Studies of end-groups in polystyrene using 1H NMR

Contact-Killing Antibacterial Polystyrene Polymerized Using a Quaternized Cationic Initiator

Contact-killing antibacterial materials are attracting attention owing to their ability for sustained antibacterial activity. However, contact-killing antibacterial polystyrene (PS) has not been extensively studied because its chemically stable structure impedes chemical modification. In this study, we developed an antibacterial PS sheet with a contact-killing surface using PS synthesized from 2,2'-azobis-[2-(1,3-dimethyl-4,5-dihydro-1H-imidazol-3-ium-2-yl)]propane triflate (ADIP) as a radical initiator with cationic moieties. The PS sheet synthesized with ADIP (ADIP-PS) exhibited antibacterial activity in contrast to PS synthesized with other azo radical initiators. Surface ζ-potential measurements revealed that only ADIP-PS had a cationic surface, which contributed to its contact-killing antibacterial activity. The ADIP-PS sheets also exhibited antibacterial activity after washing. In contrast, PS sheets containing silver, a typical leachable antibacterial agent, lost all antibacterial activity after the same washing treatment. The antibacterial ADIP-PS sheet demonstrated strong broad-spectrum activity against both Gram-positive and Gram-negative bacteria, including drug-resistant bacteria. Cytotoxicity tests using L929 cells showed that the ADIP-PS sheets were noncytotoxic. This contact-killing antibacterial PS synthesized with ADIP thus demonstrated good prospects as an easily producible antimicrobial material.

Circular Design and Functionalized Upcycling of Waste Commodity Polystyrene via C-H Activation Using Microwave-Assisted Multicomponent Synthesis

The inefficient reuse and recycling of plastics-and the current surge of medical and take-out food packaging use during the pandemic-have exacerbated the environmental burden. This impels the development of alternative recycling/upcycling methods to pivot toward circularity. We report the use of the Mannich three-component coupling reaction for the modification of polystyrene (PS) recovered with a 99.1% yield from waste food containers to form functionalized nitrogen and oxygen-rich PS derivatives. A series of functionalized PS with increasing moles of formaldehyde (F) and morpholine (M) (0.5 × 10^-2, 1.0 × 10^-2, and 2.0 × 10^-2 mol) was achieved using a sol-gel-derived Fe-TiO₂ catalyst in a solvent-free, microwave-assisted synthesis. Modified polymers were characterized with viscometry, ¹H NMR, ¹³CNMR (DEPT) FTIR, XPS, UV, and TGA. Functionalization scaled with an increasing ratio, validating the 3CR approach. Further functionalization was constrained by a competing oxidative degradation; however, the varying hydrogen bond density due to nitrogen and oxygen-rich species at higher ratios was shown to compensate for molecular weight loss. The integration of the N-cyclic quaternary ammonium cations exhibited the potential of functionalized polymers for ion-exchange membrane applications.

The Microbial Production of Polyhydroxyalkanoates from Waste Polystyrene Fragments Attained Using Oxidative Degradation

Excessive levels of plastic waste in our oceans and landfills indicate that there is an abundance of potential carbon sources with huge economic value being neglected. These waste plastics, through biological fermentation, could offer alternatives to traditional petrol-based plastics. Polyhydroxyalkanoates (PHAs) are a group of plastics produced by some strains of bacteria that could be part of a new generation of polyester materials that are biodegradable, biocompatible, and, most importantly, non-toxic if discarded. This study introduces the use of prodegraded high impact and general polystyrene (PS0). Polystyrene is commonly used in disposable cutlery, CD cases, trays, and packaging. Despite these applications, some forms of polystyrene PS remain financially and environmentally expensive to send to landfills. The prodegraded PS0 waste plastics used were broken down at varied high temperatures while exposed to ozone. These variables produced PS flakes (PS1⁻3) and a powder (PS4) with individual acid numbers. Consequently, after fermentation, different PHAs and amounts of biomass were produced. The bacterial strain, Cupriavidus necator H16, was selected for this study due to its well-documented genetic profile, stability, robustness, and ability to produce PHAs at relatively low temperatures. The accumulation of PHAs varied from 39% for prodegraded PS0 in nitrogen rich media to 48% (w/w) of dry biomass with the treated PS. The polymers extracted from biomass were analyzed using nuclear magnetic resonance (NMR) and electrospray ionization tandem mass spectrometry (ESI-MS/MS) to assess their molecular structure and properties. In conclusion, the PS0⁻3 specimens were shown to be the most promising carbon sources for PHA biosynthesis; with 3-hydroxybutyrate and up to 12 mol % of 3-hydroxyvalerate and 3-hydroxyhexanoate co-monomeric units generated.

A detailed mechanistic study of bulk MADIX of styrene and its chain extension

By combining experimental and modeling tools, a detailed characterization study of MADIX properties becomes possible.

Strong Evidence of a Phosphanoxyl Complex: Formation, Bonding, and Reactivity of Ligated Phosphorus Analogues of Nitroxides

Facile access to [W(CO)₅ (Ph₂ P-OTEMP)] is used to initiate a study on the generation, properties, and reactions of transient phosphanoxyl complexes [ML_n (R₂ PO)], the first example of which could be trapped via heterocoupling with the trityl radical. It is also demonstrated that the phosphorus nitroxyl complex acts as radical initiator in the polymerization of styrene. The quest for P-O versus O-N bond homolysis, as well as the initial steps of the polymerization were studied by DFT methods.

Strained surface siloxanes as a source of synthetically important radicals

The calcination of pure amorphous silica at temperatures up to 850 °C results in the formation of strained siloxane rings which are capable of undergoing homolytic cleavage to generate radicals when in the presence of an appropriate substrate.

Caracterização viscosimétrica de nanocompósitos híbridos PS/POSS

Nanocompósitos híbridos de poliestireno (PS) e poliedros oligoméricos silsesquioxanos (POSS) com diferentes composições e graus de hibridização foram obtidos por processamento reativo no estado fundido utilizando-se peróxido de dicumila (DCP) como iniciador, na presença ou não de estireno como agente de transferência de radical. Os materiais foram caracterizados viscosimetricamente por cromatografia de permeação em gel (GPC) usando detecção tripla por espalhamento de luz, viscosimetria e índice de refração. As amostras PS/POSS processadas com estireno apresentaram maiores valores de massa molar ponderal média (Mw) e menores valores de polidispersão (Mw/Mn), devido ao maior grau de conversão da reação de hibridização do PS-POSS (28-40%) e do menor grau de degradação (cisão) das cadeias do PS, quando comparadas com amostras PS/POSS processadas sem estireno nas quais o grau de conversão ficou em torno de 24-28%. Para os sistemas PS e PS/POSS em solução com THF, os parâmetros da equação de Mark-Houwink-Sakurada (MHS), α ≅ 0,7 e log K ≅ -3,5 a -3,9 e os valores dos parâmetros de interação polímero-solvente, χij ≅ 0,49, não apresentaram diferenças significativas com relação aos tamanhos moleculares. Por outro lado, essas diferenças de tamanhos moleculares foram caracterizadas por uma função cumulativa da fração mássica de cadeias em função da distância média quadrática entre pontas de cadeia (< r² >0½).