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Papers by M. Aguilar-vega

Research paper thumbnail of Gas transport properties of polyphenylene ethers

Gas transport properties of the polyphenylene ethers poly (2,6-dimethyl-l,4-~henylene oxide), PDM... more Gas transport properties of the polyphenylene ethers poly (2,6-dimethyl-l,4-~henylene oxide), PDMPO, and poly (2,6-diphenyl-l,4-phenylene oxide), PDPPO, and the thioether poly ( 1,4phenylene sulfide), PPS, have been measured as a function of pressure and temperature. The PPS material and free volume correlations were used to estimate the behavior of the unavailable poly( 1,4-phenylene oxide), PPO. The results show that symmetrical substitution of phenyl groups on the backbone of polyphenylene ether, PDPPO, increases the gas transport properties by one order of magnitude relative to the unsubstituted material, PPO. Symmetrical methyl substitution, PDMPO, however, increase the permeability, apparent diffusion and sorption coefficients even further. The gas transport coefficients correlate with the fractional free volume of the polymers. PDMPO has the largest fractional free volume and gas transport coefficients followed by PDPPO and then PPS. The results show that substitution of phenyl groups, which leads to polymers that have better thermal and oxidative stability than methyl substituted ones, can be a useful means for increasing free volume and gas permeability coefficients. While methyl groups appear to be more effective for the latter, the enhanced chemical stability of phenyl rings maybe useful when gas separation membranes are to be used in harsh environments. 0

Research paper thumbnail of Synthesis and characterization of aromatic polyamides obtained from 4-4'-(9-fluorenylidene)diamine, 4-4'-(hexafluro-isopropylidene)dianiline and 4-4'-diamine-benzophenone

High Performance Polymers - HIGH PERFORM POLYMERS, 2002

Page 1. High Performance Polymers http://hip.sagepub.com/ Synthesis and Characterization of Aroma... more Page 1. High Performance Polymers http://hip.sagepub.com/ Synthesis and Characterization of Aromatic Polyamides Obtained from 4-4'-(9-Fluorenylidene) Diamine, 4-4'-(Hexafluoro-lsopropylidene)Dianiline and 4-4'-Diamine ...

Research paper thumbnail of Production of leather-like composites using short leather fibers. II. Mechanical characterization

Polymer Composites, 2002

Leicestershire LEI 1 3TU, United Kingdom J. L. CRUZ MACHIN Escuela Militar de lngenieros Calz. Mt... more Leicestershire LEI 1 3TU, United Kingdom J. L. CRUZ MACHIN Escuela Militar de lngenieros Calz. Mtkico-Tacuba, Mkxico, D. F.

Research paper thumbnail of Gas transport properties of polycarbonates and polysulfones with aromatic substitutions on the bisphenol connector group

Journal of Polymer Science Part B: Polymer Physics, 1993

The effect that substitution of aromatic groups on the bisphenol connector unit of bisphenol-A ba... more The effect that substitution of aromatic groups on the bisphenol connector unit of bisphenol-A based polycarbonate and polysulfone materials has on their gas transport properties was assessed. Replacement of a methyl group by a phenyl ring (bisphenol acetophenone polycarbonate, PC-AP, and bisphenol acetophenone polysulfone, PSF-AP ) gives a small increase in permeability coefficients with similar or slightly higher selectivity for all gases compared to bisphenol-A polycarbonate, PC, or polysulfone, PSF. Substitution of two locked phenyl rings ( fluorene bisophenol polycarbonate, FBPC, and fluorene bisphenol polysulfone, FBPSF) in place of the methyl groups in the connector unit leads to permeability and solubility coefficients that are about twice those observed for PC or PSF. Increases in permeability for the polycarbonate and polysulfone materials with aromatic substitutions are related to their larger fractional free volume. FBPC and FBPSF have the largest fractional free volume and the largest permeability coefficients. Thermal measurements show that the fluorene based polycarbonate and polysulfone materials have the highest thermal and oxidative stability. Such aromatic substitutions can be useful for developing gas separation membranes to be used in harsh thermal or oxidative environments. 0 1993 John Wiley & Sons, Inc.

Research paper thumbnail of Gas transport properties of poly(2,2,4,4-tetramethyl cyclobutane carbonate)

Journal of Polymer Science Part B: Polymer Physics, 1993

ABSTRACT

Research paper thumbnail of Dynamic mechanical and gas transport properties of blends and random copolymers of bisphenol-A polycarbonate and tetramethyl bisphenol-A polycarbonate

Journal of Polymer Science Part B: Polymer Physics, 1992

Dynamic mechanical and gas transport properties for homogeneous homopolymer blends and random cop... more Dynamic mechanical and gas transport properties for homogeneous homopolymer blends and random copolymers of bisphenol-A and tetramethyl bisphenol-A polycarbonates ( PC-TMPC) were determined. The gas transport measurements were performed at 35°C for the gases He, H,, O,, Ar, NP, CH4, and CO,. The results show that the copolymers have lower permeability, apparent diffusion, and solubility coefficients than the blends. Permeability coefficients for blends follow a semilogarithmic ideal mixing rule while copolymers exhibit negative deviations from this. Specific volume measurements show that the free volume available for gas transport is slightly larger in copolymers than in blends of the same composition, These apparently contradictory results may relate to the differences in local mode chain motions observed for the copolymer and blend series. The y relaxation processes in PC and TMPC seem to operate independently in the blends (no intermolecular coupling) while there is clear evidence for intramolecular coupling in the copolymers.

Research paper thumbnail of Grafting of poly(acrylic acid) onto cellulosic microfibers and continuous cellulose filaments and characterization

Journal of Applied Polymer Science, 2002

Results from the grafting of poly(acrylic acid) (PAA) onto cellulosic microfibers and continuous ... more Results from the grafting of poly(acrylic acid) (PAA) onto cellulosic microfibers and continuous cellulose filaments are presented. The grafting of PAA onto cellulosic fibers offers the possibility of developing enhanced ion exchange and fluid absorbency on the fibers. The grafting of PAA was carried out with a two-step procedure. First, vinyl-terminated ethoxy silane was deposited on the surface of the fiber. This was followed by a grafting polymerization reaction in aqueous media of acrylic acid with different concentrations of potassium persulfate (KPS), which acted as the initiator. The percentage of grafting increased with increasing KPS concentration and reached a maximum value at a concentration of about 0.4 wt % with respect to the weight of the fiber. The grafted copolymer was characterized by Fourier transform infrared spectroscopy. Strong evidence that the grafting reaction was successful was given by the presence of a band, with a maximum at 1732 cm Ϫ1 , that was characteristic of carbonyl group absorption and was not initially present in the cellulosic fibers. The water absorption of the cellulosic microfibers grafted with PAA was three times greater than the water absorption of the nongrafted microfibers. The mechanical properties of continuous cellulose filaments did not change drastically with PAA grafting.

Research paper thumbnail of Solid phase synthesis of aromatic isophthalic oligoamides with controlled molecular weight

European Polymer Journal, 2009

The synthesis of oligo(hexafluoroisopropylidene isophthalamide) on a solid support of Syn-Phase T... more The synthesis of oligo(hexafluoroisopropylidene isophthalamide) on a solid support of Syn-Phase TM Lanters is described. The repetitive coupling steps using symmetrical diamines and diacid chlorides allows to obtain aromatic oligoamides with controlled molecular weight (M w = 5480 g/mol) and narrow molecular weight distribution (PDI = 1.03) as evidenced by gel permeation chromatography. Moreover, the FTIR and 1 H NMR analysis demonstrated their chemical nature and OH-end groups functionality. The thermal properties of aromatic oligoamides were found to be lower, as expected, than those of poly(hexafluoro-isopropylidene isophthalamide), the same repeating unit high molecular weight polyamide, as judged by differential scanning calorimetry and thermogravimetrical analysis.

Research paper thumbnail of Synthesis of HMDI-based segmented polyurethanes and their use in the manufacture of elastomeric composites for cardiovascular applications

Journal of Biomaterials Science, Polymer Edition, 2007

For short-term cardiovascular application, segmented polyurethanes (SPUs) based on 4,4-methyleneb... more For short-term cardiovascular application, segmented polyurethanes (SPUs) based on 4,4-methylenebis(cyclohexyl isocyanate) (HMDI), polytetramethylenglycol (PTMG) and 1,4-butanediol (BD) were synthesized and characterized by spectroscopy (FT-IR, (1)H-NMR) and thermal (TGA, DMA, DSC) and mechanical techniques. The segmented nature of the SPUs was not easily established by spectroscopic means; however, TGA allowed the quantification of the rigid segments content by the significant mass loss between 348 and 356 degrees C. The alpha transition was detected by DMA and related to the T(g) of the soft segments at -50 degrees C, while DSC showed the presence of an endothermic transition above 80 degrees C attributed to the melting of rigid segments. Two types of composites were prepared using the synthesized SPUs and Lycra (either T162B or T162C). The first one consisted of a two layers casting laminated while the second one was a classic unidirectional fibre-reinforced material. Laminate composites prepared with SPU containing 23.9% and 33.9% of rigid segments and Lycra T162C exhibited a higher tensile modulus but lower tensile strength than composites prepared with Tecoflex SG-80A (39.7% of rigid segments). The energy of adhesion between layers on these composites ranged from 475 to 2150 J. Fibre-reinforced SPUs exhibited higher moduli than the two layer laminated composites with increasing amounts of rigid segments in the matrix and by increasing Lycra T162C content (up to 10%). This behaviour was explained by SEM, which showed a good fibre-matrix bonding.

Research paper thumbnail of Gas transport properties of polyphenylene ethers

Gas transport properties of the polyphenylene ethers poly (2,6-dimethyl-l,4-~henylene oxide), PDM... more Gas transport properties of the polyphenylene ethers poly (2,6-dimethyl-l,4-~henylene oxide), PDMPO, and poly (2,6-diphenyl-l,4-phenylene oxide), PDPPO, and the thioether poly ( 1,4phenylene sulfide), PPS, have been measured as a function of pressure and temperature. The PPS material and free volume correlations were used to estimate the behavior of the unavailable poly( 1,4-phenylene oxide), PPO. The results show that symmetrical substitution of phenyl groups on the backbone of polyphenylene ether, PDPPO, increases the gas transport properties by one order of magnitude relative to the unsubstituted material, PPO. Symmetrical methyl substitution, PDMPO, however, increase the permeability, apparent diffusion and sorption coefficients even further. The gas transport coefficients correlate with the fractional free volume of the polymers. PDMPO has the largest fractional free volume and gas transport coefficients followed by PDPPO and then PPS. The results show that substitution of phenyl groups, which leads to polymers that have better thermal and oxidative stability than methyl substituted ones, can be a useful means for increasing free volume and gas permeability coefficients. While methyl groups appear to be more effective for the latter, the enhanced chemical stability of phenyl rings maybe useful when gas separation membranes are to be used in harsh environments. 0

Research paper thumbnail of Synthesis and characterization of aromatic polyamides obtained from 4-4'-(9-fluorenylidene)diamine, 4-4'-(hexafluro-isopropylidene)dianiline and 4-4'-diamine-benzophenone

High Performance Polymers - HIGH PERFORM POLYMERS, 2002

Page 1. High Performance Polymers http://hip.sagepub.com/ Synthesis and Characterization of Aroma... more Page 1. High Performance Polymers http://hip.sagepub.com/ Synthesis and Characterization of Aromatic Polyamides Obtained from 4-4'-(9-Fluorenylidene) Diamine, 4-4'-(Hexafluoro-lsopropylidene)Dianiline and 4-4'-Diamine ...

Research paper thumbnail of Production of leather-like composites using short leather fibers. II. Mechanical characterization

Polymer Composites, 2002

Leicestershire LEI 1 3TU, United Kingdom J. L. CRUZ MACHIN Escuela Militar de lngenieros Calz. Mt... more Leicestershire LEI 1 3TU, United Kingdom J. L. CRUZ MACHIN Escuela Militar de lngenieros Calz. Mtkico-Tacuba, Mkxico, D. F.

Research paper thumbnail of Gas transport properties of polycarbonates and polysulfones with aromatic substitutions on the bisphenol connector group

Journal of Polymer Science Part B: Polymer Physics, 1993

The effect that substitution of aromatic groups on the bisphenol connector unit of bisphenol-A ba... more The effect that substitution of aromatic groups on the bisphenol connector unit of bisphenol-A based polycarbonate and polysulfone materials has on their gas transport properties was assessed. Replacement of a methyl group by a phenyl ring (bisphenol acetophenone polycarbonate, PC-AP, and bisphenol acetophenone polysulfone, PSF-AP ) gives a small increase in permeability coefficients with similar or slightly higher selectivity for all gases compared to bisphenol-A polycarbonate, PC, or polysulfone, PSF. Substitution of two locked phenyl rings ( fluorene bisophenol polycarbonate, FBPC, and fluorene bisphenol polysulfone, FBPSF) in place of the methyl groups in the connector unit leads to permeability and solubility coefficients that are about twice those observed for PC or PSF. Increases in permeability for the polycarbonate and polysulfone materials with aromatic substitutions are related to their larger fractional free volume. FBPC and FBPSF have the largest fractional free volume and the largest permeability coefficients. Thermal measurements show that the fluorene based polycarbonate and polysulfone materials have the highest thermal and oxidative stability. Such aromatic substitutions can be useful for developing gas separation membranes to be used in harsh thermal or oxidative environments. 0 1993 John Wiley & Sons, Inc.

Research paper thumbnail of Gas transport properties of poly(2,2,4,4-tetramethyl cyclobutane carbonate)

Journal of Polymer Science Part B: Polymer Physics, 1993

ABSTRACT

Research paper thumbnail of Dynamic mechanical and gas transport properties of blends and random copolymers of bisphenol-A polycarbonate and tetramethyl bisphenol-A polycarbonate

Journal of Polymer Science Part B: Polymer Physics, 1992

Dynamic mechanical and gas transport properties for homogeneous homopolymer blends and random cop... more Dynamic mechanical and gas transport properties for homogeneous homopolymer blends and random copolymers of bisphenol-A and tetramethyl bisphenol-A polycarbonates ( PC-TMPC) were determined. The gas transport measurements were performed at 35°C for the gases He, H,, O,, Ar, NP, CH4, and CO,. The results show that the copolymers have lower permeability, apparent diffusion, and solubility coefficients than the blends. Permeability coefficients for blends follow a semilogarithmic ideal mixing rule while copolymers exhibit negative deviations from this. Specific volume measurements show that the free volume available for gas transport is slightly larger in copolymers than in blends of the same composition, These apparently contradictory results may relate to the differences in local mode chain motions observed for the copolymer and blend series. The y relaxation processes in PC and TMPC seem to operate independently in the blends (no intermolecular coupling) while there is clear evidence for intramolecular coupling in the copolymers.

Research paper thumbnail of Grafting of poly(acrylic acid) onto cellulosic microfibers and continuous cellulose filaments and characterization

Journal of Applied Polymer Science, 2002

Results from the grafting of poly(acrylic acid) (PAA) onto cellulosic microfibers and continuous ... more Results from the grafting of poly(acrylic acid) (PAA) onto cellulosic microfibers and continuous cellulose filaments are presented. The grafting of PAA onto cellulosic fibers offers the possibility of developing enhanced ion exchange and fluid absorbency on the fibers. The grafting of PAA was carried out with a two-step procedure. First, vinyl-terminated ethoxy silane was deposited on the surface of the fiber. This was followed by a grafting polymerization reaction in aqueous media of acrylic acid with different concentrations of potassium persulfate (KPS), which acted as the initiator. The percentage of grafting increased with increasing KPS concentration and reached a maximum value at a concentration of about 0.4 wt % with respect to the weight of the fiber. The grafted copolymer was characterized by Fourier transform infrared spectroscopy. Strong evidence that the grafting reaction was successful was given by the presence of a band, with a maximum at 1732 cm Ϫ1 , that was characteristic of carbonyl group absorption and was not initially present in the cellulosic fibers. The water absorption of the cellulosic microfibers grafted with PAA was three times greater than the water absorption of the nongrafted microfibers. The mechanical properties of continuous cellulose filaments did not change drastically with PAA grafting.

Research paper thumbnail of Solid phase synthesis of aromatic isophthalic oligoamides with controlled molecular weight

European Polymer Journal, 2009

The synthesis of oligo(hexafluoroisopropylidene isophthalamide) on a solid support of Syn-Phase T... more The synthesis of oligo(hexafluoroisopropylidene isophthalamide) on a solid support of Syn-Phase TM Lanters is described. The repetitive coupling steps using symmetrical diamines and diacid chlorides allows to obtain aromatic oligoamides with controlled molecular weight (M w = 5480 g/mol) and narrow molecular weight distribution (PDI = 1.03) as evidenced by gel permeation chromatography. Moreover, the FTIR and 1 H NMR analysis demonstrated their chemical nature and OH-end groups functionality. The thermal properties of aromatic oligoamides were found to be lower, as expected, than those of poly(hexafluoro-isopropylidene isophthalamide), the same repeating unit high molecular weight polyamide, as judged by differential scanning calorimetry and thermogravimetrical analysis.

Research paper thumbnail of Synthesis of HMDI-based segmented polyurethanes and their use in the manufacture of elastomeric composites for cardiovascular applications

Journal of Biomaterials Science, Polymer Edition, 2007

For short-term cardiovascular application, segmented polyurethanes (SPUs) based on 4,4-methyleneb... more For short-term cardiovascular application, segmented polyurethanes (SPUs) based on 4,4-methylenebis(cyclohexyl isocyanate) (HMDI), polytetramethylenglycol (PTMG) and 1,4-butanediol (BD) were synthesized and characterized by spectroscopy (FT-IR, (1)H-NMR) and thermal (TGA, DMA, DSC) and mechanical techniques. The segmented nature of the SPUs was not easily established by spectroscopic means; however, TGA allowed the quantification of the rigid segments content by the significant mass loss between 348 and 356 degrees C. The alpha transition was detected by DMA and related to the T(g) of the soft segments at -50 degrees C, while DSC showed the presence of an endothermic transition above 80 degrees C attributed to the melting of rigid segments. Two types of composites were prepared using the synthesized SPUs and Lycra (either T162B or T162C). The first one consisted of a two layers casting laminated while the second one was a classic unidirectional fibre-reinforced material. Laminate composites prepared with SPU containing 23.9% and 33.9% of rigid segments and Lycra T162C exhibited a higher tensile modulus but lower tensile strength than composites prepared with Tecoflex SG-80A (39.7% of rigid segments). The energy of adhesion between layers on these composites ranged from 475 to 2150 J. Fibre-reinforced SPUs exhibited higher moduli than the two layer laminated composites with increasing amounts of rigid segments in the matrix and by increasing Lycra T162C content (up to 10%). This behaviour was explained by SEM, which showed a good fibre-matrix bonding.