Reactive Blending of Functional PS and PMMA: Interfacial Behavior of in situ Formed Graft Copolymers

Linear, Graft, and Beyond: Multiblock Copolymers as Next-Generation Compatibilizers

Properly addressing the global issue of unsustainable plastic waste generation and accumulation will require a confluence of technological breakthroughs on various fronts. Mechanical recycling of plastic waste into polymer blends is one method expected to contribute to a solution. Due to phase separation of individual components, mechanical recycling of mixed polymer waste streams generally results in an unsuitable material with substantially reduced performance. However, when an appropriately designed compatibilizer is used, the recycled blend can have competitive properties to virgin materials. In its current state, polymer blend compatibilization is usually not cost-effective compared to traditional waste management, but further technical development and optimization will be essential for driving future cost competitiveness. Historically, effective compatibilizers have been diblock copolymers or in situ generated graft copolymers, but recent progress shows there is great potential for multiblock copolymer compatibilizers. In this perspective, we lay out recent advances in synthesis and understanding for two types of multiblock copolymers currently being developed as blend compatibilizers: linear and graft. Importantly, studies of appropriately designed copolymers have shown them to efficiently compatibilize model binary blends at concentrations as low as ∼0.2 wt %. These investigations pave the way for studies on more complex (ternary or higher) mixed waste streams that will require novel compatibilizer architectures. Given the progress outlined here, we believe that multiblock copolymers offer a practical and promising solution to help close the loop on plastic waste. While a complete discussion of the implementation of this technology would entail infrastructural, policy, and social developments, they are outside the scope of this perspective which instead focuses on material design considerations and the technical advancements of block copolymer compatibilizers.

Facile Fabrication of Size-Tunable Core/Shell Ferroelectric/Polymeric Nanoparticles with Tailorable Dielectric Properties via Organocatalyzed Atom Transfer Radical Polymerization Driven by Visible Light

An unconventional but facile approach to prepare size-tunable core/shell ferroelectric/polymeric nanoparticles with uniform distribution is achieved by metal-free atom transfer radical polymerization (ATRP) driven by visible light under ambient temperature based on novel hyperbranched aromatic polyamides (HBPA) as a functional matrix. Cubic BaTiO3/HBPA nanocomposites can be prepared by in-situ polycondensation process with precursors (barium hydroxide (Ba(OH)2) and titanium(IV) tetraisopropoxide (TTIP)) of ferroelectric BaTiO3 nanocrystals, because precursors can be selectively loaded into the domain containing the benzimidazole rings. At 1200 °C, the aromatic polyamide coating of cubic BaTiO3 nanoparticles are carbonized to form carbon layer in the inert environment, which prevents regular nanoparticles from gathering. In addition, cubic BaTiO3 nanoparticles are simultaneously transformed into tetragonal BaTiO3 nanocrystals after high temperature calcination (1200 °C). The outer carbon shell of tetragonal BaTiO3 nanoparticles is removed via 500 °C calcination in air. Bi-functional ligand can modify the surface of tetragonal BaTiO3 nanoparticles. PMMA polymeric chains are growing from the initiating sites of ferroelectric BaTiO3 nanocrystal surface via the metal-free ATRP technique to obtain core/shell ferroelectric BaTiO3/PMMA hybrid nanoparticles. Changing the molar ratio between benzimidazole ring units and precursors can tune the size of ferroelectric BaTiO3 nanoparticles in the process of polycondensation, and the thickness of polymeric shell can be tailored by changing the white LED irradiation time in the organocatalyzed ATRP process. The dielectric properties of core/shell BaTiO3/PMMA hybrid nanoparticles can be also tuned by adjusting the dimension of BaTiO3 core and the molecular weight of PMMA shell.

Interfacial tension of reactive, liquid interfaces and its consequences

Dispersions of immiscible liquids, such as emulsions and polymer blends, are at the core of many industrial applications which makes the understanding of their properties (morphology, stability, etc.) of great interest. A wide range of these properties depend on interfacial phenomena, whose understanding is therefore of particular importance. The behaviour of interfacial tension in emulsions and polymer blends is well-understood - both theoretically and experimentally - in the case of non-reactive stabilization processes using pre-made surfactants. However, this description of the interfacial tension behaviour in reactive systems, where the stabilizing agents are created in-situ (and which is more efficient as a stabilization route for many systems), does not yet find a consensus among the community. In this review, we compare the different theories which have been developed for non-reactive and for reactive systems, and we discuss their ability to capture the behaviour found experimentally. Finally, we address the consequences of the reactive stabilization process both on the global emulsions or polymer blend morphologies and at the interfacial scale.

Controlled radical polymerization of an acrylamide containing L-alanine moiety via ATRP

Homopolymerization of an optically active acrylamide having an amino acid moiety in the side chain, N-acryloyl-L-alanine (AAla) was carried out via atom transfer radical polymerization (ATRP) at room temperature using 2-hydroxyethyl-2'-methyl-2'-bromopropionate (HMB) or sodium-4-(bromomethyl)benzoate (SBB) as initiator in pure water, methanol/water mixture and pure methanol solvents. The polymerization reaction resulted in the optically active biocompatible amino acid-based homopolymer in good yield with narrow molecular weight distribution. The number average molecular weight increased with conversion and polydispersity was low. The structure and molecular weight of synthesized polymer were characterized by (1)H NMR, FT-IR spectroscopic techniques and size-exclusion chromatography.

'Pseudo-star' Copolymers Formed by a Combination of RAFT Polymerization and Isocyanate-Coupling

We describe the formation of pseudo-star copolymers via incorporation of an isocyanate-bearing monomer, dimethyl meta-isopropenyl benzyl isocyanate (TMI) into a homopolymer of butyl acrylate (BA) using a one-pot, two-step synthesis. The resultant product maintains the functionality of the isocyanate moiety, which is used to attach poly(ethylene glycol) methyl ether onto the copolymeric chain under benign reaction conditions. The resultant pseudo-star copolymers were isolated and their self-assembly in the presence of water studied.

Engineering nanostructured polymer blends with controlled nanoparticle location using Janus particles

Janus particles are used on a multigram scale for the blend compatibilization of two polymers in a twin screw mini-mixer. It is shown that the Janus particles can be located exclusively at the interface of the two polymer phases despite the high temperature and shear conditions. The domain sizes of the dispersed phase decrease with increasing content of Janus particles. The decrease is yet ongoing for high contents of Janus particles. Furthermore, the biphasic particles exhibit an ordered arrangement at the interface. Thus, the approach demonstrates that a nanoscopic structuring of the interface can be achieved under macroscopic processing conditions. The structural order occurs on two levels. The first is the complete adsorption at the interface and the second is the lateral ordering at the interface. The strong adsorption at the interface is explained in terms of the increased desorption energy of Janus particles. Secondly, the compatibilization efficiency is critically compared to state-of-the-art compatibilizers. The efficiency of the Janus particles is found to be superior as compared to block copolymer-based compatibilizers. The efficiency gap between Janus particles and block copolymer compatibilizers widens for larger amounts added.

Synthesis of PCL-PS Star-Block Copolymer by Combination of Lipase-Catalyzed Ring-Opening Polymerization and ATRP

Poly(ε-caprolactone) (PCL)-polystyrene (PS)star-block copolymer with a cross-linked microgel core were synthesized by the combination of atom transfer radical polymerization (ATRP) of St and lipase-catalyzed ring-opening polymerization (ROP) of ε-CL. The characterization of PCL-Br, PCL-PS-Br macroinitiator and PCL-PS Star-block copolymers was detected by GPC and 1H NMR. Results showed that the target star-block copolymers were successfully prepared.

Design and properties of co-continuous nanostructured polymers by reactive blending

With an annual production of hundreds of millions of tons, the few commodity polymers that dominate the plastics market cannot satisfy all the applications and expectations. In this context, the fabrication of thermodynamically stable polymer blends structured on submicrometre scales raises much hope, but poses significant scientific and industrial challenges. Here, we propose and demonstrate for an industrially relevant system, polyethylene and polyamide, that hitherto inaccessible co-continuous morphologies can be produced over a wide range of compositions by reactive blending. Paradoxically, the self-assembled structures are thermodynamically stable because of the molecular polydispersity inherent in the production method. These nanostructured materials present a unique combination of properties impossible to achieve with classical blends. This versatile, low-cost and simple strategy should be widely applicable.