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Comparison of the Mechanism and Kinetics of Living Carbocationic Isobutylene and Styrene Polymerizations Based on Real‐Time FTIR Monitoring
Author(s) -
Puskas Judit E.,
Shaikh Sohel
Publication year - 2004
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.200451119
Subject(s) - isobutylene , polymerization , methylcyclohexane , reaction rate constant , chemistry , kinetics , styrene , cationic polymerization , fourier transform infrared spectroscopy , polymer chemistry , copolymer , chemical engineering , organic chemistry , polymer , catalysis , physics , quantum mechanics , engineering
This paper will compare the mechanism and kinetics of living carbocationic polymerization of isobutylene (IB) and styrene (St), initiated by the 2‐chloro‐2,4,4‐trimethyl‐pentane (TMPCl) / TiCl 4 ) system in 60/40 (v/v) methylcyclohexane / methyl chloride mixed solvent at −80 and −75 °C. The rate of initiation was found to be first order in TiCl 4 in both systems. While initiation is instantaneous in IB polymerization at [TiCl 4 ] 0 ⩾ [TMPCl] 0 , it is slow in St polymerization. Kinetic derivation showed that initiating efficiency is dependent on [M] in this latter system, which was also demonstrated experimentally. The apparent initiation rate constant was determined from initiator consumption rate data and was found to be k i,app = 1.39 l 2 /mol 2 sec. The rate of St consumption measured using a real time fibre‐optic mid‐FTIR monitoring technique compared well with gravimetric data and was found to be closer to first order in TiCl 4 at [TiCl 4 ] 0 < [TMPCl] 0 . However, the rate followed a close to second order in TiCl 4 at [TiCl 4 ] 0 ⩾ [TMPCl] 0 . The mechanistic model proposed earlier for living carbocationic IB polymerization, which yielded good agreement with experimental data, seems to apply to carbocationic St polymerization as well. This model reconciles the discrepancy between rate constants published for carbocationic IB and St polymerizations, and accounts for shifting TiCl 4 orders. However, independent investigations are necessary to verify the proposed mechanistic model. Optimized conditions led to living carbocationic St polymerization producing high molecular weight PS with 100% initiating efficiency.