The formation and melting of the two crystalline modifications of poly‐1‐butene have been studied by the techniques of differential thermal analysis, infrared spectroscopy, dilatometry, and polarizing microscopy. On cooling the melt, modification 2 (Tm = 120–126°C.) appears within minutes. This form is unstable and gradually transforms to modification 1 (Tm = 135–142°C.). A density change of over 4% accompanies this latter transformation. As torsional damping experiments have shown the amorphous content to decrease by only about 5%, the stable modification must be much more dense than the unstable form. The kinetics of the crystallization of modification 2 from the melt were studied primarily dilatometrically at several temperatures. The data generally followed the Avrami equation with n equal to 4. This crystallization shows a high negative temperature coefficient (T1/2 = 380 min. at 110°C. and 2 min. at 90°C.) and becomes too rapid to measure by this technique at lower temperatures. The kinetics of the transformation of modification 2 to modification 1 were followed in infrared spectral, density gradient tube, and dilatometric studies. At room temperature, halftimes ranging from 250 to 1600 min. were observed, depending on the mechanical and thermal history of the sample. The observed discrepancies have been shown to be due, at least in part, to orientation effects. In dilatometric studies of the temperature dependence, the transition rate showed a pronounced maximum in the region of 15°C. Large increases in the torsional modulus and offset yield point of the specimen were observed to accompany the transition.
The preparation and characterization of syndiotactic polypropylene are reported. The influence of polymerization variables on the syndiotactic regulating capacity of the VCl4–AlEt2Cl catalyst were investigated. Vanadates could be substituted for VCl4, and Al(C6H5)2Cl or AlEt2Br for AlEt2Cl under suitable conditions. Hydrogen functioned as a chain transfer agent for the AlEt2Cl–VCl4 catalyst, and polymerizations which were terminated with tritiated alcohols yielded polymers containing bound tritium. The syndio‐regulating capacity of the AlEt2Cl–VCl4 catalyst was increased under specific conditions when cyclohexene, oxygen, or tert‐butyl perbenzoate was incorporated. A polymerization mechanism is proposed. According to this mechanism, preference for a monomer complexing mode which minimizes steric repulsions between methyl groups of the new and last added monomer unit is responsible for syndiotactic propagation. Characterization included determination of infrared syndiotactic indices, melting points (65–131°C.), glass transition temperature, densities (0.859 to 0.885 g./cc.), nuclear magnetic resonance spectra, birefringence, differential thermal analysis spectrograms, solubility, and heat of fusion (∼450 cal./mole).
In a previous paper we reported on the kinetics of crystallization and a crystal-crystal transition in poly-1-butene.1 (For earlier references, refer to this paper; also, note a recent publication by Zannetti et a1.2) In the absence of stresses and high pressures the two transformations ( a ) melt + modification 2 and ( 6 ) modification 2 + modification 1 were shown under optimal conditions to be fast (minutes) and slow (days), respectively. The unstable modification 2 is characterized by a fourfold helix similar to that of poly-3-methyl-1-butene, while the stable modification 1 is characterized by a threefold helix similar to that of polypropylene.3In the course of the transformation modification 2 -f modification 1, poly-1-butene becomes more rigid and less readily permanently deformed. The acceleration of this transformation was thus of both practical and theoretical interest. In the present work we have shown that the addition of certain compounds to the polymer can bring about some acceleration of the crystal-crystal transition. From the nature of the materials causing the acceleration and from the temperature dependence of the effect, it can be concluded that an increase in nucleation rate is involved. To the best of our knowledge such an effect has not previously been reported for polymeric systems.Offset tensile yield points were used to obtain initial indication of the effectiveness of the various additives as transition accelerators (Table I). The offset tensile yield point (ASTM D638-58T) is the stress a t which the stress-strain curve departs from the straight line representing Hooke's law behavior by a specified strain, the offset. Arbitrarily, we have chosen an offset of 5% elongation.Without an additive, the control samples had an offset yield point of about 1000 psi if the determination was made 23 hr. after the molding of the test specimen. But when 2 to 5 wt.-% of certain additives was blended into the poly-1-butene, offset yield points in the range 1700-2400 psi were obtained under comparable test conditions. Crystalline polymers such as isotactie polypropylene (>95 wt.-% insolubles in boiling heptane) and high-density polyethylene (HIFAX, d = 0.96), as well as low molecular weight compounds such as biphenyl and stearic acid, were found effective. Dilatometric measurements elucidated further the effect of these additives on the crystallization rate in poly-1-butene. Two samples containing 5 wt.-% stearic acid and 5 wt.-% crystalline polypropylene were examined and compared with the parent poly-lbutene containing no additive (Table 11, Fig. 1). Table I1 shows the times required to attain standard contraction levels (0.82, 1.64, and 3.28 m1./100 g. of polymer) at various temperatures, while in Figure 1 we have illustrated one of these contractions levels to show more graphically the effect of these two additives. Both additives caused a considerable acceleration of the phase transformation a t certain temperatures, resulting in a displacement of the maximum rate toward higher temperatures. As bo...
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