SYNOPSISAn experimental investigation on the kinetics of free-radical polymerization of behenyl ( a mixture of 14.8% n-octadecyl, 15.1% n-eicosyl, and 70.1% n-docosyl) acrylate initiated with benzoyl peroxide was conducted at 70°C using a HAAKE rotational viscometer. Molecular weight measurements and differential scanning calorimetric studies of the samples are also described and the results are compared with those obtained by batch reactions conducted under a nitrogen atmosphere. A high monomer order of 1.61 f 0.11 and a low initiator order of 0.35 f 0.04 was obtained. The role played by the long methylene chain in behenyl acrylate is also discussed. 0 1994 John Wiley & Sons, Inc.
I NTRODU CTlO NA linear polymer with a pendent alkyl side chain of specific length is one of the general structural characteristics of flow improvers (FI ) /pour-point depressants ( P P D ) for crude oils.',' The FIslPPDs considerably reduce the natural pour point, viscosity, and yield value of the waxy crude, which enables the transportation of the crude well below the pour point. A number of patents describe the use of polymers of acrylates and methacrylates as PPDs /FIs. However, the kinetic data of the higher acrylate / methacrylate systems are scanty. Like many industrial polymers, polymerization to synthesize PPDs/ FIs are conducted in high viscous media. Therefore, it is important to establish a quantitative relation between polymerization rate and solution viscosity.The polymerization of alkyl acrylate in bulk or in solution shows a strong Trommsdorff effect or gel effect even though the polymerization is carried out above the glass transition temperatures ( T,) .Due to the gel effect, considerable deviations from the normal kinetic parameters are observed in highconversion polymerization. Onset of the gel effect * Systematic IUPAC nomenclature: n -docosy1 acrylate.' To whom correspondence should be addressed. is reported to occur between 20 and 40% conversion, depending on the temperature and the amount of initiator used.3 During the radical polymerization, the conversion first increases according to first-order kinetics and then accelerates because of the gel effect, which is characterized by an increase in viscosity resulting from higher conversion and increase in chain length.4 When the gel effect predominates, the critical chain length above which the chain radicals are entangled also decreases due to higher viscosity. In the termination step of high-conversion kinetics, it is necessary to consider two types of polymer radicals: ( i ) those that are entangled and (ii) those that are not entangled. When the solution viscosity is very high, the chain-termination reaction and, eventually, the chain propagation reaction becomes diffusion-controlled.
Journal of AppliedThe population of propagating radicals also decreases with the decrease of termination rate. At a very high degree of conversion, Rp slows down due to the consumption of monomers and the diffusioncontrolled rate of propagation. Numerical ~t u d i e s~-~ on high-co...
