Molybdenum alkylidyne N-heterocyclic carbene (NHC) complexes of the type [Mo(C-p-C6H4Y)(OC(R)(CF3)2)2 (L)(NHC)][B(ArF)4] (Y = OMe, NO2; R = CH3, CF3; L = none, pivalonitrile, tetrahydrofuran; NHC = 1,3-dimesitylimidazol-2-ylidene, 1,3-dimesityl-3,4-dihydroimidazol-2-ylidene, 1,3-dimesityl-3,4-dichloroimidazol-2-ylidene (IMesCl2), 1,3-diisopropylimidazol-2-ylidene; B(ArF)4- = tetrakis(3,5-bis(trifluoromethyl)phen-1-yl)borate) were used in the ring expansion metathesis polymerization (REMP) of cyclic olefins. With cis-cyclooctene (cCOE) cyclic, low molecular weight oligomers were obtained at low monomer concentration and the exclusive cyclic nature of the polymer was confirmed by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. High-molecular weight cyclic poly(cCOE) became available at high monomer concentration. Also, post-REMP allowed for converting low-molecular weight cyclic poly(cCOE) into high molecular weight cyclic poly(cCOE). Tailored catalysts together with suitable additives offered access to the stereoselective REMP of functional norbornenes providing functional cis-isotactic (cis-it), cis-syndiotactic (cis-st) and trans-it poly(norbornene)s with up to 99 % stereoselectivity. Mechanistic details supported by density functional theory calculations are outlined.
A cationic molybdenum alkylidyne NHC complex selectively immobilized inside the pores of ordered mesoporous silica (OMS) with pore diameters of 66Å and 28Å, respectively, also allows the REMP of cyclic olefins to yield cyclic polymers. Application of a strong confinement effect offers access to low molecular weight cyclic polymers even at high monomer concentration in the REMP of cCOE, 1,5-cyclooctadiene (COD), (+)-2,3-endo,exo-dicarbomethoxynorborn-5-ene ((+)-DCMNBE), and 2 methyl-2-phenylcycloprop-1-ene (MPCP). The exclusive formation of cyclic polymers was again demonstrated by MALDI-TOF mass spectrometry. Confinement also influences stereoselectivity resulting in a pronounced increase in Z-selectivity and in an increased cis-syndiospecificity.

A recent advancement in film formation of emulsion copolymers is the exploitation of nanoengineered latex particles of multiblock copolymers (MBCPs), synthesized via RAFT emulsion polymerization in water as a versatile and environmentally friendly process. These MBCP nanoparticles can overcome the limitations of other methods such as core-shell systems by producing films with excellent mechanical properties via direct latex casting (particle coalescence).1 Microphase separation occurs within particles between chemically incompatible polymers: polystyrene (Tg=100 ºC), providing desired mechanical properties, and poly(n-butyl acrylate) (Tg= -54 ºC), forming the outer layer of the particles to improve film-forming properties.2,3 As a result of the soft outer layer, the minimum film formation temperature is near room temperature despite the overall copolymer Tg being well above room temperature.
FIGURE1 MacroRAFT emulsionpolymerization of MBCP latexes, followed by filmformation.
In successfully synthesizing MBCPs, RAFT emulsion polymerization of the initial seed latex is a crucial step, significantly affected by the structure of macroRAFT agents. To this aim, a detailed study was conducted on the impact of hydrophilic and hydrophobic chain lengths of amphiphilic macroRAFT agents poly(methacrylic acid-b-methyl methacrylate) on latex nanoparticle behavior (colloidal stability, morphology, and latex viscosity). The optimized poly(n-butyl acrylate) nanoparticles were chain extended sequentially with styrene and n-butyl acrylate to prepare high molecular weight MBCP particles which were directly film formed. The results showed the macroRAFT structure significantly influences RAFT emulsion polymerization, leading to the successful preparation of well-defined MBCP films with a high styrene content (>65%) but yet soft as a promising material for advanced applications.

Various types of porous biodegradable polymers based on polycaprolactone (PCL), polylactide (PLA), and polyurethane were synthesized and used as drug delivery vehicles for bupivacaine and carboplatin. Porous biodegradable microspheres were fabricated by successful RAFT polymerization of methyl vinyl ketone (MVK) onto PCL and PLA, which was first synthesized by ring opening polymerization of lactide followed by an oil/water emulsion-evaporation method, then finally photodegradation of PMVK blocks by UV irradiation. Biodegradable porous polyurethane nanoparticles have also been fabricated using water-in-oil-in-water double emulsion and solvent evaporation methods. These nanoparticles are composed of biodegradable and biocompatible polyfumarateurethane (PFU) and L-threonine polyurethane (LTHU), designed for degradation through hydrolysis and enzymatic activity, facilitated by the presence of ester bonds and peptide bonds within the polymer backbone. The morphology of microspheres was spherical with smooth surfaces before UV irradiation. Microspheres fabricated only from PCL homopolymers could also retain their smooth surface after UV irradiation. However, those from PCL-PMVK and PCL-PLA-PMVK block copolymers had rough surfaces and porous structures after UV irradiation due to the photodegradation of PMVK blocks as a porous template. The porosity and shape of the microspheres and shape of microspheres were dependent on the PMVK contents and size of microspheres. In addition, the drug loading, encapsulation efficiency, and drug release profiles, using UV-Vis spectroscopy, showed the highest encapsulation efficiency with 2.5% drug, and sustained release profile.

Miniemulsion polymerization is used for co-polymerization of hydrophobic monomers and requires significant energy input to form fine monomer droplets that act as polymerization reactors. Dynamic volatile amphiphiles [1] are intended to facilitate the emulsification efficiency of surfactants and improve emulsion stability during the reaction. Reducing the total surfactant content in the latex by evaporation of the volatile amphiphile can improve the performance of latexes in coatings [2].
This work highlights the role of the aroma molecules benzyl acetate (BAc) and linalool (LO) as multifunctional agents in the miniemulsion copolymerization of styrene (St) and plant oil-derived acrylic monomers [3,4]. Varying the fraction of BAc (or LO) in their mixtures with the conventional surfactant sodium dodecyl sulfate (SDS) resulted in a slight systematic increase in emulsion droplet size upon ultrasonic treatment. The macroscopic kinetic stability was comparable to that of emulsions stabilized with SDS alone. Miniemulsion copolymerization was successful in emulsions containing up to 70% BAc in the surfactant mixture, whereas LO/SDS systems showed a decrease in conversion with increasing LO content. These observations have been attributed to differences in the hydrotropic functionality of the aroma molecules [5]. The synthesized polymers were tested as organic solvent-free, bio-based textile finishing formulations with a hydrophobic effect. Besides the challenge of efficient copolymerization of water-insoluble unsaturated monomers from plant oils, the results emphasize the need to consider the multifunctional behavior of aroma molecules in heterophase polymerization.

Energy efficiency is a key factor in reducing the environmental impact of buildings, with nearly 50% of global energy consumption dedicated to heating and cooling. Cellular Polystyrene (PS foams) serve as essential thermal insulators in these applications, but optimising their properties is crucial to improving performance while minimising raw material usage. A major challenge is to reduce foam density while enhancing insulation efficiency, for example, by decreasing cell size or increasing nucleation density.
This study examines how the cellular structure is directly influenced by the molecular architecture of PS chains. A range of PS samples with controlled average molecular weight (Mw) and polydispersity index (PDI) was synthesised to investigate their impact on foam formation [1] (Fig 1). This was combined with precise gas dissolution foaming conditions, which were tailored to each resulting microstructure [2]. Key parameters such as expansion ratio, nucleation density, and cell morphology were analysed, demonstrating the synergies that can be achieved by carefully tuning Mw and PDI of polymers, and foaming conditions. The results demonstrated a strong dependence of PDI on achieving more homogeneous cellular structures across different Mw ranges. This approach enabled the production of foams with near-nanoscale cell sizes (below 2 µm), leading to significant improvements in both mechanical and insulating properties while also achieving extremely low densities, as light as 42 kg/m³. These findings open new opportunities for tailoring PS foams to address current environmental challenges.

Currently, scientific research aimed at designing materials that are easily recyclable or degraded constitutes an important direction in academia and industry.[1] Polyesters such as polylactide (PLA) or polycaprolactone (PCL) are broadly exploited materials due to their nontoxicity and suitable mechanical properties. The goal of our study was to develop ABA block copolymers with enhanced degradability by combining polyacetal middle blocks with polyester outer blocks.[2] Copolymers with a required structure were obtained by the ring-opening polymerization of lactide (LA) or caprolactone (CL) catalysed by commercially available tin(II) octoate, using α,ω-hydroxy-terminated polyacetals as macroinitiators (Figure 1).

Figure 1: Synthesis of "ABA" block copolymers containing polyester external "A" blocks and internal polyacetal "B" blocks.
The results show that the length of polyester blocks could be easily tailored by varying the cyclic ester ratio to hydroxyl groups in the starting polymerization mixture. High conversions of cyclic esters (>95%) afforded block copolymers formation with monomodal molar mass distributions and molar masses ranging from 10 000 to 56 000 g mol-1. The obtained copolymers were characterized in terms of their structure, hydrophilicity, and thermal propertiesBased on the degradation studies we concluded that the decomposition of these triblock copolymers may be purposefully controlled, making them potentially useful recyclable materials.