[The] effect of Lewis base additives on the addition of 1,1-diphenylethylene to living polyisoprene

Abstract

Polymeric materials are used for a wide range of applications of daily products to nanotechnology-based functional materials. Polymers are produced by a polymerization process, which merge monomers through covalent bonding in a controlled way to create target chain structures. In polymerization, monomer sequence control is very important to obtain target physical and chemical properties of polymers, especially for ionomers with strongly interacting ionic groups.

For future work, optimization of the THF-based polymerization process and employing non-lithium counter ions with a different diene monomer are proposed.

In order to produce ionomers with controlled spacing and ionic character, we employed anionic polymerization techniques in conjunction with a positioning monomer. This strategy allows for controlled polymerizations of strands between ionic groups, and the strands have precisely controlled molecular weights with narrow distributions. In order to create ionic groups located at controlled positions, 1,1-diphenylethylethylene (DPE) is utilized as a positioning monomer. DPE does not self-polymerize under most reaction conditions due its large steric hindrance, and well-established functionalization chemistry of phenyl groups for conversion to ionic groups can be utilized. These two properties make 1,1-diphenylethylene highly useful for the synthesis of precisely tailored ionomers.

Ionomers have fractional ionic groups in the mainly non-ionic chains, and the strong inter-associations between the ionic groups result in unique physical properties. Most current methods of ionomer synthesis produce random ionomers without control of ion group locations in the ionomer chains. The lack of sequence control generally makes random ionomers nearly incompatible with most of common solvents for processing and their nanoscale structures irreproducible very important for applications utilizing the microphase separated ionic groups.

Polymerization of polyisoprene functionalized with DPE was attempted using various Lewis bases as promoters in a non-polar solvent medium. Tetrahydrofuran was found to be the most effective Lewis base for the functionalization of polyisoprene with DPE, but the high reactivity of tetrahydrofuran with anions resulted in uncontrolled termination of living polyisoprene chains. Other amine-based Lewis bases were tested for the end-functionalization efficacy of polyisoprene with DPE and reinitiation efficiency from DPE anions, but the results were generally unsatisfactory, with triethylamine possibly meriting further examination.