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Ziegler–Natta polymerization is another form of addition or chain‐growth polymerization used for synthesizing linear polymers over branched polymers. The catalyst used for polymerization is the Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, who developed it in 1953. This catalyst is an organometallic complex of titanium tetrachloride and triethyl aluminum, with the active form of the catalyst being an alkyl titanium compound. Using the Ziegler–Natta...
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The mechanism for anionic chain-growth polymerization involves initiation, propagation, and termination steps. In the initiation step, a nucleophilic anion, such as butyl lithium, initiates the polymerization process by attacking the π bond of the vinylic monomer. As a result, a carbanion, stabilized by the electron‐withdrawing group, is generated. The resulting carbanion acts as a Michael donor in the propagation step and attacks the second vinylic monomer, which acts as a Michael...
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Polymerization generates chiral centers along the entire backbone of a polymer chain. Accordingly, the stereochemistry of the substituent group has a significant effect on polymer properties. Polymers formed from monosubstituted alkene monomers feature chiral carbons at every alternate position in the polymer backbone. Relative to the predominant orientation of substituents at the adjacent chiral carbons, the polymer can exist in three different configurations: isotactic, syndiotactic, and...
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Unlike ionic or small covalent molecules, polymers do not form crystalline solids due to the diffusion limitations of their long-chain structures. However, polymers contain microscopic crystalline domains separated by amorphous domains.
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The polymerization process that involves carbanion as an intermediate is called anionic polymerization. It is also a type of addition or chain-growth polymerization. Anionic polymerization gets initiated by a strong nucleophile such as an organolithium or a Grignard reagent. The most commonly used initiator for anionic polymerization is butyl lithium. Monomers involved in anionic polymerization must possess a vinyl group bonded to one or two electron-withdrawing groups. For instance,...
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The skeletal structure of polymers synthesized via radical polymerization is always branched. For example, the polymerization of ethylene by radical polymerization results in a low-density grade of polyethylene with a heavily branched skeletal structure. Here, the radical site abstracts hydrogen from the growing chain, and the radical site shifts from the end (a primary carbon center) to anywhere within the growing chain (a secondary carbon center). Consequently, the part of the chain from the...
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Scrolled Poly(L-Lactic Acid) Single Crystals via Chain End-Induced Symmetry-Breaking.

Shichen Yu1, Seyong Kim1, Kingsley O Ojima2

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Angewandte Chemie (International Ed. in English)
|January 2, 2025
PubMed
Summary
This summary is machine-generated.

Researchers discovered scrolled single crystals in biodegradable poly(L-lactic acid) (PLLA). This unique crystal formation, dependent on polymer molecular weight, breaks traditional translational symmetry in polymer single crystals (PSCs).

Keywords:
Chiral crystalscrystal engineeringpolymer single crystalsscrolled crystalssustainable polymers

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Area of Science:

  • Materials Science
  • Polymer Chemistry
  • Crystallography

Background:

  • Single crystals typically exhibit translational symmetry.
  • Non-flat polymer single crystals (PSCs) and twisted crystals in polymers are known phenomena.
  • Classical poly(L-lactic acid) (PLLA) single crystals formed in solution are typically flat.

Purpose of the Study:

  • To report the formation of scrolled single crystals of biodegradable poly(L-lactic acid) (PLLA).
  • To investigate the factors influencing the formation of these non-flat PSCs.
  • To demonstrate a new mechanism for breaking translational symmetry in PSC growth.

Main Methods:

  • Solution crystallization of poly(L-lactic acid) (PLLA) with varying molecular weights.
  • Microscopic analysis to observe crystal morphology.
  • Analysis of the influence of polymer chain ends and molecular weight on crystal structure.

Main Results:

  • PLLA single crystals were observed to bend into scrolls when the polymer molecular weight was low.
  • The formation of these scrolled PLLA single crystals is dependent on polymer chain ends and molecular weight.
  • A new mechanism for breaking translational symmetry in PSC growth was identified.

Conclusions:

  • Scrolled single crystals of PLLA represent a novel morphology that deviates from traditional flat PSCs.
  • Polymer molecular weight and chain ends are critical factors controlling the transition from flat to scrolled crystal structures.
  • This study reveals a new pathway for achieving non-centrosymmetric crystal structures in polymers.