New Insight into the ATRP of Monovinyl and Divinyl Monomers

Universal Scaling Behavior during Network Formation in Controlled Radical Polymerizations

Despite the ubiquity of branched and network polymers in biological, electronic, and rheological applications, it remains difficult to predict the network structure arising from polymerization of vinyl and multivinyl monomers. While controlled radical polymerization (CRP) techniques afford modularity and control in the synthesis of (hyper)branched polymers, a unifying understanding of network formation providing grounded predictive power is still lacking. A current limitation is the inability to predict the number and weight average molecular weights that arise during the synthesis of (hyper)branched polymers using CRP. This study addresses this literature gap through first building intuition via a growth boundary analysis on how certain environmental cues (concentration, monomer choice, and cross-linker choice) affect the cross-link efficiency during network formation through experimental gel point measurements. We then demonstrate, through experimental gel point normalization, universal scaling behavior of molecular weights in the synthesis of branched polymers corroborated by previous literature experiments. Moreover, the normalization employed in this analysis reveals trends in the macroscopic mechanical properties of networks synthesized using CRP techniques. Gel point normalization employed in this analysis both enables a polymer chemist to target specific number and weight average molecular weights of (hyper)branched polymers using CRP and demonstrates the utility of CRP for gel synthesis.

Expanding the monomer scope of linear and branched vinyl polymerisations via copper-catalysed reversible-deactivation radical polymerisation of hydrophobic methacrylates using anhydrous alcohol solvents

The use of anhydrous alcohols for Cu-catalysed reversible-deactivation radical polymerisation of a wide range of hydrophobic methacrylates has been explored in detail.

Preparation and Properties of Branched Polystyrene through Radical Suspension Polymerization

Radical solvent-free suspension polymerization of styrene with 3-mercapto hexyl-methacrylate (MHM) as the branching monomer has been carried out using 2,2'-azobisisobutyronitrile (AIBN) as the initiator to prepare branched polymer beads of high purity. The molecular weight and branching structure of the polymers have been characterized by triple detection size exclusion chromatography (TD-SEC), proton nuclear magnetic resonance spectroscopy (¹H-NMR), and Fourier transform infrared spectroscopy (FTIR). The glass transition temperature and rheological properties have been measured by using differential scanning calorimetry (DSC) and rotational rheometry. At mole ratios of MHM to AIBN less than 1.0, gelation was successfully avoided and branched polystyrene beads were prepared in the absence of any solvent. Branched polystyrene has a relatively higher molecular weight and narrower polydispersity (Mw.MALLS = 1,036,000 g·mol-1, Mw/Mn = 7.76) than those obtained in solution polymerization. Compared with their linear analogues, lower glass transition temperature and decreased chain entanglement were observed in the presently obtained branched polystyrene because of the effects of branching.

Radical polymerization in the presence of a peroxide monomer: an approach to branched vinyl polymers

In this paper, we report radical polymerization in the presence of a peroxide monomer for the preparation of branched vinyl polymers.

Self-condensing reversible complexation-mediated copolymerization for highly branched polymers with in situ formed inimers

In this work, reversible complexation-mediated polymerization (RCMP) was modified to suit self-condensing vinyl polymerization (SCVP) aimed at the synthesis of highly branched polymers.

Supramolecular host-guest polycationic gene delivery system based on poly(cyclodextrin) and azobenzene-terminated polycations

This article describes the supramolecular host-guest polycationic gene delivery system based on poly(β-cyclodextrin) (PCD) and azobenzene-terminated polycations. The azobenzene-terminated linear (Az-LPDM) and branched (Az-BPDM) cationic polymers were synthesized by atom transfer radical polymerization (ATRP) of 2-dimethylamino ethyl methacrylate (DMAEMA). The formation and photosensitive behavior of the supramolecular polycations of azobenzene-terminated polycations Az-LPDM and Az-BPDM with PCD were confirmed by UV-vis and NMR analysis. The supramolecular PCD/Az-BPDM/DNA and PCD/Az-LPDM/DNA polyplexes showed smaller size and were less positive than those of their corresponding polyplexes without PCD. Moreover, the UV irradiation may promote release of DNA from the photosensitive supramolecular polyplexes due to dissociation of supramoelcular polyplexes. In vitro experiments revealed that the photosensitive supramolecular polycationic polyplexes (PCD/Az-LPDM/DNA and PCD/Az-BPDM/DNA) exhibited enhancement of cellular uptake, higher transfection efficiency, and lower cytoxicity compared to the azobenzene-terminated polycation/DNA polyplexes in the absence of PCD. Branched polycationic polyplexes showed higher transfection efficiency than its linear polycationic polyplexes. Furthermore, after UV irradiation, the transfection efficiency of photosensitive supramolecular polyplexes was improved resulting from more DNAs delivered and released inside of the cell nuclei. Thus this photoresponsive supramolecular host-guest system containing azobenzene-terminated branched cationic polymers and PCD is a promising gene vector.

Light and Temperature as Dual Stimuli Lead to Self-Assembly of Hyperbranched Azobenzene-Terminated Poly(N-isopropylacrylamide)

Hyperbranched poly(N-isopropylacrylamide)s (HBPNIPAMs) end-capped with different azobenzene chromophores (HBPNIPAM-Azo-OC₃H₇, HBPNIPAM-Azo-OCH₃, HBPNIPAM-Azo, and HBPNIPAM-Azo-COOH) were successfully synthesized by atom transfer radical polymerization (ATRP) of N-isopropylacrylamide using different azobenzene-functional initiators. All HBPNIPAMs showed a similar highly branched structure, similar content of azobenzene chromophores, and similar absolute weight/average molecular weight. The different azobenzene structures at the end of the HBPNIPAMs exhibited reversible trans-cis-trans isomerization behavior under alternating UV and Vis irradiation, which lowered the critical solution temperature (LCST) due to different self-assembling behaviors. The spherical aggregates of HBPNIPAM-Azo-OC₃H₇ and HBPNIPAM-Azo-OCH₃ containing hydrophobic para substituents either changed to bigger nanorods or increased in number, leading to a change in LCST of -2.0 and -1.0 °C, respectively, after UV irradiation. However, the unimolecular aggregates of HBPNIPAM-Azo were unchanged, while the unstable multimolecular particles of HBPNIPAM-Azo-COOH end-capped with strongly polar carboxyl groups partly dissociated to form a greater number of unimolecular aggregates and led to an LCST increase of 1.0 °C.

A light and reduction dual sensitive supramolecular self-assembly gene delivery system based on poly(cyclodextrin) and disulfide-containing azobenzene-terminated branched polycations

Light and reduction sensitive supramolecular host–guest gene vectors can regulate gene release upon exposure to reduction environments and light radiation inside cells.