Organ, S.J.; Li, J.; Terry, A.E.; Hobbs, J.K. and Barham, P.J.
Crystallization of hydroxybutyrate oligomers. Part 2. Growth and thickening of solution grown crystals observed in situ using synchrotron radiation.
Polymer, 45(26) pp. 8925–8936.
Synchrotron X-ray radiation has been used in situ to follow the crystallization of a hydroxybutyrate oligomer containing 32 repeat units from dilute solution in propylene carbonate, and to study chain unfolding during heating in oligomers with 24 and 32 repeat units. A discontinuity in growth rate occurs at 36-37˚C for the 32-mer: crystals grown below this temperature contain folded chains, which transform during heating through a process of partial dissolution and re-crystallization to form extended chain crystals. Crystals grown above the transition temperature contain extended chains that do not rearrange during heating. A similar change happens in the 24-mer between 35 and 40˚C. Thermal expansion in the (110) lattice direction (the fold direction) was in the range 5.3 +/- 0.3 x 10-5 nm degreesC<sup-1</sup>, with an additional discontinuous increase in 0.001 nm accompanying chain unfolding.
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