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Positional and compositional heterogeneity of partially modified poly(propyleneimine) dendrimers
Author(s) -
Froehling Peter E.,
Linssen Harry A. J.
Publication year - 1998
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/(sici)1521-3935(19980801)199:8<1691::aid-macp1691>3.0.co;2-y
Subject(s) - dendrimer , chemistry , branching (polymer chemistry) , steric effects , polymer chemistry , end group , distribution (mathematics) , stereochemistry , polymerization , organic chemistry , polymer , mathematical analysis , mathematics
The partial end group modification of dendrimers leads to two types of heterogeneity in the product's structure: compositional heterogeneity (distribution of degree of substitution) and positional heterogeneity (spatial distribution of the substitutents over the dendrimer molecule). Poly(propyleneimine) dendrimers were partially modified by direct amidation at 150°C with stearic acid. The compositional distribution (analysed by HPLC and ES‐MS) follows a random pattern, governed by a binomial distribution. The positional distribution can be expressed as the distribution of dyads AA (two unreacted end groups), AB (one unreacted, one reacted) and BB (both reacted), where a dyad consists of two end groups originating at a common final branching point in the dendrimer. 13 C NMR and a Cu(II) complexation titration were used for determining the dyad distribution. Lower generations of dendrimers give a random distribution of dyads. In higher generations a marked preference for single substitution of dyads was found, possibly caused by intramolecular interactions or steric hindrance.