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Different paths to explore confined crystallisation of PCL
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this work, different paths to confined crystallisation of poly(ε-caprolactone) (PCL) havebeen explored. Innate confinement effects due to the presence of bulky end groups wereshown to affect crystalline characteristics for strictly monodisperse ε-caprolactone oligomers. The interaction between end groups and end groups, as well as that between end groups andε-caprolactone repeating units, created an obstacle for unfolding the crystal structures that hadinitially formed even at the high-temperature limit of crystallisation where crystallisationoccurred over hundreds of hours. Very rapid X-ray imaging of the in situ crystallisationprocess showed that rapid shifts in the unit cell occurred during the first minute ofcrystallisation due to the difficulty of fitting the bulky end groups in a stable unit cell.Confinement effects also arose when polymer chains were crystallised in systems with smallpore sizes. For linear poly-ε-caprolactone, chains confinement depended mainly on thedimensionalities of the pores. Linear polymers with Mn = 10 000 and 42 500 were stronglyinhibited from forming crystal structures in 10 nm pore systems, but not hindered in 23 nmpore systems. Linear polymers with Mn = 80 000 also experienced limited confinement in the23 nm pores. A star-shaped oligomer with four arms of approximately Mn = 1 000 each evenexperienced confinement in 290 nm pores, although having smaller molecular size and radiusof gyration compared to the linear chains. The innate confinement created by the challenge ofpacking four arms amplified the effect of physical confinement. Another limitation wascreated on the crystallisation process by solving PCL in supercritical CO2 and depositingduring extremely fast phase transfer to gas-like state. The formed structures were limited bythe very low temperature that resulted from the phase change and by the rapid evaporation ofthe solvent. These limitations resulted in entrapment of crystal structures in metastablephases. As a consequence, crystals of hitherto unreported rectangular form were observed aswell as the common six-sided form. The former crystals had considerably lower melting pointcompared to the latter. X-ray analysis showed that two sets of lattice constants existed,supporting the notion of entrapment in metastable phases. Another way of achievingconfinement was precise deposition of droplets in the pikolitre volume range of highly dilutesolutions. The microcrystals which formed were confined by both the low polymer content ineach droplet and by the time constraint on crystal formation that arose by the rapidevaporation of the small droplets. Confinement led to entrapment into metastable phases,evident by the presence of unusual eight-sided and rectangular crystals.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , 72 p.
Keyword [en]
crystallisation, poly-ε-caprolactone, end groups, morphology, nanoconfinement, melting, monodisperse, RESS, injet printing
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-109792OAI: oai:DiVA.org:kth-109792DiVA: diva2:584339
Public defence
2013-01-25, D3, Lindstedtsvägen 5, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research , 2006-3559, 2009-3188
Note

QC 20130109

Available from: 2013-01-09 Created: 2013-01-08 Last updated: 2013-01-09Bibliographically approved
List of papers
1. Crystallization and Melting Behavior of Monodisperse Oligomers of epsilon-Caprolactone
Open this publication in new window or tab >>Crystallization and Melting Behavior of Monodisperse Oligomers of epsilon-Caprolactone
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2012 (English)In: Journal of macromolecular science. Physics, ISSN 0022-2348, E-ISSN 1525-609X, Vol. 51, no 10, 2075-2092 p.Article in journal (Refereed) Published
Abstract [en]

Monodisperse epsilon-caprolactone (CL) oligomers with different end groups (t-butyldimethylsilyl, benzyl, hydroxyl, and carboxylic acid) and different numbers of repeating units (4-64) have been studied by differential scanning calorimetry and small-angle X-ray scattering (SAXS) in order to gather information regarding the melting temperature, long period, and melting enthalpy. Oligomers crystallized at their maximum temperatures (different for the different oligomers) to full crystallinity yielded extended-chain crystals for oligomers with 4, 8, and 16 repeating units with the important exception of the oligomers with four and eight repeating units and hydroxyl and benzyl end groups that showed double-layer crystals. Oligomers with 32 and 64 repeating units exhibited remarkably stable once-folded (32-mer) and thrice-folded (64-mer) crystals. Only the oligomer with 16 repeating units showed two crystallization temperature regimes resulting in once-folded crystals (low temperatures) and extended-chain crystals (high temperatures). The end groups had a profound effect on the structures. Hydrogen-bonding groups promoted the formation of crystal bilayers and led to a very high melting enthalpy (150 J g(-1)) exceeding the melting enthalpy of 100% crystalline poly (epsilon-caprolactone). The bulky end groups, in particular t-butyldimethylsilyl, reduced the crystallinity and favored chain tilting and probably preventing the unfolding of crystal stems in the oligomers with 32 and 64 repeating units. Melting temperatures of mature crystals obeyed a linear relationship with inverse CL stem length. The intercept (equilibrium melting temperature) was in the range of 350 to 357 K.

Keyword
end groups, long period, melting, monodisperse, poly-epsilon-caprolactone
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-103105 (URN)10.1080/00222348.2012.661678 (DOI)000308022800014 ()
Funder
Swedish Research Council, 2006-3559 2009-3188
Note

QC 20121004

Available from: 2012-10-04 Created: 2012-10-04 Last updated: 2017-12-07Bibliographically approved
2. Inkjet printing as a possible route to study confined crystal structures
Open this publication in new window or tab >>Inkjet printing as a possible route to study confined crystal structures
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2013 (English)In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 49, no 1, 203-208 p.Article in journal (Refereed) Published
Abstract [en]

Inkjet printing is a technique for the precise deposition of liquid droplets in the pL-volume range in well-defined patterns. Previous studies have shown that inkjet printing is attractive in polymer technology since it permits the controlled deposition of functional polymer surfaces. We suggest that the technique might also be useful for studying crystallization, in particular confined crystallization. Inkjet printing is a non-contact deposition method with minimal risk of contamination, which allows the exact deposition of both polymer solutions and polymer melts. This paper demonstrates the possibility of utilizing the technique to create surfaces where polymer chains form isolated small structures. These structures were confined by both the low polymer content in each droplet and the time constraint on crystal formation that arose as the result of the rapid solvent evaporation from the pL-sized droplets. In theory, inkjet printing enables the exact deposition of systems with as few as a single polymer chain in the average droplet. With appropriate instrumentation, the versatile inkjet technology can be utilized to create whole surfaces covered with polymer structures formed by the crystallization of small, dilute and rapidly evaporating droplets. 110 pL droplets of a 10 -6 g L -1 poly(ε-caprolactone) solution in 1-butanol have been deposited and studied by atomic force microscopy. Small structures of ca. 10 nm thickness and ca. 50 nm diameter also seemed to exhibit crystalline features. Some of the small structures had unusual rectangular forms whilst others were interpreted to be early precursors to six-sided single crystals previously observed for poly(ε-caprolactone). The unusual forms observed may have resulted from the entrapment of crystal structures into metastable phases, due to the limited amount of polymer material present and the rapid evaporation of the droplets.

Keyword
Confinement, Crystallization, Inkjet printing, Poly(ε-caprolactone)
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-109805 (URN)10.1016/j.eurpolymj.2012.10.001 (DOI)000315306200021 ()2-s2.0-84872291066 (Scopus ID)
Funder
Swedish Research Council, 2006-3559 2009-3188
Note

QC 20130207

Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2017-12-06Bibliographically approved
3. Confined space crystallisation of poly(epsilon-caprolactone) in controlled pore glasses
Open this publication in new window or tab >>Confined space crystallisation of poly(epsilon-caprolactone) in controlled pore glasses
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2013 (English)In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 49, no 8, 2073-2081 p.Article in journal (Refereed) Published
Abstract [en]

A series of controlled pore glasses (CPGs) with pore diameters ranging from 10 nm to 293 nm were impregnated with three poly(epsilon-caprolactone)s (PCL) differing in number average molar mass (10-80 kDa), and their crystallisation kinetics were studied with differential scanning calorimetry. Scanning electron microscopy and thermogravimetry confirmed that the polymers were mainly housed within the pore channels. The PCLs housed in the CPG with the finest pores (10 nm) showed a markedly different crystallisation behaviour from that of the corresponding bulk pristine polymers: a significantly slower crystallisation, a low Avrami exponent (<1), a higher product of the surface free energies of the fold and lateral surfaces of the formed PCL crystals and a lower initial melting peak temperature. This behaviour of confinement was similar for the three PCLs studied. In the CPGs with wider pore channels (23-293 nm), the PLCs showed essentially the same crystallisation kinetics as the pristine polymers. These differences in the crystallisation kinetics were attributed to the confinement, i.e. to the small available volume with respect to crystal size and to interactions with the pore walls. The results obtained suggest that the initial stages of crystallisation, presumably including other crystal phases or mesophases, occurred according to different paths for bulk PCL and for PCL housed in narrow nanopores.

Keyword
Poly(epsilon-caprolactone), Controlled pore glasses, Silica aerogel, Confined crystallisation
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-109807 (URN)10.1016/j.eurpolymj.2013.04.034 (DOI)000322503800020 ()2-s2.0-84880173550 (Scopus ID)
Funder
Swedish Research Council, 2006-3559 2009-3188
Note

QC 20130909. Updated from submitted to published.

Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2017-12-06Bibliographically approved
4. Unusual crystals of poly(epsilon-caprolactone) by unusual crystallisation: The effects of rapid cooling and fast solvent loss on the morphology, crystal structure and melting
Open this publication in new window or tab >>Unusual crystals of poly(epsilon-caprolactone) by unusual crystallisation: The effects of rapid cooling and fast solvent loss on the morphology, crystal structure and melting
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2013 (English)In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 54, no 5, 1497-1503 p.Article in journal (Refereed) Published
Abstract [en]

The lateral habit, unit cell structure and melting behaviour of single crystals of poly(epsilon-caprolactone) (PCL) prepared by the rapid expansion of a supercritical solution technique was studied by AFM at ambient and higher temperatures and by grazing-incident X-ray scattering using a synchrotron source. After dissolving PCL in a solution of supercritical CO2 and 0.1 vol.% chloroform, an extremely fast phase transfer from a supercritical to a gas-like state occurred during expansion into atmospheric conditions, leading to a temporary temperature drop to below -;50 degrees C at the silica surface where the crystals were deposited. Single crystals of a hitherto unreported rectangular lateral habit were observed. Six-sided crystals were also observed, but they were fewer than the rectangular crystals and in addition the angles between the lateral faces were different from the theoretical angles between adjacent {110} faces and {110} and {100} faces. X-ray scattering indicated a polymorphic structure also including the orthorhombic (110) and (200) diffraction peaks. Distinct low angle peaks essentially along the c-axis indicated a stacking on a very fine scale (3.7-4.7 nm) within the crystals. The equatorial diffraction peaks indicated a less dense packing of the PCL stems. Rectangular single crystals with a height according to AFM of 11-27 nm melted between 40 and 45 degrees C, which is lower than the melting points (55 degrees C) recorded for the distorted six-sided crystals. The unusual conditions for crystallisation used gave the polymer molecules a severe limitation to rearrange from the initial random coil state. The facetted crystals consisted of a stack of 4 nm thick blocks; these blocks most probably constituted a regular variation in molecular packing, i.e. molecular order. The pronounced changes in the angles between adjacent faces from those observed in mature PCL crystals and the wide-angle X-ray scattering data indicated the presence of conformational disorder in the crystals.

Keyword
Poly(ε-caprolactone), Polymer single crystal, Rapid expansion of a supercritical (CO2) solution
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-109808 (URN)10.1016/j.polymer.2013.01.014 (DOI)000315746300005 ()2-s2.0-84873715767 (Scopus ID)
Funder
Swedish Research Council, 2006-3559 2009-3188Knut and Alice Wallenberg Foundation
Note

QC 20130404. Updated from submitted to published.

Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2017-12-06Bibliographically approved
5. Crystallisation kinetics of a star-shaped poly-ε-caprolactone oligomer confined in controlled pore glasses
Open this publication in new window or tab >>Crystallisation kinetics of a star-shaped poly-ε-caprolactone oligomer confined in controlled pore glasses
(English)Manuscript (preprint) (Other academic)
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-109809 (URN)
Note

QS 2013

Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2013-01-09Bibliographically approved
6. Influence of bulky and hydrogen bonding end groups on molecular packing of monodisperse oligomer ε-Caprolactone
Open this publication in new window or tab >>Influence of bulky and hydrogen bonding end groups on molecular packing of monodisperse oligomer ε-Caprolactone
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(English)Manuscript (preprint) (Other academic)
Keyword
Poly(ε-caprolactone); Polymer single crystal; Rapid expansion of a supercritical (CO2) solution
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-109810 (URN)
Note

QS 2013

Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2013-01-09Bibliographically approved

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