Abstract
A copolymer of ethylacrylate(EA) and 2-chloroethylacrylate(CEA)(95/5 wt%), one of polyacrylate rubbers, has been vulcanized by using tetraethylenepentamine (TEPA) as a curing agent (Table 2, Table 3).
The molecular weight Mc, between crosslinks of vulcanized rubber was plotted against the number average molecular weight Mn of the uncured sample (Table 4, Fig. 1, Fig. 3). For fractionated samples, the critical primary molecular weight, above which the effect of polymer ends does not occur, was estimated from the relation between logMc and logMn (Fig 1). The critical primary molecular weight decreased with increasing amount of TEPA or degree of cross linking, on account of the effect of network imperfection resulting from chain ends (Fig. 3).
Mc, the corrected values of Mc for imperfection resulting from chain ends for samples of low molecular weight and those obtained by using small amounts of curing agent, were smaller than those of the vulcanized samples obtained from rubber with high primary moleeular weight and those obtained by using large amounts of curing agent (Fig. 1, Fig, 3, Fig. 6), because the Mc values were affected by the number (fraction) of chain ends of cured rubber. The sol fraction of cured sample has been investigated with respect to primary molecular weight of sample (Fig. 2) and amounts of curing agent (Fig, 4). The sol fraction was nearly zero with respect to the sample having molecular weight above the critical primary molecular weight. The critical molecular weight decreased as the amount of the curing agent increased(Fig. 4). Effects of curing time on properties ef cured samples have been investigated by using the curves between Mc and Mn, and those between sol fraction and Mn (Fig.5, 7), The cross linking efficiency of TEPA was about 50 percent (Table 5). The rate of formation of cross linking was constant for samples in the wide range of primary molecular weight (Fig. 6).
