It is generally believed that cyano functionality is "toxic" to the classical MoCl 5-and WCl6based metathesis catalysts, but we here present such an example in which a group of cyano-containing acetylene monomers are polymerized by the "simple" metal halides. The WCl6(-Ph4Sn) catalysts in dioxane initiate the polymerizations of n-{ [(4′-cyano-4-biphenylyl)oxy]carbonyl}-1-alkynes (AnCN; n ) 2, 3, 8), yielding polymers (PAnCNs) with relatively narrow molecular weight distributions (Mw/Mn down to 1.3). The same metal-halide mixtures in toluene, however, are generally ineffective in polymerizing AnCNs, suggesting that the tungsten-oxo complexes are involved in the active center formation. The differential scanning calorimetry, polarizing optical microscopy, and X-ray diffractometry analyses reveal that all the PAnCNs are mesomorphic, with the longer flexible spacer favoring the better ordering of the mesogenic groups. PA2CN shows monotropic nematicity, PA3CN exhibits enantiotropic nematicity, and PA8CN displays enantiotropic smecticity with an interdigitated molecular packing arrangement (s Ad) over a wide temperature range (ca. 110 °C). In-domain banded structures within the sAd layers of PA8CN are observed during the transit of the ba ˆtonnets to the focal-conic fan textures, and the formation of large scale band morphology is achieved by the application of shear force to PA8CN in its liquid crystalline state.
Two types of three-arm or four-arm star-shaped hydroxy-terminated poly( -caprolactone) (PCL) were successfully synthesized via the ring-opening polymerization of -caprolactone (CL) with multifunctional initiator, such as trimethylolpropane (TMP) or pentaerythritol (PTOL), and stannous octoate (SnOct 2) catalyst in bulk at 110 °C. The number-average molecular weight of PCL is proportional to the molar ratio of monomer to initiator. 1 H NMR spectroscopy of the resulting PCL indicates that it contains a primary hydroxy end group in each arm. The star-shaped PCL with hydroxy end groups can be used as a macroinitiator for block copolymerization with DL-3-methylglycolide (MG) using SnOct2 catalyst in bulk at 115 °C. 1 H NMR spectra of the resulting block copolymers show that the molecular weights and the unit compositions of the block copolymers were controlled by the molar ratios of MG monomer to hydroxy groups of PCL and MG to CL in feed, respectively. Moreover, the molecular weights of the resulting block copolymers linearly increased with the increase of the molar ratios of MG to CL in feed. The molecular weight distributions of the block copolymers were rather narrow (M w/Mn ) 1.09-1.26). 13 C NMR spectra of the resulting block copolymers clearly show their diblock structures, that is, PCL as the first block and poly(DL-lactic acid-alt-glycolic acid) (DL-PLGA50) with alternating structures of lactyl and glycolyl units as the second block. Therefore, two types of three-arm or four-arm star-shaped diblock copolyesters comprising the first block PCL and the second block DL-PLGA50 were successfully synthesized via the sequential ring-opening polymerization of CL with multifunctional initiator and SnOct2 catalyst and then followed by copolymerization with MG.
We have succeeded in synthesizing soluble, stereoregular, and high
molecular weight
polyacetylenes containing polar cyano functional groups in high yields.
Two new cyanoalkyne monomers,
[4-[[[n-[(4‘-cyano-4-biphenylyl)oxy]alkyl]oxy]carbonyl]phenyl]acetylenes
(1; n = 6, 12), are synthesized
via multistep reactions. [Rh(nbd)Cl]2
effects the polymerization of 1, producing polymers
(2) with high
molecular weights (M
w up to 158 000) in high
yields (up to 71%). Spectroscopic analysis reveals that
the
polymers possess alternating-double-bond backbones with high
stereoregularity. The electronic and
thermal transitions in 2 are sensitive to their
stereostructures: The polymer with higher
stereoregularity
absorbs at longer wavelength and melts at higher temperature. The
polymers prepared in DMF-based
solvents are completely soluble in DMF, THF, and chloroform, although
the dissolution takes quite a
long time (up to a week) due to the high stereoregularity of the
polyacetylene backbones and the strong
electronic interaction among the push−pull mesogenic pendant groups.
The polymers are thermally very
stable (temperature for 5% weight loss: ca. 400 °C) and can be
melt-processed in a moderate temperature
range (ca. 100−150 °C).
For the purpose of increasing the hydrophilicity of a polylactide, a new monomer, (3S)-3-[(benzyloxycarbonyl)methyl]morpholine-2,5-dione, was successfully polymerized. The benzyl protective group of the polymer was completely removed to give poly(glycolic acid-alt-L-aspartic acid). The structures and properties of both protected and deprotected polymers were carefully studied by NMR, GPC, and DCA. It is found that the morpholine-2,5-dione derivatives with side functional groups which have no substituent on the 6 position of the morpholine ring are much more reactive than those monomers with a substituent on the 6 position of the ring in polymerization. The resulting polymer shows promising hydrophilicity, as can be seen from the DCA result.
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