Morphology and properties of trans-1,4-polyisoprene crystallized from solution

Abstract

trans-1,4-Polyisoprene (TPI) fractions with Mn = 4.7 X 103 to 2.5 X 106 and MW/MD = 2.0-1.3 were crystallized from solutions, mainly at a concentration of 1 g/100 cm3, by cooling directly from 100 °C to an (apparent) Tc of -15 to +32 °C, by precooling to 0 °C, redissolving at 35-45 °C, and crystallizing at Tc, and by cooling to 0 °C and heating to 10,20, or 30 °C. Most of the structures obtained were characterized, while suspended in the crystallization liquid, by interference contrast microscopy and with crossed polaroids; the crystalline fraction from the density and the crystal form from X-ray diffraction and differential scanning calorimetry were determined for the dry products. The morphology obtained by direct crystallization was dependent on molecular weight, crystallization temperature, and solvent, with a-and /3-hedrites (sheaves), a-and /S-spherulites, and /3-aggregates of cup-shaped lamellas being found. The precooling method yielded overgrown lamellas in most cases; however, more complex morphologies developed when the thermal history was changed. The density depended on molecular weight, concentration, and crystallization temperature. The crystallinity was mainly a function of crystal form and molecular weight. The equation of Tseng, Herman, Woodward, and Newman was used to explain the molecular weight dependence of the crystallinity at low Mn and to calculate the average number of monomer units per fold and interlamellar traverse. Epoxidation of some TPI structures suspended in amyl acetate at 0 °C was carried out. At high concentrations of the epoxidizing agent, m-chloroperbenzoic acid, the fraction epoxidized approached or exceeded the noncrystalline fraction as obtained from density measurement.

Intrinsically Conductive Polymer Fibers from Thermoplastic trans-1,4-Polyisoprene

“…The lamellar distances were 0.47, 0.39, 0.33, and 0.29 nm after calculation. The results indicated that there were two kinds of crystalline forms in the fibers: monoclinic (α) and orthorhombic (β). , After doping with iodine, WAXD results of the two fibers were shown in Figure S2 of the Supporting Information. The non-drawn fibers showed the TPI crystalline signal with very weak intensity compared to before doping and also very low orientation, while the drawn fibers showed almost no TPI crystalline signal but a visible high orientation.…”

Regulation of trans‐1,4‐polyisoprene crystallinity and mechanical properties of styrene‐butadiene rubber/trans‐1,4‐polyisoprene vulcanizate

“…WAXD patterns of different SBR/TPI/SiO 2 /Si69 vulcanizates are shown in Figure . TPI is polymorphic, and two crystalline forms are generally observed: orthorhombic β and monoclinic α form . TPI can be converted exclusively in its β form by crystallizing the polymer melt below 40 °C .…”

“…TPI is polymorphic, and two crystalline forms are generally observed: orthorhombic b and monoclinic a form. [14][15][16] TPI can be converted exclusively in its b form by crystallizing the polymer melt below 40 8C. 17 The diffraction peaks of TPI in the SBR/TPI vulcanizates are located at 18.88 and 22.78, reflecting the (120) and (200) lattice planes of the b form crystal.…”

Processing and characterization of electrospun trans-polyisoprene nanofibers

“…Partially crystalline TPI can exist with only the α form, only the β form, or both crystal forms present. DSC scans of TPI and its fibers given in Figure 8 indicate the presence of both α and β, as represented by two distinguished peaks at Tendo = 57°C and Tendo = 49°C, respectively, with predominating β form in the pure TPI [21]. The melting temperature of each peak was found to shift toward a higher temperature while the TPI was electrospun.…”