No abstract

l-Lactide was ring-opening polymerized in the melt by using different organic monocarboxylic iron complexes. The complexes were those of iron and acetic acid, butyric acid, isobutyric acid, dichloroacetic acid, and trifluoroacetic acid. The polymerization temperature was in the range 170−210 °C, polymerization time between 0.5 and 25 h, and amount of catalyst added varied between 0.12 and 1.20 wt %. Iron butyrate and iron dichloroacetate complexes were low efficient catalysts in the ring-opening polymerization due to hydrolysis during the preparation. Iron acetate, iron trifluoroacetate, and iron isobutyrate complexes were efficient catalysts yielding a high molar mass poly(l-lactide) with a high monomer conversion. Under optimum conditions a poly(l-lactide) with a molar mass (M w) of ca. 150 000 g/mol could be prepared. Monomer conversions over 85% were obtained in many experiments. High polymerization temperatures are required though with these kinds of iron catalysts, and some racemization of the polymerization products is evident. The polymerization experiments indicate that the oxidation state of the iron has an influence on the efficiency of the catalysts and that the iron is chemically bound to the polymer.

No abstract

Poly(lactic acid) (PLA) stereocomplexes have high potential as renewable materials for advanced polymer applications, mainly due to their high melting temperature (Tm, typically 230–240°C). The properties of PLA stereocomplexes consisting of linear high molar mass homopolymers have been studied extensively in the past, but the available information about the possibilities to affect the thermal properties of the stereocomplex by varying the structure of the blend components has not been sufficient. Novel stereocomplexes containing linear or star‐shaped D‐lactic acid (D‐LA) oligomers and high molar mass poly(L‐lactide) (L‐PLA) were thus prepared. The Tm and melting enthalpy (ΔHm) of the racemic crystallites were found to depend strongly on both the blending ratio and the arm‐length of the D‐lactic acid oligomer. The preparation method of the oligomers, i.e. step‐growth polymerization or ring‐opening polymerization (ROP), did not affect the Tm or ΔHm of the blends significantly. Slightly higher ΔHm values were, however, obtained, when linear oligomers were used. The results thus indicated that the Tm and ΔHm of PLA stereocomplexes could be optimized, simply by selecting a D‐LA oligomer having a suitable arm‐length and structure as the other blend component. The possibility to adjust the melting behavior of the stereocomplex blend is a significant advantage and could make PLA suitable for a wider range of products used at elevated temperatures. Copyright © 2010 John Wiley & Sons, Ltd.

ABSTRACT:The condensation reaction product of poly-(lactic acid) (PLA) and a hydroxyl-terminated four-armed poly(-caprolactone) (PCL) was studied by size-exclusion chromatography, DSC, and NMR. The use of both l-lactic acid (LLA) and rac-lactic acid (rac-LA) was studied and the use of two different catalysts, stannous 2-ethylhexanoate [Sn(Oct) 2 ] and ferrous acetate [Fe(OAc) 2 ], was also investigated. The thermal stability and adhesive properties were also measured for the different formulations. The characterization results suggested the formation of a blend of PLA and a block-copolyester of PLA and PCL. The results further indicated partial miscibility in the amorphous phase of the blend showing only one glass-transition temperature in most cases, although no randomized structures could be detected in the block-copolymers. The polymerization in the Fe(OAc) 2 -catalyzed experiments proceeded slower than in the Sn(Oct) 2 -catalyzed experiments. The discoloring of the polymer was minor when Fe(OAc) 2 was used as catalyst, but significant when Sn(Oct) 2 was used. The ferrous catalyst also caused a slower thermal degradation. Differences in the morphology and in the adhesive properties could be related to the stereochemistry of the poly(lactic acid).

L‐lactide was bulk‐polymerized in the presence of various commercially available iron compounds. The polymerization temperature was in the range of 140 and 230 °C, the monomer to initiator/catalyst ratio varied between 100 and 10 000, and the polymerization time between 30 minutes and 24 hours. Iron oxides, iron chlorides and sulfuric iron compounds were low efficient and are not suitable for melt polymerization of lactide. The oxidation state was noticed not to affect the efficiency. Ferrocene required long polymerization times and a high concentration of the compound before a high molar mass polymer was received. Organic iron salts were also found to be efficient initiators/catalysts, except for the hydrated iron(III)citrate. Especially iron(II)acetate caused a rapid polymerization with a high conversion and molar mass.

Five different iron monocarboxylates were used as catalysts in the two-step preparation route of lactic acid based poly(ester-urethane)s (PEU). In the first step, a hydroxyl-terminated poly(lactic acid) prepolymer was prepared, which in the second step was linked with 1,6-hexamethylene diisocyanate. The resulting polymers were characterized by titration, size exclusion chromatography, differential scanning calorimetry, and nuclear magnetic resonance spectroscopy, and the mechanical properties were tested as well. Iron monocarboxylates proved to be efficient catalysts in the preparation of a hydroxyl-terminated prepolymer (lowest acid number obtained: 0.08). The same catalyst systems proved also to be highly efficient in the linking step yielding a high molar mass PEU. Semicrystalline PEUs could be prepared at 160 and 180 degrees C by using the iron acetate of different oxidation state. PEU prepared at 200 degrees C was amorphous, which could be related to racemization during the polycondensation. By using the fluorinated iron acetate amorphous PEUs was prepared at all reaction temperatures. The molar mass of the prepolymers and the PEUs increased as a function of the polycondensation temperature for all catalysts used. The highest weight-average molar masses (M(w)) were obtained by using the fluorinated iron acetate.

The stability of 70 : 24 : 6 w/w/w blends of a lactic acid-based hot melt adhesive (LHM), oxidized potato starch (dried or nondried), and polyethylene glycol (PEG) was studied. Pure LHM was used as a reference material. The methods used included tensile testing, water absorption, and scanning electron microscopy (SEM). During the ageing period of 56 days at ambient conditions (23 6 18C and 42 6 4% RH), the tensile properties of the blends were close to each other, and all of the studied materials had relatively low Young's moduli, compared to reported PLA-starch blends. In the water absorption experiment (23 6 18C), the blends reached significantly higher maximum values than the LHM. The blends also started to disintegrate already after 3 days in water, while the water absorption of pure LHM could be studied for 49 days without detectable disintegration. The SEM images showed that the tensile testing fractures occurred via the continuous LHM matrix in the blends.