Spontaneous synthesis of a homogeneous thermoresponsive polymer network composed of polymers with a narrow molecular weight distribution

Abstract

We have developed a method to obtain a polymer gel consisting of a relatively homogeneous network structure composed of polymers with a narrow molecular weight simply by mixing the necessary compounds. In this method, a radical chain polymerization reaction with a fast reaction rate is combined with a radical addition cross-linking reaction that has a sufficiently slow reaction rate compared with the polymerization reaction. For the polymerization reaction, a multifunctional initiator with a strictly controlled number of polymerization initiation sites was used to prepare a star polymer with a chain number and length determined by living radical polymerization. In the cross-linking reaction, a multifunctional terminating agent was used to prepare a star polymer from a polymer with a narrow molecular weight via living radical polymerization followed by coupling with multiple polymer chains using a termination reaction. As a result, two kinds of reactions with greatly different kinetics occurred sequentially only when all of the compounds were mixed and allowed to stand at a constant temperature, and a relatively homogeneous network structure comprising cross-linked polymers with a low molecular weight distribution was inherently constructed. Japanese researchers have developed an easy method for synthesizing networks of more uniformly sized polymer molecules which produce soft materials with a greater range of functionality. Polymer gels are made of three-dimensional chains of connected polymer molecules within a swollen solvent. These soft materials have potential applications in drug delivery, as shape memory materials and in soft robotics. Many polymer gels, however, are made up of chains of polymers with different molecular weights. These inhomogeneous networks may not have the all the functionality of a uniform polymer. Kotaro Satoh and Yukikazu Takeoka from Nagoya University and colleagues have now developed a method for synthesizing a network structure composed of polymers of similar size. The polymer gel can be created by simply mixing the necessary compounds together. We have developed a method to obtain a polymer gel consisting of a relatively homogeneous network structure composed of polymers of narrow molecular weight simply by mixing the necessary compounds. In this method, two kinds of reactions with greatly different kinetics occurred sequentially only when all the compounds were mixed and allowed to stand at a constant temperature, and a relatively homogeneous network structure comprising cross linked polymers of low-molecular-weight distribution was spontaneously constructed.