Cationic ring‐opening polymerization (CROP) major mechanistic phenomena

A number of today's accepted basic viewpoints related to cationic ring‐opening polymerizations (CROP) were a matter of vivid disagreements between various research groups in the past. These controversies are described in this article and reasons of some differencies in opinions are explained. It is shown in which way we learned that polyacetals are not exclusively cyclic (as it was assumed), why CROP ions and ion pairs have similar reactivities, and why it was necessary to propose that CROP proceeds at certain conditions by Activated Monomer Mechanism. Among other subtle kinetic problems, application of the dynamic NMR and “temperature jump” techniques in determining rate constants of active species interconversions are discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1919–1933, 2000     

Free‐Radical Polymerization with Long‐Chain Branching and Scission in a Continuous Stirred‐Tank Reactor

Free‐radical polymerization that involves the polymer transfer reactions leading to both long‐chain branching and scission, as in the cases of high‐pressure olefin polymerization, is considered. In CSTR, the residence time distribution is broad and the primary polymer chain, whose residence time is large, is subjected to polymer transfer reaction for a longer time, leading to a larger number of branching and scission points. The distributions of both branching and scission density are much broader in a CSTR than in a batch, or equivalently, a PFR. The radius of gyration for larger sized polymers formed in a CSTR tends to be much smaller than that for randomly branched polymers.

     

Molecular Weight Development during Simultaneous Chain Scission,Long‐Chain Branching and Crosslinking, 1

A general matrix formula is proposed for the weight‐average molecular weights of the polymer systems formed through simultaneous scission, branching and crosslinking of N types of chains, assuming the chain connection statistics are Markovian. For the polymerization systems in which chains are generated consecutively, such as for free‐radical polymerization, the present theory can be applied by increasing the number of chain types N to infinity, by considering the chains formed at different times as different types of chains. The gel point determination reduces to the eigenvalue problem and the present theory extends the classical gelation theory to non‐random, history‐dependent reaction systems. From the mathematical point of view, this theory is capable of describing complex molecular build‐up processes through end‐linking, T‐ and H‐shaped chain connections, irrespective of reaction/reactor types used.

Schematic representation of the 0^th generation segment and the connection to the 1^st generation segments.     

Incorporation of ketone groups into poly(4‐hydroxystyrene)s main chain by radical copolymerization of 2,2‐diphenyl‐4‐methylene‐1,3‐dioxorane with O‐protected hydroxystyrenes and their photodegradable behavior

Here we report the incorporation of ketone groups into poly(4‐hydroxystyrene)s main chain by radical copolymerization of O‐protected hydroxystyrenes such as 4‐ethoxyethoxystyrene and 4‐acetoxystyrene with 2,2‐diphenyl‐4‐methylene‐1,3‐dioxorane (DPMD) followed by removal of the protective groups and the photodegradable behavior of obtained copolymers. The copolymerization of O‐protected hydroxystyrenes with DPMD gave the corresponding copolymers bearing DMPD‐derived ketone groups in the main chain, of which content could be controlled by changing monomer feed ratio. The ethoxyethyl and acetyl groups of the obtained copolymers were completely removed under acidic and basic conditions, respectively, to afford poly(4‐hydroxystyrene)s having ketone moieties in the main chain. The molecular weights of these copolymers decreased under photoirradiation due to the Norrish‐type reactions of the ketone groups distributed in the main chain. These results demonstrate that poly(4‐hydroxystyrene)s having ketone groups in the main chain possess good photo‐scissibility. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Green Nanocomposites from Renewable Resources: Biodegradable Plant Oil‐Silica Hybrid Coatings

Green nanocomposite coatings based on renewable plant oils have been developed. An acid‐catalyzed curing of epoxidized plant oils with 3‐glycidoxypropyltrimethoxysilane produced transparent nanocomposites. The hardness and mechanical strength improved by incorporating the silica network into the organic polymer matrix, and good flexibility was observed in the nanocomposite. The nanocomposites showed high biodegradability.

     

Facile Synthesis of Thiol‐Functionalized Long‐Chain Highly Branched ROMP Polymers and Surface‐Decorated with Gold Nanoparticles

The synthesis of thiol‐functionalized long‐chain highly branched polymers (LCHBPs) has been accomplished in combination of ring‐opening metathesis polymerization (ROMP) and thiol‐Michael addition click reaction. A monotelechelic polymer with a terminal acrylate and many pendent thiol groups is first prepared through adding an internal cis‐olefin terminating agent to the reaction mixture immediately after the completion of the living ROMP, and then utilized as an AB_n‐type macromonomer in subsequent thiol‐ene reaction between acrylate and thiol, yielding LCHBPs as the reaction time prolonged. Au nanoparticles are then covalently conjugated onto the surface of thiol‐functionalized LCHBP to fabricate novel hybrid nanostructures, which is shown as one interesting application of such functionalized metathesis polymers. This facile approach can be extended toward the fabrication of novel nanomaterials with sophisticated structures and tunable multifunctionalities.

     

Preparation of poly(propylene‐co‐γ‐butyrolactone carbonate) and release profiles of drug‐loaded microcapsules

A new aliphatic poly(propylene‐co‐γ‐butyrolactone carbonate) (PPCG) was successfully synthesized through the copolymerization of carbon dioxide, propylene oxide (PO), and γ‐butyrolactone (GBL). GBL was inserted into the backbone of PO–CO₂. The glass transition of PPCG was as high as 16 °C, far higher than that (?1.5 °C) of poly(propylene carbonate) (PPC). The decomposition temperatures of PPCG and PPC were only slightly different. Because of the existence of the GBL ester unit, PPCG had stronger degradability than PPC in a pH 7.4 phosphate‐buffered solution. However, when the PO/GBL ratio increased beyond 5:2, the excessive amount of GBL was not added to the polymerization. PPCG and PPC microcapsules were prepared by the water‐in‐oil‐in‐water multiple‐emulsion method. Glucose was encapsulated. The PPCG microcapsules, about 2 μm in diameter, had smooth and spherical surfaces. The glucose release test revealed that the glucose release speed of the PPCG–glucose microcapsules was more than eight times faster than that of the PPC–glucose microcapsules in a pH 7.4 phosphate‐buffered solution. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2468–2475, 2005     

Long‐wavelength‐absorbing dialkylphenacylsulfonium salt photoinitiators: Synthesis and photoinduced cationic polymerization

A series of sulfonium salt photoinitiators with the general structure Ar′S⁺CH₃(C₁₂H₂₅)SbF, where Ar′ is phenacyl (I), 2‐indanonyl (II), 4‐methoxyphenacyl (III), 2‐naphthoylmethyl (IV), 1‐anthroylmethyl (V), or 1‐pyrenoylmethyl (VI), were prepared with a novel, simple one‐pot process that involves the reaction of an α‐bromoalkylarylketone (Ar′Br) with the dialkylsulfide (CH₃SC₁₂H₂₅) in the presence of sodium hexafluroantimonate in 2‐butanone at room temperature. The photoreactivity of photoinitiators II–VI were evaluated and compared to the unsubstituted analogue, I, in the polymerization of a variety of epoxide monomers. Real‐time infrared spectroscopy and differential scanning photocalorimetry studies revealed that the indanonyl initiator II is more active than I. However, sulfonium salts IV–VI, which contain polycyclic aromatic structures, are much less effective as cationic photoinitiators. Interestingly, photoinitiator III is either more or less reactive compared to I, depending on the monomer used. Our work also showed that the efficiency of the unsubstituted phenacylsulfonium salt I can be significantly enhanced through the use of photosensitizers. Mechanistic aspects of the photopolymerization studies are discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1433–1442, 2000     

Rapid Ring‐Opening Polymerization of D,L‐Lactide by Microwaves

Summary: Poly(D ,L ‐lactide) with a molar mass of 10⁵ g · mol⁻¹ and a yield over 90% was produced in 10 min by the ring‐opening polymerization of D ,L ‐lactide under microwave irradiation with forward power of 255 W. A degradation of the poly(D ,L ‐lactide) was also induced by microwaves with a power level over 340 W. The molar mass of poly(D ,L ‐lactide) was dependent upon the competition between the polymerization of D ,L ‐lactide and the degradation of the resulting polymer.

Profiles of molar mass versus microwave irradiation time (1.8 g DLLA, 0.1% Sn(Oct)₂).     

Cationic addition polymerization of 1,4‐dioxene using gacl3 as lewis acid catalyst: Long‐lived species‐mediated polymerization

Effective cationic addition polymerization of 1,4‐dioxene, a six‐membered cyclic olefin with two oxygen atoms adjacent to the double bond, was performed using a simple metal halide catalyst system in dichloromethane. The polymerization was controlled when the reaction was conducted using GaCl₃ in conjunction with an isobutyl vinyl ether–HCl adduct as a cationogen at –78°C to give polymers with predetermined molecular weights and relatively narrow molecular weight distributions. The long‐lived properties of the propagating species were further confirmed by a monomer addition experiment and the analyses of the product polymers by ¹H NMR and MALDI–TOF–MS. Although highly clean propagation proceeded, the apparent rate constant changed during the controlled cationic polymerization of 1,4‐dioxene. The reason for the change was discussed based on polymerization results under various conditions. The obtained poly(1,4‐dioxene) exhibited a very high glass transition temperature (T_g) of 217°C and unique solubility. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Formulation of Environmentally Safe Graffiti Remover Containing Esterified Plant Oils and Sugar Surfactant

The removal of graffiti or over-painting requires special attention in order to not induce the surface destruction but to also address all of the important eco-compatibility concerns. Because of the necessity to avoid the use of volatile and toxic petroleum-based solvents that are common in cleaning formulations, much attention has recently been paid to the design of a variety of sustainable formulations that are based on biodegradable raw materials. In the present contribution we propose a new approach to graffiti cleaning formulations that are composed of newly synthesized green solvents such as esterified plant oils, i.e., rapeseed oil (RO), sunflower oil (SO), or used cooking oil (UCO), ethyl lactate (EL), and alkylpolyglucosides (APGs) as surfactants. Oil PEG-8 ester solvents were synthesized through the direct esterification/transesterification of these oils using monobutyltin(IV) tris(2-ethylhexanoate) and titanium(IV) butoxide catalysts under mild process conditions. The most efficient formulations, determined by optimization through the response surface methodology (RSM) was more effective in comparison to the reference solvents such as the so-called Nitro solvent (denoting a mixture of toluene and acetone) and petroleum ether. Additionally, the optimal product was found to be effective in removing graffiti from glass, metal, or sandstone surfaces under open-field conditions in the city of Wrocław. The performed studies could be an invaluable tool for developing future green formulations for graffiti removal.     

Controlled Cationic Polymerization of 1‐Methoxy‐1,3‐Butadiene: Long‐Lived Species‐Mediated Reaction and Control over Microstructure with Weak Lewis Bases

Controlled cationic polymerization of trans‐1‐methoxy‐1,3‐butadiene was achieved through the design of appropriate initiating systems, yielding soluble polymers with controllable molecular weights. The combined use of SnCl₄ or GaCl₃ as a Lewis acid catalyst and a weak Lewis base in conjunction with HCl as a protonogen resulted in efficient and controlled polymerization. The M_n values of the product polymers increased linearly along the theoretical line, which indicates that intermolecular crosslinking reactions negligibly occurred. In addition, the polymer microstructure was critically dependent on the weak Lewis base employed. In particular, the use of tetrahydrofuran as an additive resulted in the highest 4,1/4,3‐structure ratio (96/4). Weak Lewis bases also affected the polymerization rates but exhibited unique trends that differed from their effects on the cationic polymerization of alkyl vinyl ethers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 288–296     

Effect of Fatty Acid Polyunsaturation on Synthesis and Properties of Emulsion Polymers Based on Plant Oil-Based Acrylic Monomers

This study demonstrated that polymerization behavior of plant oil-based acrylic monomers (POBMs) synthesized in one-step transesterification reaction from naturally rich in oleic acid olive, canola, and high-oleic soybean oils is associated with a varying mass fraction of polyunsaturated fatty acid fragments (linoleic (C18:2) and linolenic (C18:3) acid esters) in plant oil. Using miniemulsion polymerization, a range of stable copolymer latexes was synthesized from 60 wt.% of each POBM and styrene to determine the impact of POBM chemical composition (polyunsaturation) on thermal and mechanical properties of the resulted polymeric materials. The unique composition of each plant oil serves as an experimental tool to determine the effect of polyunsaturated fatty acid fragments on POBM polymerization behavior and thermomechanical properties of crosslinked films made from POBM-based latexes. The obtained results show that increasing polyunsaturation in the copolymers results in an enhanced crosslink density of the latex polymer network which essentially impacts the mechanical properties of the films (both Young’s modulus and toughness). Maximum toughness was observed for crosslinked latex films made from 50 wt.% of each POBM in the monomer feed.     

Ultrasonic Decomposition of Ammonia‐Nitrogen and Organic Compounds in Coke Plant Wastewater

The investigations of the ultrasonic decomposition of NH₃‐N and organic compounds (i.e., COD_Cr) in coke plant wastewater are presented in this work. The process parameters were controlled with respect to the presence (or absence) of air atmosphere, initial pH value, initial concentration, and ultrasonic power density in the process of ultrasonic decomposition. It is noted that the ultrasonic removal efficiencies for both the NH₃‐N and the COD_Cr were increased in the presence of the air atmosphere and significantly affected by the initial pH value. The removal efficiencies increased with increasing the ultrasonic power density while they decreased with increasing the initial concentration. The effects of n‐butyl alcohol as an effective OH radical scavenger on the removal efficiencies indicates that the ultrasonic decomposition of the NH₃‐N was carried out mainly via the mechanism of thermal decomposition in cavitation bubbles or in the interfacial region, whereas the ultrasonic decomposition of the COD_Cr mainly resulted from the reactions with OH radicals in the bulk solution. The GC/MS analysis indicates that most of the organic compounds in the wastewater were effectively destroyed by ultrasound.