David G. Westmoreland

Polymerization rate and mechanism of ultrasonically initiated emulsion polymerization of n-butyl acrylate

The factors affecting the induction period and polymerization rate in ultrasonically initiated emulsion polymerization of n-butyl acrylate (BA) were investigated. The induction period takes only an instant in ultrasonically initiated emulsion polymerization of BA without any added initiator by enhancing the N2 flow rate. Increasing temperature, power output and SDS concentration, decreasing the monomer concentration results in further decreasing induction period and enhanced polymerization rate. Under optimized reaction conditions the conversion of BA reaches 92% in 11 min. The polymerization rate can be controlled by varying reaction parameters. The apparatus of ultrasonically initiated semi-continuous and continuous emulsion polymerization were set up and the feasibility was first studied. Based on the experimental results, a free radical polymerization mechanism for ultrasonically initiated emulsion polymerization was proposed, including the sources of the radicals, the process of radical formation, the locus of polymerization and the polymerization process. Compared with conventional emulsion polymerization, where the radicals come from thermal decomposition of a chemical initiator, ultrasonically initiated emulsion polymerization has attractive features such as no need for a chemical initiator, lower reaction temperature, faster polymerization rate, and higher molecular weight of the polymer prepared.

“Living” radical polymerization of methyl methacrylate with diethyl 2,3‐dicyano‐2,3‐diphenylsuccinate as a thermal iniferter

The bulk polymerization of methyl methacrylate (MMA) initiated with diethyl 2,3-dicyano-2,3-diphenylsuccinate (DCDPS) was studied. This polymerization showed some “living” characteristics; that is, both the yield and the molecular weight of the resulting polymers increased with reaction time, and the resultant polymer can be extended by adding MMA. The molecular weight distribution of PMMA obtained at high conversion is fairly narrow (Mw/Mn = 1.24≈1.34). It was confirmed that DCDPS can serve as a thermal iniferter for MMA polymerization by a “living” radical mechanism. Furthermore, the PMMA obtained can act as a macroinitiator for radical polymerization of styrene (St) to give a block copolymer.

A novel thermal iniferter for radical polymerization

Abstract A novel thermal iniferter, 1-hydroxy-2-( p -tolylaminocarbonyloxy)-1,1,2,2-tetraphenylethane (HTTPE), was prepared from 1,1,2,2-tetraphenyl-1,2-ethanediol (TPED) and p -tolyl isocyanate. The thermal iniferter is a complex of HTTPE with acetone, designated as HTTPE·Acetone. Characterization of HTTPE·Acetone was performed by FTIR, 1 H-NMR and elemental analysis. The melting point of the complex is 98–99.5°C. The polymerization of methyl methacrylate (MMA) with HTTPE·Acetone can be carried out in bulk or in DMF solution at 70 and 80°C, and the polymerization proceeds by a “living” polymerization mechanism. The resultant polymer can reinitiate a second monomer, n -butyl methacrylate, (nBMA), to form a PMMA- b -PnBMA block copolymer.

BULK POLYMERIZATION OF STYRENE WITH DIETHYL 2,3-DICYANO-2,3-DI(p-TOLYL)-SUCCINATE AS A THERMAL INIFERTER

The bulk polymerization of styrene (St) was investigated using diethyl 2,3-dicyano-2,3-di(p-tolyl)succinate (DCDTS), a hexa-substituted ethane compound, as an initiator. The polymerization data show that DCDTS behaves as a thermal iniferter, and the polymerization proceeds by a “living” radical polymerization mechanism with a reversible deactivation. The polymerization can be carried out at quite low temperatures (such as 65–85°C) and the final conversions are high. The PSt possessed high molecular weights and molecular weight distributions (M w M n in the range of 1.4 to 1.6). End-group analysis by 1H NMR spectroscopy reveals that the resultant PSt contains the fragments of DCDTS at its chain ends. This polymer with an ω-penta-substituted C─C bond end group could be used as a macroinitiator to carry out chain-extension reaction with St and could also block copolymerization with methyl methacrylate.