Synthesis and characterization of poly(5‐alkyl‐2‐norbornene)s by cationic polymerization. Effect of alkyl substituent length on monomer reactivity, polymer structure and thermal properties

Abstract

Cationic polymerizations of various 5-alkyl-2-norbornenes (R-NB, where R=H, CH,, C,Hs, CSH,,, C,HIS, and C,,H,,) were carried out by the AlEtCl,/tert-butyl chloride catalyst system, and the effect of the length of the alkyl substituents on the monomer reactivity and polymerizability, polymer structure, and softening point (SP) were investigated. The introduction of an alkyl substituent into 5-position of the norbornene ring remarkably reduces the monomer reactivity and polymerizability, although the length of alkyl group does not affect them. 13C NMR structural analysis of poly(R-NB)'s revealed that not only the normal 5or 6-alkyl-2,3-unit but also other structures such as 5-or 6-alkyl-2,7-, 4-alkyl-3,6-units, etc., are the most plausible structures for the repeating units. Furthermore, the existence of the 4-alkyl-3,6-repeating unit and of the alkylidene type end-group indicates the presence of an intermediate tertiary cation (5-alkyl-5-norbornyl cation), which causes the low reactivityand polymerizability of the monomers. The SP of oligomers of equal molecular weight (DP, = 3-5) decreases in the following order: H-NB,The effect the alkyl substituent length on the SP is discussed on the basis of the I3C spin-lattice relaxation times (T,) for the carbons in the alkyl group.

Homopolymerization of 5-alkyl-2-norbornenes and their copolymerization with norbornene over novel Pd(acac)2/PPh3/BF3OEt2 catalyst system

“…As shown in Table 4, the glass transition temperatures of the polymers decrease substantially with increasing alkyl substituent length at approximately similar average polymerization degrees (P n ). The decrease of the T g 's with increasing number of carbons of the substituent was explained on the basis of the mobility of the substituent, which acts as an 'internal diluent' [29]. The average polymerization degree and molar mass distributions of 5-alkyl-2-norbornenes did not display a marked difference between the types of monomers.…”

“…Sagane et al [29] have synthesized 5-alkyl-2-norbornenes with AlEtCl 2 /tert-butylchloride catalyst system and investigated the effect of an alkyl substituent on monomer reactivity, polymer structure and thermal properties. A further improvement in the polymerization of 5-alkyl-2-norbornenes has been achieved through use of late transition metal catalysts [5,6,10,11].…”

“…Endo/exo mole ratios of 5-alkyl-2-norbornenes were determined from 13 C NMR spectra in deuterocloroform. The carbon peaks were assigned in comparison with that reported early [29] and summarized in Table 1. 5-alkyl-2-norbornenes were twice distilled in vacuum directly before use.…”

“…5-Propyl-2-norbornene (bpZ 85 (8C/13 mm Hg, endo/exoZ76/24), 5-butyl-2-norbornene (bpZ100 8C/7 mm Hg, endo/exoZ78/22), 5-hexyl-2-norbornene (bpZ90 8C/3 mm Hg, endo/exoZ78/22) and 5-decyl-2-norbornene (bpZ136 8C/3 mm Hg, endo/exoZ 80/20) were synthesized by the Diels-Alder reactions of cyclopentadiene with the corresponding 1-alkenes (1-pentene, 1-hexene, 1-octene and 1-dodecene) as described elsewhere [29]. Endo/exo mole ratios of 5-alkyl-2-norbornenes were determined from 13 C NMR spectra in deuterocloroform.…”

Ethylene‐norbornene copolymers prepared with metallocene‐ based catalysts: new sequence assignments by 13 C NMR

“…Here the lack of such a shift must be due to the d substituents C7 and C39. Indeed for 5-decylnorbornene, where only C7 is present, a small shift of -0.8 ppm is observed 10) . Calculations on various ethylene-norbornene oligomers suggest that the absence of such a shift may be due to molecular distortions.…”