Triangular polymer single crystals: Stereocomplexes, twins, and frustrated structures

Laurent Cartier, Takumi Okihara, Bernard Lotz

Research output: Contribution to journalArticlepeer-review

227 Citations (Scopus)


The crystallographic origins leading to the formation of polymer single crystals with highly unusual triangular shapes are analyzed. Triangular crystals are obtained: (a) for stereocomplexes of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) crystallizing in a trigonal unit cell with A3c (or A-3c) symmetry. In this case, the triangular morphology results from the different molecular characteristics (mainly molecular weight) of the stereoisomer polymers used to form the complex, which in turn introduce different rates of deposition on opposite sides of the (110) crystallographic growth plane and therefore to the triangular morphology. A contrario, when molecularly (near) identical stereoisomers are used in equal concentrations, or when an (achiral) homopolymer crystallizing in the same crystal structure is used, the growth rates are equal and hexagonal crystals are formed (b) for some multiple twins, in particular triple growth twins of PLLA in its α form (c) for frustrated trigonal polymer crystal structures, in which different nucleation sites exist on opposite sides of a given growth plane. This difference in growth rates results from a genuine lack of symmetry of the crystal structure: triangular crystals are a morphological marker of the frustrated character of the packing in the unit cell. Further consequences of this frustration, such as differences in lamellar thicknesses for nominally equivalent growth sectors, shed new light on the details of nucleation and growth theories of polymer single crystals.

Original languageEnglish
Pages (from-to)6313-6322
Number of pages10
Issue number20
Publication statusPublished - Oct 6 1997

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry


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