An Unconventional Route for Synthesis and Solid‐State Processing of Low‐Entangled Ultra‐High Molecular Weight <i>Isotactic</i> Polypropylene

Romano, Dario; Marroquin‐Garcia, Ramiro; Gupta, Virendrakumar; Rastogi, Sanjay

doi:10.1002/marc.202300039

Cited by 8 publications

(8 citation statements)

References 26 publications

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“…Based on previous knowledge acquired by our group on UHMW-polyethylene and UHMW-isotactic polypropylene, it can be anticipated that the ability of processing the polymer below the melting point is attributed to a lower degree of entanglement in the noncrystalline region of the semicrystalline polymer. 36,51 Such an opportunity provides a possible method to process a brittle material such as PLA (without melting or dissolution in organic solvents) via an environmental-friendly route, thus avoiding/reducing thermally activated chain degradation (hydrolysis), a common challenge in melt processing of aliphatic polyesters. The Figure 3.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Another fundamental aspect of interest in achieving the crystallization of the PLA during synthesis is the possibility of decreasing chain overlap (entanglement) during polymer growth, thus accessing the low entangled state. If chain overlap is decreased and the polymer produced has a lower amount of entanglement, then uniaxial orientation below the melting point (without any solvent) is feasible, as demonstrated for ultrahigh-molecular-weight (UHMW)-polyethylene and UHMW- isotactic -polypropylene . This processing route allows the production of fibers or tape without the need to melt the material.…”

Section: Introductionmentioning

confidence: 99%

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Synthesis and Characterization of High-Molecular-Weight PLAs with a Well-Controlled Particle Morphology

Li,

Rastogi,

Romano

2023

Ind. Eng. Chem. Res.

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The synthesis of high-/ultrahigh-molecular-weight poly(L-lactide) (PLLA) having a controlled morphology remains a challenge because of the low crystallization rate of the material and the absence of a proper nucleation site during polymer synthesis. Using three different polymerization routes, the synthesis of highand ultrahigh-molecular-weight PLLA (weight-average molecular weight up to 1.1 million g/mol) having a well-defined particle morphology is reported. A comparative study on the evolution of the structure, morphology, and crystallization behavior of PLLA, influenced by different nucleating agents during polymerization, is addressed. The structure and the morphology of the resulting polymers, crystallization kinetics, and thermal properties of the PLAs are investigated systematically by GPC, SEM, TEM, NMR, DSC, and XRD. In the presence of PDLA, with the formation of the PLLA/PDLA stereocomplex crystal, spherical particles having a flakelike micromorphology are formed. The flakelike structures are proven to be single crystals of the stereocomplex PLLA and PDLA. The nascent reactor powder, having single crystals, could be compressed below the melting point and can be drawn into uniaxial objects in the solid state without melting. The solid-state deformation circumvents the entropic relaxation that is detrimental to chain orientation and restricts thermal degradation experienced during melt processing. Moreover, the proposed routes for controlling the nascent reactor particle morphology open the path to PLA synthesis in a continuous process, avoiding any postpolymerization treatment of the synthesized polymer.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Synthesis and Characterization of High-Molecular-Weight PLAs with a Well-Controlled Particle Morphology

Li,

Rastogi,

Romano

2023

Ind. Eng. Chem. Res.

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“…For example, the average size of the particles increases from 0.9 μm in 2 h to 1.6 μm after reacting for 13 h. Increasing the polymerization time to 24 h resulted in the micro flowers type morphology build-up with interstacked petals having an average size of 4.2 μm. Similar “flower-like” morphology on low-entangled ultrahigh molecular weight polyethylene (dis-UHMWPE) and low-entangled ultrahigh molecular weight isotactic polypropylene is reported while using postmetallocene single-site catalyst systems. , The average size of the crystalline nascent particles is observed to be increasing with increasing reaction time (0.9–4.2 μm), as the molecular mass of the isolated polymer also shows a progressive increase from 1.3 × 10 5 to 4.0 × 10 5 g mol –1 (entries 1, 2, 3, and 4, Table S1, Supporting Information section). At a higher reaction temperature, at 60 °C (entry 2, Table ), the highly ordered crystalline morphology, which is found at the low polymerization temperature of 25 °C, is disrupted, and more porous-like structures (Figure d) are formed.…”

Section: Resultsmentioning

confidence: 99%

Controlling Surface and Crystalline Lamellar Morphologies of Nascent Poly(ethylene-alt-CO) Under Different Polymerization and Thermal Conditions

Raman,

Zhao,

Puthiyaveettil

et al. 2023

Macromolecules

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“…Rastogi et al reported 65 the synthesis of the ultrahigh-molecular-weight polyethylene and isotactic-polypropylene. 66 At lower polymerization temperature and lower catalyst concentration, the crystallization rate is higher than the polymerization rate, and folded chain crystals with less entanglement are produced. The present work first showed a new route to synthesize the less entangled high-molecular-weight trans-1,4-PBD (1,4-t-PBD) with M w = 500 kg/mol under tailored polymerization conditions using a homogeneous catalyst and the formation of single crystals during polymerization.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Besides the solution crystallization, varying the polymerization conditions − is a more advanced method to produce polymer with high-molecular weight and less entanglement density in the amorphous region. Rastogi et al reported the synthesis of the ultrahigh-molecular-weight polyethylene and isotactic -polypropylene . At lower polymerization temperature and lower catalyst concentration, the crystallization rate is higher than the polymerization rate, and folded chain crystals with less entanglement are produced.…”

Section: Introductionmentioning

confidence: 99%

Primary Thickening in Nascent Single Crystals of High-Molecular-Weight trans-1,4-Polybutadiene

Zhao,

Sharahili,

Romano

et al. 2023

Macromolecules

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Fine-tuning the polymerization conditions, in particular, solvent medium, catalytic system, and thermodynamic parameters, it is feasible to crystallize the growing polymer chain directly into single crystals. Using these basic concepts, the resultant polymer, having a trans-isomer of ∼99% and a molecular weight of ∼500 kg/mol, during polymerization forms platelet-like single crystals having crystal thickness of 7.8 nm. The crystal thickness corresponds to the attachment of approximately 63 covalently linked carbon atoms along the c-axis of the unit cell. Considering the crystal thickness and chain length of approximately 37 000 covalently linked carbon atoms, electron diffraction of the nascent crystals suggests chain folding along the ab-plane of the single crystal. In view of the polymerization kinetics, followed by crystallization leading to chain packing, these platelet-like single crystals are expected to have the low entangled state. DSC thermogram of the crystals suggests solid–solid transition from the low entropy (monoclinic) to high entropy (hexagonal) phase, prior to melting. The phase transition temperature, from the monoclinic to hexagonal phase, shifts to higher temperatures on annealing crystals in the high entropy phase. Cause for the shift in the phase transition temperature, on annealing, is attributed to increase in crystal thickness. To follow chain mobility during thickening, 13C solid-state NMR techniques are employed. Similar to the trans-1,4-polybutadiene, prepared from solution crystallization, the reversal phase transition from the hexagonal to monoclinic phase is followed in the single crystals by 13C solid-state NMR. The SEM images and 13C CP/MAS spectra of the nascent and the annealed single crystals in the hexagonal phase have proven the lamellae thickening of the isolated single crystals, accompanied by the reversal in the phase transition to the monoclinic phase with crystal thickening. We attribute crystal thickening in the isolated single crystals as the primary thickening that requires high-chain mobility facilitated by the high entropy hexagonal phase and driven by the thermodynamics of reducing the surface energy. Amazing aspect is that the primary thickening that requires desired cooperative motion of the covalently linked carbon atoms reduces the crystal planar surface area to accommodate crystal thickening that starts from several nanometers and reaches several tens of nanometers with the phase transformation from the monoclinic to hexagonal phase. The ease in crystal thickening, in the high entropy phase, is suggestive of adjacent re-entry perceived with deposition of the growing chain after suppression of the nucleation barrier.

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An Unconventional Route for Synthesis and Solid‐State Processing of Low‐Entangled Ultra‐High Molecular Weight Isotactic Polypropylene

Cited by 8 publications

References 26 publications

Synthesis and Characterization of High-Molecular-Weight PLAs with a Well-Controlled Particle Morphology

Synthesis and Characterization of High-Molecular-Weight PLAs with a Well-Controlled Particle Morphology

Controlling Surface and Crystalline Lamellar Morphologies of Nascent Poly(ethylene-alt-CO) Under Different Polymerization and Thermal Conditions

Primary Thickening in Nascent Single Crystals of High-Molecular-Weight trans-1,4-Polybutadiene

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