Liane Lucy de Lucca Freitas

Caracterização e estabilidade físico-química de sistemas poliméricos nanoparticulados para administração de fármacos

Polymeric nanoparticle systems such as nanocapsules and nanospheres present potential applications for the administration of therapeutic molecules. The physico-chemical characteristics of nanoparticle suspensions are important pre-requisites of the success of any dosage form development. The purpose of this review is to present the state of the art regarding the physico-chemical characterization of these drug carriers, in terms of the particle size distribution, the morphology, the polymer molecular weight, the surface charge, the drug content and the in vitro drug release profiles. Part of the review is devoted to the description of the techniques to improve the stability of colloidal systems.

Influence of the comonomer content on the thermal and dynamic mechanical properties of metallocene ethylene/1-octene copolymers

Studies of ethylene/1-octene copolymers prepared by a metallocene catalyst were carried out through dynamic-mechanical experiments (DMTA), differential scanning calorimetry (DSC), Raman spectroscopy and gel permeation chromatography (GPC). The influence of comonomer content on the ethylene/1-octene properties, specially those related to the dynamic-mechanical behaviour were studied. It was observed that the intensity of the β-transition increases as the comonomer content increases and decreases crystallinity.

Mechanical relaxation in miscible polymer systems: the glass transition regime in poly(vinylmethylether) (PVME)-cross-polystyrene (PS) semi-interpenetrating networks

Abstract Miscible semi-interpenetrating polymer networks (semi-IPN) of varying composition are prepared by crosslinking polystyrene containing few maleic anhydride groups with a diamine in the presence of linear poly(vinylmethylether) (PVME). The resulting PVME-c-P(ScoMA) semi-IPNs are characterized by their thermal and thermomechanical behaviour. Comparison with the corresponding uncrosslinked material proves that weak crosslinking has a negligible effect on the location of the glass transition as measured by d.s.c. Both the Tg data and the temperatures of the loss modulus maximum E″ (at 1 rad/s) show the same non-linear curved composition dependence. Contrary to this the tan δ maximum varies linearly with composition. These experimental results, in combination with frequency dependent measurements show that the temperature dependence of the mechanical response in the glass transition region is thermorheological complex. The results are interpreted by different segmental mobilities of PS and PVME chain segments in the glass transition region.

Dynamic-Mechanical Properties of Ethylene/α-Olefin Copolymers Prepared by a Metallocene Catalyst

The influence of comonomer content and type on the dynamic-mechanical behavior of some ethylene/α-olefin (1-hexene, 1-octene, 1-decene, 1-octadecene and 4-methyl-1-pentene) copolymers was studied. It was observed that the comonomer content has great influence on α- and β-transitions, but almost no influence on γ-transition. Thus the α-transition intensity decreases and β-transition intensity increases as the comonomer content increases. Only 1-octadecene shows a different behavior. A higher comonomer content, ethylene/1-octadecene copolymer shows two defined transitions in the α-transition region, suggesting the presence of crystals of different sizes.

Dynamic mechanical properties of semi-interpenetrating networks based on poly(styrene-co-maleic anhydride)

SummarySemi-interpenetrating networks based on linear anionic polystyrene (PS) and poly(styrene-co-maleic anhydride) P(ScoMA) of low MA content are prepared by crosslinking the P(ScoMA) with 4,4′-diphenylmethanediamine (DPMDA). It is demonstrated by dynamic mechanical analysis and by DSC that immiscible semi-IPNs are obtained for MA contents greater 5 wt.-%. In miscible semi-IPNs the relaxation of free PS chains is observed as a second maximum in the loss tangent at higher temperatures. The position of this maximum is shifted to higher temperatures for a polystyrene of molecular weight 500000 compared to a polystyrene of molecular weight 150000. The experimental temperature shift is in good agreement with a M3 dependence of the terminal relaxation time. In addition the temperature of this second tan δ maximum is shifted to higher temperatures with increasing crosslink density. Again the shift is in good agreement with the theoretical prediction of an increased terminal relaxation time of the relaxing chains with decreasing tube diameter.

Dynamic mechanical properties of semi-interpenetrating networks based on poly(styrene-co-maleic anhydride): 3. Poly(2,6-dimethyl-1,4-phenylene ether)-cross-poly(styrene-co-maleic anhydride)

Semi-IPNs based on linear poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and diamine crosslinked poly(styrene-co-maleic anhydride) (PScoMA) copolymers containing small amounts of maleic anhydride (PSA=4.7wt.-% MA, PSB=5.8 wt-% MA) are studied with respect to the influence of cross-linking on the phase behavior. Temperature-dependent dynamic mechanical analysis (DMA) and DSC show that the semi-IPNs prepared from concentrated solution show weak crystallinity of the PPE phase. After heating above the PPE melting transition the semi-IPNs remain amorphous and the relaxation in the glass transition region as well as the terminal relaxation of the free PPE chains in the network is studied as a function of PPE concentration and network density.