Initial Intrinsic Viscosity

In the study of the linear response, it is convenient to consider quantity independent of concentration and viscosity - the characteristic (intrinsic) viscosity 

The limit of the characteristic viscosity at low frequencies, according to (6.20), is defined as 

Theoretical estimates of the quantity zv — 1 are in the range from 0.5 (non-draining Gaussian coil), to 1.11 (draining coil with excluded-volume interaction). A compilation of empirical values of K and of the power exponents for different polymers and different solvents may be found in the literature (Flory 1969, Tsvetkov et al. 1964). The empirical values of the exponent zv — 1 do not exceed 0.9, which indicates significant impermeability of the macro-molecular coil in a flow. We may note that once a relation of type (6.24) 

For a non-draining coil, the characteristic viscosity defined by equation (6.23) can be expressed in the form 

Equation (6.25) makes it possible in this case to interpret a dilute solution of macromolecules as a suspension of solid non-deformable spheres with a radius close to the mean square radius of inertia. 

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Figure 5.21 Solid-state polycondensation using different prepolymers, shown as the initial intrinsic viscosity as a function of time (at 235 °C and 0.1 mbar) [30a]. From Buxbaum, L. H., J. Appl. Polym. Sci., Appl. Polym. Symp., 35, 59 (1979), Copyright John Wiley Sons, Inc., 1979. Reprinted by permission of John Wiley Sons, Inc.

Initial intrinsic viscosity, dl/g Free polyfmethyl acrylate) Free polystyrene Block copolymer... 

The unusually high observed initial intrinsic viscosity was at first thought to be due to molecular aggregation of polymer chains, made possible by presumed interaction of the carboxyl ester groups. Molecular association is known in many polymeric systems, but in those cases the association process is also apparent in osmometric data. No evidence of association is observed in the osmometric data of poly[(a-carboxymethyl)ethyl isocyanide]. Moreover, it would be expected that, if molecular association would have taken place, different values of [>7] would have been observed upon changing of solvents. Such change is not observed upon addition of triethyl amine (i.e. 10% volume) to 1,2-dichloroethane, or by solvent change to p-dioxane. 

Fig. 30. Relationship between intrinsic viscosity [q], and radiation dose (Ry Mrads.) finitial intrinsic viscosity. effective initial intrinsic viscosity after destruction of weak links, rgej radiation dose at gel point. Ratio of chain scissions to cross-links is 0.37 (87)...

Initial intrinsic viscosity of PVAc samples Approximately MW (xlO )" Viscosity of PVAc after alcoholysis and reacetylation Approximately MW (XIO V... 

The extent of enzymatic destruction of Qins was estimated by the difference between the value of initial intrinsic viscosity of CHT solutions in acetate buffer with pH = 4.5 obtained from dm specimens and that of intrinsic viscosity of solutions from dm specimens subjected to enzymatic destmction for 1 hr. Food collage-nase (Bioprogress, Schelkovo) was used as an enzymatic preparation. The enzymatic preparation concentration on the base was 5% mass of the CHT mass. 

In benzene solution at 25°C, ZnEt2/H20, cadmium tartrate initiator Intrinsic viscosity 2.0-4.0 (14)... 

In vivo degradation studies with poly(caprolactone) were performed with samples in film and tube form with the initial intrinsic viscosities covering a range of 0.5-2.4 dl/g. The change in intrinsic viscosity of excised implants with implantation time is shown in Fig. 8. 

Estimated onset of weight loss during in vivo degradation of homo and copolymers in dependence on initial intrinsic viscosity. 

Fig. 1. Relative molecular weight (A,B,C), relative intrinsic viscosity (D) of the residue versus conversion in pyrolysis of poly(methyl methacrylate) (PMMA) (3) and polyethylene (PE) (2). PMMA initial molecular wei t A, 44,000 B, 94,000 and C, 725,000. PE initial intrinsic viscosity D, (> ]o = 20 dL/g.

The present authors12,13) also studied the polymerization of 2 with boron tri-fluoride etherate as the initiator. High molecular weight polymers with intrinsic viscosities up to 1.87 dl/g were obtained in methylene chloride at —78 °C. The polymers melted at 160—180 °C, and showed some crystallinity as observed by X-ray diffraction. 

Sam- ple Nr Kind of initial material for pectin extraction Extraction time min Yield of pectin, g per 200 g fresh material AUAC, % DE, % Molecul mass Mv Huggins constant Kh Intrinsic viscosity [ft] dl.g- Gel. strengtl TB... 

All copolymers were prepared by solution polymerization, under adiabatic conditions, giving at least 99.9% conversions. The polymer gels were granulated and then dried at 90 °C to a residual water content of 10 to 12%. The active polymer content of each sample was calculated from the initial weight of the comonomers and the weight of the dried gel. Hydrolysis of the polymers was determined by conductometric titration to be less than 0.2% of the acrylamide charge. The molecular weight of the polymers was 8-10 million as determined by intrinsic viscosity measurements. 

Anionic polymerization techniques were also critical for the synthesis of a model cyclic triblock terpolymer [cyclic(S-fo-I-fr-MMA)] [196]. The linear cctw-amino acid precursor S-fr-I-fr-MMA was synthesized by the sequential anionic polymerization of St, I and MMA with 2,2,5,5-tetramethyl-l-(3-lithiopropyl)-l-aza-2,5-disilacyclopentane as the initiator and amine generator, and 4-bromo-l,l,l-trimethoxybutane as a terminator and carboxylic acid generator. Characterization studies of the intermediate materials as well as of the final cyclic terpolymer revealed high molecular and compositional homogeneity. Additional proof for the formation of the cyclic structure was provided by the lower intrinsic viscosity found for the cyclic terpolymer compared to that of the precursor. 

In addition, data on the size, shape and solvation of the polymer particles in aqueous solutions at temperatures below and above the transition phenomena registered by HS-DSC have been obtained [42]. Table 2 shows the results of capillary viscometry and light scattering experiments for the fractions p and s of poly(NVCl-co-NVIAz) synthesized at 65 °C from the feed with the initial molar comonomer ratio equal to 85 15. Since fraction p precipitates from the aqueous solution at temperatures > 34 °C, its intrinsic viscosity can be determined only at 20 °C, whereas for the fraction s such measurements were possible above and below the temperatures of the HS-DSC-registered conformational transition. 

Schulze and Crouch [7] observed that the viscosity of the soluble fraction of copolymers from butadiene and styrene decreased sharply with the conversion after an initial increase up to the point of gelation. This decrease could not be solely attributed to a selective incorporation of higher molecular mass fractions in the gel, thus leaving fractions of low molecular mass in solution. Cragg and Manson [8] reported a similar relationship between the intrinsic viscosity and the fraction of the crosslinking DVB in the ECP with styrene. Within the concentration range up to 0.1 mass % of DVB no gel was formed. Therefore, a selective removal of species with a high molecular mass could not have taken place to explain the decrease in the intrinsic viscosity observed after its increase at lower concentrations of DVB. 

Figure 2.19 Intrinsic viscosity of the polymer melt as a function of extruder residence time and temperature for an initial water content of 3 ppm...

Besides the main depolymerization reactions, side reactions should also be considered in the kinetic description of a PET recycling process. This is emphasized by the results obtained from a PET extrusion model [85] shown in Figures 2.19-2.23. The complete set of reactions summarized below in Table 2.10 have been used, but shear effects have not been taken into account. Chain degradation, accompanied by a significant reduction of intrinsic viscosity, occurs even within residence times of a few minutes. Carboxyl end groups, vinyl end groups and acetaldehyde are formed in amounts depending on residence time, temperature and initial moisture content of the PET flakes. 

Coupling Reagent Wt. of Reagent (g)a Intrinsic Viscosity (dl/g) Initial Pol. Product ... 

Figure 3. Intrinsic viscosity of polystyrene samples, irradiated in benzene solution in the presence of initiator I-III. Polystyrene concentration 7.69x10 2 M, photoinitiator concentration 2.31 x 10-3 Ml p Pure polystyrene initiator I initiator II A initiator III. (Reproduced with permission from Polym. Deg. Stability Ref. 21).

Figure 4. Intrinsic viscosity of polystyrene samples irradiated in benzene solution under various conditions. Polystyrene concentration 7.69x 10-2 M and initiator I concentration 3.12x 10-3 M. vacuum nitrogen saturated air saturated V oxygen saturated 3.12 3 / 3-tert-butyl-4-hydroxyanisole 3.12x 10-3 M 1.4-diazobicyclo(2.2.2)-octane (DABCO).

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