) (PTMC). The sodium acetate-catalyzed ROP of TMC proceeded in the presence of an alcohol initiator under solvent-free conditions, even at very low catalyst loadings of 0.01–0.0001 mol%. This ROP system enabled the synthesis of PTMCs with predicted molecular weights ranging from 2400 to 11 700 g mol−1 and narrow dispersities (~1.23).
Well-defined poly(arylene ether sulfone)-b-polylactides (PES-b-PLAs) were successfully synthesized and their microphase separation behavior was investigated. PES was obtained via chain growth condensation polymerization, and subsequent end group modification followed by ring opening polymerization of d,l-lactide produced the diblock copolymers. By small-angle X-ray scattering experiments in bulk, the formation of ordered morphologies including spherical, cylindrical, gyroidal, and lamellar was observed. An effective interaction parameter at 150 °C was roughly estimated as 0.12 for the first time in engineering plastic-containing block copolymers.
Schwiertz et al. report on the synthesis of miktoarm star polymers based on polypept(o)ides by nucleophilic ring opening polymerization of N-carboxyanhydrides. The reported procedures allow for precise control over chain length, number of arms and end group functionality.
An efficient and straightforward strategy for the synthesis of uniform, sequence-defined oligo(ester-amide-ester)s via sequential nucleophilic substitution reactions and Passerini reaction was developed. The side groups could be easily regulated by the Passerini reaction of different aldehydes. The synthesis of uniform, symmetrical, long-chain oligomers was further demonstrated by an iterative approach. The DIC/DPTS-mediated polycondensation of the α,ω-hydroxy carboxylic acids as the sequence-defined oligomer afforded high-molecular-weight periodic poly(ester-amide-ester)s. The thermal properties of these oligo/poly(ester-amide-ester)s were also examined.
The sulfur-containing styrene derivative, 4-methylenethiochromane (META), was subjected to anionic copolymerization with isoprene (Ip) modified with different additives. The reactivity of META can be effectively regulated with additives; thus, the regulation of the alternating or gradient copolymerization of META and Ip was facilely realized through the use of additives.
By virtue of “core first” method, ABC star quaterpolymers were controllably synthesized by combination of controlled polymerization and thiolactone chemistry. The miktoarm stars were responsive to temperature, pH, CO2, O2 and oxidation, and thus the phase transition temperature, size and morphology of copolymer assemblies could be efficiently tuned via adopting a single stimulus or combined stimuli.
Herein, several synthetic procedures for the synthesis of uniform PEGs were compared. The importance of SEC as analytical method for the determination of the precise structure and purity of uniform PEGs was shown by means of simple symmetry peak analysis, revealing that SEC can detect contaminations of only 2% of oligomers with only one repeat unit difference.
