Liquid crystalline and photocrosslinkable poly(4,4′‐stilbeneoxy) alkylarylphosphates

Abstract

Three series of liquid crystalline and photocrosslinkable poly(4,4 0 -stilbeneoxy) alkylarylphosphates were synthesized from various 4,4 0 -bis(m-hydroxyalkyloxy)stilbenes (m ¼ 2, 4, 6, 8, 10) and arylphosphorodichloridates in chloroform by solution polycondensation method. Polarized optical microscope (POM) and differential scanning calorimetry (DSC) observations revealed that polymers containing less than four methylene spacer groups did not exhibit liquid crystalline (LC) texture, possibly due to smaller microdomain and restricted movement of the mesogen. In contrast, polymers containing more than four methylene spacer group established LC texture, which has been attributed to the larger monodomain and free movement of mesogens. Thermogravimetric analysis (TGA) data indicated that thermal stability and char yield decreased with increasing flexible methylene spacer groups, increased significantly for biphenyloxy and 1naphthyloxy containing polymers than that of phenyloxy containing polymers ascribed to increasing aromaticity, size, and number of aromatic rings. Photocrosslinking of stilbene containing polymers has been shown to proceed via 2p-2p cycloaddition reaction by Ultra-violet (UV) and fluorescence. The rate photocrosslinking has been found to increase with increasing number of methylene group in the main chain. The aromaticity of the side chain also increases the rate of crosslinking. POLYM. ENG. SCI., 52:598-606, 2012. ª 2011 Society of Plastics Engineers EXPERIMENTAL MaterialsBromoacetaldehyde diethylacetal, 2-chloroethanol, 4-chloro-1-butanol, 1,6-hexane diol, 1,8-octane diol,

Intensity enhancement of photoluminescent polyesters by photocrosslinking

“…These clearly indicated that dimerization occurred between the olefinic double bonds of the polymeric chain which involved 2π + 2π cycloaddition that formed a cyclobutane ring. This ring formation destroyed the conjugation of the π‐electrons and thus caused a decrease in the absorption maxima of the π–π* transition with a concomitant in the absorbance at a shorter wavelength which was due to single bond formation from the cyclobutane ring . The intensity of the absorption band at 335.5 nm gradually decreased until the irradiation time reached 1400 s when maximum photocrosslinking was achieved.…”

“…The extent of photocrosslinking was evaluated by calculating the photocrosslinking percentage of the photoreactive olefinic chromophore. Polyesters PTI1 − PTI5 showed an increase in the percentage of photocrosslinking followed by a plateau where the photocrosslinked network resisted further reaction subsequent to the exposure of UV light . PTI1 − PTI5 achieved a maximum percentage of photocrosslinking (77% − 80%) after 1400 s of UV irradiation and showed no significant effect from an increase in flexible alkyl chain length.…”

Photoluminescent enhancement of polyesters via photocrosslinking

“…This behavior clearly indicated that dimerization occurred in the olefinic double bond of the polymeric chain which involved 2π+2π cycloaddition in forming a cyclobutane ring. This ring formation destroyed the conjugation of the π‐electron system thus giving a decrease in the absorption maxima of π–π* transition with a concomitant in the absorbance at a shorter wavelength which was because of the single bond formation from the cyclobutane ring . PAI1‐PAI5 reacted photochemically similar to cinnamic acid and its derivatives where a cyclobutane structure was formed after the cross‐linking .…”

“…All of these polyesters showed steady increase in the percentage of photocrosslinking followed by a plateau. PAI1 ‐ PAI5 achieved maximum percentage of photocrosslinking (70–72%) at 1300 s indicated that the formation of photocrosslinked network resisted further subsequent exposure to UV light after 1300 s . The formation of cyclobutane ring in the polymer backbones causes steric hindrance because of the bulkiness of the structure and thus hinders the ability of the ‐C=C‐ moieties to cross‐link completely …”