Eltjo J. Vorenkamp

Influence of the tacticity of poly(methyl methacrylate) on the miscibility with poly(vinyl chloride)

It can be concluded from the work of Schurer et al.10 that poly(vinyl chloride) (PVC) is more miscible with syndiotactic than with isotactic poly(methyl methacrylate) (PMMA). By choosing different molar masses for the various tactic forms of PMMA it is possible to obtain blends with PVC with similar phase behaviour, i.e. in all cases a cloud-point curve with a minimum in the vicinity of 190°C. In this way a more quantitative statement about the influence of the tacticity of PMMA on its miscibility with PVC can be made. One of the principal differences between syndiotactic or atactic PMMA and isotactic PMMA is the higher flexibility of the latter. Using Florys equation of state theory it will be shown that the effect of this difference is large enough to explain the difference in phase behaviour observed. Heats of mixing of low molar mass analogues were also measured and found to be negative.

Influence of chlorination of poly(vinyl chloride) on miscibility with poly(methyl methacrylate)

Abstract The improvement of the miscibility of poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC) with moderate chlorination of PVC was demonstrated by determination of cloud-point curves and glass transitions of the mixtures. Heats of mixing of low-molar-mass analogues for PMMA and for the various structural units present in chlorinated PVC (CPVC) were determined in a microcalorimeter along with Fourier transform infra-red spectroscopy of these mixtures. The results show that the improvement of miscibility is caused by a specific interaction between the carbonyl group of PMMA and predominantly the CHCl group of CPVC. The specific interactions present in these systems are best described as a Lewis acid-base type of interaction, considering the carbonyl oxygen of the ester as an electron donor and the hydrogen of the CHCl group as an electron acceptor: CO … HCCl. The decrease in miscibility observed when more strongly chlorinated PVC is used can be ascribed to the relatively high concentration of CCl 2 groups, which have a less favourable interaction with the carbonyl groups.

ASSOCIATION OF STEREOREGULAR POLY(METHYL METHACRYLATES) .5. STEREO-COMPLEX FORMATION IN DILUTE-SOLUTIONS

Abstract Further study was carried out on the stereocomplex formation in dilute solution using viscometry, osmometry, light scattering and gel permeation chromatography. It appears that the process can be divided in two steps. The primary step involves the formation of very compact particles by association of several isotactic and syndiotactic PMMA chains in a base-molar ratio of 1 2 . The radius of gyration of these particles remains about the same as the additive value of the original components, whereas their molecular weight increases. The secondary step involves the aggregation of the particles which is reflected by an increase of the radius of gyration. It is proposed that this aggregation is caused by interparticle stereo-association of noncomplexed chain parts.

STEREOCOMPLEXATION OF STEREOREGULAR POLY(METHYL METHACRYLATE)S .9. TEMPERATURE AND TIME-DEPENDENCE OF THE PROCESS OF COMPLEXATION

Abstract The dependence on temperature, time and concentration of the process of stereocomplexation of it- and st-PMMA in dilute solutions in DMF was investigated by means of viscometry. On raising the temperature, DMF changes from a strongly complexing to a weakly complexing solvent and eventually into a non-complexing solvent. In a strongly complexing solvent the process of complexation consists of three stages: complexation, association of complexled chain sections and aggregation of particles containing associates. The first two stages, indistinguishable with viscometry in a strongly complexing solvent, can be observed separately at higher temperatures. In a weakly complexing solvent neither association nor aggregation occurs. In DMF st-PMMA has a more compact conformation in comparison with it-PMMA, which influences the symmetry of the process of complexation with regard to the stoichiometric ratio.

Annealing-Induced Changes in Double-Brush Langmuir-Blodgett Films of alpha-Helical Diblock Copolypeptides

The effect of annealing on the structure and the helix orientation in Langmuir-Blodgett (LB) monolayers of diblock copolymers (PLGA-b-PMLGSLGs) of poly(alpha-L-glutamic acid) (PLGA) and poly(gamma-methyl-L-glutamate-ran-gamma-stearyl-L-glutamate) with 30 mol % of stearyl substituents (PMLGSLG) with unidirectional helix orientation deposited on hydrophilic silicon substrates was characterized by means of small-angle X-ray reflectivity, transmission Fourier transform infrared spectroscopy, and atomic force microscopy. Upon annealing at 100 degrees C for 24 h, the alpha-helices became less tilted toward the substrate surface normal. Surface area shrinkage accompanied the change in tilt, indicated by an increase in both film thickness and electron density, resulting in more compact and uniform films. The enhancement of the helix orientation by thermal annealing was greater for the PMLGSLG block and for the diblock copolymers with the shorter block lengths. For these diblock copolymers, annealing resulted in postorientation of the PMLGSLG block helices almost perpendicular to the substrate surface. This effect originates from a considerable increase in intermolecular packing of the PLGA block caused by hydrogen bonds between the carboxylic groups upon annealing, as well as the high mobility of the PMLGSLG block helices for rearrangement favored by the melted side chain mantle at elevated temperatures.

Synthesis and Phase Behavior of Poly(N-isopropylacrylamide)-b-Poly(L-Lysine Hydrochloride) and Poly(N-Isopropylacrylamide-co-Acrylamide)-b-Poly(L-Lysine Hydrochloride)

The synthesis of poly(N-isopropylacrylamide)-b-poly(L-lysine) and poly(N-isopropylacrylamide-co-acrylamide)-b-poly(L-lysine) copolymers was accomplished by combining atom transfer radical polymerization (ATRP) and ring opening polymerization (ROP). For this purpose, a di-functional initiator with protected amino group was successfully synthetized. The ATRP of N-isopropylacrylamide yielded narrowly dispersed polymers with consistent high yields (~80%). Lower yields (~50%) were observed when narrowly dispersed random copolymers of N-isopropylacrylamide and acrylamide where synthesized. Amino-terminated poly(N-isopropylacrylamide) and poly(N-isopropylacrylamide-co-acrylamide) were successfully used as macroinitiators for ROP of N6-carbobenzoxy-L-lysine N-carboxyanhydride. The thermal behavior of the homopolymers and copolymers in aqueous solutions was studied by turbidimetry, dynamic light scattering (DLS) and proton nuclear magnetic resonance spectroscopy (1H-NMR).

Interdiffusion of free and grafted poly(methylmethacrylate) with polyvinylchloride, studied by infrared spectroscopy

Abstract As a guide for adhesion development between two miscible polymers, interdiffusion of these polymers was studied using external reflection and attenuated total reflection infrared spectroscopy. Using gold substrates coated with a double layer of PMMA and PVC, and s-polarized infrared light, PMMA features in the external reflection spectra increase upon annealing at 150°C as a result of PMMA diffusion away from the gold substrate into regions with a higher electric field intensity. Interdiffusion can also be followed with an external reflection set-up using glass substrates and p-polarized infrared light. Interdiffusion of PVC and PMMA, free or grafted on a glass slide, was observed. Increasing the molecular weight of the PMMA slows down the interdiffusion rate, which might be a consequence of a reduction in the thermodynamic driving force for diffusion or the molecular weight of PMMA. External reflection spectroscopy as well as attenuated total reflection experiments show that interdiffusion of PVC and PMMA grafted on a silicon slide was much slower than that of free PMMA of similar molecular weight.

Dipping-Induced Azimuthal Helix Orientation in Langmuir-Blodgett Monolayers of alpha-Helical Amphiphilic Diblock Copolypeptides

The azimuthal helix orientation of the rigid-rod amphiphilic diblock copolypeptides (PLGA-b-PMLGSLGs) of poly(alpha-L-glutamic acid) (PLGA) and poly(gamma-methyl-L-glutamate-ran-gamma-stearyl-L-glutamate) with 30 mol % of stearyl substituents (PMLGSLG) in Langmuir-Blodgett (LB) monolayers was investigated using polarized transmission Fourier transform infrared spectroscopy. The relative position of dipping with respect to the previous transfer position can be used to manipulate the azimuthal orientation of the helices parallel to or tilted by an angle of 45 degrees with respect to the dipping direction in the transferred films. The study of the azimuthal order for the LB monolayers of PLGA-b-PMLGSLGs of various block lengths revealed that the observed effect arises mainly from the deformation of the PMLGSLG top brush layer, induced by the flow orientation around the transfer region. In those cases where the PMLGSLG block is tilted by a sufficiently large angle with respect to the surface normal, high azimuthal order parameters of 0.5-0.75 were obtained.

Influence of the degree of hydrolysis of poly(styrene-alt-maleic anhydride) on miscibility with poly(vinyl acetate)

Abstract The influence of the hydrolysis of anhydride groups in poly(styrene-alt-maleic anhydride) (PSMA) on its miscibility with poly(vinyl acetate) (PVAc) is investigated. The cloudpoint curves of these blends are determined as a function of the degree of hydrolysis. The miscibility is shown to improve with increasing number of carboxylic acid groups in PSMA. Specific interaction between the acid groups of PSMA and the ester group of PVAc, together with the so-called copolymer effect, is put forward as an explanation for this observation.