Branched conformational properties of macromolecules in close relation to chemical synthesis. I. Unperturbed structures.

Similar to uniform linear chains, the unperturbed structure of branched polymers forms the basis for the development of a theory on the effect of excluded volume interactions. A clear overview over the skeleton of such complex structures is obtained with a simplifying modification of the general branching theory. The use of probability generating functions permits a direct incorporation of essential details from the chemical synthesis in this branching theory. The unperturbed structure parameters, the degree of polymerization DP(w), radius of gyration R(g), hydrodynamic radius R(h), and the angular dependence of scattered light P(q) are derived for three examples: (i) randomly branched f-functional polymers, (ii) branched copolymers from A3 with B2 monomers, and (iii) AB2 hyper-branched particles. The effect of excluded volume interaction is treated in Paper II [J. Chem. Phys. 143, 114907 (2015)].

Branched conformational properties of macromolecules in close relation to chemical synthesis. II. Influence of excluded volume interactions.

The description of perturbed particle conformations needs as a prerequisite the algorithm of unperturbed chains which is outlined in Paper I [J. Chem. Phys. 143, 114906 (2015)]. The mean square segment length ⟨r(2)(n)⟩=b(2)n(2ν) with ν = 0.588 for linear chains in a good solvent is used as an approximation also for branched samples. The mean square radius of gyration is easily derived, but for the hydrodynamic, the segment distribution by Domb et al. [Proc. Phys. Soc., London 85, 624 (1965)] is required. Both radii can analytically be expressed by Gamma functions. For the angular dependence of scattered light, the Fourier transform of the Domb distribution for self-avoiding random walk is needed, which cannot be obtained as an analytical function and was derived by numerical integration. The summation over all segment length in the particle was performed with an analytic fit-curve for the Fourier transform and was carried out numerically. Results were derived (i) for uniform and polydisperse linear chains, (ii) or f-functional randomly branched polymers and their monodisperse fractions, (iii) for random A3B2 co-polymers, and (iv) for AB2 hyper-branched samples. The deviation of the Gaussian approximation with the variance of ⟨r(2)(n)⟩=b(2)n(2ν) slightly overestimates the excluded volume interaction but still remains a fairly good approximation for region of qR(g) < 10.

Dendronized Hyperbranched Macromolecules: Soft Matter with a Novel Type of Segmental Distribution.

Dendronization of a hyperbranched polyester with different generation dendrons leads to pseudo-dendritic structures. The hyperbranched core is modified by the divergent coupling of protected monomer units to the functional groups. Compared to dendrimers, the synthetic effort is significantly less, but the properties are very close to those of high-generation dendrimers. The number of functional groups, molar mass, and rheology behavior even in the early generation (G1-G4) pseudo-dendrimers strongly resembles the behavior of dendrimers in higher generations (G5-G8). Comparison of the segmental and internal structure with perfect dendrimers is performed using SANS, dynamic light scattering and viscosity analysis, microscopy and molecular dynamics simulation. The interpretation of the results reveals unique structural characteristics arising from lower segmental density of the core, which turns into a soft nano-sphere with a smooth surface even in the first generation.

Is the universal law valid for branched polymers?

A matter of phis: The size of macromolecules is determined by the "universal calibration" based on the Flory-Fox equation (see scheme). The effect of the segmental density of real branched systems on this equation is investigated. To study this effect, accurately prepared polymers with discrete molecular properties were characterized in detail and precisely evaluated.

Simultaneous determination of substituent patterns in partially acid hydrolyzed O-Me/O-Me-d(3)-cellulose and quantification of the obtained oligomers by HPLC-ESI-MS.

Substituent patterns in oligosaccharide derivatives obtained from methyl cellulose were determined up to DP10 by electrospray ionization mass spectrometry employing separation of the oligomer fractions by HPLC. Oligosaccharides were labeled with meta-aminobenzoic acid after perdeuteromethylation and partial hydrolysis of methyl cellulose, enabling simultaneous quantification according to DP by HPLC/UV. Control of the HPLC-method was performed with a defined oligomer mixture obtained from ß-cyclodextrin. Results from LC-ESI-MS are discussed in comparison with those from syringe pump injection and compared to a calculated pattern for a random distribution. Programing of instrumental parameters optimized for each DP and avoidance of competition of successively eluting analytes in the electrospray process allowed extension of the established method for determination of the substitution pattern of cellulose derivatives along the polymer chain from DP5 to DP10 and thus a significant gain of information.

Solution properties of conventional gum arabic and a matured gum arabic (Acacia (sen) SUPER GUM).

Dilute solution properties of two specially matured gum arabic samples (EM1 and EM2) were compared to the conventional gum (EM0) using static light scattering. The apparent molar mass (M(w,app) and radius of gyration (R(g,app)) for the three samples showed unusual concentration dependence. These data were satisfactorily interpreted by a simple association model that takes into account the repulsive interaction among clusters, which allowed us to obtain the true molar mass (Mw(0)) and radius of gyration (Rg(0)). A common power law relation was observed between Mw(0) and Rg(0) , giving a somewhat higher exponent than expected for linear and branched polymers in a good solvent. Mw(0) and Rg(0) obtained for the three gums do not differ significantly from each other. However, the data showed clearly a constant increase of the association from EM0 to EM2 with increasing concentration. This is in accordance with the previously observed improved functional properties for the matured products.

Carbanilation of cereal beta-glucans for molecular weight determination and conformational studies.

Cereal beta-glucans can form aggregates in aqueous solution. The presence of aggregates in cereal beta-glucan solutions led to inaccurate determination of molecular weights and it was believed that intermolecular hydrogen bonding caused the aggregation. To eliminate aggregates, a carbanilation method for molecular weight determination of cereal beta-glucans was developed. Wheat beta-glucan samples were selected for investigation. The carbanilation method can prevent intermolecular hydrogen bonding by blocking hydroxyl groups with phenyl carbamate groups. The carbanilates of cereal beta-glucans were prepared by the reaction of cereal beta-glucans with phenylisocyanate catalyzed by DMSO and pyridine. To avoid degradation during the carbanilation reaction, relatively mild conditions were used, which led to incomplete substitution (DS: approximately 2). However, after the carbanilation reaction, the carbanilates dissolved completely in 1,4-dioxane solution without any detectable aggregates, which allowed accurate molecular weight determination. The degree of substitution (DS) of carbanilates was determined by both a nitrogen content method and an FT-IR method. The FT-IR method proved to be the more effective for DS estimation. Using this method, the converted molecular weights of cereal beta-glucans were in good agreement with the results measured in 0.5M NaOH solution, which previously was shown to be a good solvent for cereal beta-glucans. After the carbanilation reaction, conformational changes of carbanilates were studied by static and dynamic light scattering techniques. The fractal dimension (d(f)=2.27) and the structure sensitive parameters (rho >2) suggested a porous globular structure for partially carbanilated beta-glucans.

Chain dynamics in microgels: poly(N-vinylcaprolactam-co-N-vinylpyrrolidone) microgels as examples.

Microgels are highly swollen colloids built up of flexible cross-linked chains. We studied the static and dynamic light scattering (LS) behavior of thermosensitive microgels based on N-vinylcaprolactam and N-vinylpyrrolidone prepared by precipitation copolymerization in H2O (CP-1) and D2O (CP-2). Striking differences in behavior were observed in the two solvents. In both cases the angular dependence of static LS could reasonably well be described by a soft sphere model (J. Polym. Sci., Polym. Phys. Ed. 1982, 20, 157) with small deviations at large qRg. At temperatures larger than the collapse temperatures, the CP-1 sample in water started to aggregate whereas the CP-2 sample in D2O showed no association and developed the expected change toward hard sphere behavior. Dynamic LS permitted the determination of internal or segmental mobility. A remarkable shift toward large qRg was found for CP-1 compared to the behavior of linear chains. The dynamic behavior is clearly displayed in a plot of Gamma*(q) = (Gamma1(q)/q3)(eta0/kT), with Gamma1(q) the first cumulant of the field time correlation function and the common meaning of the other parameters. A long range of hard sphere behavior indicated the suppression of internal modes, but at large qRg the swollen microgel CP-1 in water displayed internal motions with a spectrum similar to that of Zimm relaxations. No internal mobility could be detected with the CP-2 sample in D2O. The behavior is in agreement with observations in the literature. The differences in the two similar solvents were attributed to the poorer solvent quality of D2O.

Molecular characterisation of soybean polysaccharides: an approach by size exclusion chromatography, dynamic and static light scattering methods.

Water soluble polysaccharides from soybean (SSPS) have a pectin-like structure and are used as stabilisers in acidified beverages. Physicochemical properties such as structure, molecular weight and shape or conformation are primary factors controlling their functional properties. Two soybean polysaccharides, a native SSPS and a modified SSPS treated with beta-(1-->4)-D-galactosidase (GPase/SSPS) were studied by dynamic and static light scattering (DLS, SLS) and size exclusion chromatography (SEC). Consecutive filtrations using a range of membrane pore size removed a small fraction of macromolecular aggregates from dilute polysaccharide solutions with relatively little effect on the major component molecules as monitored by DLS and SEC measurements. Access to aggregate-free dilute solutions of SSPS and GPase/SSPS allowed the direct measurement of molecular characteristics. SLS results showed that SSPS had a weight average molecular weight of (645+/-11)x 10(3)g/mol and a radius of gyration, Rg, of (23.5+/-2.8)nm. By comparing R(g) with the hydrodynamic radius, Rh (21.1+/-0.5 nm) obtained from DLS, the structural parameter rho (Rg/Rh) was found to be 1.1, suggesting that SSPS has an overall globular shape due to a highly branched structure. The modified SSPS had a significantly lower molecular weight (287+/-18)x 10(3)g/mol but a similar radius of gyration (23.2+/-1.7 nm). The structure parameter rho of GPase/SSPS was higher (rho=1.3) because of a smaller hydrodynamic radius (17.7+/-1.8 nm). This suggests that GPase/SSPS has a much less branched structure yet still differs significantly from a linear random coil conformation (rho=1.7-2.0). The results derived from SLS and DLS are in agreement with the conclusions obtained from a chemical analysis where the reduction of molecular weight of GPase/SSPS was caused by the cleavage of galactan side chains.

Shear-induced mixing and demixing in aqueous methyl hydroxypropyl cellulose solutions.

The influence of shear flow on the phase separation of aqueous methyl hydroxypropyl cellulose solutions was investigated by means of rheoturbidity and online rheo small angle light scattering (SALS) experiments. In semidilute solution shear-induced mixing was observed and the cloud curve was shifted to higher temperatures with increasing shear rate. With higher concentrated solutions, however, shear-induced demixing was found. The shear-induced mixing is interpreted as being a disruption of slightly entangled clusters under the influence of the shear energy. The shear demixing appears in line with the observation with other systems. A characteristic butterfly pattern was observed in rheo-SALS.

Structure of artificial cytoskeleton containing liposomes in aqueous solution studied by static and dynamic light scattering.

The structure of three types of liposomes (egg yolk phosphatidylcholine (EPC) without modification and EPC vesicles containing cross-linked N-isopropylacrylamide (NIPAM) networks of low and a high concentration inside the vesicles) were analyzed by static and dynamic light scattering. Upon polymerization the network was assumed to become attached to the membrane by reactive anchoring monomers. For the sample of high poly(NIPAM) content the polymer network was assumed to fill the whole space in the vesicles. The issue of the present study was to examine hard and hollow sphere behavior of the liposomes with networks of high and low poly(NIPAM) content. The theoretical scattering curves differ markedly for uniform hard and uniform hollow spheres by the presence of specific peaks. However, polydispersity washed out the peaks and led to smoothed asymptotes with fractal dimensions of df = 2 for hollow and df = 4 for hard spheres. The experimental data could efficiently be fitted with weakly polydisperse hollow spheres. No clear conclusion could be drawn from the angular dependence alone for the liposome of high poly(NIPAM) content. The two wavelengths from the HeNe and Ar lasers proved to be too long for the studied liposomes of about 100 nm in radius. However, evidence for hollow sphere behavior was found for fractionated liposomes from the ratio rho = Rg/Rh = 1.04 +/- 0.02 (theory rho = 1.00 for hollow spheres). Finally, from the molar mass and the sphere radius, an apparent density was determined. The analysis gave the expected density for the pure EPC lecithin vesicles and a poly(NIPAM) network density of 0.244 g/mL. For the liposome of low poly(NIPAM) content the network appeared to be attached to the inner surface of the lecithin shell to form a layer of about 18 nm thickness.

Peculiarities of aqueous amaranth starch suspensions.

Among the starches the granules from amaranth starch (a. hypochondriacus, amylopectin type) are singular because of their extremely small size of 1-3 microm and high uniformity. However, large spherical particles of 30-80 microm in diameter were observed from spray-dried amaranth starch by environmental scanning electron microscopy (ESEM) which exhibited a characteristic fine structure. After the mixture was stirred in cold water, the large particles disintegrate into small ones of 1-3 microm diameter. The particles from the stirred suspension were characterized by static and dynamic light scattering and viscometry. Almost the same diameters were found by the three techniques which were 1.76 times larger than those for the dry starch particles investigated by ESEM. The difference in size is explained by reversible uptake of water. A molar mass of M(w,granule) = 177 x 10(9) g/mol was measured for the granular particle. After dissolution in 0.5 N sodium hydroxide a molar mass M(w,amylopectin) = 104 x 10(6) g/mol of the amylopectin was obtained that agreed satisfactorily with that of waxy maize. Thus the granule consists on average of 1700 amylopectin molecules. Furthermore, rheological measurements were carried out with aqueous suspensions at room temperature. A shear gradient dependence was found for concentrations higher than 6% (w/v) of granules. At c > 19% reversible gel formation was observed with G'(omega) > G"(omega) and a plateau over 2 decades. The zero shear viscosity as a function of c[eta] shows behavior similar to glycogen and to latex particles. The granules, however, differ from common latex particles because of their capability to gel formation.