ISSN:
1435-1528
Keywords:
Specific heat
;
glass temperature
;
flow temperature
;
liquid-liquid transition
;
surface tension
;
melt viscosity
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Abstract Using objective computerized statistical procedures, we have examined high precisionC p data by DSC reported by Wunderlich and Gaur for a series of alkyl acrylate and methacrylate polymers. Although they claimed the data to be linear inT aboveT g , our results do not support the linear model. One or two endothermic slope changes are revealed aboveT g in lowT f polymers (T f 〈 20 °C) and at least one exothermic slope change in highT f polymers (T f 〉 20 °C).T f is the flow temperature of Ueberreiter. Both the first endotherm and the first exotherm occur near (1.22 ± 0.07)T g , suggesting aT ll type phenomenon.T ll varies as $$1/\bar M_n $$ . The first exotherm is associated by us with wetting of the DSC pan by molten polymer on the first heating of particulate highT f polymers. The rate of wetting, and presumably the magnitude of the exotherm, depends in part on the ratio,γ/η, whereγ is surface tension andη is melt viscosity of the molten polymer. Sinceγ is relatively constant, the molecular weight and temperature dependence for rate of wetting resides inη, which depends on $$\bar M_w $$ . For $$\bar M_n 〉 〉 \bar M_c $$ , a second exothermic event caused by sintering, and also controlled by η, may be present. The interactive roles of $$\bar M_n ,\bar M_w ,\bar M_w /\bar M_n $$ ;M c (entanglement molecular weight); particle size, and heating rate onC p —T behaviour are delineated for the first time. LowT f hydrocarbon polymers, namely atactic polyalphaolefins,C 3 ,C 5 ,C 6 ; PIB; and dienes, PBD and cis-PI, exhibit single or double endotherms. Other results on highT f polymers showing exothermic effects, notably PS, PnBMA and polyglycidylmethacrylate are cited.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01332602
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