Journal of Polymer Science: Polymer Symposia最新文献

A mean field theory for diffusion-controlled cluster formation is presented by considering the competition among the different protions of a growing cluster for the incoming diffusive particles. This competition is shown to introduce a screening length that depends inversely on the density of the cluster. The Hausdorff dimensionality D of these clusters is shown to be (d² + 1)/(d + 1), where dis the eudidean dimensionality. This result is in excellent agreement with that of the computer simulations of Witten and Sander and Meakin. The theory also predicts that the growth of these clusters occurs on their periphery in any d.

PACS nos: 68.70,+ w, 82.70.Dd, 05.70.-a

Water-insoluble diols and dicarboxylic acids condense to polyesters in aqueous emulsion under relatively mild conditions in the presence of sulfonic acids. Azelaic acid and 1,10-decanediol give conversions to polymer of 50% and 75%. Molecular weights range between 1500 and 3000. The best catalysts are sulfuric acid or the sulfonic acid surfactants. Water soluble monomers give little or no increase in molecular weight. Estimates based on equilibrium constants for a typical esterification, and the observed molecular weights indicate that only minute amounts of water can be present at the site of reaction. It is suggested that the process might be related at least in some aspects to the condensation polymerization of silanol-ended polydimethylsiloxane oligomers in emulsion [1].

Membranes in the form of hollow fibers are increasingly being used for processes such as desalination, hemodialysis, and recovery of various gases. Turner Alfrey played a crucial role in the birth of this new technology: (1) He selected and taught the necessary fundamentals of polymer science to the researchers trying to make this new idea work. (2) He actively encouraged the researchers and their financial supporters by his clear understanding of the soundness and the potential of this new engineering tool. (3) He even demonstated how to tailor the properties of a polymer to the task at hand by his own elegant laboratory experiments.

Given good reactivity ratio data for free radical vinyl copolymerizations, the use of the Alfrey—Price Q—e scheme permits the assignment of reactivity parameter values for individual monomers and the prediction of unknown reactivity ratios. A new, statistically based method has been developed and tested on a set of 11 monomers to estimate Q–e values for those monomers. The results of these estimates suggest that if care is exercised in the selection of monomer pairs for use in Q–e determinations, the Q–e scheme is quite reliable for reactivity ratio prediction on many monomer pairs.

Examples of functional monomers and latex polymers are described. Use of functional monomers allows great versatility in the design of latex polymers with specialized properties. Included are examples of electrophilic, nucleophilic, crosslinkable, hydrolyzable, and metalion-chelating monomers.

A discussion of some current ideas on the molecular processes of rubber deformation is presented. Reference is made to some important experiments and to suggestions which have been proposed for their explanation.

During the past decade or more, the composite materials community has restricted itself primarily to the use of only a few structural epoxy matrix materials. Very recently, whole new families of polymer matrices have become of practical interest. In order to select from this wide range of new polymers for each specific structural application, the relation between the various polymer mechanical and physical properties, e.g., modulus, strength, strain to failure, thermal and moisture expansion coefficients, moisture absorption rate, etc., and resulting composite properties must be known. Correlations of finite element analysis predictions with actual experimental data will be presented, using measured mechanical and physical response properties of various toughened epoxy, bismaleimide, polyimide, and thermoplastic matrix systems as inputs to the analyses. Results will include fracture mechanics evaluations, the role of matrix nonlinear response, crack initiation and propagation, thermally induced damage, and the influence of the interface. Matrix properties to be modeled have been generated in the author's own laboratories, as part of several current and ongoing funded research studies for various government and industry groups. Several types of finite element analyses have been used, including 2-dimensional generalized plane strain with longitudinal shear loading, 2-dimensional axisymmetric, and fully 3-dimensional formulations. All of these analyses permit the input of actual matrix nonlinear stress-strain response, and how it varies as a function of temperature and moisture content. Fibers having anisotropic properties in a composite of arbitrary fiber volume are included. Time-dependent response, e.g., creep, recovery, and relaxation, and crack propagation are also possible response modes. Results will be presented in the form of composite stress-strain curves, plots of stress contours in the matrix, and at the fiber-matrix interface.

Laser light scattering has been used to study the static and dynamic properties of polymers in solution. Interpretation of the intermediate scattering function S(K, t) from the center-of-mass diffusion to internal motions for both polymer coils and semiflexible chains is discussed. Crossover behavior of dynamic properties in dilute and semidilute solution regimes for polymers of finite molecular weight, instead of limiting scaling law exponents, is emphasized.

The complimentary nature of modern scattering techniques, as well as the use of specific probes, including anomalous scattering with synchrotron radiation, are likely to play an increasingly important role in investigating more complex interacting polymeric species, such as block copolymers, polyelectrolytes, and ionomers.

Measurements of time correlation function and methods of data analysis have been developed to determine the molecular weight distribution of synthetic polymers in dilute solution. In addition to center-of-mass diffusion studies in dilute solution from the good solvent region to the collapsed state, determinations of both cooperative and self-diffusion coefficients in semi-dilute solutions are within reach. Further quantitative analysis of S(K, t) awaits better theoretical models in the intermediate K range in semidilute solutions.

Kinetics of gelation by additive polymerization on a two-dimensional lattice were investigated with a Monte Carlo simulation. We have determined the critical component γ and the ratio R of the critical amplitudes of the weight-average degree of polymerization (“susceptibility”) to be γ = 3.8 ± 0.5 and R = 140 ± 45. These results show that this model is neither in the universality class of standard percolation (γ ± 43/18 ± 2.38; R = 219 ± 25) nor the Flory-Stockmayer model (γ = 1, R = 1).