K. Närhi

Bio: K. Närhi is an academic researcher from Lappeenranta University of Technology. The author has contributed to research in topics: Isomerization & Order of reaction. The author has an hindex of 1, co-authored 1 publications receiving 20 citations.

Synthesis, characterization and crosslinking of functional star-shaped poly(ε-caprolactone)

Abstract: Star-shaped low molecular weight poly(e-caprolactone)s (PCLs) were synthesized and functionalized with crosslinkable terminal groups for subsequent crosslinking. The e-caprolactone (CL) prepolymers were polymerized by ring-opening in the presence of polyglycerine (PGL) as an initiator (1, 3 and 5 mol%) and Sn(II)2-ethylhexanoate as a catalyst. Characterization of the prepolymer by 13C/1H nuclear magnetic resonance (NMR) spectroscopy, size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) revealed a six-armed star-shaped structure for the prepolymer with the molecular weight controlled by the ratio of PGL and CL. Functionalization of the hydroxyl-terminated prepolymer was carried out with maleic or itaconic anhydride. In both cases, the characterization of the functionalized prepolymer showed that the hydroxyl groups were completely substituted. The functionalized PCLs were successfully crosslinked through the reaction of double bonds. The crosslinking was induced either thermally with organic peroxide or photochemically with a photosensitive initiator. Characterization of the crosslinked PCLs by Soxhlet extraction, DSC and FTIR showed that the itaconic double bond was much more reactive in thermal crosslinking than the maleic double bond. Thus, the crosslinked prepolymers that were functionalized with itaconic double bonds achieved a gel content of about 90%. A gel content of 100% was achieved with several compositions where crosslinking agents were employed. © 2002 Society of Chemical Industry

Kinetic model for the increase of reaction order during polyesterification

Abstract: A simple two-parameter model was proposed for the kinetics of polyesterification reactions. The kinetic model is based on the true reaction mechanism, i.e. on the shift of the ionic equilibria in the carboxylic acid (RCOOH) protolysis during the reaction, and on the bimolecular nucleophilic substitution of the protolysed acid with the alcohol (R′OH). The model describes the increase of the reaction order with respect to the carboxylic acid from 1 to 2 as the esterification proceeds. The rate equation r = kc COOH n c OH was used, where n is a function of the carboxylic acid concentration. The kinetic model was tested with the classical data of Flory obtained for diethylene glycol–adipic acid and the lauryl alcohol–adipic acid reactions. The model provided an excellent description of the data over the entire range of conversions of the carboxylic acids and it can be extended to new polyesterification systems.

Kinetic model for the homogeneously catalyzed polyesterification of dicarboxylic acids with diols

Abstract: A generally applicable stoichiometric and kinetic model was developed for the polyesterification of unsaturated dicarboxylic acid with diols in the presence of a homogeneous acid catalyst. The model also incorporates, besides the esterification, the cis-trans isomerization and the double-bond saturation reactions. Rate equations based on plausible mechanistic reaction steps were derived, and the parameters of the rate equations were determined with nonlinear regression analysis using the polyesterification of maleic acid with propylene glycol at 150-190 °C as a demonstration system. Comparisons of the model predictions with the experimental data showed that the approach is useful in predicting the polyesterification kinetics and the product distribution.

Kinetics of polyesterification: modelling of the condensation of maleic anhydride, phthalic anhydride, and 1,2-propylene glycol

Abstract: The kinetic model proposed by Chen and Wu (Chen, S.A.; Wu, K.C. Kinetics of polyesterification. II. Foreign acid-catalyzed dibasic acid and glycol systems. J. Polym. Sci. 1982, 20, 1819–1831.) for the formation of unsaturated polyester resins by reaction between diols and anhydrides has been modified to take into account the difference in reactivity between the two hydroxyl groups of 1,2-propylene glycol and the changes in the concentrations caused by glycol and water removal through distillation during batch polymerisation at elevated temperatures. The specific aim has been to estimate the relative difference in reactivity between maleic and phthalic anhydride to obtain the necessary data for use in computer modelling and simulation studies where the objective was the prediction of coreactant sequence lengths in prepolymers formed by the concurrent reaction of a diol with a mixture of anhydrides. It has been found that the relative reactivity of maleic and phthalic anhydride toward 1,2-propylene glycol a...