A new insight into the mechanism of 1,3‐dienes cationic polymerization. II. Structure of poly(1,3‐pentadiene) synthesized with ^tBuCl/TiCl₄ initiating system

Abstract

The microstructure of poly(1,3‐pentadiene) synthesized by cationic polymerization of 1,3‐pentadiene with tBuCl/TiCl4 initiating system is analyzed using one‐dimensional‐ and two‐dimensional‐NMR spectroscopy. It is shown that unsaturated part of chain contains only homo and mixed dyads with trans−1,4‐, trans−1,2‐, and cis−1,2‐structures with regular and inverse (head‐to‐head or tail‐to‐tail) enchainment, whereas cis−1,4‐ and 3,4‐units are totally absent. The new quantitative method for the calculation of content of different structural units in poly(1,3‐pentadiene)s based on the comparison of methyl region of 13C NMR spectra of original and hydrogenated polymer is proposed. The signals of tert‐butyl head and chloromethyl end groups are identified in a structure of poly(1,3‐pentadiene) chain and the new approaches for the quantitative calculation of number‐average functionality at the α‐ and ω‐end are proposed. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3297–3307

A New Insight into the Mechanism of 1,3‐Dienes Cationic Polymerization I: Polymerization of 1,3‐Pentadiene with tBuCl/TiCl4 Initiating System: Kinetic and Mechanistic Study

“…This allows us to conclude that the initially formed macromolecules D , due to the high reactivity of terminal conjugated double bonds, interact/copolymerize with the growing chains B with the formation of branched chains E with a trifunctional branch point and a substituted allyl cation as a terminal group (reaction IV, Scheme ). The presence of such vinyl groups in the poly(1,3‐pentadiene) was confirmed by NMR spectroscopy . Moreover, it was shown that these olefinic groups are not fragments of the 3,4‐units of the poly(1,3‐pentadiene) due to the absence of the signal of methyl carbon atom of thr 3,4‐unit in the 13 C NMR spectrum .…”

“…At low t BuCl/TiCl 4 ratio, room temperature, or under monomer‐starved conditions, however, chain branching becomes significant (Table ). Note, a terminal chlorine‐end group is formed only after “inverse” trans‐ 4,1 monomer addition to the growing chain (reaction III in Scheme ) . It should be also noted here that chain transfer to a counterion leading to chains containing tert ‐butyl head and terminal chlorine groups (i.e., giving structure similar to C ) and the regeneration of Lewis acid cannot be fully excluded.…”

“… c) Number‐average functionality at the α‐( F n ( t Bu)) and ω‐end ( F n (Cl)) calculated on the basis of NMR spectroscopy data (see ref. for details);…”

“…The calculations were based on polystyrene standards (Waters) . The microstructure and unsaturation were determined by NMR spectrometry: 1 H (500 MHz) and 13 C (125 MHz) NMR spectra were recorded in CDCl 3 (8–10 wt%) at room temperature using a Bruker AM‐500 spectrometer according to the methodology developed by us in previous work . A pulse delay of 8–12 s was given for recording the 13 C NMR spectra and 6000–8000 scans were accumulated.…”

“…A pulse delay of 8–12 s was given for recording the 13 C NMR spectra and 6000–8000 scans were accumulated. The calculation of the unsaturation degree, the relative content of different structural units, and the content of tert ‐butyl head groups and –CH 2 –Cl end groups, as well as the corresponding functionalities F n ( t Bu) and F n (Cl) was performed according to the methodology developed in that work …”