Johnson Mathew

Homopolymerization of 4‐propionoxybenzoic acid: A kinetic study

A kinetic study of the synthesis of poly(4-oxybenzoate) by melt-step growth polymerization using para-propionoxybenzoic acid is reported. The polycondensations obey second-order kinetics, irrespective of whether the reaction was catalyzed or uncatalyzed. Breaks are observed in the kinetic plots, suggesting the presence of different kinetic regimes during the course of the reaction. An elaborate kinetic model that presupposes precipitation of oligomers predicts two-stage kinetics as well as breaks in the rate plots and fits experimental data well throughout the course of the reaction and the performance of two transesterification catalysts are estimated. No isokinetic temperature is displayed for the transesterification reaction. Activation energy values for catalyzed reactions are found to be higher than the uncatalyzed reaction, indicating that entropy factors drive the reaction to completion.

Thermotropic polymers: synthesis and kinetic analysis of homopoly(esters)

Abstract Homopoly(esters) similar to those of liquid crystalline poly(oxybenzoate) were prepared by acidolysis of the monomer methyl hydroquinone diacetate and terephthalic acid at equal mole concentrations. The kinetics of catalyzed and uncatalyzed acidolysis of the hydroquinone diacetate and terephthalic acid were investigated at 245°C, 255°C and 265°C. A second-order rate model which can analyze kinetic parameters of two different kinetic regimes has been used to interpret the experimental data for 20 different experimental sets. It is observed that the correlation coefficient between observed and calculated values range between 0.98 and 0.99 confirming the validity of the said model. The nature of the kinetic behaviour in the two regimes were found to be independent of catalyst type and concentration. Second-order rate law describes the entire kinetic behaviour of this system almost adequately. The Arrhenius constants and activation energy parameters for this system have been reported. Oligomers isolated from the homopoly(esters) are expected to be liquid crystalline in nature.

Copolyesters of poly(ethylene terephthalate), hydroquinone diacetate, and terephthalic acid: A simple rate model for catalyzed synthesis in melt

Transesterification reactions between poly(ethylene terephthalate) (PET), hydroquinone diacetate (HQDA), and terephthalic acid (TA), were conducted via the melt polymerization route with the objective of analyzing the copolyesterification kinetics of a phase separated system. At first homopolymerization of HQDA and TA were conducted at 50 mol % composition of each monomer. Then the polymerization kinetics of four compositions [PET 30/70 (HQDA + TA), PET 40/60 (HQDA + TA), PET 50/50 (HQDA + TA), PET 60/40 (HQDA + TA) with 30 : 35 : 35, 40 : 30 : 30, 50 : 25 : 25, and 60 : 20 : 20 mol % PET, HQDA, and TA] were investigated. The following assumptions were made to make kinetic analysis tractable. HQDA and TA combine to form acetic acid and higher oligomers. The oligomer subsequently adds on to the PET chain to give a copolymer of PET/HQDA/TA, the product of interest. The reaction between PET, HQDA, and TA proceeds in a heter-ogeneous two-phase system consisting of PET-rich and PET-poor regions. The reaction sequence is HQDA and TA react to form a dimer and subsequently the dimer is added onto the PET chain. This reaction sequence is assumed to be valid for the PET-rich and PET-poor phases. Both these reactions were assumed to be second order with respect to the reactants. Reactions wherein the dimer reacts with HQDA or TA to form acetic acid exist, but the probabilities of these processes are small with respect to the main reaction postulated above, thus maintaining the overall mass balance. Moles of acetic acid found experimentally were computed using a standard procedure. The rate constant k under the conditions of phase separation was determined. The rate constant in the presence of PET was higher than that observed in the HQDA and TA reaction. An Arrhenius plot revealed that the catalyst plays a marginal role. Microscopic analysis revealed that the HQDA and TA polymer were nonmelting while copolyesters PET 30/70 (HQDA + TA) to PET 60/40 (HQDA + TA) melted and were liquid crystalline.

Copolyesteramides: synthesis and kinetic analysis

Abstract The synthesis of copolyesteramides using para -acetamido benzoic acid (PABA) and polyethylene terephthalate (PET) by melt polymerization has been studied in detail. The performance of three transesterification catalysts are assessed for three different initial compositions, PABA 60 mol%/PET 40%, PABA 50 mol%/PET 50% and PABA 40 mol%/PET 60%. The polycondensations are found to obey second order kinetics, irrespective of whether the reaction was catalysed or not. The mechanism of initial stage polymerization kinetics of the copolymers has been fully explained. It is suggested that acetic acid is evolved only by the homopolymerization of PABA and that the insertion of a monomer of homopolymer of PABA into PET does not yield any acetic acid. A set of differential equations containing three different rate constants, k 1 for homopolymerization of PABA, k 2 for PET reaction with dimer of PABA and k 3 for PABA reaction with copolymer of PABA and PET has been developed and numerically solved, to study the initial stage kinetics. The computed values of acetic acid are compared with the experimentally collected amount and the three rate constants are optimized using a differential algebraic optimization technique. The present model represents the data with an acceptable accuracy with an average % error of less than 5% between experimental and computed values for the entire experimental range. The correlation coefficient values range between 0.988 and 0.999. Differential scanning analysis of the copolyestermides indicates that 40 mol% PABA and 60% PET had the highest enthalpy values of the order of 18 kJ/mol. It is found that within the copolyesteramide series the degree of crystallinity increased with the increase of PET contents in the feed mixture to the batch reactor.

Estimation of inorganic and organic pollutants in Kuwait groundwaters used in irrigation: a study after the gulf war

Kuwait was invaded on August 2, 1990. Around 700 oil wells were destroyed during the Iraqi aggression. Many septic tanks and drainage systems were destroyed. One of the major concerns following the Iraqi invasion is the possibility of ground water contamination. A study of underground water in Kuwait during the period June to December 1993 with regard to irrigation is presented. Water from four different aquifers were analysed for organics and inorganics. A hydrochemical study of these waters indicated that water from (Su‐123), (E‐15) and (PW‐1OL) are suitable for irrigation. The boron concentration in these plants is less than 1 ppm, making it suitable for sensitive and semisensitive crops. Nickel and vanadium are the major inorganics found in crude oil. No appreciable rise in the concentration of these elements was observed. The concentration of polyaromatic hydrocarbons (PAH) and total organic carbon (TOC) is found to vary from 0.01 to 0.07 ppm and 0.21 to 0.9 ppm. PAH is found to vary with location while TOC is found to vary with time.

Kinetics of co-polyesters of hydroquinone diacetate and its methyl derivative with terephthalic acid

The synthesis of hydroquinone diacetate (HQDA), methyl hydroquinone diacetate (MHQDA) and terephthalic acid (TA)-based co-polyesters by melt-step growth polymerization is reported. Two different sets of melt polymerization reactions were carried out, consisting of set A, HQDA+MHQDA (25:25 mol%)+TA (50 mol%), and set B, HQDA+MHQDA (20:30 mol%)+TA (50 mol%). Kinetic models for co-polyesterification reaction were critically examined and a new simple model has been proposed and tested. The performance of sodium acetate and zinc acetate as catalysts were investigated for the polyesterification reaction. Four different reaction temperatures (255, 260, 265 and 270°C) were employed for the kinetic study of both sets A and B. Acetic acid generated by the reaction of HQDA, MHQDA and TA was measured as a function of time. This experimental data were analyzed and various chemical kinetic models in the literature were compared with the suggested model to explain the most realistic reaction mechanism of polyesteri&filigcation reactions. Sodium acetate was found to be better catalyst than zinc acetate for the tri-component system. An induction period was found to be present for the catalyzed and non-catalyzed runs.

Copolyesterification between poly (butylene terephthalate terephthalic acid and hydroquinone diacetate: a Kinetic analysis.

Abstract The kinetics of liquid crystalline copolyester synthesis via melt transesterification between poly(butylene terephthalate) (PBT), terephthalic acid (TA) and hydroquinone diacetate (HQDA) is examined. Two different copolyester compositions PBT30/(HQDA+TA) 70 and PBT 50/(HQDA+TA) 50 mol% ratio were synthesized. The ratio of HQDA to TA was kept constant for all the reactions. The copolyesters were synthesized via melt polycondensation route at 265°C, 275°C and 285°C using two different transesterification catalysts, zinc acetate and dibutyl tin oxide. A key postulation assumed in this work is that the reaction originates between TA and HQDA to form a dimer which slices PBT chain. The copolyesterification rate constant for a system containing butylene glycol a more nonpolar moiety compared to ethylene glycol in poly(ethylene terephthalate) has been determined. The activation energy values for the different copolymer systems has also been determined. The rate constants for the uncatalyzed and catalyzed copolyesterification reaction and the activation energy values for the reaction have been determined.

Isothermal Crystallization Kinetics of Tricomponent Blends of Polycarbonate, Poly(Trimethylene Terephthalate) and Polybutylene Terephthalate

The isothermal crystallization kinetics of two different types of linear aromatic polyesters, namely poly(trimethylene terephthalate) (PTT), poly(butylene terephthalate) (PBT) and their blend with polycarbonate (PC) has been investigated using differential scanning calorimetry (DSC). The blend composed of PTT25/PBT25/PC50 (wt/wt.%) was synthesized using a twin screw extruder. Isothermal studies for PTT were conducted between 129 and 159 °C. The temperature ranged between 168–177 °C for PBT and between 170 and 183 °C for the blend. Avrami, Tobin and Malkin models were used to estimate the crystallization kinetic parameters, such as crystallization rate order (n), crystallization rate constant (k) and half time of crystallization (t0.5). The values of average sum of square of errors (ASE) of all models were comparable. This detailed study indicates that the models investigated are suitable for describing the crystallization kinetics of the blend and the neat polymers.

Kinetics of copolyesters of poly(butylene terephthalate), hydroquinone diacetate and terephthalic acid: A simple rate model for catalysed synthesis in melt.

Abstract Considerable literature exists on the structural organisation of thermotropic liquid crystalline aromatic copolyesters. Majority of these copolyesters are synthesised via the copolymerisation route, which helps in tailoring the characteristic properties to the predecided values. Another major advantage of copolymerisation is that it helps in conferring specific chemical properties to the major component present in the system. Synthesis of aromatic polyesters using bromo, chloro, methyl and methoxy substituted hydroquinones have been reported, to lower the melting temperatures relative to the unsubstituted polyesters. These polyesters have applications in fabricating thermally stable high strength fibres and moulding resins with unusual properties. An understanding of the melt polyesterification kinetics is a must to economise on the process productivity and to improve the polymer properties. There is no published literature on the melt polyesterification kinetics of PBT, HQDA and TA. Kinetic investigation of copolymerisation between PET and 4-acetoxy benzoic acid (PET/OB) did not reveal precipitation of poly (4-oxybenzoate). Here we explore the kinetics of a three component system, wherein many parallel reactions take place simultaneously. Homopolymerisation between HQDA and TA lead to a rigid rod system. The work was carried out with the following objectives: (1) To identify plausible routes to simplif the kinetics of a three component system; (2) To determine the kinetic order with respect to the homopolymers of HQDA and TA as well as the copolymers of PBT, HQDA and TA; (3) To predict the rates of acetic acid generation during the homopolymersiation and copolymerisation reactions and (4) To check whether precipitation constitutes an added complication, as observed in the earlier study on one component 4-acetoxy benzoic acid system.

Chemical Kinetics of a two component phase segregated system. A simple rate model

Considerable research has been performed on polymeric systems that exhibit liquid crystalline or mesomorphic behavior. The principal reason for this effort was that these materials might be developed as ultrahigh strength materials. Jackson and Kuhfuss from Tennessee Eastman demonstrated that liquid crystalline behavior existed in copolymers based on poly(ethylene terephthalate) (PET) and para-hydroxy benzoic acid (ABA). However, intricate details pertaining to the polyesterification kinetics have remained unexamined. Transesterification reactions between poly(ethylene terephthalate) PET, and acetoxybenzoic acid (ABA) were conducted using the melt polymerization technique to understand the transesterification kinetics of a phase segregated system. The transesterification kinetics of two compositions PET 20/80 (ABA) and PET10/90 (ABA) have been studied at 260, 275, 290 and 305°C using dibutyl tinoxide (0.1 mole percent) as a catalyst. Homopolymerization of acetoxy benzoic acid was also studied at similar temperatures and catalyst concentration. In the present experimental work moles of acetic acid found experimentally is computed using a standard procedure. The rate constant k is determined. The role of the catalyst is also evaluated.