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Papers by Claudia Sandoval

Research paper thumbnail of Blends containing amphiphilic polymers. V. Compatibilization ofN-alkylitaconamic acid-co-styrene copolymers with interacting polymers

Journal of Applied Polymer Science, 2006

The phase behavior of blends containing N-alkylitaconamic acid-co-styrene copolymers (NAIA-co-S) ... more The phase behavior of blends containing N-alkylitaconamic acid-co-styrene copolymers (NAIA-co-S) with poly(N-vinyl-2-pyrrolidone) (PVP) of two different weight average molecular weights (Mw), poly(2-vinylpyridine) (P2VPy) and poly(4-vinylpyridine) (P4VPy), was analyzed by differential scanning calorimetry and Fourier transform infrared spectroscopy. Copolymers containing 80% S are miscible with PVP10, PVP24, and P4VPy over the whole range of composition. In the case of blends with P2VPy, miscibility is observed only for the first three members of the series, i.e., NEIA-co-S, NPIA-co-S, and NBIA-co-S. For copolymers containing hexyl to dodecyl moieties, phase separation is observed in blends with P2VPy. Copolymers containing 50% S are miscible over the whole range of composition irrespective of the homopolymer and the length of the side chain of the itaconamic moiety of the copolymer. This behavior is interpreted in terms of steric hindrance, in the sense that the copolymers with long side chains are not able to interact with the nitrogen of P2VPy because of the position in the aromatic ring. The interactions between copolymers and homopolymers are discussed in terms of specific interactions like hydrogen bonds between the itaconamic moiety and the different functional groups of the homopolymers, together with the hydrophobic interaction, which cannot be disregarded. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2512–2519, 2006

Research paper thumbnail of Dielectric and dynamic-mechanical study of the mobility of poly(t-butylacrylate) chains in diblock copolymers: Polystyrene-b-poly(t-butylacrylate

Polymer, 2008

Dielectric relaxation Block copolymers Glass transition A calorimetric, dielectric and dynamic-me... more Dielectric relaxation Block copolymers Glass transition A calorimetric, dielectric and dynamic-mechanical study of the dynamics of the poly(t-butyl acrylate) (PtBa) chains has been carried out in a PtBa homopolymer and two polystyrene (PS)-b-PtBa block copolymers with different PtBa chain lengths. The DSC results show that the size of the cooperative rearranging regions is similar in the homopolymers and the copolymers, both for the PtBa rich-and the PS-rich regions. Therefore, no significant contributions are found arising from composition fluctuations in the copolymers. The relaxation map obtained from dielectric relaxation indicates that there are no differences in the temperature dependence of the a-relaxation of the PtBa block in the three samples studied. However, there are larger differences for the values obtained from DMTA experiments. Contrary to the a-relaxation, the relaxation map for the (3-transition shows that the characteristic times for the PtBa blocks are smaller in the homopolymer than in the copolymers. In principle, these are unexpected results because the (3-reIaxations have a more local character than the a-ones. The width of the a-relaxation increases with T for all the samples, and it is slightly larger for the copolymers. The intensity of the a-relaxation is larger (between 3 and 4 times) for the homopolymer. Considering the molecular weights of the PtBa blocks, this effect has to be ascribed to the existence of frozen amorphous PtBa due to the existence of the glassy PS domains in the microphase separated copolymers.

Research paper thumbnail of Specific interactions in blends containing Chitosan and functionalized polymers. Molecular dynamics simulations

Polymer, 2005

Chitosan (CS)/poly(vinyl alcohol) (PVA) and Chitosan/poly(2-hydroxyethyl methacrylate) (P2HEM) bl... more Chitosan (CS)/poly(vinyl alcohol) (PVA) and Chitosan/poly(2-hydroxyethyl methacrylate) (P2HEM) blends have been studied through molecular dynamic simulations. In a previous work it was found miscibility between these polymers and it was attributed to hydrogen bonding ...

Research paper thumbnail of Inclusion complexes containing poly(ɛ-caprolactone)diol and cyclodextrins. Experimental and theoretical studies

Polymer, 2009

Inclusion complexes (ICs) between poly(3-caprolactone)diol (PEC) with a-cyclodextrin (a-CD) (a-CD... more Inclusion complexes (ICs) between poly(3-caprolactone)diol (PEC) with a-cyclodextrin (a-CD) (a-CD-PEC) and g-cyclodextrin (g-CD) (g-CD-PEC) were prepared and characterized by FT-IR, 1 H NMR, thermogravimetry, surface activity and wettability measurements. The thermal stabilities of the inclusion complexes are very similar. The thermal stability of PEC is better than ICs and CDs. Stable monolayers of PEC and a-CD-PEC and g-CD-PEC complexes have been obtained at the air-water interface using the Langmuir Technique. The surface pressure-area isotherms (p-A) were found to be of different types, depending on the CD utilized. From the surface free energy values of PEC and ICs it was possible to conclude that ICs are more hydrophobic than cyclodextrins. PEC is the most hydrophobic. The surface parameters the minimum area A 0 , the critical surface pressure p c , and static elasticity 3 0 were also estimated for ICs and PEC. In order to describe the experimental results, molecular dynamic simulation (MDS) was performed. In addition, the physical properties that stabilize CD-CD, CD-polymer and CDsolvent interactions were elucidated by MDS. Theoretical results have demonstrated that complexes are stabilized by hydrophobic interactions between the cavity of CDs and the -(CH 2 ) 5 -units of PEC, and also by hydrogen-bond formation between the hydroxyl groups situated along the rim of CD molecules threaded onto the PEC chain. CD-CD hydrogen-bond formation is maximized in 1:2 g-CD-PEC complex and 1:1 a-CD-PEC complexes.

Research paper thumbnail of Blends containing amphiphilic polymers. V. Compatibilization ofN-alkylitaconamic acid-co-styrene copolymers with interacting polymers

Journal of Applied Polymer Science, 2006

The phase behavior of blends containing N-alkylitaconamic acid-co-styrene copolymers (NAIA-co-S) ... more The phase behavior of blends containing N-alkylitaconamic acid-co-styrene copolymers (NAIA-co-S) with poly(N-vinyl-2-pyrrolidone) (PVP) of two different weight average molecular weights (Mw), poly(2-vinylpyridine) (P2VPy) and poly(4-vinylpyridine) (P4VPy), was analyzed by differential scanning calorimetry and Fourier transform infrared spectroscopy. Copolymers containing 80% S are miscible with PVP10, PVP24, and P4VPy over the whole range of composition. In the case of blends with P2VPy, miscibility is observed only for the first three members of the series, i.e., NEIA-co-S, NPIA-co-S, and NBIA-co-S. For copolymers containing hexyl to dodecyl moieties, phase separation is observed in blends with P2VPy. Copolymers containing 50% S are miscible over the whole range of composition irrespective of the homopolymer and the length of the side chain of the itaconamic moiety of the copolymer. This behavior is interpreted in terms of steric hindrance, in the sense that the copolymers with long side chains are not able to interact with the nitrogen of P2VPy because of the position in the aromatic ring. The interactions between copolymers and homopolymers are discussed in terms of specific interactions like hydrogen bonds between the itaconamic moiety and the different functional groups of the homopolymers, together with the hydrophobic interaction, which cannot be disregarded. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2512–2519, 2006

Research paper thumbnail of Dielectric and dynamic-mechanical study of the mobility of poly(t-butylacrylate) chains in diblock copolymers: Polystyrene-b-poly(t-butylacrylate

Polymer, 2008

Dielectric relaxation Block copolymers Glass transition A calorimetric, dielectric and dynamic-me... more Dielectric relaxation Block copolymers Glass transition A calorimetric, dielectric and dynamic-mechanical study of the dynamics of the poly(t-butyl acrylate) (PtBa) chains has been carried out in a PtBa homopolymer and two polystyrene (PS)-b-PtBa block copolymers with different PtBa chain lengths. The DSC results show that the size of the cooperative rearranging regions is similar in the homopolymers and the copolymers, both for the PtBa rich-and the PS-rich regions. Therefore, no significant contributions are found arising from composition fluctuations in the copolymers. The relaxation map obtained from dielectric relaxation indicates that there are no differences in the temperature dependence of the a-relaxation of the PtBa block in the three samples studied. However, there are larger differences for the values obtained from DMTA experiments. Contrary to the a-relaxation, the relaxation map for the (3-transition shows that the characteristic times for the PtBa blocks are smaller in the homopolymer than in the copolymers. In principle, these are unexpected results because the (3-reIaxations have a more local character than the a-ones. The width of the a-relaxation increases with T for all the samples, and it is slightly larger for the copolymers. The intensity of the a-relaxation is larger (between 3 and 4 times) for the homopolymer. Considering the molecular weights of the PtBa blocks, this effect has to be ascribed to the existence of frozen amorphous PtBa due to the existence of the glassy PS domains in the microphase separated copolymers.

Research paper thumbnail of Specific interactions in blends containing Chitosan and functionalized polymers. Molecular dynamics simulations

Polymer, 2005

Chitosan (CS)/poly(vinyl alcohol) (PVA) and Chitosan/poly(2-hydroxyethyl methacrylate) (P2HEM) bl... more Chitosan (CS)/poly(vinyl alcohol) (PVA) and Chitosan/poly(2-hydroxyethyl methacrylate) (P2HEM) blends have been studied through molecular dynamic simulations. In a previous work it was found miscibility between these polymers and it was attributed to hydrogen bonding ...

Research paper thumbnail of Inclusion complexes containing poly(ɛ-caprolactone)diol and cyclodextrins. Experimental and theoretical studies

Polymer, 2009

Inclusion complexes (ICs) between poly(3-caprolactone)diol (PEC) with a-cyclodextrin (a-CD) (a-CD... more Inclusion complexes (ICs) between poly(3-caprolactone)diol (PEC) with a-cyclodextrin (a-CD) (a-CD-PEC) and g-cyclodextrin (g-CD) (g-CD-PEC) were prepared and characterized by FT-IR, 1 H NMR, thermogravimetry, surface activity and wettability measurements. The thermal stabilities of the inclusion complexes are very similar. The thermal stability of PEC is better than ICs and CDs. Stable monolayers of PEC and a-CD-PEC and g-CD-PEC complexes have been obtained at the air-water interface using the Langmuir Technique. The surface pressure-area isotherms (p-A) were found to be of different types, depending on the CD utilized. From the surface free energy values of PEC and ICs it was possible to conclude that ICs are more hydrophobic than cyclodextrins. PEC is the most hydrophobic. The surface parameters the minimum area A 0 , the critical surface pressure p c , and static elasticity 3 0 were also estimated for ICs and PEC. In order to describe the experimental results, molecular dynamic simulation (MDS) was performed. In addition, the physical properties that stabilize CD-CD, CD-polymer and CDsolvent interactions were elucidated by MDS. Theoretical results have demonstrated that complexes are stabilized by hydrophobic interactions between the cavity of CDs and the -(CH 2 ) 5 -units of PEC, and also by hydrogen-bond formation between the hydroxyl groups situated along the rim of CD molecules threaded onto the PEC chain. CD-CD hydrogen-bond formation is maximized in 1:2 g-CD-PEC complex and 1:1 a-CD-PEC complexes.