Abstract
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.
Highlights
Branched polymers have some unique properties, such as lower solution and melt viscosities, increased solubility, and many more terminal groups
Several groups studied the development of branching [23,24,25,26], and concluded that the limited molecular weight and broad polydispersity of the obtained branched polymers resulted from primary chain residue and intramolecular cyclization [25,26,27]
In our previous reports, branched polymers were successfully prepared through radical polymerization in the presence of the chain transfer monomer mercapto-hexyl methacrylate (MHM) [37,38]
Summary
Branched polymers have some unique properties, such as lower solution and melt viscosities, increased solubility, and many more terminal groups. With regard to the copolymerization of vinyl and divinyl monomer, the prepared branched polymers show limited molecular weights and much broader polydispersities [32,34]. This polymerization must be performed in diluted media, or gelation will occur (except in aqueous or suspension reaction). Suspension polymerization offers some unique advantages compared to bulk and solution polymerization, since polymer beads of high purity can be obtained directly and water provides an ideal heat-transfer medium during the reaction. Since suspension polymerization has so many marked advantages, it is postulated here that beads of branched vinyl polymers with high purity can be prepared directly through radical solvent-free suspension polymerization and simple filtration, and this is the objective of our research here. We investigated the effects of branching on glass transition temperature and the rheological properties of branched vinyl polymers
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