Terminal and Internal Unsaturations in Poly(ethylene-co-1-octene) Yiyong He,* ,† XiaoHua Qiu,* ,† Jerzy Klosin,* ,‡ Rongjuan Cong, § Gordon R. Roof, ‡ and David Redwine † † Corporate R&D, The Dow Chemical Company, 1897 Building, Midland, Michigan 48667, United States ‡ Corporate R&D, The Dow Chemical Company, 1776 Building, Midland, Michigan 48667, United States § Performance Plastics R&D, The Dow Chemical Company, Freeport, Texas 77541, United States * S Supporting Information ABSTRACT: Unsaturated structures in polyolefin polymers are important in many respects. In this work, new vinyl and vinylidene structures were identified in poly(ethylene-co-1- octene) copolymers. The combination of careful sample selection and model compounds provided clear evidence for the assignment of these structures. More importantly, a new method was developed to differentiate and quantify for the first time terminal and internal unsaturations in ethylene-co-1- octene copolymers. The method described here will be generally applicable to many different polyolefins. ■ INTRODUCTION Molecular olefin polymerization catalysts (metallocene, con- strained geometry, non-metallocene) have become important industrially because of their ability to produce very high molecular weight ethylene/α-olefin copolymers with a narrow composition distribution. 1,2 Some of the most important catalytic events during olefin polymerization reactions are various chain termination reactions as they control the ultimate molecular weight of produced polyolefins. Under hydrogen-free polymerization conditions, all polymer chains are terminated with unsaturated groups, as a result of β-H transfer to either the catalyst metal or the incoming monomer. The main unsaturation in homopolyethylene formed by coordination catalysis is the vinyl group (V1); however, the complexity of unsaturation increases signi ficantly in ethylene-α-olefin copolymers due to the occurrence of chain termination events after inserted ethylene, 1,2- and/or 2,1-inserted α-olefin as well as various isomerization pathways. Analysis of unsaturated structures in polyolefins is crucial to understand the nature and the relative importance of the various possible chain termination pathways. The knowledge obtained from such analysis can be used to fine-tune catalysts and process conditions for better molecular weight control. The significance of unsaturation analysis in polyolefins is not limited to molecular weight control. 3 For example, polymers with vinyl chain ends can act as macromers and are one of the prerequisites for generating long-chain branching. 4 Unsatura- tions, as the functional groups of polyolefins, can be useful for further functionalization 5 or be disadvantageous in the undesired case of oxidation reactions. 6 Unsaturations in polyolefin chains have been widely studied in the past two decades by NMR spectroscopy. 7,8 For poly(ethylene-co-1-octene) (EO) copolymers, a family of polymers with tremendous commercial significance, the most comprehensive study on unsaturated structures was reported by Busico and co-workers. 8 However, the assignments made of various unsaturation structures were based on resonances in a 1 ppm 1 H NMR spectral region from a single polymer sample. Because of heavy peak overlapping, some structures were tentatively proposed based on simulations or peak deconvolu- tion. Another complexity of unsaturation analysis arises from frequent and simultaneous occurrence of both terminal and internal unsaturations. The position of unsaturations along a polyolefin chain was usually presumed based on proposed reaction mechanisms. 9 Busico et al. proposed several mechanisms leading to internal trisubstituted unsaturations in EO copolymers, which involve allylic CH activation of metal bound terminal unsaturated group, followed by isomerization of the resulting allyl species, ethylene propagation, and chain termination. Wasserman and coauthors used an ozonolysis method to cleave polyolefin chains at each internal double bond. 10 This approach demonstrated for the first time the presence of internal unsaturations, but its main limitation was that different types of unsaturations could not be differentiated. The accuracy of the quantification was also not satisfactory. Without a reliable method to determine the ratio between terminal and internal unsaturations in polyolefins, the precise measurement of total unsaturations has limited utility. The first objective of this work is to provide an updated understanding of unsaturations in EO copolymers. The results obtained in this work are not limited to EO copolymers as most of the reported unsaturated structures in EO copolymers have closely related analogues in other ethylene/α-olefin copoly- mers. We overcame the previous peak overlap challenge by Received: May 13, 2014 Revised: May 25, 2014 Published: June 16, 2014 Article pubs.acs.org/Macromolecules © 2014 American Chemical Society 3782 dx.doi.org/10.1021/ma500989p | Macromolecules 2014, 47, 3782-3790