Xiaoqiang Xue

Radical emulsion polymerization with chain transfer monomer: an approach to branched vinyl polymers with high molecular weight and relatively narrow polydispersity

Radical polymerization with 3-mercapto hexyl methacrylate as the chain transfer monomer (CTM) to prepare branched vinyl polymers with high molecular weights and relatively narrow polydispersities has been carried out in aqueous emulsion. Potassium persulfate was used as the initiator, and sodium dodecyl benzene sulfate or hexadecyl trimethyl ammonium bromide was used as the emulsifier. The obtained polymers were characterized using NMR and size exclusion chromatography. Compared with polymers obtained from solution polymerization and results reported in the literature, branched polymers can be prepared at higher monomer/branching monomer feed ratios (100/25) with high monomer conversion (usually >95%) without gelation. The obtained branched polymers also showed considerably higher molecular weights and relatively narrower polydispersities at the same feed ratio of monomer/branching monomer. The unique radical termination mechanism in emulsion reaction determines that soluble branched polymers with high molecular weight and relatively narrow polydispersity can be prepared at a wide range of monomer/CTM feed ratios without gelation.

Quadrangular Prism: A Unique Self‐Assembly from Amphiphilic Hyperbranched PMA‐b‐PAA

The novel hyperbranched poly(methyl acrylate)-block-poly(acrylic acid)s (HBPMA-b-PAAs) are successfully synthesized via single-electron transfer-living radical polymerization (SET-LRP), followed with hydrolysis reaction. The copolymer solution could spontaneously form unimolecular micelles composed of the hydrophobic core (PMA) and the hydrophilic shell (PAA) in water. Results show that the size of spherical particles increases from 8.18 to 19.18 nm with increased pH from 3.0 to 12.0. Most interestingly, the unique regular quadrangular prisms with the large microstructure (5.70 μm in length, and 0.47 μm in width) are observed by the self-assembly of unimolecular micelles when pH value is below 2. Such self-assembly behavior of HBPMA-b-PAA in solution is significantly influenced by the pH cycle times and concentration, which show that increased polymer concentration favors aggregate growth.

Polymerization behaviors and polymer branching structures in ATRP of monovinyl and divinyl monomers

Polymerization behaviors and polymer branching structures in atom transfer radical polymerizations of styrene with 1,6-bismaleimidohexane (BMIH), tri-ethylene glycol dimethacrylate (tri-EGDMA) and divinylbenzene (DVB) as the branching agents have been studied, the mole ratio of monomer to branching agent is 30/1.0. Their polymerization behaviors are quite different because of the different levels of interaction between styrene and the branching agents. The charge transfer complex effect between BMIH and styrene causes core-formation. The DVB system exhibits the slowest evolution of branching because there is no interaction between styrene and DVB. The branching structure indicator b(g′ = gb) from the Zimm branching factor at the same molecular weight proves that polymers formed in the tri-EGDMA and DVB systems are randomly branched molecules because tri-EGDMA and DVB were randomly distributed in their primary chains, while the BMIH system contained randomly branched molecules besides the star-like molecules due to the subsequent coupling reactions between the branched molecules after core-formation.

Facile synthesis of highly branched poly(acrylonitrile-co-vinyl acetate)s with low viscosity and high thermal stability via radical aqueous solution polymerization

Branched poly(acrylonitrile-co-vinyl acetate) [P(AN-co-VAc)] was prepared through radical polymerization using new 2-(3-mercaptopropionyloxy) ethyl methacrylate (MPOEM) as a chain transfer monomer (CTM) in sodium thiocyanate (NaSCN) aqueous solution. The development of branching and the changes of molecular weight were analyzed using triple detection size exclusion chromatography (TD-SEC). Below 50% monomer conversion in the presence of MPOEM, the weight average molecular weight (Mw.MALLS) of the copolymer increased with conversion and the molecular weights of the primary chains were much higher. The Zimm branching factor (g′) was lower than one and decreased with increasing conversion, and this result illustrated that the branched chains were formed and the highly branched structures were obtained very fast even at lower monomer conversion. While above 50% monomer conversion in conjunction with complete MPOEM consumption, Mw.MALLS slightly decreased with increasing monomer conversion and almost reached a constant at the end while PDI increased quickly. The g′ slightly increased and then remained constant with increasing conversion, which indicated that the branching degree was invariable in the absence of MPOEM. The zero-shear viscosity and glass transition temperature of branched P(AN-co-VAc)s were lower than those of their linear analogues, which further confirmed the formation of branched P(AN-co-VAc)s. Furthermore, these branched P(AN-co-VAc)s were found to have higher thermal stability than their linear counterparts. These highly branched P(AN-co-VAc)s with lower viscosity and higher thermal stability are amenable for environmentally benign processing with less solvent.

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

Self-condensing vinyl polymerization (SCVP) provides an efficient approach for synthesis of hyperbranched polymers. However, most of the inimers employed for SCVP need to be synthesized before use. Here, we report a facile strategy to synthesize hyperbranched polymers under mild conditions by using a commercially available hydroxyl-substituted methacrylate as the inimer. The hyperbranched structures of the resulting polymers were confirmed by nuclear magnetic resonance, differential scanning calorimetry and size-exclusion chromatography equipped with online light scattering and viscosity detectors. The synthesis can be performed under mild reaction conditions. Particularly, this approach can be applied to not only the SCVP of vinyl monomers but also the self-condensing ring-opening polymerization of cyclic esters for preparation of hyperbranched polyesters. The present study provides a facile strategy to synthesize hyperbranched polymers.

Facile synthesis of biodegradable and clickable polymer

Biodegradable polymers have been used in environmental and biomedical engineering, but the lack of functional groups limits their applications. In the present work, we report a facile approach to synthesize a biodegradable and clickable polymer consisting of e-caprolactone (CL) and allyl methacrylate (AMA) with phosphazene base as the catalyst via hybrid copolymerization, where AMA is selectively copolymerized leaving the allylic groups for the click reaction. The facile and efficient approach can be used to functionalize biodegradable polymers and synthesize some new polymers under mild conditions.

Influence of solvent on branching via atom transfer radical polymerisation using 1,6- bismaleimidohexane as branching agent

Abstract Branched polystyrenes have been prepared via atom transfer radical polymerisation using 1,6-bismaleimidohexane as the branching agent in two reaction systems of anisole or anisole along with N-methyl pyrrolidone (NMP). The polymerisation kinetics was studied using gas chromatography. The formation mechanism, the development of branching, the changes in molecular weight and polydispersity of branched polymers were analysed using triple detection size exclusion chromatography. The results showed that the formation mechanisms of branched polystyrenes were almost the same in both the reaction systems. The relative molecular weights were also similar at the same conversion of styrene in the two reaction systems because of similar contents of the pendent vinyl groups between the two reaction systems. However, higher absolute molecular weight and higher branching degree of the branched chains were obtained in the anisole with NMP than that in the anisole alone at the same styrene conversion.

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. The peroxide monomer, tert-butyl peroxyacetate methacrylate (BPAMA), was designed and prepared in high purity from commercially available reagents via classic organic reactions. Triple-detection size-exclusion chromatography (TD-SEC) measurements, NMR analyses, and hydrolysis experiments were used to reveal the polymerization procedure and to confirm the branching structure of the prepared polymers. Branched polymers of styrene, methyl methacrylate (MMA), and vinyl acetate (VAc) were prepared under solvent-free conditions through radical polymerization in the presence of a peroxide monomer. Furthermore, radical polymerization in the presence of the peroxide monomer can be operated in a simple polymerization composition involving only the peroxide monomer BPAMA with MMA or VAc. The obtained branched polymers exhibited high molecular weights (Mw.MALLS > 106 g mol−1) and relatively narrow molecular weight distributions (2.5 ≤ PDI ≤ 6.8). Generally, radical polymerization in the presence of a peroxide monomer as the initiator and the branching agent can make the preparation of branched vinyl polymers almost equally as facile as the preparation of their linear analogs. This approach is applicable to a wide variety of monomers and can be performed with a simple polymerization composition in the bulk under moderate conditions compared with the reported strategies.

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 conventional azo radical initiator, 2,2′-azobisisoheptonitrile (V65), a free-radical polymerization inhibitor (I2), and a highly reactive but inexpensive salt (NaI) were used to initiate and control the polymerization. The highly branched structures and process of branching were confirmed and thoroughly investigated. The reactivity of the vinyl groups incorporated into the copolymer was found to be similar to that of the monomers used in the RCMcP reaction. Large numbers of branched structures occurred when the conversion of MMA (conv.MMA) reached 56.6%, at which point the amount of pendant vinyl groups in the polymer reached a maximum value. The most significant branching occurred when the conv.MMA approached 90% because of intermolecular reactions between macromolecules. The polymerization reaction can also be performed without deoxygenation, with no obvious prolongation of induction. This work provides a simple, easy, and versatile method for the synthesis of highly branched polymers from commercially available compounds.