Search

Four polyacetylenes containing chromophores with different conjugation bridge structure or terminal substituents were designed and prepared by using [Rh(nbd)Cl] 2 as catalysts, respectively. Their structures and properties were characterized and evaluated by IR, NMR, UV, TGA, optical limiting and nonlinear optical analyses. All the polymers show high thermal and photo stability and novel optical limiting properties. The functional polyacetylene with stilbene pendant shows better optical limiting property than that with azobenzene chromophore pendant. Their optical limiting mechanisms are mainly originated from reverse saturable absorption of molecules. Their nonlinear optical properties are significantly affected by their molecular structures and the shorter spacer group will be beneficial in increasing the electronic interaction between chromophore pendant and polyacetylene conjugation backbone to result in higher third-order optical nonlinearity.

Poly(1-alkyne)s containing azobenzene pendants with different spacer lengths and ring substitutents –{HC C[(CH2)mCOO–C6H4–N N–C6H4–NO2]}n– P1(m) m=3, 8 and –{HC C[(CH2)mCOO–C6H3-o-Br–N N–C6H4–NO2]}n– P2(m) m=3, 8} are designed and synthesized. The polymers are prepared in satisfactory yields with high molecular weights (Mw up to 3.3×104 Da) by [Rh(nbd)Cl]2–Et3N in THF or dioxane. Their structures and properties are characterized and evaluated by IR, UV, NMR, TGA, nonlinear optical and optical limiting analyses. All the polymers are completely soluble in common organic solvents and lose 5% of their weights at temperatures of ∼270 °C. The spacer length and the pendant substitutent affect the nonlinear optical and optical limiting properties of the polymers, with 1(3) showing superior properties than its counterparts 1(8) and 2(3) with long methylene spacers and bromide substitutents on the azobenzene pendants, respectively.

High molecular weight polyacetylenes bearing nonlinear chromophoric pendants poly[4-ethynyl-4′-(N,N-diethylamino)azobenzene-co-phenylacetylene]s [poly(EAAB-co-PA)s] were synthesized in moderate yields by [Rh(nbd)Cl]2–Et3N. The azo unit in the copolymers can be effectively controlled by the monomer feed ratio. Whereas the homopolymer of EAAB possessed low solubility, all the copolymers, however, dissolved readily in common organic solvents when the poly(EAAB) molar content was less than 41.7%. The structures and properties of the polymers were characterized and evaluated by UV, NMR, optical limiting, and nonlinear optical analyses. All the copolymers possessed high stereoregularity and thermal stability (≥300 °C). They can attenuate intense laser pulses, with solutions of high concentrations showing better performances. The third-order nonlinear susceptibility of the copolymers was as high as 4.62×10−11 esu, which are two orders of magnitude larger than those of poly(PA), and larger than that of poly(N-carbazoylacetylene), and poly(1-naphthylacetylene).

A series of novel multifunctional initiators derived from adamantane-based derivatives have been used in the syntheses of various styrenic and (meth)acrylic star polymers by atom transfer radical polymerization (ATRP). Conditions were identified in each system to produce star polymers with nearly monomodal molecular distributions. These synthesized star polymers have glass transition temperatures similar to those known for high-molecular-weight linear polymers. We obtained a series of adamantane-contained star polymers covering a wide range of molecular weights by adjusting the monomer-to-initiator ratio and the solvent polarity. Because of reaction heterogeneity and inevitable termination processes, the occurrence of star ‐ star coupling led to a lower than predicted molecular weight polydispersity. When hydrolyzed from their cores by NaOH, the values of Mw of the arms of the PMMA star polymer did not change with reaction time, at least for the first 48 h of the reaction, which implies that no significant PMMA hydrolysis occurs within this interval of time. q 2004 Elsevier Ltd. All rights reserved.

The thermal properties and hydrogen bonding behavior of B-a type polybenzoxazine (PBZZ)/PVP blends were investigated by DSC and FTIR. The DSC result shows a single Tg over the entire compositions and a large positive deviation based on Kwei equation was observed in the Tg versus composition diagram, implying that strong hydrogen bonding interaction exists between PBZZ and PVP segments. The strength of hydrogen bonding interaction is in the order of inter-association between the hydroxyl group of PBZZ and the carbonyl group of PVP (K A =594 L mol −1 ) >self-association between the hydroxyl group of pure PBZZ (K B =72.6 L mol −1 ) >inter-association between the hydroxyl and the Mannich-based bridge of pure PBZZ (K C L mol −1 ). Good correlation between DSC and FTIR analysis were observed.

A series of poly(hydroxystyrene-co-vinylpyrrolidone-co-isobutylstyryl polyhedral oligosilsesquioxanes) (PHS–PVP–POSS) hybrid polymers with various POSS contents was prepared by free radical copolymerization of acetoxystyrene, vinylpyrrolidone with styrylisobutylpolyhedral oligosilsesquioxanes (POSS), followed by selective removal of the acetyl protective group. The POSS content of a hybrid polymer can be effectively controlled by varying the feed ratios of reactants. The Tg of the POSS hybrid increases with the POSS content of PHS–PVP–POSS hybrids. The mechanism of Tg enhancement in these PHS–PVP–POSS hybrids was investigated using DSC, FTIR and GPC. The formation of the physically cross-linked POSS in these hybrid polymers trends to restrict polymer chain motion and results in significant Tg increase.