Wenyan Huang

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.

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.

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. For this purpose, two azo-containing pre-inimers with divinyl (DMACPO) or monovinyl (MACPO) substitution groups were synthesized and copolymerized with methyl methacrylate (MMA). The effects of the pre-inimer structure, the feed ratio, and oxygen on the monomer conversions and on the degree of branching of the obtained polymers were investigated thoroughly. The polymerization process and the branching behaviour were also studied in detail. The study of the DMACPO system revealed that the branched structures were synthesized from the beginning of the polymerization and that substantial branching occurred when the MMA conversion reached 54.7%. At the end of the polymerization, the MMA conversion was greater than 80%. The use of a small amount of additional azo initiator substantially increased the CC bond content among the inimers and the MMA conversion, affording polymers with a high degree of branching. The study of the MACPO system suggested that the monovinyl-functional inimer was much more effective than the divinyl-functional inimer, as the MMA conversion reached as high as 98.0% without inducing gelation. Moreover, the present synthesis could be conducted without additional deoxygenation irrespective of the pre-inimer employed. The current work provides a simple, easy, and versatile method for the synthesis of highly branched polymers from commercially available compounds and will facilitate the application of this method in various highly branched polymer syntheses.

Phosphazene-catalyzed oxa-Michael addition click polymerization

This paper reports a new type of click chemistry via a phosphazene bases-catalyzed oxa-Michael addition of an alcohol to an acrylate. The studies on the reactions between small molecules showed that only 5 mol% phosphazene base, t-BuP2, could catalyze the reaction between the acrylate double bonds and a primary alcohol and drive the reaction to completion within a few minutes under solvent-free conditions at room temperature. Additionally, t-BuP2 was a particularly efficient catalyst for the oxa-Michael addition of secondary alcohols to acrylate double bonds under similar conditions. Moreover, applying this reaction to the synthesis of polymers could successfully afford degradable poly(ester-ether)s with excellent monomer conversions under mild conditions. Throughout the polymerization, transesterification reactions were unavoidable, which increased the randomness in the structures of the resulting polymers. Considering the remarkable features of this method, such as the ready availability of the alcohol substrates, this work provides a simple, easy, and versatile method for synthesizing degradable polymers from commercially available compounds and will be useful in polymer chemistry.

Preparation of branched polystyrene by free radical emulsion polymerization in the presence of functional monomer

ABSTRACT Several branched polystyrenes were prepared by free radical emulsion polymerization in the presence of α-mercaptohexyl methacrylate (MHM) as the chain transfer monomers, potassium peroxodisulfate as the initiator and sodium dodecyl benzene sulfate as the emulsifier. Branched polystyrenes of high molecular weight and high branching degree were obtained. The obtained polymers were characterized by using three detection size exclusion chromatography (TD-SEC). The branched polystyrenes showed considerably higher molecular weights and higher branching degrees using this reaction system. The higher the mole ratio of MHM to monomer or the higher mole ratio of MHM to initiator, the higher were the obtained absolute weight average molecular weight and the branching degree of the obtained polystyrenes. In addition, low temperature of polymerization reaction also contributed to the high average molecular weight and the high average branching degree of branched polystyrene. The higher average molecular weight of branched polystyrene obtained in this system was accompanied by the higher average branching degree of the branched polystyrene. It was also shown that the nature of branched structures was not affected by the amount of initiator and reaction temperature of the polymer.

Branched styrene-acrylic resin for coating via radical polymerization in the presence of chain transfer monomer

Abstract Branched styrene–acrylic resins were prepared through radical polymerization using cheap 2-(3-mercaptopropionyloxy) ethyl methacrylate (MPOEM) as the chain transfer monomer (CTM). The monomers were added dropwise into the reaction vessel containing xylene at 135°C to obtain styrene–acrylic resins. The formation of branching and the molecular weight were analyzed using triple detection size exclusion chromatography (TD-SEC). The viscosities of the resins were characterized using rotational rheometer and Grignard tube viscometer. By adjusting the dosage of MPOEM and the initiator, a series of branched styrene–acrylic resins were obtained. Generally, the viscosity and the flow ability of the resin were improved evidently when branching was introduced. At the mole ratio of monomer to MPOEM of 100/0.1, the branched styrene–acrylic resin showed 51% decrease in zero-shear viscosity and 62% increase in flow ability, compared with the linear analogues with similar molecular weight at 70% solid content.