Dispersion copolymerization of polyoxyethylene macronomer and styrene 4. Solution properties of polystyrene‐graft‐polyoxyethylene copolymers

Abstract

The graft copolymers (polystyrene-graft-polyoxyethylene) (PSt-graft-PEO) were prepared by the radical dispersion copolymerization of methacryloyl (MA)-terminated PEO macromonomer and styrene. By means of size-exclusion chromatography, liquid chromatography at the critical adsorption point, and light scattering, the molecular weight parameters and the solution properties of PSt-graft-PEO were investigated. The apparent average molecular weight and the molecular weight distribution (MWD) of graft copolymers were found to decrease with increasing molecular weight of PEO-MA macromonomer. This decreased molecular weight was attributed to the chain transfer to PEO unit and increased contribution of the solution polymerization. The broad MWD varied with the ratio of the polymerization in the continuous phase and the polymer particles. The number of PEO grafts per PSt backbone decreased with increasing molecular weight of the PSt-graft-PEO copolymer, which was attributed to the intramolecular association of PEO segments. The intrinsic viscosity or the coil size of graft copolymer molecules varied with temperature as a result of the dehydration of PEO segments.

Characterization and Utilization of Polystyrene and Polyacrylamide-Graft-Methoxypolyethylene as Cement Admixtures

“…This is probably attributed to the amount of water loss by evaporation from the outer surfaces of samples that is relatively higher than that of the pure cement pastes (M 0 ). This process considerably affects the degree of elasticity of the cement pastes, which in turn reflects on the setting time [4,21] . Accordingly, the setting times (initial and final) were shortened.…”

“…As a result, the compressive strength improves and enhances [16] . The compressive strength of the hardened OPC=polymer pastes of M 1 and M 2 are slightly lower than that of the neat OPC pastes (M 0 ) during the early hydration ages up to 7 d and then becomes higher during the later hydration ages up to 90 d. At early ages of hydration, the growth of crystals are so slow that minute crystals are formed which have no or a marginal effect on the strength development [1,2,21] . The decrease of compressive strength is mainly due to the sealing effect resulting from the polymer membranes or films that develop in the cement structure.…”

“…This provides a considerable increase in water tightness which temporarily prevents the diffusion of water inside the cement grains. This action tends to stop or at least reduce the rate of cement hydration [21,23] . Moreover, the increase of hydration products due to hydration usually results in an increase in the total content of the binding centers between the remaining unhydrated parts of the cement grains.…”

“…On the other hand, the increase of compressive strength at the later ages of hydration is because the polymer particles tend to concentrate inside the pore structure of the hardened cement=polymer pastes and act as a reinforcement or a co-matrix phase which gives a strong cement hydration bond. This effect increases with the increase of polymer content [7,21,23] . Further, the higher compressive strength in presence of polymer particles is mainly due to the growth of crystalline structures.…”

Poly(N-vinylcaprolactam) Microgel Particles Grafted with Amphiphilic Chains

“…Several synthetic strategies may be applied to produce PEO grafted copolymers. Functionalized polymers can be postmodified with PEO, , but also, reactive PEO methacrylates have been used as macromonomers to synthesize grafted latices in dispersion polymerizations , and graft copolymers in solution polymerization . In the latter case it needs to be taken in account that PEO may act as a chain transfer agent in radical polymerization …”