Preparação, caracterização e estudos de biodegradação de blendas à base de PDLLA e PVP

Poly(D,L-lactide), PDLLA, is a polymer with potential applications in medical, environmental, and pharmaceutical areas. Despite its versatility, the hydrophobicity limits its applications. To overcome this problem, one strategy is the preparation of blends with hydrophilic polymers such as poly(vinylpyrrolidone), PVP. In this study, we report the preparation and characterization of blends based on PDLLA and PVP and the biodegradation studies by the Sturm test. It was observed that the components of the blends PDLLA/PVP are thermodynamically immiscible, however the biodegradation is faster than that of pure PDLLA

Synthesis and characterization of the copolymer poly(3-poly(3-hydroxybutyrate)-co-?-caprolactone) from poly(3-hydroxybutyrate) and poly(?-caprolactone)

O copol?mero poli(3-hidroxibutirato-co-?-caprolactona) foi sintetizado por transesterifica??o, a partir dos homopol?meros PHB e PCL, usando acetilacetonato de zirc?nio(IV), como catalisador, nas concentra??es de 20, 50 e 80% de PHB em massa. Os copol?meros foram caracterizados por GPC, m?todos espectrosc?picos (RMN-?H, RMN-13C e IV-FT) e m?todos t?rmicos (TG e DSC). A rota de s?ntese utilizada mostrou-se eficaz na s?ntese dos copol?meros P(HB-co-CL), os quais mostraram diminui??o das cadeias polim?ricas, apresentando Mw inferior a 24.000Daltons. Todos os copol?meros obtidos s?o termicamente mais est?veis que o PHB e com menor cristalinidade que os homopol?meros de partida. Esses materiais s?o bons candidatos para utiliza??o como biomateriais em matrizes para libera??o controlada de f?rmacos ou mesmo como compatibilizante em blendas PHB/PCL.Funda??o de Amparo ? Pesquisa do Estado de Minas Gerais (FAPEMIG)Empresa de Pesquisa Agropecu?ria de Minas Gerais (EPAMIG)Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq)Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES)In the present work, the copolymer poly(3-hydroxybutyrate-co??-caprolactone), P(HB-co-CL), was prepared by transesterification reaction from PHB and PCL. Zirconium (IV) acetylacetonate was used as catalyst and the copolymers were obtained in a wide range of compositions of PHB/PCL (20/80, 50/50, 80/20). These copolymers were characterized by GPC, FT-IR, ?H-NMR, 13C-NMR, TG, and DSC. The copolymers had weight average molecular weight less than 24.000 Daltons. All the systems were thermally more stable than PHB, showing lower crystallinity than the homopolymers. These materials are good candidates to be used as biomaterials, in drug release matrices, or even as PHB/PCL blends compatibilizers

Estudo da oxidação do cicloexano catalisada pelo sistema GIF

Orientador: Ulf Friedrich SchuchardtDissertação (mestrado) - Universidade Estadual de Campinas, Insituto de QuimicaMestrad

Bioartificial polymeric materials based on collagen and poly(N-isopropylacrylamide)

Films of collagen (CLG) and poly(N-isopropylacrylamide), PNIPAAm, were prepared by casting from water solutions. These bioartificial polymeric materials were studied to examine the influence of PNIPAAm content and glutaraldehyde vapor cross-linking on the thermal and biological stability of CLG. Mixtures, ranging from 20-80 wt% CLG composition, were cross-linked through exposure to glutaraldehyde vapors. Thermal and morphological properties of the films, cross-linked or not, were investigated by differential scanning calorimetry, thermogravimetry, and scanning electron microscopy, with the aim of evaluating miscibility, thermal stability, and interactions among the constituents. The experimental results indicated that the homopolymers are not thermodynamically compatible. However, there is good evidence that effective interactions, probably due to hydrogen bond formation, takes place between the constituents. These interactions are more evident on the samples that were not cross-linked. DSC studies revealed that PNIPAAm exerts a thermal stabilizing effect on uncross-linked CLG, while the cross-linking with glutaraldehyde affects only the biological polymer, preventing the interactions with PNIPAAm. SEM micrographs of the uncross-linked mixtures showed that the morphology, in all compositions studied, remains similar to the pure collagen. In the corresponding cross-linked samples, a more compact aggregation is observed although no appreciably changes can be seen

Glycolysis of poly(3-hydroxybutyrate) via enzyme catalysis

Poly(3-hydroxybutyrate), PHB, is a polymer with broad potential applications because of its biodegradability and biocompatibility. However, its high crystallinity is a limiting factor for many applications. To overcome this drawback, one strategy currently employed involves the reduction of the molecular weight of PHB with the concomitant formation of end-functionalized chains, such as those obtained via glycolysis. The glycolysis of PHB can be catalyzed by acid, base, or organometallic compounds. However, to our knowledge, there are no reports regarding PHB glycolysis catalyzed enzymatically. Among the major types of enzymes used in biocatalysis, the lipases stand out because they have the ability to catalyze reactions in both aqueous and organic media. Thus, in this study, we performed the enzymatic glycolysis of PHB using the lipase Amano PS (Pseudomonas cepacia) with ethane-1,2-diol (ethylene glycol) as the functionalizing agent. The results indicated that the glycolysis was successful and afforded hydroxyl-terminated oligomeric PHB polyols. Nuclear magnetic resonance spectra of the products showed characteristic signals for the terminal hydroxyl groups of the polyols, while thermogravimetric and differential scanning calorimetry analyses confirmed an increase in the thermal stability and a decrease in the crystallinity of the polyols compared with the starting PHB polymer, which were both attributed to the reduction in the molecular weight due to glycolysis

P(CL-b-LLA) diblock copolymers grafting onto cellulosic nanocrystals

Cellulose nanocrystals (CNCs) have attracted growing interest as a reinforcement agent in polymer matrices thanks to their biodegradability and excellent mechanical properties. However, due to the polar nature and strong interactions among them, CNCs form aggregates which are difficult to disperse in hydrophobic matrices. To improve CNCs’ dispersion in apolar matrices, we have studied modifications via surface grafting with biodegradable polymers. In this work, CNCs were successfully modified with the P(CL-b-LLA) copolymer via a “grafting onto” method. First, the P(CL-b-LLA) copolymers (Mn molecular weight of 6190 and 10,500 Da) were synthesized by sequential copolymerization of ε-caprolactone (CL) and l-lactide (LLA) using stannous octoate and 1-butanol as initiator and co-initiator, respectively. Then, the grafted CNCs, P(CL-b-LLA)-g-CNC, were obtained through the functionalization of copolymers with toluene-2,4-diisocyanate and subsequent covalent linkage to CNCs’ surface in dry toluene. Surface grafting was confirmed using Fourier transform infrared, proton nuclear magnetic resonance (1H NMR), transmission electron microscopy (TEM), and thermogravimetry (TGA). TEM and TGA analyses indicated that the surface modification of the CNCs occurred to a greater extent with the use of the lower molecular weight copolymer. The resulting modified nanoparticles can find applications as filler and compatibilizer in the field of bionanocomposite materials

HYDROLYTIC DEGRADATION BEHAVIOR OF PLLA NANOCOMPOSITES REINFORCED WITH MODIFIED CELLULOSE NANOCRYSTALS

Bionanocomposites derived from poly(L-Lactide) (PLLA) were reinforced with chemically modified cellulose nanocrystals (m-CNCs). The effects of these modified cellulose nanoparticles on the mechanical and hydrolytic degradation behavior of polylactide were studied. The m-CNCs were prepared by a method in which hydrolysis of cellulose chains is performed simultaneously with the esterification of hydroxyl groups to produce modified nanocrystals with ester groups. FTIR, elemental analysis, TEM, XRD and contact angle measurements were used to confirm and characterize the chemical modifications of the m-CNCs. These bionanocomposites gave considerably better mechanical properties than neat PLLA based on an approximately 100% increase in tensile strength. Due to the hydrophobic properties of the esterified nanocrystals incorporated into a polymer matrix, it was also demonstrated that a small amount of m-CNCs could lead to a remarkable decrease in the hydrolytic degradation rate of the biopolymer. In addition, the m-CNCs considerably delay the degradation of the nanocomposite by providing a physical barrier that prevents the permeation of water, which thus hinders the overall absorption of water into the matrix. The results obtained in this study show the nanocrystals can be used to reinforce polylactides and fine-tune their degradation rates in moist or physiological environments