Branch length advantages

Figure 45 shows another example of the dependence of polymer physical properties on the branch length. Copolymers were made with Cr/silica catalyst to have the same approximate density and MI. Various comonomers were used, ranging from propylene to 1-octene. The ESCR of each polymer was then determined and is plotted against the number of carbon atoms in the comonomer. There is a clear advantage associated with longer branch lengths. 

Table I shows the results of periodate oxidation and methylation applied to amylopectins from various sources. If the percentage of amylose in a whole starch is known, the length of unit chain of the amylopectin component can be calculated from the results of periodate oxidation of the whole starch (see Table II). The length of unit chain appears to depend on the botanical species, but not the variety, from which the starch wras isolated. In the case of tapioca and corn amylopectins, sub-fractionation of these by precipitation with methanol, followed by periodate oxidation, showed the sub-fractions had the same degree of branching as the original amylopectins.71 The action of periodate on whole starches and amylopectins is now so well established and accurate, that it may well completely supersede the methylation technique for pure starches, in view of its many advantages.

An advantage of these condensation reactions consists in the possibility to regulate the number and length of the branches which will be attached to a given stem. 

The advantage of the system arises from the fact that, since the poly(chloroethyl vinyl ether) (PCEVE) backbone and PSt grafts can be prepared by both living cationic and anionic polymerization, it is possible to synthesize graft copolymers that possess both a backbone with controlled dimensions and an adjustable number of branches of precise length and narrow molecular weight distribution. 

Alcohol ethoxylates are relatively inexpensive and readily available, and are considered to be one of the key work-horse surfactants. The primary advantage of alcohol ethoxylates, however, lies in the flexibility of their structure. The hydrophobe can vary in terms of carbon chain length (from Ca to C20+), carbon chain distribution (single homologues or various blends), feedstock source (petrochemically based or oleochemically based), and the degree of minor (methyl) branching. 

Commercial versions contain several isomers in which Ri, R2, and R3 are alkyl gronps of varying length but with a total of 8 carbon atoms. The mixed carboxylic acid precnrsors of these highly branched esters are collectively called neodecanoic acid [27], and the ester is then called vinyl neodecanoate (VN). The advantage of VA/VN copolymers over other VA copolymers is greater hydrolysis resistance and increased hydrophobicity [27]. These advantages are realized at relatively low cost. Developments such as this are likely to increase the rate of conversion to waterborne systems. 

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