Comparison of chain structure and morphology of an olefinic blocky copolymer and a Ziegler–Natta‐based ethylene random copolymer

Abstract

The microstructure and morphology of an olefinic blocky copolymer (OBC) and an ethylene‐hexene copolymer prepared by conventional Ziegler‐Natta catalysis (ZNEH) are compared. It is found that these two samples have similar melting temperatures, but the overall comonomer content in OBC is slightly higher. The crystallization temperature and crystallinity of OBC are markedly lower than those of ZNEH. A successive self‐nucleation annealing experiment reveals that OBC has a more uniform distribution of crystal thickness, indicating a more homogeneous composition distribution in its hard blocks. Small‐angle X‐ray scattering (SAXS) results show that the long period of OBC hardly changes with temperature in the low‐temperature range, whereas that of ZNEH increases gradually with temperature due to melting of the less perfect crystals. The average lamellar thickness of crystals is larger for OBC than for ZNEH, but the thickness of the thickest crystals is comparable in the two. The SAXS profiles were analyzed using a one‐dimensional correlation function. The result reveals that the partially ordered interphases in OBC are mainly located at the interface of the crystalline and amorphous phases. In contrast, the interface of the crystalline and amorphous phases in ZNEH is quite sharp and it is inferred that the partially ordered interphases are distributed in the bulk as separated domains. Scattered tiny crystals are formed in ZNEH, but OBC exhibits a macroscopic morphology of large spherulites. It is also observed that more amorphous phases are rejected outside of the lamellar stacks and spherulites in OBC. © 2012 Society of Chemical Industry

Morphology of crystalline–amorphous olefin block copolymers in solution characterized by small-angle neutron scattering and microscopy

“…It was observed that in melts, following perturbations occurring during the sample preparation, a fraction of the molecules with a large mismatch in block length are driven away from the lamellar interface and swell the domain preferred by the longer blocks (Hustad et al, 2009). It was also observed that more amorphous phases are rejected outside of the lamellar stacks (Tong et al, 2012). Thus, it was demonstrated (Jin et al, 2010) that smaller perturbations favor the expelling of unbalanced molecules for which the entropy lost by the longer block opposes the enthalpy gained by surrounding the short blocks with similar segments.…”

A Perspective on Modeling and Characterization of Transformations in the Blocky Nature of Olefin Block Copolymers

“…5,6 The innovation of "chain shuttling polymerization" (CSP), in comparison to conventional ethylene/α-olefins copolymerization with Ziegler-Natta catalysts, lies in the use of "chain shuttling agents" (CSAs), which enable the shuttling of growing chains between different active catalyst centers. [5][6][7] The blocky nature of OBCs originates from hard crystallizable ethylene segments, at the same time, soft blocks with higher comonomer content that allow for producing copolymer chains with a new range of physical, mechanical, thermal, and rheological properties. [8][9][10][11][12][13][14][15][16] The architectural features of OBCs such as hard block fraction, average block length, and difference in comonomer content of blocks, can be controlled in the course of CSP process by careful selection of the feeding strategy of catalyst, CSA, and monomer, respectively.…”

Chain Structure, Aggregation State Structure, and Tensile Behavior of Segmented Ethylene–Propylene Copolymers Produced by an Oscillating Unbridged Metallocene Catalyst

“…Comparing the l a s of SEPs, OBCs and ZNEH, we notice that the l a s of SEPs are evidently smaller than those of OBCs (∼20 nm) 28 and ZNEH (∼15 nm). 29 This reveals that the noncrystalline segments in SEPs are shorter than those in both OBCs and ZNEH, which may originate from the rapid oscillation of the unbridged metallocene.…”

“…28 On the other hand, no clear spherulitic structure can be identified in ZNEH, though the lamellae are densely stacked. 29 The POM and TEM characterizations reveal that the crystals of SEP14 are less perfect than those of OBC-A, but more ordered than those in ZNEH. Similarly, the crystals of SEP26 are not so ordered as those in OBC-B.…”

“…The chain structure and morphology of OBCs and ZNEH were reported in our previous work, 28,29 and the related data are given in Table S1 in the Supporting Information.…”