Abstract
Olefin block copolymer (OBC), with its low hard segments, can form unique space-filling spherulites other than confined-crystallization morphologies, mainly due to its weak phase-separation. In this work, 1,3;2,4-Bis(3,4-dimethylbenzylidene) sorbitol (DMDBS), a well-known nucleating agent, was used to tailor the crystallization behavior and crystalline morphology of OBC. It was found that DMDBS can precipitate within an OBC matrix and self-assemble into crystalline fibrils when cooling from the melt. A non-isothermal crystallization process exhibited an increased crystallization rate and strong composition dependence. During the isothermal crystallization process, DMDBS showed a more obvious nucleating efficiency at a higher crystallization temperature. OBC showed typical spherulites when DMDBS was added. Moreover, a low addition of DMDBS significantly decreased the crystal size, while a large addition of DMDBS induced aggregates, due to the limited miscibility of DMDBS with OBC. The efficient nucleating effect of DMDBS on OBC led to an increased optical transparency for OBC/DMDBS composites.
Highlights
Due to so-called chain shuttling technology, olefin block copolymer (OBC) has been recently synthesized by Dow Chemical Company, and commercialized as a thermoplastic elastomer [1,2,3,4].As shown in Scheme 1, during the chain growth process, a chain shuttling agent was used to either activate or inactivate the branch incorporation of 1-octene into the chains, resulting in a multiblock copolymer of semicrystalline polyethylene (PE) hard segments, alternating with amorphous soft segments with short branches [5,6]
DMDBS with olefin block copolymers, to regulate the crystalline structure and morphology of OBC, which can generally form a dispersed polyethylene crystal or even an interconnected crystalline network embedded in the amorphous rubber network
After the temperature dropped to 116 ◦ C, the hard segments of OBC started to crystallize [2]
Summary
Due to so-called chain shuttling technology, olefin block copolymer (OBC) has been recently synthesized by Dow Chemical Company, and commercialized as a thermoplastic elastomer [1,2,3,4]. The detailed block length and block number could be regulated by changing the content of the chain shuttling agent [7] In this way, the varied apparent mechanical properties were achieved. OBC decreased the crystal size and increased lamellar thickness and the number of tie-molecules between lamellae, resulting in an obvious strain-hardening behavior [25] It is of great importance and highly efficient for OBC to tune its crystalline morphologies in order to tailor its physical properties. DMDBS with olefin block copolymers, to regulate the crystalline structure and morphology of OBC, which can generally form a dispersed polyethylene crystal or even an interconnected crystalline network embedded in the amorphous rubber network. This work may provide some guidelines on tuning crystalline morphologies of crystalline block copolymers and enrich the knowledge of nucleating effects for thermoplastic elastomers
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