Gloria Spagnoli

Thermogravimetric investigation of two classes of block copolymers based on poly(lactic-glycolic acid) and poly(ε-caprolactone) or poly(ethylene glycol)

Abstract The thermogravimetric analysis (TGA) of two classes of multi-block copolymers based on poly( d , l -lactic-glycolic acid) (PLGA) and diol-terminated poly(e-caprolactone) (PCDT) or poly(ethylene glycol) (PEG) segments is reported. These materials, having the structure of poly(ester-carbonate)s, were synthesized by a chain extension reaction. The influence of the length of PCDT or PEG segments and of the molar ratio of d , l -lactic acid (LA) and glycolic acid (GA) residues on thermal stability in air and nitrogen atmosphere has been investigated. For comparison purposes the degradation behaviour of starting oligomers was also studied. TGA under nitrogen shows two degradation processes that can be ascribed to the PLGA and PCDT or PEG segments, respectively. In addition, the thermal stability increases with the LA content in the PLGA blocks. In the tests run under air two degradation steps have also been observed, though the former occurs in general at higher temperatures.

2‐[(1‐Imidazolyl)formyloxy]ethyl methacrylate as a new chemical precursor of functional polymers

A novel activated derivative of methacrylic acid, namely 2-[(1-imidazolyl)formyloxy]ethyl methacrylate was synthesized and homopolymerized. The resulting polymer was used in exchange reactions with alcohols and amines, thus showing a potential for the synthesis of multifunctional polymers. All reactions, expecially those carried out in the presence of amines, proceeded under mild conditions. 2-[(1-Imidazolyl)formyloxy]ethyl methacrylate can also be regarded as a valuable precursor for the preparation of new and easily polymerizable functional monomers.

Thermal degradation of two classes of block copolymers based on poly(lactic-glycolic acid) and poly(e-caprolactone) or poly(ethylene glycol)

Thermodegradative investigations of two classes of multi-block copolymers containing poly(D,L-lactic-glycolic acid) (PLGA) and either poly(ethylene glycol) (PEG) or poly(e-caprolactone) diol-terminated (PCDT) segments were performed. In particular, the influence of the type and length of the segments as well as of the molar ratio between the D,L-lactic acid (LA) and glycolic acid (GA) residues was investigated at 180°C in air by viscometry, FT-IR analysis and isothermal thermogravimetry. The thermal oxidative degradation of these materials is largely affected by the LA/GA ratio, a higher LA content generally imparting higher stability. The FT-IR analysis suggests that, depending on the composition of the PLGA segments, degradative processes are triggered which can lead to a preferential degradation of the blocks.

A versatile method for obtaining hydrophobically modified hydrogels

Hydrogels with different degrees of hydrophilicity and cross-link densities were synthesized starting from epoxy monomers and aliphatic amines. Their chemical cross-link density was varied by changing the functionality of monomers or the resin/hardener ratio. Physical cross-links were introduced by incorporating in the polymer network hydrophobic segments, which in aqueous media give hydrophobic interaction. It was shown that the swelling degree, thermosensitivity and mechanical properties of these hydrogels can be easily tailored by changing the concentration and relative amount of physical and chemical cross-links.Hydrogels with different degrees of hydrophilicity and cross-link densities were synthesized starting from epoxy monomers and aliphatic amines. Their chemical cross-link density was varied by changing the functionality of monomers or the resin/hardener ratio. Physical cross-links were introduced by incorporating in the polymer network hydrophobic segments, which in aqueous media give hydrophobic interaction. It was shown that the swelling degree, thermosensitivity and mechanical properties of these hydrogels can be easily tailored by changing the concentration and relative amount of physical and chemical cross-links.

Damage initiated self-healing in ionomer blends

The development and understanding of self-healing mechanisms have been investigated in blends of ionomers (Poly(ethyelene-co-methacrylic acid), sodium & zinc ions) (EMNa & EMZn) containing both elastomers (Epoxidized natural rubbers (ENR) and cis-1,4-Polyisoprene (PISP)) and crystalline component (Poly(vinly alcohol-co-ethylene) [PVAcE]) as secondary phases. All the blends were prepared by melt-blending and self-healing behavior was studied in ballistic puncture tests. Self-healing behavior of each material was evaluated by observing the impact zones under a stereo-optical microscope and the micrographic results were further supported by the fluid flow test in the punctured zones. Interestingly, ENR50 blends of sodium ion containing ionomers exhibited complete self-repairing behavior while zinc ion containing ionomer showed limited mending but EMNa/ENR25 and EMNa/PISP blends did not show any self-healing behavior following the damage. On the other hand, a composition dependent healing behavior was observe...

EFFECT ON STRUCTURAL RELAXATION OF THE POLY(METHYL‐METHACRYLATE) COPOLYMERS CHAIN FLEXIBILITY

The structural relaxation of PMMA copolymers with different chain flexibility has been studied by DSC with two classical procedures, namely: the rate of cooling and the isothermal approaches. The apparent activation energy of enthalpy relaxation was evaluated from the dependence of the glass transition temperature on the cooling rate while a comparison of the apparent relaxation rates was appraised from the enthalpy loss by annealing the different samples at the same level of undercooling (Ta = Tg−18 °C).