An Exploration of the Universal and Switchable RAFT-Mediated Synthesis of Poly(styrene-alt-maleic acid)-b-poly(N-vinylpyrrolidone) Block Copolymers

The synthesis of poly(styrene-alt-maleic anhydride) (SMAnh) and poly(4-tert-butylstyrene-alt-maleic anhydride) (tBuSMAnh) macro-RAFT agents was investigated using universal 3,5-dimethylpyrazole dithiocarbamate and stimuli-responsive N-(4-pyridinyl)-N-methyldithiocarbamate RAFT agents. SMAnh/tBuSMAnh macro-RAFT agents of targeted molecular weight and narrow molecular weight distribution could be synthesized with intentional variation of the terminal monomer unit, allowing for the assessment of two distinctive macro-R-groups. SMAnh macro-RAFT agents were utilized to mediate the thermally initiated polymerization of N-vinylpyrrolidone (NVP), yielding SMAnh-b-PVP, but with significant thermolysis and hydrolysis of dithiocarbamate ω-chain ends. Alternatively, the redox-initiated RAFT-mediated polymerization of NVP at ambient temperatures using hydrolyzed macro-RAFT agents, i.e., poly(styrene-alt-maleic acid) (SMA) and poly(4-tert-butylstyrene-alt-maleic acid) (tBuSMA), was explored. Double hydrophilic SMA-b-PVP and tBuSMA-b-PVP block copolymers could be synthesized but with significant broadening of the molecular weight distribution. This is a result of the formation of dead chains derived from the alkaline hydrolysis of macro-RAFT agents prepolymerization and hydrolysis of dithiocarbamate chain ends throughout the polymerization. The latter is exacerbated by the insertion of NVP at the ω-chain end, which was subsequently investigated via the kinetic analysis of the xanthate- and dithiocarbamate-mediated aqueous homopolymerization of NVP.

Installing a Single Monomer within Acrylic Polymers Using Photoredox Catalysis

Incorporating exactly one monomer at a defined position during a chain polymerization is exceptionally challenging due to the statistical nature of monomer addition. Herein, photoinduced electron/energy transfer (PET) enables the incorporation of exactly one vinyl ether into polyacrylates synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Near-quantitative addition (>96%) of a single vinyl ether is achieved while retaining >99% of the thiocarbonylthio chain ends. Kinetic studies reveal that performing the reactions at 2 °C limits unwanted chain breaking events. Finally, the syntheses of diblock copolymers are reported where molecular weights and dispersities are well-controlled on either side of the vinyl ether. Overall, this report introduces an approach to access acrylic copolymers containing exactly one chemical handle at a defined position, enabling novel macromolecular architectures to probe structure-function properties, introduce sites for de/reconstruction, store information, etc.

Rational design of a multi-in-one heterofunctional agent for versatile topological transformation of multisite multisegmented polystyrenes

A “seven-in-one” initiating, coupling and stimuli-labile agent is designed to achieve topological transformations with reduced, similar and enhanced molar masses.

Photo-Iniferter RAFT Polymerization

Light-mediated polymerization techniques offer distinct advantages over polymerization reactions fueled by thermal energy, such as high spatial and temporal control as well as the possibility to work under mild reaction conditions. Reversible addition-fragmentation chain-transfer (RAFT) polymerization is a highly versatile radical polymerization method that can be utilized to control a variety of monomers and produce a vast number of complex macromolecular structures. The use of light to drive a RAFT-polymerization is possible via multiple routes. Besides the use of photo-initiators, or photo-catalysts, the direct activation of the chain transfer agent controlling the RAFT process in a photo-iniferter (PI) process is an elegant way to initiate and control polymerization reactions. Within this review, PI-RAFT polymerization and its advantages over the conventional RAFT process are discussed in detail.

Information-Based Design of Polymeric Drug Formulation Additives

Tailor-made copolymers are designed based on a peptide-poly(ethylene glycol) (QFFLFFQ-PEG) conjugate as a blueprint, to solubilize the photosensitizer meta-tetra(hydroxyphenyl)chlorin (m-THPC). The relevant functionalities of the parent peptide-PEG are mimicked by employing monomer pairs that copolymerize in a strictly alternating manner. While styrene (S) or 4-vinylbenzyl-phthalimide (VBP) provide aromatic moieties like Phe, the aliphatic isobutyl side chain of Leu4 is mimicked by maleic anhydride (MA) that reacts after polymerization with isobutylamine to give the isobutylamide-carboxyl functional unit (iBuMA). A set of copolymer-PEG solubilizers is synthesized by controlled radical polymerization, systematically altering the length of the functional segment (DP_n = 2, 4, 6) and the side chain functionalization (iBuMA, iPrMA, MeMA). The m-THPC hosting and release properties of P[S-alt-iBuMA]₆-PEG reached higher payload capacities and more favored release rates than the parent peptide-PEG conjugate. Interestingly, P[S-alt-RMA]_n-PEG mimics the sensitivity of the peptide-PEG solubilizer well, where the exchange of Leu4 residue by Val and Ala significantly reduces the drug loading by 92%. A similar trend is found with P[S-alt-RMA]_n-PEG as the exchange of iBu → iPr → Me reduces the payload capacity up to 78%.

Iodine-mediated photo-controlled atom transfer radical polymerization (photo-ATRP) and block polymerization combined with ring-opening polymerization (ROP) via a superbase

Most organocatalysts for photo-controlled atom transfer radical polymerization (photo-ATRP) are metal complexes or synthetically elaborate organic dyes, which are toxic and expensive.

Microscale synthesis of multiblock copolymers using ultrafast RAFT polymerisation

We demonstrate that ultrafast RAFT in the presence of air can be scaled down to 2 μL with good control using microvolume insert vials as the polymerisation vessel.

P(N-Phenylmaleimide-Alt-Styrene) Introduced with 4-Carboxyl and Its Effect on the Heat Deflection Temperature of Nylon 6

P(N-phenylmaleimide-alt-styrene) (P(NPMI-alt-St)) and P(N-(4-carboxyphenyl)maleimide-alt-styrene) (P(CPMI-alt-St)) were designed and synthesized via free radical copolymerization. Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (¹H NMR and 13C NMR), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC) were used to confirm the structure of P(NPMI-alt-St) and P(CPMI-alt-St). Next, the effect of P(CPMI-alt-St) on the heat deflection temperature (HDT) of nylon 6 was studied. In comparison to the PA6/P(NPMI-alt-St) blend, with the addition of 10 wt %, the HDT value of the PA6/P(CPMI-alt-St) blend increased by 15.7 °C, and the glass transition temperature (Tg) by Dynamic mechanical analysis (DMA) increased 2.3 °C. According to the analysis of DMA, dynamic viscosity, and the SEM of PA6 and its blends, P(CPMI-alt-St) promoted its compatibility with PA6, and promoted the storage modulus and dynamic viscosity of the blends. Thus, the introduction of 4-carboxyl can significantly improve the effect of P(CPMI-alt-St) on the heat resistance modification of nylon 6.

Sequence-definition from controlled polymerization: the next generation of materials

An overview is given on the state-of-the-art in synthesis of sequence-controlled and sequence-defined oligomers and polymers.

MALDI-LID-ToF/ToF analysis of statistical and diblock polyacrylate copolymers

We report the use of MALDI-LID-ToF/ToF utilising the laser induced dissociation (LID) fragmentation technique, which has been almost exclusively applied to protein/peptide analysis to date.

The downside of dispersity: why the standard deviation is a better measure of dispersion in precision polymerization

Dispersity gives a deceptively rosy picture of the extent of dispersion in molecular weight distributions. For complex structures or relatively narrow molecular weight distributions, the standard deviation of the number distribution is a better choice.

Complex multiblock bottle-brush architectures by RAFT polymerization

The combination of the reversible addition fragmentation chain transfer (RAFT) polymerization R-group grafting from approach and RAFT one-pot acrylamide multiblock methodology is used to synthesise complex bottle-brush architectures.