Concentrated Solutions of Partly Deuterated Triblock Polybutadiene. Segmental Analysis of NMR Properties

• Published in: Macromolecules 2004-03, Vol.37 (6), p.2144-2150
• Main Authors: Schillé, Eric, Cohen Addad, Jean-Pierre, Guillermo, A
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Solution and gel properties
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma0304731

The comparison of proton transverse relaxation properties observed on polybutadiene (PB, M = 1.07 × 105 or 2.08 × 105) with those observed on a triblock copolymer with deuterated end blocks (PB−DHD, M = 0.98 × 105), was used to investigate two different segmental behaviors detected along any protonated chain. All relaxation curves recorded from PB or PB−DHD as a function of temperature or polymer concentration c in deuterated cyclohexane were found to exhibit two components:  a fast decay and a long tail clearly governed by two distinct partial motional averages of proton−proton couplings called ΔI and ΔII, respectively. ΔI, independent of molecular weight, obeyed the empirical dependence on polymer concentration:  Δ1 = 1740c(1 − 0.29c) rad·s-1 while ΔII ≈ ΔI/4.5 (0.51 ≤ c ≤ 1.0 w/w). On one hand, the nonlinear 1/c dependence of the effective segmental length represented by 1/Δ1 could not be directly correlated to the c -1 dependence usually assigned to the mean segmental spacing between entanglements. On the other hand, the long tail amplitude A II observed from PB obeyed the empirical equation MA II = [5886 + 8800(1/c − 1)] corresponding to a number of monomeric units involved in the definition of A II equal to 109 in the pure polymer and independent of molecular weight; a long tail was still observed on pure PB−DHD although the total number of deuterated units (185) in end blocks was higher than 109:  the product MA II varied as [2816 + 5456(1/c − 1)] and showed that deuterated end blocks eliminated the relaxation of only 62/c units per chain. The relaxation tail observed from fully protonated PB was assigned both to monomeric units attached to so-called end segments formed from 2 × 27/c units and to neighboring units in dynamic interaction with end segments.