Solution-polymerized 776 INDEX

Experiments were conducted with a dual catalyst chain shuttling system in a continuous solution polymerization reactor. A series of ethylene-octene copolymers of similar melt index were produced with a composition of ca. 30% (by weight) hard and 70% soft blocks. The level of DEZ was systematically varied to study the effects of CSA ratio on polymer microstructure. 

First Order Stoppage Alone. If stoppage is determined solely by a first order process, such as transfer, the foregoing analysis predicts a nearly exponential distribution function. The polydispersity index must then be very close to 2.00. The same result is obtained for bulk and solution polymerizations dominated by chain transfer. Compartmentalization thus has no major effect on the polydispersity of the polymer produced, as was recognized by Gerrens (11), if the stoppage process is dominated by chain transfer. This contrasts with the significant effects of compartmentalization if bimolecular events dominate termination. 

Our discussion here explores active connections between the potential distribution theorem (PDT) and the theory of polymer solutions. In Chapter 4 we have already derived the Flory-Huggins model in broad form, and discussed its basis in a van der Waals model of solution thermodynamics. That derivation highlighted the origins of composition, temperature, and pressure effects on the Flory-Huggins interaction parameter. We recall that this theory is based upon a van der Waals treatment of solutions with the additional assumptions of zero volume of mixing and more technical approximations such as Eq. (4.45), p. 81. Considering a system of a polymer (p) of polymerization index M dissolved in a solvent (s), the Rory-Huggins model is... 

Using an earlier version of the dynamic model given in Section IV,6, Kiparissides et al (1980b) illustrated the use of such an extended Kalman Filter to infer JV(f), VJit), AJit), and X(f) from measurements taken only on conversion [X(f)J using UV turbidity spectra. Jo and Bankoff (197Q used these filters to track some of the moments of the MWD of PVAc in a solution polymerization process using measurements made on refractive index and viscosity. 

With the high-temperature solution polymerization processes, various ethylene homo- and copolymers with different average molecular mass and copolymer compositions are produced. The product portfolio comprises PE-HD, PE-LLD, PE-VLD, and the ethylene/propylene elastomers (EPM, EPDM) (see Figure 2). The thermoplastic products have a wide range of applications [1]. The elastomeric ethylene/propylene copolymers can also be applied widely in the automotive industry, for plastics modification, in industrial applications such as seals, in electrical cables, and in tires [2], Uncured ethylene/propylene copolymers are applicable as viscosity index improvers for lubricant oils [5]. 

FIGURE 235 Variation of the residence time in solution polymerization has little or no effect on the polymer melt index, for a given reaction temperature. 

Styrene-based thermoplastic elastomers (see Chapter 4) are sensitive to oxidation since they contain unsaturated soft segments. These elastomers are manufactured by solution polymerization process in aliphatic hydrocarbons. In order to prevent autoxidation during the finishing steps (stripping, drying), which manifests itself by a rise in melt flow index and discoloration of the raw polymer, antioxidant is added to the polymer solution before finishing. Hence the antioxidant has to be soluble in the polymerization solvent. 

The initial overshoot in number-average molecular weight (Fig. 2.3.6) and poly-dispersity index (Fig. 2.3.7) at low conversions seems to be consistent with the initial OA line segment of the system trajectory as depicted in Fig. 2.1.11, wherein the system follows a solution polymerization process during the first 10 min (based on Figs. 2.3.5-2.3.7). Subsequently, when the polymer-rich phase was being formed as the system traversed the OB line segment of the reaction trajectory in Fig. 2.2.5, the tendency for this phase was to go into gel effect, as seen from the sharper rise... 

Let us start with a solution of chains (polymerization index A ) in a good solvent (excluded volume parameter i = a (1 - 2 ) > 0). The chains repel each other, and this is reflected in the existence of a positive osmotic pressure II. 

Examination of this catalyst system under solution polymerization conditions carried out at 160°C in 216 ml of cyclohexane as solvent containing 10 or 20 ml 1-octene as comonomer, 140 psig total reactor pressure, the catalyst exhibited a relatively high activity of 2430 g PE/mmol catalyst/hr. Characterization of the polyethylene showed a molecular weight (Mw) of 114,000 with a polydispersity index value of 2.6, indicating near single-site MWD. 

We briefly set up a dynamic model of an entangled polymer solution in the semidilute regime, (f) > = and critical volume fraction and N being the polymerization index. In terms of the polymer volume fraction (f> and the conformation tensor W = Wij, the free energy is given by [10]... 

II.4 Self-consistency removing the hypothesis of fixed obstacles Obviously the hypothesis of fixed obstacles, crucial for the application of reptation ideas to melts or entangled polymer solutions, and which makes it possible to reduce the real many-body problem to a one-chain problem, might not be valid and has to be carefully tested experimentally. Diffusion measurement techniques in which labelled chains are used are unique tools to do so, as labelled and unlabelled chains of different polymerization index (respectively N and P) can be used systematically, to... 

Relation Eq. (85) yields, in particular, the critical concentration Ck above which mesophase is expected to be formed. This concentration scales with the total polymerization index N = Ng the same way as the critical concentration of demixing in a blend solution given by Eq. (45)... 

Bataille and Shariffi-Sanjani [34] reported the synthesis of a copolymer of 2-ethylhexyl acrylate and vinyl 2-ethyl hexanoate by solution polymerization using benzene as a solvent and benzoyl peroxide as an initiator at 65°C. The viscosity index improvement property of the purified copolymer was checked in two ISO 20 base oils. The polydispersity of the copolymers was observed to influence greatly the viscosity index improvement property. 

FIGURE 16.24 Inulin isolated from mature Topinambur tubers sparated on Bio-Gel P-6 (140 X I. Scm) flow rate 0.33 ml/min eluent H20(dest) + 0.002% NaNs detection Waters 403 R differential refractive index detector, sensitivity 8X applied sample I ml of a 20-mg/ml aqueous solution weight average degree of polymerization dp = 9 number average degree op polymerization dp = 2 polydisper-sity dp /dp = 4.5. 

To run the residence time distribution experiments under conditions which would simulate the conditions occurring during chemical reaction, solutions of 15 weight percent and 30 percent polystyrene in benzene as well as pure benzene were used as the fluid medium. The polystyrene used in the RTD experiment was prepared in a batch reactor and had a number average degree of polymerization of 320 and a polydispersity index, DI, of 1.17. 

A way to narrow the MWD and to approach the structure of dendrimers is the addition of a small fraction of a/-functional initiator, to inimers [40,71]. In this process the obtainable degree of polymerization is limited by the ratio of inimer to initiator. It can be conducted in two ways (i) inimer molecules can be added so slowly to the initiator solution that they can only react with the initiator molecules or with the already formed macromolecules, but not with each other (semi-batch process). Thus, each macromolecule generated in such a process will contain one initiator core but no vinyl group. Then, the polydispersity index is quite low and decreases with / M /Mn l-i-l//. (ii) Alternatively, initiator and monomer molecules can be mixed instantaneously (batch process). Here, the normal SCVP process and the process shown above compete and both kinds of macromolecules will be formed. For this process the polydispersity index also decreases with/,but is higher than for the semi-batch process, M /Mn=Pn//. ... 

Analysis of osmotic pressure of semi-diluted polymeric solutions by Scaling method is based [3] on two positions. Accordingly to the first one it is assumed that the polymeric chain is in good solvent for which % < 1 / 2. This position is necessary in order to index v in the expression (2) will be determined by the ratio... 

CONTENTS Preface. George W. Gokel. Cryptophanes Receptors for Tetrahedral Molecules, Andre Collett, Jean-Pierre Dutasta and Benedict Lozach. Inclusion Polymerization in Steroidal Canal Complexes, Kiichi Takemoto, Mikiji Miyata. Functionalized Tetraazamacrocycles Ligands with Many Aspects, Thomas A. Kaden. Calixarenes as the Third Supramolecular Host, Seiji Shinkai, Kyushu University, Japan. Fluorescent Chemosensors for Metal and Non-Metal Ions in Aqueous Solutions Based on the Chief Paradigm, Anthony W. Czamik. Index. 

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