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Step-Growth Polymerization: Overview01:03

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Step-growth or condensation polymerization is a stepwise reaction of bi or multifunctional monomers to form long-chain polymers. As all the monomers are reactive, most of the monomers are consumed at the early stages of the reaction to form small chains of reactive oligomers, which then combine to form long polymer chains in the late stages. Hence, the reaction has to proceed for a long time to achieve high molecular weight polymers.
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Step growth polymerization involves bi or multifunctional monomers. Bifunctional monomers react to form linear step growth polymers, whereas multifunctional monomers react to form non-linear or branched polymers.
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Polymorphism refers to the existence of a drug substance in multiple crystalline forms, known as polymorphs. Recently, this term has been expanded to include solvates (forms containing a solvent), amorphous forms (non-crystalline forms), and desolvated solvates (forms from which the solvent has been removed).
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Searching for New Polymorphs by Epitaxial Growth.

Josef Simbrunner1, Benedikt Schrode2, Sebastian Hofer2

  • 1Department of Neuroradiology, Vascular and Interventional Radiology, Medical University Graz, Auenbruggerplatz 9, Graz 8036, Austria.

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Summary

Researchers developed a new method using X-ray diffraction to identify unknown crystal polymorphs in molecular crystals grown on surfaces. This technique successfully distinguishes multiple polymorphs and determines their crystal structures, aiding materials science research.

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Area of Science:

  • Materials Science
  • Crystallography
  • Surface Science

Background:

  • Crystallization on surfaces often yields unknown polymorphs, challenging to identify.
  • Epitaxially grown molecular crystals present complex phase identification due to multiple alignments and polymorphs.

Purpose of the Study:

  • To present a novel method for identifying crystallographic phases of molecular crystals grown on surfaces.
  • To determine unit cells and crystallographic phases, even when multiple polymorphs coexist.
  • To solve crystal structures of unknown polymorphs using experimental data.

Main Methods:

  • Grazing incidence X-ray diffraction (GIXRD) studies.
  • Physical vapor deposition of conjugated molecules (PTCDA, pentacene, trans-DBPen, DCV4T-Et2) on single crystalline substrates (Ag(111), Cu(111), graphene).
  • A new method for indexing Bragg peaks to determine unit cells and identify crystallographic phases.

Main Results:

  • Successfully identified crystallographic phases of molecular crystals, including simultaneous polymorphs (e.g., DCV4T-Et2 on Ag(111)).
  • Determined epitaxial relationships between crystallites and substrate surfaces.
  • Solved the crystal structure of an unknown polymorph of trans-dibenzopentacene on Cu(111).

Conclusions:

  • The developed GIXRD analysis method enables unambiguous identification of crystallographic phases in epitaxially grown molecular crystals.
  • This approach is effective even in complex scenarios with multiple coexisting polymorphs.
  • Facilitates crystal structure solution for novel polymorphs, advancing molecular crystal research.