ISSN:
0025-116X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The potentiometric titration of syndiotactic methacrylic acid/dimethacryloylamine (MMA-MAI) copolymers is investigated. In contrast to copolymers studied before, MAA-MAI copolymers possess a highly syndiotactic backbone structure, a compositional statistics known from NMR-measurements, and a cyclic structure as a part of the chain. The statistics of the MAA-units and MAI-rings is nearly random with respect to the formation of imide rings, the rings introducing a trans and a gauche conformation for each ring. Plots of the apparent pK (pKapp) versus the degree of ionization α, or versus log [(1- α)/ α], indicate a change from a relatively dense coil (a-state) to an extended coil (b-state) when α is increased. The decisive parameter for pKapp in the b-state and for the conformational transition of the a-state to the b-state is the charge density on the chain β. The transition takes place for all copolymer compositions in an interval of Δβ ≈1 but the interval is situated at lower absolute values of β for the copolymers with higher contents of MAI-rings. The Δβ at lower β may be either due to a decrease in intramolecular attraction or to a higher electrostatic repulsion. The free enthalpy of the conformational transition is, however, approximately the same for copolymers with different MAI contents. This constancy of the free enthalpy points to a conformational transition which is energetically not much different for the MAA- and the MAI-units in the chain.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1983.021840716
