Transesterification Of Poly Research Articles

Novel PDLLA/PEG copolymer micelles as drug carriers.

In this study we attempted to develop a novel drug delivery system in the form of polymeric micelles. In order to obtain polymer chains with micelle forming abilities, we have proposed to produce copolymers by transesterification of poly(DL-lactic acid)(PDLLA)(as the hydrophobic segment) and polyethylene glycol (PEG) (as the hydrophilic segment). We first produced homopolymers of PDLLA with low molecular weights by condensation polymerization of DL-lactic acid. The PDLLA homopolymer with an average molecular weight of 1866 +/- 100 was then transesterified with PEG with a molecular weight range of 3300-4000. By changing the ratio of PEG to PDLLA, we were able to produce copolymers with different chain structures, and therefore, with different micelle forming abilities. FTIR, 1H-NMR, DSC, and GPC studies were performed to describe the structures of these PDLLA/PEG copolymers. Micelles of these copolymers were characterized by light scattering. We selected a model drug, i.e. adriamycin, and obtained the drug loadings to the PDLLA/PEG copolymer micelles. The maximum drug loading was about 12 mg g-1. We found that these micelles were degraded in phosphate buffer (pH 7.4 and temperature 37 degrees C) in about 5-6 weeks. We also investigated the release of adriamycin from these PDLLA/PEG micelles, and concluded that the drug release from these micelles was mainly 'degradation controlled'.

Poly(butylene terephthalate) polycarbonate transesterification: monitoring its progress with Fourier transform Raman spectroscopy

The evaluation of FT Raman spectroscopy for monitoring transesterification in poly(butylene terephthalate)/bisphenol A polycarbonate blends is described. The reduction in crystallinity of the poly(butylene terephthalate) portion of the blend due to transesterification can be followed by the shift of the carbonyl band of the poly(butylene terephthalate) component to higher frequency. Specular reflectance infrared evidence for transesterification is also presented.

An amphiphilic graft copolymer as a surface‐modifying additive for poly(methyl methacrylate)

AbstractAn amphiphilic graft copolymer was prepared by transesterification of poly(2‐ethylhexyl acrylate‐co‐methyl methacrylate) with poly(ethylene glycol) monomethyl ether (MPEG2000). The grafting reaction was performed in melt at 155°C. The purified graft copolymer was blended into poly(methyl methacrylate) in concentrations of 1.5‐30 wt %, either by mixing in chloroform solution or by melt mixing by means of a twin‐screw extruder or a Brabender blender. Films of the blends were prepared by solution casting onto glass plates or by hot pressing between polished Al plates. At concentrations up to 20% of the graft copolymer homogeneous blends were obtained. At higher concentrations the blends were heterogeneous, and side‐chain crystallinity was detectable by DSC analysis. The surface properties of the films were studied by measurements of water contact angles. The surface accumulation of the graft copolymer was demonstrated as a large increase in the wetting angle hysteresis, and found to depend on the procedure for film preparation as well as the casting substrate. © 1995 John Wiley & Sons, Inc.

Chemical reactions between immiscible polymers in the melt: Transesterification of poly(ethylene‐co‐methyl acrylate) with mono‐hydroxylated polystyrenes

AbstractThis article presents a unique example dealing with how chemical reactions between immiscible polymers in the melt behave differently than they would do in solution. Specifically, a model reaction was chosen: the transesterification between poly(ethylene‐co‐methyl acrylate) (EMA) and polystyrene mono‐hydroxylated at the chain end (PSOH). It was carried out in the melt in a batch mixer. The overall rate of this reaction has a similar dependence of temperature, composition of reactants, and the nature and concentration of catalyst as in solution. The reactivity of PSOH decreases drastically with increasing molecular weight, and it becomes very weak when the molecular weight exceeds 8000 g/mol. As opposed to a reaction in solution or in a homogeneous melt, mechanical mixing increases the reaction rate since it generates interfacial area and reduces the diffusion length. The EMA‐g‐PS graft copolymer formed at the interfaces reduces the interfacial tension, and increases the miscibility of the reaction mixture. However, its occupation of the interfaces reduces contact between the reactive moieties, thus decreasing the overall reactivity. More importantly and much to our surprise, adding 1 to 2 wt % of an inert solvent increased greatly the overall reaction rate. While an increased interfacial mixing and diffusion by the presence of minor amounts of solvent are thought to be the major factors contributing to the drastic increase in reactivity, numerous questions still remain. Nevertheless, this study clearly showed that as opposed to a reaction in solution, mechanical mixing and the presence of minor amounts of solvent are two additional and critical means to control chemical reactions between immiscible polymer melts. © 1995 John Wiley & Sons, Inc.

Synthesis and Some Properties of Graft Copolymers with Uniform Polyoxyethylene Side Chains

Abstract Graft copolymers with uniform polyoxyethylene (PEO) side chains were synthesized by transesterification of poly(methyl, ferf-butyl fumarate) (PMtBF) or poly(methyl, tert-butyl fumarate-co-styrene) poly-(MtBF-co-St) with potassium alkoxide of PEO monoether. The grafting efficiency increased with enhanced alkoxide reactivity, but the main factor in the ester exchange proved to be the structure of the backbone. This effect was ascribed to the thermodynamic incompatibility between fumaric polymers and PEO. The polymers were characterized by spectral methods, GPC, and DSC. In THF the graft copolymers comprising a polyfumarate backbone with PEO side chains eluted at higher elution volumes than did the backbone homopolymers. In benzene their intrinsic viscosities were lower than those of the backbones. In aqueous eluents, micelles were detected, and their aggregation number depended on the composition of the copolymer and the eluent.

Study of transesterification in poly(ethylene terephthalate) by small-angle neutron scattering

Melange de polymere deuterie et non deuterie. Influence du temps et de la temperature sur la transesterification

Terephthalate copolyesters of ethylene glycol and propane-1,3-diol

Terephthalate copolyesters of ethylene glycol and propane-1,3-diol of various compositions were prepared by trans-esterification of poly(ethylene terephthalate) (PET) with propane-1,3-diol [PrG(1,3)] . The compositions of the coDolyesters were determined by1H NMR. The melting and crystallization temperatures were measured by differential thermal analysis (DTA). Intrinsic viscosities were measured in orthochlorophenol at 30°C.

Preparation and study of terephthalate copolyester of ethylene glycol and butane-1,4-diol

Random terephthalate copolyesters of ethylene glycol and butane-1,4-diol of various compositions were prepared by trans-esterification of poly(ethylene terephthalate) (PET) with butane-1,4-diol (BD). Proton nuclear magnetic resonance spectroscopy (NMR) was used to elucidate the structure and compositions of copolyesters. The thermal behaviour of the copolyesters were investigated by differential thermal analysis (DTA). Intrinsic viscosities were measured in orthochlorophenol at 30°C.

Transesterification of poly(methyl acrylate) with optically active alcohols

AbstractTransesterifications of atactic and isotactic poly(methyl acrylate) with optically active alcohols such as (S)‐2‐methyl‐butanol, D‐borneol and L‐menthol were carried out in toluene at 100°C using p‐toluenesulfonic acid as catalyst to obtain optically active polymers. In addition a relationship between the conformation and the optical behaviour of the transesterified poly(methyl acrylate) was investigated. The specific rotation of the transesterified atactic poly(methyl acrylate) increased linearly with increasing introduced optically active groups at the lateral chain, in contrast to that of the isotactic poly(methyl acrylate) which increased nonlinearly with increasing introduced asymmetric groups. Since the specific rotations of the transesterified polymers depend on these tacticities the conclusion was drawn that the optical activity is caused not only by the asymmetric group in the lateral chain but also by molecular dissymmetry in the principal chain.

Transesterification of Poly(γ -methyl-L-glutamate)

Transesterification of Poly(γ -methyl-L-glutamate)