Molecular Motion of Polyethylene Chain Ends Tethered to a Fresh Surface of Poly(tetrafluoroethylene) in Vacuo Masato Sakaguchi* Ichimura Gakuen College, 61, Uchikubo, Inuyama 484, Japan Shigetaka Shimada and Katsuhiro Yamamoto Nagoya Institute of Technology, Gokiso, Nagoya 466, Japan Masahiro Sakai Instrument Center, Institute for Molecular Science, Myodaiji, Okazaki 444, Japan Received April 8, 1996; Revised Manuscript Received August 13, 1996 X ABSTRACT: The molecular motion of polyethylene (PE) chain ends tethered to a fresh surface of poly- (tetrafluoroethylene) (PTFE) in vacuo was studied. The tethered PE chain ends were produced by a block copolymerization of PTFE with ethylene in vacuo at 77 K. Each of the tethered PE chains has an unpaired electron at the growing chain end. The mobility of the tethered PE chain ends was observed in the range of 2.8-95 K by an electron spin resonance (ESR) spectrometer with the unpaired electron as a probe. The inter exchange motion between two R protons at the chain ends probably occurs at 2.8 K. The site exchange motion between two conformations at the chain ends occurs above 7 K and is more clearly observed at 15 K. Moreover, the torsional oscillation of the  proton occurs above 30 K. Furthermore, the rotation of the chain end about the chain axis of PE probably occurs at 95 K. The assignment of molecular motion modes was based on spectral simulations. The high mobility of the tethered PE chain ends is attributed to (1) a large space around the chains; (2) the presence of the vacuum; (3) the lack of chain aggregation, because the concentration of the chain ends is low and they are tethered; and (4) the immiscibility of PE and PTFE. The ends of PE chains tethered on the PTFE in vacuo probably behave as isolated PE chain ends in vacuo, and may reveal the mobility intrinsic to PE chain ends. Introduction Many studies on the molecular motion of polymer chains in bulk or in solution have been reported. In these systems, the mobility of the polymer chains depends greatly on their surroundings. For example, the mobility of chains in bulk relates to the amount and size of the free volume. The free volume may be influenced by interactions with inter- and intrapolymer chains. In solution, the mobility is affected by an interaction between the polymer chains and solvent molecules. Thus the polymer chains do not reveal the mobility intrinsic to an individual chain but rather reflect the features of the surroundings. Increased attention is here focused on a fundamental understand- ing of the physical properties of isolated molecules. In low molecular weight compounds, numerous stud- ies on the molecular motion of isolated molecules have been reported 1 in which the small molecules are trapped in an argon matrix that is produced by a simultaneous condensation of argon with gaseous molecules. The mobility of the molecules is high even at 4 K because the molecules are isolated by a frozen argon matrix that has very weak interaction with the molecules. The mobility is high, but some of the motion may be suppressed in the frozen argon matrix. In polymer materials, it is impossible to get a gaseous polymer. Thus isolated polymer chains in a frozen argon matrix cannot be obtained. The polymer chains which are included in the chan- nels of inclusion complexes such as urea 2 and per- hydrotriphenylene 3-7 are isolated from neighboring polymer chains by the host matrix. However, confor- mation of the chains is restricted by the channel wall. Thus, the mobility of the included chains reflects a specific conformation such as the trans form for poly- ethylene (PE), 4-7 and some of the motions may be restrained in the channel. If polymer chains have the following features, they are scarcely affected by other chains and can be re- garded as “isolated polymer chains” in vacuo: (1) a large space around the chains, (2) the presence a vacuum, and (3) an inhibition of the chain aggregation. In our previous two papers (1) the PE alkyl radical, CH 2 CH 2 • , tethered to the poly(tetrafluoroethylene) (PTFE) surface has high mobility, even at a temperature as low as 77 K, 8 and (2) the peroxy radicals at the terminal of a PE chain tethered to a PTFE surface also have high mobility. 9 The high mobility of the two kinds of PE chain ends was interpreted as an extremely low segmental concentration of PE molecules on the PTFE surface. PE chains tethered to a fresh surface of PTFE in vacuo can be regarded as “isolated PE chains” in vacuo for the following reasons: (1) the concentration of PE chains is extremely low on the PTFE surface; (2) the PE chains are present in vacuo; (3) the aggregation of PE chains is prevented by linkage to the PTFE surface with a covalent bond; and (4) PE and PTFE are immsicible. These details are described in later sec- tions. Each of the tethered PE chains has an unpaired electron at the chain terminal. The mobility of the tethered PE chain ends with the unpaired electron as a probe can be observed by an ESR spectrometer. We have reported 10 a preliminary result for the molecular motion of PE chain ends tethered to a PTFE surface in vacuo. In the present study, a detailed analysis of the molecular motion of tethered PE chain ends is discussed. X Abstract published in Advance ACS Abstracts, May 15, 1997. 3620 Macromolecules 1997, 30, 3620-3625 S0024-9297(96)00514-1 CCC: $14.00 © 1997 American Chemical Society