Jesús Contreras

Ring-opening polymerization of ε-caprolactone initiated by diphenylzinc

Abstract In the present work the polymerization of e -caprolactone ( e -CL) using Ph 2 Zn as initiator is reported. The effects of reaction temperature, molar ratio of monomer/initiator and reaction time on the yield and the molecular weight are investigated. The temperature is varied between 20 and 120 °C and the molar ratio of monomer to initiator between 200 and 800 mol/mol. The results indicate that the Ph 2 Zn induces the polymerization of e -CL to high conversion and produces polymer with high molecular weight at temperatures around 40–60 °C.

Epoxide polymerization—IX. Styrene oxide polymerization using the diphenylzinc-water system in benzene at various temperatures

Abstract The diphenylzine-water system was used as a catalyst for styrene oxide polymerization in benzene solution at 25, 60 and 90°. The system, as for polymerization of ethylene oxide or propylene oxide, is greatly influenced by the molar ratio of water to diphenylzinc; unlike the other monomers however diphenylzinc by itself produced the best yield to polymer and conversion to poly(styrene oxide) (PSO) diminished when water was added. GPC results confirm the presence of more than one active species for the system; 13C-NMR analysis indicates that the resulting PSO always has a head-to-tail arrangement, independent of the molar ratio of H2O/Ph2Zn. From viscometry results, a viscometric equation for PSO in chloroform at 40°, was derived, viz. [η] = 4.49 × 10 −5 × M v 0.873 .

Characterization of esterified cassava starch with long alkyl side chains and different substitution degrees.

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.

Epichlorohydrin polymerization using diphenylzinc-cocatalyst systems in benzene solution

SummaryVarious diphenylzinc-cocatalyst systems were used as initiators of epichlorohydrin polymerization in benzene solution. Water, acetone, butanone, acetophenone and cyclopentanone were employed as cocatalyst but in the most of the cases diphenylzinc alone produced the better conversion to polymer. GPC results suggest the presence of more than one active species for the polymerization initiated by those systems. For diphenylzinc alone as initiator the reaction at 120°C is first order with respect to monomer with kp=1.21x10 -5L mol-1sec-1.

Some aspects on the polymerization of ethylene oxide initiated by diphenylzinc-butanone and diphenylzinc-cyclohexanone systems

SummaryThe diphenylzinc-butanone and diphenylzinc-cyclohexanone systems were used as catalyst for ethylene oxide polymerization in benzene solution at 60°C. The catalytic activity of both systems is influenced by the molar ratio of ketone to diphenylzinc. Regardless of the molar ratio employed, the diphenylzinc-cyclohexanone combination was more active in the polymerization than diphenylzinc-butanone system. GPC results strongly suggest the presence of more than one active species for these systems.

Propylene oxide polymerization using the diphenylzinc-acetone system in benzene at 60°C

SummaryThe diphenylzinc-acetone system was used as catalyst for propylene oxide polymerization in benzene solution at 60°C. This system as well as the diphenylzinc-water system is greatly influenced by the molar ratio of acetone to diphenylzinc and the maximum catalyst activity was found for a ratio of unity. GPC results strongly suggest the presence of more than one active species for the system.13CNMR analysis indicates that the resulting poly(propylene oxide) has a head-to-tail arrangement. This system was not an effective catalyst for the styrene oxide polymerization.

Propylene oxide polymerization by diphenylzinc-ketone systems at 60°

Abstract Propylene oxide (PO) was polymerized by some diphenylzinc-ketone systems. Cocatalytic effects of nine ketones were examined. The systems are greatly influenced by the nature of the ketone and by the molar ratio of ketone to diphenylzinc. Methyl and cyclic ketones were the most effective as cocatalyst and the maximum catalyst activity was found, in most cases, for a molar ratio of unity. The difference in cocatalyst activities for methyl ketones is attributed to electronic effects, while steric hindrance is not relevant. Similar effects were found for PO polymerization initiated by diphenylzinc in combination with cyclic and with non-halogenated methyl ketones. However the activity of the diphenylzinc-diethyl ketone system increases with increase of the molar ratio. The diphenylzinc-benzophenone system shows a small dependence on the molar ratio. The activity of the diphenylzinc-acetylacetone decreases with increase of the molar ratio showing maximum conversion to polymer when no ketone was added. Polymerization of ethylene oxide by some of these systems showed behaviour similar to that found for PO.

Synthesis of ε-caprolactone-b-l-lactide block copolymers by mean sequential polymerization, using diphenylzinc as initiator

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 1H-NMR, 13C-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.

Synthesis and characterization of aba-type block copolymer of poly(ϵ-caproplactone) with poly(ethylene glycol), by mean of activation end groups

ABSTRACT 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 1H-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 1H 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.