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A dicationic monoradical dual initiator 3-[3,5-bis(1-chloro-1-methylethyl)phenyl]-3-methylbutyl2-bromo-2-methylpropionate (DCCBMP) was designed for the preparationof A2B type miktoarm star copolymers, where A is a polyisobutylene(PIB)-based homo or block copolymer that is produced by living carbocationicpolymerization (LCP), and B is a polyacrylate or other polymer blockproduced by atom transfer radical polymerization (ATRP). DCCBMP wasobtained by chlorination of 3-[3,5-bis(1-hydroxy-1-methylethyl)phenyl]-3-methylbutyl2-bromo-2-methylpropionate (DCOHBMP), which was synthesized in a pureform via aerobic oxidation of 3-(3,5-diisopropylphenyl)-3-methylbutyl2-bromo-2-methylpropionate using N-hydroxyphthalimide(NHPI)/Co(OAc)2·4H2O catalyst system. Initiationefficiency of DCCBMP was 0.89–0.98 for LCP of isobutylene (IB)at −70 °C targeting molecular weights of 5K, 10K, and20K g/mol, which was comparable to the standard dicationic initiator5-tert-butyl-1,3-(1-chloro-1-methylethyl)benzene(t-Bu-m-DCC). Sequential monomeraddition under LCP conditions produced narrow-polydispersity poly(styrene-b-isobutylene-b-styrene) (PS–PIB–PS)triblock copolymers. These polymers possessed a 2-bromo-2-methylpropionate(bromoester) ATRP initiating site in the approximate middle of PIBsegment and two sec-benzylic chloride groups at thePS chain ends, which were also effective in initiating ATRP. Withthese PS–PIB–PS macroinitiators, poly(tert-butyl acrylate-b-styrene-b-isobutylene)2-s-poly(tert-butyl acrylate)[(PtBA–PS–PIB)2-s-PtBA] miktoarm star polymers were readilysynthesized via ATRP of tert-butyl acrylate (tBA). The sec-benzylic chloride functionalitywas alternatively eliminated at high temperature (180–200 °C)under vacuum, yielding PS–PIB–PS macroinitiators containingonly the bromoester site (thermolyzed PS–PIB–PS). Sizeexclusion chromatography (SEC) and nuclear magnetic resonance (NMR)spectroscopy showed that thermolysis removed all sec-benzylic chlorides without destruction of bromoester moieties. ThermolyzedPS–PIB–PS allowed synthesis of poly(styrene-b-isobutylene)2-s-poly(tert-butyl acrylate) [(PS–PIB)2-s-PtBA] star polymers with the potentialhydrophilic segment attached only to the core of PS–PIB–PS.For both star terpolymer configurations, the PtBAblocks were converted to PAA via thermolysis at 150 °C to produceamphiphilic PIB-based miktoarm star polymers with narrow polydispersityindices (<1.1). [ABSTRACT FROM AUTHOR]

The dual initiator, 3,3,5,5,7-pentamethyl-7-chlorooctyl2-bromo-2-methylpropionate (IB3BMP), possessing initiatingsites for both living carbocationic polymerization (LCP) and atomtransfer radical polymerization (ATRP), was synthesized to overcomethe low initiation efficiency of previously reported dual initiatorssuch as 3,3,5-trimethyl-5-chlorohexyl 2-bromo-2-methylpropionate (IB2BMP). Low initiation efficiency of the latter and similarinitiators has been attributed to complexation between the Lewis acidpolymerization catalyst and the ester carbonyl group of the initiator.IB3BMP was synthesized by reacting IB2BMP with2-methallyltrimethylsilane at low temperature, followed by hydrochlorination.IB3BMP, which differs from IB2BMP by the inclusionof one additional isobutylene (IB) repeating unit, showed quantitativeinitiation efficiency (Ieff∼ 1)in TiCl4-co-initiated LCP of IB undervarious reaction conditions, including low temperature (−70°C) and low monomer/initiator ratios (48–164). Ieffand polydispersity index of the resultingpolyisobutylenes were identical to those obtained with the commonlyused, monofunctional cationic initiators 2-chloro-2,4,4-trimethylpentane(TMPCl) and 2-chloro-2,4,4,6,6-pentamethylheptane (PMHCl). The superiorityof IB3BMP compared to IB2BMP in carbocationicinitiation was attributed to increased separation between the tert-chloride initiating site and the TiCl4:carbonylcomplex at the ATRP initiating site. A PIB macroinitiator preparedfrom IB3BMP was used to initiate ATRP of methyl acrylate.Efficiency of radical initiation was quantitative, the targeted poly(methylacrylate) block length was obtained, and the resulting block copolymerpossessed narrow polydispersity. [ABSTRACT FROM AUTHOR]

Minimal immunogen vaccines are being developed to focus antibody responses against otherwise challenging targets, including human immunodeficiency virus (HIV), but multimerization of the minimal peptide immunogen on a carrier platform is required for activity. Star copolymers comprising multiple hydrophilic polymer chains ("arms") radiating from a central dendrimer unit ("core") were recently reported to be an effective platform for arraying minimal immunogens for inducing antibody responses in mice and primates. However, the impact of different parameters of the star copolymer (e.g., minimal immunogen density and hydrodynamic size) on antibody responses and the optimal synthetic route for controlling those parameters remains to be fully explored. We synthesized a library of star copolymers composed of poly[ N -(2-hydroxypropyl)methacrylamide] hydrophilic arms extending from poly(amidoamine) dendrimer cores with the aim of identifying the optimal composition for use as minimal immunogen vaccines. Our results show that the length of the polymer arms has a crucial impact on the star copolymer hydrodynamic size and is precisely tunable over a range of 20-50 nm diameter, while the dendrimer generation affects the maximum number of arms (and therefore minimal immunogens) that can be attached to the surface of the dendrimer. In addition, high-resolution images of selected star copolymer taken by a custom-modified environmental scanning electron microscope enabled the acquisition of high-resolution images, providing new insights into the star copolymer structure. Finally, in vivo studies assessing a star copolymer vaccine comprising an HIV minimal immunogen showed the criticality of polymer arm length in promoting antibody responses and highlighting the importance of composition tunability to yield the desired biological effect.