Synthesis and polymerization of alkyl 1-bicyclobutanecarboxylates

Abstract

Bicyclobutane monomers substituted with an ester group at the 1 position were synthesized using a practical synthesis route, starting from 1,1 -cyclobutanedicarboxylic acid, which is adaptable to the synthesis of various bicyclobutane esters and can be scaled up. Four new bicyclobutane monomers were prepared using this method, namely ethyl, isopropyl, ß,ß,ß-trifluoroethyl, and phenyl 1-bicyclobutanecarboxylate. These bicyclobutanecarboxylates were subjected to free radical polymerization under various conditions. The bicyclobutane monomers behave very similarly to their vinyl counterparts. Chain transfer to polymer occurs to some extent, especially when the size of the substituent is relatively small (methyl ester). Excessively high molecular weights and gelation can be controlled by addition of a chain-transfer agent. The temperature, the size of the ester group, or the nature of the initiator has no marked influence on the stereochemistry of the bicyclobutane polymer backbones. Poly(methyI 1-bicyclobutanecarboxylate) is an optically clear material with a refractive index no25 = 1.52. Its resistance to thermal degradation is excellent. Polymers from this family exhibited surprisingly low Tg's, which probably result from an unexpectedly high flexibility of the bicyclobutane polymer backbone, as shown by molecular modeling.

Enzymatic synthesis of a bicyclobutane fatty acid by a hemoprotein–lipoxygenase fusion protein from the cyanobacterium Anabaena PCC 7120

“…It has a bond strain energy of 66 kcal/mol, more than double the value of either cyclopropane or cyclobutane (Ϸ26 kcal/mol) (23). Extensive efforts have been made during the past 40 years to develop synthetic approaches to molecules containing a bicyclobutane subunit and to understand the chemistry of this structure (24)(25)(26)(27) Fig. 2.…”

Structural Analyses of Methyl Bicyclobutane-1-carboxylate Oligomers Formed with tert-Butyllithium/Aluminum Bisphenoxide and Mechanistic Aspect of the Polymerization

“…Methyl bicyclobutane-1-carboxylate (MBCB) was prepared according to the procedures reported previously, 3,15 and purified prior to polymerization by distillation over calcium dihydride under reduced nitrogen pressure. Toluene and heptane were purified in the usual manner, mixed with a small amount of n-butyllithium and distilled under high vacuum just before use.…”

“…3 Anionic polymerization offers potentially better control of stereochemistry of polymers, but early attempts for methyl bicyclobutane-1-carboxylate (MBCB) with n-butyllithium as an initiator gave only low molecular weight products. In the previous paper, 4 we reported the anionic polymerization of MBCB with tert-butyllithium (t-BuLi)/bis(2,6-di-tertbutylphenoxy)ethylaluminum [EtAl(ODBP) 2 ] in toluene at À78 C gave transtactic polymers (trans contents > 90%) in high yields.…”

Synthesis and thermal characterization of poly(dimethyl bicyclobutane-1,3-dicarboxylate) and its copolymers

“…Drujon 9 reported that poly(methyl bicyclobutanecarboxylate) showed a surprisingly low T g , namely 95°C compared to the T g of PMMA. Molecular mechanics calculation on poly(methyl bicyclobutane-1-carboxylate) fragments revealed an unexpected high flexibility of the bicyclobutane polymer backbone.…”

“…6 In further work they synthesized four monomers, i.e., ethyl, isopropyl, ␤,␤,␤-trifluoroethyl, and phenyl 1-bicyclobutanecarboxylate. [7][8][9] The temperature, the size of ester group, or the nature of the initiator had no marked influence on the stereochemistry of the bicyclobutane polymer backbones. Poly(methyl 1-bicyclobutanecarboxylate) is an optically clear material and shows excellent thermal degradation resistance, but all these polymers exhibit surprisingly low T g s compared to poly(1-cyanocyclobutane).…”