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Reversible addition–fragmentation chain transfer (RAFT) was applied to the copolymerization of styrene and maleic anhydride. The product had a low polydispersity and a predetermined molar mass. Novel, well‐defined polyolefin‐based block copolymers were prepared with a macromolecular RAFT agent prepared from a commercially available polyolefin (Kraton L‐1203). The second block consisted of either polystyrene or poly(styrene‐co‐maleic anhydride). Furthermore, the colored, labile dithioester moiety in the product of the RAFT polymerizations could be removed from the polymer chain by UV irradiation. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3596–3603, 2000

In theory, a miniemulsion should be an ideal environment for “living” radical polymerization via the reversible addition−fragmentation chain transfer process (RAFT). Compartmentalization minimizes radical−radical termination events, and droplet nucleation eliminates the mass transfer limitation found in conventional “living” emulsion polymerizations. In practice, however, several phenomena were observed when using the RAFT technique, indicating a deviation from this idealized theory when the miniemulsion was stabilized by an ionic surfactant. Inefficient droplet nucleation, a steadily rising polydispersity over the reaction, and the appearance of a separate organic phase after initiation were all indications of particle instability. A distinct difference between standard polymerizations and those that involve highly active RAFT agents is the fact that in RAFT polymerization there is a time interval early in the reaction where oligomers dominate the molecular weight distribution. The presence of large quantities of oligomers is postulated to be the culprit behind the destabilization observed through a detrimental interaction with the ionic surfactant of the miniemulsion. Conductivity measurements verified the increase of free surfactant in the aqueous phase over the course of reaction. Despite this, results showed clear indication of “living” character with a linear evolution of molecular weight until roughly 40% monomer conversion, after which the molecular weight showed contributions from initiator-derived chains.

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This article will provide an overview of recent developments for microneedles made using injection molding and hot embossing techniques for active transdermal drug delivery. Microneedle arrays are developed for pain‐free and efficient drug delivery without using a cold chain. The focus of this article will be on the use of engineering thermoplastics and microneedle manufacturing techniques including patterning. Recent developments demonstrate that commercialization of polymer‐based microneedle systems is feasible. POLYM. ENG. SCI., 59:877–890, 2019. © 2019 Society of Plastics Engineers

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The polymerization of styrene in latex particles by means of pulsed high-energy electrons has been studied. Using a sequence of electron beam pulses, periodic initiation is accomplished, similar to that used in pulsed laser polymerization. The larger penetration depth of electron beams offers advantages as compared to laser light in heterogeneous systems since samples do not need to be optically transparent. Therefore pulsed electron beam irradiations are more suitable to study polymerizations homogeneously irradiated in emulsion. From the molar mass distribution of the formed polymer, the monomer concentration in the particles can be determined. Polystyrene particles swollen with styrene were used. A typical dose per pulse was 1.5 Gy. The monomer concentration in 46 nm diameter particles was found to be 6 mol dm-3. Cationic and anionic polymerization of styrene was suppressed by the presence of water.

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