Manfred Prof. Dr. Rätzsch

Basis of Solid-Phase Grafting of Polypropylene

Abstract The chemical modification of polymers opens new dimensions for the development and design of materials based on plastics. The chemical modification of polymers by reactions is performed by reactions in a melt, in a solution, or in a solid phase. The modification of polymers in solid phases (powder or granular material directly from the polymerization) has great advantages compared with reactions in solution or melt. The advantages are lower costs and, most important, greater creative variability. A special advantage of solid-phase modification of polypropylene (PP) is the fact that the degradation reaction is reduced.

Solid‐state polypropylene grafting as an effective chemical method of modification

The role of vinylidene groups, formed by the action of organic peroxides, on crosslinking reactions in isotactic polypropylene (iPP), is discussed. Grafting of polymerizable monomers on powdered iPP, performed below its melting temperature, occurs with high efficiency, depending on the structure of peroxide used.

PEROXIDE GRAFTING OF POWDERED POLYPROPYLENE BY BUTYL ACRYLATE

The efficiency of the grafting of powdered polypropylene (PP) by butyl acrylate (BA) initiated by tert.-butylperoxy-2-ethylhex-as a ratio of the grafted and polymerized monomer was relatively high during the whole course of the reaction and it does not decrease under 0.5. The relatively high polymerization rate and also grafting efficiency at the beginning of the reaction is refered to the gel effect - the monomer is absorbed in the amorphous part of the powdered PP. With increasing the content of monomer in the reaction feed, the content of unsoluble cross-linked polymer increased as the consequence of the radical cross-linking of polybutylacrylate chains. The mechanism of grafting of powdered PP by BA is discussed.

Thermotropic block copolymers : polyesters with flexible poly(tetramethylene glycol) units in the main chain

Block copolymers with poly(tetramethylene glycol) (PTMG) spacers of different length and the 4,4′-(terephthaloyldioxy) dibenzoyl unit have been synthesized by high temperature solution polycondensation. The influence of the spacer length on thermal behaviour and solid phase structure of alternating polyesters in comparison with pure PTMG has been determined by d.s.c. and WAXS investigations. Up to spacer molecular weights of 650 g mol−1 (degree of polymerization, DP ≈ 9), polymers with thermotropic liquid crystalline phase behaviour are obtained. Above spacer molecular weights of 1000 g mol−1 (DP ≈ 14), the coexistence of two crystalline phases resulting in polymers with block-like character is discussed.

Liquid Crystalline Polyfumarates, 1. Synthesis and Characterization of Fumarates with Two Mesogenic Groups

Abstract The synthesis of fumarates with two mesogenic groups is described. The basic concept of synthesis is the coupling of phenyl benzoate derivatives containing free hydroxyl groups with fumaroyl chloride in the last step. The spacerless di-[4-(4-n-butoxybenzoyloxy)phenyl] fumarate 3 and some di-{ω[4(4-n-butoxyben-zoyloxy)benzoyloxy]alkyl} fumarates 7 with increasing number of alkyl groups in the spacer, between C2 and C8, were synthesized. The phase behaviour of the (ω-hydroxyalkyl)-4-(4-n-butoxybenzoyloxy)-ben-zoates 6 and the fumarates 3 and 7 was investigated by polarizing microscopy and differential scanning calorimetry (DSC). The spacerless fumarate 3 shows a liquid crystalline (lc) phase above the melting point up to decomposition. The mesomorphism of hydroxyl-terminated precursors 6 depends on spacer length. Whereas the compounds with the shortest and the longest spacer only show a monotropic lc phase the others form an enantiotropic smectic one. Among the fumarates 7 only those with C4 and C6...

PARTIAL CROSSLINKING OF THE HETEROPHASIC ETHYLENE-PROPYLENE COPOLYMER IN THE SOLID PHASE

The influence of radical modification with peroxides under solid phase conditions on mechanical properties and the morphology of an heterophasic ethylene-propylene copolymer (HECO) were investigated. The extent of crosslinking and degradation was characterized by the melt flow index and extraction data. Influence of modification on dynamic viscoelasticity of HECO was also investigated. The morphology was studied by the transmission electron microscopy (TEM). Tensil and impact tests were performed on samples of the modified HECO. Crosslinking occurred in the dispersed EPR phase of HECO in the investigated peroxide concentration range. The extent of crosslinking and degradation was dependent on the type of peroxide as a result of the modification in the melt. The modification with higher peroxide concentrations led to the morphology close to the one of the unmodified HECO powder before and also after the extrusion step. The elongation at break of HECO increased at low peroxide concentrations. Improved impact strength at 23°C was attained. Loss of toughness at −20°C was found probably due to slight degradation of PP matrix and due to an inhomogeneous crosslinking of EPR in HECO.

Effects of molding surfaces on the wettability of compression-molded polypropene films

Contact angles were measured for a series of compression-molded polypropene films blended with acrylic acid (AA) or maleic anhydride (MAH)/polyethylene oxide (PEO) (1:1) additives. The influence of different molding conditions concerning time and temperature as well as a coating of the aluminium foils used for the processing with polyethylene oxide (PEO) or polyvinyl pyrrolidone (PVP) were investigated. Films processed with uncoated aluminium foils showed, with one exception, no influence on contact angles with increasing molding temperatures and longer processing times. Upon coating the aluminium foils with hydrophilic substances the receding contact angles decrease by up to 60 ° with constant contact angle hysteresis. This behaviour corresponding to a permanent hydrophilization is attributed to chemical reactions of the coating with the functional groups of the additives.