Cyclic Ester Monomers Research Articles

Synthesis and characterization of well‐defined random and block copolymers of ε‐caprolactone with l‐lactide as an additive for toughening polylactide: Influence of the molecular architecture

ABSTRACTWell‐defined multiarmed star random and block copolymers of ε‐caprolactone with l‐lactide with controlled molecular weights, low polydispersities, and precise numbers of arms were synthesized by the ring‐opening polymerization of respective cyclic ester monomers. The polymers were characterized by 1H‐NMR and 13C‐NMR to determine their chemical composition, molecular structure, degree of randomness, and proof of block copolymer formation. Gel permeation chromatography was used to establish the degree of branching. Star‐branched random copolymers exhibited lower glass‐transition temperatures (Tg's) compared to a linear random copolymer. When the star random copolymers were melt‐blended with poly(l‐lactic acid) (PLA), we observed that the elongation of the blend increased with the number of arms of the copolymer. Six‐armed block copolymers, which exhibited higher Tg's, caused the maximum improvement in elongation. In all cases, improvements in the elongation were achieved with no loss of stiffness in the PLA blends. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43267.

Dual Catalysis for Selective Ring-Opening Polymerization of Lactones: Evolution toward Simplicity.

Much work has been directed to the design of complex single-site catalysts for ring-opening polymerization (ROP) to enhance both activity and selectivity. More simply, however, cooperative effects between Lewis acids and organocatalytic nucleophiles/Lewis bases provide a powerful alternative. In this study we demonstrate that the combination of N-heterocyclic carbenes, 1,8-diazabicycloundec-7-ene (DBU) and 4-dimethylaminopyridine (DMAP) with simple Lewis acids enables the ROP of the macrolactone pentadecalactone in a rapid and efficient manner. Remarkably, regardless of the nature of the nucleophile, the order of activity was observed to be MgX2 ≫ YCl3 ≫ AlCl3 and MgI2 > MgBr2 > MgCl2 in every case. The minimal influence of the organobase on polymerization activity allows for the use of simple and inexpensive precursors. Furthermore, extension of the study to other cyclic (di)ester monomers reveals the choice of Lewis acid to lead to monomer selective ROP activity and hence control over copolymer composition by choice of Lewis acid. This approach could lead to the realization of complex polymer structures with tunable physical properties from simple catalyst combinations.

Poly(thioester) by Organocatalytic Ring-Opening Polymerization.

Organocatalysts typically used for the ring-opening polymerization (ROP) of cyclic ester monomers are applied to a thiolactone, ε-thiocaprolactone (tCL). In the absence of an H-bond donor, a nucleophilic polymerization mechanism is proposed. Despite the decreased ability of thioesters and thiols (versus esters and alcohols) to H-bond, H-bonding organocatalysts-a thiourea in combination with an H-bond accepting base-are also effective for the ROP of tCL. The increased nucleophilicity of thiols (versus alcohols) is implicated in the increased Mw/Mn of the poly(thiocaprolactone) versus poly(caprolactone), but deleterious transesterification is suppressed in the presence of a thiourea. The thioester monomer, tCL, is shown to be thermodynamically similar to ε-caprolactam but kinetically similar to ε-caprolactone.

Synthesis of Poly(ϵ‐caprolactone‐co‐methacrylic acid) Copolymer via Phosphazene‐Catalyzed Hybrid Copolymerization

AbstractPoly(ϵ‐caprolactone‐co‐tert‐butyl methacrylate) (CL‐co‐BMA) random copolymer is synthesized via hybrid copolymerization with 1‐tert‐butyl‐4,4,4‐tris(dimethylamino)‐2,2‐bis[tris(dimethylamino)phophoranylidenamino]‐2Λ5,4Λ5‐catenadi(phosphazene) (t‐BuP4) as the catalyst. The copolymer is hydrolyzed into poly(ϵ‐caprolactone‐co‐methacrylic acid) (CL‐co‐MAA), a charged copolymer. Nuclear magnetic resonance, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis measurements indicate that cyclic ester and vinyl monomer form a random copolymer. The degradation of the copolymers has also been studied by use of quartz crystal microbalance with dissipation.

Hybrid Copolymerization of ε-Caprolactone and Methyl Methacrylate

Copolymerization of ε-caprolactone and methyl methacrylate with (1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)phophoranylidenamino]-2Λ5,Λ5-catenadi(phosphazene) (t-BuP4) as the catalyst has been studied. Nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC) measurements indicate that the cyclic ester and vinyl monomer form a random copolymer. Thermogravimetric analysis (TGA) measurements demonstrate that such a random copolymer exhibits a decomposition temperature higher than those of the corresponding homopolymers. The present study reveals a “hybrid copolymerization” i.e., a combination of vinyl polymerization and ring-opening polymerization, which makes the incorporation of cyclic and vinyl monomers into the same polymer chain possible. Hybrid copolymerization is expected to produce a number of new interesting polymers.

Molecular Design of a Speciality Polyester for Potential Use as a Fast-Absorbable Monofilament Surgical Suture

This paper describes the molecular design of a speciality polyester for use as a fast-absorbable monofilament surgical suture. In the surgical context, fast-absorbable means tensile strength loss within a period of 10-14 days, the minimum period required for secure wound approximation, after which the suture gradually loses its mass integrity leading to complete mass loss within 2-3 months. In order to be fast-absorbable, it is necessary that the main monomer used in synthesizing the polymer is glycolide since the polymer repeating unit, -OCH2CO-, is the chemical structure which hydrolyses the most rapidly in the human body. However, glycolide alone would give a monofilament suture fibre which would be too stiff and unwieldy for practical purposes and so it needs to be copolymerised with other cyclic ester monomers such as L-lactide and caprolactone to modify its mechanical properties. In this way, a monofilament fibre can be obtained which has an appropriate balance of hydrolysability and flexibility. Thus, this work enters the realm of molecular engineering insofar that it involves the strict control of both the chemical and physical microstructure of the polymer during the synthesis and processing steps respectively. This paper will describe how this controlled molecular architecture can be achieved and some preliminary results will be presented.

Synthesis and properties of star polymers with a C5 -symmetric bowl-shaped aromatic core

We report the synthesis and properties of star polymers with a C5-symmetric aromatic core. For this, corannulene-based penta-substituted polymerization initiators were synthesized. These initiators were then used to polymerize cyclic ester and styrenic monomers via ring opening polymerization and free radical polymerization methods, respectively. Preliminary results suggest that these novel polymers can interact with fullerene, C60, and the degree of interaction can be tuned by the chemical nature of the solvent. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Ring-Opening Polymerization of Cyclic Ester Monomers by Poly(propylene glycol) in the Presence of Monomer Activator and Examination of Triblock Copolymer Solution Properties

Ring-Opening Polymerization of Cyclic Ester Monomers by Poly(propylene glycol) in the Presence of Monomer Activator and Examination of Triblock Copolymer Solution Properties

Controlled hydrolysis of [Ti(O-2,4,6-Br3C6H2)2(O-iPr)2]2: Synthesis, structural characterization and studies on bulk polymerization of cyclic esters and lactide

Abstract Controlled hydrolysis of [Ti(O-2,4,6-Br3C6H2)2(O-iPr)2]2 with water results in the formation of the Ti-oxo cluster Ti8O24C66H58Br24 (1). This compound has a very interesting cage structure. The crystal structure consists of centrosymmetric neutral octamers containing two planar Ti4 layers, interlinked by four linear oxo-bridges. The four independent Ti atoms have three different coordination environments. The four unique Ti centers are rigidly coplanar, giving a unique configuration. The bridging oxygen atoms linking the two inversion-center related Ti atoms give a novel assemblage reminiscent of an inverse “cake-plate”. Compound 1 is an active initiator for the polymerization of cyclic ester monomers and lactide resulting in polymers with moderate number average molecular weights (Mn) and close to narrow molecular weight distribution (MWD).

Synthesis of the hemoglobin‐conjugated polymer micelles by click chemistry as the oxygen carriers

Amphiphilic triblock copolymers were synthesized using MPEG, cyclic carbonic ester monomer including propargyl group (MPC) and L‐lactide (LA). These copolymers could self‐assemble into core–shell spherical micelles with propargyl groups on the surface. Azided hemoglobin (Hb) was conjugated with the micelles through click reaction to form Hb‐bearing nano‐micelles. The click reaction conditions, such as the molar ratio of sodium azide to Hb, the binding ratio of Hb to copolymers, the components of catalytic solution, the reaction temperature and time, were thoroughly investigated and optimized. The resulted nano‐micelles had 100 nm diameter with 50–60 wt% of Hb content. The Hb‐based nano‐micelles showed appropriate stability and oxygen carrying capacity, and would have the potential to be used as the new type of artificial oxygen carrier. Copyright © 2011 John Wiley & Sons, Ltd.

Salen Complexes of Zirconium and Hafnium: Synthesis, Structural Characterization, Controlled Hydrolysis, and Solvent-Free Ring-Opening Polymerization of Cyclic Esters and Lactides

Dinuclear salen compounds of zirconium and hafnium are efficient initiators for the solvent-free ring-opening polymerization of cyclic ester monomers and lactides. There is a correlation between the theoretical and experimental number-average molecular weights (M(n)'s) in these polymerizations. Polymerization of β-butyrolactone gives poly(3-hydroxybutyrate) with a good M(n) and molecular weight distribution.

Design of Elastomeric Homo- and Copolymer Networks of Functional Aliphatic Polyester for Use in Biomedical Applications

An unsaturated aliphatic polyester was synthesized by condensation polymerization to yield the pre-polymer, poly(but-2-ene-1,4-diyl malonate) (PBM), which is applicable as an elastomeric network and as a macroinitiator for the polymerization of cyclic ester monomers. The method of preparation was simple and straightforward with no need to purify the monomers or add a potentially harmful catalyst. The number average molecular weight of the pre-polymer could easily be increased from 5000 to 12000 by extending the reaction time. The pre-polymer PBM was successfully cross-linked with UV-radiation to form a clear, transparent, colorless, flexible, and strong film. PBM as a macroinitiator for l-lactide (LLA) and ε-caprolactone (CL) polymerizations highly increased the ductility of the LLA-polymer, while maintaining the strength, compared to PLLA polymerized with common initiators. The tensile properties of PCL were also improved. The linear PCL-PBM and PLLA-PBM polymers were easily cross-linked to give polymers with greater strength and higher modulus as the result.

Bis(imino)phenoxide complexes of zirconium: synthesis, structural characterization and solvent-free ring-opening polymerization of cyclic esters and lactides

Bis(imino)phenoxide complexes of zirconium possess spectacular reactivity towards the solvent-free polymerization of cyclic ester monomers and lactides. Polymerization of lactide is living and the resulting product has exceptionally high number average molecular weights (Mn). Polymerization of β-butyrolactone gives syndiotactic poly(3-hydroxybutyrate) with good Mn and molecular weight distribution (MWD).

Guanidine and Amidine Organocatalysts for Ring-Opening Polymerization of Cyclic Esters

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD), N-methyl-TBD (MTBD), and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) are effective organocatalysts for the ring-opening polymerization (ROP) of cyclic esters such as lactide (LA), δ-valerolactone (VL), and e-caprolactone (CL). TBD is shown to polymerize LA, VL, and CL in a fast and controlled manner, whereas MTBD and DBU polymerized LA and addition of a thiourea cocatalyst led to the ROP of VL and CL being achieved. Each of the catalysts produced polymers displaying high end group fidelity, good correlation between theoretical and observed molecular weight, and linear relationships between conversion and molecular weight. The enhanced activity of TBD relative to MTBD and DBU is attributed to its bifunctionality, enabling the simultaneous activation of both the cyclic ester monomer and the alcohol group of the initiator/propagating species. Temperature-dependent NMR studies generated individual association constants for MTBD with benzyl alcohol and thiourea with VL. ...

First example of N-heterocyclic carbenes as catalysts for living polymerization: organocatalytic ring-opening polymerization of cyclic esters.

A novel metal-free, organocatalytic approach to living polymerization is presented. N-heterocyclic carbenes were employed as nucleophilic catalysts for the ring-opening polymerization (ROP) of cyclic ester monomers. The catalysts is used in combination with an initiator, such as an alcohol, which generates an alpha-end group bearing the ester from the initiating alcohol upon ring-opening and a hydroxyl functional omega-chain end that propagates the chain. This class of catalyst proved to be more reactive than tertiary amine and phosphine nucleophiles, producing narrowly dispersed polymers of predictable molecular weights at room temperature in 1-2 h. Catalysis with respect to both initiating alcohol and monomer was observed. Control of the alpha and omega end-groups was demonstrated with a pyrene-labeled initiator, allowing the preparation of well-defined macromolecular architectures. Analogous to the ROP of cyclic esters using biocatalysts, the polymeriztion pathway using the N-heterocyclic carbenes is believed to ensue through a monomer-activated mechanism.

Kinetics and mechanism of cyclic esters polymerisation initiated with tin(II) octoate, 4. Influence of proton trapping agents on the kinetics of ɛ-caprolactone andL,L-dilactide polymerisation

Kinetics of the polymerisation of e-caprolactone and L,L-dilactide initiated with tin(II) 2-ethylhexanoate (tin octoate (Sn(Oct)2)) and carried out in the presence of 2,6-di-tert-butylpyridine (1) and/or 1,8-bis(dimethylamino)naphthalene (2), in THF as the solvent, at 80°C was studied. The rate of polymerisation of the cyclic ester in the presence of 1 or 2, known to be a “proton trap” or “proton sponge”, respectively, is either practically the same or even exceeds that of the polymerisation conducted in the absence of these hindered amines. Consequently, the proposed earlier mechanisms of polymerisation of cyclic esters coinitiated by Sn(Oct)2, with chain growth involving active species with “protons”, i. e. primary or secondary oxonium ions, have to be put on rest. This includes also the mechanism in which propagation was proposed to proceed within a ternary complex consisting of hydroxyl group terminated macromolecule, Sn(Oct)2, and a cyclic ester monomer. The observed final increase of the rate of polymerization is in agreement with the interconversion previously decribed by us: Sn(Oct)2 + ROH ⇌ OctSnOR + OctH since OctH (a carboxylic acid) is becoming complexed with a proton trap/sponge and the concentration of OctSnOR (the actual initiator) is effectively increased.