Free Radical Bulk Polymerization Research Articles

Randomly branched styrene/divinylbenzene copolymers. I. Preparation, molecular weight characterization, and GPC analysis

A series of randomly branched copolymers of styrene and divinylbenzene were prepared using a benzoyl peroxide-initiated free-radical bulk polymerization at 78°C. DVB contents were varied from 0.01% to 2%. Two samples were polymerized with 0.4% DVB to different conversions: series 9A at 6% conversion and series 9B at 15% conversion (just short of the gelation point). Both samples were fractionated and the fractions characterized by ultracentrifugation, light scattering, osmometry, viscometry, and gel permeation chromatography. The data indicated that the fractions were not of narrow MWD and that the breadth of the MWD of the fractions from series 9B were greater than those of 9A. GPC calibration curves of M, [η], and M [η] were generated for both 9A and 9B fractions by employing curve-fitting techniques to the GPC data. For all of the fractions 9B, the molecular weight calibration provided accurate values of Mz, Mw, and Mn, suggesting that no serious peak spreading had occurred in the GPC experiments. The universal calibration parameter M[η] for the 9A fractions agreed with that of linear polystyrene, while that of the high-conversion series 9B did not. It will be shown in a later paper that series 9B is highly branched, while 9A is lightly branched. Consequently, it is recommended that any GPC analysis of branching units make an allowance for the deviation of highly branched polymers from the linear M[η] calibration curve.

On the radiation-induced solid state polymerization of N-phenyl maleimide

The solid-state polymerization of N-phenyl maleimide (NPMI) induced by 60Co γ-rays was studied above and below its melting point over the range 70–93. The conversion increases on raising the irradiation temperature. The polymers were characterized by elemental analysis, intrinsic viscosity, spectroscopy (u.v., i.r. NMR), programmed thermogravimetric analysis and X-ray diffraction. Infra-red spectra of polymers prepared by radiation were nearly identical with those of polymers obtained by free radical polymerization in bulk or in solution. The X-ray diffractograms of all samples show two rather broad peaks indicative of non-crystalline structures. The locations of the peaks do not depend upon the irradiation temperature. The average “cluster size”, calculated from the broadening of the innermost maximum, is strongly dependent on the irradiation temperature: hence it is indicative of the presence of well defined short range order. It has been suggested that some of the i.r. absorption bands in poly N-phenyl maleimides disappearing in solution may be assigned to “regularity”. The existence of such bands confirms the short range order proposed for packing in the solid state but also associated with long stereoregular chain sequences of the threo di-syndiotactic type.

Termination and other processes in the polymerization of p-methoxystyrene and 2,2-dideutero- p-methoxystyrene

The uncatalysed thermally initiated free radical bulk polymerization of ϱ-methoxystyrene and 2,2-dideutero- ϱ-methoxystyrene (65% deuterated) have been studied at 80, 100 and 120°. Both the rate of polymerization and the degree of polymerization are increased by deuteration, as would be expected from the deuterium kinetic isotope effect if disproportionation plays a part in the radical termination process. The effect of deuteration is least at the highest temperature, but it is shown that this does not mean that the extent of disproportionation decreases with increasing temperature. From a comparison of the effect of deuteration on the polymerization rate with its effect on the degree of polymerization, it is concluded that the transfer constant to monomer is less for the deuterated material than for the undeuterated material. It is suggested that the transfer process probably involves the donation of a deuterium or hydrogen atom from the growing radical to the monomer.

Effects of gamma radiation on copolymers of styrene and methyl methacrylate in the solid state

AbstractRandom copolymers of styrene and methyl methacrylate, prepared by free radical polymerization in bulk at 60°C, were irradiated under vacuum at 35°C with 60Co gamma rays to doses up to 200 Mrad. The flexural strength, with failure occurring in all cases by brittle fracture, decreased with radiation dose; the rate of this decrease increased with increasing methyl methacrylate content. Compressive strength measurements showed a transition from yield to fracture after a radiation dose which increased with styrene content and then a rapid fall in fracture stress for higher doses. Viscometry measurements showed a good correlation between changes in flexural strength and molecular weight.

The free radical bulk polymerization of ethylene at low temperatures

A method is presented to recover the polymer formed in the free radical bulk polymerization of ethylene as a powder rather than as a melt. The paper mentions several advantages of this new approach, which has been used in a study on the production of medium and high density polyethylene with the aid of radical initiators at temperatures below the melting point of polyethylene (suspension bulk polymerization). The method of preparing products with a very high stiffness comparable to that of homopolymers made by the Ziegler process is, in principle, also applicable at polymerization termperatures above the melting point of polyethylene, provided (meth) acrylamide is employed as a comonomer.

A Kinetic Study of the Free-Radical Bulk Polymerization of Ethylene

Abstract The bulk polymerization of ethylene was carried out under mild conditions, i. e. pressures of from 183 to 400 kg/cm2 and temperatures of from 30 to 140°C, using azobisisobutyronitrile as an initiator. In polymerization at the low temperature of 40°C, both the polymerization rate and the molecular weight of the polymer formed increased with the reaction time. At the above temperature, the polymerization rate was shown to be proportional to the amount of initiator, and the molecular weight was found to be independent of it. Furthermore, both the polymerization rate and molecular weight were found to be proportional to the 2.5th power of ethylene fugacity. The dependencies of the polymerization rate and the molecular weight on the reaction time decrease with the rise in reaction temperatures from 30 to 100°C. A kinetical discussion indicated that the rate of termination is almost zero at 30–40°C, but that it increases with the temperature. The polymerization rate and the molecular weight were shown to be proportional to the 0.8 and 0.2th powers of the amount of the initiator. The activation energy of the initiation reaction was evaluated to be ca. 27 kcal/mol.

Emulsion copolymerization of butadiene and styrene in the presence of carbon black

AbstractCarbon blacks inhibit and retard free radical polymerization in bulk and solution. The mechanism of this is discussed in terms of the chemical groups present on the carbon surface. It is shown that the number of free radicals which react during the induction period (polymerization of styrene with AIBN) is much less than the number of quinone groups but of the same order of magnitude as the number of easily oxidizable groups. Inhibition by carbon black was also found in an emulsion polymerization system with cumene hydroperoxide as initiator (no reducing components). By use of highly active redox recipes, reasonable rates of polymerization were obtained at both 50°C. (sugar‐iron‐hydroperoxide recipe) and 5°C. (peroxide‐polyamine recipe), with as much as 40 parts of black per 100 parts of monomers. In these systems, the carbon black was charged as an aqueous dispersion stabilized with Daxad 11; the latices were stable and showed evidence of association between some of the carbon black and some of the latex particles. The coagulated rubber stocks, when compounded and cured, gave properties closely similar to those of dry mixed stocks.

Polyvinyl Benzoate Monolayers

MONOLAYERS of polyvinyl benzoate show strong film properties strikingly similar to those of vertically oriented fatty acids and unlike those of horizontally oriented polyvinyl acetate. The polymer was prepared by free-radical bulk polymerization at 82° C. Monolayers were studied at 25° C. on the film balance1–3. The spreading solvent was twice-distilled benzene.