The effect of chain branching on the dynamic mechanical properties of polyethylene within the temperature region 80 to 380°K. has been studied using an apparatus which drives rod‐like specimens in their transverse modes. The results for three types of polyethylene having 3.2, 1.6, and less than 0.1 branches per 100 carbon atoms of the main chain are compared and discussed. Experimental results indicate that all of the three main dispersion regions (α, β, γ) characteristic of polyethylene are affected to some extent by branching. The β region, starting near 230°K., decreases with decreased branching, and for polyethylene which has negligible branching it is almost entirely absent. This suggests a direct relation between the number of branch points and the size and shape of this peak. The γ dispersion region near 170°K. appears sharper and shifted to higher temperatures with decreased branching, this being attributed to a narrowing of the relaxation times associated with the movement of a small number of CH2 units. The α dispersion region near 370°K. is also shifted to higher temperatures with decreased branching in accord with the shift of melting temperature with degree of crystallinity.

SynopsisThe dynamic mechanical properties of a polyimide (poly-4,4 '-0xydiphenylene pyromellitimide) were studied from about 4 to 800°K. a t audio frequencies. A prominent relaxation associated with absorbed water content occurs near 230°K. Below 270°K., the modulus undergoes a corresponding increase in value with increasing water content. Above 550°K. the onset of a major relaxation process is observed in the modulus data, and a maximum in the internal friction is observed at about 675°K. Minor relaxation peaks are also noted throughout the temperature range. Relatively minor differences are noted in the mechanical relaxation spectra for the polyimide when treated (after drying) with dimethylformamide, dimethylacetamide, and dimethylsulfoxide, whereas the treatment with water after drying has a marked effect on the relaxation behavior.

The dynamic mechanical properties of polymerized epoxy resins have been studied over the 80—600°K. temperature region using an appratus which drives rodlike specimens in a transverse mode. Experimental results for the mechanical loss indicate several dispersion peaks throughout the temperature range. The dynamic modulus is found to be monotonically decreasing everywhere except near the 480—550°K. range. Effects of cure time, filler, and low dose irradiations are included in the investigation.

A study of the thermal conductivity of some amorphous and partially crystalline polymers as a function of temperature (0–100°C.) is described. Experiments have been carried out, with the use of a thermal conductivity cell with cylindrical geometry, on polyethylene, polytetrafluoroethylene, polystyrene, polyhexamethylene adipamide, and polymerized epoxy resin. Results indicate that the conductivity of amorphous polymers increases with temperature and that the conductivity is significantly higher in crystalline regions than in the amorphous regions. Data concerning the change of thermal conductivity of polymerized epoxy with the addition of powdered aluminum filler are given. The results presented in the paper are discussed and compared with those reported by other investigators.

synopsisThe dynamic mechanical properties of epoxy resins cured with nonstoichiometric amounts [37yo-l03% of stoichiometric composition (SC)] of diethylenetriamine a t room temperature have been measured in the temperature range 85" to 300°K and correlated to structures of cured resins. The dynamic mechanical behavior changed above and below 62.5% of SC, at which network structures are formed. The intensities of 7-and @-peak%, -150" and -250°K, respectively, depend upon the concentration of DETA used. The processes of the y and 8-peaks are discussed.