Jd. Tong et R. Jerome, Synthesis of poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly(methyl methacrylate) triblocks and their potential as thermoplastic elastomers, POLYMER, 41(7), 2000, pp. 2499-2510
A series of well defined poly(methyl methacrylate) (PMMA)-b-poly(n-butyl ac
rylate) (PnBA)-b-PMMA triblock copolymers (MnBM) has been synthesized by tr
ansalcoholysis of PMMA-b-poly(tert-butylacrylate) (PtBA)-b-PMMA precursors
(MTM) by n-butanol. Phase separation is observed for all the investigated t
riblock copolymers, which contain PMMA outer blocks in the 5000-50 000 mole
cular weight (MW) range and PnBA inner blocks with MW in the 100 000-200 00
0 range. Although the ultimate tensile properties of these MnBM triblock co
polymers are poor compared to traditional diene-based TPEs (SBS and SIS), t
hey are much better than those ones reported for PMMA-b-poly(isooctyl acryl
ate) (PIOA)-b-PMMA triblocks (MTM). A reasonable explanation for this obser
vation is found in the average molecular weight between chain entanglements
(M-e) that has been estimated to be 28 000 for the central PnBA rubbery bl
ock, which is consistently much smaller than for PIOA (59 000) and substant
ially higher than M-e for polybutadiene (1700) and polyisoprene (6100). The
tensile behavior of MnBM copolymers cannot be fitted by either a simple el
astomer model free from chain entanglements (suitable to MIM) or by a "fill
er" modified rubber model (suitable for diene-based TPEs), supporting the h
ypothesis that the mechanical properties of the investigated (meth)acrylate
thermoplastic elastomers are significantly affected by any change in M-e o
f the central acrylate block. Viscoelastic analysis shows that MnBM tribloc
ks are of higher complex viscosity than the SBS and SIS analogs, leading to
a shift in the order-disorder transition temperature to much higher temper
ature, unless the outer PMMA blocks are of very low molecular weight (5000)
. (C) 1999 Elsevier Science Ltd, All rights reserved.