Investigation on lipase-catalyzed solution polymerization of cyclic carbonate

In this study, 26-membered macrocyclic carbonate, cyclobis(decamethylene carbonate) [(DMC)₂] was attempted to undergo ring-opening polymerization by lipase catalysis in toluene. Novozym-435 exhibited even higher catalytic activity towards (DMC)₂ polymerization compared with SnOCt₂ while high molecular weight (M_n) of 5.4 × 10⁴ and yield of 99% was still achieved at ultra-low enzyme/substrate (E/S) weight ratio of 1/200. ¹H NMR spectra demonstrated the existence of terminal hydroxyl group. Solid phase polymerization in the absence of toluene unexpectedly took place at the temperature lower than (DMC)₂’s melting point of 110 °C. Compared with solvent-free case, the addition of toluene solvent resulted in marked increase in reaction rate. As to the polymerization during 48 h with the E/S weight ratio of 1/100, a region existed at around toluene/carbonate (vol/wt, ml/g) ratio of 1∼2 where the polymerizations gave optimal results in terms of both higher molecular weight and monomer conversion. It was found that much higher molecular weight polymers may be obtained by decreasing enzyme concentrations. Plots of ln{[M]₀:[M]_t} versus reaction time were in linear agreement, indicating no chain termination, and monomer consumption follows a first-order rate law. The Novozym-435 catalyzed polymerization of (DMC)₂ in toluene presented pseudo-living characteristic. Compared with 6-membered trimethylene carbonate, much lower reaction activity of large-sized (DMC)₂ is observed, which is opposite to the result concerning the enzymatic polymerization of lactones with different ring-size.     

Study of the morphology and properties of melt-mixed polycarbonate-POSS nanocomposites

In this work, the morphology and thermo-mechanical behaviour of nanocomposites formed by a polycarbonate (PC) matrix and polyhedral oligomeric silsesquioxane with phenethyl substituents (Ph-POSS) have been studied. The Ph-POSS nanocages were added to the PC by direct melt blending at loadings between 0% and 15 wt%. Good dispersion was achieved up to 5 wt% of nanofiller. At higher loadings micron-sized aggregates were observed in the nanocomposites by scanning and transmission electron microscopy. Increasing of Ph-POSS content lead to phase separation, agglomeration and low values on the final properties. The DSC and DMA analyses showed that increasing the amount of nanocages caused a continuous decrease on the composite’s T_g. Although little increments on the polycarbonate decomposition temperature were found, the presence of Ph-POSS did not improve significantly the thermal stability. Under nitrogen atmosphere the degradation mechanism of PC was not affected by the POSS. The residual weights obtained under oxygen atmosphere were in agreement with the theoretical weights of the Ph-POSS added. With respect to the nanocomposites mechanical properties the most remarkable trend was an improvement on the composite’s yield stress having the maximum at 5 wt% of nanofiller. Higher amounts of Ph-POSS lead to a decrease on the yield stress, finding even lower values than the one corresponding to the neat matrix. This behaviour has been attributed to the presence of large POSS agglomerates with low adhesion to the polymer matrix. A continuous decrease on the strain at break was also observed, reflecting the brittle character of the formed composites.     

Tension testing of polycarbonate at high strain rates

Dynamic tensile tests were performed on polycarbonate using a split Hopkinson tension bar (SHTB) system. A prefixed short metal bar was used to generate the incident stress pulse. The shape of the incident pulse was controlled to meet the requirement of the one-dimensional experimental principle of SHTB. The dynamic tensile stress–strain responses of polycarbonate at high strain rates up to a rate of 1750 s⁻¹ were obtained. Experimental results indicate that the tensile behavior of polycarbonate is dependent on the strain rate. Its yield stress and unstable strain all increase with the increased strain rate. The yield behavior was modeled for a wide range of strain rates based on the thermally activated theory. The correlation between the experimental data and the model is good.     

High transparent thermal curable hybrid polycarbonate films prepared by the sol–gel method

Polycarbonate/epoxy/silica hybrid films were prepared by curing an epoxy reaction via in situ sol–gel process. The influence of the synthetic conditions, such as the ratio of different epoxy reagents and the contents of [2-(3,4-epoxycyclohexyl)ethyl]trimethoxysilane on the physical and optical properties of these hybrid films were investigated in details. The coefficient of thermal expansion, surface roughness, and light transmittance at a wavelength range from 250 to 800 nm were measured. These excellent overall performances make it a promising photonic packaging material.     

Synthesis of polycarbonate from dimethyl carbonate and bisphenol-a through a non-phosgene process

A novel nonphosgene process for producing bisphenol-A polycarbonate (PC) was developed through a transesterification between bisphenol-A (BPA) and dimethyl carbonate (DMC) and a melt-polycondensation of the resulting bisphenol-A bismethylcarbonate (1). The transesterification was carried out by heating bisphenol A in dimethylcarbonate in the presence of Lewis acid catalysts, removing the by-producing methanol using molecular shieves 4A. Among various catalysts, a combination of (Bu₂SnCl)₂O and dimethylaminopyridine gave the best results to produce 1 in 22% yield for 48 h. Using a larger amount of the molecular sieves further improved the yield to 80% in 120 h. The resulting 1 was heated under reduced pressure in the presence of titanium catalysts to produce PC in good yields. The resulting PC had high weight average molecular weight (M_w) of 75,000. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2087–2093, 1999     

Accelerated ratcheting testing of polycarbonate using the time-temperature-stress equivalence method

The long-term performance of polymers under cyclic loading is important for safety assessments in engineering applications. The deformation process under the cyclic loading can be accelerated through use of temperature and stress. As for asymmetric cyclic loading, so called ratcheting, a time-temperature-stress (TTS) equivalence method in which all the parameters have clear physical meanings and can be determined experimentally, was proposed to predict the long-term cyclic loading behavior for polycarbonate using short-term data. Taking into consideration the effects of both the mean stress and the stress amplitude, the ratcheting compliance was defined and its evolution function was also provided. Next, the TTS equivalence method was validated using the long-term ratcheting test results for the polycarbonate. Time, temperature, and stress do show equivalent effects on long-term ratcheting of polycarbonate. Using the proposed method, time and cost can be dramatically saved for the assessment of the long-term cyclic loading performance of polycarbonate.     

Intelligent feedback release systems and the application to neuron network model research

Intelligent feedback release systems, consisting of radiation-prepared porous polycarbonate film or silicone chip and radiation crosslinked stimuli-sensitive hydrogels with immobilized enzymes as a sensor–actuator gate were constructed. Those systems showed various signal responsive substance release functions, and selective signal transfer functions. The application of those integrated intelligent systems as neural network model was investigated.     

Amphiphilic random polycarbonate self-assemble into GSH/pH dual responsive micelle-like aggregates in water

We synthesized the GSH/pH responsive amphiphilic random polycarbonate poly(MN-co-MSS) with the disulfide and tertiary amine groups situated on the backbone. The poly(MN-co-MSS) was therefore a promising candidate for GSH/pH-sensitive drug carriers.     

Structure and anisotropy in polycarbonate III. Study of elastic and optical properties of oriented samples with the method of high resolution Brillouin spectroscopy

High resolution Brillouin spectroscopy (BS) has been used to investigate elastic and optical properties of uniaxially drawn samples of polycarbonate (PC). The results are discussed in the framework of the single phase aggregate model (SPAM) of Ward. According to a recently developed evaluation technique, the SPAM parameters of PC are determined, resulting in the following elastic constants of the structural units:c ₃₃ ⁰ =33 GPa,c ₁₁ ⁰ =7 GPa,c ₁₃ ⁰ =9.7 GPa,c ₄₄ ⁰ =1.4 GPa, andc ₆₆ ⁰ =1 GPa. A nearly quadratic dependence of the orientation parameterP ₄ onP ₃ results, which can be explained by a modified pseudoaffine deformation scheme.