RELAXATION BEHAVIOR AND DIPOLAR CORRELATIONS FOR POLYACRYLATE-BASED POLYMERS WITH AROMATIC SIDE-GROUPS

Dielectric experiments are carried out on poly(4-phenoxyphenyl acrylat e) (PPOA) and 4-phenoxyphenyl-2,4-dimethylglutarate (PPODG), a low-mol ecular-weight analogue of PPOA. The intramolecular dipolar correlation coefficient g(intra) for the polymer changes from 0.821 at 30-degrees -C to 0.835 at 60-degrees-C. This coefficient is similar to that of PP ODG (0.817 at 30-degrees-C), suggesting that the asymptotic value of g (intra) is reached for rather low molecular weights. The dipolar corre lation coefficient g that accounts for both the intramolecular and int ermolecular dipolar interactions is smaller than g(intra) for both the polymer and the low-molecular-weight compound. The dielectric spectru m of PPOA in the bulk presents a prominent glass-rubber relaxation fol lowed by a subglass absorption that seems to be the combination of a p rocess in the high-temperature zone (named beta) that overlaps with th e glass-rubber relaxation and a well developed absorption (named gamma ) in the low-temperature region. This latter process can be explained in terms of motions of the dipole associated with the C(ar)-O-C(ar) bo nds whereas motions about the C(alpha)-CO* bonds may also intervene i n the beta process. The low-molecular-weight compound only exhibits a prominent glass-liquid absorption followed by a diffuse and weak subgl ass relaxation; this behaviour cannot be explained in terms of only in tramolecular interactions, and therefore intermolecular interactions m ust play an important role in this process. The mechanical and the die lectric glass-rubber relaxations are interpreted in terms of the coupl ing scheme. This study suggests that the complexities of both processe s are similar, in contrast with what occurs in many other systems.