Currently, the most studied example of living freeradical polymerization is nitroxyl-mediated styrene polymerization. This chemistry relies upon the extremely facile and selective ability of nitroxyl radicals to trap carbon-centered radicals and the apparent reversible nature of the C-0 bond. Solomon and Rizzardol first reported this chemistry in the mid-1980s but used it to prepare mainly low molecular weight materials. Georges et aL2 reported, in 1993, the use of this chemistry to prepare narrow-polydispersity ( < 1.5) polystyrene. Over the past 2 years several research groups have been studying nitroxyl-mediated styrene polymerization. The work of Georges et al. has focused mainly upon increasing the rate of nitroxyl-mediated styrene polymerization initiated using benzoyl peroxide (BPO). They report that the nitroxyl-mediated styrene polymerization rate is significantly increased if conducted in an acidic e n~i r o n m e n t .~ The mechanism of this effect is not yet understood. Matyjaszewski et aL4 have focused on the theoretical aspects of nitroxylmediated styrene polymerization in the absence of an added initiator. Recently, Hawkel.5 synthesized I (model of the nitroxyl-mediated styrene polymerization chain end; Scheme 1) and demonstrated its use as an initiator. No effort was made to utilize I as a chain-end model to help determine the mechanism of the polymerization. Also, no acid was added to nitroxyl-mediated styrene polymerization initiated using I.The published data of these researchers consistently show the lack of truly narrow polydispersity, and the polydispersity obtained is generally proportional to the molecular weight being produced.Georges et a l . hypothesized that the lack of ability to make truly monodisperse PS using nitroxyl-mediated styrene polymerization was caused by continuous initiation of new PS chains during the p~lymerization.~ To suppress the spontaneous polymerization mechanism, camphorsulfonic acid (CSA) was added. They observed that, rather than decreasing the rate of polymerization and the polydispersity, both i n~r e a s e d .~ Matyjaszewski e t al. have proposed that the mechanism of nitroxyl-mediated styrene polymerization includes degenerative chain transfer (Scheme 2).6 Their evidence in support of this mechanism is the observation that polydispersity narrows as the polymerization temperature is increased. At the higher temperature the rate of degenerative chain transfer increases, causing the polymer chain lengths to average.One of the tools that has been used which has shed significant light on the development of an understand-0024-929719512228-6692$09.00/0 Scheme 2. Degenerative Chain-Transfer Mechanism for Nitroxyl-Mediated Styrene Polymerizationing of polymerization processes is the use of small molecules to model the living chain end.7 In this study we synthesized 2,2,6,6-tetramethyl-l-(l-phenylethoxy)-piperidine8 (TMPEP) and studied both its thermal decomposition and its use as a polymerization initiator. HPLC and IH-NMR were utilized to follow the thermal decompo...

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A family of nonphthalate plasticizers derived from well-defined glycerol/adipic acid hyperbranched poly(ester)s has been prepared. Glycerol and adipic acid are both renewable biomaterials of low toxicity. Polymerization may be accomplished under conditions that allow control of molecular weight, avoid gelation, and ensure the presence of hydroxyl end groups. Capping the end groups as esters affords materials that are effective plasticizers for PVC. These materials are thermally stable, are fully compatible with a PVC matrix, provide effective plasticization at acceptable levels, display low migratory potential, and do not accelerate degradative dehydrochlorination.

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Anionic and nitroxide-mediated (NM) radical polymerization works well for styrene but not for acrylates. We have overcome this problem and successfully prepared styrene-b-n-butyl acrylate (S-BA), styrene-b-methyl methacrylate (S-MMA), styrene-b-isoprene (S-IP), and styrene-alt-acrylonitrile-b-isoprene (SAN-IP) polymers using a sequential normal/living radical polymerization scheme. Clear (S-IP and SAN-IP) to translucent (S-BA and S-MMA) films were obtained having microphase-separated polymer morphology. GPC studies and chemical digestion of the IP segments of S-IP and SAN-IP block copolymers confirmed their block structure. The sequential normal/living radical polymerization approach provides a new route to synthesize block polymers that have previously proven very difficult to make.

Hyperbranched poly(ester)s have a variety of unique properties as a result of their abundance of end groups which make them useful in a range of applications. The synthesis of hyperbranched polymers has generally been carried out using empirically derived procedures to avoid gelation. However, such synthetic strategies lead to materials with unpredictable molecular weight and properties. It has now been demonstrated that modeling may be utilized to direct the synthesis of hyperbranched poly(ester)s from a variety of monomers to form well-defined structures and terminal-group functionality while avoiding gelation. In particular, Macosko−Miller modeling permits the synthesis of hyperbranched poly(ester)s of specific molecular weights and end-group functionality even for multifunctional monomers for which functional groups are not equally reactive.