Structure and dynamics of melt poly(ɛ-caprolactone) from inverse rheological calculation

Abstract

IntroductionThe correlation of the flow curves of a melt polymer and its molecular weight distribution (MWD) has long been a subject of discussion. The first papers on the inverse problem were published by Tuminello 1) and Malkin et al. 2)Within the last ten years, the resolution of the inverse problem has been extensively treated because the forward problem of the calculation of the dynamic moduli has received interesting new developments from a molecular point of view. For example, the concept of double reptation proposed by Tsenoglou 3) and Des Cloizeaux 4) is now viewed as the reference model for the calculation of dynamic moduli from known MWDs.Two different approaches to the inverse solution were generally used. The first one tries to solve the ill-posed problem by using either a numerical algorithm based on a Tikhonov regularization procedure (Wasserman 5) , Leonardi et al. 6) ) or a regularization method using quadratic programming (Ramkumar and Wiest 7) ). Wasserman used various relaxation spectra with a mixing rule based on the double reptation concept, whereas Leonardi et al.6) used an empirical blending law on complex viscosities. This second method also uses numerical methods but these methods postulate the shape of the MWD, giving its analytical form as some typical shapes of the MWD which are generally assumed in the case of a particular polymerization process. Different works can be cited: Tuminello 1,8,9) , Malkin and Teishev 2) , Wood-Adams and Dealy 10) . Carrot and Guillet 11) proved that a reasonable solution to the inverse problem, i. e., the determination of the MWD from dynamics experiments in the linear viscoelastic domain, can be found using simple molecular dynamics together with additional information concerning the shape of the MWD. Full Paper:The linear viscoelastic behavior of poly(ecaprolactone) (PCL) in situ synthesized between the plates of the rheometer was investigated. The polymerization of e-caprolactone was initiated and catalyzed by titanium tetrapropoxide. These polymers are very sensitive to hydrolysis of the alkoxy-titanium bonds included in the polymer chains. Two different forms of PCL can be studied: hydrolyzed or non-hydrolyzed PCL. However, only the molecular weight distribution (MWD) of the hydrolyzed chains can be accessed from size exclusion chromatography (SEC) analysis. The MWD of the in-situ synthesized poly(e-caprolactone) was calculated by solving the inverse problem of determination of the MWD from rheological data. A continuous form of the relaxation function was derived and an a priori shape (Wesslau or bi-modal Wesslau ) of the MWD was assumed. Then MWDs calculated from complex moduli curves were used to investigate the structure of the poly(e-caprolactone) at the end of the polymerization process. About 85% of the polymer chains consist of a single branched linear structure. The remaining 15% are assumed to be mainly two fold branched. The presence of star structures cannot be precluded. The present work describes an illustrative example of the s...

The influence of molar mass on rheological and dilute solution properties of poly(butylene succinate)

“…This value is in agreement with M c mentioned in the literature for other aliphatic polyesters such as poly(lactic acid) (PLA) or poly( ε ‐caprolactone) (PCL). Indeed, M c of PLA has been estimated between 9000 and 16,000 g mol −1 , while that of PCL has been estimated between 8000 and 16,000 g mol −1 …”

“…Indeed, M c of PLA has been estimated between 9000 and 16,000 g mol 21 , 27,28 while that of PCL has been estimated between 8000 and 16,000 g mol 21 . [29][30][31] The Activation Energy E a of Melt PBS. The activation energy E a of melt PBS was calculated from temperature-dependent shift factor a T , determined from the TTS principle.…”

Controlled Synthesis and Ti—O Bond Stability of Star‐Shaped Biodegradable Polyesters via Titanate‐Initiated ROP of Cyclic Esters at Ambient Temperature

“…There are only a few literature reports regarding the facile ROP of cyclic esters using titanium alkoxide complex initiated at ambient temperature. What is more, almost all publications reported typically by Kricheldorf et al,46 Michel et al41, 47 thought that Ti‐alkoxide bonds included in the polymer chains are extremely sensitive to water and alcohols, however, without detailed supporting data on the TiO bond stability in polymer chains. The star‐shaped structure is thought to breaks down when the resulting polymers are precipitated into methanol or exposed to moisture air 46, 47.…”

“…What is more, almost all publications reported typically by Kricheldorf et al,46 Michel et al41, 47 thought that Ti‐alkoxide bonds included in the polymer chains are extremely sensitive to water and alcohols, however, without detailed supporting data on the TiO bond stability in polymer chains. The star‐shaped structure is thought to breaks down when the resulting polymers are precipitated into methanol or exposed to moisture air 46, 47. Recently, we have reported a preliminary result regarding the ROP of CL using tetrabutyl titanate and demonstrated that it exhibited much higher catalytic activity for ROP of CL 48.…”

Reactive Processing of Thermoplastic Polymers: A Review of the Fundamental Aspects

“…9B shows the resulting viscoelastic master curve of the sample so in situ polymerized. From these complex moduli curves, the molecular weight distribution (MWD) of the polymer can be calculated by inverse rheological method [219] in order to investigate the structure of the poly(e-caprolactone) at the end of the polymerization process.…”