No abstract

The heterogeneous atom transfer radical polymerization (ATRP) of tert-butyl methacrylate (tBMA) using CuX/N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA) catalytic system with various initiators R-X (X ) Br, Cl) was investigated. The importance of the structure of the initiator on the polymerization of tBMA was briefly examined. Polymerization of tBMA with ethyl 2-bromoisobutyrate resulted in uncontrolled polymerization due to slow initiation because of the low back strain effect and relatively high propagation rate constant of tBMA. Well-controlled polymers were obtained with p-toluenesulfonyl chloride and 2,2,2-trichloroethanol initiators. This can be explained by the fast initiation coupled with the rapid establishment of the equilibrium between the active and dormant species in the polymerization. Poly(methyl methacrylate) macroinitiators were used to synthesize poly(tBMA-b-MMAb-tBMA) triblock copolymers in a range of tBMA compositions. The use of a mixed halogen system in the block copolymer synthesis leads to fast initiation and fast deactivation, resulting in controlled molecular weights and a low polydispersity index. Gradient polymer elution chromatography was used to confirm the block copolymer structure. The retention time of the block copolymers lie in between the retention times of the two homopolymers, indicating the existence of a (block) copolymer structure. This technique was successfully used to identify the influence of the ATRP reaction conditions on the final block copolymer structure.

Poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) adopts a preferential orientation on indium tin oxide. Although the basic building block of this polymer provides a negligible overall point-group symmetry, the polymer MEH-PPV packs with suffi cient order to exhibit band structure. The polymer is fragile with bond cleavage evident following both argon-ion impact and ultraviolet radiation, but annealing leads to the restoration of much of the bond order.

Atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) using CuCl/ N,N,N′,N′′,N′′′,N′′′-hexamethyltriethylenetetramine (HMTETA) as a catalyst system with 2,2,2-trichloroethanol (TCE) as initiator was investigated. Poly(methyl methacrylate) (PMMA) macroinitiators with defined molecular weight, low polydispersity index (PDI), and a high end-group functionality were obtained. These PMMA macroinitiators successfully initiate block copolymerization of tert-butyl methacrylate (tBMA), resulting in poly(MMA-b-tBMA) diblock copolymers with low PDI for a range of tBMA block lengths. Gradient polymer elution chromatography (GPEC) was used to confirm the block copolymer structure. Furthermore, the effect of molecular weight of the macroinitiator, nature of catalyst system (heterogeneous/homogeneous), and the amount of solvent on the degree of control achieved in the block copolymerization was studied. The GPEC technique was successfully used to demonstrate the effect of the aforementioned parameters on the block copolymer structure. In particular, the use of a homogeneous catalyst system, CuBr/4,4′-di-5-nonyl-2,2′-bipyridine (dNbpy), and a large ratio of methyl ethyl ketone (MEK) to PMMA macroinitiator led to the synthesis of well-controlled high molecular weight diblock copolymers. This can be explained by the complete solubility of the Cu(II) complex, the deactivating species in the ATRP mechanism. The use of the dNbpy ligand and the polar solvent (MEK) promotes the homogeneous catalyst conditions. The homogeneous condition leads to efficient activation/deactivation exchange reactions between the growing polymer chains and the dormant polymer chains, resulting in well-controlled block copolymers.