Molecular modelling of ring‐opening polymerisation of lactamimide‐containing macrocyclic esters

The molecular modelling of anionic (MeO^– initiated) and cationic (H⁺ initiated) polymerisation of lactamimide‐containing macrocyclic esters has been carried out at PM3 and HF/3‐21G levels of theory. It was found that it is strain release that drives the polymerisation of these macrocycles. Most likely that entropy gain on the ring‐opening can not compensate entropy loss on polymer formation due to the relative rigidity of cyclic molecules. Methanolate initiated anionic polymerisation will not lead to high molecular weight product due to the side reactions involving the attack of growing anionic species at carbonyls of lactamimide moiety, while the cationic polymerisation should proceed smoothly provided that polymerisation temperature is less than ceiling temperature.     

Computational evaluation of radical ring‐opening polymerization

The tendencies of ring‐opening processes in radical ring‐opening polymerizations were evaluated by AM1 and PM3 semi‐empirical calculations and 6‐31G*‐level calculations based on the density functional theory (DFT) B3LYP models. Sixteen cyclic monomers bearing vinyl or exomethylene groups were categorized into ring‐opening and no‐ring‐opening monomers by the evaluation of the differences of the internal energies and the lengths of the cleaving bonds between the ground states of the initial radicals and the activated states in the ring‐opening processes. Although the semi‐empirical calculations not parameterized to radical reactions resulted in the moderate categorization of the ring‐opening monomers, the DFT calculation clearly distinguished the ring‐opening and no‐ring‐opening monomers. The ring‐opening tendencies were also evaluated with the changes in the internal energies throughout the ring‐opening processes, but this method could not group the ring‐opening and no‐ring‐opening monomers clearly. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2827–2834, 2007     

Synthesis and Controlled Polymerisation of a Novel Gramicidin S Analogue

Summary: The controlled polymerisation of a bulky, peptide‐based monomer was investigated. The cyclic β‐sheet forming decapeptide gramicidin S was modified with a methacrylate handle and subsequently polymerised via atom transfer radical polymerisation (ATRP), to yield a well‐defined gramicidin‐S‐containing polymer. The secondary structure of the peptide moiety was retained within the resulting polymer, as indicated by IR spectroscopy. This is the first example of the use of ATRP to create a synthetic polymer with a cyclic peptide as a side chain.

The gramicidin S based monomers synthesised here were then polymerised by ATRP.     

Polylactides with aldaric ester end groups or chain extending groups

The synthesis and characterisation of a series of poly(S,S-lactides) and poly(RR/SS-lactides) end capped or chain extended with aldaric ester groups are described. The aldaric esters are prepared from acetyl protected d-gluconolactone, d-galactonolactone and d-mannonolactone by ring opening with butanol or 1,4-butanediol, under acidic conditions. The aldaric esters are fully characterised, including by NMR spectroscopy and mass spectrometry. They are used as co-initiators, with an ethylzinc complex, to enable the controlled ring opening polymerisation of S,S- and rac-lactide. Thus, a series of polylactides are produced with various carbohydrate chain end or extending groups and are fully characterised, including by NMR spectroscopy and gel permeation chromatography (GPC). The polymerisation kinetics are examined, under pseudo first order conditions, and indicate that chain transfer reactions are occurring more rapidly than propagation reactions. The degradation kinetics of the polylactides are examined under acidic conditions; the aldaric esters increase the degradation rates compared to unfunctionalised end groups.     

Visible‐Light‐Driven MADIX Polymerisation via a Reusable,Low‐Cost,and Non‐Toxic Bismuth Oxide Photocatalyst

The continuous amalgamation of photocatalysis into existing reversible deactivation radical polymerisation (RDRP) processes has initiated a rapidly propagating area of polymer research in recent years. We introduce bismuth oxide (Bi₂O₃) as a heterogeneous photocatalyst for polymerisations, operating at room temperature with visible light. We demonstrate formidable control over degenerative chain‐transfer polymerisations, such as macromolecular design by interchange of xanthate (MADIX) and reversible addition‐fragmentation chain‐transfer (RAFT) polymerisation. We achieved narrow molecular weight distributions and attribute the excellent temporal control of a photo‐induced electron transfer (PET) process. This methodology was employed to synthesise diblock copolymers combining differently activated monomers. The Bi₂O₃ catalyst system has the additional benefits of low toxicity, reusability, low‐cost, and ease of removal from the reaction mixture.     

Insights into post‐polymerisation modification of bio‐based unsaturated itaconate and fumarate polyesters via aza‐michael addition: Understanding the effects of CC isomerisation

Development of renewable bio‐based unsaturated polyesters is undergoing a renaissance, typified by the use of itaconate and fumarate monomers. The electron‐deficient CC bond found on the corresponding polyesters allows convenient post‐polymerisation modification to give a wide range of polymer properties; this is notably effective for the addition of nucleophilic pendants. However, preservation of unsaturated functionality is blighted by two undesirable side‐reactions, branching/crosslinking and CC isomerisation. Herein, a tentative kinetic study of diethylamine addition to model itaconate and fumarate diesters highlights the significance of undesirable CC isomerisation. In particular, it shows that reversible isomerisation from itaconate to mesaconate (a poor Michael acceptor) is in direct competition with aza‐Michael addition, where the amine Michael donor acts as an isomerisation catalyst. We postulate that undesired formation of mesaconate is responsible for the long reaction times previously reported for itaconate polyester post‐polymerisation modification. This study illustrates the pressing need to overcome this issue of CC isomerisation to enhance post‐polymerisation modification of bio‐based unsaturated polyesters. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1935–1945     

Polymerisation of cyclic monomers, 8. Synthesis and radical polymerisation of hybrid 2‐vinylcyclopropanes

Hybrid 2‐vinylcyclopropanes were synthesised by the esterification of 1‐methoxycarbonyl‐2‐vinylcyclopropane‐1‐carboxylic acid with hydroxy group containing (meth)acrylates in the presence of 1,3‐dicyclohexylcarbodiimide (DCC). The structure of the new hybrid monomers was confirmed by elemental analysis, IR, ¹H NMR and ¹³C NMR spectroscopy. The radical polymerisation of the hybrid monomers in bulk with 2,2'‐azoisobutyronitrile (AIBN) results in transparent cross‐linked polymers, whereas solution polymerisation partially results in soluble polymers with pendant 2‐vinylcyclopropyl groups.     

Development of Amino–Oxazoline and Amino–Thiazoline Organic Catalysts for the Ring‐Opening Polymerisation of Lactide

The ring‐opening polymerisation of lactide by a range of amino–oxazoline and amino–thiazoline catalysts is reported. The more electron‐rich derivatives are demonstrated to be the most highly active and polymerisation is well controlled, as evidenced by the linear relationship between the molecular weight and both the monomer conversion and the monomer‐to‐initiator ratio. Mechanistic studies reveal significant interactions between the monomer, initiator and catalyst and that the polymerisation is first order with respect to each of these components. These observations indicate that the polymerisation operates by a general base/pseudo‐anionic mechanism.     

Steric Constraints Induced Frustrated Growth of Supramolecular Nanorods in Water

A unique example of supramolecular polymerisation in water based on monomers with nanomolar affinities, which yield rod‐like materials with extraordinarily high thermodynamic stability, yet of finite length, is reported. A small library of charge‐neutral dendritic peptide amphiphiles was prepared, with a branched nonaphenylalanine‐based core that was conjugated to hydrophilic dendrons of variable steric demand. Below a critical size of the dendron, the monomers assemble into nanorod‐like polymers, whereas for larger dendritic side chains frustrated growth into near isotropic particles is observed. The supramolecular morphologies observed by electron microscopy, X‐ray scattering and diffusion NMR spectroscopy studies are in agreement with the mechanistic insights obtained from fitting polymerisation profiles: non‐cooperative isodesmic growth leads to degrees of polymerisation that match the experimentally determined nanorod contour lengths of close to 70 nm. The reported designs for aqueous self‐assembly into well‐defined anisotropic particles has promising potential for biomedical applications and the development of functional supramolecular biomaterials, with emerging evidence that anisotropic shapes in carrier design outperform conventional isotropic materials for targeted imaging and therapy.     

Synthesis of epoxy monomers that undergo synergistic photopolymerization by a radical‐induced cationic mechanism

A series of novel, cycloaliphatic, cationically photopolymerizable epoxide monomers bearing benzyl ether groups were prepared. These monomers display a considerable enhancement in the rate of their cationic ring‐opening polymerizations in comparison with monomers that do not contain such groups. In this article, a synergistic free‐radical mechanism is proposed that accounts for this effect, and supporting evidence is offered for its verification. During UV irradiation of an onium salt cationic photoinitiator, the aryl radicals that are generated abstract labile benzyl hydrogens present in such monomers to generate the corresponding carbon‐centered radicals. Subsequently, these radicals are oxidized to benzyl carbocations by the onium salt via a nonphotochemical chain process. The observed increase in the rate and extent of the cationic ring‐opening polymerization of the epoxide monomers is due to the aforementioned mechanism, which effectively increases the number of reactive cationic species present during polymerization. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3578–3592, 2001     

Calorimetric study of photopolymerisation of divinyl monomers

Isothermal differential scanning calorimetry (photocalorimetry) enables real‐time measurements of rates of polymerisation as functions of irradiation time to be made. Since it is possible to stop initiation at any point in a reaction (by cutting off the light) and to monitor the dark reaction, this method has been widely used for determinations of the (apparent) rate constants of polymerisation of multifunctional monomers at various degrees of double bond conversion. The work reported here presents the results of photocalorimetric studies of polymerisation kinetics of six related acrylates and methacrylates. Two main topics are discussed: the effects of sulphide and ether groups present in the monomers on network formation, and the determination of polymerisation rate constants according to three termination models (monomolecular, bimolecular and mixed).     

Switching the mechanism of polymerisation from vinyl addition to metathesis using single‐site catalysts

Titanium/methylaluminoxane‐based catalyst systems polymerising norbornene by vinyl addition were modified to initiate ring‐opening metathesis polymerisation by interrupting the course of polymerisation with phenylacetylene. The products showed nearly 30% ring‐opened structures according to their ¹H NMR spectra. The change in mechanism of polymerisation after the addition of the reactivity transfer reagent is seen from the kinetic data.     

Ring‐opening polycondensations

Ring‐opening polycondensation is a novel synthetic strategy using heterocycles of any ring size having two reactive bonds as bifunctional monomers in step‐growth polymerizations. The first part of this article reviews previous publications. The previous studies mainly dealt with syntheses of polyesters from tin‐containing macrocycles including cyclic polylactones. These tin‐containing cyclic oligomers or polymers were easily obtained in two ways, either by ring‐closing polycondensation of dibutyltin compounds with preformed diols or by ring‐expansion polymerizations of lactones by means of cyclic tin‐initiators. The second part of this article presents new results which deal with ring‐opening polycondensations of silicon containing macrocycles derived from oligo(ethylene glycol)s. In these cases the chain growth proceeds by elimination of dimethyl dichlorosilane. In addition to syntheses of homopolyesters, copolycondensations with silylated or stanylenated monomers were studied. Finally, the thermodynamical aspects of ring‐opening polycondensations will be discussed.     

Effects of monomer structure on the morphology of polymer networks and the electro-optical properties of polymer-dispersed liquid crystal films

Polymer-dispersed liquid crystal (PDLC) films were prepared by photochemical polymerisation with a series of (meth)acrylate monomers. The effects of monomer structure on the morphology of polymer networks in the PDLC films were studied. The acrylate monomers without sidegroup chain formed uniform polymer networks. The methacrylate monomers with methyl as their sidegroup chains formed lace-like networks. The size of the LC droplets increased with increasing the length of the flexible chain of both methacrylate and acrylate monomers. Meanwhile, the effects of the morphology of the polymer network on the electro-optical properties of PDLC films were also investigated.     

Polyethylene with Reverse Co‐monomer Incorporation: From an Industrial Serendipitous Discovery to Fundamental Understanding

A triethylaluminium(TEAl)‐modified Phillips ethylene polymerisation Cr/Ti/SiO₂ catalyst has been developed with two distinct active regions positioned respectively in the inner core and outer shell of the catalyst particle. DRIFTS, EPR, UV‐Vis‐NIR DRS, STXM, SEM‐EDX and GPC‐IR studies revealed that the catalyst produces simultaneously two different polymers, i.e., low molecular weight linear‐chain polyethylene in the Ti‐abundant catalyst particle shell and high molecular weight short‐chain branched polyethylene in the Ti‐scarce catalyst particle core. Co‐monomers for the short‐chain branched polymer were generated in situ within the TEAl‐impregnated confined space of the Ti‐scarce catalyst particle core in close proximity to the active sites that produced the high molecular weight polymer. These results demonstrate that the catalyst particle architecture directly affects polymer composition, offering the perspective of making high‐performance polyethylene from a single reactor system using this modified Phillips catalyst.     

Effects of alkyl chain length of monomer and dye-doped type on the electro-optical properties of polymer-dispersed liquid crystal films prepared by nucleophile-initiated thiol-ene click reaction

ABSTRACT

Polymer-dispersed liquid crystal (PDLC) films containing a series of monomers with different alkyl chain lengths were prepared by nucleophile-initiated thiol-ene click reaction. The effect of alkyl chain length of monomers, dye and temperature on electro-optical properties of PDLC films was investigated. It was found that the alkyl chain length and polymerisation rate of monomers together determine the size of liquid crystal (LC) droplets, thus affecting the electro-optical properties of PDLC. In addition, the type and content of dyes could be optimised to obtain PDLC materials with better comprehensive properties for display.     

Synthesis of substituted norbornenes and their polymerization to polynorbornenes with flexible aliphatic side‐chains

Synthesis and characterization of new thermally stable polynorbornenes functionalized with pendent flexible side‐chains are reported. The flexible side‐chains with terminal hydroxy groups were synthesized via S_NAr reactions of cyclopentadienyliron‐complexed chlorobenzenes with aliphatic diols. Condensation of these side‐chains with exo,endo‐5‐norbornene‐2‐carboxylic acid led to the formation of substituted monomers which were characterized using one‐ and two‐dimensional NMR techniques. Ring‐opening metathesis polymerization of these monomers yielded polynorbornenes with pendent side‐chains.     

Zinc Undecylenate Catalyst for the Ring‐Opening Polymerization of Caprolactone Monomers

The ring‐opening polymerization of two caprolactone monomers catalyzed by zinc undecylenate (ZU) is reported. Polymerizations were performed in bulk with benzyl alcohol (BnOH) as an initiator at 90 and 110 °C, respectively. A slower polymerization rate was observed for γ‐octyloxy‐ϵ‐caprolactone as compared to ϵ‐caprolactone. Diblock copolymers were synthesized by the sequential monomer addition at 90 and 110 °C. The kinetic studies performed for the ring‐opening polymerization of ϵ‐caprolactone and γ‐octyloxy‐ϵ‐caprolactone and the successful synthesis of diblock copolymers by the sequential monomer addition confirmed the controlled/living nature of zinc undecylenate catalyzed reactions.     

Living Free Radical Polymerisation Under a Constant Source of Gamma Radiation – An Example of Reversible Addition‐Fragmentation Chain Transfer or Reversible Termination?

The primary mechanism for living polymerisation under a source of gamma radiation at low dose rates is shown to be reversible addition‐fragmentation chain transfer. This was demonstrated by showing that the initial transfer step determines the success of the polymerisation. When an inappropriate leaving group is chosen for the RAFT agent, the polymerisation is non‐living. Under a reversible termination mechanism the ‘living’‐ness should be independent of this initial transfer step.     

Polyesters by a Radical Pathway: Rationalization of the Cyclic Ketene Acetal Efficiency

Radical ring‐opening polymerization (rROP) of cyclic ketene acetals (CKAs) combines the advantages of both ring‐opening polymerization and radical polymerization thereby allowing the robust production of polyesters coupled with the mild polymerization conditions of a radical process. rROP was recently rejuvenated by the possibility to copolymerize CKAs with classic vinyl monomers leading to the insertion of cleavable functionality into a vinyl‐based copolymer backbone and thus imparting (bio)degradability. Such materials are suitable for a large scope of applications, particularly within the biomedical field. The competition between the ring‐opening and ring‐retaining propagation routes is a major complication in the development of efficient CKA monomers, ultimately leading to the use of only four monomers that are known to completely ring‐open under all experimental conditions. In this article we investigate the radical ring‐opening polymerization of model CKA monomers and demonstrate by the combination of DFT calculations and kinetic modeling using PREDICI software that we are now able to predict in silico the ring‐opening ability of CKA monomers.