Characterization of emulsion polyethylene

Abstract

synopsisPolyethylene which was made by emulsion polymerization was characterized by means of osmometry, light Scattering, and viscometry. The samples have unusually high weight-and number-average molecular weights. Low molecular weight polymer which is usually present in commercial polyethylenes was not detected. The data indicate a compact, highly ramified molecular structure. The light-scattering data suggest each latex particle is made up of essentially one giant molecule which swells but does not dissolve in organic solvents a t 1 0 0 O C . Swelling factors calculated from viscosity and lightscattering data indicate low degrees of crosslinking. A clear distinction cannot be made between a highly long-chain branched structure and the crosslinked structure of microgels. Of the low-density polyethylene, 1-2 wt.-% is made up of molecules which have a comparable structure. In contrast, the greatest portion of the experimental samples is composed of the high molecular weight, highly ramified molecules.

Molecular weight distribution of emulsion‐polymerized polyethylene

“…All of our products had melting points between 103 and 120°C and crystallinity levels by DSC between 43 and 67%. As in earlier work, 1,3,6 it appears that the amount of short chain branching is in line with other free radical polymerizations of ethylene carried out in the same temperature range.…”

Light Scattering

“…This conclusion was made possible by a careful and comprehensive evaluation of all factors that could be of importance, such as fractionation, clarification of solutions, stability of solvents and solutions at high temperatures, history of the samples, refractive index increment in different solvents and at different temperatures, and proper treatment of experimental data (41-44, 84, 87, 294, 307). That the very difficult clarification of solutions of unfractionated linear and of branched polyethylenes, as evidenced by the distorted Zimm diagrams, is due to the presence of very high molecular weight species (microgel particles) is corroborated by the experiments on polyethylene with radiationinduced crosslinking (177) and on highly branched emulsion polyethylene (200).…”

Synthesis of Poly(styrene)-b-poly(dimethylsiloxane)-b-poly(styrene) Triblock Copolymers by Iodine Transfer Polymerization in Miniemulsion

“…in which M n,(2) is the mean number-average molecular weight of 2, m styrene is the mass of styrene, n (2) is the number of moles of 2, and a styrene is the conversion of styrene. As mentioned in the Experimental Section, the tailing of the molecular weight distribution on the low molar mass side (non symmetrical distribution) for the triblock copolymers could be attributed to differences in dn/dc for PDMS (dn/dc(PDMS) ) -0.0938 mL‚g -1 at 25 °C at 546 nm 78 ) and PS (dn/dc(PS) ) 0.111 mL‚g -1 at 28 °C at 546 nm 79 ).…”

“…SEC analysis of PDMS in toluene gives a negative peak (because n PDMS < n Toluene ) ( n PDMS = 1.43; n PS = 1.591 and n Toluene = 1.496). , Therefore, the PDMS was analyzed using an inverse polarity to make the peak positive. Because of the values of d n /d c and n of PS and PDMS (d n /d c (PDMS) = −0.0938 mL·g -1 at 25 °C at 546 nm and d n /d c (PS) = 0.111 mL·g -1 at 28 °C at 546 nm), the triblock copolymers give a positive peak as soon as the weight fraction of PS in the triblock is higher than 46%. Thus, the detection of PS-poor triblock copolymers by the refractometer detector is less sensitive than that of PS-rich triblock copolymers.…”