Branched and hyperbranched polymers by atom transfer radical polymerization.

摘要

The research presented in this thesis is focused on using "living" controlled radical polymerization to prepare well-defined (co)polymers with a special emphasis on the preparation of branched and hyperbranched (co)polymers. The first polymerization system that was developed was the use of degenerative transfer of iodine between active and dormant polymer chains. The second method employed was atom transfer radical polymerization, ATRP. It was with ATRP that hyperbranched polymers were prepared along with ABA block copolymers of step-growth and vinyl polymers.; A new system to prepare well-defined polystyrene and polyacrylics was developed by using iodine containing transfer agents. Molecular weights were predefined by {dollar}rm DPsb{lcub}n{rcub}=Delta{dollar}(M) /((R {dollar}-{dollar} I) {dollar}rmsb{lcub}o{rcub}+Deltalbrack Irbrack),{dollar} where {dollar}rmDeltalbrack Mrbrack{dollar} is the concentration of consumed monomer, (R {dollar}-{dollar} I) is the concentration of the iodine containing transfer agent, and {dollar}Delta{dollar}(I) is the concentration of consumed initiator. For polystyrene, the molecular weight distributions were narrow with polydispersites, {dollar}rm Msb{lcub}w{rcub}/Msb{lcub}n{rcub}<1.5.{dollar} Although the molecular weights were predefined for the polyacrylates, the polydispersities were high, {dollar}rm Msb{lcub}w{rcub}/Msb{lcub}n{rcub}=2.{dollar} Unfortunately, there was no molecular weight control for the polymerization of methacrylates and the molecular weight distributions were broad, {dollar}rm Msb{lcub}w{rcub}/Msb{lcub}n{rcub}>2.{dollar}; The development of atom transfer radical polymerization, ATRP, led to the preparation of well-defined polystyrenes, polyacrylates, polymethacrylates, and polyacrylonitrile. ATRP allowed for the control of molecular weights up to {dollar}rm Msb{lcub}n{rcub}{dollar} = 200,000, and polydispersities as low as {dollar}rm Msb{lcub}w{rcub}/Msb{lcub}n{rcub}=1.04.{dollar} To obtain such well defined (co)polymers, ATRP establishes an equilibrium between active and dormant species through a reversible redox reaction between copper (I) salts and alkyl halides.; ATRP was used to prepare hyperbranched polymers by homopolymerization of ABC* monomers. The ABC* monomers are functionalized vinyl monomers, where the vinyl group is denoted AB, and the functional group is C*. This functional group is an alkyl halide which can be activated by using copper (I) to form a radical. The newly formed radical can then initiate the polymerization of the double bonds. As the polymerization incorporates new monomer, C* groups are incorporated into the polymer as pendent groups. These C* groups can also be transformed to radicals by reaction with copper (I) to form branches. A more detailed description of the chain growth/branching process is described in the thesis.; Novel hyperbranched polystyrenes were prepared from p-chloromethylstyrene. Hyperbranched polyacrylates were prepared from a novel acrylic ABC* monomer, 2-(2-bromopropionyloxy)ethyl acrylate, BPEA. This monomer was prepared by reaction of 2-hydroxyethyl acrylate with 2-bromopropionyl bromide in the presence of pyridine.; The polymerization of BPEA was studied to evaluate the kinetics of the polymerization and the formation of chain branching in the polymerization system. These results were compared to theoretical predictions. Also, the role of copper (II) was evaluated in the hyperbranched polymerizations of p-chloromethylstyrene and BPEA.; Finally, block copolymers of polysulfone and vinyl monomers were prepared. This was done by synthesizing a polysulfone macroinitiator by reacting polysulfone (with phenolic end groups) with 2-bromopropionyl bromide in the presence of pyridine. This macroinitiator was then used in ATRP to polymerize either styrene or butyl acrylate and form well-defined ABA block copolymers.