Application of the “Strathclyde Route” to Branched Vinyl Polymers in Suspension Polymerization: Architectural, Thermal, and Rheological Characterization of the Derived Branched Products

Accessing new and scalable high molecular weight branched copolymer structures using transfer-dominated branching radical telomerisation (TBRT)

Three new synthesis strategies for branched statistical copolymers containing analogues of step-growth backbones are shown using free radical chemistries and transfer-dominated branching radical polymerisation (TBRT) conditions.

Highly branched polymethacrylates prepared efficiently: brancher-directed topology and application performance

A series of highly oil-soluble and branched polymethacrylates are prepared via ATRcP of 2-ethylhexyl methacrylate and divinyl brancher with high efficiency, focusing on the brancher effect on the structure-performance of the polymers.

Complex polymer architectures through free-radical polymerization of multivinyl monomers

The construction of complex polymer architectures with well-defined topology, composition and functionality has been extensively explored as the molecular basis for the development of modern polymer materials. The unique reaction kinetics of free-radical polymerization leads to the concurrent formation of crosslinks between polymer chains and rings within an individual chain and, thus, free-radical (co)polymerization of multivinyl monomers provides a facile method to manipulate chain topology and functionality. Regulating the relative contribution of these intermolecular and intramolecular chain-propagation reactions is the key to the construction of architecturally complex polymers. This can be achieved through the design of new monomers or by spatially or kinetically controlling crosslinking reactions. These mechanisms enable the synthesis of various polymer architectures, including linear, cyclized, branched and star polymer chains, as well as crosslinked networks. In this Review, we highlight some of the contemporary experimental strategies to prepare complex polymer architectures using radical polymerization of multivinyl monomers. We also examine the recent development of characterization techniques for sub-chain connections in such complex macromolecules. Finally, we discuss how these crosslinking reactions have been engineered to generate advanced polymer materials for use in a variety of biomedical applications.

Branched macromonomers from catalytic chain transfer polymerisation (CCTP) as precursors for emulsion-templated porous polymers

Catalytic chain transfer polymerisation (CCTP) is combined for the first time with emulsion-templating to generate polyHIPE materials where functionality and rigidity can be tightly tailored, broadening their scope of application.

Preparation of hyperbranched polymers by oxa-Michael addition polymerization

Hyperbranched polymers with high molecular weights were synthesized by t-BuP₂-catalyzed oxa-Michael addition polymerization of trifunctional hydroxyl and diacrylate monomers.

Rheological and thermal degradation properties of hyperbranched polyisoprene prepared by anionic polymerization

Hyperbranched polyisoprene was prepared by anionic copolymerization under high vacuum condition. Size exclusion chromatography was used to characterize the molecular weight and branching nature of these polymers. The characterization by differential scanning calorimetry and melt rheology indicated lower Tg and complex viscosity in the branched polymers as compared with the linear polymer. Degradation kinetics of these polymers was explored using thermogravimetric analysis via non-isothermal techniques. The polymers were heated under nitrogen from ambient temperature to 600°C using heating rates from 2 to 15°C min-1. Three kinetics methods namely Friedman, Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose were used to evaluate the dependence of activation energy (Ea ) on conversion (α). The hyperbranched polyisoprene decomposed via multistep mechanism as manifested by the nonlinear relationship between α and Ea while the linear polymer exhibited a decline in Ea at higher conversions. The average Ea values range from 258 to 330 kJ mol-1 for the linear, and from 260 to 320 kJ mol-1 for the branched polymers. The thermal degradation of the polymers studied involved one-dimensional diffusion mechanism as determined by Coats-Redfern method. This study may help in understanding the effect of branching on the rheological and decomposition kinetics of polyisoprene.

Branched polystyrenes from suspension “Strathclyde” polymerization using a vulcanization accelerator as a chain transfer agent

Branched polymers exhibit a unique three-dimensional (3D) molecular architecture and distinctive physical/chemical properties, and thus have been applied in a wide variety of fields.

Synthesis and characterisation of highly branched polyisoprene: exploiting the "Strathclyde route" in anionic polymerisation

This work aimed at developing a synthetic route towards highly branched poly(isoprene) from commercially available raw materials, in good yield and devoid of microgelation, i.e., to prepare a completely soluble polymer via the versatile technique anionic polymerisation. The polymerisations were conducted under high vacuum conditions using sec-butyllithium as initiator at 50 °C in toluene. Toluene served both as a solvent and as a chain-transfer agent. The polar modifier used was tetramethylethylenediamine (TMEDA), and a commercial mixture of divinylbenzene (DVB) was employed as the branching agent for the "living" poly(isoprenyl)lithium anions. The nature of the reaction was studied on the TMEDA/Li ratio as well as the DVB/Li ratio. The obtained branched polymers were characterised by triple detection size exclusion chromatography (SEC), proton nuclear magnetic resonance spectroscopy (1H NMR), differential scanning calorimetry (DSC) and melt rheology. Broad molecular weight distributions have been obtained for the highly branched polymer products. 1H NMR spectroscopy reveals the dominance of 3,4-polyisoprene microstructure. It was found that the complex viscosities and dynamic moduli of the branched samples were much lower compared to their linear counterparts. The results conform with earlier findings by the "Strathclyde team" for radical polymerisation systems. This methodology has the potential of providing soluble branched vinyl polymers at low cost using the readily available raw materials.

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.

Facile photo-flow synthesis of branched poly(butyl acrylate)s

We present the synthesis of branched poly(butyl acrylate)s using photo-induced free radical polymerization of (n/t)-butyl acrylate in the presence of tri(propylene glycol) diacrylate (TPGDA) as a crosslinker and varying amounts of dodecanethiol (DDT) as a chain transfer agent to prevent macroscopic gelation.

Synthesis of highly branched polymers by reversible complexation-mediated copolymerization of vinyl and divinyl monomers

Here, we report the reversible complexation-mediated copolymerization (RCMcP) of vinyl and divinyl monomers for the synthesis of highly branched polymers.

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.

Gel Point Suppression in RAFT Polymerization of Pure Acrylic Cross-Linker Derived from Soybean Oil

Here we report the reversible addition-fragmentation chain transfer (RAFT) polymerization of acrylated epoxidized soybean oil (AESO), a cross-linker molecule, to high conversion (>50%) and molecular weight (>100 kDa) without macrogelation. Surprisingly, gelation is suppressed in this system far beyond the expectations predicated both on Flory-Stockmeyer theory and multiple other studies of RAFT polymerization featuring cross-linking moieties. By varying AESO and initiator concentrations, we show how intra- versus intermolecular cross-linking compete, yielding a trade-off between the degree of intramolecular linkages and conversion at gel point. We measured polymer chain characteristics, including molecular weight, chain dimensions, polydispersity, and intrinsic viscosity, using multidetector gel permeation chromatography and NMR to track polymerization kinetics. We show that not only the time and conversion at macrogelation, but also the chain architecture, is largely affected by these reaction conditions. At maximal AESO concentration, the gel point approaches that predicted by the Flory-Stockmeyer theory, and increases in an exponential fashion as the AESO concentration decreases. In the most dilute solutions, macrogelation cannot be detected throughout the entire reaction. Instead, cyclization/intramolecular cross-linking reactions dominate, leading to microgelation. This work is important, especially in that it demonstrates that thermoplastic rubbers could be produced based on multifunctional renewable feedstocks.

A versatile strategy for synthesis of hyperbranched polymers with commercially available methacrylate inimer

This work reported a facile strategy to synthesize hyperbranched polymers by simply using a commercially available hydroxyl-substituted methacrylate, which can be applied to not only the SCVP of vinyl monomers, but also to the SCROP of cyclic esters.

Facile one-spot synthesis of highly branched polycaprolactone

First solvent-free synthesis of degradable/bioresorbable, highly branched polymers via Sn(Oct)₂ controlled ROP containing di-functional lactones to near quantitative conversion.