Synthesis Of Miktoarm Star Copolymers Research Articles

A robust strategy for the synthesis of miktoarm star copolymers by combination of ROP and photoinitiated free radical polymerization

A novel approach for the synthesis of miktoarm star copolymers by the combination of ring opening polymerization (ROP) and Type II photopolymerization is described. The method pertains to the use of a multifunctional initiator, bearing primary hydroxyl and tertiary amine functionalities, for the sequential or simultaneous polymerization of vinyl and lactone monomers under mild conditions. In the first step, phosphazene base (P2-t-Bu) catalyzed ROP of ε-caprolactone is accomplished. Subsequently, thus obtained poly(ε-caprolactone) with amine end groups was used as co-initiator for the polymerization of methyl methacrylate by utilizing conventional Type II photoinitiators. The structures, molecular weight characteristics and thermal properties of the polymers are analyzed by NMR, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) measurements, respectively.

Miktoarm Star Copolymers from the Chemical Stitching of Associating Block Copolymers

A new method for the synthesis of miktoarm star copolymers is proposed. To demonstrate its viability, diblock copolymers, PA-b-PSCOOH, with a carboxyl-bearing short PSCOOH block, and triblock copolymers, PB-b-PNH2-b-PB, with an amino-bearing short PNH2 block, were synthesized and characterized. Here PA and PB denote poly(tert-butyl acrylate) and poly(methyl methacrylate), respectively. The carboxyl- and amino-bearing blocks of the copolymers associated with one another due to carboxylate and ammonium ion pairing in dichloromethane. The addition of a coupling agent caused the amino and carboxyl groups to amidize and resulted in the fusion of the associating chains, thus producing miktoarm copolymers μ-(PA)1(PB)2 and μ-(PA)2(PB)2. Factors affecting the relative and total yields of μ-(PA)1(PB)2 and μ-(PA)2(PB)2 formation were investigated.

Arm-First Method As a Simple and General Method for Synthesis of Miktoarm Star Copolymers

Miktoarm star copolymers containing two or more arm species were synthesized by atom transfer radical polymerization using a simple and general "arm-first" method, that is, one-pot cross-linking a mixture of different linear macroinitiator (MI) species by a divinyl cross-linker, such as divinylbenzene. Using linear MIs with a high degree of bromine chain-end functionality, including polyacrylate, polystyrene, polymethacrylate and poly(ethylene oxide), resulted in high-yield star polymers (>90%). Characterized by liquid adsorption chromatography techniques, which separated star polymers on the basis of the chemical composition of arms, the obtained star product was proved to be miktoarm star copolymers containing two or more arm species in one molecule, instead of mixture of different homoarm star polymers. Within our investigation, the molar ratios of the arms in the miktoarm star copolymers were always in agreement with the composition of the initial MI mixture, indicating the powerful capacity of this arm-first method for synthesis of miktoarm star copolymers with potentially any molar ratios and species of the arms. By using a mixture containing five types of linear MIs with different chemical compositions, miktoarm star copolymers containing five kinds of arms were synthesized for the first time, which significantly expanded the methodologies for synthesis of miktoarm star copolymers by living polymerization techniques.

Synthesis of Degradable Miktoarm Star Copolymers via Atom Transfer Radical Polymerization

Both nondegradable and degradable miktoarm star copolymers were synthesized via ATRP using the “in−out” method. The synthesis consisted of three steps: synthesis of a linear macroinitiator (MI) using the first monomer, a core-forming reaction with a divinyl compound, and then further chain extension with the second monomer. Various characterization methods, including GPC, NMR, and GC, were used to analyze the initial star polymers and to identify the optimal experimental conditions for the synthesis of the multifunctional star initiators and the miktoarm star copolymers. During the synthesis of miktoarm star copolymers, both interstar and intrastar arm−arm couplings were observed. The initiating efficiency of the alkyl bromide sites in the core of the star polymers was determined by analysis of the linear block copolymers, obtained after cleavage of the degradable star and miktoarm star copolymers. The results confirmed that the initiation efficiency was reduced by the highly cross-linked star core. In the case of degradable miktoarm star copolymers, only 19% of the total Br functionality incorporated into the first star copolymer initiated the polymerization of the second monomer.