temperature determined by our probe (relaxation frequency 10" Hz) agrees well with those determined by slow thermal relaxation techniques. The answer to this question lies in the fact that molecular and submolecular motions to which the probe is sensitive contribute to the macroscopic behavior of the polymer. In addition, the steadystate fluorescence measurements average out the macrodynamic behavior of the polymer chains.Basically, two principal findings have emerged. One is the dependence of the fluorescence yield of molecular rotors on the tacticity of the polymer matrix. The other is the sensitivity of the fluorescence of molecular rotors to dynamic changes in the conformation of polymers over wide temperature ranges. One must remember that different relaxation techniques applied to polymeric materials respond with different sensitivity to the various types of molecular motion. The fluorescence probe method complements many of the well-established methods of polymer material research. Acknowledgment. We are in debt to Drs. S. Sundar-Registry No. 1,58293-56-4; atactic PMMA, 9011-14-7; isotactic arajan and T. Smith for many useful discussions. PMMA, 25188-98-1.ABSTRACT: The stepwise protonation of three polymeric amines, containing a different shielding group between the amine moieties of the repeating units, has been studied from a thermodynamic standpoint. This was done for comparison purposes with structurally related poly(amido amines) whose monomeric units had been previously found to behave independently toward protonation. This study was performed by potentiometric and calorimetric techniques, and specific methods for the treatment of either "sharp" or "apparent" thermodynamic functions in polyelectrolyte having more than one basic group in the repeating unit have been developed.
A series of liquid crystalline (LC) poly(vinyl ether)s
1 was prepared by living cationic
polymerization of a mesogenic vinyl ether monomer, 4-butoxyphenyl
4-((6-vinylhexyl)oxy)benzoate (11),
in the presence of the HI/I2 (1/1 mol/mol) initiating
system. The number average molar mass of polymers
1 increased linearly with the initial monomer to initiator
molar ratio (M
n = 3000−15 000 g
mol-1, DPn
≈ 5−50), according to the living character of the polymerization,
and their molar mass distribution was
rather narrow (M
w/M
n =
1.10−1.15). Furthermore, two sets of AB diblock
copoly(vinyl ether)s 2 and 3
were prepared by sequential polymerization of vinyl ether 11
and isobutyl vinyl ether (12) and chiral
(S)-2-methylbutyl vinyl ether (13) respectively,
by using the same HI/I2 system. While the average
degree
of polymerization of the LC block was kept constant (DPn
≈ 10), the length of the non-LC block was
varied (DPn ≈ 2−25), according to the chosen feed
conditions. An X-ray investigation proved that
polymers
1 gave rise to a sequence of ordered smectic (F or I),
smectic C, and nematic mesophases with increasing
temperature. Their transition temperatures and entropies followed
slightly different molar mass
dependences, but each of them reached a saturation value at
M
n ≈ 6000 g mol-1.
The same basic
mesophase polymorphism was also observed for the LC block copolymers
2 and 3, thus suggesting that
the chemically different blocks were microphase separated within the
solid and LC phases.
ABSTRACT:The phase and orientational behaviors of a series of liquid crystalline (LC) AB-type diblock copolymers comprising thermotropic main-chain (MC) polyester and side-group (SG) polymethacrylate blocks were investigated by X-ray diffraction. The MC and SG blocks were phase separated and gave rise to their individual mesophases that coexisted at equilibrium. The samples were oriented by using either a magnetic field or a mechanical field. In magnetically aligned samples both the MC and SG microphases were oriented with their smectic planes orthogonal to the magnetic field direction, independent of the copolymer composition. Mechanically aligned, fiber samples showed different orientations of the MC and SG smectic planes for different sample compositions. In this case the disposition of the smectic planes of the MC and SG blocks was driven by the relative length of the two blocks. Some features of the X-ray patterns of the copolymers were compared to those of the MC and SG homopolymers. In addition, the MC smectic domains crystallized on annealing without affecting the orientation that had been achieved by applying a magnetic field.
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