The synthesis of two types of polystyrene with dendritic branching was achieved through the development of a novel method that combines living anionic polymerization with a convergent process in a one-pot reaction. The method is based on the slow addition of a reactant such as 4-(chlorodimethylsilyl)styrene (CDMSS), which contains a polymerizable vinyl group and a moiety capable of undergoing quantitative SN2 reaction, to a solution of living polystyryl anions. The sequence of reactions results in star-shaped polymers with the initial chains forming the arms and the residue from the CDMSS forming a hyperbranched core. Different amounts of styrene monomer were added along with the CDMSS in order to increase the molecular weight between branch points. The molecular weights and polydispersities of the dendritic polystyrenes were characterized by GPC coupled with MALLS. The molecular weights of dendritic polystyrenes without added comonomer corresponded to dendritic growth of the core of 3.1−3.4 average generations with polydispersities less than 1.5. The observed narrow molecular weight distributions were interpreted using a kinetic model that relates increased steric hindrance around the reactive site to the reaction rate constants of different size dendritic polymers formed during the reaction. Adding a comonomer along with the coupling agent allowed for the synthesis of high molecular weight dendritic polystyrene (up to M n > 600 000 g/mol) and generational growth approaching an average of six generations. Intrinsic viscosities of all dendritic polystyrenes produced were found to be much lower than that of linear polystyrene. Thermal analysis of the dendritic polystyrenes showed that T g versus molecular weight corresponded well to that of linear polystyrene normalized to the number of end groups, being slightly higher due to the effect of branching.

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Polylactides (PLA) have been known for several decades and are recently of considerable commercial significance. However, the literature on basic chain properties and solution characterization is divided and inconsistent. In this study, a comprehensive and well‐controlled set of experiments is combined with rigorous quantitative analysis to resolve existing apparent contradictions. Homopolymers and copolymers spanning wide ranges of molecular weight and stereoisomer proportions were prepared by ring‐opening polymerizations of L‐ and D‐lactides using stannous octanoate as the catalyst. Samples were characterized by means of: (1) dilute‐solution viscometry in three different solvents; (2) size exclusion chromatography in tetrahydrofuran (THF) with light scattering detection; (3) static multiangle light scattering in a mixed acetonitrile–dichloromethane solvent; (4) variable‐angle spectroscopic ellipsometry; and (5) melt rheology. The data imply that PLA are typical linear flexible polymers; unperturbed PLA chain dimensions are describable in terms of a characteristic ratio of 6.5 ± 0.9, regardless of stereoisomer content. The Schulz‐Blaschke and Mark‐Houwink constants for dilute PLA solutions in chloroform and in THF are determined. For chloroform at 30°C, the correct values are kSB = 0.302, K = 0.0131 (mL/g), and a = 0.759, while for THF at 30°C, the correct values are kSB = 0.289, K = 0.0174 (mL/g), and a = 0.736. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3100–3111, 2005

The development of base-stable cationic groups for anion exchange membranes is important for application in alkaline fuel cells.

Unique rheological properties of combined low melt viscosity and high melt elasticity are reported for a novel series of dendritically branched polystyrenes. Unlike previous studies, dendritically branched materials having different molecular weights but all possessing the same number of generations are studied; this allows the determination of true scaling relationships. Zero shear viscosities scale with the second power of molecular weight until corrected to a state of constant free volume, upon which they scale with the first power of molecular weight. Importantly, the steady state shear compliance for the materials increases with increasing molecular weight and is very large compared to other chain architectures. This finding holds potential technological importance as it may be possible to simultaneously decrease viscosity and increase elasticity by blending with these novel structures. Dynamic light scattering and small-angle neutron scattering studies demonstrate the self-similar nature of these highly branched polymers, thereby establishing that the chain architecture is well-defined. Evidence of entanglements is missing. Remarkably, this implies that it is possible to prepare unentangled polystyrenes having a molecular weight in excess of 1 000 000 (g/mol). Melt dynamics are complex; exhibited behavior encompasses aspects of both classical Rouse-Zimm response and the power-law behavior associated with fractal or gelling systems. Neither Rouse-Zimm nor power-law relaxation time distributions are capable of quantitatively describing the data. However, the corrected viscosity scaling and the viscosity shear thinning behavior are in rough agreement with a theory of polymeric fractals proposed by Muthukumar [