The influence of molecular weight (900 to 1.8 × 106) on the glass transition temperature of low polydispersity polystyrene (anionically prepared) has been studied by differential scanning calorimetry at heating rates of 5 to 80 °C min−1. Over the range of molecular_weight studied, and at an extrapolated heating rate of 1 °C min−1,[Formula: see text] A thermally prepared polystyrene sample ([Formula: see text]and Pd = 3.2) showed a Tge value of 93 °C, some 10° below the value predicted by the above equation. Low molecular weight species in the highly polydisperse sample are believed to be responsible for the discrepancy. The changes in heat capacity brought about by the glass transitions are accompanied in all cases on heating by an endothermic peak and this regardless of the heating rate (even extrapolated to 1 °C min−1) or the molecular weight of the sample, suggesting that the glass transition phenomenon encountered with polystyrene is a process involving a positive heat effect.

Aminosilanes hydrolyze rapidly in aqueous acidic solutions and exhibit good stability; however 1H NMR measurements indicate that γ‐MPS (γ‐methacryloxypropyltrimethoxy silane) hydrolyzes slowly and condenses rapidly under similar conditions. The rate constant of these two reactions depends upon the pH of the solution, and the rate constant of the condensation reaction also depends upon the initial γ‐MPS concentration. The hydrolysis is faster and the condensation slower at low pH's. These factors explain why an induction period is observed before the adsorption of γ‐MPS onto mica takes place and why it does not occur if the induction period is too long. Using the Lentz technique, it is also shown that the main species resulting from the condensation of a concentrated γ‐MPS solution is a cyclic trimer or tetramer, in agreement with literature results.

No abstract

No abstract

SynopsisCarbon analysis was used as a method for measuring the quantity of a cationic vinyl benzyl silane (CVBS) adsorbed onto the surface of mica. The results obtained indicate that CVBS can be applied from aqueous solution over a wide pH range with best treatment in neutral and acidic media. The amount adsorbed depends on the concentration of the treating solution in the lower concentration range while in the higher range, the adsorption is less dependent on concentration. The relationship, silane adsorption vs. time of treatment, shows a steplike dependence. It is suggested that each step corresponds to a monolayer coverage. The data indicate that CVBS on mica is a highly ordered and closely packed multilayer phase with the silane molecules oriented normal to the surface. The multilayer adsorption of silane onto silane in this system may be compared in some respects to polymer crystal growth.