Abstract
Copolymerizations of dibenzofulvene (DBF) with methyl methacrylate (MMA), 2-hydroxyethyl methacrylate (HEMA), methyl acrylate (MA), and 2-hydroxyethyl acrylate (HEA) were conducted under free radical conditions in toluene using α,α′-azobisisobutylonitrile (AIBN) as the initiator. In the copolymerizations, DBF indicated much higher reactivity than the comonomers, and the products comprised mainly of DBF units. NMR, UV, and fluorescence spectra, as well as electrochemical features indicated that the copolymers possess both isolated and rather short, sequential (meth)acrylate units, as well as π-stacked and unstacked DBF sequences. Isolated (meth)acrylate units are proposed to be sandwiched between DBF units. The ratios of π-stacked and unstacked side-chain fluorene groups of DBF units in excited states were accurately determined on the basis of fluorescent emission spectra; DBF units are mostly π-stacked in excited states as disclosed by fluorescence spectra. Two types of π-stacked sequences were suggested to be present in the ground state by electrochemical analysis. The copolymers exhibited higher solubility than pure poly(DBF).
Highlights
Polymer chain conformation plays important roles in macromolecular materials
The products were fractionated into the three parts, namely: (i) the THF-insoluble part; (ii) the THF-soluble, hexane-insoluble part (poly(DBF-co-methyl methacrylate (MMA)), and poly(DBF-co-methyl acrylate (MA))) or THF-soluble, diethyl ether-insoluble part (poly(DBF-co-hydroxyethyl methacrylate (HEMA)) and poly(DBF-co-hydroxyethyl acrylate (HEA))); and (iii) the hexane-soluble part (poly(DBF-co-MMA) and poly(DBF-co-MA)) or diethyl ether-soluble part (poly(DBF-co-HEMA)
Copolymers of DBF with MMA, MA, HEMA, and HEA were prepared by free radical random
Summary
Polymer chain conformation plays important roles in macromolecular materials. A helix is one typical example of controlled chain conformation, and wide varieties of helical polymers have been synthesized and characterized [1,2,3,4,5]. As another type of controlled conformation, a π-stacked structure was introduced; poly(dibenzofulvene) (poly(DBF)) was the first example of vinyl polymer having a π-stacked structure [6,7,8]. The examples of π-stacked polymers include poly(DBF) and derivatives [6,7,8,9,10,11,12,13,14,15], poly(benzofulvene) and derivatives [16,17], polymers consisting of cyclophane-based monomeric units [18,19,20], polyurethanes [21], polyphenanthrolines [22], polyethers [23], and side-chain aromatic vinyl polymers [24,25]. Poly(DBF) indicates intriguing photo-electronic properties including characteristic photo-absorbance and emission profiles and rather high charge mobility due to the π-stacked side-chain fluorene moieties, and its derivatives with substituents on the fluorene backbone of the DBF unit have been synthesized. Copolymerization of DBF with other types of monomers have not been reported so far in spite of the fact that copolymerization is a simpler method than the new monomer
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