142 Advances in Polymer Science Editorial Board: A. Abe. A.-C ...

Poly(macromonomers), Homo- and Copolymerization 155
Table 2. Glass transition temperatures of PSt polymacromonomers
MW of macromonomer
10
Tg of polymacromonomer/˚C
–3Mn 10 –3Mw obs. cal. a
0.81 0.9 56–68 44
2.9 3.1 84–90 84
12.4 13.1 98 96
14.0 14.6 100 97
27.0 28.1 – 98
a Calculated by Eq. (18), based on Tg =T g ¥ - 1.0´10 5 2Mw with T g ¥ =100
Therefore, their bulk properties are expected to be significantly different from
those of the corresponding linear polymer. Indeed, detailed studies by Tsukahara
et al. [31, 83] revealed that the glass transition temperature, T g , of PSt polymacromonomers
from 24 is predominantly determined by the excess free volume
effect of end group per unit MW, as summarized in Table 2. Generally, the
T g value was found to increase with increase of the MW of macromonomer and
also that of polymacromonomers. The chain end effect on the glass transition
temperature is described by the relation [84]
(18)
where T g ¥ is Tg for the polymer of infinite MW, M 0 and M are the MWs of monomeric
unit and the macromonomer, v m is the free volume per monomeric unit,
and v is the excess free volume at a chain end. The value of T g of the polymacromonomers
calculated by Eq. (18) is given in Table 2. Hatada and Kitayama
[33] also reported that the value of T g of it-PMMA polymacromonomer from 25
(n=30) is 44 ˚C.
Tsukahara et al. [83] have reported that when PSt polymacromonomers are
cast onto Teflon or glass plates, many cracks are generally created during the solvent
evaporation and the resulting films are too brittle to handle. They ascribed
the result to a lack of chain entanglement networks in the polymacromonomers
[85]. In fact the SAXS profiles of the polymacromonomers in the bulk state demonstrated
that the polymacromonomer molecules exist independently of each
other [86, 87]. Such behavior was confirmed directly by STM [88] and tapping
scanning force microscopy [89]. The incompatibility was also observed between
high MW linear polystyrene and PSt polymacromonomers with high degree of
polymerization, in spite of the fact that they are athermally mixing [85, 90, 91].
The PSt polymacromonomers have been reported to form lyotropic main chain
liquid crystals in toluene solution and in the bulk state [82, 90, 91]. The crystallization
behavior of PEO comb-shaped polymers from 27b was reported by
Wesslén et al. [92]. The polymacromonomers from n=9 and 23 were amorphous
material with T g=–55~–60 ˚C but those from n=45 were crystalline with mp=
38–44 ˚C.