Characterization of Some New Olefinic Block Copolymers

Abstract

Exciting new developments in polyolefin synthesis give rise to olefinic block copolymers with properties typical of thermoplastic elastomers. The blocky copolymers synthesized by chain shuttling technology consist of crystallizable ethylene-octene blocks with low comonomer content and high melting temperature (hard blocks), alternating with amorphous ethylene-octene blocks with high comonomer content and low glass transition temperature (soft blocks). This paper describes the materials science of these unique polymers as characterized by thermal analysis, X-ray diffraction, microscopy, and tensile deformation. The crystallizable nature of the hard block and the crystalline morphologies are consistent with an average hard block length that is well in excess of 200 carbon atoms. The crystallizable blocks are long enough to form well-organized lamellar crystals with the orthorhombic unit cell and high melting temperature. The lamellae are organized into space-filling spherulites in all compositions even in copolymers with only 18 wt % hard block. The morphology is consistent with crystallization from a miscible melt. Crystallization of the hard blocks forces segregation of the noncrystallizable soft blocks into the interlamellar regions. Good separation of hard and soft blocks in the solid state is confirmed by distinct and separate β-and R-relaxations in all the blocky copolymers. Compared to statistical ethylene-octene copolymers, the blocky architecture imparts a substantially higher crystallization temperature, a higher melting temperature and a better organized crystalline morphology, while maintaining a lower glass transition temperature. The differences between blocky and statistical copolymers become progressively more apparent as the total comonomer content increases.

Enzymatic Synthesis and Chemical Recycling of Novel Polyester-Type Thermoplastic Elastomers

“…The degree of crystallinity decreases with increasing content of soft segments; thus, the polymer changes from a rigid plastic to a soft elastomer [1][2][3].…”

“…The detection was performed in the refraction mode, a cobalt matrix was used for oligomers, sodium bromide was used as a cation source, and positive ionization was used. 1 H NMR spectra were recorded on a Varian 300 Fourier transform spectrometer (Varian Inc., CA, USA) operating at 300 MHz.…”

Block Index for Characterizing Olefin Block Copolymers

“…When compared to random copolymers, OBCs in the solid-state have a unique crystal morphology and show improved physical properties such as compression set, elastic recovery, and abrasion resistance. [3,5] Figure 3 shows the analytical TREF profile comparing an olefin block copolymer (0.878 g/cc, 1.5 I 2 ) to a random copolymer (AFFINITY TM VP8770, 0.887 g/cc, 0.9 I 2 ) and a polymer blend (0.89 g/cc, 1.0 I 2 ) with components that are representative of the hard and soft segments within the olefin block copolymer. Although not a perfect comparison, the differences shown in Figure 3 cannot be reconciled by the slight differences in density and melt index of these polymers.…”

Structure and Properties of Low-Isotacticity Polypropylene Elastomeric Fibers Prepared by Sheath-Core Bicomponent Spinning

“…Conventionally, PE and PP have been polymerized applying Ziegler-Natta catalyst. Development of metallocene catalyst provided the technologies for designing new types of polymers such as those with narrow molecular weight and composition distributions, controlled stereo regularity [1][2] , copolymerization [3][4][5][6][7] etc. Especially, development of polymers with elastomeric characteristics is widely investigated recently [8][9][10][11][12][13].…”