Crystallization of trans‐1,4‐polyisoprene

Abstract

Crystals of fractionated trans‐1,4‐polyisoprene (TPI) were grown from amyl acetate solution at two weight fractions, 5.7 × 10−4 and 0.011; for the lower concentration a precooling followed by heating and then crystallization at temperatures in the 10–32°C range was used, while for the higher concentration this method and direct crystallization at a temperature TC in the 0–32°C range were employed. The precooling method yielded samples crystallized in the α form, while direct crystallization led to formation of β‐TPI at low TC and α at higher TC. The value for the DSC endotherm, characteristic of α‐form melting, increased with increasing TC, with a shift to lower values with increasing concentration for precooled samples. A β to α transformation was found to occur for synthetic unfractionated TPI when swollen with amyl acetate at 35°C for 17h. Swelling in n‐butyl acetate for one day at 25°C or 17 h at 35°C also led to this transformation. From experimental results 74°C is chosen as the temperature at which the α and β forms coexist in the bulk, and this is used to calculate the enthalpy of fusion of β‐TPI, yielding a value of 8.6 kJ mol−1.

Shape memory behavior of carbon nanotube‐reinforced trans‐1,4‐polyisoprene and low‐density polyethylene composites

“…As shown in Figure , there was no significant peak shift for either the LDPE (high‐temperature peaks) or TPI portions with the increase in CNTs content. Pure TPI usually possesses two different crystal forms, an α form (62°C) and a β form (52°C), which can be obtained by crystallization at room temperature from the molten state . Because of the presence of LDPE in addition to the TPI polymer, the melting point of TPI is somewhat offset compared with that of pure polymers.…”

Morphology of solution crystallized trans-1,4-polyisoprene

“…The regular occurrence of two crystal forms, low melting form (LMF) having orthorhombic unit cell [12], and high melting form (HMF) having monoclinic unit cell [13,14], is generally known. Morphology of dilute solution grown single crystals, of both forms obtained by self seeding technique [8], and of HMF obtained by precipitation method [10,11], are reported, but all these reports show highly multilayered and overgrown single crystals. Chaturvedi [15] obtained isolated single crystals and various stages of complex growth features of LMF using film formation method (FFM).…”

Preparation of epoxidized Eucommia ulmoides gum and its application in styrene‐butadiene rubber (SBR)/silica composites

“…Eucommia ulmoides gum, a special biomaterial, is present in the leaves, bark, and seeds of E. ulmoides Oliv that is mainly grown in China. This gum, also called gutta percha or balata, is a kind of rubber with a molecular structure of trans ‐1,4‐polyisoprene that crystallizes easily, which is the reason why the E. ulmoides gum can usually be used as plastics, shape memory materials and rubber with different crosslinking degree like synthetic trans ‐1,4‐polyisoprene . Actually, trans ‐1,4‐polyisoprene has been widely used in many fields, such as machinery, chemicals, electronics, transportation, etc .…”