A New Insight into the Mechanism of 1,3‐Dienes Cationic Polymerization III: Polymerization of 1,3‐Pentadiene with CF₃COOD/TiCl₄ Initiating System: Chain‐Ends Structure and Kinetics

Abstract

A novel method for the investigation of the chain-end structure of poly(1,3-pentadiene)s synthesized using the CF 3 COOD/TiCl 4 initiating system is developed. It is shown for the fi rst time that the content of trans -1,2-structures in the fi rst monomer unit is considerably higher than the content of trans -1,4-structures, whereas the content of trans -1,4-units is substantially higher than trans -1,2-units for the polymer chain as a whole. Another important observation is that chain transfer to monomer is signifi cant even at the earlier stages of the 1,3-pentadiene polymerization (after 1 s of reaction). The very low functionality at the ω-end ( F n (Cl) < 0.15) confi rms the intensive chain transfer to monomer. This method is also applied for the estimation of the concentration of active species and the rate constant for propagation ( k p ) for the cationic polymerization of 1,3-pentadiene using the CF 3 COOD/TiCl 4 initiating system: rate constants for propagation, k p , of 1.5 × 10 3 and 3.3 × 10 3 L mol −1 min −1 are determined for 1,3-pentadiene polymerization at 20 and -78 °C, respectively.

The Structure of Cationic Polyisoprene: Branching versus Cyclization

“…According to some authors, this feature is connected with the occurrence of intramolecular cyclization with the formation of six‐membered cyclic structures. Others proposed another explanation of the observed reduced unsaturation, which is consistent with the formation of branched macromolecules due to the intensive chain transfer to polymer …”

A New Approach toward Investigation of Structure of Terminal Units of Poly(1,3‐Pentadiene) using T2‐Filtered NMR Spectroscopy

“…The formation of trans-1,4-(structure HI) and trans-1,2-units (structure HII) in a head group during the cationic polymerization of 1,3-pentadiene with CF 3 COOH/TiCl 4 initiating system, according to the literature, [7,18,38] can be presented as it is depicted in Figure 4.…”

“…One known method of determination of the relative content of structures HI and HII developed by our team consists in using deuterated initiator (CF 3 COOD) in the cationic polymerization of 1,3-pentadiene. [18,38,40] In this case, the position of signals of deuterium atoms in HI and HII head groups on 2 H NMR spectrum differs significantly (1.6 and 0.9 ppm, respectively) that allows calculating quantitatively the content of these head groups. [18,38] In respect to end groups of a polymer chain of CPPD, the noticeable increase of relative intensity of signal at 45.2 ppm (Figure 1a,b) is observed on 13 C NMR spectrum recorded with T 2 -filter.…”

“…[1] The 1,3-pentadiene (piperylene), other conjugated 1,3-diene, is used for the production of aliphatic hydrocarbon resins, [2] liquid rubber SKOP (synthetic caoutchouc oligomer of piperylene) [3][4][5] as well as low molecular weight polymers and copolymers for using in CF 3 COOD/TiCl 4 initiating system. [18] However, the structure of head and end groups of industrially relevant polymers of 1,3-pentadiene, synthesized by cationic polymerization using protic initiators, remains unknown up to date.…”

Comprehensive structural characterization of polyisoprene synthesized via cationic mechanism

“…The fragments of 13 C NMR spectra of two polyisoprene samples synthesized with t BuCl/TiCl 4 (sample CPI‐1) and CCl 3 COOH/TiCl 4 (sample CPI‐3), respectively, are presented in Figure . The last polymer sample does not contain tert ‐butyl head group because of polymerization initiated by protons …”