Crystallization studies of poly(ε‐caprolactone).I. Morphology and kinetics

Phillips, P. J.; Rensch, G. J.; Taylor, Kevin

doi:10.1002/polb.1987.090250814

Cited by 115 publications

(104 citation statements)

References 16 publications

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“…From the equilibrium melting temperature T m 1 (¼342 K) 37 and the heat of fusion for perfect PCL crystals DH m 1 (¼135 J g À1 ), 25 we find l from DT m throughequations (6) and (7). Figure 6 shows dS for 1 g PCL blocks and l for one PCL block plotted against f PCL , where dS increases steadily with increasing f PCL , suggesting that the conformational entropy of PCL blocks confined in the PE lamellar morphology is considerably reduced when it is compared with that in PCL-b-PB.…”

Section: Discussionmentioning

confidence: 99%

Significant increase in the melting temperature of poly(ɛ-caprolactone) blocks confined in the crystallized lamellar morphology of poly(ɛ-caprolactone)-block-polyethylene copolymers

Sakurai

Nojima

2011

Polym J

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The melting temperature of poly(e-caprolactone) (PCL) blocks, T m,PCL , in PCL-block-polyethylene (PCL-b-PE) is investigated as a function of the volume fraction of PCL blocks in the system, / PCL , and compared with that in PCL-block-polybutadiene (PCL-b-PB), the precursor of PCL-b-PE with an identical PCL molecular weight. The amorphous PCL block in PCL-b-PE is spatially confined within the solid lamellar morphology formed by the advance crystallization of PE blocks (PE lamellar morphology), which will bring about a considerable depression in the conformational entropy of amorphous PCL blocks. On the other hand, PCL-b-PB forms some microdomain structure when the PCL block is amorphous, so that the conformational entropy of amorphous PCL blocks is not so depressed. The value of T m,PCL for PCL-b-PE is always higher than that for PCL-b-PB, and the difference in T m,PCL , DT m , increases steadily with increasing / PCL . However, DT m drops to almost zero when the PCL block in PCL-b-PE crystallizes in the microdomain structure without forming the PE lamellar morphology, which will be ascribed to the recovery of conformational entropy in the amorphous PCL block. The chain stretching of PCL blocks confined in the PE lamellar morphology is discussed on the basis of DT m .

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Section: Discussionmentioning

confidence: 99%

Significant increase in the melting temperature of poly(ɛ-caprolactone) blocks confined in the crystallized lamellar morphology of poly(ɛ-caprolactone)-block-polyethylene copolymers

Sakurai

Nojima

2011

Polym J

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“…Since tP can be measured accurately, if a quantitative relationship between crystallization rate constant and tP is available, the rate constant can be calculated from tP. Such a quantitative relationship may be formulated easily by considering the Avrami equation: (1) where xc(t) is relative crystallinity, n is the Avrami exponent depending on the nucleation mechanism and growth geometry, kn is the crystallization rate constant. It is noted that the rate constant is expressed with a subscript n, km to indicate that the unit of the rate constant is [s]-n dependent on the value of n. If the rate constant is written as k, the rate constant is given by k=k; 1 n and has the unit of [sr 1 .…”

Section: And Discussionmentioning

confidence: 99%

“…The present study extends the previous investigation to discuss the influence of MW on bulk crystallization kinetics and crystallizability of PCL. 1 To whom correspondence should be addressed.…”

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confidence: 99%

Bulk Crystallization Behavior of Poly(ε-caprolactone) with a Wide Range of Molecular Weight

Ou-Yang

Chen

et al. 1997

Polym J

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ABSTRACT:Bulk crystallization kinetics and crystallizability of poly(a-caprolactone) (PCL) with number average molecular weight (M.) ranging from 1900 to 64700 were investigated. Most PCL samples crystallized rapidly at 30 and 40°C, such that the crystallization started before the equilibration of DSC signal. As a consequence, the relative crystallinity required for Avrami analysis could not be calculated accurately from the recorded DSC exotherms. An alternative method is proposed to evaluate the A vrami crystallization rate constant from the peak time of the isothermal crystallization exotherm. The calculated crystallization rate constants of PCL displayed a maximum in variation with molecular weight (MW). Such behavior was attributed to interplay between the MW effects on the thermodynamic driving force and the segmental mobility associated with crystallization. A kinetic formula proposed by Hoffman was used to obtain the crystal surface free energy product (crcr,). In contrast to the conventional Lauritzen-Hoffman analysis based on crystallization rates measured at different crystallization temperatures (Tc) for a given MW, the present analysis was based on rates measured for different MW at a given T,. MW variation of degree of crystallinity also displayed a maximum rather than a monotonic drop. Crystallizability was suggested to be controlled by the presence of uncrystallizable short chains and the entanglements in the polymer. The fraction of the uncrystallizable short chains played the main role in controlling the crystallinity for the low MW samples, while entanglement density was the principal factor for the high MW samples.KEY WORDS Poly(a-caprolactone) / Crystallization / Molecular Weight / Crystallization Kinetics / Crystallinity / Poly(B-caprolactone) (PCL) is a semicrystalline biodegradable polymer with a glass transition temperature (Tg) of ca. -60°C and observed melting point around 55°C. Extensive research of PCL and its blends has been reported. 1 -9 > In a prior study, 10 we prepared PCL with a wide range of molecular weight (MW) (Mn ranging from 1900 to 64700) via fractionation by either precipitating PCL/chloroform solutions into different amounts of methanol or adding methanol into PCL/tetrahydrofuran (THF) solutions. The samples thus obtained were used to investigate the MW effects on the spherulite growth rate, equilibrium melting point (Tr:;), nucleation density, and morphology of PCL. The variation of spherulite growth rate with MW was found to exhibit a maximum rather than conventional monotonic drop. A growth kinetics analysis was also devised to extract the crystal surface free energy based on a MW-growth rate relationship proposed by Hoffman. This analysis was conducted using MW as the variable but crystallization temperature (Tc) as a fixed parameter.In addition to spherulite growth, bulk crystallization behavior such as bulk crystallization kinetics and crystallizability is also a very important aspect of crystalline polymers. The present study extends the previous investigati...

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“…PCL was crystallized at 40°C after isothermal crystallization of PP The formation of such kind of spherulites has been often reported in partially miscible polymers blends containing PCL [6,48] or in block copolymers with a PCL block [45]. However, they have been also observed for PCL homopolymers under specific temperature conditions [49] or in low-molecular-weight PCL fractions [50]. While we observed such superstructures in the PCL crystallized in the blend, under our crystallization conditions, we did not observe banding in the PCL extracted from the same blend.…”

Section: Melting Point Depression Of the Pcl Phasementioning

confidence: 98%

Nucleation versus melting point depression of the polycaprolactone phase in polypropylene/polycaprolactone blends

Balsamo

Gouveia²

2004

E-Polymers

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Polypropylene/poly(ε-caprolactone) (PP/PCL) blends were prepared by melt mixing. The thermal behaviour of the blends was investigated using differential scanning calorimetry (DSC) and dynamical rheology in the solid state (RSA). Both non-isothermal and isothermal crystallizations were performed. The Avrami equation was applied to the latter case. DSC and RSA results demonstrated in agreement with morphological observations that PP/PCL blends are immiscible in the whole composition range. PP acts as a nucleating agent for PCL, and when PP forms the disperse phase, it crystallizes in a fractionated fashion. When PCL is the disperse phase, it exhibits an unexpected melting point depression after cooling at 10 °C/min. Such depression was not observed after isothermal crystallizations, indicating that under non-isothermal crystallization kinetic problems show up. Thus, global crystallization is governed by a competition between nucleation and diffusion, which depends on crystallization conditions and composition.

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Crystallization studies of poly(ε‐caprolactone).I. Morphology and kinetics

Cited by 115 publications

References 16 publications

Significant increase in the melting temperature of poly(ɛ-caprolactone) blocks confined in the crystallized lamellar morphology of poly(ɛ-caprolactone)-block-polyethylene copolymers

Significant increase in the melting temperature of poly(ɛ-caprolactone) blocks confined in the crystallized lamellar morphology of poly(ɛ-caprolactone)-block-polyethylene copolymers

Bulk Crystallization Behavior of Poly(ε-caprolactone) with a Wide Range of Molecular Weight

Nucleation versus melting point depression of the polycaprolactone phase in polypropylene/polycaprolactone blends

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