Sustained release polymeric gene delivery systems offer increased resistance to nuclease degradation, increased amounts of plasmid DNA (pDNA) uptake, and the possibility of control in dosing and sustained duration of pDNA administration. Furthermore, such a system lacks the inherent problems associated with viral vectors. Biodegradable and biocompatible poly(DL-lactide-co-glycolide) polymer was used to enacapsulate pDNA (alkaline phosphatase, AP, a reporter gene) in submicron size particles. Gene expression mediated by the nanoparticles (NP) was evaluated in vitro and in vivo in comparison to cationic-liposome delivery. Nano size range (600 nm) pDNA-loaded in poly(DL-lactideco-glycolide) polymer particles with high encapsulation efficiency (70%) were formulated, exhibiting sustained

A computational study of the branching in polyacrylates is performed for both atom-transfer radical polymerization (ATRP) and free radical polymerization (FRP). In both cases the secondary radical formed can transfer to polymer to generate a tertiary radical, which can propagate with monomer to re-form the secondary species. The critical difference between these two processes is that the exchange between tertiary and secondary species is supplemented in ATRP by additional activation and deactivation reactions for both the secondary and tertiary species. This leads to a competition between the activation–deactivation and exchange processes in ATRP, while there is no such competition in FRP. This introduces the idea of competing processes or equilibria. These competing processes can alter the fate of the tertiary radical in ATRP, by introducing a deactivation step, in addition to the propagation, or branch formation, available in FRP. Various simulations show that, in order to effectively decrease the branching fraction in ATRP, the tertiary radical must be deactivated relatively rapidly. Then, the rate of branch formation is slower than the rate of transfer, resulting in a decrease in the branching fraction. Kinetic simulations also find that concentrations of copper catalysts have minimal effect on the branching fractions and that higher initiator concentrations tend to decrease the branching levels in ATRP. Furthermore, Monte Carlo simulations found that chain length dependence and presence or absence of intermolecular transfer had minimal effect on the branching fraction.

The kinetics of the anionic polymerization of e-caprolactone, including the kinetics of macrocyclization and the kinetics of macrocycles propagation in THF solution, initiated with (CH,),SiONa, were investigated. Rate constants of propagation (kpCn,) and of back-biting (kdCn,) involving monomer and cyclic oligomers (macrocycles) with n = 2, 3, . . . monomeric units were determined for n 9 7 . It was found that starting from the tetramer kdCnin-1*4io*'and kp(n) -n0,7i0,15 (in Jacobson-Stockmayer's theory kpcn)n). This discrepancy is explained in terms of "conformational hindrance", increasing for small cycles with the increase of the ring size until a certain ring size is reached. This hindrance decreases the availability of some of the ester groups in the macrocyclics for attack of the growing species, lowering in this way the exponent in the dependence of kP(,,) on n from one to a lower value.(kp(n)n).