Györgyi Szarka

Thermal properties, degradation and stability of poly(vinyl chloride) predegraded thermooxidatively in the presence of dioctyl phthalate plasticizer

Thermooxidative degradation of poly(vinyl chloride) (PVC) is inevitable during its processing. Recycling of this polymer requires reprocessing in most cases, and due to the low thermal stability of PVC, it is of paramount importance to reveal the effect of thermooxidation on the thermal stability of this commercially important polymer. However, detailed systematic investigations are lacking on this crucial problem. In this study, the thermal behavior of PVCs thermooxidized in dilute dioctyl phthalate (DOP) (di(2-ethylhexyl) phthalate, DEHP) plasticizer was investigated by DSC, thermal gravimetry and isothermal degradation under inert atmosphere. It was found that thermooxidation leads to PVCs with certain extent of internal plasticization by DOP chemically bound to the PVC chains and by the oxidized chain segments as well. Thermogravimetry and isothermal dehydrochlorination under inert atmosphere revealed that even low extent of thermooxidation of PVC (0.4 mol% of HCl loss in 30 min at 200°C) leads to dramatically decreased thermal stability of this polymer with 50–60°C lower onset decomposition temperature than that of the virgin resin. This unexpected finding means that at least part of the oxidized moieties formed during oxidation of the PVC chains acts as initiators for thermal dehydrochlorination at relatively low temperatures, resulting in significant decrease of the thermal stability of the polymer. These striking results also indicate that the decreased thermal stability caused by thermooxidation in the course of the primary processing of this polymer should be taken into account in order to efficiently stabilize PVC products for reprocessing and recycling.

Synthesis of Poly(poly(ethylene glycol) methacrylate)–Polyisobutylene ABA Block Copolymers by the Combination of Quasiliving Carbocationic and Atom Transfer Radical Polymerizations

Systematic investigations are carried out on the synthesis of a series of new, unique ABA-type triblock copolymers consisting of the hydrophobic and chemically inert polyisobutylene (PIB) inner and the hydrophilic comb-shaped poly(poly(ethylene glycol) methacrylate) (PPEGMA) polymacromonomer as an outer block. Telechelic PIB macroinitiators with narrow molecular weight distributions (MWD) are synthesized by quasiliving carbocationic polymerization of isobutylene with a bifunctional initiator followed by quantitative chain end derivatizations. Atom transfer radical polymerization (ATRP) of PEGMAs with various molecular weights is investigated by using these macroinitiators. It is found that CuBr is an inefficient ATRP catalyst, while CuCl leads to high, nearly complete conversions of the PEGMA macromonomers. Gel permeation chromatography (GPC) analyses reveal slow initiation of PEGMA at relatively high PIB/PEGMA ratios or with PEGMAs of higher molecular weights due to steric hindrance between the macroinitiator and macromonomer. The occurrence of slow initiation, and not permanent termination, is proven by highly efficient ATRP of a low-molecular-weight monomer, methyl methacrylate, with the block copolymers as macroinitiators. Successful synthesis of PPEGMA-PIB-PPEGMA ABA block copolymers is obtained by using either low-molecular-weight PEGMA or relatively low macroinitiator/macromonomer ratios. Differential scanning calorimetry (DSC) indicates phase separation and significant suppression of the crystallinity of the pendant poly(ethylene glycol) (PEG) chains in these new block copolymers.

Amphiphilic hyperbranched polyglycerols in a new role as highly efficient multifunctional surface active stabilizers for poly(lactic/glycolic acid) nanoparticles

Amphiphilic hyperbranched polyglycerols (HbPG) were synthesized by dodecyl and octadecyl alcohols as direct initiators for the ring-opening multibranching polymerization of glycidol. These polymers possess molecular weight dependent surface activity, and are efficient surfactants and stabilizers for poly(lactic/glycolic acid) (PLGA) nanoparticles, opening new possibilities for functionalized drug carriers, targeting, imaging agents, etc.

Poly(methyl methacrylate-co-2-hydroxyethyl methacrylate) four-arm star functional copolymers by quasiliving ATRP: Equivalent synthetic routes by protected and nonprotected HEMA comonomers

Comprehensive investigations were carried out on the synthesis of well-defined poly(methyl methacrylate-co-2-hydroxyethyl methacrylate) P(MMA-co-HEMA) copolymers, i.e., PMMA with predetermined average number of pendant hydroxyl functionalities, by using HEMA and trimethylsilyl-protected HEMA (TMS-EMA) under quasiliving ATRP conditions by a tetrafunctional initiator and CuCl/2,2′-bipyridyl (bpy) catalyst system in methanol at 10°C. It was found that these two synthetic routes, that is the direct and protected approaches, are equivalent in terms of yields, hydroxyl functionality and molecular weight distribution (MWD). Bulk copolymerization of MMA and HEMA by ATRP led to broad multimodal MWD in contrast to copolymers with narrow MWD in the presence of methanol. A two-step purification method applying silica-alumina chromatography followed by treatment with an acidic ion-exchange resin, used also as the deprotecting agent, was found to provide copolymers free of catalyst contamination. At higher monomer conversions, GPC analyses indicate the occurrence of chain-chain coupling by recombination of the macroradicals resulting in lower than theoretical apparent initiating efficiencies. According to the results on the effect of reaction time on monomer conversion, relatively short reaction times, less than 2 h, are sufficient to obtain high yields and PMMA with desired functionalities and MW under the applied quasiliving ATRP conditions. The resulting four-arm star hydroxyl-functional P(MMA-co-HEMA) copolymers offer a variety of new possibilities for the preparation of a variety of novel PMMA-based macromolecular architectures.

Synthesis of Poly(methyl methacrylate)-poly(poly(ethylene glycol) methacrylate)-polyisobutylene ABCBA Pentablock Copolymers by Combining Quasiliving Carbocationic and Atom Transfer Radical Polymerizations and Characterization Thereof

Novel, unique amphiphilic pentablock terpolymers consisting of the highly hydrophobic polyisobutylene (PIB) mid-segment attached to the hydrophilic combshaped poly(poly(ethylene glycol) methacrylate) (PPEGMA) polymacromonomer chains, which are coupled to poly(methyl methacrylate) (PMMA) outer segments were synthesized by the combination of quasiliving carbocationic polymerization and atom transfer radical polymerization (ATRP). First, a bifunctional PIB macroinitiator was prepared by quasiliving carbocationic polymerization and subsequent quantitative chain end derivatizations. Quasiliving ATRP of PEGMAs with different molecular weights (Mn = 188, 300 and 475 g/mol) led to triblock copolymers which were further reacted with MMA under ATRP conditions to obtain PMMA-PPEGMA-PIB-PPEGMA-PMMA ABCBA-type pentablock copolymers. It was found that slow initiation takes place between the PIB macroinitiator and PEGMA macromonomers with higher molecular weights via ATRP. ATRP of MMA with the resulting block copolymers composed of PIB and PPEGMA chain segments led to the desired block copolymers with high initiating efficiency. Investigations of the resulting pentablock copolymers by DSC, SAXS and phase mode AFM revealed that nanophase separation occurs in these new macromolecular structures with average domain distances of 11-14 nm, and local lamellar self-assembly takes place in the pentablocks with PPEGMA polymacromonomer segments of PEGMAs with Mn of 118 g/mol and 300 g/mol, while disordered nanophases are observed in the block copolymer with PEGMA having molecular weight of 475 g/mol. These new amphiphilic block copolymers composed of biocompatible chain segments can find applications in a variety of advanced fields.