Controlled/living free radical polymerization of styrene and butyl acrylate was performed in
bulk and emulsion using a reversible addition−fragmentation transfer (RAFT) process. The effect
of the transfer agent to initiator ratio was explored in bulk and emulsion polymerizations. The
effect of monomer addition was investigated in emulsion, and two different processes were
used: batch and semicontinuous. Better control was obtained with the continuous addition of
the monomers, resulting in clear films of the styrene−butyl acrylate copolymers. These
copolymers were characterized and studied by size exclusion chromatography, scanning
differential calorimetry, dynamic mechanical analysis, transmission electron microscopy, and
simulation, indicating that the semicontinuous process produces copolymers with a block of
styrene and a block of tapered random copolymer.
A series of controlled microstructure polybutadiene rubbers (PBs) was synthesized via anionic polymerization. Their structure and properties are analyzed by means of GPC, 13 C NMR, DSC, and DMA, and compared to the behavior of some commercial high cis rubbers. Thermal analyses results indicate the presence of crystalline domains of different nature in PBs with high cis-1,4 and high trans-1,4 isomers content, while rubbers with high content of vinyl-1,2 units do not show evidence of crystals. A shift in T g to higher temperatures as vinyl content increases is observed; an expression was found for predicting T g of rubber from microstructure data.
Tert‐butoxy radicals generated in the photolysis of di‐tert‐butyl peroxide in benzene at 25°C react with vinyl monomers by double‐bond addition and, in most cases, also by competitive hydrogen abstraction. The rate constant for the double‐bond addition changes by a factor of 17 between isoprene, which shows the highest reactivity, and the methacrylate derivatives, which are the least reactive of the monomers considered. The fraction of tert‐butoxy radicals that react by hydrogen abstraction varies considerably with the monomer structure, ranging from 0.9 (cyclohexyl methacrylate) to less than 0.05 (styrene and conjugated diolefins). In the methacrylate derivatives, most of the hydrogen abstraction takes place, not in the α‐methyl group, but in the alkyl chain.
High impact polystyrene (HIPS) series was synthesized by the mass-suspension process using polybutadiene (PB) rubbers with different cis-1,4, trans-1,4, and vinyl-1,2 isomers content. The HIPS were characterized by TEM, GPC, DMA, and DSC analyses. It was found that the dynamic mechanical properties of HIPS strongly depend upon the microstructure of PB used as a modifier due to the different tendency of PB isomers to promote grafting, cross-linking, and crystallization. The DMA for HIPS synthesized from high cis and high trans rubbers show additional relaxations at the low temperature region. The DSC results for gels extracted from these HIPS exhibited melting endotherms confirming the existence of crystalline domains.
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