Spectroscopy, block copolymers

Key Words Mechanical Hole Burning Spectroscopy, Block Copolymer, Order-Disorder Transition, Rheology, Heterogeneity. 

The main experimental techniques used to study the failure processes at the scale of a chain have involved the use of deuterated polymers, particularly copolymers, at the interface and the measurement of the amounts of the deuterated copolymers at each of the fracture surfaces. The presence and quantity of the deuterated copolymer has typically been measured using forward recoil ion scattering (FRES) or secondary ion mass spectroscopy (SIMS). The technique was originally used in a study of the effects of placing polystyrene-polymethyl methacrylate (PS-PMMA) block copolymers of total molecular weight of 200,000 Da at an interface between polyphenylene ether (PPE or PPO) and PMMA copolymers [1]. The PS block is miscible in the PPE. The use of copolymers where just the PS block was deuterated and copolymers where just the PMMA block was deuterated showed that, when the interface was fractured, the copolymer molecules all broke close to their junction points The basic idea of this technique is shown in Fig, I. 

Neagu, C., Puskas, J.E., Singh, M.A., and Natansohn, A. Domain sizes and interface thickness determination for styrene-isobutylene block copolymer systems using solid-state NMR spectroscopy. Macromolecules, 33, 5976-5981, 2000. 

Most of the sample preparations and contact angle measurements were made by A. D. Karnas. K. W. Littlepage and G. G. Engerholm did the ESCA spectroscopy. J. Burns did the electron microscopy on the block copolymers. I thank D. F. Hager and G. B. Butler for helpful discussions. 

Bis(ethylacetoacetonate)-lanthanide(III) alkoxides, represented by structure (314), also initiate the well-controlled ROP of CL.895 Mn increases linearly with conversion (with Mw/Mn<1.10 throughout), and increasing [M]0/[I]o- Kinetic analysis implies a first order dependence on the lanthanide initiator, consistent with a non-aggregated active site. Block copolymers with moderately narrow polydispersities (1.25-1.45) have also been prepared using these initiators. NMR spectroscopy confirms well-controlled block sequences suggesting that these initiators are less susceptible to transesteriflcation than other lanthanide alkoxides. Initiation occurs exclusively at the alkoxide bond, and the tris(ethylacetoacetonate) analogs are inactive under the same conditions. 

Recent studies on PEO-PPO, PEO-PBO di- and triblock copolymers include the works of Bahadur et al. [121], who examined the role of various additives on the micellization behavior, of Guo et al. [122], who used FT-Raman spectroscopy to study the hydration and conformation as a function of temperature, of Booth and coworkers [ 123], who were mainly interested in PEO-PBO block copolymers with long PEO sequences, and of Hamley et al., who used in situ AFM measurements in water to characterize the morphology of PEO-PPO micelles [56,57]. 

TEM was coated with 6 nm of the random copolymer and 34 nm of the block copolymer. Annealing at 170 °C and exposure to acetic acid generates the desired nanoporosity. After floatation of the film on a dilute aqueous solution of HF the authors picked it up on a TEM grid. The fate of the random copolymer was not described. Water contact angle and X-ray photoelectron spectroscopy (XPS) experiments were consistent with the migration of the PMMA chains to the top of the thin film to generate the desired porosity. 

The exclusive formation of the block copolymer has been confirmed by selective fractionation, NMR spectroscopy, and SEC analysis. For instance, the copolymerization of eCL and 6VL has been followed by SEC. Figure 2 compares the SEC chromatograms of the first PCL block and the final poly(eCL-h-6VL) diblock copolymer. The molecular weight of the macroinitiator is shifted towards higher values in close agreement with the theoretical value expected from the comonomer-to-Al(OzPr)3 molar ratio, and the MWD remains very narrow during the copolymerization process (PDI=1.10). 

The structural characterization of the resulting diblock copolymers was performed by means of SEC, NMR spectroscopy, thermal gravimetric analysis (TGA), and DSC. In most of the cases the PDI values were found to be lower than 1.3. However, the calculation of the molar masses of the diblock copolymers was not straightforward since the calibration standards (PEG, PS, and PMMA) used in SEC systems do not provide accurate data. Moreover, the folding behavior of the different block copolymers significantly infiuence the hydrodynamic volume and,... 

Reed 332) has reported that reaction of ethylene oxide with the a,(a-dilithiumpoly-butadiene in predominantly hydrocarbon media (some residual ether from the dilithium initiator preparation was present) produced telechelic polybutadienes with hydroxyl functionalities (determined by infrared spectroscopy) of 2.0 + 0.1 in most cases. A recent report by Morton, et al.146) confirms the efficiency of the ethylene oxide termination reaction for a,ta-dilithiumpolyisoprene functionalities of 1.99, 1.92 and 2.0j were reported (determined by titration using Method B of ASTM method E222-66). It should be noted, however, that term of a, co-dilithium-polymers with ethylene oxide resulted in gel formation which required 1-4 days for completion. In general, epoxides are not polymerized by lithium bases 333,334), presumably because of the unreactivity of the strongly associated lithium alkoxides641 which are formed. With counter ions such as sodium or potassium, reaction of the polymeric anions with ethylene oxide will effect polymerization to form block copolymers (Eq. (80) 334 336>). 

Graft and block copolymers of cotton cellulose, in fiber, yam, and fabric forms, were prepared by free-radical initiated copolymerization reactions of vinyl monomers with cellulose. The properties of the fibrous cellulose-polyvinyl copolymers were evaluated by solubility, ESR, and infrared spectroscopy, light, electron, and scanning electron microscopy, fractional separation, thermal analysis, and physical properties, including textile properties. Generally, the textile properties of the fibrous copolymers were improved as compared with the properties of cotton products. 

The formation of block copolymers from styrene-maleic anhydride and acrylic monomers was also indicated by pyrolytic gas chromatography and infrared spectroscopy. A comparison of the pyrograms of the block copolymers in Figure 7 shows peaks comparable with those obtained when mixtures of the acrylate polymers and poly(styrene-co-maleic anhydride) were pyrolyzed. A characteristic infrared spectrum was observed for the product obtained when macroradicals were added to a solution of methyl methacrylate in benzene. The characteristic bands for methyl methacrylate (MM) are noted on this spectogram in Figure 8. 

Macroradicals obtained by the heterogeneous copolymerization of styrene and maleic anhydride in poor solvents such as benzene were used to initiate further polymerization of selected monomers. This technique was used to produce higher molecular weight alternating copolymers of styrene and maleic anhydride and block copolymers. Evidence for the block copolymers was based op molecular weight increase, solubility, differential thermal analysis, pyrolytic gas chromatography, and infrared spectroscopy. 

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