On Morphology of Polyhydroxybutyrate - Progress in Organic and Physical Chemistry: Structures and Mechanisms - page 236

One of the progressive polymers applied in medicine, is poly(3-hydroxybutyrate)
(PHB). This bacterial biopolymer possesses high crystallinity [3].
Therefore, changing degree of crystallinity of polymer at a stage of formation of
¿ lms from a solution, it is possible to control over a wide range their transport proper-
ties [4].
The purpose of the yielded work consisted in de¿ nition of inÀ uence of dissolvent
of various polarities on formation of structure PHB of ¿ lms.
18.2 OBJECT AND RESEARCH METHOD
As subjects of inquiry served weed PHB Lot M-0997 (Germany, “Biomer”), M h =
2,50,000, Solvents was chemically pure dioxane, chloroform, formic acid, and dichlo-
roethane. The PHB dissolved in the specified solvents at temperature 90 ɨ ɋ and jolted
on a glass surface. For residual solvent removal the generated films subjected to heat
treatment in pressure (0, 2 bar) at temperature 110 ɨ ɋ in a current of 30 min.
Research of structure of ¿ lms made method differential scanning calorimeter
(DSC) at speed of scanning of 20 wasps/min by mean of a differential scanning calo-
rimeter of ¿ rm “Mettler” (USA).
18.3 DISCUSSION AND RESULTS
In Figure 1 typical thermograms of heating PHB of films are presented. From the
analysis of thermograms follows, that after machining by dissolvents initial structure
PHB is broken: there is the amorphous phase characterized by obviously expressed
transferring of glass transition and there is a fine-crystalline modification or areas with
the broken crystallinity. Emersion of low temperature peak of fusion testifies to it.
In Table 1 thermal parametres of ¿ lms on the basis of PHB and parametres of dis-
solvents are presented.
From the table it is visible, that to growth of electrical dipole moment of dissolvent
there is a perfection (streamlining) of crystal phase PHB. Growth of melting point of
polymer testi¿ es to it, see Figure 2.
Simultaneously with it heat capacity PHB decreases. It can be connected with
decrease of a share of an amorphous phase of polymer.
Molecule PHB contains an ester group in the main circuit, capable to enter inter-
acting with polar molecules of dissolvent [5].
The change of conformation of macromolecules in crystal and amorphous regions
of polymer under the inÀ uence of dissolvent molecules is thus possible. The structure
of crystallites thereof is stabilized, and macromolecules in an amorphous phase lose
À exibility. The yielded effects have been revealed by the authors [6], investigating
agency of molecules of water on ¿ lms from PHB. They have installed, that under
the inÀ uence of polar molecules of water communication between links of the next
chains, result inning stabilization of a crystal structure of polymer is realized. Formed
on boundary line of crystallites the grid of hydrogen bridges promotes more strongly
pronounced orientation of crystallites in a polymer matrix.
In an observed number of the dissolvents, having electrical dipole moment more
low or above (dichloroethane), than at water (1,84 D) [7], the described phenomena