عنوان

Preparation of uniform micron size particles of polystyrene by anionic dispersion polymerization

شماره

TLpq304209285

زبان متن نوشتاري يا گفتاري و مانند آن

انگلیسی

عنوان اصلي

Preparation of uniform micron size particles of polystyrene by anionic dispersion polymerization

نام عام مواد

[Thesis]

نام نخستين پديدآور

M. A. Awan

نام ساير پديدآوران

M. S. El-Aasser

نام ناشر، پخش کننده و غيره

Lehigh University

تاریخ نشرو بخش و غیره

1995

نام خاص و کميت اثر

198

جزئيات پايان نامه و نوع درجه آن

Ph.D.

کسي که مدرک را اعطا کرده

Lehigh University

امتياز متن

1995

متن يادداشت

Anionic dispersion polymerization in a hexane medium was applied to the synthesis of monodisperse polystyrene particles with a controlled size in the range of 1.41-7.14 mum, and having narrow molecular weight distributions (polydispersity index ranging from 1.02 to 1.28). Sec-butyllithium was used as the initiator. A polystyrene-block-polybutadiene diblock copolymer containing 23% polystyrene, having a molecular weight of 147,000 g/mol, and a narrow molecular weight distribution (polydispersity = 1.05) was found to be the most suitable steric stabilizer tested. Tetrahydrofuran, used as a promoter, produced narrow molecular weight distributions; however, the addition of small amounts of tetrahydrofuran broadened the particle size distribution. High solids content polystyrene dispersions (44%) were also prepared without using any promoter by both batch and/or multi-addition monomer processes. To characterize the diblock copolymer stabilizer a combination of transmission electron microscopy (TEM), dynamic (DLS) and static (SLS) light scattering, and flow FFF techniques was used. These results showed that this diblock copolymer forms micelles in selective solvents e.g. hexane with hydrodynamic radii (R{\rm h}) of 70 nm. Flow FFF was used to analyze the diblock copolymer in hexane and in a solution of hexane and ethylbenzene. The data obtained showed the presence of both single polymer molecules and micelles. By titration of the diblock copolymer/hexane solution with ethylbenzene, the micelles started dissolving, and at 23% ethylbenzene the micelles completely dissolved. The adsorption behavior of the diblock copolymer on polystyrene was studied via ellipsometry using model planar surfaces. A theoretical analysis of the adsorption kinetics was applied to investigate the total amount adsorbed at each concentration and the occupation area per diblock copolymer chain. The adsorption rate was found to depend strongly on the chemical nature of the substrate, the bulk concentration of the adsorbent, and the temperature. Furthermore, it was discovered that both single polymer molecules and micelles contribute to the adsorption process. Particles of increasing size were formed with decreasing stabilizer concentration and temperature or by increasing the initiator concentration. A delay in the time for the onset of particle nucleation occurred at lower stabilizer concentrations and temperatures. The formation of larger size particles at lower stabilizer concentration, lower temperatures, higher initiator concentrations, and the dissolution of the stabilizer in ethylbenzene and adsorption kinetics of diblock copolymer provided supporting evidence that particle nucleation in anionic dispersion polymerization is due to a polymer chain aggregation mechanism. This study also showed that the polystyrene chains are living and that particle growth is the result of propagation reactions by which monomer adds to the living ends of the chains inside the particles.

موضوع مستند نشده

adsorption

موضوع مستند نشده

Polymers

موضوع مستند نشده

Pure sciences

مستند نام اشخاص تاييد نشده

M. A. Awan

مستند نام اشخاص تاييد نشده

M. S. El-Aasser

نام الکترونيکي

فرمت انتشار

p

نوع ماده

[Thesis]

کد کاربرگه

276903

سطح دسترسي

a

تكميل شده

Y