The physical and chemical modification of cassava starch was carried out to prepare compounds that were evaluated as corrosion inhibitors of carbon steel under alkaline conditions in 200
mg
L
−1 NaCl ...solutions. Two species were tested: an activated starch (AS) and a carboxymethylated starch (CMS) with two different degrees of substitution (
DS). The success of the chemical procedure was confirmed by
13C NMR. The
DS was determined by back titration and products with 0.13 (CMS
0.13) and 0.24 (CMS
0.24) were obtained. The inhibitive properties were studied by means of electrochemical impedance spectroscopy. It was found that modified starches have corrosion inhibitive properties and that their protection level depends on the type and amount of active groups present in the molecules. AS showed better performance than CMS, whose inhibition ability increases with the degree of substitution. This result was explained by the strong ionic interaction between AS and ferrous cations, which was confirmed by the electrostatic potential mapping of the monomeric units. After the corrosion experiments, the surfaces also were investigated through atomic force microscopy. It was found that a densification of the inhibitive layer was responsible for the higher protection level afforded by AS after 24
h of immersion.
A series of polyacrylamide hydrogels (PAAm HGs) and polymers were synthesized by free radical polymerization in the same reaction conditions but using two different media as solvent: water/ethanol at ...100/0, 80/20, 70/30, 60/40, 50/50, 40/60, 30/70, and 20/80 (
V
/V) and water/DMSO at 100/0, 90/10, 80/20, 70/30, 60/40, 50/50, 40/60, 30/70 and 20/80 (
V
/V). In most cases hydrogels were obtained in high yields and their swelling degree showed a significant dependence with the solvent used in the synthesis. When HGs were synthesized in water/ethanol mixture, the maximum equilibrium swelling (S
eq
) was reached when the water/ethanol ratio was 60/40(
V
/V), while for water/DMSO it was obtained for a water/DMSO ratio 80/20. In both cases, these swelling values were higher than when the HGs were synthesized in pure water. The swelling degree achieved by the HGs in water/ethanol was directly related to the yields and the pore size, but this behavior was not observed for the HGs obtained in water/DMSO. In all cases the HGs obtained in water/DMSO swell more than those obtained in water/ethanol. On the other hand, the molar mass of the PAAm polymers prepared in the same reaction conditions, decrease as the proportion of ethanol or DMSO increase. However, the molar mass reached by the polymers obtained in water/DMSO were higher than those obtained in water/ethanol.
The present work describes the characterization and thermal properties of hydrophobic starch obtained by the esterification of cassava starch with acyl imidazoles, acid chlorides and methyl ester ...derivatives of fatty acids with n-alkyl chains with 12–22 carbon atoms, in order to compare the dependence of their properties as a function of the length of the side chain and the methodology used for their synthesis. The n-acyl starches presented degrees of substitution (DS) between 0.06 and 1.2. Most of the derivatives obtained with acyl imidazoles were found to be stable at temperatures up to 300°C, whereas those synthesized with acid chlorides or methyl ester decomposed below. Finally, when the n-acyl starches were substituted with n-alkyl side chains of 16 or more carbon atoms, they were capable to crystallize in separate paraffinic phases independent of the starch backbone.
Poly(ϵ-caprolactone)-b-poly(ethylene glycol)-b-poly(ϵ-caprolactone) (PCL-b-PEG-b-PCL) triblock copolymer were synthesized by mean anionic activation of the hydroxyl end groups of poly(ethylene ...glycol) in presence of diphenylmethylsodium. Copolymers were characterized by SEC, FT-IR and
1
H-NMR spectroscopy, TGA and DSC. Size exclusion chromatographic analysis of obtained copolymers indicated incorporation of CL monomer into PEG without formation of PCL homopolymer. Characterization by FT-IR and
1
H NMR spectroscopy of the resulting polymeric products, with respect to their structure, end-groups and composition, showed that they are best described as ester-ether-ester triblock copolymers, whose compositions can be adjusted changing the feeding molar ratio of PEG to CL. The thermal stability of triblock copolymers was less that PEG precursor, but higher that PCL homopolymer. Analysis by mean DSC showed that all copolymers were semi-crystalline and their thermal behavior depending on their composition.
Starch complexes were obtained from activated and pregelatinized cassava starch (AS) or carboxymethyl starch (CMS) by using quaternary ammonium salts (QAS). The synthesis of the CMS was carried out ...by a single or double step carboxymethylation reaction with monochloroacetic acid. Different parameters were assayed to prepare the ionic complexes: CMS or AS as starting materials, anhydroglucose unit/QAS ratio, and length of the alkyl chain of the alkyltrimethylammonium bromide (C
n
TAB) salt. The products were characterized by FTIR,
1H and
13C NMR, and the Kjeldhal method. The results indicated a much more favorable complex formation when using CMS, obtaining the highest degree of substitution or complexation (0.72) and reaction efficiency (0.96) when C
18TAB was employed. DSC and WAXS experiments evidenced the crystallization of the octadecyl chain introduced in the starch, exhibiting a dependence on sample water content. TGA and TVA analysis showed the stability of the complexes up to ∼150
°C and that degradation takes place in at least two stages with the release of the surfactant moiety in a first stage and the degradation of the starch skeleton in a second stage.
Block copolymers of ε-caprolactone (CL) and
l
-lactide (
l
-LA) were synthesized by sequential polymerization using diphenylzinc as initiator. The composition of the copolymers was adjusted changing ...the comonomers in ratio. Copolymers were characterized by
1
H-NMR,
13
C-NMR, DSC, and GPC. Results indicate that poly(ε-caprolactone)-
b
-poly(
l
-lactide) (PCL-
b
-PLA) block copolymers had a narrow molecular weight distribution and well-controlled sequences without random placement.
A series of acrylamide/itaconic acid (AAm/IA), acrylamide/monomethoxyethyl itaconate (AAm/MEI), and acrylamide/dimethoxyethyl itaconate (AAm/DEI) hydrogels were synthesized in AAm/comonomer molar ...ratios of 100/0, 90/10, 80/20, and 70/30. In all cases, almost quantitative yields were obtained, and the swelling ability increased when comonomer proportion increased. AAm/MEI and AAm/IA reach swelling values more than 40,000, and both systems swelled more than AAm/DEI. This fact pointed out that the carboxylic acid groups present in IA and MEI are mainly responsible for the swelling. All of these hydrogels are stable up to 150 °C as indicated by the TGA measurements. For comparison, the synthesis of a series of
N
-2-hydroxyethyl acrylamide/itaconic acid (HEAAm/IA),
N
-2-hydroxyethyl acrylamide /monomethoxyethyl itaconate (HEAAm/MEI), and
N
-2-hydroxyethyl acrylamide /dimethoxyethyl itaconate (HEAAm/DEI) hydrogels were also carried out. The swelling behavior of HEAAm/IA and HEAAm/MEI was opposite to the former; in these cases the presence of the itaconate comonomer diminish the swelling ability. A diffusion mechanism study was carried out for all the series.
The (S)‐4‐alkoxo‐2‐azetidinecarboxylic acids are optically active β‐lactam derivatives of aspartic acid, which are used as precursors of carbapenem‐type antibiotics and poly‐β‐aspartates. The crystal ...structures of three (S)‐4‐alkoxo‐2‐azetidinecarboxylic acids with alkyl chains with 10, 12 and 16 C atoms were solved using parallel tempering and refined against the X‐ray powder diffraction data using the Rietveld method. The azetidinone rings in the three compounds display a pattern of asymmetrical bond distances and an almost planar conformation; these characteristics are compared with periodic solid‐state, gas‐phase density‐functional theory (DFT) calculations and MOGUL average bond distances and angles from the CSD. The compounds pack along 001 as corrugated sheets separated by approximately 4.40 Å and connected by hydrogen bonds of the type N—H...O.
Two series of copolymers of styrene with di-
n
-alkyl itaconates or methyl
n
-alkyl itaconates with
n
-alkyl side chains of 12, 14, 16, 18, and 22, using different compositions in the feed have been ...prepared in bulk via radical at 60 °C with AIBN as initiator. In most of the cases the copolymers were obtained in goods yields, their composition being close to the feed composition and their physical states depending on the composition and the itaconate structure. The copolymers were characterized by FTIR and NMR spectroscopy. The
1
H NMR studies indicate that the copolymers have a mainly random distribution of the monomeric units. The thermal degradation process occurs in one step with decomposition temperatures intermediate between those of polyitaconate and polystyrene. Finally, the alkyl side chains of the itaconate moieties are able to crystallize in a paraffinic phase where the melting temperature and enthalpy increase as the itaconate content and the side chain length rise.
