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SEC/MALLS measurement of the branched structure of methyl methacrylate + ethylene glycol dimethacrylate copolymers synthesized by atom transfer radical polymerization
Publication . Trigo, Ivone; Gonçalves, Miguel A.D.; Dias, Rolando; Costa, Mário Rui
In the last few years, atom transfer radical polymerization (ATRP) of acrylate and methacrylate monomers
in the presence of a small amount of cross-linker has been investigated in order to produce branched
polymers and gels with applications in microelectronics, coatings industries or biomedicine (Wang
and Zhu, 2005; Gao et al., 2007). In this context, it is being explored the production by ATRP of
branched/crosslinked polymers with a lower degree of heterogeneity than that obtained by conventional
free radical polymerization (FRP). This work reports an experimental study on the ATRP of
methyl methacrylate (MMA) + ethylene glycol dimethacrylate (EGDMA) initiated by MBPA (methyl
-bromophenylacetate) and mediated by copper bromide (CuBr) ligated with HMTETA (1,1,4,7,10,10-
hexamethyltriethylenetetramine). The synthesized copolymers were analyzed by size exclusion chromatography
(SEC) with simultaneous detection of refractive index (RI) and multi-angle laser light scattering
(MALLS) signals. Important details of the molecular architecture of these materials can therefore
be measured, namely absolute molecular weights and z-average radius of gyration. Different experimental
runs were performed in order to investigate the influence of the operating conditions (e.g. temperature
and initial molar ratios MMA/EGDMA/MBPA/CuBr/HMTETA) on the structure of the products.
Prediction of mean square radius of gyration of tree-like polymers by a general kinetic approach
Publication . Costa, Mário Rui; Dias, Rolando
This paper describes a kinetic method to predict the z-average molecular mean square radius of gyration of tree-like polymers formed by irreversible reactions, assuming Gaussian chains. It is based on the population balance equations for the two-sided molecular distributions of pendant chains associated with every chemically distinguishable kind of bonds. An automated method for the solution of those equations is valid both before as well as after gelation for complex kinetic schemes. Examples of its use are presented with polycondensation systems leading to hyperbranched polymers, the anionic polymerization of mono- and divinyl monomers and a radical polymerization with terminal branching and transfer to polymer.
Kinetic Modeling of Non-Linear Polymerization
Publication . Costa, Mário Rui; Dias, Rolando
Recent developments of a method based upon population balances of generating functions of polymer chain length distributions (CLD) are presented. The calculation of the CLD and how to take into account chain length dependent reactivity are discussed. Prediction of polymer properties is also possible but only easily done for the average molecular radius of gyration; some results are presented for a radical polymerization including transfer to polymer and propagation with terminal double bonds.
Molecular architecture of non-linear polymers: kinetic modeling and experimental characterization of the system methyl methacrylate + Ethylene Glycol Dimethacrylate
Publication . Trigo, Ivone; Gonçalves, Miguel A.D.; Dias, Rolando; Costa, Mário Rui
A general kinetic approach allowing the prediction of the molecular architecture of non-linear polymers is applied to the study of the copolymerization of methyl methacrylate (MMA) with ethylene glycol dimethacrylate (EGDMA). Dynamic predictions of molecular weight distributions, sequence length distributions and mean square radius of gyration are possible before and after gelation. A set of experiments concerning the copolymerization of MMA and EGDMA was carried out in toluene solution at 60 8C for which classic radical kinetics is a good approximation.
The time evolution of key polymer properties was followed using a SEC system with a
refractive index detector coupled with MALLS allowing the determination of absolute
weight average molecular weight and apparent molecular size distributions as well as
z-average radius of gyration. Special focus was given to assess the influence of the
initial amount of cross-linker on the dynamics of the non-linear structure build-up of these products. A kinetic scheme comprising 23 different chemical species and 76 chemical reactions was used in the modeling studies of this chemical system. Most of the kinetic parameters used in the simulations have been collected from previous
studies. For experiments at low monomer conversion (up to about 0.5) a good
agreement between predictions and experimental measurements is observed for
molecular weights and z-average radius of gyration by fitting a small number of
parameters describing gel effect (with a conversion dependent but chain length
independent termination rate parameter) and the relative propagation on pendant
double bonds. However, predicted values of weight-average molecular weights and
z-average radius of gyration before gelation are too low at higher monomer
conversions with non-linear systems. The likely cause is the presence of intramolecular reactions which should not be neglected in these circumstances.
Experimental study of the TEMPO mediated copolymerization of styrene with divinylbenzene
Publication . Gonçalves, Miguel A.D.; Dias, Rolando; Costa, Mário Rui
Since the discovery of controlled radical polymerization (CRP) in the early nineties (Georges et al.,
1993), an ever increasing activity has been focused on the production of polymers with narrow molecular
weight distributions and well-de ned architectures (such as block copolymers, stars or brushes). This
work describes an experimental research on the nitroxide-mediated radical polymerization (NMRP) of
styrene (S) and divinylbenzenes (DVB) in xylene (X) solution at 130 °C, using the stable radical TEMPO
(2,2,6,6-tetramethylpiperidinyl-1-oxy) as mediator and AIBN (azobisisobutyronitrile) as initiator. Measurements
of absolute molecular weights and z-average radius of gyration of the produced copolymers
have been performed for different polymerization times using a SEC system with coupled refractive
index (RI) and multi-angle laser light scattering (MALLS) detectors.
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Funding agency
Fundação para a Ciência e a Tecnologia
Funding programme
POCI
Funding Award Number
POCI/EQU/60483/2004