Sequential Crystallization and Multicrystalline Morphology in PE-b-PEO-b-PCL-b-PLLA Tetrablock Quarterpolymers
Müller, Alejandro J.
KAUST DepartmentChemical Science Program
KAUST Catalysis Center (KCC)
Physical Science and Engineering (PSE) Division
Polymer Synthesis Laboratory
Online Publication Date2021-07-23
Print Publication Date2021-08-10
Embargo End Date2022-07-23
Permanent link to this recordhttp://hdl.handle.net/10754/670566
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AbstractWe investigate for the first time the morphology and crystallization of two novel tetrablock quarterpolymers of polyethylene (PE), poly(ethylene oxide) (PEO), poly(ε-caprolactone) (PCL), and poly(l-lactide) (PLLA) with four potentially crystallizable blocks: PE187.1-b-PEO3715.1-b-PCL2610.4-b-PLLA197.6 (Q1) and PE299.5-b-PEO268.8-b-PCL237.6-b-PLLA227.3 (Q2) (superscripts give number average molecular weights in kg/mol, and subscripts give the composition in wt %). Their synthesis was performed by a combination of polyhomologation (C1 polymerization) and ring-opening polymerization techniques using a ″catalyst-switch″ strategy, either ″organocatalyst/metal catalyst switch″ (Q1 sample, 96% isotactic tetrads) or ″organocatalyst/organocatalyst switch″ (Q2 sample, 84% isotactic tetrads). Their corresponding precursors—triblock terpolymers PE-b-PEO-b-PCL, diblock copolymers PE-b-PEO, and PE homopolymers—were also studied. Cooling and heating rates from the melt at 20 °C/min were employed for most experiments: differential scanning calorimetry (DSC), polarized light optical microscopy (PLOM), in situ small-angle X-ray scattering/wide-angle X-ray scattering (SAXS/WAXS), and atomic force microscopy (AFM). The direct comparison of the results obtained with these different techniques allows the precise identification of the crystallization sequence of the blocks upon cooling from the melt. SAXS indicated that Q1 is melt miscible, while Q2 is weakly segregated in the melt but breaks out during crystallization. According to WAXS and DSC results, the blocks follow a sequence as they crystallize: PLLA first, then PE, then PCL, and finally PEO in the case of the Q1 quarterpolymer; in Q2, the PLLA block is not able to crystallize due to its low isotacticity. Although the temperatures at which the PEO and PCL blocks and the PE and PLLA blocks crystallize overlap, the analysis of the intensity changes measured by WAXS and PLOM experiments allows identifying each of the crystallization processes. The quarterpolymer Q1 remarkably self-assembles during crystallization into tetracrystalline banded spherulites, where four types of different lamellae coexist. Nanostructural features arising upon sequential crystallization are found to have a relevant impact on the mechanical properties. Nanoindentation measurements show that storage modulus and hardness of the Q1 quarterpolymer significantly deviate from those of the stiff PE and PLLA blocks, approaching typical values of compliant PEO and PCL. Results are mainly attributed to the low crystallinity of the PE and PLLA blocks. Moreover, the Q2 copolymer exhibits inferior mechanical properties than Q1, and this can be related to the PE block within Q1 that has thinner crystal lamellae according to its much lower melting point.
CitationMatxinandiarena, E., Múgica, A., Tercjak, A., Ladelta, V., Zapsas, G., Hadjichristidis, N., … Müller, A. J. (2021). Sequential Crystallization and Multicrystalline Morphology in PE-b-PEO-b-PCL-b-PLLA Tetrablock Quarterpolymers. Macromolecules. doi:10.1021/acs.macromol.1c01186
SponsorsThis work has received funding from MINECO through projects MAT2017-83014-C2-1-P and MAT2017-88382-P, from the Basque Government through grant IT1309-19, and from the ALBA synchrotron facility through granted proposal u2020084441 (March 2020). We would like to thank the financial support provided by the BIODEST project; this project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement no. 778092
PublisherAmerican Chemical Society (ACS)