Direct Melt Polycondensation Research Articles

Studies on aliphatic -aromatic random copolyester- based nano-biocomposite materials

Aliphatic-aromatic biodegradable random copolyester, poly (butylene succinate-co-butylene isophthalate) PBSI was synthesised by a two step direct melt polycondensation method. This copolyester was characterised by solubility, viscosity measurements, IR, 1 H NMR, 13 C NMR and thermal studies. But, to be a real alternative to classical synthetic polymers and find applications, biodegradable polymer properties have to be enhanced. Synthesis of nano-biocomposites, which are obtained by incorporation of nanofillers into a biomatrix, is an interesting way to achieve the polymers with characteristic property. In present study, the nano- biocomposites were synthesised by dispersing different weight percentage (1, 3 and 5 %) of organo modified montmorillonite clay (OMMT) into the biodegradable polyester matrix by solvent intercalation method. The structural characterisation and thermal analysis have been carried out to understand better the relationship between the nanofillers structuring and the properties of nano-biocomposites. The X-ray diffraction patterns obtained for the systems confirmed the nanodispersion of OMMT-clay in the polyester networks. The results show that the clay incorporation and the obtained structures enhanced the thermal properties of PBSI, and thus may increase the applicability of this biodegradable polymer in different fields.

Studies on aliphatic -aromatic random copolyester- based nano-biocomposite materials

Aliphatic-aromatic biodegradable random copolyester, poly (butylene succinate-co-butylene isophthalate) PBSI was synthesised by a two step direct melt polycondensation method. This copolyester was characterised by solubility, viscosity measurements, IR, 1 H NMR, 13C NMR and thermal studies. But, to be a real alternative to classical synthetic polymers and find applications, biodegradable polymer properties have to be enhanced. Synthesis of nano–biocomposites, which are obtained by incorporation of nanofillers into a biomatrix, is an interesting way to achieve the polymers with characteristic property. In present study, the nano- biocomposites were synthesised by dispersing different weight percentage (1, 3 and 5 %) of organo modified montmorillonite clay (OMMT) into the biodegradable polyester matrix by solvent intercalation method. The structural characterisation and thermal analysis have been carried out to understand better the relationship between the nanofillers structuring and the properties of nano-biocomposites. The X-ray diffraction patterns obtained for the systems confirmed the nanodispersion of OMMT-clay in the polyester networks. The results show that the clay incorporation and the obtained structures enhanced the thermal properties of PBSI, and thus may increase the applicability of this biodegradable polymer in different fields. Keywords: Nano- biocomposites, biodegradable, montmorillonite clay, aliphatic-aromatic random copolyesters.

Synthesis and Characterization of Stereoblock Poly(lactic acid)s with Nonequivalent D/L Sequence Ratios

Stereoblock poly(lactic acid)s (sb-PLA) consisting of different ratios of d- and l-sequences were synthesized by a process involving solid-state polycondensation (SSP) of polymer blends of poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) of medium molecular weight. Both PLLA and PDLA prepolymers were first prepared by direct melt-polycondensation of l- and d-lactic acids, respectively. These prepolymers were melt-blended in different ratios where their respective partial stereocomplexation could aid in the crystallization of the rich polymer. The melt-blends were then subjected to SSP at a temperature of 140−160 °C, which was lower than the melting temperature of the homochiral polymers. The resultant polymers consisted of longer block chains of the rich components and had molecular weights of higher than 100 kDa when either the PLLA or PDLA ratio in the feed was larger.

Thermal Properties of Copoly(L‐lactic acid/glycolic acid) by Direct Melt Polycondensation

Poly(L‐lactic acid‐co‐glycolic acid) (PLGA) was prepared from hydroxy‐acids with melt polymerization. In this way, the copoly(L‐LA/GA) (PLGA) was synthesized directly using a binary catalyst (tin chloride dihydrate/p‐toluenesulfonic acid). The thermal properties of PLGA were studied by differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR). The results show that the melting point of PLGA decreases with increasing mole fraction of GA units in the copolymer. In addition, the melting point of polymer also decreases with increasing degree of racemization of the polymer.

Syntheses of poly(lactic acid)‐poly(ethylene glycol) serial biodegradable polymer materials via direct melt polycondensation and their characterization

AbstractDirectly starting from lactic acid (LA) and poly(ethylene glycol) (PEG), biodegradable material polylactic acid‐polyethylene glycol (PLEG) was synthesized via melt copolycondensation. The optimal synthetic conditions, including prepolymerization method, catalyst kinds and quantity, copolymerization temperature and time, LA stereochemical configuration, feed weight ratio mLA/mPEG and Mn of PEG, were all discussed in detail. When D,L‐LA and PEG (Mn = 1000 Da) prepolymerized together as feed weight ratio mD,l‐LA/mPEG = 90/10, 15 h copolycondensation under 165°C and 70 Pa, and 0.5 wt % SnO as catalyst, gave D,L‐PLEG1000 with the highest [η] of 0.40 dL/g, and the corresponding MW was 41,700 Da. Using L‐LA instead of D,L‐LA, 10 h polymerization under 165°C and 70 Pa, and 0.5 wt % SnO as catalyst, gave L‐PLEG1000 with the highest [η] of 0.21 dL/g and MW of 15,600 Da. Serial D,L‐PLEG with different feed weight ratio and Mn of PEG were synthesized via the simple and practical direct melt copolycondensation, and characterized with FTIR, 1H NMR, GPC, DSC, XRD, and contact angle testing. D,L‐PELG not only had higher MW than PDLLA, PLLA and L‐PELG, but also better hydrophilicity than PDLLA. The novel one‐step method could be an alternative route to the synthesis of hydrophilic drug delivery carrier PLEG instead of the traditional two‐step method using lactide as intermediate. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 577–587, 2006

Synthesis of poly(L-lactic-co-glycolic acid) telechelic prepolymers by direct melt polycondensation, and their characterization

A series of L-lactic/glycolic acid polymers (PLLGAc) differing in molar ratios of L-lactic (L-LAc) to glycolic (GAc) acid and of relatively low molecular weights [Mn(theor) = 4000] were synthesized by direct melt polycondensation in the presence of 1,4-butanediol and sulfuric acid as a molecular weight regulator and catalyst, respectively. The characterization experiments (FT-IR, 1H NMR) demonstrated a good correlation between the polymer compositions and the ratios of L-LAc and GAc in the feed. The DSC studies of the prepolymers indicated that the melting point as well as degree of crystallinity of PLLGAc decreased with the increase in the molar fraction of GA units in the copolymer. The glass transition temperatures of the polymers varied from 29 to 45 C degrees, depending on the polymer composition. The alkaline hydrolyzability (0.1 M NaOH, 37 C degrees) of the polymers is strongly affected by GA content in PLLGAc. With increasing GA content in the prepolymer, weight loss of a sample becomes faster.

Syntheses of poly(lactic acid‐co‐glycolic acid) serial biodegradable polymer materials via direct melt polycondensation and their characterization

AbstractThe optimal synthetic conditions of poly(lactic acid‐co‐glycolic acid) (PLGA) via melt copolycondensation directly from L‐lactic acid (L‐LA) and glycolic acid (GA) with a feed molar ratio of 50/50 are discussed; the important drug‐delivery carrier PLGA50/50 is used as a special example. With reaction conditions of 165°C and 70 Pa and with 0.5 wt % SnCl2 as the catalyst, 10 h of polymerization gave the L‐PLGA50/50 with the biggest intrinsic viscosity ([η]), 0.1993 dL/g. The optimal synthetic conditions were verified by the synthesis of D,L‐PLGA50/50 with D,L‐lactic acid (D,L‐LA) instead of L‐LA, but the biggest [η] was 0.2382 dL/g. Under the same synthetic conditions with L‐LA and D,L‐LA as starting materials, serial PLGA with different molar feed ratios, including 100/0, 90/10, 70/30, 50/50, 30/70, 10/90, and 0/100, were synthesized via simple and practical direct melt copolycondensation, and their solubilities were investigated. When the glycolic acid feed molar percentage was equal to or more than 70%, solubilities in tetrahydrofuran and CHCl3 became worse, and some samples were even wholly insoluble. These biodegradable polymers were also systematically characterized with gel permeation chromatography, Fourier transform infrared spectroscopy, 1H‐NMR spectroscopy, differential scanning calorimetry, and X‐ray diffraction. PLGA synthesized from L‐LA and D,L‐LA had many differences in weight‐average molecular weight (Mw), glass‐transition temperature, crystallinity, and composition. When the molar feed ratio of LA to GA was 50/50, both the [η] and Mw values of D,L‐PLGA were higher than those of L‐PLGA. With D,L‐LA as the starting material, the structure of the PLGA copolymer was relatively simple, and its properties were apt to be controlled by its GA chain segment. When the feed molar percentage of the monomer (LA or GA) was more than or equal to 90%, the copolymer was apt to be crystalline, and the aptness was more obvious for the L‐LA monomer. The composition percentage of GA in PLGA was not only higher than the feed molar percentage of GA, but also, the GA percentage in D,L‐PLGA was higher than in L‐PLGA. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 244–252, 2006

Thermal decomposition kinetics of thermotropic copolyesters made from trans‐p‐hydroxycinnamic acid and p‐hydroxybenzoic acid

AbstractA series of thermotropic copolyesters were synthesized by direct thermal melt polycondensation of p‐acetoxybenzoic acid (PHB) with trans‐p‐acetoxycinnamic acid (PHC). The dynamic thermogravimetric kinetics of the copolyesters in nitrogen were analyzed by four single heating‐rate techniques and three multiple heating‐rate techniques. The effects of the heating rate, copolyester composition, degradation stage, and the calculating techniques on the thermostability and degradation kinetic parameters of the copolyesters are systematically discussed. The four single heating‐rate techniques used in this work include Friedman, Freeman–Carroll, Chang, and the second Kissinger techniques, whereas the three multiple heating‐rate techniques are the first Kissinger, Kim–Park, and Flynn–Wall techniques. The decomposition temperature of the copolyesters increases monotonically with increasing PHB content from 40 to 60 mol %, whereas their activation energy exhibits a maximal value at the PHB content of 50 mol %. The decomposition temperature, activation energy, the order, and the frequency factor of the degradation reaction for the thermotropic copolyester with PHB/PHC feed ratio of 50/50 mol % were determined to be 374°C, 408 kJ/mol, 7.2, and 1.25 × 1029 min−1, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 445–454, 2004