Ann-Christine Albertsson

Aliphatic Polyesters: Synthesis, Properties and Applications

The synthesis of aliphatic polyesters by polycondensation and ring-opening polymerization is reviewed. This includes homopolyesters, random, block, graft, star, and hyper-branched (co)polyesters. Recent progress in the synthesis of high molecular weight aliphatic polyesters is described. Specific properties of these polymers are also given. The biomedical and ecological applications of these biodegradable polymers show their technological importance and relevance.

Degradable Polymer Microspheres for Controlled Drug Delivery

Controlled drug delivery technology is concerned with the systematic release of a pharmaceutical agent to maintain a therapeutic level of the drug in the body for a sustained period of time. This may be achieved by incorporating the therapeutic agent into a degradable polymer vehicle, releasing the agent continuously as the matrix erodes. This review is concerned with degradable polymers for use in controlled drug delivery with emphasis on the preparation, applications, biocompatibility, and stability of microspheres from hydrolytically degradable polymers.

From Lactic Acid to Poly(lactic acid) (PLA) : Characterization and Analysis of PLA and Its Precursors

The quality of the monomers lactic acid and lactide as well as the chemical changes induced during polymerization and processing are crucial parameters for controlling the properties of the resulting poly(lactic acid) (PLA) products. This review presents the most important analysis and characterization methods for quality assessment of PLA and its precursors. The impurities typically present in lactic acid or lactide monomers and their possible origins and effects on resulting PLA products are discussed. The significance of the analyses for the different polymer production stages is considered, and special applications of the methods for studying features specific for PLA-based materials are highlighted.

The mechanism of biodegradation of polyethylene

LDPE films have been exposed to abiotic and biotic environments. The films were UV irradiated for periods of 0, 7, 14, 26 and 42 days before being mixed with water and soil. Degraded LDPE films were examined by infra-red spectroscopy. The carbonyl peak increased with time in the abiotic environment and the oxidative degradation reported in our earlier works was confirmed. In the presence of a biotic atmosphere, however, this peak decreased. At the same time there was an increase in double bonds which was related to weight loss. An explanation of this behavior is presented as a proposed mechanism for the biodegradation of polyethylene. This mechanism is compared, on the one hand, with abiotic photooxidation, Norrish type I and II degradation, and, on the other, with the biotic paraffin degradation. Abiotic, as well as biotic, ester formation mechanisms are also presented. An ESR spectrum confirms the presence of radicals on the polyethylene samples. At the beginning of the degradation the main agents seem to be UV light and/or oxidizing agents. When carbonyl groups have been produced, these are attacked by microorganisms which degrade the shorter segments of polyethylene chains and form carbon dioxide and water as end products. There is a synergistic effect between photooxidative degradation and biodegradation. The biodegradation of polyethylene can be compared with the biodegradation of paraffin.

Controlled ring-opening polymerization: Polymers with designed macromolecular architecture

This paper reviews ring-opening polymerization of lactones and lactides with different types of initiators and catalysts as well as their use in the synthesis of macromolecules with advanced architecture. The purpose of this paper is to review the latest developments within the coordination-insertion mechanism, and to describe the mechanisms and typical kinetic features. Cationic and anionic ring-opening polymerizations are mentioned only briefly.

Novel pH-sensitive chitosan hydrogels: swelling behavior and states of water

Physically crosslinked chitosan hydrogels were synthesized by grafting D,L-lactic acid (LA) and/or glycolic acid (GA) with different feed ratios. The physical crosslinking was formed due to the hyd ...

Weight losses and molecular weight changes correlated with the evolution of hydroxyacids in simulated in vivo degradation of homo- and copolymers of PLA and PGA

Abstract Homo- and copolymers of poly(lactide)s (PLA) and poly(glycolide)s (PGA) were hydrolysed at 37 and 60 °C for periods up to 80 days. We propose that the hydrolyses of PLA100 (100% L-lactide), PLA37.5GA25 (75% D,L-lactide and 25% glycolide) and PLA25GA50 (50% D,L-lactide and 50% glycolide) in buffer solutions at 37 and 60 °C proceed in three stages. During the first stage the molecular weights decrease rapidly with little weight loss. In stage two, the decrease in molecular weight slows down and severe weight loss starts in parallel with which monomer formation is initiated. During the final third stage, when total weight loss is observed, about 50% of the polymer is converted to monomer. The hydrolyses of the soluble oligomers continues until all are transferred to lactic acid and glycolic acid.

Polyesters based on diacid monomers

Polymers with ester linkages in their main chain comprise a family of polymers with immense diversity and versatility. This review deals with the preparation of such polymers from dicarboxylic acid monomers, and the result in terms of properties and applicability. Polyesters alone, and their copolymers with amides, anhydrides, urethanes, imides, ethers or other functional groups, offer countless opportunities to tune the properties of the resulting material within a broad range. Of particular interest is the inherent biodegradability of the ester linkage. Biodegradability is sought after in a wide range of applications, above all in the preparation of environmentally friendly polymers and biomedical materials for temporary surgical use and in drug delivery.

Chemical and morphological changes of environmentally degradable polyethylene films exposed to thermo-oxidation

Abstract Thermo-oxidation of blown low density polyethylene (LDPE) films modified with different combination of biodegradable filler, prooxidant and photosensitizers was conducted in oven at 60 and 100°C for a period of 14 days. Volatile and semivolatile degradation products were extracted by solid phase micro extraction (SPME) technique and identified utilizing gas chromatography–mass spectrometry (GC–MS). Chemical and morphological changes were monitored and these are given as carbonyl index, crystallinity and melting behavior, molecular weight and molecular weight distribution. The samples containing solely prooxidant showed the highest susceptibility to thermal degradation during the test period. The second most degradable samples were LDPE modified with 20% masterbatch (containing starch and a prooxidant). LDPE containing only starch did not show any degradation during the test period. The major degradation products were homologous series of carboxylic acids, ketones, hydrocarbons and lactones. 4-Oxopentanoic acid, 5-oxohexanoic acid and benzoic acid were identified only in LDPE containing prooxidant (LDPE-PO) and LDPE modified with 20% masterbatch (LDPE-MB). A small number of aldehydes (3-methyl pentanal, benzaldehyd and 2-propyl 5-oxohexanal) were identified solely in LDPE-MB. Esters could be identified only from LDPE-Starch and pure-LDPE samples. The crystallinity of all the samples increased after aging at 60°C except for LDPE-Starch which showed no significant change in crystallinity. The melting thermograms of LDPE-PO and LDPE-MB (first heating) exhibited low temperature shoulders around 75°C (after treatment at 60°C) and appears to move downward with increasing exposure temperature (treatment at 100°C). The shoulders near 115°C (second heating) increase with increasing exposure temperature which is due to a preferential scission at the tertiary carbon atom as observed by increased crystalline melting point. ATR and transmission FTIR show that the absorbance of carbonyl containing groups is almost the same on the surface as in the bulk for virgin samples and samples aged at 60°C. Opposite to the other materials, LDPE-MB samples aged at 100°C show a much faster increase in the absorbance of carbonyl containing groups in the bulk of the film than on the surface layer. This indicates that the bulk of the latter films are more labile than the surface which could be a consequence of higher starch concentration on the surface than in the bulk.

Degradation product pattern and morphology changes as means to differentiate abiotically and biotically aged degradable polyethylene

Degradation product pattern and morphology changes as means to differentiate abiotically and biotically aged degradable polyethylene