The gutta isolated from chicle has been demonstrated to be structurally identical with trans‐polyisoprene from gutta percha and balata but has a molecular weight of 16,000–18,000, about one‐half that of the latter two polymers. Its ease of purification and marked crystalline behaviour suggested its use in a study of gutta polymorphism.The α‐and β‐forms of chicle gutta were prepared and their identities were established by means of x‐ray diffraction measurements and melting properties. The degree of crystallinity and internal molecular strain were shown to affect the melting points of the two forms of gutta through wide ranges. Interconversions of α‐and β‐guttas were effected by means of heat conditioning, solution and reprecipitation, melting and resolidification, and treatment of the gutta with nonsolvents. Dilatometric data were used to describe the change of specific volume when β‐gutta was converted to α‐gutta in a conditioning bath as the temperature was increased stepwise from 30°C. to 80°C. at the rate of 1°C. per hour. The discontinuous, saw‐toothed nature of the specific volume vs. time curve was rationalized on a basis of reactions involving changes in degree of molecular order and relief of strain within the gutta. The curve suggested the following gross reactions: 30–36°C., thermal expansion of β‐gutta of low crystallinity; 36–52°C., increase in degree of crystallinity of β‐gutta; 52–60°C., melting of β‐gutta; 60–64°C., transition of β‐ to α‐gutta; 64–72°C., melting of α‐gutta; 72–80°C., thermal expansion of molten gutta. α‐Gutta, in the melted condition, was shown to undergo a transition, above 72°C., to a form whose stereo identity has not yet been established. The rate of transition from β‐to α‐gutta at temperatures at which α‐is the stable form, appeared to be hastened in the presence of certain liquids.

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Gutta, the polyisoprene hydrocarbon obtained from gutta percha or balata, is usually considered to differ from rubber in that gutta is a trans‐isomer and rubber a cis‐isomer of polyisoprene. Most of the data on the basis of which these structures have been assigned come from x‐ray diffraction pictures of polycrystalline polymer. Single crystal data have not been published, although such data would provide more detailed information. Chicle gutta has been shown to be a lower molecular weight modification of gutta from gutta percha. As a consequence of its lower molecular weight chicle gutta is a granular, free‐flowing powder, whereas gutta percha gutta is horny and tends to clump together. Because of its physical characteristics and lower molecular weight, chicle gutta was used first in an attempt to grow single crystals of gutta. By working with dilute solutions, well‐shaped single crystals of chicle gutta as large as 0.35 mm. in the long direction were obtained. From gutta percha Pahang, crystals 0.10 mm. long were isolated. Crystals could be grown either by slow diffusion of solvent or by cooling a supersaturated solution. Crystals were found to be optically anis tropic and to exhibit parallel extinction when examined under crossed Nicols with the polarizing microscope. Crystals obtained were of the alpha modification of gutta.

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