Transesterification Of Poly Research Articles

Disulfide Bond Accelerated Transesterification in Poly(β-hydrazide disulfide esters) toward Fast Network Rearrangements.

The development of catalyst-free ester-based covalent adaptable networks (CANs) provides a new approach to achieve milder reaction conditions to reprocess thermoset resins. Despite recent advances, however, accelerating network rearrangements requires the introduction of hydroxyl groups into the network. In this study, disulfide bonds are introduced into the CANs to add new kinetically facile pathways to accelerate network rearrangement. Kinetic experiments using small molecule models of the CANs show that the presence of the disulfide bonds can accelerate transesterification. These insights are applied to synthesize new kinds of poly(β-hydrazide disulfide esters) (PSHEs) using thioctic acyl hydrazine (TAH) as a precursor for ring-opening polymerization with the hydroxyl-free multifunctional acrylates. The PSHE CANs have lower relaxation times (505-652 s) than the polymer containing only β-hydrazide esters (2903 s). The ring-opening polymerization of TAH improves the crosslinking density, heating resistance deformation temperature, and UV shielding performance of the PSHEs. Thus, this work provides a practical strategy to reduce the reprocessing temperatures of CANs.

Characterisation of end groups of hydroxy-functionalised scl-PHAs prepared by transesterification using ethylene glycol

Polyhydroxyalkanoates (PHAs) are a family of biodegradable polyesters with good potential in applications ranging from packaging to implants. The synthesis of block copolymers based on PHAs is one approach to tailoring these physical properties. This work considers the transesterification and end-group characterisation of hydroxy‑terminated PHAs for the chemical synthesis of PHA-based block copolymers. There is currently incomplete knowledge of the relative amounts of the different end-groups in the as-produced materials. Further, the reported hydroxy‑terminated PHAs have relatively low molecular weights (Mn < 4 kDa); hydroxy‑terminated PHAs of intermediate molecular weights (Mn > 20 kDa) - which are more favourable as building blocks for industrially relevant high molecular weight PHA - have not yet been fully characterised for use in such applications, to our knowledge. Here, a more comprehensive strategy for the preparation and characterisation of hydroxy‑terminated PHAs of intermediate molecular weights was applied. Hydroxy-functionalised PHAs were produced via transesterification of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) of differing 3HV contents and with narrow compositional distribution, followed by purification through solvent processing. The functionalised PHAs and reaction by-products were then characterised using FT-IR, 1H-NMR, 13C-NMR, 31P-NMR, GPC and DSC analyses, allowing the determination of the nature and distribution of the end groups. It was found that transesterification does indeed generate both primary and secondary hydroxyl end-groups, while original PHBV materials (PHBpre-sol) had only secondary hydroxyl end groups present. 41% of hydroxy‑functionalised PHBV (PHBtr-sol-D) were likely terminated with either crotonic groups or carboxylic acids. Further, the analysis showed that a proportion of commercial and laboratory derived PHBVs (PHBpre-sol and PHBVpre-sol) was likely dicarboxylic acid-terminated.

Effect of re-modified nanoclays on the extent of transesterification in poly (ethylene terephthalate)/poly (ethylene 2,6-naphthalenedicarboxylate) blend nanocomposites

In the present work, the extent of transesterification reaction was investigated in the poly (ethylene terephthalate) /poly (ethylene 2,6-naphthalenedicarboxylate) (PET/PEN) (90/10 and 75/25 w/w) blends filled with three nanofillers, i.e., an organo-modified nanoclay (NC), a transition metal ion re-modified NC (TMI-NC), and a [3-(glycidyloxy)propyl]trimethoxysilane re-modified NC (GPTMS-NC). FTIR test confirmed the successful re-modification of NC. The results of the wide-angle X-ray scattering (WAXS) test revealed that the PET/PEN (75/25 w/w) blend containing 3 phr TMI-NC indicated the best intercalation. Also, the proton nuclear magnetic resonance (1 H NMR) demonstrated that the extent of transesterification was decreased by incorporating the nanofillers into the PET/PEN blend. The 75/25 blend containing 3 phr GPTMS-NC showed the highest decrement. In addition, thermogravimetric analysis (TGA) revealed that the 75/25 blend containing 3 phr TMI-NC showed the best thermal stability.

Investigation of the Initiating and Catalytic Behavior of Tri-n-butyltin(IV) n-Butoxide in Ring-Opening Polymerization of ε-Caprolactone and Transesterification of Poly(L-lactic acid)

T ri-n-butyltin(IV) n-butoxide (nBu3SnOnBu) was successfully synthesized and utilized as a stable and homogeneous initiator for the small-scale synthesis of biodegradable polymers in our laboratory. From our previous works, the initiating performance of nBu3SnOnBu in the ring-opening polymerization (ROP) of cyclic ester monomers was completely investigated by differential scanning calorimetry (DSC). It was found that nBu3SnOnBu acted as the slow initiator in the ROP of ε-caprolactone (ε-CL) due to its high steric hindrance around the active center. Moreover, it could be used in the stereoselective ROP of racemic-lactide (rac-LA). The synthesized nBu3SnOnBu showed higher stereoselectivity than the conventional tin(II) octoate (Sn(Oct)2) system. In this present work, the effectiveness of nBu3SnOnBu in scaled-up (250 g) of the synthesis of poly(ε-caprolactone) (PCL) was further investigated comparing to small-scale polymerization (4 g). Furthermore, the catalytic performance of this nBu3SnOnBu in the transesterification of high molecular weight poly(L-lactic acid) (PLA) was also investigated for the first time. The transesterification of PLA with 0.05 M and 0.10 M of soluble nBu3SnOnBu catalyst in CHCl3 was successfully investigated by the gel permeation chromatography (GPC) technique. It was found that the molecular weight of PLA dramatically decreased with increasing time and nBu3SnOnBu concentration. From the kinetics study, nBu3SnOnBu acted as a highly active transesterification catalyst for PLA. From a mechanistic study, the transesterification mechanism of PLA with nBu3SnOnBu catalyst was proposed through intramolecular transesterification.

Influence of tin(II), aluminum(III) and titanium(IV) catalysts on the transesterification of poly(L-lactic acid)

Influence of tin(II), aluminum(III) and titanium(IV) catalysts on the transesterification of poly(L-lactic acid)

Effect of Re-Modified Nanoclays on the Extent of Transesterification in Poly (Ethylene Terephthalate)/Poly (Ethylene 2,6-Naphthalenedicarboxylate) Blend Nanocomposites

Effect of Re-Modified Nanoclays on the Extent of Transesterification in Poly (Ethylene Terephthalate)/Poly (Ethylene 2,6-Naphthalenedicarboxylate) Blend Nanocomposites

Transesterification of Poly(ethyl glyoxylate): A Route to Structurally Diverse Polyglyoxylates

Polyglyoxylates are a class of self-immolative polymers that depolymerize in solution and the solid state. The glyoxylic acid degradation product is a metabolite in the glyoxylate cycle and can als...

Sequential Structure, Crystallization, and Properties of Biodegradable Poly(ethylene Terephthalate-Co-Ethylene Oxide-Co-Lactide) Copolyester

The sequential structure, isothermal crystallization, tensile property, and degradation behavior of poly(ethylene terephthalate-co-ethylene oxide-co-lactide) (ETOLA) copolyester based on melt transesterification of poly(ethylene terephthalate) with poly(ethylene oxide) and oligo(lactic acid) was investigated. The degree of randomness was calculated to be 0.38, showing the incorporation of poly(ethylene oxide) (PEO) blocks into the homogeneous sequences of ethylene terephthalate (ET) and lactide (LA) units. The isothermal crystallization kinetics results revealed that the crystallization activation energy of the copolyester calculated using the Arrhenius’ equation was lower than that reported for poly(ethylene terephthalate) (PET), indicating that the addition of PEO and LA units into PET retarded the crystallization of PET. The copolyester exhibited the same crystal structure at different crystallization temperatures, similar to that of PET homopolymer, based on wide angle X-ray diffraction results. The size of the spherulites of ETOLA increased with crystallization temperature. The increase of crystallization temperature reduced the elongation at break of the copolyesters, as well as the enzymatic degradation.

Thermally Initiated Trans-esterification in Poly(ε-caprolactone) and Its Dependence on Molecular Weight

Biodegradability and biocompatibility of poly(e-caprolactone) (PCL) are the prime properties which advanced the use of this polymer in fields of tissue engineering and biomedicals. Being an aliphatic polyester, PCL is prone to undergo trans-esterification which is one of the mechanisms reported for its degradation besides being used in making its copolymers. Trans-esterification occurs both, inter- and intra-molecularly and in this work we report that the mechanism of trans-esterification depends on the molecular weight of the polymer when it is subjected to 160 °C for time up to 24 h. For low molecular weight PCL (Mp = 10,000 g/mol) inter-molecular trans-esterification is the predominant mechanism while for the high molecular weight PCL (Mp = 80,000 g/mol) it is intra-molecular. A mid molecular weight PCL (Mp = 43,000 g/mol) showed presence of both, inter- as well as intra-molecular trans-esterification, when heated at 160 °C for 24 h. A decrease in relative crystallinity for all the samples showed reduction in crystalline component of the polymer confirming occurrence of trans-esterification at chosen conditions. An increase in tensile strength and modulus is observed after treatment at 160 °C for 24 h due to formation of more entangled network of polymer chains as a result of trans-esterification reactions.

In-melt transesterification of poly(lactic acid) and poly(ethylene-co-vinylalcohol)

Transesterification of poly(lactic acid) and poly(ethylene-co-vinylalcohol) was realized in-melt using different catalysts. Reactions were first conducted in an internal mixer and the different reaction parameters effect on exchange reactions and the obtained copolymers were optimized. Among the used catalysts, 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) and Tin(II) bis(2-ethylhexanoate) (Sn(Oct)2) were particularly efficient.In a second part, reactions were made by reactive extrusion. In most of reaction conditions, compatible blends were obtained with a fine micro phase separation. Only under extreme reaction conditions, high temperature and intensive mixing, nanostructured graft copolymers were obtained.

Inhibited Transesterification of Poly(Butylene Terephthalate)/Poly(Ethylene Terephthalate)/SiO2 Nanocomposites by Two Processing Methods

Nanocomposites composed of SiO2 nanoparticles and a poly(butylene terephthalate) (PBT)/poly(ethylene terephthalate) (PET) binary blend were prepared by melt blending in a twin-screw extruder. The phase morphology, crystallization behavior, and transesterification of the nanocomposites were investigated by field emission scanning electron microscopy (FE-SEM), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) spectroscopy, etc. The effects of microstructure and interfacial reaction on the mechanical and thermal properties of the nanocomposites are discussed in detail. Owing to the excellent dispersion of SiO2 nanoparticles in the PBT/PET matrix, the transesterification between PBT and PET was inhibited and the melting point was increased in the presence of SiO2 nanoparticles. SiO2 nanoparticles in PBT/PET/SiO2–1, produced by a one-step method, had a more effective inhibition of transesterification between PBT and PET than that in PBT/PET/SiO2–2 produced by a master batch method, with the former exhibiting the best properties.

The changes of transesterification level in PET/PEN blends with the addition of PET–PEN copolymer

AbstractThe extent of transesterification in poly(ethylene terephthalate) (PET)/poly(ethylene‐2,6‐naphthalate) (PEN) blends with the addition of PET–PEN copolymers was examined by DSC and 1H‐NMR measurements to evaluate the factor affecting the reaction level at a given temperature and time. Both block (P(ET‐block‐EN)) and random (P(ET‐ran‐EN)) copolymers were used as the copolymers. At a given treatment temperature and time, the level was increased by the addition of P(ET‐block‐EN) into PET/PEN blends. On the other hand, a reverse change was observed when P(ET‐ran‐EN) was mixed with PET/PEN blends. During the treatment, an inhomogeneous phase of the blends changed into the homogeneous one; however, the change showed little effect on the reaction level. The effects of molecular weight on the reaction level were also examined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Transesterification of Poly(4,4′‐isopropylidene‐2,2′‐dimethyldiphenylene terephthalate) and Poly(ethylene adipate) Blend in Solution

AbstractSummary: Transesterification of poly(4,4′‐isopropylidene‐2,2′‐dimethyldiphenylene terephthalate) and poly(ethylene adipate) (PEA) has been carried out in concentrated o‐dichlorobenzene solution at 210 °C with Bu2SnO as a catalyst. According to GPC data, during transesterification the reaction product acquires Flory MWD and only a slight degradation of chains proceeds in the system: on average each chain having undergone about one scission in 100 min. Chain structure of the reaction products was studied using 1H NMR spectroscopy. The kinetic and statistical analysis of the process was performed using following assumptions: transesterification proceeds in a homogeneous medium as a reversible second‐order reaction between diads, and the product chain structure obeys the first‐order Markov statistics. Calculated dependences of the parameters characterizing an evolution of the chain structure during the reaction fit experimental data fairly well. In 100 min the reacting system reaches a state close to the equilibrium. The difference between distributions of diads of residues and units is considered.Change of the terephthalate‐centered r‐triads content with time.magnified imageChange of the terephthalate‐centered r‐triads content with time.

Transesterification of poly(ethyl‐α‐hydroxymethacrylate) prepared via reversible addition–fragmentation chain transfer polymerization

Living free radical polymerization was employed to prepare poly(ethyl-α-hydroxyl methacrylate) of various chain lengths, which was subsequently treated to undergo rapid intramolecular lactonization along the polymer backbone, offering access to tailored polymers of both defined chain length and degree of lactonization.

Mechanism and kinetics of transesterification in poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalene dicarboxylate) polymer blends

In a previous work [L. Alexandrova, A. Cabrera, M.A. Hernández, M.J. Cruz, M.J.M. Abadie, O. Manero, D. Likhatchev, Polymer 43 (2002) 5397. [1]], a model compounds study on the kinetics of a transesterification reaction in poly(ethylene terphthalate)–poly(ethylene naphthalene 2,6-dicarboxylate), PET–PEN blends, resulting from melt processing, was simulated using model compounds of ethylene dibenzoate (BEB) and ethylene dinaphthoate (NEN). A first-order kinetics was established under pseudo first-order conditions for both reactants, and thus the overall transesterification reaction was second-order reversible. Direct ester–ester exchange was deduced as a prevailing mechanism for the transesterification reaction under the conditions studied.In this work, the actual PET–PEN system was melt processed by mixing the polymers below the critical reaction temperature in a twin-screw extruder. Thereafter, the reaction was induced by temperature in open glass ampoules. A second order reversible kinetics was measured, in agreement with the kinetics established in the previous model compounds study. The equilibrium constant value corresponds to a forward rate constant which is four times larger than the reverse rate constant. The activation thermodynamic parameters confirmed the direct ester–ester exchange mechanism for the reaction.

Synthesis and characteristics of biodegradable copolyesters from the transesterification of poly(butylene adipate-co-succinate) and poly(ethylene terephthalate)

Poly(butylene adipate-co-succinate) (PBAS), an aliphatic polyester, is known for its excellent biodegradability, but its physical and mechanical properties are poor. To improve the physical properties, stiff aromatic rings were added to PBAS through transesterification with poly(ethylene terephthalate) (PET). New biodegradable copolyesters were prepared by the intermolecular ester-exchange reactions between molten PBAS and PET. The transesterification reaction was carried out at 280°C without a catalyst. The newly synthesized copolyesters were characterized with 1H-NMR spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. The mechanical properties were measured with a universal test machine, and the biodegradability was also investigated. By the new peaks appearing in 1H-NMR spectra of the copolyesters, the occurrence of the transesterification reaction between PBAS and PET was confirmed. A reduction of the melting temperature was observed for the copolyesters. The elongations at break of the new copolyesters increased for all compositions and reaction times, in comparison with PBAS. However, the tensile strength decreased with the induction of terephthalate units in the copolyesters. The biodegradability of the copolyesters also depended on the number of terephthalate units. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3266–3274, 2004

Copoly(γ, dl-glutamate)s containing short and long linear alkyl side chains

Copoly(α-alkyl γ, dl-glutamate)s containing octadecyl and ethyl side groups were prepared from racemic poly(γ, dl-glutamic acid) of bacterial origin, and their structure in the solid state examined by DSC, polarized IR spectroscopy and X-ray diffraction methods. Copolymers with a blocky microstructure were prepared by transesterification of poly(α-ethyl γ, dl-glutamate) with octadecanol for a wide range of compositions. Random copolymers were prepared by sequential alkylation of the polyacid with ethyl bromide and octadecyl bromide in solution. All the multiblock copolymers were found to adopt the layered structure characteristic of comb-like polypeptides with the octadecyl side chains crystallized in extended conformation in a separate phase, and aligned normal to the main chains, which are arranged in helical conformation. Melting of paraffinic crystallites reversibly happened in the 50–55 °C range without significant alteration of the layered arrangement. Upon heating at 150 °C, the structure contracted but no indication on the existence of a second transition, as it is known to occur in comb-like poly(α-alkyl γ-glutamate) homopolymers, was observed by DSC. Random copolymers did show nor thermal transition neither evidence of any organized supramolecular structure.

Enzyme‐Catalyzed Preparation of Aliphatic Polyesters Containing Thioester Linkages

AbstractAliphatic polyesters containing thioester linkages were enzymatically prepared by both the copolymerization of lactone with mercaptoalkanoic acid and by the transesterification of polyesters with mercaptoalkanoic acids. The enzymatic copolymerization of ε‐caprolactone with 11‐mercaptoundecanoic acid (11MU) and 3‐mercaptopropionic acid (3MP) was performed under reduced pressure using an immobilized lipase from Candida antarctica (CA). The transesterification of poly(ε‐caprolactone) and poly[(R)‐3‐hydroxybutyrate] was carried out with 11MU and 3MP using lipase CA under reduced pressure. magnified image

Synthesis of Poly(-alkyl ,L-aspartate)s by Transesterification

A new procedure for the preparation of poly(α-alkyl β,L-aspartate)s based on the transesterification of poly(α-benzyl β,L-aspartate) with alcohols in the presence of titanium tetrabutoxide is described. The reaction proceeded to almost total conversion without substantial racemization or imidation. Thermal properties of the resulting polymers were comparable to those of their homologues obtained by anionic ring-opening polymerization of β-lactams and their thermal stability is even higher.

Transesterification in poly(ethylene terephthalate) and poly(ethylene naphthalate 2,6-dicarboxylate) blends: model compounds study

Kinetics of transesterification reaction in poly(ethylene terephthalate)–poly(ethylene naphthalate 2,6-dicarboxylate), PET–PEN, blends resulting from melt processing was simulated using model compounds of ethylene dibenzoate (BEB) and ethylene dinaphthoate (NEN). The exchange reaction between BEB and NEN was followed by 1H NMR spectroscopy using signals from the aliphatic protons of ethylene glycol moieties at 4.66 and 4.78 ppm, respectively. The first-order kinetics was established under pseudo-first-order conditions for both reactants. Thus, the overall transesterification reaction was second order reversible. The reversibility was confirmed experimentally by heating a mixed sequence of 1-benzoate 2-naphthoate ethylene (BEN) under similar conditions. Both forward reaction of the equimolar amounts of the reagents and reverse reaction came to equilibrium at the same molar ratio of the reactants and reaction products of roughly 0.25:0.50:0.25 for BEB, BEN, and NEN, respectively. The rate equation for the transesterification reaction in the model system was modified using half-concentration of BEN, which is the only effective in the intermolecular exchange. Direct ester–ester exchange was deduced as a prevailing mechanism for the transesterification reaction under the conditions studied, and the values of equilibrium and rate constants, as well as other basic thermodynamic and kinetic parameters were determined. The use of Zn(OAc) 2 as a catalyst resulted in a significant decrease in the activation enthalpy of transesterification, which might be due to the partial switch of the reaction mechanism from primarily pseudo-homolytic to more heterolytic where Zn II acts as a Lewis base which binds to the ester carbonyl oxygen.