Search

Esterification of microbial poly(malic acid) is performed with either ethanol or 1-butanol to obtain polymalate conjugates capable to form nanoparticles (100-350 nm). Degradation under physiological conditions takes place with release of malic acid and the corresponding alcohol as unique degradation products. The anticancer drugs Temozolomide and Doxorubicin are encapsulated in nanoparticles with efficiency of 17 and 37%, respectively. In vitro drug release assays show that Temozolomide is almost completely discharged in a few hours whereas Doxorubicin is steadily released along several days. Drug-loaded nano-particles show remarkable effectiveness against cancer cells. Partially ethylated poly(malic acid) nano-particles are those showing the highest cellular uptake., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

PMLA nanoparticles with diameters of 150-250 nm are prepared, and their hydrolytic degradation is studied under physiological conditions. Degradation occurs by hydrolysis of the side chain methyl ester followed by cleavage of the main-chain ester group with methanol and L-malic acid as the final degradation products. No alteration of the cell viability is found after 1 h of incubation, but toxicity increases significantly after 3 d, probably due to the noxious effect of the released methanol. Anticancer drugs temozolomide and doxorubicin are encapsulated in the NPs with 20-40% efficiency, and their release is monitored using in vitro essays. Temozolomide is fully liberated within several hours, whereas doxorubicin is steadily released from the particles over a period of 1 month., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Methyl esters of microbial poly(beta,L-malic acid) for conversion degrees of 25, 50, 75, and 100% were prepared by treatment of the polyacid with diazomethane. Esterification proceeded with retention of the molecular weight of the parent polyacid and the copolymers displayed a blocky microstructure consisting of short segments of malic and methyl malate sequences. The thermal stability of the copolyesters was lower than those of the parent homopolymers and all of them were fairly crystalline with melting temperatures within the range of 170-175 degrees C. They were degraded rapidly by water, the hydrolysis rate being highly dependent on the methylation degree. Microspheres with mean-average diameters in the range of 1-20 microm were prepared from the 100% methylated product by the emulsion-evaporation solvent method. Encapsulation of erythromycin was efficiently performed in these microparticles and its releasing upon incubation in simulated physiological medium was evaluated for different drug loads. Drug delivery was observed to occur by a releasing mechanism largely determined by the hydrodegradation of the host polymer and independent of the amount of loaded drug.

The preparation of nanoparticles from 75% methylated poly(beta-L-malic acid) is described. Their degradation in aqueous environments was examined and the influence of pH and lipase on the rate of hydrolysis was evaluated. Six proteins were used to estimate the loading efficiency of the nanoparticles. The amount of protein retained in the nanoparticles was found to depend on the acid/basic character of the protein. Protein release from the loaded nanoparticles upon incubation in water under physiological conditions encompassed polymer hydrolysis and happened steadily within 3-10 d. The activity loss of entrapped alpha-chymotrypsin caused by loading and releasing depended on the method used for loading.

The hydrolytic degradability and erythromycin release from stoichiometric ionic complexes of biotechnological poly(beta,L-malic acid)s and poly(gamma,D-glutamic acid)s with alkyltrimethylammonium surfactants were investigated. The influence of pH, temperature and antibiotic load on hydrolysis rate was examined. It was found that poly(malic acid) complexes degraded by a surface erosion mechanism at a higher rate than poly(glutamic acid) complexes, which eroded in bulk. Erythromycin was lodged in the paraffinic subphase of the complexes and upon aging it was delivered according to a sigmoidal profile that appeared to be independent on the antibiotic load.

Ionic complexes of microbially produced poly(beta,L-malic acid) and alkyltrimethylammonium surfactants with linear alkyl chains containing even numbers of carbon atoms from 14 up to 22, were investigated. Complexes with a stoichiometric or nearly stoichiometric composition were prepared by precipitation from equimolar mixtures of aqueous solutions of the two components. All complexes were found to adopt supramolecular stratified structures made of alternating layers of poly(beta,L-malate) and surfactant with a periodicity on the length scale of 3-5 nm, which increased proportionally to the length of the polymethylene chain. In these complexes, alkyl side chains with more than 16 carbon atoms were partially crystallized showing reversible melting at temperatures between 40 and 70 degrees C. After melting, a smectic LC phase that isotropicized at approximately 100 degrees C was observed for all of the complexes. Conformational and dimensional changes taking place in the complexes by effect of heating were analyzed by (13)C CP-MAS NMR and powder X-ray diffraction.

Low-molecular-weight poly(alpha-methyl beta,L-malate) made of approximately 25-30 units was prepared from microbial poly(beta,L-malic acid) by treatment with diazomethane. The thermal characterization of the polymalate methyl ester was carried out and its crystalline structure was preliminary examined. Its ability to crystallize both from solution and from the melt was comparatively evaluated.

Cyclic butylene furandicarboxylate (c(BF)n) and butylene isophthalate (c(BI)n) oligomers obtained by high dilution condensation reaction were polymerized in bulk at 200 °C with Sn(Oct)2 catalyst via ring opening polymerization to give homopolyesters and copolyesters (coPBFxIy) with weight average molar masses in the 60,000–70,000 g·mol−1 range and dispersities between 1.3 and 1.9. The composition of the copolyesters as determined by NMR was practically the same as that of the feed, and they all showed an almost random microstructure. The copolyesters were thermally stable up to 300 °C and crystalline for all compositions, and have Tg in the 40–20 °C range with values decreasing almost linearly with their content in isophthalate units in the copolyester. Both melting temperature and enthalpy of the copolyesters decreased as the content in butylene isophthalate units increased up to a composition 30/70 (BF/BI), at which the triclinic crystal phase made exclusively of butylene furanoate units changed to the crystal structure of PBI. The partial replacement of furanoate by isophthalate units decreased substantially the crystallizability of PBF. [ABSTRACT FROM AUTHOR]

Abstract: Poly(styrene-co-p-tert-butyldimethylsilyloxystyrene) copolymers, P(S/p-TBDMSOS), with contents in the substituted comonomer within the 0–50% range were prepared using combined Ph2Zn–CpTiCl3–MAO initiator systems and some of them were used as precursors of poly(styrene-co-p-hydroxystyrene), P(S/p-HOS), copolymers. p-tert-Butyldimethylsilyloxystyrene was synthesized from p-hydroxybenzaldehyde by protecting the hydroxyl group with tert-butyldimethylchlorosilane and converting the aldehyde group into vinyl through the Wittig reaction. The P(S/p-TBDMSOS) copolymers with contents in substituted units equal or higher than 25% were atactic and those with content higher than 5% were amorphous. P(S/p-HOS) copolymers containing up to 20% of hydroxylated units were obtained by full hydrolysis in acidic medium of the corresponding P(S/p-TBDMSOS). The hydroxylated copolystyrenes displayed crystallinity for the whole range of studied compositions and their crystalline structure was essentially similar to that of s-PS homopolymers. The influence of the substituent on the modified-MAO catalyzed copolymerization and on the thermal properties of the resulting copolymers was comparatively examined. [Copyright &y& Elsevier]

Abstract: Poly(ethylene terephthalate-co-1,4-cyclohexane dicarboxylate) copolymers, abbreviated as PETCHD, containing from 2 up to 40mole% of the cycloaliphatic diacid, as well as the two parent homopolymers, PET and PECHD, were prepared from comonomer mixtures by a two-step melt-polycondensation procedure. Polymer intrinsic viscosities varied from 0.6 to 0.8dLg−1 with weight-average molecular weights spanning in the range from 30,000 to 70,000. The copolymers were found to have a random microstructure and a composition according to that used in their corresponding feeds. Thermal and mechanical properties of PETCHD were evaluated as a function of composition. Copolymers were found to be crystalline for all examined compositions although they crystallize from the melt only when the cycloaliphatic comonomer composition was below 20mole%. Both melting and glass transition temperatures of the copolyesters decreased rapidly with the content in CHD units, whereas the thermal stability appeared to be barely affected by copolymerization. Incorporation of 1,4-cyclohexane dicarboxylate units increased the Young’s modulus and the maximum tensile strength of these materials but elongation to break drastically diminished. Preliminary X-ray diffraction studies revealed that PETCHD copolyesters seem to adopt the same crystal structure as PET. [Copyright &y& Elsevier]

Abstract: A series of polyamides 6,4 were prepared from 1,6-hexanediamine and active esters of 2,3-di-O-acylated l-tartaric acid by polycondensation in solution. Both O-alkoyl and O-benzoyl esters were used as hydroxyl protecting groups. The resulting acylated polytartaramides were found to be semicrystalline polymers with Tm between 100 and 200°C and T g slightly above 100°C. Controlled hydrolysis of the ester side group led to the preparation of poly(hexamethylene l-tartaramide)s with different content in free hydroxyl groups. These polyamides continue being crystalline but their properties largely differ from those displayed by their parent acylated polymers. [Copyright &y& Elsevier]

The influence of incorporating 5-tert-butyl isophthalic units (tBI) in the polymer chain of poly(ethylene terephthalate) (PET) on the crystallization behavior, crystal structure, and tensile and gas transport properties of this polyester was evaluated. Random poly(ethylene terephthalate-co-5-tert-butyl isophthalate) copolyesters (PETtBI) containing between 5 and 40 mol% of tBI units were examined. Isothermal crystallization studies were performed on amorphous glassy films at 120 °C and on molten samples at 200 °C by means of differential scanning calorimetry. Furthermore, the non-isothermal crystallization behavior of the copolyesters was investigated. It was observed that both crystallinity and crystallization rate of the PETtBI copolyesters tend to decrease largely with the comonomeric content, except for the copolymer containing 5 mol% of tBI units, which crystallized faster than PET. Fiber X-ray diffraction patterns of the semicrystalline PETtBI copolyesters proved that they adopt the same triclinic crystal structure as PET with the comonomeric units being excluded from the crystalline phase. Although PETtBI copolyesters became brittle for higher contents in tBI, the tensile modulus and strength of PET were barely affected by copolymerization. The incorporation of tBI units slightly increased the permeability of PET, but copolymers containing up to 20 mol% of the comonomeric units were still able to present barrier properties. [Copyright &y& Elsevier]