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Vyazovkin, Sergey

doi:10.1002/1521-3927(20020901)23:13<771::aid-marc771>3.0.co;2-g

Cited by 213 publications

(103 citation statements)

References 20 publications

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“…The corrected relative degree of crystallization, X(t), can be obtained by simple integration of Equation (8).…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…[1] Recently, a major concern has been raised for the use of these procedures in obtaining DE, since they have been formulated for heating experiments (i.e., positive values of a) and dropping the negative sign for a is a mathematically invalid procedure that may sometimes result in erroneous values. [8] The use of multiple heating rate methods such as isoconversional methods is recommended. [5,6] An isoconversional method can in principle be applied to non-isothermal crystallizations for evaluating the dependence of the effective activation energy on conversion and temperature.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…[5][6][7] The popular Kissinger equation used to evaluate the effective activation energy of non-isothermal crystallization has been criticized and proved invalid for processes that occur on cooling such as melt crystallization. [8] According to these authors, since the overall crystallization rate is generally determined by the rates of both nucleation and nuclei growth, the effective activation energy evaluated using Equation (2) should be a function of temperature. [7] All the problems associated with this treatment are eliminated when an advanced isoconversional method is applied.…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of the Isoconversional Approach to Estimating the Hoffman‐Lauritzen Parameters from the Overall Rates of Non‐Isothermal Crystallization of Polymers

Achilias

Papageorgiou

Karayannidis

2005

Macro Chemistry & Physics

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Summary: The isoconversional approach proposed by Vyazovkin for evaluating the Hoffman‐Lauritzen parameters from overall rates of non‐isothermal crystallization was critically applied to two new and fast crystallizing polymers, poly(propylene terephthalate) and poly(butylene naphthalate), which are used for the production of fibers. Non‐isothermal crystallization data were corrected for the effect of the thermal lag and the effective activation energy as a function of temperature was calculated using the method of Friedman. The estimated Hoffman‐Lauritzen parameters, U* and Kg, were consistent with corresponding values from isothermal crystallization experiments obtained either from DSC measurements or using polarized optical microscopy (POM). It was found that the proposed method could simulate the experimental data very well, and the temperature interval under consideration did not allow the detection of any critical breakpoints denoting regime transitions.

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“…The corrected relative degree of crystallization, X(t), can be obtained by simple integration of Equation (8).…”

Section: Theoretical Backgroundmentioning

confidence: 99%

Section: Theoretical Backgroundmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Evaluation of the Isoconversional Approach to Estimating the Hoffman‐Lauritzen Parameters from the Overall Rates of Non‐Isothermal Crystallization of Polymers

Achilias

Papageorgiou

Karayannidis

2005

Macro Chemistry & Physics

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“…The main objective of these methods is to define a finite relationship between the peak temperature T p obtained for a given condensed phase reaction and the heating rate φ used. A major concern for use of these procedures in obtaining the kinetic information for the nonisothermal crystallization process which occurs on cooling has recently been raised [22], since the original mathematic expression for these procedures does not permit substitution of the negative heating rates, φ (i.e. cooling rates).…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…In this work, the Friedman method will be used, due mainly to the reliability and simplicity of the method [22,26]. The Friedman equation is expressed as…”

Section: Theoretical Backgroundmentioning

confidence: 99%

Nonisothermal melt-crystallization kinetics for three linear aromatic polyesters

et al. 2003

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The kinetics of nonisothermal crystallization of three different types of linear aromatic polyester, namely poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), and poly(butylene terephthalate) (PBT), which are different in their number of methylene groups (i.e. 2, 3, and 4 for PET, PTT, and PBT, respectively), was investigated using differential scanning calorimetry (DSC). Analysis of the data was carried out based on the Avrami, Tobin, Ozawa, and Ziabicki models. It was found that the Avrami model provided a more satisfactorily good fit to the experimental data for these polyesters than did the Tobin model. The Ozawa model was found to describe the experimental data fairly well. The Ziabicki's kinetic crystallizability parameter G for these polyesters was found to be of the following order: PBT > PTT > PET. The effective energy barrier for nonisothermal crystallization process of these polyesters, determined by the Friedman method, was found to be an increase function with the relative degree of crystallinity.

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Catalytic Asymmetric CN Bond Formation: Phosphine‐Catalyzed Intra‐ and Intermolecular γ‐Addition of Nitrogen Nucleophiles to Allenoates and Alkynoates

et al. 2013

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The first examples are described of catalyzed -additions of nitrogen nucleophiles to -substituted alkynoates or allenoates that proceed with good efficiency, specifically, intra-and intermolecular processes that employ distinct and useful families of nitrogen nucleophiles (anilines and 2,2,2-trifluoroacetamide), catalyzed by spirophosphine 1. Furthermore, the first demonstrations are reported of asymmetric reactions, affording interesting classes of target molecules such as enantioenriched pyrrolidines, indolines, and -amino-, -unsaturated carbonyl compounds. Keywords amination; asymmetric catalysis; heterocycles; organocatalysis; phosphanesThe use of chiral phosphines as nucleophilic catalysts represents an important second dimension to their utility in catalytic asymmetric synthesis, [1] in addition to their more familiar role as ligands for transition metals. [2] Cognizant of the paucity of general methods for the catalytic enantioselective -functionalization of carbonyl compounds, [3] we have recently pursued the development of phosphine-catalyzed processes that couple nucleophiles with allenoates and related compounds in the -position (Figure 1). [4][5][6] Given the ready availability of the starting allenes, along with the plethora of methods for stereoselectiveand -functionalization of , -unsaturated carbonyl compounds, [7,8] this approach should provide straightforward access to highly functionalized, stereochemically rich, target molecules ( Figure 1).To date, we have established the viability of this approach with oxygen (intramolecular additions to alkynes), carbon (intermolecular/allenes), and sulfur (intermolecular/allenes) nucleophiles. [4] In view of the biological significance of amines, [9,10] including -amino-, -unsaturated carbonyl compounds, [11][12][13] achieving catalytic enantioselective -additions with nitrogen nucleophiles is a particularly important objective. [14] However, attempts to effect phosphine-catalyzed -addition (even non-enantioselective) of nitrogen nucleophiles to -substituted 2,3-allenoates and 2-alkynoates (and related compounds) have been unsuccessful (≤30% yield), [15] due in part to the propensity of such electrophiles to isomerize to 1,3-dienes. [16] In this report, we demonstrate that spirophosphine 1 not only can achieve C-N bond formation in good yield for the first time, but it can also provide good enantioselectivity, both for intra-and for intermolecular processes [Eq. (1) and Eq. (2); CPME = cyclopentyl methyl ether; TBME = tbutyl methyl ether].(1) (2) From the outset of our investigation of phosphine-catalyzed -additions of nitrogen nucleophiles, we decided to address simultaneously the two key challenges: accomplishing C-N bond formation and controlling the stereochemistry of the -carbon. Upon examining an array of conditions for the enantioselective cyclization of the amino-alkyne illustrated in entry 1 of Table 1, we developed a method whereby spirophosphine 1 [17][18][19] catalyzes the desired intramolecular -addition to generate the target pyrro...

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Cited by 213 publications

References 20 publications

Evaluation of the Isoconversional Approach to Estimating the Hoffman‐Lauritzen Parameters from the Overall Rates of Non‐Isothermal Crystallization of Polymers

Evaluation of the Isoconversional Approach to Estimating the Hoffman‐Lauritzen Parameters from the Overall Rates of Non‐Isothermal Crystallization of Polymers

Nonisothermal melt-crystallization kinetics for three linear aromatic polyesters

Catalytic Asymmetric CN Bond Formation: Phosphine‐Catalyzed Intra‐ and Intermolecular γ‐Addition of Nitrogen Nucleophiles to Allenoates and Alkynoates

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