Methacrylate Star Synthesis by GTP

Abstract

All process conditions were picked to minimize the back-biting termination reaction so the maximum level of living arm could be carried into the core-forming step. Major contributors to control of termination were: 1. Using 0.2% (mole basis) of catalyst on initiator instead of higher concentrations. Within the constraints defined below, this produces a robust process that is insensitive to minor changes in materials, temperatures, and rates of addition. 2. Minimizing the time between arm formation and core formation. Polymerization of arm monomethacrylate to about 96 to 98% before core formation was the aim because conversion to >99% would have allowed too much time for termination to proceed. 3. Adding core-forming monomer (ethylene glycol dimethacrylate) in about 5 min to keep monomer concentration high in this step. Faster add times may not be desirable because of mixing difficulties in this extremely fast polymerization. 4. Reaction solvent mixture containing 50% tetrahydrofuran. This allowed the reflux temperature to be about 85°C. 5. Keeping monomer concentration high in the arm-forming step by starting the polymerization with half of the monomer in the reactor. This forced the polymerization past the trimer stage, where termination is fastest. 6. Starting the reaction at room temperature so the exotherm could be dissipated by the heat capacity of the system. Two lots of trimethylsiloxyethyl methacrylate used to introduce hydroxyl groups into the product (after unblocking) gave different rates of polymerization, with one lot reaching the core-forming step in about half the time of the other. The monomer lot with the higher reactivity also led to higher levels of free arm. Stars made at high (2.0%) catalyst levels were quite unstable to molecular weight and viscosity increase. Mechanistic studies show that the increase is probably because of star/ star free-radical methacrylate polymerization involving pendant residual methacrylate unsaturation from the core-forming step. Stars made under the recommended conditions using 0.2% catalyst and the above process steps are probably stable enough for commercial use.

Microphase separation under constraints: a molecular thermodynamic theory for polyelectrolytic amphiphilic model networks in water

“…f 0 , the polymer volume fraction in the unperturbed state was taken equal to 0.2, the same as the volume fraction upon synthesis in our experimental system [14,16]. b, the number of arms at the cross-links was fixed to 20, close to the values determined by static light scattering for star polymers prepared by analogous methods [16,[40][41][42]. c B , the FloryHuggins interaction parameter between the hydrophobic block and water, was set equal to 2.0, typical for the value of the propylene oxide-water pair [16,43].…”

“…To understand the coefficient of 2/3 in the Symbols. Constants: f 0 , polymer volume fraction in unperturbed state, taken as that upon synthesis; set equal to 0.2 [14,16]; b, number of arms per cross-link, taken to be equal to 20 throughout the manuscript [16,[40][41][42]; c B , Flory-Huggins interaction parameter between water and the hydrophobic units; set equal to 2.0 [16,43]; c A , Flory-Huggins interaction parameter between water and the hydrophilic units; set equal to 0.45 [15,44]. Independent variables: i, degree of ionization of ionizable groups: varied between 0.001 and 1; z, number of units in the hydrophobic block (or one half of the hydrophobic units between crosslinks; each elastic chain has two hydrophobic blocks); varied between 2 and 238; h, number of units in the hydrophilic semi-block (or one half of the hydrophilic units between cross-links; only one half of each hydrophilic block is located within the unit cell); varied between 238 and 2.…”

Copolymerization of methyl methacrylate with lauryl methacrylate using group transfer polymerization

“…Examples are block copolymers, 2 rylate. They could prepare copolymers with M V n macromonomers, 3 telechelics, 4 end-functionalized ú 100,000 and MWD's in the range of 1.1-1.3 uspolymers, 5 star-branched polymers, 6 and graft coing TASHF 2 as catalyst. Billingham 10 and copolymers.…”

Synthesis of new amphiphilic star polymers derived from a hyperbranched macroinitiator by the cationic ‘grafting from’ method

“…Traditionally, a number of star polymers composed of polystyrene 3) , polyisoprene 4) or polybutadiene 5) have been prepared by anionic polymerization and the 'arm first' method, that proceeds by addition of a linking agent (divinylbenzene) to linear precursor polymer chains. Recently, also other living processes including group transfer polymerization 6) , living cationic polymerization based on isobutylene 7) or vinyl ether 8) and metathesis polymerization 9) have been reported for the synthesis of star polymers. Unfortunately, the 'arm first' technique requires rigorous synthetic conditions and the core molecule and the number of linear arms cannot be controlled completely.…”