Polymerization Of Cyclic Ketene Acetals Research Articles

Radical Ring Opening Polymerization of Cyclic Ketene Acetals Derived From d-Glucal.

A cyclic ketene acetal (CKA) derived from d-glucal was synthesized, and its polymerization using free radicals has been investigated. NMR analysis of the resulting polymers revealed the formation of polyacetal-polyester copolymers, with up to 78% of ester linkages formed by radical ring-opening polymerization (rROP). Conversely, the polymerization of the monomer-saturated analogue only produced acetal linkages, demonstrating that the alkene functionality within the d-glucal pyranose ring is essential to promote ring-opening and ester formation, likely via the stabilization of an allyl radical. The thermal properties of the polymers were linked to the ratio of the ester and acetal linkages. Copolymerization with methyl methacrylate (MMA) afforded statistically PMMA-rich copolymers (66-98%) with linkages prone to hydrolytic degradation and decreased glass-transition temperatures. The retention of the pseudoglucal alkene function offers opportunities to functionalize further these bioderived (co)polymers.

A Mechanistic Study on the Hydrolysis of Cyclic Ketene Acetal (CKA) and Proof of Concept of Polymerization in Water

AbstractThe present work systematically investigates the hydrolysis mechanism of cyclic ketene acetal (CKA) monomers in detail and explores polymerization in water under organic solvent‐free and surfactant‐free conditions. To understand the effect of CKA structure on hydrolysis, the ring size of the monomers is varied from 5–8‐membered rings systematically and hydrolysis experiments are performed. In all cases, hydrolysis yields monoacetylated diol products. Deuterium and 17O‐isotopic labeled experiments are carried out for 5‐ and 7‐membered‐(2‐methylene‐1,3‐dioxepane, MDO) CKAs to understand the reaction pathway. The experimental analysis from the reaction of CKA with water revealed that the increasing hydrophobicity from 5–8‐membered rings and the pH of the reaction medium play important roles in the order of reactivity. Density functional theory (DFT) and experimental studies demonstrated that basic reaction conditions have some control over the hydrolysis rate of CKA. Despite this progress, achieving controlled polymerization of CKA in water while suppressing hydrolysis remains challenge. Only up to 3 mol% CKA incorporation is attained in polyacrylate and polyacrylamide backbone via radical ring‐opening polymerization (rROP) of MDO and 8‐membered CKAs with 2‐hydroxyethyl acrylate (HEA) and acrylamide (AAm) in water. The results serve a proof of concept for advancing aqueous copolymerizations using CKA monomers.

Current Standing on Radical Ring-Opening Polymerizations of Cyclic Ketene Acetals as Homopolymers and Copolymers with one another.

Radical Ring-opening polymerization (RROP) of cyclic ketene acetals (CKAs) emerges to be a valuable polymerization technique. In attracting more attention, RROP has seen a new spike in publications, which the authors will put into perspective. This review will hence address the progress made on the number of available CKAs and the synthetic strategies to get them. In grouping, the available monomers into distinct categories, the enormous variety of available CKAs will be highlighted. Polymerizations of CKAs without vinylenes have the potential to yield fully biodegradable polymers, which is why this kind of polymerization is the focus of this review. Detailing the current understanding of the mechanism, the various side reactions will be noted and also their effect on the overall properties of the final polymers. Current attempts to control the ring-retaining and branching reactions will be discussed as well. In addition to the polymerization itself, the available materials will be discussed as well as homopolymers, copolymers of CKAs, and block-copolymers with pure CKA-blocks have significantly widened the range of possible applications of materials from RROP. Altogether this review highlights the progress in the entire field of RROP just of CKAs to give a holistic overview of the field.

Branched polyesters from radical ring-opening polymerization of cyclic ketene acetals: synthesis, chemical hydrolysis and biodegradation

A new synthetic route to the cyclic ketene acetal, 2-methylene-4-methyl-1,3-dioxepane (Me-MDO) is reported. The introduction of side-groups to the polyester affects its degradability.

Vinyl copolymers with faster hydrolytic degradation than aliphatic polyesters and tunable upper critical solution temperatures

Vinyl polymers are the focus of intensive research due to their ease of synthesis and the possibility of making well-defined, functional materials. However, their non-degradability leads to environmental problems and limits their use in biomedical applications, allowing aliphatic polyesters to still be considered as the gold standards. Radical ring-opening polymerization of cyclic ketene acetals is considered the most promising approach to impart degradability to vinyl polymers. However, these materials still exhibit poor hydrolytic degradation and thus cannot yet compete with traditional polyesters. Here we show that a simple copolymerization system based on acrylamide and cyclic ketene acetals leads to well-defined and cytocompatible copolymers with faster hydrolytic degradation than that of polylactide and poly(lactide-co-glycolide). Moreover, by changing the nature of the cyclic ketene acetal, the copolymers can be either water-soluble or can exhibit tunable upper critical solution temperatures relevant for mild hyperthermia-triggered drug release. Amphiphilic diblock copolymers deriving from this system can also be formulated into degradable, thermosensitive nanoparticles by an all-water nanoprecipitation process.

Mechanistic investigation of cyclic ketene acetal radical ring-opening homo- and co-polymerization and preparation of PEO graft copolymers with tunable composition

Radical ring-opening polymerization of cyclic ketene acetals (CKAs) led to homogeneous ester insertion during semi-batch reactions with N-vinyl pyrrolidone (NVP). Investigation of CKA radical transfer allowed for CKA–NVP graft copolymer preparation.

Reversible-deactivation radical polymerization of cyclic ketene acetals

This review discusses the history of reversible-deactivation radical ring-opening polymerization of cyclic ketene acetals, focusing on the preparation of degradable complex polymeric architectures.

DFT-calculation-assisted prediction of the copolymerization between cyclic ketene acetals and traditional vinyl monomers

The ring-opening polymerization of cyclic ketene acetals (CKAs) and vinyl monomers is an elegant method to produce degradable copolymers. Owing to DFT calculations, we are now able to better understand the reactivity of CKAs & common vinyl monomers.

Alternating Radical Ring-Opening Polymerization of Cyclic Ketene Acetals: Access to Tunable and Functional Polyester Copolymers

Radical ring-opening polymerization of cyclic ketene acetals (CKAs) provides a route to synthesize degradable polyesters or to impart degradability onto traditionally nondegradable vinyl polymers under the mild conditions afforded by radical polymerization. Copolymerization of CKAs with vinyl monomers is a promising strategy to prepare functional degradable polymers. However, such copolymerizations often result in poor incorporation of the ester moiety due to low relative reactivity of CKAs and the propensity to polymerize through the exomethylene bond via 1,2-addition, without ring-opening to the ester moiety. We demonstrate that the copolymerization of 5,6-benzo-2-methylene-1,3-dioxepane (BMDO) with a variety of maleimides proceeds in a highly alternating fashion with quantitative ring-opening of BMDO to the ester, producing alternating polyester copolymers. Modifying the N-substituent of the maleimide provided a straightforward route to tuning the thermal properties of the polymers and introducing func...

New Chemistry in Functional Aliphatic Polyesters

Aliphatic polyesters are important biodegradable polymers with wide applications. Polyesters prepared by ring-opening polymerization often have a limited range of properties, because of the minimal functional diversity of available lactone monomers. In this review, synthetic strategies in preparing functional lactone monomers are highlighted, as well as recent controlled polymerization strategies to synthesize functional aliphatic polyesters, which include proton-transfer polymerization, ring opening polymerization of O-carboxyanhydrides, radical ring-opening polymerization of cyclic ketene acetals, and copolymerization of epoxide/anhydride.

Elucidation of a side reaction occurring during nitroxide-mediated polymerization of cyclic ketene acetals by tandem mass spectrometric end-group analysis of aliphatic polyesters.

In order to prevent side reactions while developing new polymerization processes, their mechanism has to be understood and one first key insight is the structure of the end-groups in polymeric by-products. The synthetic method scrutinized here is the nitroxide-mediated polymerization (NMP) of a cyclic ketene acetal, a promising alternative process to the production of polyesters. Polymer end-group characterization was performed by mass spectrometry (MS), combining elemental composition information derived from accurate mass data in the MS mode with fragmentation features recorded in the MS/MS mode. Electrospray was used as the ionization method to ensure the integrity of original chain terminations and a quadrupole time-of-flight (QTOF) instrument was employed for high-resolution mass measurements in both MS and tandem mass spectrometry (MS/MS) modes. Occurrence of side reactions in the studied polymerization method, first evidenced by an unusual increase in dispersity with conversion, was confirmed in MS with the detection of two polymeric impurities in addition to the expected species. Fragmentation rules were first established for this new polyester family in order to derive useful structural information from MS/MS data. In addition to a usual NMP by-product, the initiating group of the second polymeric impurities revealed the degradation of the nitroxide moiety. Unambiguous MS/MS identification of end-groups in by-products sampled from the polymerization medium allowed an unusual side reaction to be identified during the NMP preparation of polyesters. On-going optimization of the polymerization method aims at preventing this undesired process.

Scope and limitations of the nitroxide-mediated radical ring-opening polymerization of cyclic ketene acetals

The ring-opening polymerization of cyclic ketene acetals (CKAs) by controlled radical mechanisms represents an alternative route for the synthesis of aliphatic polyesters. For the first time, 5,6-benzo-2-methylene-1,3-dioxepane (BMDO) and 2-methylene-4-phenyl-1,3-dioxolane (MPDL) were homopolymerized by nitroxide mediated polymerization (NMP), from the commercially available SG1-based BlocBuilder MA alkoxyamine. Various experimental conditions (i.e., reaction temperature, nature of solvent, and nature of the alkyl initiating radical) were varied to determine the optimized conditions in terms of polymerization kinetics and living character of the final polymer. Chain-end extensions from either PS-SG1 or PBMDO-SG1 were also performed in order to furnish PS-b-PBMDO and PBMDO-b-PS, respectively, thus demonstrating the synthesis of block copolymers comprising a CKA block. In order to have a better insight into the polymerization mechanism, the occurrence of side reactions was analyzed by 31P NMR spectroscopy and ESI-MS. It was supposed that the ketal-based macroradical could be irreversibly trapped by nitroxide and thus the corresponding macroalkoxyamine decomposed by CO–N bond dissociation. DFT calculations as well as PREDICI modeling were also undertaken in order to support this hypothesis.

Chemistry, chances and limitations of the radical ring-opening polymerization of cyclic ketene acetals for the synthesis of degradable polyesters

This article highlights the progress in the field of radical ring-opening polymerization (RROP) of cyclic ketene acetals for the synthesis of functionalised polyesters, (bio)degradable vinyl polymers, and speciality designed degradable polymers. The method of radical ring-opening polymerization offers the advantage in either making special functional polyesters which are not possible by conventional methods or for making polyesters for special applications where low volume shrinkage is of utmost importance. Furthermore, the beauty of radical ring-opening polymerization is in making a new class of degradable materials called poly(vinyl-co-ester)s. Having ester linkages distributed onto the vinyl polymer backbone is emphasised, no other method can combine vinyl polymer backbone with ester units in a random way. The method has opened new opportunities of using the known biomaterials for degradable applications. Other possibilities and challenges in using this method are making specialised degradable materials like ionomers and polymeric-inorganic hybrid materials, which are also discussed in detail.

Mapping the characteristics of the radical ring‐opening polymerization of a cyclic ketene acetal towards the creation of a functionalized polyester

AbstractRadical ring‐opening polymerization of cyclic ketene acetals is a means to achieve novel types of aliphatic polyesters. 2‐methylene‐1,3‐dioxe‐5‐pene is a seven‐membered cyclic ketene acetal containing an unsaturation in the 5‐position in the ring structure. The double bond functionality enables further reactions subsequent to polymerization. The monomer 2‐methylene‐1,3‐dioxe‐5‐pene was synthesized and polymerized in bulk by free radical polymerization at different temperatures, to determine the structure of the products and propose a reaction mechanism. The reaction mechanism is dependent on the reaction temperature. At higher temperatures, ring‐opening takes place to a great extent followed by a new cyclization process to form the stable five‐membered cyclic ester 3‐vinyl‐1,4‐butyrolactone as the main reaction product. Thereby, propagation is suppressed and only small amounts of other oligomeric products are formed. At lower temperatures, the cyclic ester formation is reduced and oligomeric products containing both ring‐opened and ring‐retained repeating units are produced at higher yield. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4587–4601, 2009

Biodegradability of Poly(ester‐ether) and Poly(ester) Obtained from a Radical Ring‐Opening Polymerization of Cyclic Ketene Acetals

2‐Methylene‐1,3,6‐trioxocane (MTC) and 2‐methylene‐1,3‐dioxepane (MD) were synthesized and polymerized via ring‐opening in the presence of a radical initiator. The obtained poly(ester‐ether) (PMTC) and poly(ester) (PMD) were found to be enzymatically degradable by total organic carbon (TOC) analysis using lipase. The enzymatic degradability of PMTC was higher than that of PMD. PMTC and PMD were also found to be biodegradable with a biological oxygen demand (BOD)‐tester using soil. The degradability of PMTC using soil was also higher than that of PMD. The higher degradability of PMTC by enzyme and soil are thought to be due to its higher hydrophilicity.

Cationic polymerization of cyclic ketene acetals via zwitterion formation with cyanoallene

Cationic polymerization of cyclic ketene acetals via zwitterion formation with cyanoallene

Cationic polymerization of cyclic ketene acetals via zwitterion formation with cyanoallene

This article deals with the polymerization of the cyclic ketene acetals (CKAs) 2-methylene-4-phenyl-1,3-dioxolane (2), 2-methylene-4-phenyl-1,3-dioxane (3), 4,7-dimethyl-2-methylene-1,3-dioxepane (4), 2-ethylidene-4-phenyl-1,3-dioxolane (5), 2-phenylmethylene-1,3-dioxolane (6), and 2-isopropylidene-4-phenyl-1,3-dioxolane (7) in the presence of cyanoallene (1). For 2 and 3, the homopolymerization of the CKAs proceeded without ring opening, and the number-average molecular weights of the obtained polymers depended on the feed ratio of 1. However, the reactions of 1 with 4–7 afforded no polymers but did afford spirocyclic 1 : 1 adducts possessing cyclobutane rings. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2075–2081, 2000

Cationic 1,2-vinyl addition polymerization of cyclic ketene acetals initiated by conventional acids

Pure 1,2-addition polymers, poly(2-methylene-1,3-dioxolane), 1b, poly(2-methylene-1,3-dioxane), 2b, and poly(2-methylene-5,5-dimethyl-1,3-dioxane), 3b, were prepared using the cationic initiators H2SO4, TiCl4, BF3, and also Ru(PPh3)3Cl2. Small ester carbonyl bands in the IR spectra of 1b and 2b were observed when the polymerizations were performed at 80°C (1b) and both 67 and 138°C (2b) using Ru(PPh3)3Cl2. The poly(cyclic ketene acetals) were stable if they were not exposed to acid and water. They were quite thermally stable and did not decompose until 290°C (1b), 240°C (2b), and 294°C (3b). Different chemical shifts for axial and equatorial H and CH3 on the ketal rings were found in the 1H NMR spectrum of 3b at room temperature. High molecular weight 3b (M̄n = 8.68 × 104, M̄w = 1.31 × 105, M̄z = 1.57 × 105) was obtained upon cationic initiation by H2SO4. Poly(2-methylene-1,3-dioxane), 2b, underwent partial hydrolysis when Ru(PPh3)3Cl2 and water were present in the polymer. The hydrolyzed products were 1,3-propanediol and a polymer containing both poly(2-methylene-1,3-dioxane) and polyketene units. The percentages of these two units in the hydrolyzed polymer were about 32% polyketene and 68% poly(2-methylene-1,3-dioxane). No crosslinked or aromatic structures were observed in the hydrolyzed products. The molecular weight of hydrolyzed polymer was M̄n = 5740, M̄w = 7260, and M̄z = 9060. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3707–3716, 1997

Cationic 1,2‐vinyl addition polymerization of cyclic ketene acetals initiated by conventional acids

Cationic 1,2‐vinyl addition polymerization of cyclic ketene acetals initiated by conventional acids

Ring opening during the cationic polymerization of 2-methylene-1,3-dioxepane: Cyclic ketene acetal initiation with sulfuric acid supported on carbon

The stable cyclic ketene acetal, 2-methylene-1,3-dioxepane, 7, has been polymerized cationically in pentane, CH 2 Cl 2 and THF at 25°C to form a polymer which is composed of both ring-opened (40-50% ) and ring-retained (50-60%) structures-Initiation was catalyzed by using H 2 SO 4 -supported on activated carbon black. This unique outcome differs significantly from the cationic polymerization of several other five- and six-membered ring cyclic ketene acetals which gave 100% 1,2-vinylpolymerization under these conditions. As the polymerization temperature increased in cationic polymerization of 7 the ring-opened content increased and the molecular weight of the polymers decreased in such solvents as cyclohexane, 1,2-dichloroethane, dimethoxyethane, and bis-(2-methoxyethyl) ether. The mechanism of this polymerization is discussed. This research also illustrated the ability to initiate the cationic polymerization of cyclic ketene acetals by acidified carbon black while avoiding subsequent polymer decomposition.