The Effect of Molecular Weight

The most basic and fundamental struc-ture/property question that must be answered with any new system, especially one prepared by a living polymerization, is the molecular weight or degree of polymerization at which its thermotropic behavior no 

The G-SmA-N-I transition temperatures of syndiotactic poly(6-[4 -(4 - -bu-toxyphenoxycarbonyl)phenoxyl)phenoxy]-hexyl methacrylate prepared by aluminum porphyrin initiated polymerizations also level off at approximately 25 repeat units [91]. Similarly, the glass and nematic-isotropic transition temperatures of poly[6-(4 -methoxy-4 - Z-methylstilbeneoxy)hexyl methacrylate] prepared by group transfer polymerization become independent of molecular weight at approximately 20 repeat units [48]. Both polymethacrylates reach the same transition temperatures as the corresponding polymers prepared by radical polymerizations, which have nearly identical tacticities. 

III Molecular Engineering of Side Chain Liquid Crystalline Polymers 

The thermotropic behavior of liquid crystalline polynorbornenes also reach their limiting values at 50 repeat units or less [22, 182, 188-190]. For example, Fig. 9 demonstrates that the glass and nematic-isotropic transitions of both terminally and laterally attached systems level off at 25-50 repeat units, and correspond to the transition temperatures of the infinite molecular weight polymers. The same is true of the crystalline melting and smectic-isotropic transition temperatures of poly ( )-endo, exo-5,6-di [ -[4 -(4 -methoxyphenyl)-phenoxy]hexyl]carbonyl bicyclo[2.2.1]-hept-2-ene) [190]. 

Although most well-defined SCLCPs have been prepared by cationic polymeriza- 

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T is the glass-transition temperature at infinite molecular weight and is the number average molecular weight. The value of k for poly(methyl methacrylate) is about 2 x 10 the value for acrylate polymers is approximately the same (9). A detailed discussion on the effect of molecular weight on the properties of a polymer may be found in Reference 17. 

Only a limited amount of information is available concerning the effects of molecular weight distribution. There is, however, evidence that the narrower the distribution the more Newtonian are the melt flow properties. It has been noted... 

All of the observations above relate well to our own with respect to the effects of molecular weight on the available cure speed in manufacturing, both in plywood and OSB. They also correlate with our experience on the effects of molecular weight and dry-out on bond quality. 

As with resoles, the central issue in design of novolacs is molecular weight. The effects of formaldehyde-to-phenol molar ratio and formaldehyde conversion on molecular weight of novolacs has been well studied and reported [192,193]. The effects of molecular weight on most of the important properties are also available [193]. These include Tg, melt viscosity, gel time, hot-plate flow, glass-plate flow. 

According to the concepts, given in the paper [7], a significant difference between the values of yield stress of equiconcentrated dispersions of mono- and polydisperse polymers and the effect of molecular weight of monodisperse polymers on the value of yield stress is connected with the specific adsorption on the surface of filler particles of shorter molecules, so that for polydisperse polymers (irrespective of their average molecular weight) this is the layer of the same molecules. At the same time, upon a transition to a number of monodisperse polymers, properties of the adsorption layer become different. 

Recently, we explored the effect of molecular weight on the pattern and employed post-dewetting processes to alter the shape of the dewetted polymer droplets. Since the viscosity of a polymer solution is nonlinear with respect to concentration and also strongly dependent on polymer weight, we expected a drastic effect. Figure 11.4... 

The adsorption of fully and partially hydrolyzed (88%) polyvinyl alcohol (PVA) on 190-1lOOnm monodisperse polystyrene latex particles was investigated. The effect of molecular weight was investigated for 190 nm-size particles using the serum replacement adsorption and desorption methods. The adsorption density at the adsorption-isotherm plateau followed the relationships for the fully hydrolyzed... 

Because the adsorbed HM-HEC molecules exhibit such slow rates of chain reorientation, the effects of molecular weight, amount of hydrophobic substitution and chain lengths of the hydrophobes on the interfacial properties of HM-HEC monolayers can be investigated by two kinds of dynamic experiments hysteresis and stress-jump, using a Langmuir trough film balance. 

Akashi and coworkers prepared small platinum nanoparticles by ethanol reduction of PtCl in the presence of various vinyl polymers with amide side chains [49]. These authors studied the effects of molecular weight and molar ratio [monomeric unit]/[Pt] on the particle sizes and size distributions by electron microscopy, and in some cases by the dispersion stability of the Pt colloids. The hydrogenation in aqueous phase of allyl alcohol was used as a model reaction to examine the change in catalytic activity of polymer-stabilized Pt colloids upon addition of Na2S04 to the reaction solution. The catalytic tests were performed in water or in Na2S04 aqueous solution at 25 °C under atmospheric pressure of... 

Laboratory and pilot plant studies [14] on the Stillwater ore showed that the molecular weight of the CMC affected both PGM grade and recovery. Figure 18.3 shows the effect of molecular weight of CMC on PGM grade-recovery relationship. 

Figure 6.14 The effect of molecular weight of a cationic polyacrylamide on the microelectrophoretic mobility of microcrystalline cellulose (figures in brackets are negative).

The synthesis and phase behavior of the model polydiethylsiloxane networks have also been studied. The networks were made by hydrosilylation of well-defined vinyl and allyl telechelic siloxanes obtained by kinetically controlled polymerization of cyclic trisiloxane.314 The effects of molecular weight between the cross-linkings on segment orientation in polydiethylsiloxane elastomers were studied.315... 

Cheng, Y.-Y., Brillhart, M., Cebe, P. and Capel, M., X-ray scattering and thermal analysis study of the effects of molecular weight on phase structure in blends of polybutylene terephthalate with polycarbonate, J. Poly. Sci., Polym. Phys., 34, 2953-2965 (1996). 

Hamilton, D. G. and Gallucci, R. R., The effects of molecular weight on polycarbonate-polybutylene terephthalate blends, J. Appl. Polym. Sci., 48, 2249-2252 (1993). 

The effect of molecular weight of the resist on degree of planarization is shown in Figure 30a where the amplitude of fluctuation of 2 - pm thick PMMA films with average molecular weight of 500,000, 150,000, and 33,000 respectively, is plotted as a function of periodicity of 0.8 - pm high... 

The prime object of the present study was to determine the compositional polydlspersity of commercial cellulose triacetate and to examine the effect of molecular weight and molecular weight distribution on the mechanical properties of the fibres. 

Effect of 6- Caprolactone and Adipic Acid Molar Ratio for Copolyester III on the Hydrolysis by R. delemar Lipase. The hydrolysis of various copolymers by R. delemar lipase was exam ed to see whether there was an optimum chemical structure or not. Mn of those copolyesters was selected from 17 0 to 2220, to diminish the effect of molecular weight. Optimum molar ratio of e- caprolactone and adipic acid was about from 90 10 to 70 30 (Figure 5). The Tm at the optimum molar ratio was the lowest of all. So it seemed that the existence of optimum molar ratio came from the lowest Tm, which would show the most amorphous material, rather than the optimum chemical structure. 

Table 4.3 summarises the absorption data for some steroid structures and illustrates the effect of molecular weight on the A (1%, 1 cm) value. The strength of the enone chromophore is similar for all the steroids since the A (1%, 1 cm) value is based on the absorption of a 1 % w/v solution it will thus decrease as the molecular weight of the steroid increases. This is of course true for all molecules. 

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