Facile Synthesis of Branched Poly(vinyl alcohol)s

Thiol-Lactam Initiated Radical Polymerization (TLIRP): Scope and Application for the Surface Functionalization of Nanoparticles

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Controlled polymerization techniques make the possible fabrication of polymers with desired molecular weights, narrow dispersity, and tailor-making of advanced hybrid materials. Thiol- Lactam Initiated Radical Polymerization (TLIRP) was introduced in 2002 and developed during the last two decades. The thiol/lactam combination enables one to generate radicals that can initiate the polymerization of vinyl-based monomers. The study of the mechanism and kinetics of TLIRP revealed the characteristics of living polymerization for TLIRP. Moreover, TLIRP has been used successfully for the synthesis of homopolymers, block copolymers, and statistical copolymers with polydispersity below 2.0. Especially, TLIRP provides a very straightforward method for grafting polymer brushes on the surface of nanoparticles. We review herein the systems developed for TLIRP and their applications for macromolecular engineering, emphasizing the surface functionalization of nanoparticles via the grafting-from approach.

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.

Effect of poly(acrylic acid) architecture on setting and mechanical properties of glass ionomer cements

OBJECTIVE

This work focuses on the influence of poly(acrylic acid) (PAA) architecture (linear or branched) on setting behavior and compressive strength of glass ionomer cements (GICs).

METHODS

Branched and linear poly(acrylic acid)s were synthesized according to the Strathclyde methodology or by free radical polymerization. They were characterized by ¹H-NMR spectroscopy and size exclusion chromatography to determine their molecular weight and size distribution. GIC setting was characterized by oscillating rheometry and time-dependent FTIR spectroscopy. In addition, compressive strength was tested on cylindrical samples (6 × 4 mm; n = 8/cement composition) after storage in deionized water at 37 °C for one day.

RESULTS

We used two different routes to prepare PAA. One direct route in order to provide straightforward access to branched PAA and a two-step approach in order to get more control about the PAA molecular weight using tert-butyl acrylate (tBA) for polymerization with subsequent deprotection. Using the second approach we obtained several linear PAA of which a mixture was used in order to mimic the molecular weight and size distribution of branched PAA. This allowed the direct comparison of properties relying only on the polymer architecture. Comparing linear PAA to branched samples in general led to faster setting but at the same time decreased the compressive strength. Increasing molecular weight of branched PAA resulted in even faster GIC setting while increasing compressive strength and this correlates well with the trends reported for linear PAA in literature. Mixing of branched and linear PAA, however, turned out to be an effective way of tailoring GIC properties.

SIGNIFICANCE

our results suggest that both molecular weight and dispersity need to be considered when choosing suitable PAA architecture for obtaining specific GIC properties.

Synthesis and degradation of branched, photo-labile poly(acrylic acid) and polystyrene

We present the synthesis, characterization and photolytical degradation of branched photo-responsive poly(acrylic acid) and polystyrene using free radical polymerization of acrylic acid/styrene in the presence of a newly synthesized asymmetric o-nitrobenzyl-based crosslinker and different amounts of dodecanethiol (DDT) as a chain transfer agent.

Synthesis of hypergrafted poly[4-(N,N-diphenylamino)methylstyrene] through tandem anionic-radical polymerization of radical-inimer

In this paper, we present a tandem anionic-radical approach for synthesizing hypergrafted polymers. We prepared 4-(N,N-diphenylamino)methylstyrene (DPAMS) as a new radical-based inimer. Linear PDPAMS was prepared through anionic polymerization. Hypergrafted PDPAMS was synthesized through the self-condensing vinyl polymerization of DPAMS with linear PDPAMS. The linear backbone of PDPAMS, which incorporated latent radical initiating sites, served as a ‘hyperlinker’ to link hyperbranched side chains. The molecular weights of hypergrafted polymers increased as the length of the linear backbone chain increased. The hypergrafted structure of the resulting polymer was confirmed using a conventional gel permeation chromatograph apparatus equipped with a multiangle light scattering detector, nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. This strategy can be applied to synthesize other complex architectures based on hyperbranched polymers by changing the structure of a polymer backbone through anionic polymerization.

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.

Copolymerisation of isoprene and divinylbenzene was achieved in toluene via anionic chain transfer polymerization to yield highly branched polymers with good solution and rheological properties.

Facile synthesis of branched polyvinyl acetate via redox-initiated radical polymerization

Although branched polymers find widespread applications, the rational design and synthesis of branched vinyl polymers via the conventional radical (co)polymerization of commercially available monomers is still a challenge for researchers in this field.

Polyvinyl alcohol-based hydrophilic monoliths from water-in-oil high internal phase emulsion template

Herein, we report a new approach to fabricate polyvinyl alcohol (PVA) based hydrophilic monoliths by alcoholysis of porous emulsion-templated polyvinyl acetate (PVAc). The precursory PVAc-based monolith is obtained by polymerization of a W/O high internal phase emulsion (HIPE) containing vinyl acetate as the external phase while water as the internal phase. As an alcoholysis-stable tri-functional commonomer, triallyl isocyanurate is chosen as the crosslinking agent to prevent possible collapse of the polymeric skeleton and the consequent losses in mechanical properties during the alcoholysis step. By alcoholysis of the resulting PVAc-based monolith, the PVA-based monoliths are successful prepared as confirmed by FTIR analysis. BET analysis and SEM observation confirm the formation of open-cell and highly interconnected porous structures of PVA-based monoliths with surface areas of around 16m²/g. Stemming from the intrinsic hydrophilicity of hydroxyl and morphology, PVA-based monoliths exhibit great enhancement in hydrophilicity with a much lower water contact angles than that of PVAc-based monoliths.

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.

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.

A rapid crosslinking injectable hydrogel for stem cell delivery, from multifunctional hyperbranched polymers via RAFT homopolymerization of PEGDA

A novel injectable hydrogel for stem cell delivery was prepared from multifunctional hyperbranched polyPEGDA and thiolated hyaluronic acid.

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.

Thermally-labile segmented hyperbranched copolymers: using reversible-covalent chemistry to investigate the mechanism of self-condensing vinyl copolymerization

A thermally-reversible inimer was used to confirm the controlled growth of individual branches during self-condensing vinyl atom transfer radical polymerization (ATRP).

A facile one pot strategy for the synthesis of well-defined polyacrylates from acrylic acid via RAFT polymerization

Linear and hyperbranched polyacrylates were successfully synthesized by the combination of in situ esterification of acrylic acid with halogenated compounds promoted by 1,1,3,3-tetramethylguanidine (TMG) and RAFT polymerization.

Size-exclusion chromatography (SEC) of branched polymers and polysaccharides

Branched polymers are among the most important polymers, ranging from polyolefins to polysaccharides. Branching plays a key role in the chain dynamics. It is thus very important for application properties such as mechanical and adhesive properties and digestibility. It also plays a key role in viscous properties, and thus in the mechanism of the separation of these polymers in size-exclusion chromatography (SEC). Critically reviewing the literature, particularly on SEC of polyolefins, polyacrylates and starch, we discuss common pitfalls but also highlight some unexplored possibilities to characterize branched polymers. The presence of a few long-chain branches has been shown to lead to a poor separation in SEC, as evidenced by multiple-detection SEC or multidimensional liquid chromatography. The local dispersity can be large in that case, and the accuracy of molecular weight determination achieved by current methods is poor, although hydrodynamic volume distributions offer alternatives. In contrast, highly branched polymers do not suffer from this extensive incomplete separation in terms of molecular weight.

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PMMA Star-Like Polymers via One-Pot Conventional Free-Radical Copolymerization

Poly(methyl methacrylate)-based star-like polymers (SLPs) were synthesized by a one-pot conventional free-radical copolymerization. Two aryl ester-based cross-linkers, bisphenol A dimethacrylate and 1,4-bis(methacryloxy)benzene, were found to induce SLP formation by reactivity control when copolymerized with methyl methacrylate. The formulation domain diagrams for these systems were established and high monomer concentrations (up to 70 wt-%) were achievable without the occurrence of macrogelation. Kinetic experiments confirmed that the SLP formation occurs via a pseudo two-step mechanism. Parallel plate rheological analysis of the SLP solutions demonstrated that these polymers had low viscosities, typically several orders of magnitude lower than the analogous linear polymer solution.